11 PLASTIC MOLDING PROCESSES

1. What type of products are obtained through plastic extrusion?. A) Short, complex 3D parts. B) Long parts with constant cross sections. C) Hollow parts only. D) Thermoset components.

2. Plastic extrusion is applicable exclusively to which type of polymers?. A) Thermosets. B) Elastomers. C) Thermoplastics. D) Composite polymers.

3. What determines the cross sectional shape of an extruded product?. A) The hopper size. B) The screw speed. C) The geometry of the die orifice. D) The cooling rate.

4. Why is extrusion considered a continuous process?. A) The die changes shape during operation. B) Material flows without interruption through the die. C) The screw stops between cycles. D) Products are made one at a time.

5. Which type of extruded geometry increases die design complexity?. B) Open geometries. A) Closed geometries. C) Flat geometries. D) Circular geometries.

6. What is the first main stage of the extrusion process?. A) Cooling and calibration. B) Post processing. D) Forming in the extruder. C) Cutting and stacking.

7. What happens during the second stage of extrusion?. A) The polymer melts. B) The product is calibrated and cooled. C) The screw rotates. D) The pellets are mixed.

8. How are flexible extruded products typically stored?. B) In wooden crates. A) In large coils. C) In metal molds. D) In refrigerated containers.

9. What is the function of the extruder?. A) To cool the polymer. D) To convert solid pellets into a homogeneous melt. C) To cut the final product. B) To remove impurities from the polymer.

10. What feeds the plastic material into the extruder barrel?. A) A conveyor belt. B) A vacuum pump. C) The hopper. D) A cooling system.

11. What component moves the plastic through the extruder barrel?. A) A piston. B) A rotating screw. C) A hydraulic ram. D) A vibrating plate.

12. What is the purpose of the feed section of the screw?. A) To build pressure. B) To homogenize the melt. C) To preheat the material. D) To remove impurities.

13. What happens in the compression section of the screw?. A) The polymer cools. B) The screw diameter decreases. D) Friction melts the plastic pellets. C) The melt is filtered.

14. What controls temperature in the extruder barrel?. A) Cooling fans. B) Thermocouples and heating bands. C) Pressure sensors. D) The die geometry.

15. What is the purpose of the metering section?. B) To add colorants. A) To control flow and homogenize the melt. C) To cool the melt. D) To remove air bubbles.

16. What does the wire filter screen do?. A) It cools the melt. D) It removes unmelted pellets and impurities. C) It increases pressure. B) It shapes the final product.

17. What is the function of the breaker plate?. A) To heat the melt. B) To remove the rotational component of the flow. C) To cut the extruded product. D) To add additives.

18. Why must the rotational component of the melt flow be removed?. B) To reduce friction. A) To achieve a uniform, parallel flow into the die. C) To increase melting speed. D) To improve color distribution.

19. What ultimately pushes the molten polymer through the die?. A) Gravity. B) Air pressure. C) The pressure generated by the screw movement. D) Manual force.

20. What determines the final cross section of the extruded product?. A) The screw length. B) The hopper size. C) The die orifice geometry. D) The cooling temperature.

21. What determines the shape of the final extruded product?. A) The screw speed. B) The die opening geometry. C) The hopper size. D) The cooling method.

22. What is “die swell”?. A) The shrinkage of the material after cooling. B) The expansion of material after exiting the die. C) The deformation caused by stretching. D) The collapse of hollow sections.

23. Which factor does NOT influence die swell?. A) Die temperature. B) Pressure. C) Length of the die. D) Color of the polymer.

24. What type of dies are used to produce rods, bars, plates, and sheets?. A) Spider dies. B) Coextrusion dies. C) Simple profile dies. D) Multi plate dies.

25. What is the main challenge in dies for complex profiles?. A) Achieving transparency. B) Preventing inward collapse of hollow sections. C) Increasing extrusion speed. D) Reducing material cost.

26. How are complex profile dies typically constructed?. A) As a single solid block. B) Using several consecutive plates. C) With rotating mandrels. D) With adjustable screws.

27. What is the function of the first plates in a complex profile die?. B) To cool the melt. A) To divide the flow and create internal cavities. C) To cut the extrudate. D) To remove impurities.

28. What type of die is used for tubular profiles?. A) Coat hanger die. B) Spider type die. C) Multi layer die. D) Flat slit die.

29. What component creates the hollow space in a tubular profile?. A) The breaker plate. d) The mandrel. C) The calibrator. b) The hopper.

30. In cable coating extrusion, what passes through the mandrel?. B) A stream of cooling water. A) The metal core of the cable. C) A vacuum line. D) A second polymer.

31. What shape does the manifold in sheet extrusion resemble?. A) A spiral. B) A coat hanger. C) A cylinder. D) A funnel.

32. What is a major difficulty in sheet and film extrusion?. A) Achieving transparency. B) Maintaining uniform thickness across the width. C) Preventing crystallization. D) Avoiding color variation.

33. How is thickness uniformity adjusted in sheet extrusion?. A) By changing screw speed. B) By using cooling fans. C) With adjustment screws that regulate friction. D) By altering pellet size.

34. What is the purpose of coextrusion dies?. A) To increase extrusion speed. B) To combine multiple layers or materials. C) To reduce die swell. D) To remove moisture.

35. Why is coextrusion more complex than single material extrusion?. A) It requires higher temperatures. D) It uses multiple extruders and materials. C) It eliminates the need for cooling. B) It produces only hollow parts.

36. Why is calibration necessary after extrusion?. B) To remove impurities. A) To achieve dimensional and geometric specifications. C) To increase melt temperature. D) To reduce viscosity.

37. What is the purpose of cooling the extrudate?. A) To increase die swell. B) To preserve the corrected shape. C) To remove colorants. D) To reduce friction.

38. What equipment is used to pull the hardened extrudate?. B) Metal rollers. A) Rubber pad pullers. C) Vacuum pumps. D) Hydraulic clamps.

39. What defect is caused by moisture in the polymer?. A) Sharkskin. B) Orange peel. C) Bubbles and blisters. D) Surging.

40. What defect results from periodic fluctuations in extrusion output?. A) Lumpy surfaces. B) Surging. C) Orange peel. D) Die swell.

41. What is the main purpose of injection molding?. B) To produce long continuous profiles. A) To introduce polymer into a mold to form discrete parts. C) To melt thermosets repeatedly. D) To remove moisture from polymers.

42. How is a formable state achieved in thermoplastic injection molding?. A) By adding catalysts. B) By applying heat. C) By mixing two liquid resins. D) By cooling the material.

43. How is a formable state achieved in thermoset injection molding?. A) By heating the pellets. B) By dissolving the polymer. C) By mixing reagents that polymerize. D) By cooling the mold.

44. What type of components are obtained through injection molding?. A) Continuous profiles. B) Discrete finished parts. C) Only hollow parts. D) Only flexible parts.

45. What does the cycle time NOT include?. A) Injection time. B) Solidification or curing time. C) Mold opening and ejection. D) Extruder calibration time.

46. How can productivity be increased in thermoplastic injection molding?. A) By reducing injection pressure. B) By using cooling channels or multi cavity molds. C) By lowering mold temperature. D) By increasing pellet size.

47. Why must injected parts have constant wall thickness?. A) To reduce material cost. B) To allow easy removal from the mold. C) To improve color uniformity. D) To reduce shrinkage.

48. What is overmolding?. B) Injecting metal into plastic. A) Injecting plastic onto a previously molded plastic part. C) Coating the mold with resin. D) Removing excess material after molding.

49. What is insert injection molding?. A) Injecting plastic around metal inserts. B) Injecting two plastics simultaneously. C) Injecting plastic into a rotating mold. D) Injecting plastic into a hollow tube.

50. Why are injection molds expensive?. A) They are made of disposable materials. B) They require frequent replacement. C) They must reproduce fine details with high precision. D) They are made of plastic.

51. Why must some thermoplastics be dried before injection?. A) To increase viscosity. B) To avoid bubble formation due to moisture. C) To reduce shrinkage. D) To improve color uniformity.

52. What is volumetric shrinkage?. A) Increase in volume after cooling. D) Difference between mold cavity volume and final part volume. C) Reduction of mold temperature. B) Expansion of the polymer during injection.

53. What are the two main units of an injection molding machine?. A) Hopper and heater. B) Extruder and calibrator. C) Injection unit and clamp unit. D) Cooling unit and cutting unit.

54. What is the function of the reciprocating screw?. A) To cool the polymer. B) To push and melt the polymer. C) To remove impurities. D) To eject the part.

55. What is the purpose of the non return valve?. B) To cool the melt. A) To prevent backflow during injection. C) To increase screw speed. D) To remove moisture.

56. What determines the closing force required in an injection machine?. A) Mold temperature. D) Injection pressure × cross sectional area. C) Screw diameter. B) Cooling time.

57. In which stage is plastic injected into the mold cavity?. A) Mold close. B) Injection. C) Plasticating. D) Mold open.

58. What is the purpose of packing pressure?. A) To cool the mold. B) To compensate for shrinkage. C) To remove air bubbles. D) To increase viscosity.

59. What happens during plasticating?. A) The mold opens. D) The screw rotates and melts new material. C) The part is ejected. B) The mold is cooled.

60. When does cooling occur during the injection cycle?. B) Only after ejection. A) From injection until mold opening. C) Only during mold closure. D) Only during plasticating.

61. What is the main function of an injection mold?. A) To cool the polymer. C) To provide the desired shape and dimensions. B) To mix different polymers. D) To remove moisture from the material.

62. What forms the cavity inside an injection mold?. A) A single solid block. D) Two or more mold halves joined together. C) A rotating screw. B) A cooling plate.

63. What is the parting line?. A) The channel where plastic enters. B) The flat joining area between mold halves. C) The location of the ejector pins. D) The cooling channel.

64. What ensures proper alignment of mold halves during closing?. B) Cooling channels. A) Guide pins. C) Gates. D) Inserts.

65. What is the sprue?. A) The cavity of the part. B) The first runner through which material enters the mold. C) The cooling channel. D) The ejector system.

66. What is the purpose of the cold slug well?. B) To cool the mold. A) To trap the first, colder material entering the mold. C) To remove air from the mold. D) To increase injection pressure.

67. What do branch runners do?. A) Remove impurities. C) Distribute polymer to multiple cavities. B) Cool the molten plastic. D) Eject the part.

68. What are gates?. A) Channels that remove air. D) Narrow entrances to the part cavity. C) Cooling channels. B) Supports for inserts.

69. What element contains the negative shape of the part?. A) Sprue. B) Gate. C) Cavity. D) Runner.

70. How does air escape from the mold during injection?. A) Through the sprue. B) Through small recesses at the parting line. C) Through the cooling channels. D) Through the screw.

71. Why are cooling channels included inside the mold?. B) To increase viscosity. A) To evacuate heat and reduce cycle time. C) To remove impurities. D) To increase mold weight.

72. What distinguishes hot runner molds?. A) All material solidifies inside the mold. B) Runners remain filled with molten plastic. C) They require no temperature control. D) They are cheaper than cold runner molds.

73. What is an advantage of hot runner molds?. A) Lower mold cost. D) Reduced waste and shorter cycle time. C) No need for temperature control. B) Easier mold maintenance.

74. What distinguishes two plate molds from three plate molds?. A) Number of cavities. B) Location of the runner system. C) Type of polymer used. D) Cooling method.

75. What is co injection?. A) Injecting plastic around a metal insert. C) Injecting multiple materials through the same nozzle. B) Injecting gas into molten plastic. D) Injecting plastic into two molds simultaneously.

76. What is the purpose of co injection?. B) To reduce mold cost. A) To obtain multi material parts with different properties. C) To eliminate shrinkage. D) To cool the mold faster.

77. What is over injection?. A) Injecting plastic into a rotating mold. B) Injecting a second polymer over a first polymer. C) Injecting plastic into a hollow tube. D) Injecting plastic at very high pressure.

78. What type of mold is required for over injection?. B) Spider mold. A) Indexable mold with multiple cavities. C) Hot runner mold. D) Single plate mold.

79. What is the purpose of gas or water assisted injection molding?. A) To increase part density. D) To obtain hollow parts without moving mold components. C) To reduce mold temperature. B) To improve color uniformity.

80. What is injection with metal inserts?. A) Injecting metal into plastic. B) Surrounding a metal component with injected plastic. C) Injecting plastic into a metal mold. D) Injecting plastic into a metal tube.

81. What is the main difference between thermoset and thermoplastic injection molding?. A) Thermosets melt repeatedly. B) Thermosets require much higher temperatures in the screw. C) Thermosets must not cure inside the screw. D) Thermoplastics require lower mold temperatures.

82. Why must thermosetting resins be kept at low temperature inside the screw?. A) To reduce viscosity. B) To prevent premature curing. C) To increase injection speed. D) To avoid shrinkage.

83. What is the approximate screw temperature for epoxy resin in thermoset injection?. A) 250 °C. B) 170 °C. C) 85 °C. D) 60 °C.

84. What is the mold temperature in thermoset injection molding?. A) 60 °C. B) 85 °C. C) 250 °C. D) 170 °C.

85. Why is the cycle time longer in thermoset injection molding?. A) Because cooling takes longer. B) Because curing requires more time. C) Because the mold must be reheated. D) Because the screw rotates more slowly.

86. Why do thermoset injection machines use shorter screws?. B) To reduce material cost. A) To avoid curing inside the barrel. C) To increase melting speed. D) To improve color mixing.

87. Why do thermosets require more robust clamping units?. A) They cool faster. B) They are less viscous. C) They require higher injection pressures. D) They shrink more.

88. What causes sink marks in injected parts?. A) Excessive mold temperature. B) Non uniform wall thickness. C) High injection pressure. D) Excessive cooling.

89. What causes flashing?. B) Moisture in the material. A) Mold not closing properly. C) Low injection pressure. D) Excessive cooling.

90. What is the main cause of bubbles in injected parts?. A) High mold temperature. B) Moisture in the starting material. C) Excessive injection pressure. D) Too many gates.

91. What defect occurs when the mold cavity is not completely filled?. A) Flashing. B) Sink marks. C) Short shots. D) Weld lines.

92. What can cause short shots?. A) High mold temperature. B) Low temperature or low injection pressure. C) Excessive drying. D) Too many runners.

93. What are flow lines?. B) Cracks caused by trapped gases. A) Wavy surface patterns due to uneven cooling. C) Marks caused by mold misalignment. D) Lines caused by excessive pressure.

94. What causes weld lines?. A) Moisture in the material. D) Polymer streams meeting at different temperatures. C) Excessive injection speed. B) Incorrect mold closing force.

95. What was the first plastic molding process used in 1908?. A) Injection molding. B) Transfer molding. C) Compression molding. D) Extrusion.

96. What materials are mainly processed by compression molding?. A) Only thermoplastics. B) Thermosets, elastomers, and some thermoplastics. C) Metals and ceramics. D) Only elastomers.

97. What happens during compression molding after the charge is compressed?. B) The part melts. A) The part cures and then cools. C) The mold rotates. D) The material is injected again.

98. What is an advantage of compression molding over injection molding?. A) Higher part complexity. B) Lower mold cost and less scrap. C) Faster cycle times. D) Better suitability for thermoplastics.

99. What is a disadvantage of compression molding?. A) High mold cost. B) High residual stresses. C) Lower part complexity due to low flow capability. D) Excessive material waste.

100. What distinguishes transfer molding from compression molding?. A) The material is injected through runners into the cavity. B) The mold is always colder. C) No pressure is required. D) The material is always liquid.

101. What do all hollow part manufacturing processes have in common?. A) They use ceramic molds. B) They use metal molds. C) They require thermosets only. D) They produce only small parts.

102. Which type of plastic is used in most hollow part processes?. A) Only thermosets. B) Only elastomers. C) Mostly thermoplastics. D) Mostly composites.

103. What is the first stage of injection blow molding?. A) Blowing. B) Cooling. C) Parison injection. D) Stretching.

104. What part of the bottle is already formed in the parison?. A) The base. B) The neck and shoulder. C) The entire body. D) The handle.

105. What causes the preform to expand during blow molding?. A) Vacuum pressure. B) Pressurized air. C) Mechanical stretching only. D) Centrifugal force.

106. Why is the preform wall thickness variable?. B) To reduce material cost. A) To avoid tearing during blowing. C) To improve transparency. D) To reduce cycle time.

107. What is the purpose of the stretching rod in tall bottles?. A) To cool the preform. D) To stretch the preform before blowing. C) To remove moisture. B) To create the bottle thread.

108. What characteristic mark identifies injection blow molded bottles?. A) A seam along the side. B) A rough neck finish. C) A mark on the bottom from the injection gate. D) A double layer wall.

109. In extrusion blow molding, how is the parison formed?. A) By injection. B) By vacuum. C) By vertical extrusion. D) By rotational molding.

110. What is a typical defect of extrusion blow molded containers?. A) Perfectly smooth bottoms. B) A rough linear seam at the bottom. C) A mark from the injection gate. D) No visible marks.

111. Why is the neck thread less precise in extrusion blow molding?. A) The mold is not cooled. D) The parison is simply expanded against the mold. C) The material is too viscous. B) The mold rotates during blowing.

112. What is produced using blown film extrusion?. B) Thick structural panels. A) Transparent films and bags. C) Rigid bottles. D) Foam insulation.

113. What creates the “balloon” in blown film extrusion?. A) Vacuum suction. B) Pressurized air through the die mandrel. C) Mechanical stretching. D) Centrifugal force.

114. What indicates the point where the polymer solidifies in blown film extrusion?. B) The injection mark. A) The frozen line. C) The seam line. D) The cooling ridge.

115. What happens at the top of the blown film equipment?. A) The film is melted again. B) The film is cut into pellets. C) Pinch rolls flatten the tube into two sheets. D) The film is injected into a mold.

116. What is thermoforming mainly used for?. A) Thick structural parts. B) Shell type products with low detail. C) Metal plastic composites. D) High pressure containers.

117. How is the sheet shaped in vacuum thermoforming?. A) By injecting air into the sheet. B) By pressing it between two molds. C) By applying vacuum to pull it against the mold. D) By stretching it mechanically only.

118. What is a disadvantage of thermoforming?. A) Very high equipment cost. B) Only applicable to thermosets. C) Non uniform thickness and more scrap. D) Very long cycle times.

119. What type of parts are commonly made by thermoforming?. A) Car engines. B) Single use food packaging. C) High pressure tanks. D) Structural beams.

120. What is a key advantage of rotational molding (rotomolding)?. B) It produces only small parts. A) It allows closed hollow parts in one operation. C) It requires no mold. D) It produces extremely detailed surfaces.