5. Which of the following are reasons why injection molding of thermosets is mor

Question

5. Which of the following are reasons why injection molding of thermosets is more difficult than injection molding of thermoplastics: (a) allowances must be made for cross-linking of thermosets, (b) barrel temperatures must be hotter for thermosets, (c) cycle times are longer because of curing, (d) thermosets are denser, or (e) two injection units are required? 6. Which of the following processes are used to produce PVC sheet and film: (a) blown film extrusion process, (b) calendering, (c) chill roll extrusion, (d) doctor blade method, (e) spinning, (f) thermoforming, and (g) transfer molding? 7. Which of the following processes would be most applicable to produce hulls for small boats: (a) blow molding, (b) compression molding, (c) injection molding, (d) rotational molding, and (e) vacuum thermoforming? 8. What are some of the advantages of thermoforming compared to injection molding: (a) The tooling is cheaper, (b) the geometrical accuracy is better, (c) thermosetting polymer can be used, (d) higher production rate possible, (e) room-temperature operation.

Explanation / Answer

Injection molding of thermosets is more difficult than injection molding of thermoplastics:

Thermosets have cross linked polymers during curing which are irreversible chemcial bond. They cannot be remolded or shaped. The scenario is opposite in thermoplastics. The reason lies in the curing cycle time. As forming of cross linked chains during curing is time consuming, injection molding is difficult.

Option C

Related Questions

Navigate

• Browse (All)
• Browse 5
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.