This set of Composite Materials Multiple Choice Questions & Answers (MCQs) focuses on “Bag Moulding and Pultrusion”.
1. Which is not a type of bag molding process?
a) Pressure bag molding
b) Vacuum bag molding
c) Autoclave molding
d) Resin transfer molding
View Answer
Explanation: Bag molding process can be categorized, based on the method of application of external pressure as Pressure bag molding, Vacuum bag molding and Autoclave molding. Resin transfer molding is another process used for the production of composites. In this process, the resin is injected into mold cavity with pressure.
2. The bag molding layout is set up between a steel mold plate and _________
a) peel plies
b) bleeder plies
c) caul plate
d) release fabric
View Answer
Explanation: Caul plates are metal plates which have a shape as a composite lay-up, used during the curing process right after in contact with the lay-up. They provide a smooth surface on the finished laminate and transmit normal pressure and temperature. The complete composite layup is covered with a sheet of glass fabric separator, a caul plate, and then a thin heat-resistant vacuum bag.
3. ____________ is used to coat the mold plate in the bag moulding process.
a) Release coat film
b) Peel plies
c) Bleeder plies
d Breather plies
View Answer
Explanation: The release coat film is coated over the mold plate in order to ensure that the composite laminate part does not get stuck to the mold plate after the bag molding process so that the product can be successfully taken out from the mold.
4. What is used to cover the composite parts in bag molding process?
a) Peel plies
b) Breather plies
c) Caul plate
d) Bleeder plies
View Answer
Explanation: Peel plies are tightly woven materials which protect the composite laminate against contaminating agents. The peel plies allow the resin to bleed through the material producing a finished surface.
5. What is the function of bleeder plies in bag molding process?
a) Protection of composite
b) Absorption of excess resin
c) Curing of composite
d) Release of air bubbles
View Answer
Explanation: The bleeder papers are placed on top of the prepreg stack. It is used to absorb the excess resin in the prepreg as it flows out during the molding process.
6. What is used for the release of air bubbles from composites in bag molding process?
a) Bleeder plies
b) Caul plate
c) Breather plate
d) Peel plies
View Answer
Explanation: The breather plies act as a pathway for air bubbles and volatile materials to exit out from the composite laminate during curing. It is able to allow air through it even when compressed.
7. ______________ is the most important factor to ensure good dimensional accuracy and surface finish.
a) Pressure
b) Volume of mold
c) Temperature
d) Force
View Answer
Explanation: The application of pressure is important to ensure dimensional accuracy, good surface finish and also to eliminate the presence of air as well as porosity in the laminate.
8. Pressure bag molding is relatively expensive due to tooling costs comparing to vacuum bag molding and autoclave molding.
a) True
b) False
View Answer
Explanation: The Pressure bag molding is relatively expensive due to its tooling costs since it is integrated with the curing pressure system. In contrast, autoclave molding approaches are relatively inexpensive as it makes use of the atmospheric pressure and the basic curing equipment doesn’t change.
9. The stacking operation of the prepreg can be done either manually or by numerically controlled automatic tape-laying machines.
a) True
b) False
View Answer
Explanation: The prepreg laminates are laid onto the mould base. After that, a number of layers or materials are covered over the laminates such as release coat film, release fabric, bleeder layer, breather layer, peel plies and at last a vacuum bag is placed to cover the laminate and all the layers.
10. The flow of excess resin from the prepregs is extremely important in reducing the void content in the cured laminate.
a) True
b) False
View Answer
Explanation: The excess resin flows out into the bleeder papers when external pressure is applied on the prepreg laminate stack. The excess resin flow is very important as it helps the removal of entrapped air and volatiles from the prepreg and thereby reducing the void content in the laminate after curing. In a bag-molding process resin flow by face bleeding is preferred over edge bleeding since it is more effective.
11. Which of the factors doesn’t affect the maximum temperature inside the layup in bag molding process?
a) Maximum cure temperature
b) Heating rate
c) Initial layup thickness
d) Applied pressure
View Answer
Explanation: At high heating rates and greater layup thickness, the heat generated by the curing reaction is very high. Also, the maximum cure temperature is determined from the time-temperature–viscosity characteristics and is usually suggested by the producers based on the resin–catalyst system used in the prepregs.
12. Which of the factors doesn’t affect the resin flow in the layup in bag molding process?
a) Maximum pressure
b) Layup thickness
c) Heating rate
d) Layup volume
View Answer
Explanation: The cure pressure and the layup thickness is inter-related. As the layup thickness increases, more cure pressure is required to squeeze out the resin. Also, if the heating rate is very high, the resin will start to gel before the excess resin is squeezed out from each and every ply in the prepreg layup.
13. The entire assembly is placed inside an_________ where a combination of external pressure, vacuum, and heat is applied to consolidate and densify separate plies into a solid laminate.
a) autoclave
b) compressor
c) vacuum bag
d) furnace
View Answer
Explanation: While curing undergoes at elevated temperatures in an autoclave molding, the composite prepreg is subjected to vacuum pressures and elevated pressures simultaneously. The whole composite and covering layers are enclosed in a bag connected to a vacuum pump and the exterior of the bag is subjected to pressures more than 1 bar. Finally, curing of the resin occurs by raising the temperature of a material in the autoclave mold.
14.____________ is a butyl-based vacuum bag sealant giving high elasticity and tenacity.
a) Tacky tape
b) Breather fabric
c) Perforated release films
d Vacuum bag film
View Answer
Explanation: Tacky tape has excellent sealant properties which eliminate the risk of imperfect seals sometimes found in the initial phases of vacuum bag applications. As a result, it improves the vacuum efficiency and reduces labour.
15. ____________ are made from modified polypropylene and can be rigid or elastic.
a) Perforated release films
b) Vacuum bag film
c) Bleeder fabric
d) Release fabric
View Answer
Explanation: Perforated Release Film is used as the first barrier between the prepreg laminate and the rest of the vacuum bagging materials. They have good performance at elevated temperature, naturally self-releasing and have very good mechanical properties.
16. Vacuum bag film is a polypropylene film, modified to resist elevated temperatures.
a) True
b) False
View Answer
Explanation: The vacuum bag film is suitable for use with prepreg and wet-lay-up laminating systems. The elastic nature of the film offers resistance to puncture, also allows the film to be stretched over molds without many number of folds and thereby improving the efficiency of the vacuum.
Sanfoundry Global Education & Learning Series – Composite Materials.
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