MMET 281 Exam II Questions with
100% Correct Answers
What are the disadvantages of compression molding? - Answer- -the depth of the
molded holes is limited to 2 or 3 times their diameter
-shot weight must be tightly controlled
-unacceptable parts cannot be reproduced
Describe transfer molding - Answer- similar to injection molding in the way the charge is
preheated in a separate chamber and then injected into the mold
What should be considered as far as mold design and gates goes? - Answer- -make
sure the part fills before the gate freezes
-gate type dependent on aesthetic requirements and processing needs
What are the three common types of ejection systems used in mold design? - Answer- -
knockout pins (ejector pins)
-knockout or ejector sleeves
-stripper plate
When designing a part, what kind of wall thickness should be considered? - Answer- as
uniform as possible
When designing a part, what should be considered as far as draft? - Answer- must be
added to push part off tool, 0.5 degree minimum angle; more surface area or a rough
surface requires more draft
What material is often used for transfer molding? - Answer- thermoset plastics
What are the pro's and con's of transfer molding? - Answer- pro's-complex parts and
delicate inserts can be molded because the raw material is fluid
con's- compared to compression molding, high molding pressures are required, more
waste from runners and sprues
What are the two parts of an injection mold? - Answer- cavity half and core half
Cavity Half (Injection Mold) - Answer- A side; external shape
Core Half (injection mold) - Answer- B side; internal shape
, Define multi-cavity mold - Answer- a tool that has multiple cavities for the same part
Define Family Mold - Answer- a tool that has multiple cavities for unique parts
Define Sprue - Answer- carries plastic from the nozzle to the runners
Define Runners - Answer- convey molten plastic from the sprue to the cavities
Define gate? - Answer- the point of entry into the mold cavity
What is used to allow trapped air to come out of the mold? - Answer- vents
Where are vents typically placed? - Answer- at ejector pins and parting lines
Name two processes used to put a coating on a wire. - Answer- extrusion coating and
calendar coating
What process is used to place coatings on tool handles? - Answer- dip coating
Name a method that may be used to place a coating on fabric. - Answer- Transfer
coating
What causes the powder to atomize in fluidized-bed processing? - Answer- the bottom
of the tank has a porous membrane to allow air or inert gas to atomize the powdered
plastics
Name four reasons for coating a substrate. - Answer- Protecting, insulating, lubricating,
or adding durable beauty
In electrostatic-bed coating, how is the dry powder deposited on the part? - Answer- A
fine cloud of negatively charged plastics powders is sprayed and deposited on a
positively charged object.
Name a process in which an image if transferred from the carrier film to the product by
stamping with rigid or supple shapes and with heat and pressure. - Answer- Hot leaf
stamping
Name the six methods of forming the cellular structure in the expanding processes. -
Answer- 1. Thermal breakdown of a chemical blowing agent, freeing a gas in a plastics
particle
2. Dissolving a gas that expands at room temperature in the resin
3. Adding a liquid or solid component that vaporizes when heated in the melt
4.Whipping air into the resin and rapidly curing or cooling the resin
5. adding components that liberate gas within the resin through a chemical reaction
6. volatizing moisture
100% Correct Answers
What are the disadvantages of compression molding? - Answer- -the depth of the
molded holes is limited to 2 or 3 times their diameter
-shot weight must be tightly controlled
-unacceptable parts cannot be reproduced
Describe transfer molding - Answer- similar to injection molding in the way the charge is
preheated in a separate chamber and then injected into the mold
What should be considered as far as mold design and gates goes? - Answer- -make
sure the part fills before the gate freezes
-gate type dependent on aesthetic requirements and processing needs
What are the three common types of ejection systems used in mold design? - Answer- -
knockout pins (ejector pins)
-knockout or ejector sleeves
-stripper plate
When designing a part, what kind of wall thickness should be considered? - Answer- as
uniform as possible
When designing a part, what should be considered as far as draft? - Answer- must be
added to push part off tool, 0.5 degree minimum angle; more surface area or a rough
surface requires more draft
What material is often used for transfer molding? - Answer- thermoset plastics
What are the pro's and con's of transfer molding? - Answer- pro's-complex parts and
delicate inserts can be molded because the raw material is fluid
con's- compared to compression molding, high molding pressures are required, more
waste from runners and sprues
What are the two parts of an injection mold? - Answer- cavity half and core half
Cavity Half (Injection Mold) - Answer- A side; external shape
Core Half (injection mold) - Answer- B side; internal shape
, Define multi-cavity mold - Answer- a tool that has multiple cavities for the same part
Define Family Mold - Answer- a tool that has multiple cavities for unique parts
Define Sprue - Answer- carries plastic from the nozzle to the runners
Define Runners - Answer- convey molten plastic from the sprue to the cavities
Define gate? - Answer- the point of entry into the mold cavity
What is used to allow trapped air to come out of the mold? - Answer- vents
Where are vents typically placed? - Answer- at ejector pins and parting lines
Name two processes used to put a coating on a wire. - Answer- extrusion coating and
calendar coating
What process is used to place coatings on tool handles? - Answer- dip coating
Name a method that may be used to place a coating on fabric. - Answer- Transfer
coating
What causes the powder to atomize in fluidized-bed processing? - Answer- the bottom
of the tank has a porous membrane to allow air or inert gas to atomize the powdered
plastics
Name four reasons for coating a substrate. - Answer- Protecting, insulating, lubricating,
or adding durable beauty
In electrostatic-bed coating, how is the dry powder deposited on the part? - Answer- A
fine cloud of negatively charged plastics powders is sprayed and deposited on a
positively charged object.
Name a process in which an image if transferred from the carrier film to the product by
stamping with rigid or supple shapes and with heat and pressure. - Answer- Hot leaf
stamping
Name the six methods of forming the cellular structure in the expanding processes. -
Answer- 1. Thermal breakdown of a chemical blowing agent, freeing a gas in a plastics
particle
2. Dissolving a gas that expands at room temperature in the resin
3. Adding a liquid or solid component that vaporizes when heated in the melt
4.Whipping air into the resin and rapidly curing or cooling the resin
5. adding components that liberate gas within the resin through a chemical reaction
6. volatizing moisture
