1. What is the important characteristics of plastics?
It can be molded into finished product by application of heat and pressure.
- Low weight
- Corrosion resistance
- Insulation properties
- Electrical properties
- Cheaper
- Easy to handle
- Surface properties
- Reusable
- Low strength
- Low heat resistance
- Poor mechanical properties
- Difficulty to repair
- Natural : milk of rubber tree, cellulose
- Semi synthetic
- Synthetic
- Thermo plastics
- Thermosetting plastics
- Can be re softened and reused
- No chemical changes during heating.
- In granular form
- Needle structure
- Hard but not brittle
- Cannot be re softened and reused
- Chemical changes during heating etc.
- In powder form
- Cross linked structure
- Hard and brittle
ABS, PP, CA, PMMA, PS, PC, POM etc.
8. Perspex is the trade name of ---- ?
CA
10. Perspex is the trade name of ---- ?
CA
11. Nylon is the trade name of ---- ?
PA
12. Delrin is the trade name of ---- ?
POM
13. Teflone is the trade name of ……….?
PTFE
14. What is MFI?
Flow capacity of different grades of thermoplastics are inversely proportional to molecular weight.
15. About ABS?
Shrinkage 0.5%. It is heat resistant, provides good insulation and exhibit electrical properties. Examples are general purpose safety helmets, pipe fittings, television, radio etc.
16. About CA ?
Shrinkage 0.3-0.8%. Its main properties are transparency and surface texture. Examples are Tool handle, goggles, TV screens.
17. About HDPE?
Shrinkage 3-4%. Main features of HDFE are high density, rigidity, strength, hardness and chemical resistance. Examples are milk bottle crates, fish boxes etc.
18. About LDPE?
Shrinkage 0.8-1.5%. It is crystalline and not available in transparent form. Examples are shopping baskets, waste baskets etc.
19. About PA?
Shrinkage 0.7-1.5%. It is tough and high rigid. Examples are light duty gears, sprockets, bearings etc.
20.About PC?
Shrinkage 0.5-0.7%. It is known optical transparency, rigidity and toughness. Examples are goggles, lenses, safety helmets etc.
21.About PP?
Shrinkage 1-3%. It is flammable and degradable in sun light and stable. Examples are air cleaner, garden furniture etc.
22.About PS?
Shrinkage 0.2-0.8%. It is clear, brittle and it can be easily molded. Examples are toys, house hold appliances, electronic housings etc.
23.About PVC?
Shrinkage (FLEXI 1.5-3%,RIGID 0.2-0.4%). It is rigid and not very tough and very low cost. Example - Pipes fittings.
24. Examples for thermosetting materials ?
Alkyds, epoxies, pf, mf, urea, polyester
25. What is fillers and additives?
Adding of small molecules to plastics to get some characteristics (color, flexibility etc.). Fillers are commonly used with thermosetting plastics. Additives are of two types,
- Physical means such as plasticizer
- Chemical means--- stabilizer.
26. What are the mold release agents?
- External with mold surface e.g. Polyvinyl alcohol
- Internal with resins eg. Silicon oil
27. What are the types of injection molding machines?
- Plunger injection cylinder
- Two stage plunger injection cylinder
- Pre plasticizer two stage screw injection cylinder
- Reciprocating screw injection cylinder
28. What are the divided sections of screw of injection molding machines ?
- Feed zone
- Compression zone
- Melting zone
29. What do you meant by nozzle ?
Nozzle connected to the end of the barrel through which soften materials inserted in the mold.
30. What are the types of nozzle ?
- Reverse taper (melt valve)- for PA, ABS etc.
- Removable tip
- Standard of general purpose
30. What are the types of nozzle ?
- Reverse taper (melt valve) - for PA,ABS etc.
- Removable tip
- Standard of general purpose
