Skip to main content

Rockwell Hardness Test on Metals

The Rockwell Hardness Test is based on the indentation of the hard tip, or indenter, into the test piece under the action of two consecutively applied loads - minor (initial) and major (final). In order to eliminate zero error and possible surface effects due to roughness or scale, the initial or minor load is first applied and produces an initial indentation.

A conical shaped diamond (called a brale) with 120* apex angle and 0.2 mm radius is used as the indenter or penetrator in the Rockwell test for hard materials. For softer materials, a hardened steel ball 1.5 mm in diameter is generally used.



A number of different scales are used, each scale being suitable for certain classes of materials. It should be understood that each scale is entirely arbitary, the hardness number obtained having relevance to that particular scale only. 

Rock well Hardness Scale ,

Scale - A  

Diamond cone Indenter, Major load 60 kg , Dialed number - black , For materials - Cemented Carbides, thin steel , case hardened surfaces.

Scale - B

Indenter -1.5 mm ball, Major load 100 kg , Dial number - Red, For materials - Copper , Aluminum, brass, malleable iron, Grey cast iron.

Scale - C 

Indenter - Diamond cone, Major load 150kg , Dial number - Black , For Materials - Hard Cast iron , Hardened Steel 

Scale - D 

Indenter - Diamond Cone , Major Load 100 Kg , Dial number - Black , For Materials - Thin Steel Specimens

Scale - E 

Indenter - 3mm ball, Major load -100 kg , Dial number - Red , For materials Soft Aluminum and alloys, magnesium alloys, bearing metals.

Scale - F 

Indenter - 1.5 mm ball , Major load - 60 kg , Dial number - Red , For materials Annealed copper alloys, bearing alloys.



After loading, The major load is removed . The Rockwell Hardness number is the difference in depths of the indentations made by applying the Major and 10 kg Minor load, measured after removing the major load. 

The load is applied and maintained for upto 15 secs and then released, the hardness number then being read off the scale graduated in hardness units to the nearest whole number.

Rockwell tests are widely applied in the industry due to the rapidity and simplicity with which they may be performed , high accuracy achieved and due to the small size of the impressions produced. The Rockwell Hardness number may be converted into Brinell number using special tables or charts. 

 


Labels

Labels:

Comments

Post a Comment

Popular posts from this blog

Advantages And Disadvantages Of Air Refrigeration System :

 Advantages Of  Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of  Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content. 
Post a Comment
Read more

SIMPLE CARBURETOR - CONSTRUCTION AND WORKING

CONSTRUCTION OF SIMPLE CARBURETOR :  The main Components of Simple Carburetor are : Float Chamber, float, nozzle, venturi, throttle valve, inlet valve, and metering jet . In the float chamber, a constant level of petrol is maintained by the float and a needle valve.  The float chamber is ventilated to atmosphere.  This is used to maintain atmospheric pressure inside the chamber. The float which is normally a metallic hollow cylinder rises and closes the inlet valve as the fuel level in the float chamber increases to certain level. The mixing chamber contains venturi, nozzle and throttle valve. The venturi tube is fitted with the inlet  manifold. This tube has a narrow opening called venturi. A nozzle is provided just below the centre of this venturi. The nozzle keeps the same level of petrol as that of the level in the float chamber. The mixing chamber has two butterfly valves.  One is to allow air into the mixing chamber known as choke valve. The other is to al...
Post a Comment
Read more

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of  detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of  a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of  the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of  electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a  roll. The objec...
Post a Comment
Read more