810G covers exposure of equipment to dry blowing sand and dust. Think Afghanistan. As with Method 509.5 for Salt Fog exposure, Blowing Sand and Dust is one of the more commonly performed tests. Method 510.5 covers 13 pages. This is one of the shorter duration Methods and can be finished in a day. Dust is defined as particles measuring less than 150um and sand measures in the range of 150 to 850um. There are specs for size distribution within that range for the test dust or sand. Dust exposure is examined for the ability of the item under test to resist vents being clogged, penetration through cracks, crevices, bearings and joints and to evaluate the effectiveness of filters. Sand exposure is designed to test the item for its ability to be stored and operated in blowing sand conditions. Blowing sand can be very erosive, easily stripping the finish from an item allowing subsequent corrosion or operational failure. Blowing sand can quickly render optical devices unusable. This method is not used to evaluate in-flight material such as air frames, propellers, helicopter rotors, etc. due to the velocities involved. This Method is also not used to evaluate the build-up of electrostatic charge. Some care should be exercised with the equipment regarding ESD. Blowing sand and dust can impart a fairly high charge on an item and subsequent handling of the item may cause damage from a discharge. Assure the item and operator are grounded before handling during or after a test. Blowing sand and dust is usually associated with hot-dry regions though it can be experienced in most other regions depending on the season and weather. In addition, military operations can generate large quantities of loose sand and dust which can be picked up by the wind or, potentially, rotorcraft or other aircraft. The effects can include:
- Abrasion and erosion of surfaces.
- Penetration of seals.
- Degradation of electrical circuits.
- Obstruction/clogging of openings and filters.
- Physical interference with mating parts.
- Fouling/interference of moving parts.
- Reduction of thermal conductivity.
- Interference with optical characteristics.
- Overheating and fire hazard due to restricted ventilation or cooling.
- Wear (increased fretting due to imbedding between mating surfaces).
- Increased chaffing between non-mating contacting surfaces.
- Weight gain, static/ dynamic balance.
Because of potential damage to an article, Humidity, Salt Fog and Fungus Growth testing should be accomplished prior to Blowing Sand and Dust testing. Also consider the corrosive effects of dust or dust residue since salt and highly alkaline materials may be present in the end-use environment. Method 510.5 provides two procedures:
Procedure I – Blowing Dust (less than 150um)
Procedure II – Blowing Sand (150 to 850um)
As you will recall, MIL-STD-810G is not a set of tests to pass or not pass but a document guiding the creation of test procedures which are agreed upon between the vendor and customer as to the intended environment. Therefore, part of the process for Method 510.5 is to identify the climatic conditions appropriate for the geographic areas in which the material will be operated and stored. Specific test conditions should be based, if possible, on field data. Method 510.5 offers guidance which can be used in the absence of field data. The test itself, while straight forward, can be brutal. For Blowing Dust, the item under test should be maintained at its high operating or storage temperature. Humidity should be maintained below 30 percent. The air velocity for the test should be a minimum of 300 +/-200 feet/min with a higher velocity of 1750 +/-250 feet/min typical of desert winds. Use local conditions if they are more representative of the intended environment. The dust should have a chemical composition similar to the dust found in the intended environment. For example, in arid regions, soluble salts are common and can cause fouling, corrosion, and electrical shorts. If possible, actual dust from the region should be used in the test. The goal is to have as realistic test as possible. The item under test should be rotated to assure all surfaces face the blowing dust. The test duration should be at least 6 hours at ambient temperature with an additional 6 hours at the high storage or operational temperature. For Blowing Sand, the test is very similar regarding temperature and humidity. However, the velocity is increased to 40-65 mph (3500-5700 ft/sec). The material should be common silica sand. As with Dust testing, it is preferred to match the properties of the sand found in the end-use environment to the test sand. There are 90 deserts in the world, each with different particle size distributions. The quantity of sand in the air during the test is determined by the expected environment:
- For materiel likely to be used close to helicopters operating over unpaved surfaces: 2.2 ± 0.5 g/m3.
- For material never used or exposed in the vicinity of operating aircraft, but which may be used or stored unprotected near operating surface vehicles: 1.1 ± 0.3 g/m3.
- For material that will be subjected only to natural conditions: 0.18 g/m3, -0.0/+0.2 g/m3.
The item under test should be oriented so that the most vulnerable surface faces the blowing sand. Rotate the item every 90 minutes if more than one vulnerable surface exists. The Blowing Sand test should last 90 minutes per vulnerable face. For Blowing Dust, evaluate the item for binding, clogging, seizure, etc. Does it operate correctly? Check air filter operation to assure the filters are up to the task. For Blowing Sand, evaluate the item for abrasion and operation. Examine protective coatings and seals. Does the item operate correctly? CP Technologies has taken our military chassis and displays through Blowing Sand and Dust testing and can work with the customer to put a plan in place for 810G compliance.