4.1 Test Facility
The required apparatus consists of a chamber or cabinet together with auxiliary instrumentation capable of establishing and maintaining the specified test conditions. Use a facility equipped so that test conditions within the chamber can be stabilized soon after the test item is installed. Arrange water delivery equipment to minimize the collection of puddles/ice in the chamber. Make continuous recordings of chamber temperature measurements and, if required, test item temperatures.
4.2 Controls
Before each test, verify the critical parameters. Ensure the nozzle spray pattern is wide enough to guarantee uniform impingement for all test wind velocities. Unless otherwise specified, if any action other than test item operation (such as opening the chamber door) results in a significant change in the test item or chamber temperature (more than 2°C
(4°F)), restabilize the test item at the required test temperature before continuing. If the operational check is not completed within 15 minutes, reestablish the test item temperature conditions before continuing.
4.3 Test Interruption
Test interruptions can result from two or more situations, one being from failure or malfunction of test chambers or associated test laboratory equipment. The second type of test interruption results from failure or malfunction of the test item itself during operational checks.
4.3.1 Interruption Due To Chamber Malfunction
- a. General. See Part One, paragraph 5.11 of this Standard.
- b. Specific to this Method.
- (1) Undertest interruption. Interruption of an icing/freezing rain test is unlikely to generate any adverse effects. Normally, continue the test from the point of interruption once the test conditions have been re-established.
- (2) Overtest interruption. Follow any interruption that results in more extreme exposure of the test item than required by the requirements document by a complete operational and physical checkout. If there are no problems, restore the test item to its pretest condition and restart the test.
4.3.2 Interruption Due To Test Item Operation Failure
Failure of the test item(s) to operate as required during operational checks presents a situation with several possible options.
- a. The preferable option is to replace the test item with a “new” one and restart from Step 1.
- b. A second option is to replace / repair the failed or non-functioning component or assembly with one that operates as intended, and restart the entire test from Step 1.
NOTE: When evaluating failure interruptions, consider prior testing on the same test item and consequences of such.
4.4 Test Setup
- a. General. See Part One, paragraph 5.8.
- b. Unique to this Method.
- (1) Clean all outside surfaces of any contamination not present during normal operation. Even thin films of oil or grease will prevent ice from adhering to the test item and change the test results.
- (2) To facilitate measurement of ice thickness, mount depth gauges such as copper bars or tubes of an appropriate size in places where they will receive the same general water spray as the test item. Other thickness measurement techniques may be used if they can be shown to indicate the ice thickness.
NOTE: Since artificially produced freezing accretion rates tend to depend on the distance between the test item and spray device, for structures with large height variations such as antenna masts, place test bars at different heights.
- (3) Using chilled water (between 0 °C and 3 °C (32 °F and 37 °F)) in the spraying system will cause a faster ice buildup rate than unchilled water.
4.5 Test Execution
The following steps, alone or in combination, provide the basis for collecting necessary information concerning the materiel in an icing/freezing rain environment.
4.5.1 Preparation for Test
MIL-STD-810H
METHOD 521.4
4.5.1.1 Preliminary Steps
Before starting the test, review pretest information in the test plan to determine test details (e.g., procedures, item configuration, cycles, durations, parameter levels for storage/operation, ice thickness, etc.).
4.5.1.2 Pretest Standard Ambient Checkout
All items require a pretest standard ambient checkout to provide baseline data. Conduct the checkout as follows:
- Step 1 Install temperature sensors in, on, or around the test item as described in the test plan.
- Step 2 Install the test item in the chamber (Part One, paragraph 5.8.1) in the required configuration and orientation, and at standard ambient conditions (Part One, paragraph 5.1).
- Step 3 Conduct a visual examination of the test item with special attention to stress areas such as corners of molded cases, and document the results.
- Step 4 Conduct an operational checkout (Part One, paragraph 5.8.2) as described in the plan to obtain baseline data, and record the results.
- Step 5 If the test item operates satisfactorily, proceed to paragraph 4.5.2. If not, resolve the problems and repeat Step 4 above.
4.5.2 Procedure - Ice Accretion
Step 1 Stabilize the test item temperature at 0 °C (-0/+2 °C (32 °F (-0/+4 °F)).
- Step 2 Deliver a uniform, pre-cooled water spray for 1 hour to allow water penetration into the test item crevices/openings (although a water temperature of 0 to 3 °C (32 to 37 °F) is ideal, a water temperature of 5 °C (41 °F) and a water delivery rate of 25 mm/h (1 in/h) has proven satisfactory).
- Step 3 Adjust the chamber air temperature to -10 °C (14 °F) or as specified, and maintain the water spray rate until the required thickness of ice has accumulated on the appropriate surfaces. Wind or a side spray may be used to assist accumulation of ice on the sides of the test item.
NOTE: If it is difficult to produce a satisfactory layer of glaze ice, vary one or more of the parameters as necessary, i.e., water or test item temperature, spray rate or duration, distance between the nozzles and the test item, etc. Generally an air temperature no warmer than -2 C (28°F) is more likely to produce glaze ice.
NOTE: It may be easier to stop spraying during the temperature reduction to facilitate temperature adjustment and to minimize frosting of test chamber refrigeration coils.
- Step 4 Maintain the chamber air temperature for a minimum of 4 hours to allow the ice to harden. Examine for safety hazards and, if appropriate, attempt to operate the test item. Document the results (with photographs if necessary).
- Step 5 If Step 4 resulted in failure, or if the specification requires or allows ice removal, remove the ice. Limit the method of ice removal to that determined in paragraph 3.1b, e.g., built-in ice removal systems, plus expedient means that could be expected to be employed in the field. Note the effectiveness of ice removal techniques used. Examine for safety hazards and, if appropriate (and possible), attempt to operate the test item. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 6 Examine for safety hazards and, if appropriate (and possible), attempt to operate the test item at the specified low operating temperature of the materiel. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 7 If required, repeat Steps 3 through 6 to produce other required thicknesses of ice.
Step 8 Stabilize the test item at standard ambient conditions and perform a post-test operational check. See paragraph 5 for analysis of results.
Step 9 Document (with photographs if necessary) the results for comparison with pretest data.