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

What is Annealing ?

Annealing:- Annealing Process :- Annealing is a heat treatment process by which the properties of steel are enhanced to meet machinability requirements. In this process Hypoeutectoid steels (less than 0.83% carbon) are heated above upper critical temp., soaked and cooled slowly and Hypereutecoid (above 0.83%) are heated above lower critical temp., soaked and allowed to cool slowly. Annealing Process Steps: 1.Heat material into the asutenite region (i.e. above 1600F) – rule of thumb: hold steel for one hour for each one inch of thickness 2.Slowly furnace cool the steel – DO NOT QUENCH 3.Key slow cooling allows the C to precipitate out so resulting structure is coarse pearlite with excess ferrite 4.After annealing steel is quite soft and ductile The purpose of Annealing is : 1)Reduce hardness and brittleness 2)Alter microstructure for desired mechanical properties 3)Soften...

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4 job interview mistakes hiring managers will eliminate you for, according to LinkedIn

4 Things to avoid during interview If you've applied for a job and are lucky enough to score an interview, don't let one mistake ruin your chances of getting the job. A LinkedIn survey of more than 550 hiring managers found that when it comes to a job interview, even small mistakes can put a candidate out of the running. Here are four things you should never be caught doing, according to the survey: 4. Checking your phone Even the slightest glance at your phone during a job interview could cost you. More than one out of every three hiring managers polled said they would eliminate a candidate for looking at his or her cell. Checking your phone gives the impression that you're not totally there mentally and don't respect the person sitting right in front of you. Be safe and before the interview, turn your phone, and it's thousands of notifications, off. 3. Looking disheveled Nearly half of interviewers — 46 percent, to be exact — said they had el...

Mechanical Engineering

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