ASTM C448-88(R2021) pdf free download

ASTM C448-88(R2021) pdf free download.Standard Test Methods for Abrasion Resistance of Porcelain Enamels
3.2 The second test is intended for the determination of the resistance to surface abrasion of porcelain enamels for which the unabraded 45° specular gloss is 30 gloss units or less. It consists of determining the weight loss by a specified abrasive treatment and multiplying this weight loss by an adjustment factor associated with each abrasive tester, lot of abrasive, and lot of calibrated plate glass standards used. The adjusted weight loss is taken as an index of resistance to surface abrasion.
3.3 The third test is intended for the determination of the resistance of porcelain enamels to subsurface abrasion. It consists of determining the slope of the linear portion of the abrasion time-weight loss curve and multiplying by an adjust- ment factor associated with each abrasion tester, lot of abrasive, and lot of calibrated plate glass standards used. The adjusted slope is taken as an index of resistance to subsurface abrasion.
4. Significance and Use
4.1 When a porcelain enamel is first subjected to abrasion of the type involved in these tests, the rate of wear or attrition is relatively low. As the enamel is subjected to continued abrasion, the rate of wear increases until it reaches a steady value. Thereafter, the rate of wear remains almost constant until the enamel is penetrated and the underlying ground coat or metal exposed. The abrasion that occurs during the period of increasing rate-of-weight loss is defined as surface abrasion and results in reduced gloss and cleanability with high-gloss enamels and a modification of color, appearance, or surface texture, or combination thereof with low-gloss enamels. The abrasion that occurs during the period of steady rate-of-weight loss is defined as subsurface abrasion and results in the destruction of the continuity of the coating.
5.3 Apparatus for Measuring Specular Gloss, 4 conforming to the requirements of Test Method C346 and having a repeatable precision of not less than 60.5 gloss unit. Means shall be provided for positioning the specimen, with respect to the gloss head, so that, for a given orientation, the position of the specimen during the final gloss reading may be controlled to within 1 ⁄ 16 in. (1.6 mm) of that during the original gloss reading. N OTE 1—Care should be taken to keep the interior of the glossmeter free of dust. If a glossmeter is used with the opening at the top, a piece of phenolic resin or similar material should be placed over the opening when the instrument is not in use. The lenses should be cleaned at regular intervals with a soft camel’s-hair brush. The black gloss standard should be kept free of scratches, and should be protected by wrapping with a soft cloth when not in use.
5.4 Apparatus for Oscillating Specimens 5 —The apparatus used for oscillating the specimens during test shall impart to nine specimens simultaneously a horizontal circular motion such that every point on each specimen describes a circle 7 ⁄ 8 in. (22.2 mm) in diameter. The apparatus shall be provided with an automatic timing device capable of being preset to within 1 s of the desired time and shall operate at a frequency of 300 6 3 cpm (for machine manufactured prior to July 1981) or 345 6 3 cpm (for machines manufactured after July 1981). The apparatus shall be operated on a firm and level surface.
5.5 Retaining Rings—The retaining rings shall be con- structed of metal lined with rubber. The inside height and diameter of the rubber-lined ring shall be 1 3 ⁄ 16 6 1 ⁄ 16 in. (30.2 6 1.6 mm) and 3 7 ⁄ 16 6 1 ⁄ 16 in. (87.3 6 1.6 mm), respectively. Provision shall be made for clamping the retaining ring to an enameled metal specimen to produce a watertight seal. Means shall be provided for introducing an abrasive charge after the specimen is secured. Nine retaining rings are required.