6. Apparatus and Material7
6.1 Fig. 2 shows a typical design and Fig. 3 and Fig. 4 are photographs of the test apparatus which may be constructed from readily available materials. Also, see Ref (2). Several elements are of critical importance to ensure uniformity in test results among laboratories. These are the type of rubber used on the wheel, the type of abrasive and the shape, positioning and the size opening of the sand nozzle, and a suitable lever arm system to apply the required force.
6.2 Rubber Wheel The wheel shown in Fig. 5 shall consist of a steel disk with an outer layer of chlorobutyl rubber molded to its periphery. Uncured rubber shall be bonded to the rim and fully cured in a steel mold. The optimum hardness of the cured rubber is Durometer A-60. A range from A58 to 62 is acceptable. At least four hardness readings shall be taken on the rubber approximately 90° apart around the periphery of the wheel using a Shore A Durometer tester in accordance with Test Method D 2240. The gage readings shall be taken after a dwell time of 5 s. The recommended composition of the rubber and a qualified molding source is noted in Table 1. (See 9.9 for preparation and care of the rubber wheel before and after use and see Fig. 2 and Fig. 5.)
6.3 Abrasive The type of abrasive shall be a rounded quartz grain sand as typified by AFS 50/70 Test Sand (Fig. 6).8 The moisture content shall not exceed 0.5 weight %. Sand that has been subjected to dampness or to continued high relative humidity may take on moisture, which will affect test results. Moisture content may be determined by measuring the weight loss after heating a sample to approximately 120°C (250°F) for 1 h minimum. If test sand contains moisture in excess of 0.5 % it shall be dried by heating to 100°C (212°F) for 1 h minimum and the moisture test repeated. In high-humidity areas sand may be effectively stored in constant temperature and humidity rooms or in an enclosed steel storage bin equipped with a 100-W electric bulb. Welding electrode drying ovens, available from welding equipment suppliers are also suitable. Multiple use of the sand may affect test results and is not recommended. AFS 50–70 Test Sand is controlled to the following size range using U.S. sieves (Specification E 11).