Recently Updated Molding Interview Questions Part – 1

1. What is the important characteristics of plastics?

It can be molded into finished product by application of heat and pressure.

2. What are the advantages of plastics over metals?

Low weight
Corrosion resistance
Insulation properties
Electrical properties
Cheaper
Easy to handle
Surface properties
Reusable

3. Explain the disadvantages of plastics?

Low strength
Low heat resistance
Poor mechanical properties
Difficulty to repair

4. How to classify the plastics?

Natural : milk of rubber tree, cellulose

Semi synthetic
Synthetic

5. Types of plastics based on chemical behavior?

Thermo plastics
Thermosetting plastics

6. Difference between thermo set and thermo plastics?

Thermoplastics:
Can be re softened and reused
No chemical changes during heating.
In granular form
Needle structure
Hard but not brittle

Thermo set plastics:

Cannot be re softened and reused
Chemical changes during heating etc.
In powder form
Cross linked structure
Hard and brittle

7. Give Example of thermoplastics

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

31. Define drooling ?

Leakage of plastic material through the nozzle in between shots.

32. What is injection capacity or short capacity?

Maximum volume material injected by the screw during one cycle of operation.

33. What is plasticizing capacity ?

It is the amount of material that can be processed by the machine per hour. It is expressed in kg/h.

34. What is injection pressure?

It is the maximum pressure by which the material is injected through the nozzle. It is given in kg/cm2.

35. What is Injection rate or Injection velocity ?

It is the maximum rate at which the screw can inject or shoot materials from the barrel during one shot.

36. What do you meant by clamping force?

It is the maximum force that the clamping system can exert on the mold or it is the maximum force by which the mold halves can be closed together. It is given in ton or kilo Newton.

37. What is maximum daylight?

It is the maximum distance that the machine platen can be separated from each other and it can be obtained by adding the maximum mold thickness to the maximum opening stroke.

38. What is a mold ?

It is a custom build tool in which we converts plastic raw material into finished product.

39. What are the main elements of mold ?

The main parts of molds are core and cavity.

40. What are the general types of mold ?

Injection molds, compression molds, transfer molds.

41. What are the types of injection mold ?

Two plate mold
Three plate mold
Hot runner mold
Insulated runner mold
Hot manifold mold
Stacked mold

42. What is two plate mold ?

Mold which consists of core and cavity situated in plates. It is logical type tool where component require large gate. For simple type components there is only one daylight.

43. What is 3 plate mold?

It consists feed plates with core and cavity.

44. What is hot runner mold?

In this, runner kept hot to keep the molten metal into fluid state also called runner less mold. In this, runner contained in a plate of its own runner section of the mold is not opened during molding cycle.

45. Note down the advantages of runner mold ?

No molded side products
No separating of gate
Cycle time can be reduced

46. What is insulated runner mold ?

It is a variation of hot runner mold in this type of molding. The outer surface of the material in the runner acts as a insulator.

47. What is hot manifold mold ?

This is a variation of the heated hot runner and not the runner plate. This is done using electric cartridge.

48. What do you meant by stacked mold?

A stacked mold is a multiple two plate mold with mold placed one over the other. A stacked mold construction doubles the output from a single molding machine and requires the same clamping force.

49. Explain about injection molding?

In this process, the plastic material is injected in to the mold through a sprue bush by means of a screw plunger. This process can be used for both thermosetting and thermoplastic materials.

50. What is compression molding?

In this process, the plastic material is placed in the cavity and use a force for compressing the compound as the mold closes, these molds are generally used for thermosetting materials.

51. What is transfer mold?

In this process, the plastic materials is transferred from a transfer pot and then forced in to the cavity by means of plunger. This method is used for molding thermosetting materials only.

52. Write a short note about blow molding ?

Blow molding is very much like compression molding because the blow mold generally closes on a hollow shape that has been deposited in between the halves of the mold. Air or gas pressure is introduced at the center. This internal pressure causes a flow of the heated material in to intimate contact with the relatively cold mold sections. Here the plastic material solidifies and is subsequently ejected.

54. Explain vacuum molding?

The mold used for this process is similar that of the female half of the compression or blow mold auxiliary equipment on the machine heats the material and drags it over the cavity as indicated by the precise technique chosen.

55.Elaborate about rotational molding?

The machine provides the means of holding the mold and rotating it about two axis at the same time. This rotation causes the powdered material that was loaded in to the mold before it was clamped in to the machine to solidify and cling to the wall of the mold.

56. What is impression ?

Gap between core and cavity is called impression. Impression provides the shape of the component.

57. What do you meant cavity?

Female portion of the mold and it gives external form.

58. What is core ?

Male portion of the mold and it gives internal form.

59. What is sprue bush?

Connecting member between register ring and runner.

60. What is register ring ?

It is used to align the mold with machine platen.