1. A standard ground drill has a point angle of
2. When the grains of a grinding wheel becomes dull, then it must be
3. Steel cast iron pipes are cast by
(a) die casting
(b) continuous casting
(c) centrifugal casting
(d) investment casting
4. Facing sand used in foundry work comprises
(a) alumina, silica and clay
(b) silica and clay
(c) clay and alumina
(d) silica and alumina
5. The criteria for the selection of electrode diameter in arc welding is
(a) type of welding process
(b) the thickness of the components to be welded
(c) voltage used
(d) current used
6. In arc welding, an arc is created between electrodes work by
(a) flow of current
(c) contact resistance
(d) electrical resistance
7. Hot-working improves the mechanical properties of the metal due to
(a) recovery of grain
(c) grain growth
(d) refinement of grain size
8. In four high rolling mills the bigger rollers are called
(a) guide rolls
(b) back up rolls
(c) main rolls
(d) support rolls
9. In drawing operation, the metal flows due to
(b) work hardening
10. Centering can be done most accurately on
(a) four jaw chuck
(b) three-jaw chuck
(c) collet chuck
(d) magnetic chuck
Answers with explanations
- (c) The general purpose drill points found on most jobber drills are 118° angled drills. They are typically used for cutting into soft metals such as aluminium, whereas the 135° variant is best suited for hardened materials, such as stainless steel. A 135° drill is flatter than 118°,
- (c) When the sharpness of the grinding wheel becomes dull because of glazing and loading, dulled grains and chips are removed (crushed or fallen) with a proper dressing tool to make sharp cutting edges and simultaneously, make recesses for chips by properly extruding to grain cutting edges.
- (c) Cast iron pipe is manufactured by the pit, horizontal or centrifugal method. In the vertical pit method, a mould is made by ramming sand around a pattern and drying the mould in an oven. A core is inserted into the mould and molten iron is poured between the core and the mould. In the horizontal method, a machine is used to ram sand around horizontal moulds that have core bars running through them. The molten iron is poured into the moulds from a multiple-lipped ladle designed to draw the iron from the bottom to eliminate the introduction of impurities. In the centrifugal method (see figure), sand-lined moulds are used that are placed horizontally in centrifugal casting machines. While the mould revolves, an exact quantity of molten iron is introduced, which, by the action of the speed of rotation, distributes itself on the walls of the mould to produce pipe within a few seconds.
- (b) Sand that is used before pouring the molten metal, on the surface is called facing sand. It is specially prepared sand from silica sand and clay. It is sprinkled on the inner surface of the mould cavity to give a better surface finish to the castings.
- (b) The selection of an electrode is very important in order to get a joint welded with the required strength. The selection of electrode size in order to get sound quality weld depend upon: (i). The thickness of metal to be welded (ii) Edge preparation of joints (iii) Root run, intermediate or covering run (iv) Welding position (v) Welder’s skill.
- (c) When the current flows, the gap between the electrode and workpiece mainly acts as an impedance for the flow of the current. This resistance for the flow of current results in the generation of the heat, which results in the welding of the metal. Hence we can say that arc is created between the electrode and work by contact resistance. Because though there was a gap the resistance was created due to the contact between electrode and work
- (d) Hot working improves the engineering properties of the workpiece because it replaces the microstructure with one that has fine spherical shaped grains. These grains increase the strength, ductility, and toughness of the material.
- (b) The mill has four horizontal rolls, two smaller diameters and two much larger. The larger rolls are called backup rolls. The smaller rolls are the working rolls, but if they would be thicker in the centre and thinner at either end. Backup rolls hold the working rolls and restrict deflection when the material is being rolled. The usual products of these mills are hot and cold plates and sheets.
- (b) In drawing operation, the metal flows due to Plasticity. Drawing is a metalworking process that uses tensile forces to stretch (elongate) metal, glass, or plastic. As the metal is drawn (pulled), it stretches to become thinner, to achieve a desired shape and thickness. Drawing is classified into two types: sheet metal drawing and wire, bar, and tube drawing. Sheet metal drawing is defined as plastic deformation over a curved axis. For wire, bar, and tube drawing, the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing is usually performed at room temperature, thus classified as a cold working process, however, the drawing may also be performed at elevated temperatures to hot work large wires, rods or hollow sections in order to reduce forces.[
- (c) Collet chuck. These are small chucks that fit into the headstock spindle and are used for holding bar stock (long bar or rods). These chucks are particularly useful in cases where accurate centring and quick setting are required.
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