CENTRAL INSTITUTE OF PLASTICS ENGINEERING & TECHNOLOGY
Question Bank
4/5 MARK ----QUESTION
COURSE : DPMT
SEMESTER: IV
SUBJECT : Plastics Processing Techniques
(2 MARK ---QUESTION)
1.Write down different types of Injection molding machine.
Ans:(a) Plunger type injection molding machine.
(b) Screw type injection molding machine.
(c) Plunger-Plunger type injection molding machine.
(d) Screw-Plunger type injection molding machine
2. Write four advantages of Injection molding of Plastics?
Ans:The advantages of Injection molding of Plastics are:
(a) Moldings are produced in the finished state.
(b) Plastics can be molded to require shape and size with repeatable precision.
(c) Functional features such as metal inserts, threads and holes can be molded.
(d) High production rate.
3. What is the disadvantage of Injection molding process?
Ans:(a) Initial cost is high as compared to other molding machines.
(b) Mold cost is high.
(c) Difficult to mold the articles with large thickness variation.
4. How many motions are there in injection moulding screw? Write down the functions of different motions.
Ans:Generally there are two motions of screw in injection moulding machine, one is linear and other is rotational. In linear motion, the screw travels backward and forward and push or inject the material into the mould through nozzle. On the other hand, in rotary motion, screw rotates to fill the injection chamber for next shot. During the rotational motion, the screw simultaneously moves backward.
5. What are the advantages of Hot Runner Mold?
Ans: The advantages of Hot Runner Mold (Runnerless mold) are:
(a) It eliminates conventional cold runner thereby saving polymer and energy recovery expenses.
(b) Cycle time is reduced as no additional time is required for cooling comparatively thicker runner.
(c) Fully automatic molding is possible without further operations like degating manually.
6. Define Back pressure.
Ans:Back pressure is the pressure exerted by the plastics melts material ahead of the screw as the screw is rotated. Screw rotation pushed the material though the non-return valve in the space ahead of the screw tip. The steady supply of the melt makes space for itself by pushing the screw in the opposite direction.
7. Why screw speed is important?
Ans:The rate of plasticizing is proportional to screw speed (generally given in RPM) and heat generated due to shearing of the polymer is also proportional to screw speed. Higher screw rotation will result in the high frictional heat, more plasticizing efficiency.
8. Define L/D ratio of the screw? What is the significance of larger L/D ratio?
Ans:L/D ratio is the ratio of the flighted length of the screw to its outside diameter.
The larger L/D ratio provides
(a) More shear heat be generated gradually and uniformly in plastics.
(b) Greater opportunity for mixing will result in the better homogeneity of the melt.
(c) Greater residence time of plastics will permit faster cycle of larger shots.
9. What is Compression Ratio (CR)? What is the significance of higher CR?
Ans:Compression ratio is the ratio of the first flight depth of feed zone to last flight depth of metering zone. It is the ratio of volume enclosed by first turn of screw to the volume of last turn of screw.
The significance of higher compression ratio are:
(a) Higher heat imparted to the material.
(b) Better homogeneity of the melt.
(c) High energy consumption
(d) High potential for creating stresses in some resins.
10. Write down the functions of different zones of screw.
Ans:The screw has three zones; feed zone, transition zone and metering zone. In the feed zone, the plastic material first enters the screw and is conveyed along a constant root diameter. In transition zone, the plastic is conveyed, compressed and melted along a root diameter that increases with a constant taper; and finally in metering zone, the melting of the plastic is completed and the melt is conveyed forward along a constant root diameter reaching a temperature and viscosity to form parts.
11. Differentiate between hydraulic and toggle clamping unit.
Hydraulic clamping system
1. Non positive clamping
2. Unlimited stroke potential
3. Clamp speed easily controlled at any point
4. Low maintenance
5. Higher initial cost
Toggle clamping system
1. Positive clamping
2. Limited stroke potential
3. Clamp speed more difficult to control
4. Higher maintenance cost
5. Low initial coast
12. Write down different methods of blow moulding.
Ans: The common types of blow moulding methods used are:
1. Extrusion Blow moulding
2. Injection Blow moulding
3. Stretch Blow moulding
4. Press Blow moulding & Dip Blow moulding for squeeze
5. Multilayer Co extrusion Blow moulding
13. Write advantages of injection blow molding process.
Ans: Some advantages of injection blow moulding are:
1. Accurate shaping of the neck.
2. Multi-cavities can be operated.
3. The highest quality surface finish.
4. A high level of dimensional accuracy.
5. Very low wastage.
14. Differentiate between preform and parison.
Ans: Preform
Preform is generally prepared by injection moulding through which the blown part is made. It is a tube opening at one end with neck and threads, if required, for blowing of air. Preform is mostly used in injection blow moulding and stretch blow moulding for making long bottle and other long hollow products.
Parison
Parison is generally formed in extrusion blow moulding through which the finished part is made. The parison is a tube-like piece of plastic melt which is entrapped into the mould and air is blown into it. The air pressure then pushes the plastic out to match the mould
15. Define blowiup ratio.
Ans: In blow molding, blow-up ratio is defined as the ratio of the diameter of the product (usually its greatest diameter) to the diameter of the parison from which the product is formed. In blown film extrusion, the ratio between the diameter of the final film tube and the diameter of the die orifice.
16. Define pinch off blow pin.
Ans: Pinch off - Pinch off is defined as the section of the mould where the extruded parison is squeezed and welded together.
Blow pin - Blow pin usually a hollow tube through which air is blown into mould to inflate the parison according to mould shape.
17. Define axial ratio?
Ans:Axial ratio is defined as the ratio of length measured after axial stretching of the product (L1) to the original length of the preform (L2). In short, it can be written as:
RA = , generally, it ranges from 14 to 26.
18. What do you meant by biaxial stretch blow moulding? Write down its advantages.
Ans:Biaxial stretch blow moulding is the method in which the stretching is done in both longitudinal and transverse direction.
Advantages of biaxial stretch blow moulding: Biaxial orientation increases the tensile strength, gas barrier properties, drop impact strength and clarity of plastics.
19. Write down some applications of stretch blow moulding.
Ans:Some applications of stretch blow moulding are:
Containers made for packing of oil, wine, sprits, milk, mineral water, carbonated drinks, soft drinks & medicine.
20. What are the advantages and disadvantages of single stage injection stretch blow moulding process?
Ans:The advantages and disadvantages of single stage injection stretch blow moulding process are:
Advantages
1.Low investment
2.Requires no capping ring
3.All process are done at one place.
Disadvantages
1.Low barrier properties
2.The products are heavier
3.Requires more skilled operation
21. What are the advantages and disadvantages of two stage injection stretch blow moulding process?
Ans:The advantages and disadvantages of two stage injection stretch blow moulding process are:
Advantage
1.Low cost per bottle
2.The products have low weight
3.High barrier properties
4.High productivity
5.Preform making and bottle making can be done at different places.
Disadvantages
1.High capital investment
2.More blemishes than single stage
3.Requires capping ring on the preforms.
22. In 5 layers blow moulded part, what are the 5 layers consists of?
Ans:A five layers structure consists of one inside and one outside structural layer, a central functional layer and two adhesive layers one on each side of the functional layer.
23.Define the term plasticizing capacity.
Ans:Plasticizing capacity can be defined as the amount of material that can be process by the machine per hour. It is express in kg/h.
24. Differentiate between general purpose screw and typical PVC screw.
Ans:
General purpose screw
1.It has three distinct sections
2.Diameter of screw in all three zones s different
3.NRV is necessary for general purpose screw
PVC screw
1.It has no distinct sections
2.Diameter of screw gradually increase
3.No requirement of NRV
25. What do you mean thrust bearing?
Ans:Thrust bearing is located behind the feed hopper, the function of thrust bearing is to absorb the thrust force acting on the screw inside the extruder barrel.
26. Why do we need hopper cooling?
Ans:Hopper cooling is needed to prevent bridging of material and to protect the rubber parts present in the screw assembly.
27. What is breaker plate and screen pack?
Ans:Breaker plate is a circular metallic disk, with a multitude of small diameter holes. The breaker plate is placed in between the screw and the die assembly. Its principle function is to provide support for the screen pack.
Screen pack is usually a multilayered, nearly symmetrical sandwich of metallic wire screens. It is placed between the screw and breaker plate. Its role is to eliminate the particulate contaminants.
28. Write down different types of screws used.
Ans:Different types of screws use are:
1.General purpose screw
2.PVC screw
3.Nylon screw
4.Two stage screw/vented screw
5.Segmented screws is also available for special purpose
29. What are the different methods for barrel heating? Why is the electric heating most commonly used?
Ans:There are three methods of barrel heating:
1.Electric
2.Fluid
3.Steam heating
The electric heating is most commonly used due to:
1.Accuracy
2.Reliability
3.Easy to hook up
30 Compare mica insulated and ceramic insulated heaters.
Ans:
Mica insulated
1.Flexible and supplies as single piece
2.Can withstand a load of 23 – 31 KW/m2
3.Shorter service life
4.Less expensive
PVC screw
1.Rigid and supplied in 2 halves
2.Can withstand higher heating load
3.Better service life
4.More costly
31. Classify different types of die.
Ans: The dies can be classified using different criteria. For example, considering cross section of the extrudate one may recognize dies to produce:
1.Solid cross sections
2.Hollow cross sections
Another classifications scheme is based on the die attachment to the extruder barrel:
1.Straight through dies
2.Cross heat dies
3.Offset dies
32. Define draw down ratio.
Ans:Draw down ratio is defined as the ratio of the die orifice gap to the film thickness at the nominal blow ratio, given by the product of the measured film thickness and blow ratio.
33. Differentiate between co - rotating and counter rotating screw.
Ans:
Co-rotating screw
1.Both screw rotate either clockwise or anti-clockwise
2.More complete self-wiping
3.Better mixing
4.Total shear is more
5.Less power consumption than single screw
Counter rotating screw
1.One screw turn clockwise and other anti-clockwise
2.Less self-wiping
3.Less than co-rotating
4.Less shear compared to co-rotating
5.Less power consumption than single screw
34. Differentiate between blown film and cast film.
Ans:
Blown film
1.Tougher than cast film
2.More stiffer
3.Less gloss and clarity
4.Easily changeable film width by changing air pressure
Cast film
1.Less tougher
2.Less stiffer
3.High gloss and clarity
4.Not so easy
35. What are the advantages of co-injection molding or multi-colour injection moulding?
Ans: Following are the advantages of co-injection molding:
(a) Improve Part Physicals - High Strength cores with soft skins
(b) Reduce Cost - Inexpensive material hidden inside
(c) Decorative - Attractive user friendly skin surface
(d) Innovative Solution - Reduced assembly cost
36. What are the advantages of gas assisted injection molding process?
Ans: The advantages of gas assisted injection molding are:
1. Material savings, since 20 to 30 % of the plastic material can be replaced by gas.
2. Faster cooling of the moulded part and shorter cycle times are achieved.
3. Shrinkage reduced through more even pressure conditions in the cooling phase.
4. It improves weight/strength ratio of the moulded part.
5. Higher surface finish quality.
37. Define co-extrusion sheet. What are the types of dies used to produce co-extrusion sheet?
Ans:The processing method used to produce sheets side by side is called co-extrusion sheet, where multiple resin are extruded side by side in a multilayer sheet rather than on top of each other in layer.
The dies used to produce co-extrusion sheets are; Coat hanger die, T-die.
38. What are the parts used in co-extrusion sheet?
Ans:Following are the common parts used in co-extrusion sheet:
1. Die
2. Three roll stack
3. Conveyor to support sheet
4. An edge timing device
5. Two sets of nip or puller rolls
6. A winder or stacker
7. Thickness measurement
39. What are the advantages of co-extrusion sheet?
Ans: The advantages of co-extrusion sheets are:
1. Multiple properties are achievable on a single converting operation.
2. No solvents are used in this process.
3. Thin layers of sheet that will be difficult to handle separately can be produced by lamination.
4. Pigmented layers could be sandwiched without affecting the sealability.
5. To reduce cost, it is sometimes possible to recycle reclaimed materials, if they are compatible.
40. What are the disadvantages of co-extrusion sheet?
Ans: The disadvantages of co-extrusion sheet are:
1. It is necessary to balance melt viscosities and the chemical properties of the resin to be co-extruded.
2. Equipment are quite expensive.
3. Make ready costs are high, so the co-extrusion process requires longer production runs to be cost effective.
41. Name the equipment required for pipe extrusion.
Ans: Following are the major equipment required for pipe extrusion:
1. Extruder
2. Die
3. Sizing device
4. Cooling bath
5. Cater puller
6. Cutter or winder
42. What is bambooing in extrusion?
Ans:Bambooing is the defect that is observed during the extrusion of pipe or other circular cross section products. This defect arises due to improper die design, die not having proper polish , defective or intermittent working of melt pump which causes melt surge.
43. What are different types of moulds used in compression moulding?
Ans:There are three types of mould generally used in compression molding.
1. Flash type
2. Positive type
3. Semi positive-flash type
44. Write down the merits of compression moulding.
Ans: The merits of compression moulding are:
1. No or very less wastage
2. Lowest cost mould
3. Lower labour costs
4. Maximum number of cavity
5. Shrinkage is minimized
45. What are the types of transfer moulding process?
Ans:The different types of transfer moulding are:
1. Pot transfer molding
2. Plunger transfer molding
3. Semi-automatic transfer molding
4. Fully automatic transfer molding
46. Write down the disadvantage of transfer molding.
Ans: The disadvantages of transfer moulding are:
1. Cycle time is larger than injection molding
2. Product consistency poor than injection molding
3. Wastage is more
4. Mould cost is high
47. Write down moulding sequence in compression moulding.
Ans: The general sequence followed in compression moulding process is:
1. Mold opening, Cavity cleaning
2. Pellet loading, Mould closing
3. Mould closed, Breathing, Curing
4. Mould open, part ejection.
48. Write down different types secondary processes.
Ans: The different types of secondary processes used are:
1. Joining and assembling – gluing, welding, mechanical connections
2. Machining – cutting, punching, blanking, filing etc.
3. Finishing – filing, sanding, grinding, polishing and buffing
4. Surface treatment – flame treatment, chemical etching, corona treatment, plasma treatment
5. Coating – extrusion coating, calender coating, fluidized bed coating, electrostatic bed coating, electrostatic powder gun coating, transfer coating.
49. Write advantage of all electric injection moulding.
Ans:Advantage of all electric moulding machine are:
1. Up to 25% to 60% lower power consumption.
2. Water requirement reduce up to 50%
3. Fully close loop control with less fluctuation in position in velocity is easily performed by use of highly accurate servo motor.
50. What are the advantages of using automation in production?
Ans:Advantages of using automation in production are:
1. Setup Time reduction
2. Easier operator tuning
3. Smoother operation
4. Input Energy reduction
5. Printing & documentation
6. Highly safe
7. Easy maintenance
8. Robots can easily operate.
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