AATCC 133-2020 Test Method for Colorfastness to Heat: Hot Pressing.
13. Precision and Bias
13.1 Precision. Precision for this test method has not been established. Until a precision statement is generated for this test method, use standard statistical tech- niques in making any comparisons of test results for either withinlaboratory or be- tween-laboratory averages.
13.2 Bias. Colorfastness to heat, hot pressing, can be defined only in terms of a test method. There is no independent method for determining the true value. As a means of estimating this property, the method has no known bias.
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14.3 To obtain the pressure per unit area 40 ± 10 g/cm 2 the total area of the wool flannel padding should bear a suitable relationship to the mass of the plate pressing down on the padding. If the fabric to be tested has an ap- preciable thickness, it is necessary either to in- crease the area of the test specimen or to augment the pressure-bearing surface using a suitable template made from the same material as the test specimen. If the plates of the heat- ing device are smaller than the specimen size, the pressure depends on the design of the apparatus (ratio of mass and area of top plate).
14.4 For less critical testing, a household iron may be used; but its temperature should be measured with a surface pyrometer or with temperature sensitive papers. The iron should be weighted so that its area and total weight are in the approximate ratio to exert a pressure of 40 ± 10 g/cm 2 . However, due to tempera- ture fluctuation during on-off differences over the iron surface, the accuracy and reproduc- ibility are limited. When a hand iron is used, it must be stated in the report.
14.5 The heat resistant sheet is used for in- sulation and should be smooth and not warped. It is best to complete specimen assembly on the heat resistant sheet before placing it on the heating device. This insulating material must be used, whether the bottom plate is heated or not, to prevent heat to or from the bottom of the test assembly.
14.6 The pressing temperature selection de- pends to a large extent on the type of fiber and on the construction of the fabric or garment. In the case of blends, use the temperature appropriate to the fiber with the lowest heat resistance.
14.7 For very critical evaluations and in the case of litigation, ratings must be based on the geometric Gray Scale for Staining or the instrumental equivalent.AATCC 133 pdf download.