Test Your Knowledge Welcome to the Plastic411 Processing Assessment. Upon completion, this test is designed to identify plastic injection skill level. Skill range is from material handler to process engineer. 1. If a material ratio is identified at 25:1, or 4%.. the correct mixture would be: 25 grams color per 1 pound of material 25 pounds colorant per 400 pounds material 3 pounds colorant per 100 pounds material 4 pounds colorant for every 100 pounds of material 2. The orifice of a nozzle tip should be ________________ the sprue bushing orifice 1/16 the same size as 1/2 a different radius than 3. Color swirls can be caused by: a) Poor mixing of resin in the screw b) Poor cleaning of the nozzle tip at color change c) A cracked check ring d) Both A and B e) A, B and C 4. What steps are taken to develop a decoupled molding process? Both material and colorant are added to hopper for mixing. Hold and pack are removed from process. Shot size is adjusted to produce part at 95-98% fill. Pack and hold are added back into process to complete fill of part. Hold and pack are reduced 30%. Part is filled quickly to 80%, and then pack and hold are added back to fill out part. Shot size is adjusted until part flashes at parting line, then lowered until flash goes away. 5. A gate seal study is performed to: a) Assure that hold pressure is set properly. b) Verify that mold temperature has been properly adjusted. c) Verify that material is not flowing back through gate after hold pressure. d) Assure that part weight remains consistent. e) Both C and D 6. A dryer that is working properly should: Have a hot supply hose at the top and a warm return hose at the bottom. Have a warm hose at both the top and bottom. Have a hot supply hose at the bottom and a cold return hose at the top. Have a hot supply hose at the bottom and a warm return hose at the top. 7. A material that is hygroscopic is prone to drawing in moisture and must be dried at the temperature and time determined by the material manufacturer.TrueFalse 8. Which of the following shows an example of a submarine gate? All of the above. None of the above. 9. The purpose of Process Monitoring is: To assure that processing stays within the upper and lower limits set by the processor. To prevent poor quality parts from reaching the customer. To allow the press to alarm when an an out of tolerance condition occurs, thus notifying the technical support crew and operator. All of the above. 10. The glass transition temperature (Tg) is: a) The temperature of the gate when gate seal is achieved. b) The temperature of the mold when gate seal is achieved. c) The temperature of a crystalline material when it goes from solid to molten state. d) Both a and b. 11. Peak pressure is: The maximum pressure used in the hold pressure profile. The pressure limit set to prevent pressures from exceeding process set points. Beginning of fill pressure as the screw begins to shoot plastic through the gate. Maximum pressure measured as the screw switches over from injection to hold at the cut-off position. 12. Melt temperature is measured by: Measuring purge puddle temperature near the center with a temperature indicator. This occurs after the screw has been pulled from a running state, and purged continuously for 50 seconds. Reading the actual temperature of the nozzle zone on the temperature controller. Reading the actual temperature of the metering zone on the temperature controller. Measuring purge puddle temperature near the center with a temperature indicator. This occurs after the screw has just heated to temperature, and has been purged continuously for 50 seconds. 13. Shear heat from the screw rotation and back pressure supplies 70-90% of the total heat in the screw. Heater bands supply the rest and help prevent fluctuations.TrueFalse 14. When venting a mold, what percentage of the cavity parameter should be vented and at what spacing? a) 20% of the parameter should be vented at 1 inch intervals. b) 30% of the cavity parameter should be vented at equal intervals. c) 60% of the cavity parameter should be vented per the recommendations of the material supplier. d) Vent length, width and land are calculated based on material and mold temperature data. e) Both b and c. 15. A press uses 85 pounds of material per hour, producing 170 parts. How much material will be used in 5 hours, and how many parts will be produced? How much does 1 part weigh? 170 pounds/ 340 parts/ .5 pound part weight. 450 pounds/ 900 parts/ .7 pound part weight. 425 pounds/ 850 parts/ .5 pound part weight. 850 pounds/ 1700 parts/ .5 pound part weight. None of the above. 16. The flash pictured needs to be corrected using process changes. Choose answers below to correct condition. a) Verify that shot size is correct by removing pack and hold. If part is not at 95-98% fill without pack and hold, correct and add hold back until part is full and defect has been fixed. b) Decrease clamp force and increase fill speed. c) Apply bluing agent to parting line, and close mold under pressure. Visually inspect for areas that show signs of poor seal off. d) Raise nozzle temperature and reduce hold pressure. e) A and c are both correct. 17. Gassing is common with many materials, such as nylon. How often should a mold be cleaned and checked for proper greasing? Once per week. Once per day. Once or twice per shift, depending on mold history. Every hour. 18. A burn at the flow front’s end of fill can be a sign of: a) Poor venting. b) Filling the cavity too fast. c) Tonnage set too high. d) Both A and B. e) All of the above. 19. What reasons below might lead to an erratic and inconsistent cushion? a) Rear zone temperature too high. b) A cracked or leaking check ring. c) Barrel wear. d) Improperly set decompression after rotate (speed and/ or pressure). e) B, C and D. 20. A press keeps alarming because the metering zone temperature is higher than normal. The monitoring is set at 25 degrees above the setpoint. What reasons below could be causing it? a) Rear zone temperature is set too low, causing higher shear rate in metering zone. b) Heater band in metering zone is not heating properly. c) Check ring is cracked causing barrel to overheat d) Both A and B. 21. Runner size should be ____________ the wall thickness dimension of a part. 3/4 the size of 1/2 the size of 1 1/2 times None of the above 22. When is it important to close a mold in set-up mode? a) The mold has slides, and someone has been working between the mold halves. b) After resetting the mold open position. c) When starting a press that you did not shut down d) All of the above e) Both A and C 23. This part has signs of heavy splay at end of fill. Which of the following changes may improve the condition, or identify the cause? a) Slow down fill rate at beginning of fill. b) Check moisture content of material. c) Check melt temperature to Safety Data Sheet. d) Both A and B. e) All of the above. 24. Based on this gate seal chart, Hold time for this process should be: 4 seconds 5 seconds 6 seconds 7 seconds None of the above 25. This burn defect is on every shot. The burn is occurring half way through the injection. If the part has a 10″ inch shot size, how should the injection be profiled? a) Slow injection speed between 8 and 6 inches. b) Fast injection speed between 6 and 4 inches. c) Mold and vents should be cleaned and verified before making any attempt to profile injection. d) Slow injection speed starting between 6 and 4 inches, but may need adjusted further once change is reviewed. e) Both C and D. 26. If this part was pulled from the mold with the side marked “warp” being the stationary half, what adjustment would you make to get rid of the warp (after you checked to make sure mold set up was correct)? Raise mold temperatures. Run lower temperature on stationary half, warmer on movable mold half. Lower mold temperature. Run higher temperature on stationary half, lower mold temperature on movable half of mold. 27. Where in the screw does the majority of plastic melting occur? a) Feed Zone b) Transition Zone c) Metering Zone 28. If bar x is moved to the right, what direction will the gears move the bottom bar? a) Left b) Right c) Left and right 29. When installing clamps, the bolts should be torqued to: a) 50 PSI b) 95 PSI c) 140 PSI d) Torque specifications for bolt size and thread depth recommended by manufacturer 30. T or F: When changing a hot runner mold, hot runner can be heated to temperature 30 minutes prior to changing mold to reduce mold change time.TrueFalse 31. When making a change to back pressure, how long does it take for barrel temperature to stabilize? a) Result is seen on next shot b) 20 minutes c) 2 hours d) There will be no change in barrel temperature 32. After confirming that melt temperature is in the middle of the melt window, what happens to material viscosity and fill time when heats are raised? a) Viscosity is lower and fill time increases b) Viscosity is higher and fill time decreases c) Viscosity and fill time remain unchanged d) Viscosity is lower and fill time decreases 33. What is the normal drying time and temperature for unfilled nylon? a. 240 F for 4-8 hours b. 150 F for 2-4 hours c. 180 F for 2-4 hours d. None of the above 34. What conditions lead to bubble (void) defects in a part? a. under packing the part b. over packing the part c. moisture content d. None of the above e. All of the above 35. What is the purpose of a nylon tip? a. Plastic tip used to prevent damage to the bushing b. Increases peak pressure for better packing c. Reduces drooling and provides better sprue separation d. A and B e. All of the above 36. The typical peak pressure for nylon is: a. at or around 1000 PSI b. at or around 500 PSI c. at or around 750 PSI d. Dependent upon viscosity of material and mold design 37. When changing from nylon to polypropylene during a mold change: a. Heats should be lowered, and then polypropylene should be purged through the barrel b. Hopper, filters, barrel and material lines should be cleaned thoroughly c. The nozzle tip should be changed if a nylon tip was used. If same tip is to be used, tip face must be cleaned. d. All of the above e. Both B and C 38. True or false: Size and shape of material from grinder does not affect how it mixes with virgin material or the production process.TrueFalse 39. The material manufacturer recommends a melt window of 500-550 F, and the melt temperature checks at 546. What result might you get if you increase back pressure? a. Degradation of material leading to poor part quality b. Improved finish due to higher temperature c. Slower fill time d. A or B, depending on end result/ quality requirements 40. Parts you are producing are too small according to print. What changes might you make to increase their dimensions? a. Raise injection speed to increase packing b. add cooling time to reduce shrinkage c. add hold pressure to improve packing d. increase mold temperature to improve shrinkage e. Both B and C f. Both B and D 41. T or F: A part that is short (not completely filled) and has flash should be checked for signs of tool damage or wear at the parting line.TrueFalse 42. What is the drying time and temperature for Polypropylene? a. 180 F for 4-8 hours b. Not required for unfilled material, but with talc additive 140 F for 2-4 hours c. Not required for talc filled, but without talc 140 F for 2-4 hours d. 240 F for 4-8 hours 43. True or False: A pressure drop study is best utilized when injection pressures are close to or at maximum pressure at middle to end of fill within the molding process.TrueFalse 44. When making a change from injection to hold pressure (cut-off), how long does it take for the change to take effect in the process? a. The next cycle that the press injects b. 5 minutes after the change c. 20 minutes for the change to take effect d. None of the above 45. Which is the best method of ejector set up? a. Use maximum stroke with slower speed to assure that part falls b. Use minimum stroke with multiple pulse strokes to agitate part into falling c. Use minimum stroke with fastest eject speed. Watch process closely for 20 minutes to assure part falls correctly every time d. Both B and C 46. When setting a mold, clamps should be attached: a. with the clamp toed in to the groove, with the gap between the rear of the clamp and platen being larger than the gap in the front b. The clamp should be tied in parallel to the platen with equal gap between platen and rear or front of clamp c. the clamp should be toed out, with the gap between the front of the clamp and platen being larger than the gap in the rear d. None of the above 47. When making changes to back pressure, how long does it take for those changes to take effect? a. change will be seen at next screw rotation b. change will be complete after 5 minutes producing parts if barrel temperatures are reading correctly c. change will usually take about 20 minutes for screw temperature to level out, but longer time is possible d. back pressure has little if any effect on process 48. Flash that is feather-like in appearance: a. Is a sign of high heat b. Is a sign of poor material flow c. Points towards heats being too low d. Is proof of tool damage 49. Splay at end of fill happens when: a. Material ia over dried b. The screw is being starved and material isn't feeding properly c. Material is being over heated through a gate or drop due to excessive injection speed d. Material hasn't been dried long enough, and moisture is pressent 50. A mold that has details the flow front must pass around at 50 % fill might require: a. Fast fill with high hold pressure b. 5 stages of injection speed, ramping from fast to slow c. 3+stages of injection speed, faster speeds at the beginning and end of fill. The flow front would slow as it wraps around the details d. Slow fill for 80% of the shot, slowing for the last 20% of fill as the flow front passes around the details 51. When a parting line is being checked for damage: a. Apply bluing agent to the parting lines of both the cover and ejector halves of the mold. Close the mold under pressure, and inspect mold for areas bare of bluing b. Inspect lifters for damage and scarring c. Apply bluing agent to the cover half parting line areas. Put the mold under pressure then open the mold to review the parting line for bare areas, which are signs of parting line damage d. Both B and C 52. Valve gate delay timers: a. Determine what time gates open, which allows control of material flow in the cavity b. Can be set to zero, allowing all gates to fire open at the same time c. Improve hot runner performance by controlling rates of viscoty d. Both A and B 53. True or False: Nylon regrind can be used over and over, with little effect on process controlTrueFalse 54. True or False: Polypropylene regrind can be used over and over, with little effect on process control.TrueFalse 55. Molds that have valve gates set up properly require a gate seal study once a process has been established. True False 56. Material with a high relative viscosity: a. Normally will require a lower cooling time than the same base material with a lower viscosity b. May lead to over packing of ribs and details due to slower fill speed of a thicker flow front c. May improve part strength due to slower flow front speeds d. All of the above 57. Best practice for shutting down a clear Polycarbonate hot runner tool would be: a. shut down press and purge Polypropylene through hot runner b. Turn off hot runner, and keep producing parts until parts short due to low hot runner temperature c. Chase clear polycarb with purge compound until parts produced show signs of purge streaks. Shut down press, and purge through the hot runner until all that comes out is purge compound d. All of the above 58. Dispersion discs can be used for: a. Better mixing of color b. Improved baffling of water circuits c. Reduction of contaminants as they relate to hydraulic vales d. Reduction of large contaminants such as steel for prevention of these finding their way into tool hoy drops e. Both A and D 59. Measuring the flex of a tool within the platen configuration can identify: a. Whether hold pressure has been set too low, leading to a shorts/ unfill condition b. Whether a tool has adequate support pillars to prevent flexing, and potential flashing conditions c. Whether platen conditions are parallel at all four corners of tool d. Whether injection speeds are too high for existing tool requirements e. Both B and C f. None of the above 60. Which Screw/ Barrel measurements best identify cause for inconsistent cushion? a. Check ring wear/ fracture b. Screw shank metering zone c. Screw flights/ Barrel ID in metering zone d. All of the above f. A and B 61. Which material used for purging doesn’t belong? a. Polypropylene b. Acrylic c. Styrene d. Acetal e. None of the above 62. You are trying to achieve 95-98% fill with no hold pressure. You are currently at 80%. What adjustments can be made to achieve 95-98%? A) Add hold pressure B) Lower cut-off C) Increase fill speed D) Increase Shot size E) B, C and D F) A, B. C and D 63. When having issues with color swirl, you should: A) Increase Back Pressure B) Increase injection speed c) Set screw rotate time to 1.5 to 2 seconds faster than cool time set point D) Both A and C 64. T or F: When picking a nozzle tip, it should have the same size orifice as the sprue bushingTrueFalse 65. T or F: Low Pressure close should be set to the minimum pressure required to achieve lock up pressure.TrueFalse 66. When having problems with contamination with a hot runner tool, you may need to: A) Purge through the hot runner with a pressure-safe purging agent B) Clean the nozzle tip C) Purge new color through the hot runner, generously, then turn hot runner off to cool allowing tips to cap D) Inspect purge puddle from nozzle for signs of contamination from screw E) All of the above 67. Glass transition temperature refers to: A) The temperature at which a thermoplastic material waxes in the cavity B) The temperature at which a chrystalline material liquifies and flows C) Both A and B D) None of the above 68. When making temperature changes to a hot runner, manifold temperatures: A) Will raise or lower slower than drop temperatures B) Will raise or lower faster than drop temperatures C) Will raise or lower at the same rate as drop temperatures 69. If the actual temperature of a thermolator reads much lower than the set point, it is likely that: A) The thermolator is not heating properly B) Water lines attached to the mold have not been attached properly C) A valve has stuck open, not allowing thermolator to heat properly D) Both A and B E) Both A and C 70. When having problems removing a part from a mold with a robot, you should: A) verify that cups are clean,, free of tears and properly placed for part removal B) Inspect part and lifters for signs of burring, or damage leading to hang ups C) Consider mold temperature and cool time as a possible cause due to part shrinkage D) All of the above E) Both A and B 71. T or F: Material that is hot to the touch has been dried and is ready for useTrueFalse 72. Support pillars in a mold: A) Help to prevent flexing and flash B) Give the ejector plate guidance as parts are ejected C) Reduce the need for back pressure, and help reduce the potential for sink D) None of the above 73. Vented Pins: A) Allow gas a way to escape in hard to vent areas B) Have holes in the center that serve as a port for gas to escape C) Can become plugged as a mold, leading to gas trap defects D) All of the above E) Both A and C 74. When changing material from Nylon to clear polycarbonate, you should: A) Purge with an opaque polypropylene, then follow it with clear polycarbonate B) Lower barrel temperatures to 470F, then purge with Polycarbonate C) Purge generously with clear polycarbonate at nylon temperatures D) None of the above 75. When changing materials during a mold change, nylon to polypropylene should be: A) Purged through with Polypropylene at the end of change, then temperatures should be lowered to Polypropylene temperatures B) Purged with Acetal at beginning of change, then lowered to Polypropylene temperatuires C) Purged with Purge compound or Polypropylene at beginning of mold change, then lowered to Polyproylene temperatures D) Lower temperatures at beginning of mold change, then purge with purge compound or Polypropylene before starting press 76. When setting Decompression after rotate, you should: A) Set position to .50 or 1.00 B) Use the highest speed possible to be sure that the check ring sets C) Use the minimum speed and lowest position possible to prevent splay defects D) Both and B E) None of the above 77. Poor knits that lead to cracking weaknesses or visual defects are generally signs of: A) Injection speed too slow at end of fill causing a poor knit B) Injection speed too fast in area of knit leading to poor knit C) Injection speed too slow at the beginning of fill causing poor knit D) Excess packing (hold pressure) in area of a feature, leading to a poor knit 78. If part color is light, but color set point and equipment operation is correct: A) Verify melt temperature and barrel temperature set points are correct B) Decrease hold pressure and increase fill speeps C) Increase barrel and/ or mold temperature to tighten molecule alignment D) Both A and C 79. When shutting a press down for the weekend: A) Clean mold and spray liberally with mold saver B) Turn off hot runner C) Run screw dry, and purge with purge compound D) Close mold, leaving 1/8 E) Turn off thermolators, shutting off valves to prevent leaks F) All of the above G) A ,C and D are correct 80. The correct pressure to torque bolts into a platen is: A) 100 ft/lbs B) 120 ft/ lbs C) 160 ft/ lbs D) based on bolt diameter, thread, depth and grade as it relates to the platen 81. Splay is caused by: A) Moisture B) Injection speed C) Screw decompression: Speed and position D) Barrel and mold temperatures E) All of the above F) A, B and D 82. You are running a 4 cavity hot runner tool. One part has a burn at end of fill, and higher part weight than another that is short and has a low part weight. You should: Increase the temperature of the cavity with a burn, and lower the temperature of the part with low part weight. Lower the temperatures of all cavities free of the burn condition Increase back and hold pressures Raise the temperature of the part with a low part weight and lower the temp of the cavity that has burn at end of fill 83. A tool you are running has a valve gate that isn’t firing. You should: A) Run the valve gates manually and visually check the valve gate for proper operation B) Verify that all lines have been attached properly C) Raise barrel and mold temperatures to improve function D) Check valve gate timers to verify they are set correctly E) All of the above F) A, B and D 84. When mold temperature is causing warp, you should: a) Lower mold temperature on side warp is leaning towards to change cooling result b) Raise mold temperature on side of warp c) Lower barrel temperatures and reduce cooling time d) raise hot runner temperatures and slow mold open speeds 85. A mold you are running has a shine appearance that is occurring on a textured surface. You should: A) Inspect the mold for texture wear or damage B) Decrease hold pressure, and increase fill speed C) If mold is textured correctly, increase mold temperature to improve texture grain D) Lower cool time to improve graining E) Both B and D F) Both A and C 86. Lamination (flaking) is caused by: A) Barrel temperature B) Material cross- contamination C) Poor purging D) Mold temperature E) None of the above F) Both B and C 87. Water pressure measured going into a mold measures at 14 GPM, The pressure coming out is at 11 GPM. This condition should be: A) Seen as an abnormality, and inspected for potential cause of defects B) expected, due to normal resistance as water flows through the mold C) compared to previous recorded conditions, to assure that flow has not changed D) A and C are correct E) Both A and C are correct 88. At start up, there is a problem at the feed throat that is causing a Polycarbonate material to load poorly. Potential fixes to the problem might be: A) Verify nozzle temperature is sufficient for a chrystalline material B) Raise back pressure, and increase temperatures in the metering zone C) Choke off water to feed throat, to warm throat. After press has run 20 minutes, reopen water to feed throat D) Raise feed zone temperature E) Both C and D F) All of the above 89. When setting process monitoring for fill time, the +/- set point should be: A) .1 seconds above and below actual fill time B) .5 seconds above or below actual fill time C) 1 second above or below actual fill time D) Be set according to process and part variables 90. A process has been validated when: A) It has run 8 hours at 100% efficiency, with little to no scrap being produced B) Once parts on the belt have been confirmed to be acceptable by quality C)The process has been confirmed to be repeatable, with good parts being produced after 2-3 shots for 3 runs D) None of the above E) Both A and C 91. T or F: If adding back pressure to a process does not result in a temperature increase, the result may lead to material degradation and poor material properties,TrueFalse 92. During mold changes, if a material change requires changing from PCABS to polypropylene, you should: Purge with Polypropylene or purge compound at beginning of change, then lower to polypropylene temps Lower to Polypropylene temperatures, then purge press at end of mold change Purge with Polypropylene or suitable purge compound, then lower lemperatures at end of change Lower temperatures, then purge with styrene generously, followed by purging the barrel dry 93. If a thin-walled part tends to stick on the stationary side of the mold, you may need to: A) Slow the speed of mold open as it breaks the seal B) Raise the mold temperator on the stationary side C) Decrease barrel temperature to improve cooling D) Add divots or grooves on the movable side of tool to reduce sticking (non class A side) E) C and/ or D F) A and/ or D 94. Jetting (Worming) is caused by: A) Low mold temperature B) Excessive injection speed C) Low barrel temperature D) All of the above 95. If the size of a gate is to small, it could lead to the following defects: A) Flash B) Warp C) Splay D) Gate Blush E) Both C and D F) B, C and D 96. If an ejection pin is too small, it can cause the following conditions: A) Frequent breaking B) Burn on ribs C) Pin Push Marks D) Poor ejection E) All of the above F) A, C and D 97. The following conditions can cause problems that can affect process control consistency: A) Press operator B) Mold performance C) Conditions related to material D) Performance of press E) Maintenance: Planned and unplanned F) A, B and D G) All of the above 98. T or F: When heating a press from cold state, a front, metered or feed zone temperature that rises at a different rate could be a sign of bad heater bands.TrueFalse 99. T or F: Hot runner temperatures are generally used as an extension of nozzle temperature into the hot runner manifold. As such, nozzle temperature and manifold temperatures are usually the same.TrueFalse 100. T or F: Raising barrel and mold temperatures leads to increased peak pressure and viscosity.TrueFalse Please fill in the comment box below.