Rockwell Hardness Test

The Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load FO usually I 0 kgf. When equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter is set to a datum position. While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration . When equilibrium has again been reach, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, so reducing the depth of penetration. The permanent increase in depth of penetration, resulting from the application and removal of the additional major load is used to calculate the Rockwell hardness number.

H R = E - e

FO = preliminary minor load in kgf

F1 = additional major load in kgf

F = total load in kgf

e = permanent increase in depth of penetration due to major load Fl measured in units of 0.002 mm

E = a constant depending on form of indenter: I 00 units for diamond indenter, 130 units for steel

ball indenter

HR = Rockwell hardness number

D = diameter of steel ball

BEND TESTS

BEND TESTS Object: To determine the soundness of weld metal, heat affected zone and weld zone.These tests may also be used to give some measure of the ductility of the weld zone. It is not usual to use transverse and longitudinal bend tests for the same application. Method: All specimens to be removed and prepared without causing significant distortion or heating. The cap and root are ground flush. The specimen is bent by the movement of a former of prescribed diameter, the relevant side of the specimen to be placed in tension. Angle of bend and diameter of former should be as specified in the appropriate standard. Reporting Results: Thickness of specimen Direction of bend (root or face) Angle of bend Diameter of former Appearance of joint after bending e.g. type and location of flaws

Part -3 Most commonly asked Mechanical Interview Questions

Most commonly asked Mechanical Interview Questions with answer 1. What is the difference between Technology and Engineering? Ans. Engineering is application of science. Technology shows various methods of Engineering. A bridge can be made by using beams to bear the load,by an arc or by hanging in a cable; all shows different technology but comes under civil engineering and science applied is laws of force/load distribution. 2. How to Measure Temperature in Wet Bulb Thermometer? Ans. Wet bulb temperature is measured in a wet bulb thermometer by covering the bulb with a wick and wetting it with water. It corresponds to the dew point temperature and relative humidity. 3. What are the Advantages and Disadvantages of using LPG in Car? Ans. Advantages 1. Complete combustion 2. Fuel saving 3. Homogenous combustion Disadvantages 1. As complete combustion is occurring ,more heat liberated,not advised for long journey, engine will be over heated 2. In...

SIDE BEND TEST

SIDE BEND TEST Object: To determine the soundness of the weld metal and HAZ in a cross section. This may be preferred to the transverse bend test on thick materials. It is also used on processes or procedures expecting lack of fusion (e.g. thick plate using MIG). Method: The testing method is the same as that used for transverse bends except the cap and root are not ground flush, to allow testing across the complete weld. Report Results: Width and thickness of specimen. Angle of bend. Diameter of former. Appearance of joint after bending e.g. type and location of flaws.

Mechanical Engineering

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