Freeze and Thaw | Congelamento e Scongelamento

MIL STD 810 G – Test Method 524 – Freeze and Thaw

 

SCOPE

NOTE: This is a new method that was adapted from NATO STANAG 4370, AECTP 300, Method 315.
Purpose
The purpose of this test is to determine the ability of materiel to withstand:
  1. The effects of moisture phase changes between liquid and solid, in or on materiel, as the ambient temperature cycles through the freeze point;
  2. The effects of moisture induced by transfer from a cold-to-warm or warm-to-cold environment.
Application
This test is applicable to materiel that will experience one or more excursions through the freeze point while wet or in the presence of moisture (free water or vapor). See paragraph 2.1 for specific examples. For additional information, see Part Three, paragraph 5.9.
Limitations
This test is not intended to evaluate the effects of low temperature, thermal shock, rain, or icing. These may be determined using Methods 502.5, 503.5, 506.5, and 521.3, respectively.

 

TEST PROCESS

 

Procedure I – Diurnal Cycling Effects
  • Step 1. Spray the test item sufficient to fill any horizontal pockets to simulate water collected during a rain storm.
  • Step 2. Reduce the temperature inside the chamber to 10°C (18°F) below the freeze point or as otherwise specified for the initial conditions at a rate not exceeding 3°C (5°F) per minute. Maintain the condition for a minimum of one hour after the test item temperature has stabilized.
  • Step 3. Increase the chamber temperature linearly over a period of three hours. When the chamber air temperature reaches 0°C (32°F), introduce moisture using water vapor, steam, vapor generator or other means to raise and maintain the humidity at or close to saturation.
  • Step 4. When the test item surface temperature reaches 0°C (32°F), ensure frost has formed on the test item surfaces. If so, go to Step 6; if not, repeat Steps 2 and 3 using a faster heating rate.
  • Step 5. Continue raising the test chamber towards a test item surface temperature of 4°C (39°F) (water at maximum density) until the frost just melts, then reduce the temperature linearly to l0°C (18°F) below the freeze point over a period of three hours. Maintain the conditions for a minimum of one hour following test item temperature stabilization.
  • Step 6. Repeat Steps 4-6 as required to complete the number of cycles identified in paragraph 2.3.4.
  • Step 7. Maintain the chamber and test item at the low temperature conditions until a visual examination and/or operational checks have been completed. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2. Otherwise go to Step 8.
  • Step 8. Return the test item to standard ambient conditions. Perform a complete visual and operational check, and document the results. See paragraph 5 for analysis of results.
Procedure II – Fogging
  • Step 1. Adjust the chamber temperature to l0°C (18°F) below the freezing point or as otherwise specified for the initial conditions at a rate not exceeding 3°C (5°F) per minute. Maintain the condition until the test item temperature has stabilized plus one hour.
  • Step 2. Transfer the test item to another chamber (previously adjusted to the upper specified temperature) as quickly as possible such that condensation or fogging occurs. The use of insulated transport containers is recommended. Maintain this second chamber at the specified upper temperature (usually room ambient) with a relative humidity of 95 ± 5 %.
  • Step 3. Start operation and any performance tests of the test item 60 ± 15 seconds after completion of the transfer, and document results. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 4. Return the test item to the low temperature chamber and repeat Steps 1-3 as required to complete the number of cycles identified in paragraph 2.3.4.
  • Step 5. Return the test item to standard ambient conditions. Perform a complete visual and operational check, and document the results. See paragraph 5 for analysis of results.
Procedure III – Rapid Temperature Change
  • Step 1. Adjust the chamber temperature to the specified upper temperature (usually standard ambient) at a rate of approximately 3°C (5°F) per minute, and a relative humidity of 95 ± 5%. Maintain these conditions until the test item temperature has stabilized plus one hour.
  • Step 2. Transfer the test item as quickly as possible and in not more than 5 minutes to another chamber stabilized at 10°C (18°F) below the freeze point. Recommend using insulated transport containers. Stabilize the test item temperature and hold for one additional hour.
  • Step 3. Unless otherwise specified, perform an operational check. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 4. If more than one cycle is required, stabilize the test item at room ambient temperature and at a RH of 95% as in Step 3, note the presence of any free water, and repeat Step 2.
  • Step 5. Return the test item to above-freezing conditions as soon as possible.
  • Step 6. As any ice melts, note location(s) of free water.
  • Step 7. Perform an operational check and physical inspection, and document results. If the test item fails to operate as intended, see paragraph 5 for analysis of results, and follow the guidance in paragraph 4.3.2 for test item failure.
  • Step 8. Adjust the test item to standard ambient conditions and repeat Steps 2-7 as necessary to verify prior results.

 

NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.

 

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