Rockwell tests

Brinell Tests of Steel Products Comparison Hardness Tester Practice Rockwell Test on Cemented Carbides Rockwell Test for Sintered Materials Knoop Test for Electrodeposited Coatings Webster Hardness Gauge Barcol Test of Aluminum Alloys... 

The Rockwell superficial test was developed to accommodate smaller and thinner samples than the standard Rockwell test. The test principle is identical to the standard Rockwell test but the major and minor loads are substantially smaller. The test machine is also similar but modified to accommodate the smaller loads. Dual purpose machines can handle both standard and superficial tests. 

The indenter/load combinations used for superficial Rockwell testing are Hsted in Table 5. As with the standard Rockwell test it is necessary to include the superficial load/indenter combination used for the hardness number to be meaningful, eg, HR30N 65 or HR30T 65. 

The standard Rockwell test requires a relatively smooth surface (120 grit or better) for reproducibiUty. Superficial Rockwell test samples must be ground to 600 grit or better for accuracy and reproducibiUty. 

Although the Rockwell test is intended to be used on flat parallel-sided specimens, its use can be extended to rounded surfaces by using a curvature correction factor. Compound surfaces such as gear teeth can be tested but the results must be corrected for curvature. 

Recommended procedures for use with Rockwell and superficial Rockwell tests are detailed in ASTM E18 (2). 

International Rubber Hardness. The International mbber hardness test (ASTM D1415) (2) for elastomers is similar to the Rockwell test ia that the measured property is the difference ia penetration of a standard steel ball between minor and major loads. The viscoelastic properties of elastomers require that a load appHcation time, usually 30 seconds, be a part of the test procedure. The hardness number is read directly on a scale of 0 to 100 upon return to the minor load. International mbber hardness numbers are often considered equivalent to Durometer hardness numbers but differences ia iadenters, loads, and test time preclude such a relationship. 

Yes, because the Rockwell test is a penetration test, if the material is too thin, the supporting anvil will alter the readings. This is called the anvil effect. 

In the most used Rockwell tests, the hardness number does not measure total indentation but only the irreversible portion after a heavy load is applied for a given time and reduced to a... 

The hardness of a polymer may be measured by the Rockwell tests, in which steel balls of specified diameter are used to indent the polymer specimen (ASTM-D785). The indentation hardness of rubbery polymers is measured by an indenter called a durometer (a rounded surface of specified weight and dimensions) (ASTM-D2240) which acts as the indenter onto test specimens. 

Rockwell. The invention of the Rockwell hardness tester in 1919 was an advance over previous indentation tests requiring accurate indentation measurement and tabular reduction to derive a hardness number. In the Rockwell test the hardness number is read direcdy from the instrument dial (1,3). 

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 Rockwell testing machine is thus a framework permitting stable support of the workpiece on one side and means to impress the indenter under specified load on the other. A dial indicator attached to the indenter spindle is used to read direcdy the depth of indentation in hardness numbers. 

Hardness Measurements. Hardness was measured on two scales, the Rockwell R scale, and the Shore D scale. The Rockwell test measures nonrecoverable deformation after a %-inch sphere has been pressed into a molded sheet of the plastic and the load released. In the Shore... 

There are four major indentation hardness tests, which differ from each other in the shape of the indenter (Figure 10.23). The first of these, described in 1900, was the Brinell test, using a 10 mm steel ball indenter (Figure 10.23a), giving the Brinell hardness number, BHN. This was suitable only for metals softer than steel. In 1920 Rockwell developed a number of tests, including the B, E, F and G scales, in which the indenter is steel, and the A, C and D scales, using a conical diamond indenter with a spherical tip (Figures 10.23b and 10.23c). In the Rockwell test the difference in size between the... 

The Rockwell test is standardized also in BS 2782, Method. 65C [9], and ASTM D785 [10]. The British standard is identical (dual numbered) and the ASTM technically equivalent, although this does add the even more severe scale K to the list given in Table 1. 

Like the Rockwell test, the Brinell method uses a spherical indentor. but here the diameter of the impression is measured rather than the depth of penetration, the hardnes.s relationship being given by the expression... 

The Rockwell test differs fi om the other three tests because the depth of the indent rather than its surface area is taken as a measure of hardness. A hardened steel ball is used as the indentor. A major advantage of the Rockwell test is that no visual measurement of the indentation is necessary, and the depth of the indent is read directly as a hardness value on the scale. 

Hardness refers to the resistance of steel to indentation. The three important methods to determine the hardness are (1) the Brinell test, (2) the Vickers test, and (3) the Rockwell test. All these methods use the same basic principle wherein a ball or a pointed indenter is forced onto the material surface under a given load and the area of indentation thus created is measured. The Brinell test uses a 10-mm-diameter tungsten ball indenter under a load of 29,420 N. The Rockwell C hardness test uses a diamond cone indenter under a load of 1471 N. The Vickers test uses a diamond pyramid indenter, and the load varies. The greater the hardness of a material, the smaller the area of indentation. 

Another micro-hardness test is the Knoop Hardness Test (henceforth KHT, discussed below). It is worth mentioning that superficial Rockwell tests are also used for ceramics measurements. Hardness tests have been upgraded by the application of instrumented Knoop and Vickers hardness measurements. 

Because the materials under consideration are plastic in nature, the usual Rockwell test procedures for metal testing cannot be followed exactly. A special procedure as described below was developed. 

Indentation Depth Reading Rockwell Test, in this test, the depth of the indentation is read from a dial indicator no microscope is required (34). In the Rockwell hardness tests, a load of 98 N is first applied to the surface and the depth of penetration is thereafter reckoned as the zero of measurement. A further load of 588, 980, or 1470 N is applied and removed leaving the additional depth of indentation recorded on a dial. The hardness is then expressed in terms of the dial reading on an arbitrarily numbered scale. The indenter used may be a steel spherical penetrator or a diamond cone with a hemispherical tip. The scales, indenter, and loads employed are chosen to adapt to the material properties. Results given by different testers are not readily interconverted. 

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. 

Indentation Hardness n Resistance to penetration by an indenter. The hardness of a material as determined by either the size of an indentation made by an indenting tool under a fixed load, or the load needed to produce penetration of an indenter to a predetermined depth. The instruments commonly used with plastics are the Shore Durometer (indenter A for soft resins and elastomers, D for hard materials) described in ASTM D 2240, and the Barcol Impressor, ASTM D 2583. In D 2240, the authors say, No simple relationship exists between indentation hardness determined by this method and any fundamental property of the material tested. For specification purposes it is recommended that Test Method D 1415 (section 09.01) be used for soft materials and method A of D 530 or Test D 785 be used for hard materials. D 530 and D 785 use the Rockwell test in which a ball of suitable diameter is pressed into the... 

The Rockwell tests constitute the most common method used to measure hardness because they are so simple to perform and require no special skills. Several different scales may be used from possible combinations of various indenters and different loads a process that permits the testing of virtually all metal alloys (as well as some polymers). 

With this system, a hardness number is determined by the difference in depth of penetration resulting from the application of an initial minor load followed by a larger major load utilization of a minor load enhances test accuracy. On the basis of the magnitude of both major and minor loads, there are two types of tests Rockwell and superficial Rockwell. For the Rockwell test, the minor load is 10 kg, whereas major loads are 60,100, and 150 kg. Each scale is represented by a letter of the alphabet several are listed with the corresponding indenter and load in Tables 6.5 and 6.6a. For superficial tests, 3 kg is the minor load 15, 30, and 45 kg are the possible major load values. These scales are identified by a 15, 30, or 45 (according to load), followed by N, T, W, X, or Y, depending on the indenter. Superficial tests are frequently performed on thin specimens. Table 6.6b presents several superficial scales. 

Maximmn specimen thickness and indentation position (relative to specimen edges) as well as minimmn indentation spacing requirements are the same as for Rockwell tests. In addition, a well-defined indentation is required this necessitates a smooth, flat surface in which the indentation is made. 

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