Rockwell hardness scale

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. 

Strength in static bending, MPa Charpy impact ductility, kJm Rockwell hardness, scale M Shrinkage, cm/cm Water absorption, %... 

Rockwell hardness scale is widely used for plastics—test ASTM D785... 

Fig. 17. Isothermal transformation (IT) diagram for a plain carbon eutectoid steel (1). Ae1 is temperature at equilibrium BHN, BrineU hardness number Rc, Rockwell hardness scale C. C is 0.89% Mn, 0.29% austenitized at 885°C grain size is 4—6. Photomicrographs originally x2500.

HRC - Rockwell hardness scale C AISI 420 or DIN 1.2083 steel - stainless steel. Martensitic, chromium steel ... 

Figure 5.25 Coefficient of sliding friction versus roughness of a sliding steel disk Rockwell Hardness Scale C (HRC) = 54-56 at 40°C, P = 1 MPa, V = 0.5 m/s) for two BASF Ultraform POM-Co plastics [9].

Table 6.6a Rockwell Hardness Scales Table 6.6b Superficial Rockwell Hardness Scales ...

Rockwell Hardness A number which indicates the hardness of a material as measured by an standard indentation test. The use of different loads and indentors gives several Rockwell hardness scales R and M are commonly applied to plastics. 

---