Lec 20 Plastic

8/10/2019 Lec 20 Plastic

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Lesson Outcomes:

After todays lecture, students areexpected to:

Analyze the process of elastomer

and polymer composite production,metal-matrix composite processes

Analyze the design considerationsfor plastics technology


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Processing Elastomers

Commonly shaped by extrusion orinjection moulding.

Extruded parts such as tubing, hoses &inner tubes.

Injection-moulded parts mostly used forautomobiles.

Also can be shaped by blow moulding &thermoforming.

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Calendering

For rubber & some thermoplastic sheet.

A warm mass of the compound is fedinto a series of rolls and then strippedoff in the form of a sheet.

Sheets produced are subsequently usedin thermoforming.


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Calendering

Schematic illustration of calendering. Sheets produced by this process

subsequently are used in thermoforming. The process also is used in

the production of various elastomer and rubber products.

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Dipping

Discrete rubberproduct likesglove.

Metal form

repeatedlydipped into aliquid compound.


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ProcessingReinforcedPlastics

To obtain good bonding between thereinforcing fibers and the polymermatrix, fibers surface treated byimpregnation (sizing).

Short fibers added to thermoplastics forInjection moulding.

Long fibers used in the compressionmoulding.

Partially cured sheets called by variousterms such as;

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1. Prepregs The continuous fibers aligned. Through surface treatment to

enhance adhesion to the matrix.

Individual sheet combined intolaminated structures Eg : Stabilizer for the jet fighter Typical products from prepreg are

panels for construction and electricalinsulation.

ProcessingReinforcedPlastics (cont.)


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Tapes used inMaking ReinforcedPlastic Parts

(a) Manufacturing process for polymer-matrix composite tape. (b) Boron-epoxy prepregtape. These tapes are then used in making reinforced plastic parts and components with

high strength-to-weight ratios, particularly important for aircraft and aerospace applications

and sports equipment. Source: (a) Courtesy of T. W. Chou, R. L. McCullough, and R. B.

Pipes. (b) Courtesy of Avco Specialty Materials/Textron.

(b)

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Tape and Tape-Laying System

(b)(a)

(a) Single-ply layup of boron-epoxy tape for the horizontal stabilizer for an F-14 fighter

aircraft. (b) A 10-axis computer-numerical-controlled tape-laying system. This machine

is capable of laying up 75- and 150-mm (3- and 6-in.) wide tapes on contours of up to +/-

30 degrees and at speeds of up to 0.5m/s (1.7 ft/s). Source: (a) Courtesy of Grumman

Aircraft Corporation. (b) Courtesy of The Ingersoll Milling Machine Company.


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Forms of fibreglass (a) continuous strand roving (b)chopped strand (c) chopped strand mat (d) wovenroving

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Production of Fiber-ReinforcedPlastic Sheets

Schematic illustration of the manufacturing process for producing fiber-reinforced

plastic sheets. The sheet still is viscous at this stage and later can be shped into

various products. Source: After T. W. Chou, R. L. McCullough, and R. B. Pipes.


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2. Sheet moulding compound(SMC) Chopped fibers deposited in random

directions over a layer of resin paste. Second layer of resin paste is deposited on

top, then pressed between rollers.

3. Bulk moulding compound (BMC)

The compounds are in the shape of billets


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4. Thick moulding compound (TMC) Combines a characteristics of lower cost

BMC & higher strenghth SMC



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Moulding of Reinforced Plastics

Common moulding processes forreinforced plastics are;

1. Compression moulding Material placed between two moulds and

pressure is applied.

2. Vacuum-bag moulding/Pressure Prepregs are laid in the mould

Pressure to shape the product obtained bycovering the lay-up with a plastic bag andcreating a vacuum

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Vacuum-Bag Forming andPressure-Bag Forming

Schematic illustration of (a) vacuum-bag forming, and (b) pressure-bag

forming. These processes are used in making discrete reinforced plastic

parts. Source: After T. H. Meister.


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3. Contact moulding (Open mouldprocessing) Used in making products with high surface-

area-to-thickness ratios. Use a single male or female mould. Can be done by hand lay-up or spray lay-

up.

Moulding of Reinforced Plastics(cont.)

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Open-Mold Processing

Manual methods of processing reinforcedplastics: (a) hand lay-up, and (b) spray

lay-up. Note that, even though the

process is slow, only one mold is

required. The figures show a female

mold, but male molds also are used.

These methods also are called open-mold

processing. (c) A boat hull made by

these processes.


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Some other processes for reinforcedplastics are:

1. Filament Winding Resin and fibers are combined at the time

of curing Parts are formed on a rotating mandrel The reinforcing filament, tape is wrapped

continuously around the mandrel. Products example: pressure vessel,propellers, blades


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Filament-Winding

(b)

(a) Schematic illustration of the filament-winding process; (b) fiberglass being

wound over aluminum liners for slide-raft inflation vessels for the Boeing 767

aircraft. The products made by this process have high strength-to-weight ratio and

also serve as lightweight pressure vessels. Source: Courtesy of Brunswick

Corporation.


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2. Pultrusion Produces long parts with various uniform

cross-section such as rod, flat strips andtubing.

Continuous reinforcement is suppliedthrough bobbins (prepreg feed system)

The bundle is mixed with a thermosettingbath then a performing die and a heated

steel die. The product is cured then.


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Pultrusion

(a) Schematic illustration of the pultrusion process. (b) Examples of parts

made by pultrusion. The major components of fiberglass ladders (used

especially by electricians) are made by this process. Unlike aluminum

ladders, they are available in different colors but are heavier because of the

presence of glass fibers. Source: Courtesy of Strongwell Corporation.

(b)


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Metal matrix-compostie can be made bythe following processes:

1. Liquid-phase processing Casting involving liquid-matrix material

(aluminium, titanium) and solid reinfoircement(graphite, SiC, Al2O3)

2. Solid-phase processing

Powder-metallurgy techniques including coldand hot isostatic pressing.

Products examples, tungsten-carbide tools anddies with cobalt as the matrix.

Processing Metal-matrixComposite

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Design Considerations ofplastics

Considerations for product design: Material selection to meet product

requirements

Product without stress concentration, sink

marks, ... Position of gate, runner, ejection pin for

tool design,

Elimination of premature failures based onliterature reviews.


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Considerations for tool design:

Tool material for manufacturing volumeand life

Tonnage of press & number of cavities in atool

Position of gate, runner, ejection pin for

tool design, ...

Design Considerations of plastics(cont.)

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Design Modifications to MinimizeDistortion in Plastic Parts

Examples of design modifications to eliminate or minimize distortion in plastic parts:

(a) suggested design changes to minimize distortion; (b) stiffening the bottoms of

thin plastic containers by dominga technique similar to the process used to shape

the bottoms of aluminum beverage cans; and (c) design change in a rib to minimize

pull-in (sink mark) caused by shrinkage during the cooling of thick sections in

molded parts.


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Avoid sharp variation of wall thickness Avoid sharp corners

Example of Design Considerationsfor Plastics Processing

Provide generous draft angles, 5o or more

Avoid needs of side-pull (reading assignment)



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Core bosses to ensure uniform thickness (minimize impact ofvariable shrinkage)


Thats all for today..

Any questions??


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IQ + EQ + SQ = TQ

Thank You for coming and

see you again..

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Lec 20 Plastic