6. Apparatus and Material
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).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 a100 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).
6.4 Sand Nozzle—Fig. 7 shows the fabricated nozzle design which was developed to produce an accurate sand flow rate and proper shape of sand curtain for test procedures. The nozzle may be of any convenient length that will allow for connection to the sand hopper using plastic tubing. In new nozzles, the rate of sand flow is adjusted by grinding the orifice of the nozzle to increase the width of the opening to develop a sand flow rate of 300 to 400 g/min. During use, the nozzle opening must be positioned as close to the junction of the test specimen and the rubber wheel as the design will allow. (See Fig. 8.)