1. PLASTIC PROCESSING
polymer

2. INTRODUCTION
Polymer are long chain giant organic molecules assembled from many small molecules called monomers .
More monomer molecules joined in units of long polymer.
Example;
polyethylene

3. POLYMER MATERIALS
The polymers are a diverse group of engineering materials.
They are the main components of plastics, rubbers, resins, adhesives and paints.
These materials have distinctive microstructures built from macromolecular chains and networks of carbon and other light elements.

4. CLASSIFICATIONS OF POLYMERS
Thermoplastics
Thermosets
Long chain Polymers
Natural polymers
Homopolymer
Copolymer

5. THERMOPLASTICS
A type of plastic that can be softened by heat, hardened by cooling, and then softened by heat over and over again. Thermoplastics are not cross-linked.
Thermoplastics such as polyethylene, Nylon, Polyvinyl chloride which soften on heating.
Example; Polyvinyl chloride

6. POLYVINYL CHLORIDE Pipes Electric cables Clothing and furniture
Unplasticized polyvinyl chloride (uPVC) for construction
Healthcare(Components of dialysis installations and temporary blood storage devices)
Flooring( buildings covering the home, hospitals, offices, schools, etc.)

7. THERMOSET
Thermoset - having the property of becoming permanently hard and rigid when heated or cured; "the phenol resins and plastics were the original synthetic thermosetting materials"
They are hard and rigid at room temperature and do not soften on heating.
Examples and uses of thermoset plastic materials:
Epoxy resins - used as coating materials, caulks, manufacture of insulating materials, etc ...
Phenolic resins - tool handles, billiard balls, sprockets, insulation, etc ...
Unsaturated polyester resins - manufacture of plastics reinforced fiberglass commonly known as polyester,
fillers, etc ...

8. Properties of Polymers
The physical properties of a polymer, such as its strength
and flexibility depend on:
Chain length - in general, the longer the chains the stronger the polymer;
Side groups - polar side groups give stronger attraction between polymer chains, making the polymer stronger;
Branching - straight, un branched chains can pack together more closely than highly branched chains, giving polymers that are more crystalline and therefore stronger;
Cross-linking - if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.

9. Characteristics of Polymers
Low Density.
Low coefficient of friction.
Good corrosion resistance.
Good mould ability.
Excellent surface finish can be obtained.
Can be produced with close dimensional tolerances.
Economical.
Poor tensile strength.
Low mechanical properties.
 Poor temperature resistance.
 Can be produced transparent or in different colours

10. Applications of Polymers
Polymeric materials are used in and on soil to improve aeration, provide mulch, and promote plant growth and health. Medicine Many biomaterials, especially heart valve replacements and blood vessels, are made of polymers like Dacron, Teflon and polyurethane. Consumer Science Plastic containers of all shapes and sizes are light weight and economically less expensive than the more traditional containers. Clothing, floor coverings, garbage disposal bags, and packaging are other polymer applications.

11. Industry Automobile parts, windshields for fighter planes, pipes, tanks, packing materials, insulation, wood substitutes, adhesives, matrix for composites, and elastomers are all polymer applications used in the industrial market. Sports Playground equipment, various balls, golf clubs, swimming pools, and protective helmets are often produced from polymers.

12. Compression and Transfer Molding Process
Processing of Thermosetting Plastics
Compression and Transfer Molding Process

13. Compression Molding

14. Compression Molding Process
The process of molding a material in a confined shape by applying pressure and usually heat.
Compression molding process is followed by two step first one preheating and pressurizing.

15. Process Description

16. Process Description
Charge is placed in cavity of matched mold in the open position,
Mold is closed by bring the two halves together,
Pressure is exerted to squeeze the resin so that it fills the mold cavity,
While under pressure the mold is heated which cures the resin.

17. Process Description

18. Stages in Compression molding cycle

19. Stages in Compression molding cycle
The various stages of the compression molding cycle time can be represented as a function of the force required to close the old at a constant rate.
In the “plastication” stage the force increases rapidly as the polymer feed is compressed and heated.

20. Stages in Compression molding cycle
The second stage flow commences, once the yield stress of the elastomer is exceeded.
tc is the point at which the mold fills and compression of the melt occurs.
Mold filling the majority of chemical reaction should take place after tc.

21. Parameters 1.The quantity of molding material
 2.Pressure of the molding process
Range of pressure psi( MPa)
3.Mold temperature
Temperature range 300ºF to 375ºF (149⁰C- 191⁰C)
4.Cure time variables.
The period required to harden thermosetting material to partial and complete polymerization is called cure time

22. Applications & products
Radio Cases
Automotive
ash trays & electrical parts

23. Transfer Molding Process
In the transfer molding, polymer charge is transferred from the transfer pot to the mold. The mold is cooled and molded part is ejected.
Generally, thermoset plastics (such as epoxy, polyester, phenol-formaldehyde, vinyl ester, silicone) are processed by transfer molding process, but certain thermoplastic materials can also be processed.
This process is widely used to encapsulate items such as integrated circuits, plugs, connectors, pins, coils etc.

24. Steps In Transfer Molding
The required amount of polymer charge is weighted and inserted into the transfer pot.
The transfer pot is heated by the heating element above the melting temperature of the polymer charge.
The plunger is used to push the liquid polymer charge from the transfer pot into the mold cavity.
The mold cavity is held closed until the resin gets cured. The mold cavity is opened and the molded part can be removed.
Process Parameters
 Heating time
 Melting temperature of the charge
 Applied pressure
 Cooling time

25. Pros Cons Fast setup time and lower setup costs Wastage of material
Low maintenance cost
Plastic parts with metal inserts can be made
Design flexibility
Dimensionally stable
Wastage of material
Production rate lower than injection molding
Air can be trapped in the mold

26. Processing of Thermoplastics
1. INJECTION MOLDING 2. BLOW MOLDING 3. THERMOFORMING 4. EXTRUSION MOULDING

27. INJECTION MOLDING
Injection molding is one of the most commonly used processing method for the plastic components
It is defined as
“ A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold “.

28. INJECTION MOLDING (CONTINUED)
It is used to process thin walled plastic parts for a wide variety of shapes and products .
BASIC PRINCIPLE
Plastic material is melted in a heated chamber and then injected in the mold , where it cools and finally the finished plastic part is ejected out of the cavity .

29. INJECTION MOLDING MACHINE
The raw material in the form of powder/pellets is introduced through hopper into the cylinder

30. Machine parts
Hopper is a tapered container working with a hopping motion to transfer grains into cylinder
Inside the cylinder there is a piston /plunger which is used to move the material from cylinder into the mold
Heating arrangement is placed above and below the cylinder .
The mold is in two halves , it has a mold cavity and the mold has two ejector pins.

31. Process
As soon as the plastic is melted it will be pushed by the piston into the sprue through which the material would go into the mold cavity .
The cavity will be filled by the pressure of the piston and the mold should not be opened until the plastic solidifies.
When the plastic solidifies the ejector pins are hydraulically moved backwards .

32. Stages of Injection molding
Clamping : The two halves of mold are tightly closed before the molten plastic is injected.
Injection : Injection of raw material from hopper into cylinder to the cavity is called the injection stage.
Cooling : The material is cooled for at least sec
Ejection : The 2nd mold plate moves back by ejector pins and the product is tapped out

33. IMPORTANT POINTS PRODUCTION RATE :
Production rate depends upon the clamping and de-clamping time of the mold halves.
INJECTION TIME:
The filling process should be optimal not too slow in order to stop the production of cracks.
SHOT VOLUME :
The amount of material that is injected into the mold is referred to as shot volume
PRESSURE and CYCLE TIME :
The pressure applied is in the range of MPa while the cycle completes in 2-60 sec

34. MATERIALS USED Acetate Acrylonitrile butadiene styrene (ABS)
Cellulose acetate
PVC ( poly vinyl chloride)
Polycarbonate
Polyesters
e.t.c.

35. DISADVANTAGES ADVANTAGES Higher production rate
Minimum wastage of material
Complex geometry can easily be produced
DISADVANTAGES
Tooling cost higher
High setup cost
Large undercuts can not be formed

36. APPLICATIONS
It can be used to produce thin walled plastic products of varying size and dimensions e.g.
Medical devices such as surgical syringes
Open container like buckets
Plastic housings of different tools
Daily use products such as tooth brushes

37. Parts manufactured:
Table
Chair

38. BLOW MOLDING
“ It is a plastic processing technique which is used to produce hollow plastic parts by inflating a heated plastic until it fills a mold and forms the desired shape”
The raw material used for processing in blow molding is called parison
Parison is a preform tube that is hollow and it has a hole at one end

39. PROCEDURE
First the parison is obtained by means of extrusion or injection molding process
Above the preform there is a blower and the preform is positioned between two split halves of the mold.
The mold closes over the tube and the hot air is injected from the blower into the hollow tube . The air expands the tube against the sides of the mold
After sufficient cooling , the mold opens to release the product.

41. Important Process Parameters
Cooling temperature of plastic material
Air pressure required ( usually 2-4 Mpa)
Cooling time
Pressure is exerted both axially and radially , both cavities are pressurized with a non-reactive gas such as argon.

42. Types of Blow molding Extrusion blow molding Injection blow molding
Stretch blow molding
MAJOR DIFFERENCE:
All the types have one primary difference that is making of parison by extrusion , injection and stretching .

43. INJECTION BLOW MOLDING
The injection blow molding is used for the production of hollow objects in large quantities . The main applications are bottles, jars and other containers.
The process is divided into three sections
Injection
Blowing
Ejection

44. EXTRUSION BLOW MOLDING
In this process the blow molding machine is based on a standard extruder barrel and screw assembly to plasticize the polymer.
The polymer is heated inside the barrel , the molten polymer is led through a right angle and through a die to emerge as a hollow section.
When the parison has moved enough length it is cut through by a knife and fits inside the bottle mold .
The bottle mold moves toward the jet where the air blows and the product is obtained after cooling .

46. Stretch blow molding
Stretch blow molding is also carried out by injection . Used the production of high quality containers.
This process is divided into four steps
Injection : The material is injected as discussed before.
Stretching : One conditioned to correct temperature , the parison is stretched by the blow pin/stretch rod that stretches it longitudinally .
Blowing : Using two levels of air pressure , the preform is blown circumferentially.
Discharge : After a set time for cooling the molds open and the product is removed .

47. Limited to hollow parts .
ADVANTAGES
Low tooling costs .
Fast production rates .
Ability to mold complex parts .
Little scrap generated .
Large hollow shape can be produced .
Produced parts can be recycled .
DISADVANTAGES
Limited to hollow parts .
Thick parts cannot be manufactured.

48. Applications
Different types of plastic products can be manufactured by this process such as:
Bottles in different shapes and sizes
Jars and containers
Fluid oil tanks
Mugs
Toys etc

49. THERMOFORMING
“ Thermoforming is a plastic processing technique in which the thermoplastic sheets are formed by applying temperature and pressure inside the mold .”
The raw material here is usually plastic sheet
Different types of this process are
Vacuum forming
Pressure forming
Matched die forming

50. VACUUM FORMING
The vacuum pressure is used to form the heated thermoplastic sheet into the desired shape.
Thermoplastic sheet is placed on the mold surface and fixed with the help of clamping unit.
The sheet is heated until it softens and there after , vacuum needs to be applied quickly.
There is tank with nozzles that suck air and creates vacuum in between sheet and mold.

52. Few important parameters
How much heat is required ?
Amount of vacuum needed .
These parameters solely depends upon the type of thermoforming and the thickness needed.

53. PRESSURE FORMING
The forming process is closely related to the vacuum forming .
The air pressure required is much higher as compared to the pressure required in the vacuum forming
The preheated plastic sheet is placed on the mold surface and then air pressure is applied quickly above the sheet.
The high pressure is developed in between the softened sheet and pressure box
Due to the high pressure, the preheated plastic sheet can be deformed into the mold cavity in a fraction of second (means high production rate).

54. The formed sheet is held in the mold cavity for cooling for few seconds
The formed parts thereby solidifies and is ejected.

56. MATCHED DIE FORMING
A matched die forming is also called mechanical forming .
Mold consists of two parts i.e. (i) die and (ii) punch
Thermoplastic sheet is heated with the application of heat until it softens
Preheated sheet is placed into the die and through the punch , pressure is applied on sheet
Air between the die and sheet is evacuated by using vacuum pump , and sheet conforms to the mold shape.
Formed part is cooled and ejected from the mold.

57. Materials used ABS (Acrylonutrile butadiene styrene) Celloluse acetate
LDPE (Low density polyethylene)
HDPE (High density polyethylene)
PVC etc

58. ADVANTAGES Design flexibility Rapid prototype development
Low initial setup costs
Low production cost
Less thermal stresses
Good dimensional stability
DISADVANTAGES
Poor surface finish
Parts may have non-uniform thickness
All parts needs to be trimmed
Limited materials can be made

59. Applications Thermoforming has many applications like Food packaging
Automotive parts
Aircraft windscreens
Vehicle doors

60. Extrusion Moulding
Continuous process  used to produce both solid and hollow products that have a constant cross-section.
Ex: - Window frames, hose pipe, curtain track, garden trellis.
Thermoplastic granules are fed from a hopper by a rotating screw through a heated cylinder.
The tapered screw compacts the plastic as it becomes elasticised. The die which is fitted to the end of the extruder barrel  determines the cross-section  of the extrusion.
Thicker cross-sections are extruded more slowly as more time is required  for the initial heating and subsequent cooling of the larger quantities of material which are involved.
As the extrusion leaves the die it is cooled  by passing through a cooling trough containing cold water.

61. Extrusion Moulding

62. End of UNIT III