Rockwell hardness test

AHMAD EJAZ

DEPARTMENT OF MATERIAL SCIENCE

In The Name Of Allah Who Is Most Beneficent And Merciful

HARDNESS TEST

CONTENT

HardnessGeneral type of hardness test

Rockwell hardness test

HARDNESS:-

Hardness is simply the resistance to plastic deformation or permanent deformation of material.

The term hardness may also refer to resistance to bending, scratching, abrasion or cutting.

Hardness is dependent on ductility, elasticity plasticity, strain,  strength,

GENERAL TYPES OF HARDNESS MEASUREMENT

There are three general type of hardness test: Scratch hardness test Indentation harness test Rebound hardness test

SCRATCH TEST

Scratch hardness is the measure of how resistant a sample is to permanent plastic deformation due to friction from a sharp object. The principle is that an object made of a harder material will scratch an object made of a softer material.

In scratch test Moh’s scale are usually adopted.

This consist of a list of materials arranged in order of hardness

MOH’S SCALE ARRANGEMENT

Mineral hardness number Talc 01 Gypsum 02 Calcite 03 Fluorite 04 Apatite 05 Feldspar 06 Quartz 07 Topaz 08 Corundum 09 Diamond 10

INDENTATION TEST

Indentation hardness measures the resistance of a sample to material deformation due to a constant compression load from a sharp object.

They are primarily used in engineering  and metallurgy fields.

it is most widely used for measurement of harness

it measure the brinell hardness , Rockwell hardness, Vickers hardness etc.

ROCKWELL HARDNESS TEST

The Rockwell Hardness test also uses a machine to apply a specific load and then measure the depth of the resulting impression.

Rockwell hardness test devised in USA. It is useful for finished material testing . Hardness no. is indicated on dial. Test piece is place on table of the instrument. Indenter is brought into contact with surface of test

piece under light load(minor load). Scale is then adjusted to zero. Major load is applied ,hardness index is read from

the scale.

Penetration depth “e” of impression is messure by instrument.

This penetration depth is convert into harness value appear on dial.

Rockwell hardness formula HR = E - e

F0 = 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 F1 measured in units of 0.002 mm

E = a constant depending on form of indenter: 100 units for diamond indenter, 130 units for steel ball indenter

HR = Rockwell hardness number

SCALE USE ON DIAL scale being determined by indenter and full

load use . Scale A : which is use in conjunction with

diamond cone and 60kgf load .it is use for very hard material such as tool steel.

Scale B : which is use in conjunction with 1/16 inch diameter steel ball and 100kgf load.it is use for soft material such as copper alloy ,mild steel etc.

Scale C: which is use in conjunction with diamond cone 120 degree angle and 150 load .it is use for hardend steel , hard cast iron.

ADVANTAGE/DISADVANTAGE

Advantages of the Rockwell hardness include: The direct Rockwell hardness number readout

on the dial. Rapid testing time. Can be used for a very wide range of materials. Disadvantages include: Possible errors due to shifting of the sample under test

load during test cycle Quality of the indenter has a strong influence on the

test result