Injection molding quiz

These questions are excerpted from a quiz posted by Garrett MacKenzie at www.plastic411.com. The correct answers and your score will display at the end of this 15-question quiz when you click on "done." PlasticsToday thanks Garrett for allowing us to use part of his quiz.

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

A) 25 grams color per 1 pound of material

B) 25 pounds colorant per 400 pounds material

C) 3 pounds colorant per 100 pounds material

D) 4 pounds colorant for every 100 pounds of material

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* 2. The orifice of a nozzle tip should be [fill in the blank] the sprue bushing orifice

A) 1/16" smaller than

B) the same size as

C) 1/2" bigger than

D) a different radius than listed above

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* 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

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* 4. What steps are taken to develop a decoupled molding process? (The term "decoupled molding" is registered by RJG Inc.)

A) Both material and colorant are added to hopper for mixing.

B) Hold and pack are removed from process. Shot size is adjusted to produce part at 95 to 98% fill. Pack and hold are added back into process to complete fill of part.

C) Hold and pack are reduced 30%. Part is filled quickly to 80%, and then pack and hold are added back to fill out part.

D) Shot size is adjusted until part flashes at parting line, then lowered until flash goes away.

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* 5. A gate seal study is performed to

A) Ensure 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) Ensure that part weight remains consistent

E) Both C and D

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* 6. A dryer that is working properly should:

A) Have a hot supply hose at the top and warm return hose at the bottom

B) Have a warm hose at both the top and bottom

C) Have a hot supply hose at the bottom and a cold return hose at the top

D) Have a hot supply hose at the bottom and a warm return hose at the top

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* 7. 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.

True

False

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* 8. The purpose of process monitoring is:

A) To ensure that processing stays within the upper and lower limits set by the processor

B) To prevent poor quality parts from reaching the customer

C) To allow the press to alarm when an an out-of-tolerance condition occurs, thus notifying the technical support crew and operator

D) All of the above

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* 9. 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 a solid to molten state

D) Both A and B

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* 10. Peak pressure is:

A) The maximum pressure used in the hold pressure

B) The pressure limit set to prevent pressures from exceeding process set points

C) Beginning of fill pressure as the screw begins to shoot plastic through the gate

D) Maximum pressure measured as the screw switches over from injection to hold at the cut-off position

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* 11. Melt temperature is measured by:

A) The 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

B) Reading the actual temperature of the nozzle zone on the temperature controller

C) Reading the actual temperature of the metering zone on the temperature controller

D) The 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

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* 12. Shear heat from the screw rotation and back pressure supplies 70 to 90% of the total heat in the screw. Heater bands supply the rest and help prevent fluctuations.

True

False

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* 13. 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

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

A) Once per week

B) Once per day

C) Once or twice per shift, depending on mold history

D) Every hour

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* 15. A burn at the flow front 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