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: Nylon regrind can be used over and over, with little effect on process control

Question #2: 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 #3: Melt temperature is measured by:

Question #4: A burn at the flow front’s end of fill can be a sign of:

Question #5: 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 #6: Splay at end of fill happens when:

Question #7: Measuring the flex of a tool within the platen configuration can identify:

Question #8: The glass transition temperature (Tg) is:

Question #9: What reasons below might lead to an erratic and inconsistent cushion?

Question #10: When venting a mold, what percentage of the cavity parameter should be vented and at what spacing?

Question #11: If a material ratio is identified at 25:1, or 4%.. the correct mixture would be:

Question #12: 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 #13: What conditions lead to bubble (void) defects in a part?

Question #14: 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 #15: What is the normal drying time and temperature for unfilled nylon?

Question #16: When changing from nylon to polypropylene during a mold change:

Question #17: Polypropylene regrind can be used over and over, with little effect on process control.

Question #18: The typical peak pressure for nylon is:

Question #19: You are trying to acheive 95-98% fill with no hold pressure. You are currently at 80%. What adjustments can be made to achieve 95-98%?

Question #20: Molds that have valve gates set up properly require a gate seal study once a process has been established.

Question #21: When making changes to back pressure, how long does it take for those changes to take effect?

Question #22: What is the purpose of a nylon tip?

Question #23: Based on this gate seal chart, Hold time for this process should be:

Question #24: A dryer that is working properly, should:

Question #25: What is the drying time and temperature for Polypropylene?

Question #26: True or false: Size and shape of material from grinder does not affect how it mixes with virgin material or the production process.

Question #27: 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 #28: Peak pressure is:

Question #29: 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 #30: What steps are taken to develop a decoupled molding process?

Question #31: If bar x is moved to the right, what direction will the gears move the bottom bar?

Question #32: When a parting line is being checked for damage:

Question #33: 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 #34: Parts you are producing are too small according to print. What changes might you make to increase their dimensions?

Question #35: Where in the screw does the majority of plastic melting occur?

Question #36: Which Screw/ Barrel measurements best identify cause for inconsistent cushion?

Question #37: Dispersion discs can be used for:

Question #38: When setting a mold, clamps should be attached:

Question #39: 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 #40: Best practice for shutting down a clear Polycarbonate hot runner tool would be:

Question #41: Runner size should be ____________ the wall thickness dimension of a part.

Question #42: Gassing is common with many materials, such as nylon. How often should a mold be cleaned and checked for proper greasing?

Question #43: The orifice of a nozzle tip should be ________________ the sprue bushing orifice

Question #44: The purpose of Process Monitoring is:

Question #45: A gate seal study is performed to:

Question #46: Flash that is feather-like in appearance:

Question #47: 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 #48: Which material used for purging doesn’t belong?

Question #49: Which of the following shows an example of a submarine gate?


Question #50: The flash pictured needs to be corrected using process changes. Choose answers below to correct condition.

Question #51: 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 #52: 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 #53: 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 #54: When installing clamps, the bolts should be torqued to:

Question #55: Color swirls can be caused by:

Question #56: Valve gate delay timers:

Question #57: 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 #58: Material with a high relative viscosity:

Question #59: When is it important to close a mold in set-up mode?

Question #60: A mold that has details the flow front must pass around at 50 % fill might require:

Question #61: When making a change to back pressure, how long does it take for barrel temperature to stabilize?

Question #62: Which is the best method of ejector set up?


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