ASTM-C839:82(R2020) pdf free download – Standard Test Method for Compressive Stress of Porcelain Enamels by Loaded-Beam Method.
7.1.4 Fire the strips in a vertical hanging position at the optimum time and temperature for the ground coat. The preferred procedure is to tire multiples of six simultaneously. Cool in a suspended position, avoiding drafts or forced cooling.
7.1.5 Weigh and record the weight of each strip to the nearest 0.01 g.
7. 1.6 Place each strip on the test apparatus with the scrihed side down.
7.1.7 Measure and record the ground coat residual load, which is the weight in grams required to cause the strip to just rest on the three knife edges of the fixture. Discard any strips having zero or negative stress (reverse bow) or having positive load of more than 50 g.
NOTE 2—More consistently unifom and usable specimens will result if a spraying technique is developed whereby a few hundredths of a gram less enamel is applied to the back than to the face. This practice reduces the possibility of developing a concavity in the strip as viewed from the face side.
7.2 Application of Test Enamel:
7.2. 1 Apply test enamel to the face side of six ground- coated specimens by spraying. Apply the enamel to yield a dry weight of 30 g/ft2 (323 g/m2, or 2½ g per strip). Use a relatively dry spray to avoid formation of beads along edges. After drying and cooling, use a template to brush back I ‘V16 in. (43 mm) from each end of strip, leaving 8% in. (179 mm) of cover coat on the strip. Wipe the edges and back of strips with a felt pad and dust with a soft-bristled brush or wool duster.
7.2.2 Fire panels, again in a vertical hanging position, at optimum temperature and time for the test enamel as cover coat. Cool in a vertical position, avoiding forced cooling. Rapid cooling produces greater residual compressive stresses.
7.2.3 Weigh each strip to the nearest 0.01 g and record.
7.3 Measurement of Load:
7.3.1 Center each coated strip individually over the three knife edges of the fixture with face side upward and punched hole to left. Stops or blocks may he of aid in centering the strips on knife edges.
7.3.2 Centrally load the strip with slotted weights over the center knife edge until the strip just touches the central knife edge. A strong diffuse light source behind the test fixture facilitates observation of the end point.
7.3.3 Measure and record the uncorrected compressive load of each of the cover-coated test strips. The load, in grams. required to cause the strip to just touch the central knife edge is the uncorrected compressive load.
7.3.4 Corrected load is uncorrected compressive load minus residual ground coat load (see 7.1.7).
8. Calculation
8.1 Calculate the corrected load. L, by subtracting the residual ground coat load from the uncorrected compressive lOad.