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Environmental Test Chambers for GM 9540P: Accelerated corrosion test


A brief introduction of Shanghai Lenpure company Compound salt spray test chamber

During the Fog Function, the corrosion tester typically operates as a conventional salt spray unit:
• Corrosive solution from the internal reservoir is pumped to the nozzle;
• Compressed air is humidified by passing through the bubble tower on
its way to the nozzle;
• Nozzle atomizes solution air into a fine, corrosive fog mist;
• Chamber heaters maintain the programmed chamber temperature.
 
Dry-Off & Dwell Functions:
During the Dry-off Function, a purge blower forces room air over an air heater, through diffusers, and across specimens in the chamber. This creates a low humidity condition inside the chamber, drying the specimens. The chamber temperature is controlled by the chamber heaters and the air heater. During the Dwell Function (not shown) the chamber temperature is controlled by only the chamber heater.
 
Humid Function:
During the Humid Function in CCT models, the chamber is maintained at 95-100% relative humidity by forcing hot water vapor into the chamber. Deionized water is required for proper operation. The vapor generator heater maintains the programmed chamber temperature.
 
This procedure describes an accelerated laboratory corrosion test method to evaluate assemblies and components. The test procedure provides a combination of cyclic conditions (salt solution, various temperatures, humidity, and ambient environment) to accelerate metallic corrosion.The procedure is effective for evaluating a variety of corrosion mechanisms, such as general, galvanic, crevice, etc.
 
The test duration can be individually tailored to achieve any desired level of corrosion exposure. Also, synergistic effects due to temperature, mechanical and electrical cycling can be comprehended by this test.
 
TEST PROCEDURE
4.1 COUPON/TEST SAMPLE PREPARATION.
4.1.1 Each coupon shall be permanently identified by stamping numbers onto the surface.
 
4.1.2 Corrosion coupons can be cleaned with methanol on acetone solution and accurately weighed prior to use, The weight, in milligrams (mg), shall be recorded and retained for future reference.
 
NOTE: It is critical that all forming or preservation oils/lubes be removed prior to exposure to allow for general/uniform corrosion of the coupon. This process can be aided by using a commercial grade degreaser prior to methanol or acetone clean.
 
4.2 COUPON RACK PREPARATION. Prior to start of test prepare the coupon rack with sufficient coupons to monitor the test.
 
4.2.1 The coupons shall be secured to an aluminum or non metallic coupon rack with fasteners as shown in Figure 1. The bolt, nut and washers shall be made from a non black plastic material, preferably nylon. Figure 1 shows a completed coupon rack configuration. The number of coupons required for different test durations are shown in Table 1.

4.2.2 The exact location of each coupon on the rack shall be identified and recorded using the prestamped numbers for reference as illustrated in Figure 1.

4.2.3 Allow a minimum 5 mm spacing between the coupons and the rack surface. All coupons shall be secured at most 15 from vertical and must not contact each other.
 
4.2.4 The coupon rack shall be placed in the general vicinity of the parts being tested, such that the coupons receive the same environmental exposure as the test samples.
 
4.3 TEST METHOD. See Table 4 for the steps that comprise the test method. Repeat the cycle daily as necessary until the test duration requirements are met. At the option of the test requester, the test can be continued throughout weekends to decrease the over all test time.
 
4.3.1 For each salt mist application, use the sprayer to mist the samples and coupons until all areas are thoroughly wet.The mist application occurs while the samples and coupons are in the ambient environment. The times in Table 4 for the salt mist application can be varied by ± 30 minutes, as long as the parts are visibly dry before each application.


4.4 TEST ACCELERATTON. Humidity ramp times between the ambient and wet condition and between the wet and dry conditions are critical to test acceleration (this is because corrosion rates are highest during this transition period) Typically, the time from ambient to the wet condition should be approximately 1 h and the transition time between wet and dry conditions should be approximately 3 h.
 
If a test is conducted with ramp times different than described above, the number of cycles to reach coupon mass loss targets may increase or decrease. Test acceleration can be optimized and tracked by using standard corrosion coupons as monitoring devices. Ramp time is to be included as part of the specified exposure period.
 
4.5 TEST MONTTORING. Corrosion coupons shall be removed and analyzed after each phase throughout the test to monitor the corrosion. To analyze coupons remove 1 coupon from each end of the rack and prepare for weighing and mass loss determination. (EXAMPLE: For a B duration, 2 coupons are removed and analyzed after 8 cycles, and another 2 coupon after 16 cycles.)
 
4.5.1 Before weighing, clean the coupons using a mild sand blast process to remove all corrosion by-products from the coupon surface. Wipe the coupons free of grit and weigh to determine the coupon mass loss using the formula:
Mass Loss-(Initial Mass)-(End-of-Phase Mass)
 
4.5.2 Compare the actual mass loss to the targeted values.Refer to Table 2 for targeted mass loss values, in milligrams, for various test durations as a function of the coupon's original thickness.
 
NOTE: Coupon mass loss targets for every phase are not included in Table 2. To check test progress and assure that the test is being run correctly, assume a linear corrosion rate. Thus.if the test is 40% complete the coupon mass loss value should be approximately 40% of the end-of-test targeted range.
 
NOTE: If the actual mass loss does not coincide with the targeted values listed in Table 2 the test should be repeated. Also, the reasons why the targeted value(s) was not obtained should be investigated and corrected before resuming the test.
 
4.6 INSPECTION. The test sample(s) shall be inspected for corrosion and photographed at the end of predetermined cycles. If plastic materials are being tested any discoloration or degradation and/or adhesive bond failure (delamination) shall be noted and recorded.
 
4.7 END OF TEST. At the end of test the samples shall be rinsed with fresh tap water and allowed to dry before evaluating. One (1) test cycle is equal to 24 h, 1 phase is equal to 8 .
 
 
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