Downloaded from https://www.everyspec.com TOP 1-2-621 6 February 2009 blowing sand is recommended when the objective is to detect material penetrations. The higher wind speed will increase the likelihood of dust penetration, but clogging and caking issues might not occur for certain test articles. (6) Exposure Time. This TOP recommends an exposure duration of 90 minutes per face. The MIL-STD-810 dust test specifies the exposure time to be 6 hours at ambient temperature and 6 hours at high temperature (i.e., 12 exposures for a 6 sided item which is 90 minutes per face per temperature).
The combined sand/dust method test time is limited to the MIL-STD-810 sand test value (90 minutes per face) due to the concentration of sand employed in the test. Shorter time periods (e.g.; 30 minutes per side) may be acceptable if the only test objective is to determine sand/dust intrusion through seals, etc, during non-operational UUT scenarios. 2. FACILITIES AND INSTRUMENTATION. 2.1 Facilities. Item Requirement Outdoor Test Area Selected to provide adequate protection for personnel and equipment and to facilitate emplacement of the test articles and wind machine and sand/dust injection system. Figures 1 and 2 show typical test facilities and equipment.
Wind Generation Machine To be able to provide wind speeds up to 18 m/s (40 mph) over a broad area. Two or more machines may be necessary for extremely large test items. [The149 KW (200 HP) wind machine in Figure 1 produces 18 m/s (40 mph) winds at 6 m (20 feet). The airboat design of Figure 2 produce 316 KW (425 HP) and wind speeds up to 45 m/s (100 mph).] Note, an axial propeller fan will cause rotational swirl in the fan outlet airflow and a centrifugal fan will create a gradient in the airflow across the fan exit plane. In either case, a flow straightener is recommended at the fan exit to create a more uniform airflow at the test item.
Sand and Dust Injection System (see Figure 1) System must be capable of dispersing the sand/dust media uniformly across the face of the UUT at the desired flow rates/volumes. Air Flow Straightener (see Figure 2) An air flow straightener will improve test bed resistance to ambient side/crosswinds which can disrupt direction of intended sand particle impact target. The straightener can be simply constructed from telephone poles dropped into metallic welded U-channel end pieces. 3