5.3 Abrasion (Aa)

A sample of size 30 x 30 x 10 mm is lapped on a 250 mm diameter cast iron flat, rotating at 60 rpm. The test piece is located 80 mm from the centre of the flat and is under a 9.8 N {1kgf} load. 20 ml of water containing 10 g of aluminous abrasive as the lapping material, with mean grain size 20 µm (#800), is supplied evenly to the test piece for 5 minutes. The weight loss of the test piece is then measured and compared to the standard glass by using the following equation:

Glasses showing a higher value are less resistant to abrasion.