7 Polymer Shaping Processes

Question 1

1. Viscosity is an important property of a polymer melt in plastic shaping processes. Upon what parameters does viscosity depend? (2)

Answer 1

1 Shear Rate Parameter

2 Temperature Parameter

Polymer melt’s viscosity decreases (thus becomes thinner and flows more easily) with a higher shear rate and higher temperature.

Question 2

2. Briefly describe the plastic extrusion process. (1 long)

Answer 2

1) Process of a heated polymer material (such as thermoplastics and elastomers) forced to flow through a die orifice

1.a) Die orifice produces a long and continuous product with a cross- section based on the die orifice opening

1.b) The end shape of the material is then cut to the desired length.

Question 3

3. Discuss some of the defects that can occur in plastic injection molding. (4)

Answer 3

1 Non-uniform molds

Material either being;

2 Too thin

3 Too thick

4 Simply unfirm

Question 4

4. What kinds of products are produced by blow molding? (7)

Answer 4

Everyday thermoplastic products:

1 Disposable beverage containers,

2 Large shipping drums

3 Containers holding powders and or liquids

4 Storage tanks

5 Gasoline tanks

6 Toys

7 Small boats

Question 5

5. Why can’t thermosetting polymers be used in thermoforming processes? (2)

Answer 5

They are 1 already cross-linked

and

therefore thermosetting polymers 2 can not be softened by reheating

Question 6

6. What are some of the general considerations that product designers must keep in mind when designing components out of plastics? (4)

Answer 6

1) Plastics are not as strong or stiff as metals

2) Plastics must avoid applications where high stresses will occur, and creep resistance is limited

3) Plastics are subject to degradation from sunlight and other forms of radiation

4) Thermal expansion is more significant for metals than plastics.

Question 7

7. Comparing the advantages and disadvantages of injection molding and transfer molding. (4)

Answer 7

INJECTION MOLDING

Advantages (4. MMHP)

1 Machine’s fast speed

2 Minimum waste

3 High capacity and

4 Pre-heat materials immediately

Disadvantages (3. HRT)

1 High setup costs

2 Rounded corners

3 Thin unfirm walls

TRANSFER MOLDING

Advantages (5. SLFCA)

1 Sharper edges

2 Low repair cost

3 Fast set up

4 Cheap setup

5 Allows for metal inserts.

Disadvantages

1 Production of small quantities

2 Low process

3 Material waste.

Question 8

8. What fabrication process is used to coat the insulation layers of electrical wires? (1)

Answer 8

Extrusion is the fabrication process that is used to coat the insulation layers of electrical wires.

Question 9

9. If a company is to make plastic food containers, what polymer forming process will the company use? Why? (2)

Answer 9

Variation of Injection Molding called 1 Stretch Blow Molding

because this polymer forming process 2 stretches the soft parison for a more favorable stressing of polymer than conventional blow molding.

Question 10

10. Your phone chargers have the connect pins fixed in a plastic package, what polymer forming process is used to make the part like this. (1)

Answer 10

**The polymer forming process used to make phone chargers have connect pins fixed in a plastic package is Transfer Molding.