Manufacturing Rocesses - i - Unit III - Plastic Processing

7/30/2019 Manufacturing Rocesses - i - Unit III - Plastic Processing

1/22

PLASTIC PROCESSINGFine powder (plastic, ceramic, metal)

Join powder particles (heat to just below melting point)

balls used in ball-point pens

gears, cams

cutting tools (inserts)

porous metal filters

oil-impregnated bearings

piston rings in engines

Shape by compacting in a die

Prof. Pramod R. Wadate


2/22

Plastics Processing

Plastics are usually supplied as moulding powder, granules or chips which have to

be processed.

Processing includes the thorough mixing of additives with the moulding powder,

granules or chips to produce plastic compounds.

The use of additives allows a relatively small number of base plastics to be

transformed into wide range of very versatile materials.


3/22

Types of Plastic Processing

Injection Moulding Usually for thermoplastics. Molten plastics are injected

under pressure into a mould. The mould surface detail (profile of the product) can

be accurately reproduced.

Compression Moulding Usually for thermosetting plastics. Plastic is moulded

under pressure before the polymerisation begins.

Extrusion Usually for thermoplastics. The molten plastics are fed under pressureby a screw through a hole or a die. Long continuous lengths, such as sheets, rods

and tubes, can be produced.


4/22


Thermoforming (Vacuum Forming)- Heat-softened thermoplastic sheet is drawn

or sucked over a mould. It can be used for a variety of products from chocolate

box trays to acrylic baths.

Blow Moulding An extruded thermoplastic tube is heated and air is blown into it

to force the plastic to take on the form of the mould in which it is enclosed.

Rotational Moulding Usually for thermoplastics. Powder is heated inside aclosed mould which is then rotated around two or three axes. This forces the

plastic to take the form of the surface of the mould. It can be used to make very

large hollow articles.


5/22


Calendering Usually for thermoplastics. Molten plastics are squeezed between

hot rollers to form film or sheets.

Casting Useful for thermosetting plastics. Molten plastic is poured into a mould.

Bending Thermoplastics can be heated along a line using an electric strip heater

and then folded to the desired angle. A bending jig is sometimes used to hold the

plastic in position until it resets.


6/22


Fabrication Plastics can be joined together using a variety of fixings and

adhesives.

Coating Powdered thermoplastic melts on the surface of a heated product

giving it a thin film coating.

Forming Layers of glass fibre (Glass Reinforced Plastic) matting and polyester

resin can be formed over a mould. As the resin cures it will harden to give

rigidity to this fibre/resin matrix. Thermoplastic can also be formed by heating

the whole sheet in an oven until it becomes floppy. The sheet is then

pressed between two formers.


7/22

Compression Molding

The process requires plastic to be placed into a mouldcavity where it is heated and plasticised. It is thencompressed into shape by a heated punch.

The materials used -

melamine formaldehyde

phenol formaldehyde

urea formaldehyde.

These materials can be formed into different shapesthrough applying both heat and pressure, other plasticsdo no have these properties


8/22


9/22


10/22

Injection Moulding

The Process

Injection moulding is one of the most important industrialprocesses in the mass production of plastic goods. The cost ofmachining the original moulds can be very high. Therefore it is

necessary to sell large numbers of the products beingmanufactured to recover costs

Thermoplastic granules are heated until they soften. Then thematerial is forced under pressure into a mould. When cool, the

mould is opened and a component which is the exact shape of thecavity is extracted


11/22

Injection Molding


12/22

Ram / Plunger Injection Molding


13/22

Screw Type Injection Molding


14/22

Blow Molding


15/22

Thermoforming Vacuum Forming


16/22

ClampingThe clamp frame ensures the plastic sheet is held firmly in place during the formingprocess.HeatingRadiant heaters are normally used to heat the sheet which has been positioned overthe aperture of the vacuum forming machine. For thicker sheet both surfaces mayneed to be heated and more sophisticated machines allow this. Heaters move intoposition both above and below the sheet.Pre-stretchIs used to achieve "even" wall thickness. Air is introduced to blow a small "bubble"and the mould is then raised into the pre-stretched sheet.Vacuum

A vacuum is applied, the sheet is drawn into intimate contact with the mould and themould detail is picked up.Plug AssistWhere a deep draw is required a top "plug" may be used to push material into themould during the forming process.Cooling and ReleaseThe material is allowed to cool. The cooling process may be shortened with blown air

or even a fine water spray. The moulding may then be released from the mould byintroducing a small air pressure.FinishingAfter moulding, any mould finishing may be performed, trimming, cutting, drilling,polishing, decorating etc.


17/22

Thermoforming Pressure Forming


18/22

ExtrusionA machine used to extrude materials is very similar to the injection moulding machine.

A motor turns a thread which feeds granules of plastic through a heater. The granules

melt into a liquid which is forced through a die, forming a long 'tube like' shape.

The extrusion is then cooled and forms a solid shape. The shape of the die determinesthe shape of the tube.


19/22

Extrusion of Film


20/22

Extrusion of Sheet


21/22

Extrusion of Pipe


22/22

Extrusion of Cables

Date post:	14-Apr-2018
Category:	Documents
Upload:	pramod-wadate
View:	220 times
Download:	0 times

Manufacturing Rocesses - i - Unit III - Plastic Processing

Documents