Lecture/Homework 3: Polymer Processing

Polymer processing: Which of the following are true statements?

(Everything except the ones below):

* As temperature increases, the density of a polymer also increases.

Which can be melted and cooled repeatedly without degradation?

* PVC
* Nylon
* ABS
* Polymethyl methacrylate

(T/F) All thermoplastics have the potential to be recycled.

True

Which is the correct order of sections in an extruder from the die back to hopper?

Metering, compression, feed

The physical property of plastics that is utilized in spider dies to make tubing is:

Viscoelasticity

In which of the following characteristics do plastic parts often do better than metals:

* Strength to weight ratio
* Impact resistance

(T/F) Two-plate molds are used to separate the sprue and runners from the parts.

False

(T/F) Compression molding and transfer molding do not use an extrusion barrel and are primarily used for thermosets and elastomers.

True

Thermoforming is limited to which plastic types?

Thermoplastic

Which are true statements about structural foam molding?

* The density of material within a part depends heavily on its local temperature during curing. Colder regions will be more dense and hotter regions less dense.
* SFM can make parts with a higher strength-to-weight ratio than other polymer manufacturing methods.

Which can make parts with different color layers of plastics?

Rotomolding

(T/F) Injection molding used high pressure for molding whereas RIM utilizes low pressure.

True

Which process has the shortest cycle time?

Injection molding

(Injection molding): Which of the following statements are true?

(Everything except the ones below):

* If threading is needed in an injection molded part, either usue an insert, or design it with very fine threads.
* Blow molding can be used to form both thermoplastic and thermosetting materials.