Plastic411: Plastic Injection Testing

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.

Thanks for using this platform, and feel free to contact me for help with training development onsite at your facility. Plastic411 training is floor intensive, taught only on the floor using your presses, equipment, materials, processes:

Garrett MacKenzie
Owner/ Editor


Question #1: When changing from nylon to polypropylene during a mold change:

Question #2: When setting a mold, clamps should be attached:

Question #3: When venting a mold, what percentage of the cavity parameter should be vented and at what spacing?

Question #4: 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?

Question #5: What is the purpose of a nylon tip?

Question #6: Runner size should be ____________ the wall thickness dimension of a part.

Question #7: What steps are taken to develop a decoupled molding process?

Question #8: The purpose of Process Monitoring is:

Question #9: The orifice of a nozzle tip should be ________________ the sprue bushing orifice

Question #10: The glass transition temperature (Tg) is:

Question #11: 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?

Question #12: 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.

Question #13: Based on this gate seal chart, Hold time for this process should be:

Question #14: What is the drying time and temperature for Polypropylene?

Question #15: Parts you are producing are too small according to print. What changes might you make to increase their dimensions?

Question #16: Color swirls can be caused by:

Question #17: This part has signs of heavy splay at end of fill. Which of the following changes may improve the condition, or identify the cause?

Question #18: Melt temperature is measured by:

Question #19: What reasons below might lead to an erratic and inconsistent cushion?

Question #20: 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)?

Question #21: True or false: Size and shape of material from grinder does not affect how it mixes with virgin material or the production process.

Question #22: If bar x is moved to the right, what direction will the gears move the bottom bar?

Question #23: When is it important to close a mold in set-up mode?

Question #24: What conditions lead to bubble (void) defects in a part?

Question #25: What is the normal drying time and temperature for unfilled nylon?

Question #26: 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?

Question #27: Where in the screw does the majority of plastic melting occur?

Question #28: Which of the following shows an example of a submarine gate?


Question #29: Peak pressure is:

Question #30: 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?

Question #31: 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

Question #32: A dryer that is working properly, should:

Question #33: 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?

Question #34: When making changes to back pressure, how long does it take for those changes to take effect?

Question #35: Which is the best method of ejector set up?

Question #36: 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.

Question #37: A gate seal study is performed to:

Question #38: A burn at the flow front’s end of fill can be a sign of:

Question #39: The typical peak pressure for nylon is:

Question #40: When installing clamps, the bolts should be torqued to:

Question #41: 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

Question #42: 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.

Question #43: A material that is hydroscopic is prone to drawing in moisture and must be dried at the temperature and time determined by the material manufacturer

Question #44: If a material ratio is identified at 25:1, or 4%.. the correct mixture would be:

Question #45: Gassing is common with many materials, such as nylon. How often should a mold be cleaned and checked for proper greasing?

Question #46: When making a change to back pressure, how long does it take for barrel temperature to stabilize?

Question #47: The flash pictured needs to be corrected using process changes. Choose answers below to correct condition.


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