- 2022-03-07 14:54:47
You may find the introduction article from following link: https://pals.com.tr/blog/environmental-test-engineering-and-pals-service-article-series-1
We will proceed to elaborate the “Methods” and “Procedure”s of environmental standards of MIL-STD-810 in our article series. Instead of writing down the obvious information already given in the standard, we will be discussing more practical information on product design, features regarding “Equipment Under Test” (EUT), and conducting tests.
Test Method 506.5 – Rain
This method is used to evaluate material likely to be exposed to rain, water spray, or dripping water during storage, transit, or operation.
The purpose of this method is to help determine the following concerning rain, water spray, or dripping water:
a. The effectiveness of protective covers, cases, and seals in preventing the penetration of water into the material.
b. The capability of the material to satisfy its performance requirements during and after exposure to water.
c. Any physical deterioration of the material caused by the rain.
d. The effectiveness of any water removal system.
e.The effectiveness of protection offered to a packaged materiel.
Picture PDA-150-MIL Antenna System During Rain Test (Actual Footage) For more info: https://pals.com.tr/product/pda-150-mil
Procedures of this method are as follows:
Procedure I - Rain and Blowing Rain. Procedure I is applicable for materiel that will be deployed out-of-doors and which will be unprotected from rain or blowing rain. The accompanying wind velocity can vary from almost calm to extremely high. The rainfall rate used in Procedure I may be tailored to the anticipated deployment locale and duration. Although various rainfall intensities have been measured in areas of heavy rainfall, recommend a minimum rate of 1.7 mm/min (4 in/hr) since it is not an uncommon occurrence, and would provide a reasonable degree of confidence in the material. The following image is actually for the test facility to prepare the test chamber. We decided to add this image to give you the chance to grasp the idea of what your material is up against.
Procedure II - Exaggerated. Consider Procedure II when a large (shelter-size) materiel is to be tested and a blowing-rain facility is not available or practical. This procedure is not intended to simulate natural rainfall but will provide a high degree of confidence in the water-tightness of the material. This procedure uses (as a guideline) a 276 kPa (40 psig) nozzle pressure that should produce water droplets traveling at approximately 64 km/h (40 mph) when using a nozzle. The following image is actually for the test facility to prepare the test chamber. We decided to add this image to give you the chance to grasp the idea of what your material is up against.
Procedure III - Drip. Procedure III is appropriate when the material is normally protected from rain but may be exposed to falling water from condensation or leakage from upper surfaces. There are two variations to the drip test: for materiel that may experience falling water (generally from condensation), and for materiel that may be subjected to heavy condensation or leaks from above. The drip test requires a volume of water greater than 280 l/m2/hr (7 gal/ft2/hr) dripping through a pre-determined hole pattern. An alternative requirement is for items exposed only to 140 L/m2/hr: Appropriately reduce the drip rate as long as the duration of the test is extended to 30 minutes to ensure the equivalent volume of waterfalls on the test item. The following image is actually for the test facility to prepare the test chamber. We decided to add this image to give you the chance to grasp the idea of what your material is up against.
Tips and Tricks;
• As a rule of thumb tailoring is essential. Meaning choosing a procedure with the customer beforehand.
• Discuss EUT configuration with the customer. Prefer conditions for EUT most likely to be affected in real life. I.e. Storage, Packed, Unpack, Deployed, etc.
• Set pass/fail criteria clearly with the customer; which operational features needed to be tested after storage or during tests. Prepare instructions for test laboratory experts step by step about how to test EUT.
• Please note either EUT or rainwater temperature is required to be 10 +2 above, except for procedure II. This requirement intends to increase the chance of water leakage inside sealed parts of the EUT due to rapid temperature change.
• If your EUT is designed to be a sealed shut enclosure or have such parts, make sure to use proper gaskets and most importantly gasket cavities during the design phase. Gaskets tend to respond to temperature and pressure. Make sure cavities are properly sized according to storage and operational temperature.
• Make sure your lubricants are not water-soluble on your moving parts. Temperature also causes changes viscosity of such material.
• Use rust-resistant painting or cover on metal parts. Rust takes time to occur. It may not incidentally result from this test but keep in mind water causes rapid corrosion.
• Corrosion tends to happen on metal parts. To prevent this to happen, the designer needs to know why and how corrosion took place. Do not mix up corrosion and rust. Rust is one of the results of corrosion. Corrosion happens where there is a two metal (a same or different kind) part that meets (i.e. cover of a box). When there is an electrical potential difference exists between these two metal parts, water becomes a conductive element to start electrons to flow. Do you remember the subject of electrolysis from science class? Combine this occurrence with oxygen in the air, it will speed up metal electrons to bind oxygen and start metal oxide a.k.a. rust. The easiest and cheap solution to prevent this is to make sure every metal part of a EUT is properly bound and grounded to prevent electrical potential differences. Please note Author intentionally used bonded and grounded; not use “or” instead of “and” in this sentence.
• Please note there is a wind speed of 18 m/s (approx 60 fps) which is equivalent to approx 60 km/h (40 mph) exists during the blowing rain test. Thus where its name comes from. Wind makes water droplets act as a projectile to increase water penetration and erosion.
DID YOU KNOW?
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