Metal Casting Technologies : MCT SEP 2018 (3RD QRT) WHOS WHO OF METALS
34 www.metals.rala.com.au METAL Casting Technologies 3rd Quarter 2018 35 Introduction ardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting. The hardness of ferrous alloys is commonly measured using the Brinell hardness test. The test was first proposed by J.A . Brinell in 1900 and consists of applying a load to a steel or tungsten carbide ball into the surface of the test piece and measuring the diameter of the indentation left in the surface of the test piece. Figure 1 shows sections of castings with Brinell impression on the surfaces. The Brinell hardness test is generally considered to be the most satisfactory of the indentation hardness testing methods for materials of variable microstructure such as graphitic cast irons. This is because irons may be microscopically composed of phases of vastly variable hardnesses such as soft graphite in a matrix of varying amounts of ferrite, pearlite and/or tempered martensite. The Brinell test covers a large enough area to average the hardness of the constituents present. A hardened steel ball is used for materials with a Brinell hardness not exceeding 450HB whilst a tungsten carbide ball is used for materials with a Brinell hardness not exceeding 650HB. The values obtained using a steel ball or a tungsten carbide ball can be significantly different for hardnesses above 350HB. When a steel ball is used for the measurement, the hardness value is designated using the symbol HBS, and for cases where a tungsten carbide ball is used the designation is HBW. The diameter of the ball, in millimetres, and the force applied, in kilograms, should also be shown in the test results. For example, a reading of: 250HBS 10/3000 denotes a Brinell hardness of 250 determined with a steel ball of 10mm diameter and an applied force of 3000 kilograms. Testing machines Brinell testing machines come in a variety of forms, typically static floor mounted or portable with the load applied hydraulically or mechanically. Some examples are shown in the following figures. The floor standing Gogan machine shown in figure 2 is hydraulically loaded with direct digital reading. The portable model shown in figure 3 uses a hydraulic ram to apply loads of up to 3000kg. and can be operated in any orientation. The model shown in figure 4 is also a portable model which can be used in any orientation. In this example, loads are applied mechanically by winding the geared crank. The apparatus shown in figures 5 and 6 is a portable impact Pin Brinell machine. The Pin Brinell uses a calibrated shear pin to control the load applied by impacting with a hammer. After impacting, the width of the impression is measured and converted to an equivalent Brinell number. Test procedure It is important to select the correct indenting force and ball diameter for the part to be tested; the section size and location of the test specimen site should be considered. BacktoBASICS Hardness measuring of metals using the Brinell Test J.F. Meredith Casting Solutions Pty Ltd H FIGURE 2. Floor standing machine. FIGURE 3. Portable C-Clamp hydraulic model. THE HARDNESS OF FERROUS ALLOYS IS COMMONLY MEASURED USING THE BRINELL HARDNESS TEST. THE TEST WAS FIRST PROPOSED BY J.A . BRINELL IN 1900 AND CONSISTS OF APPLYING A LOAD TO A STEEL OR TUNGSTEN CARBIDE BALL INTO THE SURFACE OF THE TEST PIECE AND MEASURING THE DIAMETER OF THE INDENTATION LEFT IN THE SURFACE OF THE TEST PIECE. FIGURE 4. Portable C-Clamp mechanical model. FIGURE 1. Brinell impressions on surface of castings.
MCT JUN 2018 (2ND QRT)
MCT DEC 2018 (4TH QRT)