UPMRC Fitter Maintainer (Civil) Paper with solution -2021

Answer.2. It should have low coefficient of friction

Explanation

The main requirement of a good bearing system are

(1) Good compatibility:- The material should have good compatibility which means good anti-weld and antiscoring properties. Since most journal bearings will experience occasional metal-to-metal contact, it is important that the bearing material be one that does not readily weld itself to the shaft material.

(2) Conformability: Conformability is a measure of the bearing’s ability to adjust to misalignment or other geometric errors. Materials having a low modulus of elasticity usually have good conformability.

(3) Embeddability: Embeddability, means the material is soft enough to absorb foreign materials that are too large to pass through the oil film. By allowing this embedding. wear and scoring can be prevented.

(4) Good fatigue strength: The material should have good fatigue strength because of the many applications for which the bearing loads change directions.

(5) Good corrosion resistance: Resistance to corrosion is required in those applications where the lubricating oil used may oxidize and thus corrode the bearing.

(6) Wear resistance: The rate of wear can be an important factor in determining the life of a bearing.

(7) Strength and stiffness: The material must have a high elastic limit and strength to support the load. together with adequate modulus to resist deformation.

(8) Good shock resistance: The material must be tough and ductile to be able to withstand shocks.

(9) High thermal conductivity: The ability of the material to dissipate heat resulting from friction can be important in preventing a rise in temperature to a level that could result in melting of the bearing material and seizure of the bearing or degradation of a lubricant.

(10) Cost: Last, but certainly not least important, the cost should be as low as possible.

(11) Low friction:- It should have a low coefficient of friction to reduce the frictional power loss in transmission.

Answer.3. Apron

Explanation:-

HEADSTOCK

The headstock is located at the upper left side of the engine lathe. It is comprised of a casting that contains the mechanisms used to hold and rotate the workpiece and control the rate of tool movement.

Spindle

The spindle is an important part of the headstock and lathe. The spindle is the part of the machine that holds and rotates work during machining. It is a precisely ground hollow tube supported by precision bearings. Long workpieces can be placed through the center hole of the spindle.

The front of the spindle hole contains an internal taper that can be used to align and secure tapered workholding accessories.

A knockout bar with a soft metal end is inserted through the hollow spindle to remove these accessories by forcing the mating tapers loose from each other. 

The spindle is driven by a heavy-duty electric motor through a series of either pulleys or gears.

Faceplate:-  Sometimes an irregularly shaped workpiece needs to be secured in the lathe for machining. In these situations, a faceplate can be used. A faceplate is mounted to the headstock spindle and is generally made of cast iron with a series of slots machined into its face.

Chuck:- Three jaw chucks are used to hold round or hexagonal bar stock or other symmetrical work. Four jaw chucks are used for rough castings and square or octagonal work. When irregular-shaped castings and forgings are to be machined, special chuck jaws may be used to suit the component. 

Answer.3. Austenite

Explanation

Austenite is formed in the structure of the steel on heating above the critical temperature  1250°F, the amount of austenite increasing as the processing temperature is raised.

Isothermal annealing:- In many cases, the ordinary annealing process is incapable of reducing the hardness of many grades of alloy steel to a sufficient degree. In such cases, isothermal annealing is employed. The process consists of two steps. First, the steel is heated above the upper (or only the lower) critical point and held for some time at this temperature. At this stage, austenite is formed in the metal. Then the steel is rapidly cooled to a temperature of 50 to 100°C below point A that is 600- 700°C and is held at this new temperature until the austenite is completely decomposed to form pearlite. Finally, the steel is cooled in still air. Since the decomposition of austenite takes place at a constant temperature, hence the name isothermal annealing.

Answer.2. 10

Explanation:-

For gas tungsten arc welding in the current range of 150 – 500 Amps, the minimum required protective shade number is 10 but the recommended requirement for comfort level is 14.

Answer.3. Attached abrasive stick

Explanation:-

Honing:- In honing, the cutting is done by abrasive particles held by a bond in a stick or stone. You may do cylindrical honing on a honing machine or on some other machine tools by attaching the honing device to the machine spindle, or you may do it by hand.

If the workpiece is small enough, you can hold it in your hands and move it up and down over the rotating honing tool, but this is not advisable because of the danger of your getting caught in the rotation drill press spindle.

In honing, you can use any machine tool with a rotating spindle. For instance, on a lathe, you can mount the work in a chuck and rotate it with the headstock spindle, and you can fasten the honing tool to the tailstock and move the tailstock back and forth by hand.

Answer.2. Fender Nut

Explanation

NUT

A device used with a bolt or stud to join two parts together temporarily. A nut has internal threads. A nut is expressed in terms of the diameter of the threaded hole in the nut into which a bolt or stud fits. A nut consists of a hexagonal or square prism with the top corners chamfered at an angle of 30° to 45°.

Various types of nuts are as follows:

• Hexagonal nut
• Square nut
• Flanged nut
• Cap nut
• Dome nut
• Capston nut
• Wing nut.

Answer.1. A Camshaft

Explanation

Force-feed lubrication uses an oil pump to force the oil under pressure to the parts to be lubricated, normally the engine crankshaft and camshaft.

A camshaft uses egg-shaped “cams” to open and close engine valves, while a crankshaft converts “cranks” (the up/down motion of the pistons) to rotational motion.

Answer.1. Pipe wall thickness

Explanation

Pipe wall thickness is specified by its schedule. There are schedules from schedule 10 through schedule 180. Schedule 40 pipe is considered the standard pipe or wall thickness. In general, if you ask for a steel pipe of specific nominal diameter and do not call for a specific schedule, you will get a schedule 40 pipe. Those pipes in schedules lower than schedule 40, have thinner walls; those pipes in schedules above schedule 40 have thicker walls and can sustain greater pressures. Not all wall thicknesses (or schedules) are manufactured in all pipe diameters.

Answer.4. Switch off the machine before making any adjustments or cleaning the lathe machine

Explanation:-

To maintain the accuracy built into a lathe, it must be thoroughly cleaned after each work period. Use a paintbrush (not a dust brush) to remove the accumulated chips.

Lathe chips are sharp; do not remove them with your hands. Never use an air hose to remove chips. The flying particles could injure you or others. Wipe all painted surfaces with a soft cloth. Use a soft cloth to remove any remaining chips, oil, and dirt from the machined surfaces.

Keep the machine clear of tools, and always stop the machine before cleaning and making measurements and adjustments.

Answer.1. Rectangular Rollers

Explanation

Rolling element bearings may be broadly classified as either ball bearings (spherical rolling elements) or roller bearings (nominally cylindrical rolling elements).

Rolling-element bearings are an assembly of several parts: an inner race, an outer race, a set of balls or rollers, and a cage or separator. The cage or separator maintains the even spacing of the rolling elements.

Cylindrical Roller Bearing

The cylindrical roller bearing has rolling elements that are in the shape of a cylinder. The cylindrical roller bearing provides more surface contact, allow- ing the bearing load capacity to increase in comparison to the ball bearings. These bearings are used in heavy-duty applications and are designed to handle heavy radial loads. They are not designed to run at speeds as high as the ball bearings and are mostly used in moderate-speed applications. There are three types of cylindrical roller bearing: the cylindrical roller bearing with a separable inner ring, the cylindrical roller bearing with a separable outer ring, and the nonseparable cylindrical roller bearing.

The Taper Roller Bearing

The taper roller bearing is used where a large amount of thrust load is present, as well as on radial loads. The inner and outer races of this bearing are angled in reference to the bore axis line. The outer ring is called a cup and the inner ring is called a cone. (The outer ring, because of its tapered shape, looks like a cup, and the inner ring, because of its tapered shape, looks like a cone.) The rolling elements of this bearing are very similar to the cylindrical shape of the rolling elements that are in the standard roller bearing except that the rolling element itself is tapered as well. This means that the diameter of the top edge of the rolling element is larger than the bottom edge diameter. 

Needle Bearing

The needle bearing is another type of antifriction bearing. Needle bearings are actually part of the roller bearing group, but their unique design causes them to be in a class of their own. The needle bearing is very similar to the roller bearing except that the rolling elements in a needle bearing are long and thin. The name comes from the fact that the rolling elements look similar to needles. The rolling element of a needle bearing may, in some cases, be 10 times as long as its diameter. As mentioned in the section on bearing construction, needle bearings do not generally have inner and outer rings as do the other bearings.

Barrel Roller Bearings

The roller fitted in this Bearing type of bearing has a barrel shape. Its diameter up to full length is uneven. These bearings are self-alignment type bearings so due to this reason, it has no difficulty to maintain the shaft in a straight line.