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.)
6.4.1 Any convenient material of construction that is avail- able as welded or seamless pipe may be used for the construc- tion of the fabricated nozzle. Stainless steel is preferred because of its corrosion resistance and ease of welding. Copper and steel are also used successfully.
6.4.2 Formed Nozzle Nozzles formed from tubing may be used only when they duplicate the size and shape (rectangular orifice and taper), and the sand flow characteristics (flow rate and streamlined flow) of the fabricated nozzle. (See Fig. 7 and Fig. 9.)
6.4.3 Sand Flow The nozzle must produce a sand flow rate of 300 to 400 g/min (0.66 to 0.88 lb/min).
6.4.4 Sand Curtain Fig. 9 shows the proper stream-lined flow and the narrow shape of the sand curtain as it exits from the sand nozzle. A turbulent sand flow as depicted in Fig. 10 will tend to produce low and inconsistent test results. It is intended that the sand flows in a streamlined manner and passes between the specimen and rubber wheel.
6.5 Motor Drive The wheel is driven by a nominally 0.7-kW (1-hp) d-c motor through a 10/1 gear box to ensure that full torque is delivered during the test. The rate of revolution (2006 10 rpm) must remain constant under load. Other drives producing 200 rpm under load are suitable.
6.6 Wheel Revolution Counter The machine shall be equipped with a revolution counter that will monitor the number of wheel revolutions as specified in the procedure (Section 9). It is recommended that the incremental counter have the ability to shut off the machine after a preselected number of wheel revolutions or increments up to 12 000 revolutions is attained.
6.7 Specimen Holder and Lever Arm The specimen holder is attached to the lever arm to which weights are added, so that a force is applied along the horizontal diametral line of the wheel. An appropriate number of weights must be available to apply the appropriate force (Table 2) between the test specimen and the wheel. The actual weight required should not be calculated, but rather should be determined by direct measurement by noting the load required to pull the specimen holder away from the wheel. A convenient weight system is a can filled with sand (see Fig. 2).
6.8 Analytical Balance The balance used to measure the loss in mass of the test specimen shall have a sensitivity of 0.001 g. Procedure C requires a sensitivity of 0.0001 g.
6.9 Enclosure, Frame, and Abrasive Hopper Fig. 3 and Fig. 4 are photographs of a typical test apparatus. The size and shape of the support elements, enclosure, and hopper may be varied according to the user’s needs.