Downloaded from https://www.everyspec.com MIL-STD-81OC c. 90 +2 percent of the dust shal1 pass through a 200-mesh screen d. 75 +2 percent of the dust shal1 pass through a 325-nieshscreen. NOTE: 140-mesh silica flour as produced by the Ottawa Silica Company, Ottawa, Illinois, or ‘equal,is satisfactoryfor use in the performance of these tests. 3. PROCEDURE 3.1 Procedure 1. Prepare the test item in accordan~e with General Require- ments 3.2, positioning the test item as near.the center of the chamber as practicable.
If more than one item is being tested, there shal1 be a mini- mum clearance of 4 inches between surfaces of test items or any other material or object capable of furnishing protection. Also, no surface of the test item shall be closer than 4 inches from any wall of the test chamber. Orient the.item so as to expose the most critical or vulnerable parts to the dust stream. The test item orientation may be changed during the.test if so required by the equipment specification. :. Step 1 - Set the chamber controls to maintain an internal chamber temperature of”23° C (73° F) and a relative humidity of less that 22 percent. Adjust the air velocity to.1,750 *250 feet per minute.
Adjust the dust feeder to control the dust concentrationat O.3 tO.2 grams per cubic foot. With.the ( test item nonoperating,maintain these conditions for 6 hours. Step 2 - Stop the dust feed and reduce the air velocity to 300 t200 feet per minute. Raise the internal chamber air temperature to 63° C (145°F). Hold these conditions 16 hours. Step 3 - While holding chamber temperature at 63° C 145”F) adjust the air velocity to 1,750 i250 fpm. Adjust the dust feeder to control the dust concentration at O.3 iO.2 gms per cubic foot. Unless otherwise specified, with the test item non- operating, maintain these conditions for 6 hours. Step ,4 - return to standard ambient conditions.
Remove accumulated dust from the test item by brushing, wiping, or shaking, care being taken to avoid introductionof additional dust into,the test item. Dust shal1 not be removed by either air blast or vacuum cleaning. Turn off all chamber controls and allow the test item to METHOD 510.1 510.1-2