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1、International Standard ( 6988 0 * 4 4! 5 Method of exposure of test specimens 5.1 Place the test specimens in the cabinet. The distance be- tween the test specimens shall be not less than 20 mm, the distance between the test specimens and the walls or roof of the test cabinet shall be not less than
2、100 mm. The distance between the lower edges of the specimens and the surface of the water in the base of the test cabinet shall be not less than 200 mm. The surface area of contact between a test specimen and its holder shall be as small as possible. 5.2 Arrange the test specimens so that any moist
3、ure conden- sing on any of them or on their supports does not fall on to other test specimens placed at lower levels. 5.3 The orientation of the exposed test surface is critical. In the case of flat surfaces, the angle of inclination to the vertical, unless otherwise specified, shall be 15 + 2 O. 5.
4、4 The total exposed surface area of the test specimen(s) tested at any one time should be substantially the same and, unless otherwise agreed, shall be 0,5 * 0,l m2 for the test cabinet of preferred capacity (see 3.1) and proportionately more or less for different sizes of cabinet. 5.5 The supports
5、for the test specimens shall be of non- metallic material such as glass, plastics material or suitably coated wood. Any material used to suspend the test specimens in the cabinet shall be of synthetic fibre or other inert insulating material; metallic materials shall not be used. b) by means of a ga
6、s jar of known volume filled with sulfur dioxide and opened in the chamber; 6 Procedure c) by means of a calibrated flowmeter. 4 Test specimens 4.1 The number, type, shape and dimensions of test specimens, shall be selected according to the specification for the coating or product being tested. When
7、 not so specified, details concerning the specimens shall be agreed between the interested parties. (See 5.3.) 4.2 Thoroughly clean the test specimens before testing. The cleaning method employed will depend on the nature of the surface and the contaminants, but shall not include the use of any abra
8、sives or solvents which may attack the surface of the test specimens. Take care that the test specimens are not recontaminated, after cleaning, by excessive or careless hand- ling. 4.3 If test specimens are cut from a larger coated article, the cutting shall be carried out in such a way that the coa
9、ting is not damaged, especially in the area adjacent to the cut. Unless otherwise specified, the cut edges shall be adequately pro- tected by coating them with a suitable medium, stable under the conditions of the test, such as wax or adhesive tape. 6.1 Introduce 2 + 0,2 dm3 of distilled water, havi
10、ng a con- ductivity of 500 /m or less, into the base of the test cabinet. NOTE - The quantity of water depends on the size of the test cabinet. A proportional change is valid only for test cabinets of similar shape. 6.2 Place the test specimens in position and close the door of the test cabinet herm
11、etically. 6.3 Introduce 0.2 dm3 of sulfur dioxide into the test cabinet through the inlet pipe. 6.4 Switch on the heater and raise the temperature inside the test cabinet to 40 + 3 OC in about 1.5 h. Maintain heating, under control, so as to keep the temperature inside the test cabinet at 40 + 3 OC
12、for the specified period. 6.5 One test cycle is 24 h, but this may be made up either by continuous exposure of the test specimens inside the test cabinet or by exposure inside the test cabinet for 8 h, followed by exposure to the ambient atmosphere for 16 h. For either form of test, replace the wate
13、r in the test cabinet and the sulfur dioxide in the test cabinet atmosphere before a 24 h cycle begins. 2 IS0 6988-1985 (E) 6.5.1 For a test of continuous exposure in the test cabinet for longer than 24 h, replace the water and sulfur dioxide after each 24 h period of test with minimum disturbance t
14、o the test specimens. 6.5.2 For test specimens exposed to ambient conditions for part of the test cycle, the ambient conditions shall be those described in 3.1.3, with a temperature of 23 ? 5 “C and a relative humidity of less than 75 %. 7 Test duration The test duration shall be as given in the spe
15、cification for the material or product being tested or as agreed between the pur- chaser and supplier. 10 Test report 10.1 The test report shall indicate the results of the test ac- cording to the specified criteria for evaluation of results. The result obtained for each test specimen and, when appr
16、opriate, the average result for a group of replicate test specimens shall be reported. The test report may, if required, be accompanied by photographic records of the test specimens. 10.2 The test report shall contain information about the con- duct of the test. This information may vary according t
17、o the purposes of the test and to the procedures specified, but a general list of the details likely to be required is as follows : a) the specification of the basis material; b) the type and dimensions of the test specimens or a description of the parts; 8 Cleaning of specimens after test At the en
18、d of the test period, remove the test specimens from the cabinet. Before they are examined, allow them to hang freely in a normal indoor atmosphere until any liquid corrosion products have solidified. First examine them with all corrosion products in position. Any cleaning carried out shall depend o
19、n the criteria laid down for the evaluation of the results of the test. 9 Evaluation of results Many different criteria for evaluation of the results of the test may be used to meet particular requirements, for example change in mass, alteration revealed by micrographic examin- ation, or change in m
20、echanical properties. The appropriate criteria will usually be indicated in the specification for the material or product tested. For most routine applications of the test, only the following need to be considered : a) appearance after test; b) appearance after removing superficial corrosion pro- du
21、cts; c) the number and distribution of corrosion defects, i.e. pits, cracks, blisters etc. These may conveniently be assess- ed by methods such as those described in IS0 1462 or IS0 4546, whichever is appropriate; d) the time elapsing before the appearance of the first sign of corrosion. c) the prep
22、aration of the test specimens including any cleaning treatment applied and any protection given to edges or other special areas; d) the type of coating with an indication of its surface finish: e) the number of test specimens of each coating or product subjected to the test; f) the methods, if any,
23、used to clean the test specimens after test, with, when appropriate, an indication of the loss of mass resulting from the cleaning operation; g) the temperature readings within the exposure zone of the test cabinet; h) the test duration (see 6.5 and clause 7); j) the angle of inclination of the test
24、 specimens during ex- posure; k) the character of any test panels placed in the cabinet expressly to check the correctness of the operating con- ditions, and the results obtained with them; m) whether the test was continuous or discontinuous (see 6.5); n) the concentration of sulfur dioxide used; p)
25、 the results of all inspections. 3 -,-,- IS0 6988-1985 (El Dimensions in millimetres Capacity 300 i 10 dm3 Capacity 300 + 10 dm3 7- / / C / / / C /- L- c -I- 500 I . Water trough Gas inlet m i I strip Gas inlet Temperature-regulating device (for example rod thermostat) L Pressure relief valve Figure 1 - Cabinet with door Temperature-regulating device (for example rod thermostat) i-I-.C:J J Gas inlet LPressure relief valve Figure 2 - Hooded apparatus -,-,-
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