This set of Casting Objective Questions & Answers focuses on “Blow Moulding and Thermoforming – 2”.
1. Which of the following moulding processes is widely used for the manufacturing of plastic bottles?
a) Compression moulding
b) Injection moulding
c) Jet moulding
d) Blow moulding
View Answer
Explanation: In blow moulding process, a heated tube of plastic material is situated between the two halves of mould, then the mould is closed and air or inert gas is usually blown at a pressure of 200 – 400 bars, which helps in expanding of tube outward to occupy the mould cavity. After that the part cools down to get hardened and then the part is ejected from the mould.
2. Blow moulding is a very slow process, however economical for producing products with better quality.
a) True
b) False
View Answer
Explanation: The blow moulding process is very fast and can produce components mainly plastic parts very fast and economically. The process can be completed by manual means or by semi-automatic or automatic machines. Blow moulding process is especially used for the production of plastic bottles.
3. In extrusion blow moulding process, it is very difficult to trim away excess of plastics.
a) True
b) False
View Answer
Explanation: Extrusion blow moulding process is a type of blow moulding in which air is injected into the neck of container to blow up the plastic material that then occupies the mould cavity. In this method, tooling cost is low but it includes some difficulties in trimming away of excess plastic, it also possess high scrap rate of the plastic material.
4. Single stage stretch blow moulding is always preferred than two stage stretch blow moulding for increase in production rate.
a) True
b) False
View Answer
Explanation: Two stage stretch blow moulding is same as single stage stretch blow moulding, except preforms (tube of plastic) which are already made in the two stage process. The single stage process is generally accomplished by using single machine, where the two stage process uses preforms that already present in the process. This results in saving of time which directly increases production rate.
5. Single stage stretch blow moulding process is mostly used for small level production.
a) True
b) False
View Answer
Explanation: Single stage process includes an extruder to inject liquid plastic into the mould where the plastic is cooled to form a preform (tube of plastic). This preform is reheated and placed in the bottle mould. Then it is stretched by using compressed air in the mould cavity. This all processes require too much time to accomplish themselves, so it is only suitable for small level production.
6. Thermoforming process involves injecting of molten plastic into a mould cavity by application of compressed air.
a) True
b) False
View Answer
Explanation: In thermoforming process, a sheet of plastic is used which covers the shape of any die by heating it to the desired temperature and then it is stretched over the die using vacuum, thus it is also called as vacuum forming. Then the pressure is applied to the plastic sheet by using pressurized air.
7. In thermoforming process, it is very difficult to control thickness of moulded parts or sheets.
a) True
b) False
View Answer
Explanation: In thermoforming process, the tooling is mainly cheap to produce, but the process leaves small marks on the moulded sheets that can be controlled. But the main quality control issue possesses non-uniform thickness of parts or sheets which are difficult to handle, this may also result in warping or tearing of the moulded sheet.
8. In thermoforming, it is very easy to mould the plastic materials which are of crystalline nature.
a) True
b) False
View Answer
Explanation: The most widely used plastic materials in thermoforming process are amorphous or non-crystalline nature. This mainly includes moulding of plastic materials such as polyvinyl chloride (PVC), polyethylene, polystyrene, acrylic, polycarbonate etc. Crystalline nature of materials cannot be moulded through this process.
9. Thermoforming is basically a cheap process as compared to injection and blow moulding process.
a) True
b) False
View Answer
Explanation: Thermoforming can be used in both high and low volume production processes. The main advantage of this process includes low initial tooling and equipment costs. Due to this, this process is cheaper when compared with injection and blow moulding processes. Thermoforming is widely used for production of parts for industries including medicals, appliances etc.
10. Which of the following materials is mostly used for making of thermoforming moulds?
a) Steel
b) Grey cast iron
c) Aluminium
d) White cast iron
View Answer
Explanation: Thermoforming moulds are always made of aluminum because of its light weight, machine ability, and good thermal conductivity. Aluminum moulds may also contain passages through which water can be pumped for cooling of components, which may greatly affect the shrinkage and other features of the components made.
Sanfoundry Global Education & Learning Series – Casting, Forming and Welding.
To practice all objective questions on Casting, here is complete set of 1000+ Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
- Check Mechanical Engineering Books
- Practice Mechanical Engineering MCQs
- Check Metallurgical Engineering Books
- Apply for Metallurgical Engineering Internship
- Practice Metallurgical Engineering MCQs
