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

Question #3: 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 #4: A gate seal study is performed to:

Question #5: What reasons below might lead to an erratic and inconsistent cushion?

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

Question #7: 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 #8: When making a change to back pressure, how long does it take for barrel temperature to stabilize?

Question #9: Where in the screw does the majority of plastic melting occur?

Question #10: What steps are taken to develop a decoupled molding process?

Question #11: 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 #12: A burn at the flow front’s end of fill can be a sign of:

Question #13: 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 #14: If bar x is moved to the right, what direction will the gears move the bottom bar?

Question #15: Color swirls can be caused by:

Question #16: The typical peak pressure for nylon is:

Question #17: 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 #18: The flash pictured needs to be corrected using process changes. Choose answers below to correct condition.

Question #19: What conditions lead to bubble (void) defects in a part?

Question #20: The orifice of a nozzle tip should be ________________ the sprue bushing orifice

Question #21: Which of the following shows an example of a submarine gate?


Question #22: When setting a mold, clamps should be attached:

Question #23: 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 #24: If a material ratio is identified at 25:1, or 4%.. the correct mixture would be:

Question #25: Peak pressure is:

Question #26: When installing clamps, the bolts should be torqued to:

Question #27: Based on this gate seal chart, Hold time for this process should be:

Question #28: The glass transition temperature (Tg) is:

Question #29: What is the normal drying time and temperature for unfilled nylon?

Question #30: 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 #31: Gassing is common with many materials, such as nylon. How often should a mold be cleaned and checked for proper greasing?

Question #32: 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 #33: 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 #34: 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 #35: When changing from nylon to polypropylene during a mold change:

Question #36: When venting a mold, what percentage of the cavity parameter should be vented and at what spacing?

Question #37: Parts you are producing are too small according to print. What changes might you make to increase their dimensions?

Question #38: The purpose of Process Monitoring is:

Question #39: What is the purpose of a nylon tip?

Question #40: True or false: Size and shape of material from grinder does not affect how it mixes with virgin material or the production process.

Question #41: 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 #42: When is it important to close a mold in set-up mode?

Question #43: 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 #44: What is the drying time and temperature for Polypropylene?

Question #45: Melt temperature is measured by:

Question #46: A dryer that is working properly, should:

Question #47: When making changes to back pressure, how long does it take for those changes to take effect?


First Source for Plastic Injection Information and Training