This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Casting Cleaning”.
1. Breaking of the sand mould is done after sufficient cooling of castings, to have_____
a) proper surface finish of castings
b) no any distortion to castings
c) high casting yield
d) less casting yield
Explanation: The sand mould is to be broken to extract the casting. But the breaking of the sand mould is to be done only when the castings are sufficiently cooled, since the metal at high temperature has very little strength, due to this it may cause distortion to the casting if breaking of mould is done before proper cooling of the mould.
2. Pressure change of a melt is responsible for the cooling rate of the castings in the mould.
Explanation: Pressure has no effects on cooling rate of castings; the cooling rate depends upon the casting thickness, the total mass as well as the type of mould. More the mass or density of the castings will show less cooling rate and more the surface area of castings will have fast cooling rate of the castings in the mould.
3. Which of the following types of mould will have the longest period of cooling time for the same castings?
a) Green sand mould of simple shape and size
b) Dry sand mould of simple shape and size
c) Dry sand mould of complex shape and size
d) Green sand mould of complex shape and size
Explanation: Dry sand mould of complex shape and size will have the longest period of cooling time, it is around 18-30 hours for 3000-5000 kg of mass of castings. The cooling time also depends upon the mass of the castings, for the same sand mould the cooling time can be reduced up to 50% if the mass of castings comes in the range of 1000-3000 kg.
4. Faster and uneven cooling of hot casting affects the castings badly or may cause several defects in the castings.
Explanation: When the hot casting is exposed to the air, there is likely to be faster and uneven cooling because of which the casting may wrap, crack or induce thermal stresses beneath the skin. The moulding sand provides a uniform cooling medium for the casting while producing least amount of internal stresses.
5. For ferrous alloys, the breaking of mould should be done at a temperature_____
a) 780 ⁰C
b) 850 ⁰C
c) above 700 ⁰C
d) below 700 ⁰C
Explanation: Ideally, the moulds should be broken at a temperature when no transformation occurs. For ferrous alloys, the breaking should be done at a temperature below 700 ⁰C. If the castings are fragile and thin, they should be removed at a temperature as low as 400 ⁰C to avoid any deformation to the metal castings at the time of breaking of mould.
6. Which of the following processes is known as fettling?
a) Cleaning of castings
b) Pouring of melt into mould
c) Releasing of gases from the melt
d) Inclusion of slag in the castings
Explanation: The complete process of the cleaning of castings, called fettling, involves the removal of the cores, gates and risers, cleaning of the casting surface and chipping of any of the unnecessary projections on surfaces with the help of either hand tools or pneumatic tools.
7. Flame or arc cutting method is used for the removal of dry sand cores from the castings.
Explanation: Flame or arc cutting method is used for the removal of gates and risers from the castings. The dry sand cores can be removed simply by knocking off with an iron bar, by using a core vibrator, or by means of hydro-blasting. The method depends on the size, complexity and the core material used.
8. Which of the following methods is more convenient for the removal of very large size gates and risers from the steel castings?
c) Flame or arc cutting
d) Hack sawing
Explanation: For steel and other similar materials, sawing with any metal cutting saw like a hack saw or band saw would be convenient, But for large size gates and risers, it may be necessary to use flame or arc cutting to remove them. Similarly, abrasive cutoff may also be used for the removal of gates.
9. A reduced metal section at the casting joint makes easy removal of gates and risers from the castings.
Explanation: Removal of gates and risers can be simplified by providing a reduced metal section at the casting joint, so for brittle materials such as grey cast iron, the gates can easily be broken by hitting with a hammer. The gates and risers can be removed by hammering, chipping, hack sawing, abrasive cutoff etc.
10. Which of the following techniques is used for smoothening of the rough cut gate edges on the castings?
a) Hack sawing
b) Flame cutting
c) Sand blasting
d) Pedestal or swing frame grinding
Explanation: The casting surface after removal of gates contain some rough surfaces left at the time of removal of gates, or some fins and other projections on the surface near the parting line. These rough cut gate edges can be smoothened by using either the pedestal or swing frame grinder depending on the size of the casting.
11. Which of the following methods is best for cleaning of sand particles sticking to the casting surface?
b) Sand blasting
Explanation: For cleaning the sand particles sticking to the casting surface, sand blasting is used. The casting is kept in a closed box and a jet of compressed air with a blast of sand grains or steel grit is directed against the casting surface, which thoroughly cleans the casting surface.
12. Tumbling method, for cleaning of sand and unwanted fins from the castings, can be used for thin castings with fragile or overhung segments.
Explanation: In the tumbling method, the castings are kept in a barrel which is completely closed and then rotated on a horizontal axis at 30-40 rpm. Movement of casting removes the sand and unwanted fins. However, one precaution to be taken for tumbling is that the castings should be rigid with no frail or overhung segments, which may get knocked off during the tumbling operation.
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