5. Plastic Products More Plastic Products
Plastics can be shaped into a wide variety of products:
Molded parts
Extruded sections
Films
Sheets
Insulation coatings on electrical wires
Fibers for textiles
More Plastic Products
In addition, plastics are often the principal ingredient in other materials, such as
Paints and varnishes
Adhesives
Various polymer matrix composites
Many plastic shaping processes can be adapted to produce items made of rubbers and polymer matrix composites

6. Trends in Polymer Processing
Applications of plastics have increased at a much faster rate than either metals or ceramics during the last 50 years
Many parts previously made of metals are now being made of plastics
Plastic containers have been largely substituted for glass bottles and jars
Total volume of polymers (plastics and rubbers) now exceeds that of metals
Almost unlimited variety of part geometries
Plastic molding is a net shape process
Further shaping is not needed
Less energy is required than for metals due to much lower processing temperatures
Handling of product is simplified during production because of lower temperatures
Painting or plating is usually not required

7. Thermoplastics
These plastics are made up of lines of long chain molecules (below) with very few cross linkages. This allows them to soften when heated so that they can be bent into different shapes, and to become stiff and solid again when cooled. This process can be repeated many times.
Thermoplastics
Chemical structure remains unchanged during heating and shaping
More important commercially, comprising more than 70% of total plastics tonnage

8. Plastic types: Thermoplastics
General properties: low melting point, softer, flexible.
Typical uses: bottles, food wrappers, toys, …
Examples:
Polyethylene: packaging, electrical insulation, milk and water bottles, packaging film
Polypropylene: carpet fibers, automotive bumpers, microwave containers, prosthetics
Polyvinyl chloride (PVC): electrical cables cover, credit cards, car instrument panels
Polystyrene: disposable spoons, forks, Styrofoam™
Acrylics (PMMA: polymethyl methacrylate): paints, fake fur, plexiglass
Polyamide (nylon): textiles and fabrics, gears, bushing and washers, bearings
PET (polyethylene terephthalate): bottles for acidic foods like juices, food trays
PTFE (polytetrafluoroethylene): non-stick coating, Gore-Tex™ (raincoats), dental floss

9. Thermosetting Plastics
These plastics are made up of molecules that are heavily cross-linked (below). This results in a rigid molecular structure. Although they soften when heated the first time, and can therefore be shaped, they then become permanently stiff and solid, and cannot be reshaped.
Thermosets
Undergo a curing process during heating and shaping, causing a permanent change (cross‑linking) in molecular structure
Once cured, they cannot be remelted

10. Plastic types: Thermo sets
General properties: more durable, harder, tough, light.
Typical uses: automobile parts, construction materials.
Examples:
Unsaturated Polyesters: lacquers, varnishes, boat hulls, furniture
Epoxies and Resins: glues, coating of electrical circuits,
composites: fiberglass in helicopter blades, boats, …

11. SHAPING PROCESSES FOR PLASTICS
Compression Moulding
Transfer Moulding
Extrusion Moulding
Injection Moulding
Blow Moulding
Thermoforming
Calendering
lenPolymer Foam Processing and Forming
Product Design Considerations

13. compression molding
Plastics Processing: Compression Molding

14. Plastic Processing : Compression Molding
Figure : Compression molding for thermosetting plastics:
(1) charge is loaded,
(2) and (3) charge is compressed and cured, and
(4) part is ejected and removed.

15. Plastic Processing : Compression Molding
Molding materials:
Phenolics, melamine, urea‑formaldehyde, epoxies, urethanes, and elastomers
Typical compression-molded products:
Electric plugs, sockets, and housings; pot handles, and dinnerware plates
Simpler than injection molds
No sprue and runner system in a compression mold
Process itself generally limited to simpler part geometries due to lower flow capabilities of TS materials
Mold must be heated, usually by electric resistance, steam, or hot oil circulation

16. Plastics Processing: Compression Molding

17. Plastics Processing: Compression Molding

18. Transfer Molding
TS charge is loaded into a chamber immediately ahead of mold cavity, where it is heated; pressure is then applied to force soft polymer to flow into heated mold where it cures
Two variants:
Pot transfer molding - charge is injected from a "pot" through a vertical sprue channel into cavity
Plunger transfer molding – plunger injects charge from a heated well through channels into cavity.

19. Transfer Molding
Pot Transfer Moulding

20. Pot Transfer Molding
Figure : (a) Pot transfer molding: (1) charge is loaded into pot, (2) softened polymer is pressed into mold cavity and cured, and (3) part is ejected.

21. Plunger Transfer Molding
Figure : (b) plunger transfer molding: (1) charge is loaded into pot, (2) softened polymer is pressed into mold cavity and cured, and (3) part is ejected.

22. Screw conveyor

24. Thermoplastic granules (right) are fed from a hopper by a rotating screw through a heated cylinder.
The tapered shape of the screw (right) compacts the plastic as it becomes plasticized. This part of the process is similar to the heating and compacting stages in the injection moulding process. The difference being that the softened material is allowed to flow out through a die in a continuous stream
( Extrusion moulding ) rather than be pumped intermittently in measured amounts into a mould.( Injection moulding )
The die (right) which is fitted to the end of the extruder barrel  determines the cross-section  of the extrusion.

25. Extruder
Figure : Components and features of a (single‑screw) extruder for plastics
Compression process in which material is forced to flow through a die orifice to provide long continuous product whose cross‑sectional shape is determined by the shape of the orifice of a die
Widely used for thermoplastics and elastomers to mass produce items such as tubing, pipes, hose, structural shapes, sheet and film, continuous filaments, and coated electrical wire
Carried out as a continuous process; extrudate is then cut into desired lengths

26. Extruder Screw
Divided into sections to serve several functions:
Feed section - feedstock is moved from hopper and preheated
Compression section - polymer is transformed into fluid, air mixed with pellets is extracted from melt, and material is compressed
Metering section - melt is homogenized and sufficient pressure developed to pump it through die opening

27. Die End of Extruder : Extrusion Die for Solid Cross Section
Figure : (a) Side view cross‑section of an extrusion die for solid regular shapes, such as round stock; (b) front view of die, with profile of extrudate.
Progress of polymer melt through barrel leads ultimately to the die zone
Before reaching die, the melt passes through a screen pack - series of wire meshes supported by a stiff plate containing small axial holes
Functions of screen pack:
Filter out contaminants and hard lumps
Build pressure in metering section
Straighten flow of polymer melt and remove its "memory" of circular motion from screw

28. Extrusion Die for Coating Wire
Figure : Side view cross‑section of die for coating of electrical wire by extrusion.
Polymer melt is applied to bare wire as it is pulled at high speed through a die
A slight vacuum is drawn between wire and polymer to promote adhesion of coating
Wire provides rigidity during cooling - usually aided by passing coated wire through a water trough
Product is wound onto large spools at speeds up to 50 m/s (10,000 ft/min)

29. Plastics Processing: Extrusion

30. Plastics Processing: Extrusion

31. Plastics Processing: Extrusion

32. Extrusion
This process can be compared to squeezing toothpaste from a tube. It is a continuous
process  used to produce both solid and hollow products that have a constant
cross-section. E.g. window frames, hose pipe, curtain track, garden trellis.
Process
The photo below shows a typical thermoplastic extruder.

33. Plastics Processing: Extrusion

34. Injection Molding Injection Molding Machine
Polymer is heated to a highly plastic state and forced to flow under high pressure into a mold cavity where it solidifies and the molding is then removed from cavity
Produces discrete components almost always to net shape
Typical cycle time 10 to 30 sec, but cycles of one minute or more are not uncommon
Mold may contain multiple cavities, so multiple moldings are produced each cycle
Injection Molding Machine
Two principal components:
Injection unit
Melts and delivers polymer melt
Operates much like an extruder
Clamping unit
Opens and closes mold each injection cycle

35. Plastics Processing: Injection Molding

36. Plastics Processing : Injection Molding Machine
Figure : Diagram of an injection molding machine, reciprocating screw type (some mechanical details are simplified).

37. Plastics Processing: Injection Molding
(2) melt is injected into cavity.
(1) mold is closed
(3) screw is retracted.
(4) mold opens and part is ejected.
Cycle of operation for injection molding

38. Process & machine schematics* *
Schematic of thermoplastic Injection molding machine

39. New developments- Gas assisted injection molding

41. Blow Molding Extrusion or Injection molding Blow Molding Process
Molding process in which air pressure is used to inflate soft plastic into a mold cavity
Important for making one‑piece hollow plastic parts with thin walls, such as bottles
Because these items are used for consumer beverages in mass markets, production is typically organized for very high quantities
Blow Molding Process
Accomplished in two steps:
Fabrication of a starting tube, called a parison
Inflation of the tube to desired final shape
Forming the parison is accomplished by either
Extrusion or
Injection molding

42. Extrusion Blow Molding
Figure : Extrusion blow molding: (1) extrusion of parison; (2) parison is pinched at the top and sealed at the bottom around a metal blow pin as the two halves of the mold come together; (3) the tube is inflated so that it takes the shape of the mold cavity; and (4) mold is opened to remove the solidified part.

44. Extrusion Blow Molding
Extrusion Blow Molding involves manufacture of parison by conventional extrusion method using a die similar to that used for extrusion pipes.
Extrusion Blow Molding is commonly used for mass production of plastic bottles.
The production cycle consists of the following steps:
1.The parison is extruded vertically in downward direction between two mold halves.
2. When the parison reaches the required length the two mold halves close
resulting in pinching the top of parison end and sealing the blow pin in the bottom of the parison end.
3.Parison is inflated by air blown through the blow pin, taking a shape conforming that of the mold cavity. The parison is then cut on the top.
4.The mold cools down, its halves open, and the final part is removed.

45. 1 3 4 2

46. 5

48. Injection Blow Molding
Figure : Injection blow molding: (1) parison is injected molded around a blowing rod; (2) injection mold is opened and parison is transferred to a blow mold; (3) soft polymer is inflated to conform to the blow mold; and (4) blow mold is opened and blown product is removed.

49. Injection Blow Molding
1. In Injection Blow Molding method a parison is produced by injecting a polymer into a hot injection mold around a blow tube or core rod.
2.Then the blow tube together with the parison is removed from the injection mold and transferred to a blow mold.
Following operations are similar to those in the extrusion blowing molding.
3. Injection Blow Molding is more accurate and controllable process as compared to the Extrusion Blow Molding.
It allows producing more complicated products from a wider range of polymer materials.
4. However production rate of Injection Blow Molding method is lower than that of Extrusion Blow Molding.

50. The photo (below) shows fluid containers used in hospitals,  ready to be trimmed. A wide variety of  colours can be  achieved by adding a colouring agent to the mix of thermoplastic granules (about 1% by volume).

51. Figure : A typical roll configuration in calendering
Feedstock is passed through a series of rolls to reduce thickness to desired gage
Expensive equipment, high production rates
Process is noted for good surface finish and high gage accuracy
Typical materials: rubber or rubbery thermoplastics such as plasticized PVC
Products: PVC floor covering, shower curtains, vinyl table cloths, pool liners, and inflatable boats and toys
Calendering  is a process where a large amount of molten plastic is placed between rollers and rolled to turn it into sheets.  The rollers are hot and  keep the plastic in its semi - molten state allowing it to be rolled thinner and thinner as it passes through rollers which are closer and closer together. When it is at the required thickness it is rolled through cold rollers to enable it to go hard and is then wound into rolls.
Figure : A typical roll configuration in calendering

52. Embossing

53. Welding of Plastics
Plastics welding is the process of joining two pieces of Thermoplastics at heated state and under a pressure as a result of cross linking of their polymer molecules. The work pieces are fused together with or without filler material. The joint forms when the parts are cooled below the Glass Transition Temperature (for amorphous polymers) or below the melting temperature (for crystalline polymers). Thermo sets (thermosetting resins) in cured condition cannot be welded, since cross-linking of their molecules has completed. Plastics welding processes:
Hot Gas Welding
Hot Plate Welding
Ultrasonic Welding
Spin Welding
Vibration Welding

55. Welding of Plastics :
Hot gas Welding

56. Hot Plate Welding
Welding of Plastics :

57. Welding of Plastics:
Ultrasonic Welding

58. Welding of Plastics :
Friction ( Spin ) Welding

59. Vibration Welding
Welding of Plastics :