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Climate Chambers for MIL-STD-810G Method High Temperature

Climate Chambers for MIL-STD-810G Method 501.5 High Temperature
 
MIL-STD-810G is a very huge standard. This standard is approved for use by all Departments and Agencies of the Department of Defense (DoD). Although prepared specifically for DoD applications, this standard may be tailored for commercial applications as well. The primary emphases are tailoring a materiel item's environmental design and test limits to the conditions that the specific materiel will experience throughout its service life, and establishing laboratory test methods that replicate the effects of environments on materiel, rather than trying to reproduce the environments themselves. Today we gonna talk about the method 501.5 high temperature in MIL-STD-810G. And a environmental test chamber is necessary.
 
 
1.  SCOPE.
 
1.1  Purpose.
Use high temperature tests to obtain data to help evaluate effects of high temperature conditions on materiel safety, integrity, and performance.
 
1.2  Application.
Use this method to evaluate materiel likely to be deployed in areas where temperatures (ambient or induced) are higher than standard ambient.
 
1.3  Limitations.
Limit use of this method to evaluating the effects of relatively short-term (months, as opposed to years), even distributions of heat throughout the test item. This method is not generally practical for:

a. Evaluating time-dependent performance degradation (aging) effects that occur during constant long-term exposure to high temperatures (under storage or operational modes) where synergetic effects may be involved. For such high temperature aging effects, test in the natural environment.
 
b. Evaluating materiel in a high temperature environment where solar radiation produces significant thermal gradients in the materiel. For simulating direct solar impingement, use Method 505.5, Procedure I.
 
c. Evaluating actinic (photochemical) effects (use Method 505.5, Procedure II).

d. Evaluating the effects of aerodynamic heating.

e. Although high temperature testing may be considered for assessment of munitions, accomplish safety or hazard testing in accordance with MIL-STD-2105C (paragraph 6.1, reference 6.1d).
 
2.  TAILORING GUIDANCE.
 
2.1  Selecting this Method.

After  examining  requirements  documents  and  applying  the  tailoring  process  in  Part  One  of  this  standard  to determine where high temperatures are foreseen in the life cycle of the materiel, use the following to confirm the need for this method, and to place it in sequence with other methods.  It is preferable to conduct Method 505.5,Procedure I prior to Method 501.5, in order to obtain maximum response and stabilization temperatures for items exposed to direct solar radiation.
 
2.1.1  Effects of high temperature environments.

High temperatures may temporarily or permanently impair performance of materiel by changing physical properties or dimensions of the material(s) of which it is composed. The following are examples of problems that could result from high temperature exposure that may relate to the materiel being tested. Consider the following typical problems to help determine if this method is appropriate for the materiel being tested. This list is not intended to be all-inclusive.

a. Parts bind from differential expansion of dissimilar materials.

b. Lubricants become less viscous; joints lose lubrication by outward flow of lubricants.

c. Materials change in dimension, either totally or selectively.

d. Packing, gaskets, seals, bearings and shafts become distorted, bind, and fail causing mechanical or integrity failures.

e. Gaskets display permanent set.

f. Closure and sealing strips deteriorate.
 
g. Fixed-resistance resistors change in values.

h. Electronic circuit stability varies with differences in temperature gradients and differential expansion of dissimilar materials.

i. Transformers and electromechanical components overheat.

j. Operating/release margins of relays and magnetic or thermally activated devices alter.

k. Shortened operating lifetime.

l. Solid pellets or grains separate.

m.   High pressures created within sealed cases (projectiles, bombs, etc.).

n. Accelerated burning of explosives or propellants.

o. Expansion of cast explosives within their cases.

p. Explosives melt and exude.

q. Discoloration, cracking or crazing of organic materials.

r. Out-gassing of composite materials.
 
2.1.1 Sequence among other methods.

a. General.  See Part One, paragraph 5.5.

b. Unique to this method. There are at least two philosophies related to test sequence. One approach is to conserve test item life by applying what are perceived to be the least damaging environments first. For this approach, generally apply the high temperature test early in the test sequence. Another approach is to apply environments to maximize the likelihood of disclosing synergetic effects.

For this approach, consider high temperature testing following dynamic tests, such as vibration and shock. Although not written for such, this test may be used in conjunction with shock and vibration tests to evaluate the effect of dynamic events (i.e., shipping, handling, and shock) on hot materials. Also, this test may contribute significantly to the results of low pressure testing of seals, e.g., see paragraphs 2.1.1d, e, and f.
 
2.2  Selecting Procedures.
 
This method includes three test procedures, Procedure I (Storage), Procedure II (Operation), and Procedure III (Tactical-Standby to Operational). Determine the procedure(s) to be used.
 
NOTE:  The materiel’s anticipated Life Cycle Environmental Profile (LCEP) may reveal other high temperature scenarios that are not specifically addressed in the procedures. Tailor the procedures as necessary to capture the LCEP variations, but do not reduce the basic test requirements reflected in the below procedures. (See paragraph 2.3 below.)  

NOTE: Consider the potential synergistic effects of temperature, humidity and altitude, and the use of Method 520.3 in addition to this method.
 
2.2.1 Procedure selection considerations.

When selecting procedures, consider:

a. The operational purpose of the materiel.

b. The natural exposure circumstances (ambient or induced).

c. The test data required to determine whether the operational purpose of the materiel has been met.

d. Procedure sequence. If both the storage and operation procedures are to be applied, perform Procedure I before Procedure II. Consider using Procedure III in lieu of Procedure II for unique cases where materiel  in  its  operational  configuration  is  non-operational  (awaiting  use)  and  is  exposed  to  solar heating, e.g., aircraft cockpits, ground vehicle passenger compartments, etc.

e. Other significant heat sources that could affect the materiel such as motors, engines, power supplies, or exhaust air.
 
2.2.2 Difference among procedures.

While all three procedures involve temperature conditioning and performance testing, they differ on the basis of the
temperature  load  prior  to  and  during  performance  tests. The  storage  procedure  assesses  the  effects  of  high temperature storage on subsequent materiel performance. The operation procedure assesses the effects of high
temperatures during performance. The tactical-standby to operational procedure evaluates the ability of materiel (usually  enclosed  by  transparent  or  translucent  material)  that  has  soaked  in  the  sun  in  a  high  temperature environment to become operational in a relatively short period of time.
 
a. Procedure I - Storage. Use Procedure I to investigate how high temperatures during storage affect the materiel (integrity of materials, and safety/performance of the materiel). This test procedure includes exposing the test item to high temperatures (and low humidity where applicable) that may be encountered in the materiel's storage situation, followed by an operational test at controlled or high temperature ambient conditions. For materiel inside an enclosure that is, in turn, exposed to solar heating, consider using Method 505.5, Procedure I to determine the actual level of heating of the test materiel caused by solar loading.

b. Procedure II - Operation. Use Procedure II to investigate how high ambient temperatures may affect materiel performance while it is operating. There are two ways to perform Procedure II:

(1)  Expose the test item to cyclic chamber conditions with the test item operating either continuously or during the period of maximum response (highest item temperature).

(2)  Expose the test item to a constant temperature and operate the test item when its temperature stabilizes. (To be used only for items situated in close proximity to heat-producing equipment or when it is necessary to verify operation of an item at a specified constant temperature.)

c. Procedure III - Tactical-Standby to Operational. This procedure is not a substitute for solar radiation (Method 505.5). This procedure evaluates the materiel’s performance at the operating temperatures after being presoaked at non-operational temperatures.

Since actinic effects and directional heating are not applicable in this method, consider applying this procedure when materiel is in an enclosed environment, (e.g., aircraft and ground vehicles with closed transparent or translucent areas can develop high internal temperatures prior to equipment operation due to solar heating; enclosures such as communications shelters may require immediate operation after being exposed to solar heating).

These are not items in storage or transit situation, but rather items in the operational configuration (ready-to-go as needed) that must be operational in a relatively short period of time. Usually, the “cooling” option refers to merely opening the enclosed areas and allowing the ambient air to begin cooling the interior areas so normal operation can begin. 
 
2.3  Determine Test Levels and Conditions.

Having selected this method and relevant procedures (based on the test item's requirements documents and the tailoring process), complete the tailoring process by identifying appropriate parameter levels and applicable test conditions and techniques for these procedures. Base these selections on the requirements documents and the Life Cycle Environmental Profile, and information provided with this procedure. Consider the following when selecting test levels.

2.3.1 Climatic conditions.

Identify the appropriate climatic conditions for the geographic areas in which the materiel will be operated and stored. There are two climatic categories where high temperatures are typically encountered: Hot Dry and Basic Hot (Part One, Annex C, Figure C-1). Data for these areas are shown in Tables 501.5-I, -II, and -III. Determine high temperature levels with respect to:

a. Climatic area of concern.

b. Exposure to solar radiation: Is this exposure directly on the materiel, shipping container, protective package shelter, etc.

c. Analysis of the path of heat transfer from the ambient air and solar radiation to the materiel.


 



 
From those charts, the temperature range is 30-71℃, the humidity range is 1-44%RH.
In this test, the humidity control is not necessary. Only the temperature matters. From the temperature range, we can realize that we need a temperature test chamber.

 
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