This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Dielectric Core Bakers”.
1. In dielectric core baker, several metallic plates are used for supporting the cores in the system.
a) True
b) False
View Answer
Explanation: Dielectric core bakers are basically based on dielectric heating. The core supporting metallic plates cannot be used in this type of baker because they interrupt the potential distribution in the electrostatic field. To avoid this interruption or interference, cement bonded asbestos plates can be used for supporting the cores instead of metallic plates.
2. Dielectric core bakers are faster in operation and have good control of maintaining the temperature.
a) True
b) False
View Answer
Explanation: The main advantage of dielectric core baker is that they are very faster in operation and have good control of maintaining the temperature. After baking of cores in dielectric baker, they are further smoothened by using dextrin material, sometimes water soluble binders are also used for this purpose.
3. For small cores mass production, dielectric core bakers can be preferred over continuous type ovens used for baking cores.
a) True
b) False
View Answer
Explanation: Dielectric core bakers are faster in operating the system but cannot be preferred over continuous type ovens for small cores mass production. Continuous type ovens are mainly preferred for mass production. In this baking system, core carrying conveyors are used which continuously moves through the oven.
4. After baking of cores in dielectric core bakers, they can be directly used in the moulding box.
a) True
b) False
View Answer
Explanation: After baking of cores in dielectric core bakers, finishing operation is a must before they set in the moulding box. Finishing is the last process which completes the formation of a core. This is a process in which bumps or other sand projections are removed from the surfaces of cores by filing them in a fixture.
5. Core finishing also includes a coating of refractory materials on cores to protect them.
a) True
b) False
View Answer
Explanation: Cores are generally coated with refractory or protective materials by performing several operations like brushing, dipping and spraying, which greatly improves the refractoriness and surface finish of the cores. The coating material on cores also restricts the liquid metal from entering into the pores of a core.
6. It is not possible to bake dry sand cores by dielectric core bakers.
a) True
b) False
View Answer
Explanation: Dry sand cores are basically produced by heating the green sand cores nearly about 110 ⁰C. These cores have high strength rigidity and excellent thermal stability. These cores can be easily baked by dielectric core bakers and normally stored for a long period of time to make them more stable than the green sand cores. Dry sand cores generally used for large castings production.
7. How much percentage of water or moisture is contained by green sand cores?
a) 5%
b) 10%
c) 20%
d) 40%
View Answer
Explanation: Green sand cores are made of green sand which mainly contains water or moisture nearly about 5% and 15 to 30 % of clay. It imparts very high permeability to the core material and hence reduces the chance of defects such as shrinkage or voids in the casted parts. Green sand cores are not dried but usually baked by dielectric bakers to maintain the moist content.
8. In dielectric core baker system, a metal used generally requires a low value of K (dielectric constant of material)
a) True
b) False
View Answer
Explanation: In dielectric core baker systems, a dielectric material is used that should have a high value of K (K is the dielectric constant of the material), which basically provides the required electrical properties to operate the system efficiently. More the value of K, then more will be the effect of baker system on the baking cores.
9. The process of making green sand cores generally consumes much time as compared to that of dry sand cores.
a) True
b) False
View Answer
Explanation: Green sand cores are generally preferred for simple, small and medium castings. The process of making green sand cores do not consume much of time. The process is accomplished quickly that causes less strength in green sand cores as compared to that of dry sand cores. Dry sand cores usually take longer time in making of themselves.
10. In dielectric baker systems, cement plates are normally used for supporting the cores.
a) True
b) False
View Answer
Explanation: In dielectric baker systems, the heating of core is done by placing them in the electrostatic field. The dielectric material generates heat in the system that is directly supplied to the cores. In this system, there should be no interruption of any metallic material, so cement plates are widely used instead of metallic plates in the baking system for supporting the cores.
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