Rockwell hardness number

An alternative to the measurement of the dimensions of the indentation by means of a microscope is the direct reading method, of which the Rockwell method is an example. The Rockwell hardness is based on indentation into the sample under the action of two consecutively applied loads - a minor load (initial) and a standardised major load (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 produce an initial indentation. The Rockwell hardness is based on the increment in the indentation depth produced by the major load over that produced by the minor load. Rockwell hardness scales are divided into a number of groups, each one of these corresponding to a specified penetrator and a specified value of the major load. The different combinations are designated by different subscripts used to express the Rockwell hardness number. Thus, when the test is performed with 150 kg load and a diamond cone indentor, the resulting hardness number is called the Rockwell C (Rc) hardness. If the applied load is 100 kg and the indentor used is a 1.58 mm diameter hardened steel ball, a Rockwell B (RB) hardness number is obtained. The facts that the dial has several scales and that different indentation tools can be filled, enable Rockwell machine to be used equally well for hard and soft materials and for small and thin specimens. Rockwell hardness number is dimensionless. The test is easy to carry out and rapidly accomplished. As a result it is used widely in industrial applications, particularly in quality situations. 

Hardness was measured on the Rockwell hardness scale according to the method described in ASTM D785-93. Test results are reported as a Rockwell hardness number, which is directly related to the indentation hardness of a plastic material where higher values reflect greater hardness. Measurements were done on the R scale using a minor load of 10 kg or major load of 60 kg. Testing results are provided in Table 1. 

In the Rockwell test a spheroconical diamond (Brale) indenter or a hardened steel ball is used with various load ranges to achieve a series of scales identified by a suffix letter (Table 3). The suffix letter defines both load and indenter. The most popular scales used are "C" for hard materials and MBM for soft materials. A Rockwell hardness number is meaningless without the letter suffix, eg, HRC 54 or HRB 95. 

The relationship between depth of penetration and the Rockwell hardness number is... 

Fq is the preliminary minor load in kgf, f, the additional major load in kgf, F the total load in kgf, e the permanent increase in depth of penetration due to major load f, 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, D the diameter of steel ball, HR is the Rockwell hardness number. 

Rockwell hardness number Number derived from the net increase in depth of impression as the load on a penetrator is increased from a fixed minimum load to a higher load and then returned to minimum load. Penetrators include steel balls of several specified diameters and a diamond-cone penetrator. 

Hardness is defined as the resistance of a material to deformation, particularly permanent deformation, indentation or scratching. Hardness is purely a relative term and should not be confused with wear and abrasion resistance of plastics. For example, polystyrene has a high hardness but a poor abrasion resistance. Many tests have been devised to measure hardness. However, Rockwell and Durometer hardness tests are commonly used. The Rockwell hardness test measures the net increase in depth impression as the load on an indentor is increased from a fixed minor load to a major load and then returned to a minor load. The hardness numbers derived are just numbers without units. Rockwell hardness numbers in increasing order of hardness are R, L, M, E and K scales. The higher the number in each scale, the harder is the material. The Durometer hardness test is based on the penetration of a specified indentor forced into... 

The hardness, as determined with the Rockwell Hardness Tester, is a measure of the material resistance to indentation by a spherical indenter. The higher the Rockwell hardness number, the harder the material. The scale is given in Table 3-5. The measured property is determined primarily by the elastic modulus of the material. Therefore, the addition of fiberglass increases the hardness, due to the elastic modulus being increased with increasing glass content. 

Rockwell Hardness Number. A value derived from the increase in depth of an impression as the load on an indenter is increased from a fixed minimum value to a higher value and then returned to the minimum value. Indenters for the Rockwell test include steel balls of several specific diameters and a diamond cone penetrator having an included angle of 120 deg with a spherical tip having a radius of 0.2 mm. Rockwell hardness numbers are always quoted with a prefix representing the Rockwell scale corresponding to a given combination of load and indenter. 

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