4.1 Transparent plastic materials, when used as windows or enclosures, are subject to wiping and cleaning; hence the maintenance of optical quality of a material after abrasion is important. It is the purpose of this test method to provide a means of estimating the resistance of such materials to this type and degree of abrasion.

4.2 Although this test method does not provide fundamental data, it is suitable for grading materials relative to this type of abrasion in a manner which correlates with service.

4.3 Comparison of interlaboratory data or the specification of a "haze" value has no significance if the hazemeter requirements given in 5.4 are not used. This is because light diffused from the surface of a Taber track is scattered at a narrow angle (Fig. 1 and Fig. 2) while light diffused internally by a specimen is scattered at a wide angle. In many hazemeters, when a diaphragm is inserted to limit the light beam to the width of the abraded track, the specular beam at the exit port becomes smaller. The dark annulus will then be greater than the 0.023 rad ± 0.002 rad (1.3° ± 0.1°) requirements of Test Method D1003. Since a large percentage of the narrow-angle forward-scattered light will not impinge on the sphere wall, "haze" readings become smaller. For hazemeters that have not been properly adjusted, the magnitude of this reduction is dependent both on the integrating sphere diameter and the reduction of the entrance beam.

FIG. 1 Light Scattering from Surface of Abraded Tracks (Photograph)

Note 1: This photograph shows light pattern of the scattering from the surface of a Taber abraded specimen. The circles show how increasing the 1.3° dark annulus dramatically changes the amount of light impacting the sphere wall.

FIG. 2 Light Scattering from Surface of Abraded Tracks (Graph)

Note 1: This graph shows goniophotometric curves for Taber abraded tracks. The specular angle of transmission is at 180°.

4.4 For many materials, there may be a specification that requires the use of this test method, but with some procedural modifications that take precedence when adhering to the specification. Therefore, it is advisable to refer to that material specification before using this test method. Table 1 of Classification System D4000 lists the ASTM materials standards that currently exist.

4.5 For some materials, abrasion tests utilizing the Taber abraser may be subject to variation due to changes in the abrasive characteristics of the wheel during testing.

4.5.1 Depending on abradant type and test specimen, the wheel surface may change (that is, become clogged) due to the transfer of coating or other materials from test specimens and must be cleaned at frequent intervals.

4.5.2 The type of material being tested and the number of test cycles being run is known to sometimes influence the temperature of the running surface of the wheel with an effect on the final haze measurement. To reduce any variability due to this temperature effect, stabilize the wheels surface temperature prior to performing actual measurements. This shall be accomplished by conducting multiple refacings on an ST-11 refacing stone, followed by a test on the sample material to be tested (with results to be discarded).