General Motors GM4298P Salt Spray Test
General Motors GM4298P Salt Spray Test
GENERAL MOTORS ENGINEERING STANDARDS & Materials and Processes-Procedures
JOEO Factory are professional support for this standard of corrosion test machine, our SSTC-Series are special design for this testing.Details of GM4298 ,Please reference with below :
1 SCOPE.
This standard covers the requirements necessary to attain the conditions found in a neutral salt spray test cabinet.
1.2 The salt spray test is better suited for quality control and process control evaluations. Other tests may be better suited to simulate field performance.
2. REFERENCED STANDARDS.
GM4298P
GM4465P
GM9102P
ASTM B117
ASTM D1193
3 PREPARATION OF TEST SPECIMENS.
3.1 The methods of application, film thickness, curing and conditioning of the test surface shall be as specified, consistent with the normal production practices (cleaning, pretreatment, etc.).
3.2 The backs, cut edges of plated, coated, or duplex materials and those areas containing identification marks or in contact with racks or supports shall be protected with a suitable coating that is stable under the conditions of the test.
3.3 Specimens shall be suitably cleaned. The cleaning method shall be optional depending on the nature of the surface and the contaminants. The cleaning shall not include the use of abrasives, other than a paste of pure magnesium oxide, nor of solvents which are corrosive or that will deposit either corrosive or protective films. Care shall be taken that specimens are not contaminated after cleaning by excessive or careless handling.
3.4 Specimens for evaluation of paints and other organic coatings shall be prepared according to applicable specifications for the material being tested.
3.5 Whenever it is desirable to determine the development of corrosion from an abraded area in the paint or organic coating.a scratch or scribed line shall be made through the coating as described in GM9102P.
4 TEMPERATURE.
4.1 The temperature within the exposure zone of the Joeo salt spray test chamber(SSTC -series) shall be maintained @ 35±2C and recorded continuously throughout the test duration by an external recorder.
5 WATER QUALITY
5.1 See GM4465P.
6 TEST SOLUTION.
6.1 The salt solution shall be prepared by dissolving 5 g±1 g of salt (NaCL) to 95 mL of water as described in 5.1. The salt used shall be of reagent grade. A solution having a specific gravity of 1.0255 to 1.0400 is required.
6.2 The pH of the collected solution must be in the pH range of 6.5 to 7.2. The pH of the collected solution shall be checked and recorded daily. Readings on weekends need not be taken. The pH measurement shall be made electronically using a glass electrode with a saturated potassium chloride bridge (mild agitation is recommended). The pH of the collected solution will be higher than the pH of the original solution due to the loss of carbon dioxide at the higher temperature. The pH of the make up solution may be adjusted with the addition of small amounts of hydrochloric acid (HCI) or sodium hydroxide (NaOH,) solution.
6.3 Specific gravity of the collected solution shall be 1.0255to 1.0400 when measured at 25'C.
7 ATOMIZATION AND QUALITY OF FOG.
7.1 Chest type cabinets require 1 fog collector for every 0.55 square meter (6 square feet) of test area. The larger, walk in type test cabinets require 1 fog collector for every 1.40 square meter (15 square feet). The collectors must be placed within the exposure zone so that no drops of solution from the test specimens or any other source shall enter collectors. The collectors shall be placed in the proximity of the test specimens and at the same height as the test specimens. Collectors shall be evenly distributed to produce a representative measure of the fog collection rates throughout the chamber. The fog shall be such that for each 80 cm2 (approximately 10 cm diameter) of horizontal test area there will be 1.0 to 2.0 ml of fog per h collected in each collector. This rate of collection shall be based on a minimum run of at least 16 h.
7.2 Chambers must demonstrate compliance to all parameter sprior to placing samples in test. At least 24 h of cabinet operation would be required prior to test sample exposure. Mapping must be performed after any major change or at least yearly.
7.3 Collection rate mapping of a chamber throughout the exposure zone, to ensure conformance to the collection rate requirement, is required as a means of reducing test variability.
7.4 Air pressure and temperature at the humidifying towershall conform to Appendix X1.4 of ASTM B117.
ASTM B117 -X1.4 Air for AtomizationX1.4.1 The air used for atomization must be free of grease, oil, and dirt before use by passing through well-maintained filters. Room air may be compressed, heated, humidified, and washed in a water-sealed rotary pump if the temperature of the water is suitably controlled. Otherwise cleaned air may be introduced into the bottom of a tower filled with water through a porous stone or multiple nozzles. The level of the water must be maintained automatically to ensure adequate humidification. A chamber operated in accordance with this method and Appendix X1 will have a relative humidity between 95 and 98%. Since salt solutions from 2 to 6% will give the same results (though for uniformity the limits are set at 4 to 6 %), it is preferable to saturate the air at temperatures well above the chamber temperature as insurance of a wet fog. Table X1.2 shows the temperatures, at different pressures, that are required to offset the cooling effect of expansion to atmospheric pressure.
X1.4.2 Experience has shown that most uniform spray chamber atmospheres are obtained by increasing the atomizing air temperature sufficiently to offset heat losses, except those that can be replaced otherwise at very low-temperature gradients.
8 CONTINUITY OF TEST.
8.1 Test interruptions should be limited to a maximum of 3 in any 24 h period. The duration of any single interruption shall be limited to a maximum of 10 minutes. If a special test is being run which requires longer or more frequent interrup. tions, that test shall not be run simultaneously in the same chamber with any other test. Collections must be evaluated and recorded daily. (Weekends and holidays are exceptions).
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