Info Bandas

8/10/2019 Info Bandas

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NEW

Edition2009

Steel belts for the production ofwood based panels


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The steel belt is one of the most versatile tools available to industry and is found

in applications as diverse as baking, chemical processing, materials handling,

wood based panel production and, in recent years, paper manufacturing too.

As far as the wood based panels industry is concerned, the steel belt is the

fundamental machinery element in all continuous presses, be they rotation or

double belt presses. In short, steel belts are essential to the ongoing success of

this technology.

The publication of this handbook has only been possible through the much

appreciated co-operation of companies such as Siempelkamp, Dieffenbacher,

Hymmen, Pagnoni, Held and ,previously, Ksters and Metso Panelboard (Bison),

who have contributed pictures, illustrations and valuable comments.

As a neutral supplier to all these companies, and others, our position is clear.

Whoever we are supplying, we do so with one sole objective to deliver thebest quality steel belt, together with all associated services, and to be a

competent and reliable partner for OEMs and end-users wherever they are in

the world.

We hope you find this book both interesting and informative.

Copyright 2009

by AB Sandvik Process Systems, Sandviken/SwedenAll rights reserved.

Printed in Germany - PS-SB-440 ENG 2.09

Foreword

The production of this booklet hasinvolved the input and supportof a number of technical exper ts.Particular credit is due to thefollowing people:

Editors:J.O. Jonsson, Senior Technical ManagerWBP IndustryAB Sandvik Process SystemsS-81181 SandvikenSascha Porst, Regional Sales ManagerSandvik Surface Solutions(former Hindrichs-Auffermann)Mhlenfeld 101D-58256 Ennepetal/Germany

Ralf Griesche, Marketing ManagerDesign & Engineer ing, Wood Division

G. Siempelkamp GmbH & Co.,D-47803 Krefeld/Germany

Detlef Kroll, Engineering Manager,Dieffenbacher GmbH & Co., KGHeilbronner Str. 20D-75031 Eppingen/Germany

Andreas Lentner,Vice President Sales and MarketingHymmen GmbH -Maschinen - und AnlagenbauD-33613 Bielefeld

Ulrich Koletzki, Sales Manager

Held Technologie GmbHWeigheimer Str. 11D-78647 Trossingen-Schura

Ennio Codogno, Technical ManagerPagnoni Impianti s.r.lI-20040 Aicurzio-(Mi)/Italy

Gottfried Bluthardt (former SalesManager Presses)Metso PanelboardPress & Energy DivisionD-30559 Hannover

Consultant and German copy writing:Hansgert Soin, Senior Consultantfor Press History D-38173 Evessen/Germany


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1. Historical review 4

1.1 Pioneering the way to particleboard 4

2. Cycle pressing technology 4

3. The Bison-Mende process 6

4. The first continuous flat bed presses: 10

Bartrev - Sandvik

5. The change of opinion in favor of continuouspressing technology 10

6. Continuous pressing technology for theproduction of wood based panels withsteel press belts 13

6.1 Continuous roller bed presses 13

6.1.1 Ksters/Contipress History 14

6.1.2 The ContiRollsystem from Siempelkamp 16

6.1.3 Dieffenbacher CPS 22

6.1.4 Hymmen Presses 26

6.1.5 Held Technology 27

6.1.6 Pagnoni Easylam 31

7. Steel belts for wood based panels 33

8. Sandvik Surface Solutions

press plates and endless press belts 36

9. Innovation & investment 42

10. Sandvik Site Service 45

11. Questions and answers 47

Steel press belts, a technology that

has revolutionized production

processes in the wood based panel

industry

I N D E X

Sandvik is a high-technology

engineering group with advanced

products and a world-leading

position within selected areas

tools for metal cutting, machiner y

and tools for rock excavation,

products in stainless steel, special

alloys, metallic and ceramic

resistance materials as well as

process systems. Worldwide

business activities are conducted

through 300 companies and

representation in 130 countries.

Sandvik Process Systems is a world

force in the design and

manufacture of steel belts, press

plates and steel belt-based

industrial processing systems.

Markets served include food,

chemicals and pressing equipmentfor wood and other materials.


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1. Historical review

Dr. Fred Fahrni of Zrich, Switzerland, reported(HRW 1/57, p. 24) on a patent of the year 1889:

Krammer suggests gluing wood chips on canvas with

an adhesive, arranging them in parallel individual

layers, with the layers alternating lengthwise and

crosswise. The number of layers depends on the

thickness of the product. In 1905, Watson tried to

press thin wood platelets to boards of varying

thickness.

1.1. Pioneering the way toparticleboard

The worlds first par ticleboard factory was Torfit

Werke AG in Bremen-Hemelingen, Germany, where

a 10 tons/day-plant was in operation from 1941. In

this plant, boards with a raw density between 800

and 1100 kg/m3(Pek-Pressholz) were produced

from a mixture of wood chips with 8-10% phenolic

resins on a single-opening press made by Becker &

van Hllen, with pressures applied up to 1000 N/cm2.

In 1943, the company supplied compact wood in raw

densities around 600 kg/m3. Shor tly thereafter, the

company was bombed and was never reconstructed.

In 1942, Westdeutsche Sperrholzwerke, Wieden-

brck, a plywood mill in Germany, purchased Kaurit -

brand UF resins from BASF for producing boards

made from beech veneer scrap with raw densities of

700-800 kg/m3. A similar production was then started

by the plywood factory Schtte-Lanz in Mannheim,

Germany.

About that time, Dr. Fahrni launched his idea of the

three-layer boards with a middle layer of coarse chipsand outside layers of thin, laminar chip material. This

idea was first put into practice by the Keller plywood

factory in Klingnau, Switzerland. Production of

high-quality, lightweight particleboard named

Novopan was started in 1946.

In the late 1940s and into 1950s, a number of small

units with capacities of about 10 tons/day were installed.

Many were operated by furniture factories utilizing

their own wood waste material. This was a boon for

the furniture manufacturers as they could add theirown board-making facilities to their existing saw mills.

2. Cycle pressing technology

Multi-daylight presses with accompanying loading andunloading systems were known from the much-older

fiberboard industry, which preceded par ticleboard by

many years. They are closely connected with the

names of two machine works located in Krefeld,

Germany: Siempelkamp and Becker & van Hllen.

(The latter withdrew from the market in the 1980s.)

Apart from the complicated handling of the thick

mats and the panels in and out of the press, the time

required for heat transfer from press to the mats was

another obstacle in reaching the goal of highercapacities. Moreover, the steel platens had a tendency

to alter in shape under the effect of heat, which

disrupted the layers of the small wood fragments in

the mat. By using aluminum platens or, even better,

brass, these cited disadvantages could be reduced, but

the pressing time still remained unsatisfactorily long.

Faced with these disadvantages, multi-daylight

pressing gave way to the single-opening press. The

German Bison-Werke in Springe (SES Siempelkamp

since 2007) developed a semi-automatic production

system for particleboards known as the Bison system.

It is a combination of a very long single-opening press

with a rotating steel belt to carry the mat and moving

stepwise through the press.

The first plant of this type was delivered in 1957

and soon became popular. Over the next few years,

100 such presses were built.

Since then, Bison, Becker & van Hllen, Dieffen-

bacher, Motala, Siempelkamp, Sunds and other

machine works have delivered over 600 single-

opening presses. Their length and width increasedgradually over the years to meet growing capacity

demands, finally reaching an optimum length of

approx. 52 m.

The 1300C grade steel belt used for this process is

supplied almost exclusively by Sandvik. It is a hardened

and tempered carbon steel with an average carbon

content of 0.65% (see page 34). The single-opening

pressing procedure is uneconomical for the

production of thin panels, as the ratio between dead

time and reaction time change unfavorably in relationto the output. Dead time is a constant, while pressing

times are variable depending on final panel thickness.

Steel press belts, a technology that has revolutionized productionprocesses in the wood based panel industry


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The situation is similar to that of the sanding

allowance required to obtain the correct panel

thickness. The allowance is a constant; thus, the

percentage of (expensive) resin-containing wood

material which has to be removed in the sanding

process increases with diminishing panel thickness.

To overcome these deficiencies of cycle presses, the

concept of continuous, nonstop presses was

developed.

Single opening presses (SOP)

Graphite bar for maintenance-free lubrication of steel belts for

single opening presses

wear plateidlersgraphite pad

forming machine

brush main press

1,400 mm 2,500 mm

drive steel belt support rollers tracking tensioning

Diagram of SOP (Single Opening Press)


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3. The Bison-Mende process

The first commercially successful procedure for the

continuous production of thin particleboard and

fiberboard was the Bison-Mende process. The press

is a derivative of a plant which had been designed for

continuous bonding of rubber sheets and laminatingof thermoplastic sheets (Auma press).

The process was further developed and adapted

to the requirements of wood based panel production

through close cooperation between the Mende

panel-manufacturing concern and Bison.

The process first reached the market in 1971, and

since then over 90 presses of this type have been

put into service. Many are still operating throughout

the world. An essential feature of the plant is a

continuous steel belt which runs through the formingmachine and around a heated press drum with a

diameter of 3, 4 or 5 m. The forming station can also

be separate from the steel belt. In these plants,

panels with a thickness of 2-8 mm, max. 12 mm are

produced, (lines are usually devoted to the

production of thinner panels) and widths range

from 1.2 to 2.5 m. The system was built by Bison and

Metso Panelboard up to 2007, who purchase the

basic press from Berstorff of Hanover, Germany, and

offer it as complete turnkey unit ready for operation

(see pages 7-9). Nowadays, the company BINOS in

Springe/Germany are also producing Mende presses.

The total stress on the steel belt is very high in the

Mende process, as the belt is exposed to high

reversed bending and thermal stress. During each

rotation, the belt is bent six times as well as being

heated up and cooled down. The belt must

already be maintained under high tension in order

to be able to exert high pressure on the panel being

pressed. Additional pressure is applied from up to

three calibrating drums arranged around the largeheated main press drum.

Apart from the stresses mentioned above, there

are several other influences which can shorten belt

life: hard particles falling between drum and belt,

uneven shape of the mat, belt tracking problems,

scratches on the belt, corrosion, etc.

During the early stages when Sandvik 1300C belts

were used, the inherent operating conditions were

hard to overcome. In par ticular, the high number ofreversed bendings per rotation reduced the lifetime

of the belts to a level which was barely economical.

Moreover, due to the required heat treatment of the

weld, repair welding was very time-consuming.

For all these reasons, users showed great interest

in a steel belt quality with higher strength and easier

repairability.

This situation led Sandvik to develop Sandvik1450SM a high-strength steel belt grade in the

mid-1970s. In 1980, it was further improved and

named 1650SM and this steel belt grade is now

used in continuous roller bed presses worldwide.

It is a precipitation-hardened, corrosion-resistant

steel which obtains its excellent mechanical

properties by a simple heat treatment in air.

Steel belt grade Sandvik 1650SM (PH) offers the

following advantages, compared with Sandvik 1300C

(see page 34/35):

Very high strength

Very high fatigue strength

Optimal strength of weld (welding factor almost 1)

Ease of repairability

Easy to weld

Deformation-resistant

As a result of the development of the high-strength

steel grade, the service life of belts increased

considerably, and the cost situation improved. By the

1990s, it became normal for a belt in a traditional

Mende plant for particleboard to be used for 30-40

months, provided that the plant is well-maintained.

The service life of belts in the new Mende plants

for MDF, however, is only 9-15 months. The reason

is that belts are much shorter and speeds much

higher, which means an increased number of load

reversals per time unit. Moreover, the pre-tension

is higher in order to achieve the higher pressure on

the mat for increased panel raw density. Finally, as therequirements for panel integrity are very stringent,

markings from the repair welding must not be visible.

For many years the Mende system was the

unrivalled No. 1 method for continuous production

of thin par ticleboards. For thicker panels, the process

was unsuitable due to the bending of the boards

around the main press drum.


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1 Cooling and belt return drum

2 Infeed and first pressing drum

3 Press belt return drum, heated,

line pressure 3,500 N/cm

4 Press belt drive drum5 Press belt tensioning drums

6 Main press drum, heated, available

in 3, 4 or 5 m diameter

7 + 8 Pressing and calibrating drums

9 Infrared heating elements (600C) to ensure

uniform temperature of press belt

10 Steel press belt. Belt tension applies a pres-

sure of approx. 20 N/cm2

to the product11 Finished product outlet

12 Hydraulic tensioning unit, which also ensures

accurate belt tracking

13 Hydraulic control of infeed drum

14 Press belt cleaning brushes

15 Induction motor for cleaning brush

Press plant of Bison-Mende system


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Bison-Mende system using a single belt for forming and pressing

Bison-Mende system using high-frequency preheating for increased capacity. Forming belt and steel press belt are separate.

Directly before the press infeed, a discharge device can be opened above a pit for faulty batches.

Pressing station High-frequency

preheater

Spreading station Cutting station

Pressing station Spreading station Cutting or sanding station

Typical data for a 3.2 mm panel

Rawboard density 800 kg/m3 5%

Bending strength 35-50 kg/mm2

Wood portion of the panel 750 kg/m3

Glue portion of the panel 90 kg/m3

Electricity 300 kWH/m3

Heat required for dryer 2 GJ/m3

Heat required for press 0.4 GJ/m3

Steam required for refiner 500 kg/m3


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With the Bison-Mende system, the pressed panel continuous ribbon returns above the plant and is sanded inline

(not shown in the picture) and cross-cut. The crosscut saw is designed so that it can operate with short cutting cycles.

View of the outfeed of the press inthe Bison-Mende system, showing the

press belt on the tension drum


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4. The first continuousflat bed presses

Bartrev

Bartrev presses were equipped with platens arranged

as plate chains which rotated in the machine

supported on two rollers on each side similar tocaterpillar tracking. The individual platens were lined

up horizontally without a gap between them: however,

they were also covered by steel belts, which could be

cleaned more easily than the plates. The lower steel

belt also transported the mat through the pre-press,

the HF heating electrode and the press. Only the

chains had a dr ive; the steel belts were dragged along

with them. However, the wear of the pressplates was

too much so the experiment ended in the 1960s.

Sandvik

Sandvik Process Systems was the first company to

design and manufacture a continuous Double-Belt

Press System and its design principle is still used for

continuous belt presses today: Multiple rolling bars

guide the steel belt on one side and establish the heat

transfer to the product via the heat plate on the

other side. The process is continuous and the product

is moved by the upper and lower belt. A similar

design is employed in double-belt cooler systems.

The idea of using "rolling bars in a row" for heating

and cooling was progressive and established a long time

before it was used for wood based panel production.

The Sandvik Double-Belt Press can be used at

temperatures of up to 400C and can achieve

tolerances as fine as 0,05 mm. Such a system was

tested for pressing wood based panels and for

laminating finished chipboards.

However, as an outsider in the wood based panel

industry, Sandvik decided against further development

for this industry due to the cost and complexity ofthe system. In the early 80s Sandvik backed out of the

business of designing presses for wood based panels

entirely, leaving the market mainly to Siempelkamp

and Dieffenbacher.

Today, all suppliers of press systems for the wood

based panel industry are customers of Sandvik, using

both their steel belts and their service.

Sandvik didn't leave the double-belt press market

entirely though, using its experience to concentrate

on the plastics, composite materials and laminateindustries.

To this day Sandvik remains a supplier of such

press systems and has sold more than 40 systems for

these applications. A further 200 Sandvik double-belt

press systems have been used for other applications,

e.g. artificial marble, polyester, acrylics, phenol, epoxy

and other resins, silicon, rubber, antioxidants, wax,

nylon, polyurethane foam and expanded polystyrene.

5. The change of opinion in favor ofcontinuous pressing technology

In complete contrast to the situation in the early

days of the panel industry, characterized by fierce

and drawn out patent disputes, the changeover to

continuous pressing took place peacefully. It was

accompanied by the evolution of suitable steel

press belts needed in the production process, as the

newer belts were able to handle considerable tensile

forces. In fact, it was the steel belt which sparked this

development.There were many years between the completion

of the last Bartrev press and the appearance of the

first ksters press. After a period of industrial trials at

a German particleboard mill, the first ksters press

was installed on a full-time commercial production

basis at the Spano particleboard mill in Belgium. The

change of opinion was then so surprising that its

worth looking closer at the reasons behind this.

Ksters, a highly reputable supplier to the textile

and paper industries, decided to enter a third field ofactivities and opened the Ksters press division in the

wood based panel industry. Since 1999, the press

Sandvik press at Symalit


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division has been an integrated part of the Metso

Panelboard GmbH, Hannover/Germany, and the

name of the press changed to Contipress. Spanos

ksters press, a pioneer in a new field, was a success

right from the start.

In 2007 Siempelkamp took over the Hannoverpremises and, with that, production of the Ksters

Contipress was ceased (although Siempelkamp has

guaranteed to support existing presses in terms of

both service and elongations).

The first unit, of course, raised a number of

new challenges. Not only were there the start-up

problems to be overcome, but also the up- and

down-stream equipment had to be designed

separately and contracted out to other suppliers,

since the Ksters shops only made the press.Thiswas the main reason for the slow acceptance of

the ksters pressand also the reason for the later

success of the Siempelkamp ContiRollpress, which

was part of a complete production line supplied from

a single source.

Moreover, a lack of incentives to change to a new

technology hindered widespread acceptance at that

time. Loading and unloading techniques of cycle

presses worked perfectly and did not hamper the

continuity of materials flow. There was no actual need

to make pressing a continuous process.

In none of the publications on Bartrev presses wasthere a hint as to why the risk of such an innovation

had been taken. Variable product lengths were not a

high-priority reason, and continuous =economical

was not proven.

Spano, the first successful user of a ksters press,

kept their operating experience confidential for a

certain period; however, important findings could not

be concealed from the public for long. Interested

companies had product samples made for their own

laboratories and the findings of even the simplesttest were clear: Particleboards with a raw density of

only 640 kg/m3produced in the ksters presswere

as good as boards with a density of 680 kg/m3which

had been produced in cycle presses. The somewhat-

lower bending strength was outweighed by improved

internal bond transverse tensile strength.

The reasons favoring the continuous units

acceptance are the substantial differences in pressing

technology. In contrast to traditional cycle presses,

continuous presses can be operated with a defined

pressure and temperature profile over the whole

effective length. The high number of hydraulic

cylinders employed across the width of the

production line, together with the use of a thinner

heating platen, means that a continuous press is able

to deliver more efficient steam release across the full

production width. Oval steam nests, as used in cycle

presses (where steam can only evaporate via the

edges by opening the press), no longer exist.

However, material savings of 5% did not trigger

any reactions by the competitors, as long as only oneuser turned this advantage into profit. This situation

changed as soon as Siempelkamp launched its

ContiRolland Bison simultaneously presented its

Hydro-Dyn-press, the latter having a completely

different design concept.

Apart from the material savings due to reduced

density, further savings were achieved through

minimal sanding allowance. This is possible because

the continuous press imparts to the pressed panel

very compact surface layers and is already quiteaccurately calibrated for thickness. The sanding

removes 0.2-0.3 mm each side of the panel

Characteristic curve of the specific pressure in continuousparticleboard production: pressure build-up high-pressure zone

pressure drop calibration

pres

sleng

th

spec.pressure


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(continuous press), compared with 0.4-0.6 mm

(single-opening press) and 0.6-1.0 mm (multi-daylight

units). Continuous presses are economical consumers

of electrical and thermal energy. They need minimal

hydraulic forces, the only purpose of which is to

maintain the pressure applied, or to decrease orincrease it slightly, whereas cycle presses shuttle back

and forth between zero and maximum.

Also with regard to driving forces, continuous

presses show a favorable balance. Although press belt

drives must be specified sufficiently strong for starting

the press, their power consumption is considerably

reduced during continuous operation. With cycle

presses, especially multi-daylight presses for feeding,

closing and opening, each load of panels requires high

and sudden amounts of energy.Savings of thermal energy result from the

deaeration of the web in the continuous presss

conical infeed and absence of any dead time with

radiation losses involved.

Panel-size variability is as easily achieved with

modern multi-daylight presses as with continuous

presses; however, with the former, capacity losses

have to be accepted not only in case of reduction of

width, but also of length.

As dead times are completely eliminated in

continuous presses, their capacity, depending on

product-specific heating times, remains constant. With

cycle presses, however, the capacity decreases with

decreasing product thickness, as the negative impact

of their constant dead times gains importance; for

panels below 8 mm thickness, the process becomes

uneconomical and a technological risk due to the

deaeration problems. On cycle presses, no thin panels

are produced (with one exception: hard fiberboard,

which can be deaerated through the screens used in

pressing).

Technological press data show a fur ther plus for

continuous presses. The pressing time factor

approaches 4.0 s/mm for the optimal panel thicknessof 16-19 mm. It strongly depends on press

temperature, which can reach almost 240C. Other

factors are of less, but still measurable influence: an

extension of the press length of 10 m means an

advantage of approx. 0.5 s/mm, i.e., a 40 m long press

can achieve a time saving of approx. 1.0 s/mm

compared with a 20 m press. The pressing width

obviously plays a more-important role with cycle

presses than with continuous presses. This is due to

the deaeration problems mentioned above. For cyclepresses, an increase of press time of 0.5 s/mm per

300 mm effective width is mentioned. If it amounted

to about 5.0 s/mm for one of the 1.2 m (4-ft) wide

pioneer units, it would amount to 7.0 s/mm for an 8-ft

unit. Spano, however, mentioned only a time

difference of 0.5 s/mm, between the narrowest

(1850 mm) and the widest (2630 mm) ksters press.

Another possibility of press time reduction with

system-dependent efficiency is cooling under

pressure without loss of heat energy. Since a cooling

section reduces internal steam pressure in the panel

effectively, press times can be shor tened and par tly

converted into curing time. Furthermore, the press

can be entered with higher mat moistures, thus

resulting in higher production capacity as a result

of improved heat transfer. Other advantages are a

decrease in board swelling and an increase in board

moisture which is closer to the equilibrium moisture

content.

Unfortunately, this cooling is in direct contradiction

to the heating-up of the press. An economic coolingof single-opening or multi-daylight presses is not

possible due to the mass of the heating platen, which

has to be cooled down and heated up again in each

pressing cycle. Even in continuous presses the amount

of heat energy stored in the material of the rolling

system has been too high to allow economic cooling.

It was Ksters once again who, in 1997, solved this

problem. The latest generation of ksters pressis

equipped with an integrated cooling zone at the

outlet end of the press. The rolling system of theksters press, a chain system, is driven by pressure

between heating platens, product and the turningKsters/Contipress: heating and cooling


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steel belts, whereas no separate drives are needed.

The chain system can be easily divided into two separate

systems within an extremely shor t distance, splitting

the press into a heating zone and a cooling zone.

This means that the chain in the heating zone

remains hot and the chain in the cooling zoneremains cool all the time.

Therefore, in the cooling zone of the ksters

pressonly the steel belts have to be cooled in

addition to the board, not the rolling system. The

effective cooling zone length covers 25% - 30% of

the total press length.

The first four ksters press-based MDF lines

featuring integrated cooling zones went into

succesful operation in 1998 and by 2001 the first

such paricleboard line together with further MDFlines had also been supplied.

The wear of roller elements, however, is an almost

negligible cost factor. Todays steel press belts are no

longer the high-cost factor they were in earlier times

either, as the alloys are constantly being improved, the

belts made thicker and stronger and repair easier.

After more than two decades of the ksters press

operation, the estimates are becoming more reliable.

Cycle presses, based on industry experience, must

be replaced after 20 years at the latest. Their frames

and hydraulic elements are subject to wear and fatigue

due to the pressing cycles. This does not apply to

continuous presses. In fact, the oldest ksters press,

installed in 1977 at Spano, remains fully operable.

Therefore, a lifetime of 30 years could be realistic,

provided that the press is properly serviced.

There is one obvious argument against continuous

presses: they need more-sensitive controls. Cycle

presses are comparable to a blacksmiths hammers,

whereas continuous presses are more like punching

tools. Continuous presses must be in thermal balancein order to function properly.

Sensitivity to the processed particle material,

however, disappears with the increasing thickness

of steel press belts. Such high-quality steels, together

with the increased thickness, reduce wear and the

belt-tracking problems which have sometimes caused

significant problems.

It can be concluded, after comparing the various

disadvantages and advantages, that the continuous

press technology absolutely is the future as we haveseen now in the new century.

6. Continuous pressing technology for theproduction of wood based panels withsteel press belts

Apart from the extrusion press, there is no

continuously working press system that does not use

steel press belts. They all function according to theprinciple of single-opening presses. The steel belts

known from the Bartrev press were only carriers of

the mat as they are still used in single-opening cycle

presses. The lower belt is extended to provide a

forming zone, if mat-forming is discontinuous.6.1 Continuous roller bed presses

The steel belts used in todays continuous presses are

driven components subject to high tensile stresses,

depending on the strength of the frictional forces, andare the principal element of such presses. Without

them, nothing would happen.

To overcome the main problem to avoid or

minimize gliding friction acting on the belt the

concept of the ball bearing has been transferred to

the belt support within the press: the press platen

corresponds to the (fixed) internal ring of the ball

bearing, the roller elements of the press systems to

the balls and the steel belt to the movable outer ring

of the bearing.

Movable elements and a number of procedures

make the difference between discontinuous pressing

techniques:

Carpets formed by roller chain strands in close

succession (see page 15) or roller bars extending

over the whole plate width (see page 20) and

rolling off between the press plates and the steel

belts, with their return strands running above/

below the press.

End drums with diameters increasing with the

press belt thickness, their surface mostly ribbedwith friction linings for transmission of the driving

forces and for safe belt control.

Infeeds which can be adapted to the different

configurations of chips, strands, flakes and fibers, to

the degree of compaction i.e. thickness and

density of the web, and to different kinds of raw

materials.

More or less flexible, sometimes articulated

upper and lower press plates, which serve in the

short high-pressure zone on the infeed side,together with the movable press infeed, to control

the mat thickness and to influence the density.


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Steel press belts are active, driven elements, which

draw the product through the pressure zones,

tensioned and guided hydraulically. The precise

synchronization of upper and lower belts eliminates

any shearing forces on the product.

The press characteristics of these systems are

called isochoric, which means that they work with

varying pressures on the inevitable local differences of

raw density. Isochoric systems calibrate products to a

uniform thickness independent of such density

differences. All traditional single-opening and multi-

daylight presses have the same press characteristics.

Different thickness of the roller elements results in

different heat transfer between heating plate and

steel belt. This difference can be compensated by a

higher infeed temperature of the heat carrier. All

systems work at a speed of abt. 4.5 s/mm for

particleboard and abt. 9.0 s/mm for MDF. The speed

is also closely related to press length (reducingpressing time) and press width (increasing pressing

time).

6.1.1 Ksters/Contipress History

After the last Bartrev press had gone out of service

(refer to section 4), some time went by before the

Ksters company in Krefeld launched a new generation

of continuous flat bed presses. In 1977, the first

ksters presswas put into service at the Spano

companys particleboard mill in Belgium.Since then, the names of both the press

(Contipress by Siempelkamp) and the customer

(METSO Panelboard) have changed but the

outstanding feature remains a rotating carpet of

individual rollers without a separate drive.

The numerous small rolls are of varying lengths;

therefore, a wave-like arrangement of the roller links

is necessary. This arrangement ensures a uniform

pressure distribution on the pressed surface, as every

point is constantly rolled-over (see page 15).

The design allows very narrow arcs of the roller

carpet, which simplifies a subdivision of the complete

press, in order to obtain a highly efficient cooling zone

on the outfeed side. The narrow pressureless area of

the separating line remains covered by the steel press

belt (see page 12).

The carpet of small rollers of only 12.5 mm in

diameter with its narrow center distance reduces the

bending stress of the steel press belts by the

counter-pressure of the compressed product a

stress which inevitably increases with the space

between bigger roller elements.The roller carpet elements are recirculated in a

closed carpet above and below the press, on rollers

in a heat-insulated channel, where most of the

residual heat is conserved.

The fact that the rollers in the roller carpet are only

12.5 mm in diameter leads to a large surface contact

between the steel belts and the heating platens. This

in turn gives a very efficient heat transfer, meaning

that the temperature difference between the heating

platens and the belt surfaces is very low. For astandard particleboard press, it can be as low as

10-20C. This efficient heat transfer allows lower

The latest generation Contipress with self-stabilized press body structure


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15

heating oil temperatures, giving energy savings and

reducing the risk of fire. Conversely, if the

panelboard mills line is limited in productivity, a

higher oil temperature similar to other presses on the

market may be used, thereby increasing the effective

capacity of the line.

After several years of research work, a new roller

carpet design is now available to press users, thus

allowing the mill operators to change the working

width of their board production lines by more than

2 feet. With the redesign of the roller carpet to

incorporate somewhat wider roller segments, the

presses can make a swing of two feet with no loss in

product quality or operating efficiency. Thus the new

roller carpet design gives the panelboard producers

additional flexibility to meet the changing demands

from the marketplace (see above).The press frame construction in combination

with the press profile control system is another

important feature of the Contipress. The

window-frame is manufactured out of a solid plate of

steel where the window is milled out. The upper

heating platen, designed as a rigid counter-bearing, is

connected to the upper part of the frame.

The control of the press profile was

uncompromising right from the beginning: the

lower heating platen, 70 mm thick, softly yielding,rests on numerous hydraulic cylinders with a center

distance of only 300 mm over the whole pressing

width, resulting in one cylinder per foot of width.

The hydraulic cylinders in each press frame have

their own HNC controlled, proportional hydraulic

valve which is integrated, together with its thickness

(press platen distance) measuring system, into a

computer-controlled system. Groups of individual

frames can be controlled by either distance or

pressure, whichever is preferred. The use of differential

cylinders (with 2 pressure chambers of different

size resulting in 4 pressure steps) over the width of

the press frames allows so-called "cross correction",

delivering varying pressure over the press width.

This keeps the spreading forces of the consolidating

product in balance with the pressure applied and

enables all variations resulting from wood species,

spreading density, wood moisture and steam pressure

to be compensated for. The accurately controlledcalibration at the outlet end makes it possible to

guarantee thickness tolerance of less than 0.10 mm.

Up to 2007, Contipress has been manufactured

to lengths of more than 50 m, with a product width

up to 3.30 m and operating press speeds of up to

90 m/min. Worldwide ser vice for these presses

is delivered by Siempelkamp Maschinen- und

Anlagenbau, Krefeld.

The roller carpet is composed of a great number of rollers (12.5 mm diameter) connected by the links. The roller carpet elements used at theoutside of the roller carpet are 550 mm wide, allowing a width variation of the product of more than 2 feet.

As a result of the different roller lengths, the fabric shows a special pattern with the characteristic wave-like lines formed by the links; this

arrangement ensures good pressure distribution and leaves no line marks on the panel.


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6

Siempelkamp ContiRoll System 3 sizes

6.1.2 TheContiRollsystem fromSiempelkamp

In 1984, Siempelkamp entered the market with a

system based on a continuous rod carpet. The

technique was not new. Early patents existed in

Sweden and are still used by Sandvik for special plants.It was considered an important breakthrough for this

German company at that time to have turned to the

production of wood based panels via the continuous

method. The firm had established itself as a market

leader in their par ticular sector of press technology.

It is considered to be the principal company among

the various competitors who supply turnkey plants

ready for operation from a single source; certain

components not made by Siempelkamp are

out-sourced and integrated into the overallproduction process, e.g. such equipment that is

required for fiber preparation and panel sanding.

The first ContiRollwas delivered to Louisiana-

Pacific Corp., USA, for MDF and was hailed as a major

news event in the panel field. Its effective length was

16 m. Suddenly, continuous press technology had

become accepted for both par ticleboard and MDF.

The ContiRollwas constantly improved andadapted to the new findings of continuous press

technology. One of the basic features, however,

remained unchanged: the frame construction,

which mirrored that used in cycle-pressing. Heavy

longitudinal girders take up the high counteracting

forces resulting from the high belt tension which is

necessary for continuous pressing; the foundations

thus have to support only the dead weight of the

press, eliminating the need for anchoring rods with

additional foundations to take up horizontal forces(see page 21).

Both the upper and the lower press platens in


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the feed area are 60 mm thick. The lower plate is

the fixed counter support for the flexibly mounted

upper platen, which can be accurately adapted

to the conditions and requirements in the press

gap thanks to its double-acting pressing hydraulics.

Product thickness and density profile are veryflexibly controlled over the whole length. This is

also to the advantage of lower-density MDF in the

area of 450 kg/m3, which is very much in demand

today. The upper end of the spectrum is covered

by thin boards of densities of abt. 960 kg/m3. These

boards came under the designation of HDF, High

Density Fiberboard. In view of the fact that light

(i.e. low density), standard and thick (both in the

middle range of around 750 kg/m3) are now made

on generally similar ContiRolls, one can see thenumerous possibilities of a wide range of applications

of MDF boards made by the continuous press.

Across the effective press width, the product

thickness is also accurately controlled by a close

sequence of press plungers. Thickness control on the

longitudinal and transversal profiles is part of a very

complex press control system and enables thickness

tolerances as small as +/- 0.1 mm.

The radii of the press infeed can be optimized

for any mat thickness by means of the hydraulics.

Following the infeed drums, the steel belt is fed into

the curved press infeed section. Here the required

thermal energy is immediately provided for the high-

density outer layers of HDF, which, with the close

thickness tolerance, means that the sanding step can

be eliminated but the panel can still attain a surface

which can be laminated or wet-finished.

All parameters determining the raw density and

the compaction geometry can be stored and the

programs requested within the complex plant

control system.The roller carpet for transmitting the pressure

forces, which is typical for this system, is formed by

rotating rods going across the full width of the press

plate below the upper platen and above the lower

one (see page 20).

By using these full-width roller elements, edge

impressions on the steel belts as they might be

caused by narrower rollers are avoided. (The marks

resulting from such impressions are sometimes visible

on the pressed panel.) Rods used as full-width rollerelements cause no gliding friction at all but merely

rolling friction; therefore, the lubricant consumption is

low. The rods are flexibly supported by chains at

both ends, which ensure orderly return and safe

re-entrance. The chains do not serve for guiding,

as the rods run freely at a secured distance of

2 mm through the pressing zone, and back in the flat,

heat-insulated ducts above/below the press frame, inwhich the steel belts are also returned.

Continuous, full-width roller elements offer

another advantage: the uninterrupted, homogeneous

heat transfer from the heating plate to the steel

belt. The combination of components chosen by

Siempelkamp for the ContiRollpress, i.e. heating

plate full-width rods steel belt, is matchless from

the heat-technological point of view, as it minimizes

the number of heat transfer functions. The integrity

of heat transfer from the heating plate to the rods isfurther improved by the microfinish of the heating

plate surface, which ensures full contact with the rods.

The high share of supporting area between plate and

rods has another positive effect: it reduces belt

displacement.

The first generation ContiRollworked to speeds

of 300 mm/s. With todays improved technology, the

presses are running at speeds of up to 2000 mm/s.

The presses are longer, and very thin panels can now

be produced. A 33.8 m long thin panel ContiRoll

can produce 2-mm-thick MDF at a speed of 1650

mm/s, with a daily capacity of 660 m3.

Over time, the many presses built and learning

processes that took place were of special importance

for the steel belt. It was found that the belt lifetime

depends mainly on the design of the components of

the press which are in direct contact with the belts.

Right from the beginning, drums with a big diameter

had been used for the drive and return terminals

in order to keep the bending stress of the belts low.

This, of course, only makes sense if bending radii atother points are equally large. Therefore, the design

of the ContiRollpress avoids joints and break points

along the path of the steel belts. Transitions between

different radii are gradual. Guiding elements for the

steel belts are designed as roller baskets with the

belt-supporting rollers arranged on a circular arc

section with big radius. This applies both to the feed

terminal of the press and to the controls of the

return strands of the belts.

Siempelkamp attached great importance to thecompilation of binding specifications for the steel belts.

They have been available for quite a long time and


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8

include all relevant data such as dimensions, material

specifications, technical-physical values, tolerance data,

finish, grinding pattern in the weld area, etc. By now,

comprehensive information on endurance and fatigue

strength has been added to these data.

The quality of the steel belts has a great influence

on the quality of the pressed board the higher the

pressing speed, the stronger the influence. This applies

especially to the belt geometry in the area of the

longitudinal welds. As a result of the grinding of theseams, there is a slight depression in this area

compared with the surrounding surfaces of the two

belt halves. Although the thickness differences are

minimal, any improvement even if only 0.01 mm is

welcome. Due to the inherent stiffness of the steel

belts, with lower pressures they do not come into

close contact with the rods in the area of the

depression, with the consequence that the heat

transfer is different from the neighboring zones. This

results in a different technological effect on thepressed product. The end product, therefore, can

show differences in the technical-physical values and

the surface color. The development of the belts was

forced by Siempelkamp with special regard to this

aspect, which is of particular impor tance in the

production of thin MDF, which can be prepared for

market without going through the sanding step. The

slightest thickness variations within the boards can

cause problems when lacquer is applied.

Siempelkamp pioneered the use of thicker steel

belts firstly with 2.7 mm and, more recently, 3.5 mm!

Such belts offer a number of significant advantagesto the user which more than compensate for the

higher price of the belts, thus offering a higher heat

potential. This has a technologically favorable effect

in the infeed area of the press, i.e. reduction of the

heating factor. The belts have a higher thickness

rigidity and are, therefore, less susceptible to damage.

The considerably higher transversal rigidity results in a

stable and smooth belt run.

Another aspect of steel belt development was the

reduction of belt width. Originally the belt edgescovered the side plates of the chains accompanying

the rod carpet to protect them against contamination.

Siempelkamps ContiRollPress , 7 x 55,3 m for MDF, Location: Yildiz Kimya, Turkey


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19

Therefore, the belts had to be much wider than the

heated press plates. The temperature of the belt edge

zones beyond the heated area was much lower than

that of the belt areas in contact with the mat, which

caused comparatively high tensions resulting in edge

damage (cracks). Todays belts are narrower than therods of the roller carpet, and their width in turn

exceeds the heating plate width only slightly.

Contamination of the side chains is avoided by

suction devices which clean off the edge zones of the

belts at the infeed. This method is more efficient than

the former protection method.

Along with the reduction of the belt width,

Siempelkamp attached great importance to the

machining of the belt edges. They are now specially

machined according to the latest standards ofmechanical engineering in order to eliminate edge

and peak tensions, thus gaining longer belt life.

The aforementioned reduction of the belt width

can, of course, only be seen in relation to the heating

plate width.

Another development was the use of very wide

steel belts for new, wider presses. These belts could

not be made just by joining two belt strips by a

longitudinal weld and Siempelkamp cooperated

closely with the steel belt manufacturers. The width of

the strips had to be planned carefully as did the

position of the welds in the upper and lower belt inthe press. Under no circumstances may the welds

be positioned exactly opposite each other (this, of

course, also applies to belts composed of three strips;

however, in that case it is much easier with a view to

the economical use of belt material).

The care of steel belts, which are the

most-expensive components of a press, is not

only important in the press itself. Siempelkamp

has incorporated comprehensive precautions for

protection of the steel belts well ahead of the press,and ample control and cleaning equipment at proper

points in the press. The first safety device in an MDF

line is a sifter for eliminating undesirable foreign

matter from the fiber stream ahead of the production

lines. The sifter is followed by equalizing spreading

rollers (at the fiber spreaders) which break up fiber

Siempelkamp ContiRollPress


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0

bundles and glue lumps before the mat is formed.

As with all types of pressed products, a metal

detector incorporated into the line will trigger the

removal from the line of any mat portion containing

metal particles. The sensitivity of the coil is

automatically adjusted by the setting of the thicknessof the boards to be pressed. As a fur ther precaution

in particleboard lines, a magnet is installed directly

after the spreading machines so any magnetized

metal parts are removed from the mat before they

pass the metal detector. (Magnets are not used in

MDF lines, as they would be unreliable due to the

felting of the fibers.)

At the prepress, sensors scan any thickness

increase in the mat which could cause asymmetrical

pressure application and belt displacement in theContiRollpress and trigger automatic rejection.

Ahead of the ContiRoll, a thickness control instrument

is positioned to prevent accidental accumulations of

particles or foreign matter on the mat from getting

into the press, where they could cause extreme local

stresses and consequent belt damage. Defective mat

sections are automatically rejected. Lines for the

production of thin panels, when threatened, are

automatically stopped by a secondary control unit.

With the new thin panel presses a compactor

is used to press the mat to nominal thickness and

thereby removing of risk of steel belt damage.

At the press outfeed on thin panel lines, cleaning

and safety devices are mounted for both belts to

ensure that product residues do not adhere to thebelts and are not carried along on the belt.

The efficient cleaning systems for the steel belts

feature rotating metal brushes for the product sides

of the belts and plate-type scrapers for the inside of

the belts to prevent accumulation of lubricant.

The protection of the steel belts begins even

before production commences, namely, after the

erection of the press, when the belts must be

drawn into the press enclosure. To make sure that

this job is done properly, the winding of the beltsin the delivery coil, for instance, is prescribed in the

above-mentioned specifications, considering the local

erection situation.

Siempelkamps scope of delivery always includes

the unwinding and drawing-in facilities, which are

temporarily fixed to the press during erection and

which ensure safe and careful handling of the belts

during the installation. These facilities are, of course,

designed in accordance with all relevant regulations

for the safety of erection personnel. Furthermore, in

the Erection Manual for ContiRollpresses, 25 of 41

pages are dedicated to the installation of the steel

belts, clear evidence of the importance attached to

the proper handling of these valuable components.

Rod carpet typical of Siempelkamp ContiRollpress


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21

View of ContiRollinfeed end. On the left, the belt infeed drums are directly followed by the return and entrance of the rod carpet. In

the high-pressure zone, the frames are arranged in pairs. On the right can be seen how closely the press cylinders are spaced to enable

precision adjustment of the flexibly supported upper press plate.

View of ContiRoll

outlet endwith rod carpet return, belt tension

terminal and drive


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2

6.1.3 Dieffenbacher CPSDieffenbacher Conti-Panel System an innovative, user-oriented technologicalconcept

With the successful introduction of the continuous

Conti-Panel System, Dieffenbacher has underlined its

position as a world-leading manufacturer of presses

and press lines for wood-based panels. This innovative

concept is the result of many years of experience in

hydraulic press manufacture, in conjunction with the

use of the most-modern high-tech control elements.

The CPS is a synergistic product from the domain of

metal forming and plastics molding presses, achieving

dynamic accuracies in the range of some thousandths

of millimeters, e.g. on parallel motion control systems.

The CPS embodies a close cooperation with the

user : It is a highly flexible press with a low rate of wear,

fully meeting users demands:

High specific performance based on highavailability

Operator-friendly controls

Transparency in modular setup, remarkable

robustness

Good access and simple maintenance facilities

At Dieffenbacher, the principle for further

developments and long-term sales strategy is to

include the user and his concrete ideas of innovation

and technology in the realization of such complexlines. Thus it is ensured that only reliable, mature and

optimized systems will go into operation.

The Dieffenbacher Conti-Panel System features an

all-round press; it is suited for the production of

particleboard, MDF, HDF, OSB, LVL and other

wood-based panels. High capacities, consistent

finished product quality and maximum flexibility are

guaranteed, among other factors, by:

an online adjustable infeed geometry (wedge

compactor)

high advance speeds of up to 2000 mm/s

fast compression phase

optimized heat supply at the right time

adjustable position or pressure control (online)

minimum thickness tolerances

highly flexible forming profiles, length- and

crosswise

modular tie rod design with pressure cylinders

arranged on the outside

optimum range of width adjustability

Widest Dieffenbacher press at

Footner/Canada: heating plate width

approx. 4000 mm board width for

approx. 3900 mm product width


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Operational principle of theDieffenbacher CPS:Heat supply and distribution

Depending on the length of the press, the

Dieffenbacher Conti-Panel System is provided with a

suitable number of heating circuits.Pressure and heat are transferred by platens that are

heated through thermal oil channels and protected

by thin protection plates. The heat is transmitted via

rolling rods onto rotating steel belts and hence onto

the material to be pressed.

By the use of suitable material pairs unhardened

heating plates with high thermal conductivity and

well-hardened thin protection plates combined with

wear-resistant function elements the CPS meets

the criteria imposed by the user with regard to aneffective heat transfer (see page 24).

To increase the heat supply, the rolling rod and steel

belt systems are guided back in an insulating

channel. A preheating device for the rolling rods

supplies additional heat energy that is available right

at the inlet. With this feature, it is also possible to

achieve a high degree of process stability.

Heat transfer from the heating platens onto the steel

belts is a dynamic process using the turning

rolling rods that ensure a uniform, uninterrupted heat

supply over the entire width.

Operational principle of theDieffenbacher CPS:Pressure build-up and distribution

For the Conti-Panel System, Dieffenbacher uses the

proven modular frame design with the pressure

cylinders arranged along both sides of the press, on

the outside.

This leads to advantages that have been proven inpractical use, such as good access for maintenance

purposes and gentle operating conditions for the

hydraulic components to ensure a long service life.

The open frame design comprises a stationary frame

bottom part (table) and a moving upper part (ram).

Forces are transmitted via removable pull rods that

are fastened to the table.

In the middle of the press, calibrating (multipot)

cylinders are installed in the frames. By means of

these cylinders, it is possible to select the crossprofiles that are necessary according to technological

requirements in keeping with the customers request.

The cylinders are controlled by proportional

control valves and form closed-loop control circuits,

together with the digital position pickups. Thus panels

with optimum thickness tolerances and high process

stability can be produced.

By a deliberate separation of functions and thehighly versatile design of the heating platen system,

the press profile can be set online in an optimum

manner in longitudinal and transverse directions to

suit the respective product demands.

As a result of a new concept, the frame supports are

able to compensate for thermal expansion. The

advantage is that the platen temperature can be

changed without any restriction and without

interrupting the production. This is also a major

benefit for the CPS user.The press infeed section (see page 24) is specially

designed to meet the requirements of panel production

using different raw materials, i.e. particleboard, MDF

or OSB.

The wedge compactor equipped with an intelligent

double joint system can adjust automatically to the

respective mat height and can be set to any angular

position. Hence the compression speed curve can be

set in an optimum manner in this zone, which is an

important phase in the technological process.

Maximum pressure and high temperatures are

available at the ear liest moment possible. Thus the

crucial conditions for the shortest possible pressing

times and panel products are optimized for minimum

sanding allowance, and best possible density

profiles are achieved.


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4

The rolling rods of the CPS are connected coaxially with the links of the hollow chain by resilient rods

Infeed of the rolling rods by means of gear wheels and spr ing leafs at both ends .

Footner OSB production with belt width 4,080 mm, belt thickness 3.0 mm.

Heated press plate

Protection plate

Rolling rods, 21 mm thick

Hollow chain

Steel press belt

Connecting rod


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25

Dieffenbacher press for

particle boards

Dieffenbacher press for

MDF boards

Smallest Dieffenbacher press for LVL production: heating plate

width approx. 1300 mm board width, approx. 1400 mm product width


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6.1.4 Hymmen IsoPressand IsoRoll

Hymmen is the only supplier in the field of

continuous double belt presses to offer both

isobaric and isochoric press systems, and is leader

in various product applications which make use of

these technologies.Isobaric double belt presses:

The isobaric press is based on the environmentally

friendly air cushion system and is characterized by

an optimal distribution of pressure and an exact

control of the temperature profile. Isobaric presses

generate pressures up to 100 bar and temperatures

up to 400C . An additional specific advantage of this

technology is the ability to achieve a heating- and

cooling process without a pressure interruption. Theworking width of an isobaric press can be up to 2300

mm, while the press length depends on capacity

requirements and the press technology.

The isobaric Double Belt Press is suited to the

lamination of board material as well as the pressing of

roll material & granulates, such as:

Decorative laminates (CPL)

Technical laminates (Copper cladded laminates for

printed circuit boards, ski-laminates)

Melamine lamination of flooring & furniture

boards

PVC & rubber flooring

Lightweight conveyor belts

Plastic cards & further high-tech products made

out of composites

With an experience based on having sold more than

170 double belt presses, Hymmen takes a worldwide

dominating position on the market for the continuous

production of decorative and technical laminates as

well as laminate floorings.

Isochoric double belt presses:

The strengths of the isochoric double belt press are in

the field of pressing soft materials out of granulate or

roll material together to one product with a defined

material thickness.

Isochoric presses can be constructed for heating- as

also particularly combined heating- and cooling

processes.

Typical production fields are

Fibreboards

Cork or rubber flooring

Industrial laminates

Rubber boards

Heavy transport belts

Hymmen double belt press Iso PressType HPL

Hymmen double belt press Iso RollType ISR


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27

6.1.5 Held Technologie GmbH

The beginning of isobaric press technology

In 1975, the Held company brought the first

isobaric Double Belt Press (DBP) to the world.

Further pioneering achievements followed, bringing

technological leadership to the company in its field ofisobaric presses:

Worlds first isobaric high-pressure DBP providing

a surface pressure of 100 bars (1,450 psi),

Worlds first isobaric high-temperature DBP to

provide a heating temperature of 400C (750F),

Worlds first isobaric high-speed DBP for

production speed as high as 48m/min (160 fpm).

At the beginning of the 1970s a DBP was nothing

new; its principle had been known for quite a while.Even the idea of exerting completely uniform

pressure upon a surface by means of an isobaric

cushion had already been conceived. However,

until then it seemed impossible to press a fluid

medium against a moving steel belt and hold it there

without leakage. Only the seal system developed

by Held made an old dream come true: continuous

production under isobaric pressure.

A business partner in the furniture industry had

triggered the development by requesting a machine

that could make thermo-set edge-banding strips on a

roll. He had enough of wasting material only because

the available strips of fixed length never quite fit his

application.

This challenge eventually led to the building of

the first isobaric DBP, on which resin-impregnated

paper could be laminated into endless edge-banding

material under the influence of pressure and

temperature. With a useful width of 500 mm (20 in.)

the machine had only relatively modest dimensions.

Its reaction zone, i.e. the working area between thesteel belts, could not yet be heated; therefore, the

necessary process heat had to be loaded on to

the belts by heating the inlet drums. For reasons of

simplicity air was chosen as the pressure medium

for the pressure cushion. At 7 bars (100 psi) the

generated pressure was far below the level reached

by modern oil-supported DBPs. But at least it was

possible for the first time to produce from roll to roll,

i.e. continuously, even though production speed was

rather modest compared with todays numbers:1.8 m/min with a 2.1 m long reaction zone. Today, ten

times that output is achieved.

The machine proved so useful that a licensee was

soon found and the concept developed by Held went

on to form the basis of all isobaric DBPs used around

the world.

Evolution of the high-performance press high pressure and high temperature

This success encouraged research into how to

improve efficiency and productivity. Higher cushion

pressure would permit the use of more cost-effective

paper with lower resin content, but would result in

increased leakage of the air from the pressure cushion,

leading to considerable waste of energy which would

render the economic advantage useless. A pressure

medium more viscous than air promised to be kept

more easily on the moving belts without leakage. The

solution was the oil-supported DBP. The oil-cushion

brought a very helpful side-effect: an extremely

efficient lubrication of the seal system, an advantage,

whose importance became apparent only much later

when air-cushion machines had problems handling

high process pressure. Oil-cushion machines could be

run with 80 bars continuously without compromising

the life expectancy of the seals or generating blisters

on the product. They were also found fundamentally

more advantageous with regard to safety. Like allliquids, oil is incompressible and therefore cannot

Worlds first Isobaric press (1975), 200C, 7 bar

Basic design of an isobaric DBP


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8

store any mechanical energy by being reduced in

volume. In contrast, all gases are compressible, so

under pressure they contain a considerable amount

of energy. In the event of an accident, air cushions can

release their stored energy in an explosion.

After a way had been found to feed process heatdirectly into the reaction zone where it was really

needed, further benefits were reaped: higher output

(the additional supply of energy permits higher

production speed) and energy savings (lower thermal

losses by reducing heat radiated by the inlet drums).

First, indirectly heated heat bridges, and later on

directly heated heat bars provided solutions that

went far beyond the original goal and permitted

the processing of new materials demanding much

higher process temperatures (up to 400C or 750F).Excellent heat conduction through direct contact of

the metallic heat bars with the steel belts allows the

transfer of large amounts of thermal energy with

high efficiency. The directly heated reaction zone

is an outstanding feature which proves extremely

useful in particular with thicker materials that can be

processed at significantly higher speeds.

Better quality through lower inlet

temperature

Heating the reaction zone provides further important

advantages: melting and tearing of thin plastic films or

detrimental pre-curing of laminate surfaces by heat

radiated by the hot belts in the nip region of the press,

which can happen when heating the belts only via the

inlet drums, is now easily avoided when running with

a low inlet drum temperature.

If a resin impregnated web does not enter the

press sufficiently flat, stripe patterns from variations

in gloss level are unavoidable. One might imagine that

choosing a higher production speed could reduce

this effect by reducing the webs residence time in

the inlet region. Unfortunately, this will not help, since

the higher speed will also require a faster curing resin,

which in turn will also pre-cure in less time. A number

of protective devices have been devised to avoid theeffect, but have mostly proven ineffective, since they

can only influence the very outer part of the nip.

A sufficiently low inlet drum temperature is

needed to eliminate the problem and ensure that

surface curing only starts when the material in

under pressure in the reaction zone. Of course, this

temperature pattern can only be achieved if enough

heat can be applied to the belts inside the pressure

zone, enabling the high process temperature to be

reached here and here alone. This also makes possiblethe processing of thin plastic films, which would

otherwise tear and melt at first contact with the hot

belts in the nip of the press.

Decorative laminate HPL vs. CPL

The quality of a laminate is highly dependent upon

the pressure level it was subjected to during the

manufacturing process. The old DIN 16 926 standard

(since superseded by EN 438) stipulated a working

pressure of 70 bar for the production of HPL (High

Pressure Laminate), which air-cushion machines

could not provide. As a result, continuously-produced

laminate was, for a long time, considered a low quality

product.

Today, while the quality of Low Pressure Laminate

is still not comparable with that of genuine HPL, the

market share now being won by CPL shows that

there are applications for which low pressure CPL is

perfectly well suited. Furthermore, as oil-supported

DBPs are now available with working pressure of up

Service friendly: high-performance heating platen can be drawn out User friendly: setting the gap-width is just a push button operation


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to 80 bars, this differentiation no longer makes sense.

Indeed, the only differentiation that remains relevant

is that of press type (cycle or continuous press).

And it is Held's isobaric, hydro-static DBP >system

contilam< that holds the advantage, delivering

continuous HPL (CHPL), a material that offers thelowest production costs and optimum laminate

uniformity.

DBP or cycle press?

The principles of isobaric DBP operation offer a

number of other important advantages.

A DBP can produce uniform quality more easily

than a cycle press as every piece of laminate is

subjected to exactly the same pressure, temperature,

and residence time. Differences in temperature

history between various pieces of laminate cannot

occur in a continuous press, but are unavoidable in a

cycle press due to each laminate's relative position

in a multi-daylight press. And for very long pieces of

laminate, there is no alternative to a continuous DBP.

With regard to the basic question: "Cycle

press or continuous press?", a comparison with

the printing industry may be of interest. When

Gutenberg invented book printing, he used a cycle

press. However, today's printed matter is, with few

exceptions, manufactured on high-speed rotaryprinting presses. Why so? Because they are more

economical. This is why the future belongs to

continuous processes, and why examples can be

found in every industry.

Profitability

Further aspects contribute to the superior

profitability of DBP-based laminate manufacture.

Almost complete automation means the entire

process can be run with just two operators (one tosupply material and one to unload finished product)

and also results in low handling losses.

In times of rising energy costs, a directly-heated,

hydro-static DBP >system contilam< is particularly

economical. Heat is supplied directly to the pressure/

heating zone, i.e. where it is needed. The pressure

medium only needs to convey pressure - it does not

need to carr y process heat. This means there is noneed to circulate a large amount of pressure medium

and heat/pressure losses are reduced to a minimum.

Since a DBP never needs to open its gap for loading

and unloading of material, it uses energy even more

efficiently. And last but not least, trim waste only

occurs on two sides while cycle press laminate needs

to have all four sides trimmed.

High-gloss laminate heating and cooling

under pressure

Cost-effective manufacturing of high-gloss laminate

is another application for Held's isobaric DBPs

due to their efficient cooling without affecting

process pressure. The cooling process is particularly

economical as heating/cooling zones are thermally

isolated from each other, and therefore remain at

their respective temperature levels. Heat only needs

to be extracted from the material and the thin steel

belts (1 mm thick) passing the press whereas, in a

multi-daylight-press, the thick press platens

(ca. 100 mm thick) must also be cooled, renderinga process with heating and cooling rather

uneconomical.

Isochoric or isobaric?

One question remains regarding DBP operating

principles: "Which is best: isochoric (mechanical,

supported by rollers) or isobaric (fluid, supported by

air or oil)?"

Isochoric presses are well established in the

processing of compressible materials such as particleboard made from wood chips. Their inherent

calibrating effect is an advantage here; the unavoidably

High-performance DBP for decorative laminate, two formats, 1.30 m and 1.50 m, 80 bars , 30 m/min (CLEAF, Italy)


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0

non-uniform compaction and hence non-uniform

density is acceptable for this type of product.

Other materials need processing with a

completely uniform surface pressure. Those with

demanding visible surfaces which soften during the

manufacturing process, for instance, can only be

produced continuously on an isobaric DBP where

there no risk of pressure differences impacting on

the material and distorting the pattern. For similar

reasons, copper-clad laminate for demanding

electronic applications require a process as free from

tensions as possible in order to eliminate the risk

of tensions trapped in the laminate being released

during soldering and warping the product. As well as

delivering the necessary uniformity of pressure, an

oil-supported, hydrostatic DBP offers the additional

advantages of high profitability and the ability to

be used in cleanrooms - a prerequisite for this

application - making it the ideal choice.

Continuous high-gloss laminate, two formats, 1.35 m and 1.55 m, 80 bars, 30 m/min (Westag & Getalit)

High-temperature press suitable for clean-room operation, pressure

zone 0.7 m x 3.1 m, 400C, 80 bars, 20 m/min

Worlds largest isobaric DBP for decorative laminate. Press platens 5.20 m x 2.30 m, 80 bars, 48 m/min (SIT Gruppo Mauro Saviola, Italy)


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6.1.6 Pagnoni Easylam

In the late 90s, Pagnoni Impianti, the Italian

manufacturer of single/multi-opening presses for

panels production (particleboard, MDF, plywood,

HPL) and short cycle lamination (with melamine or

phenol papers), entered the continuous press market

with its Pagnoni Easylam, a double steel belt press

specifically designed to apply glued overlays and to

flatten veneer on boards.In these applications the press is the bottleneck

of the whole process: conventional multi-daylight

presses are very slow and high frequency presses

have often failed to live up to users expectations.

The innovative technology behind the Pagnoni

Easylamnot only removes this bottleneck through

its inherent speed but also offers the additional

advantage that the lack of press loading/unloading

dead time allows the use of fast reaction glues, further

increasing the production capacity of the line.

The press

The Pagnoni Easylampress is modular in design and

its main elements are the drums, the hot platens, the

rollers, the bearings and the steel belts.

The press structure consists of 2 m long modules.

The upper part moves vertically in relation to

the lower one, while the lower section lays on

base beams which are fixed to the foundation.

The structure is open on one side to allow easyreplacement of the steel belt.

Two motorized drums and two idle ones, 1200

mm diameter, provide the drive and guiding/

tensioning of the steel belts. The in-feed drums

are heated with thermal oil, through axial rotary

joints, and the temperature in each drum can be

independently adjusted.

The sliding platens are placed between the upper/

lower structures and the relevant steel belt. They

are made up of modular elements, positioned sideby side. Each element consists of a canalized platen

(with heating circulation to ensure correct working

Continuous press Pagnoni Easylamfor engineered parquet, pressing hot platens 1000 x 4200 mm


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temperature), and a frame which is fixed to the base

platen and supports the bearings and the rollers. Each

frame can be easily disassembled for maintenance

purposes. Two heating circuits enable different

temperatures to be set in the platens.

This new press belongs to the family of isochoricpresses, but is significantly different from other such

presses in that there is no rod carpet moving inside

the press; instead, independent rollers rotate on their

own axis on a bed of ball bearings. With this patented

system, the squareness of the rollers and axial

feed is guaranteed by the accuracy of mechanical

construction, thereby avoiding any difficulty in

the steel belts guidance. This ensures outstanding

precision (max. 1 mm deviation) around the

theoretical movement axis, even with asymmetricalloads. Furthermore, the rollers always remain warm,

enabling considerable savings in energy costs.

Pagnoni Impianti uses Sandvik 1,4 mm thick

stainless steel belts. The out-feed drums drive the

belts; their tension is provided by 2+2 cylinders

placed on the in-feed drums. The guide is controlled

by lateral sensors which, based on the position of

the belt with respect to the longitudinal press axis,

adjust the pressure in the tensioning cylinders. The

out-feed drums are equipped with cleaning scrapers

and rotating brushes to remove any glue waste. The

inner part of the belts is also continuously cleaned by

brushes, moving transversally.

Pagnoni Easylam characteristics

Specific pressure: max 80 N/cm2

Inlet drums temperature: max 150C

Hot platens temperature: max 120C

Mechanical speed: max 30 m/min

Heating circuits: no. 4 independent

Press opening/closing control: with electroniccontrol

Pagnoni Easylamis available in several standard

sizes with widths varying from 350 mm to 2300

mm and lengths from 1900 mm to 8200 mm. The

flexibility in size makes it easy to combine press

length and width to meet customers technical and

commercial needs.

Designed for versatility

The Easylam continuous press has been designed

by Pagnonis technical team to deliver maximum

flexibility through the ability to:

- respond quickly to production changes- process panels that have been inaccurately or

randomly positioned on the introduction belt- carry out different processes with the same press

Pagnoni Easylamgets great results in terms

of production capacity, final product quality and

operating costs for a whole range of products/

processes including panel veneering, two and

three layers engineered flooring, five components

doors (honeycomb frame + thin MDF + veneer),

five components doors post (chipboard + MDF+ veneer), thin plywood (up to 7 ply), tops for

postforming made with MDF or chipboard overlaid

with glossy HPL.

Pagnoni Easylampanel veneering 2300x8200 mm

(A view of the security roller installed before the upper inlet drum)


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7. Steel belts for wood based panels

Steel belt manufacturer Sandvik has a number of

significant firsts to its credit, not least of which was

the development of the worlds first steel belt in 1901.

This was used for the transportation of sawdust, and

the company has maintained its close connectionwith the wood industry to this day.

In 1957, Sandvik was responsible for introducing

the steel belt to the wood based panel industry,

when the first press to be fed by a steel belt, a single-

opening intermittent press, was developed by Bhre

& Greten in Springe, Germany.

Just a few years later, Sandvik itself designed the

basis of the presses that have had such a major

impact on this industry over the last two decades,

building the first double belt press with a roller bed.With this level of involvement over the years, it will

come as no surprise to learn that the largest single

market for Sandvik steels belts is the WBP industry.

While the company does still make its own double

belt presses (only for fiberglass reinforced

thermoplastics), as far as the WBP industry is

concerned, it is as a specialist manufacturer of steel

belts that its name is best known. The companys steel

belts are now at the heart of press systems worldwide.

Over the years, special grades have been

developed to cope with the changing and ever-more-

demanding requirements. Improvements continue to

be made in the manufacturing process, but the

essential qualities that make the steel belt ideal for

this process remain virtually unchanged.

A properly manufactured steel belt combines

hardness and strength with flexibility, a smooth

surface and excellent heat transferability. It is durable,

resistant to corrosion and easily maintained. Once

the steel belt was introduced to the market in the

1950s, it didnt take long for WBP producers or pressmanufacturers to recognize this unique combination

of qualities, and Sandvik has continued to build on

these fundamental benefits ever since.

Steel grades 1300C and the new 1320C

The steel grade used in single-opening presses has

traditionally been Sandvik 1300C, a hardened and

tempered carbon steel. Over the 50-plus years

that these presses have been in use, more than a

thousand 1300C belts have been supplied, and somehave given their users well over two decades of

reliable service.

The late 90s saw the introduction of a new steel

grade suitable for this application, Sandvik 1320C, a

low carbon, dual phase steel (with a microstructure

of martensite and ferrite) which has excellent

mechanical and fatigue properties but is particularly

notable for its welding characteristics.By eliminating the need to carry out post-weld

annealing (even though the weld is harder than the

parent material, it will run without cracking),

installation costs are lower than thos

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