ISO 12844 pdf download

ISO 12844 pdf download.Raw optical glass — Grindability with diamond pellets — Test method and classification 1 Scope This International Standard specifies a test method for determining the grindability of raw optical glass with diamond pellets, and defines a classification of optical glasses according to the grindability determined by this method. 2 Terms and definitions For the purposes of this International Standard, the following term and definition applies. 2.1 grindability volume removed from a glass specimen when it is ground with a diamond pellet tool for a fixed period of time, relative to that removed from a standard reference glass 3 Principle The grindability of any glass type is compared to a standard reference glass type and classified. Twenty samples of the unclassified glass and twenty samples of the standard reference dense barium crown glass are first prepared using aluminium oxide and then ground using a standard diamond pellet tool and water coolant for a period of 30 s. The samples are weighed to determine the mean mass of material removed, taking into account the density of the glass to determine the volume reduction. The grindability class of the unknown glass is established according to the classification table given in this International Standard. 4 Reagents and materials 4.1 Standard diamond pellet, 1 0 mm in diameter and 3 mm thick. The pellet shall be produced by the hot pressing technique using diamond of particle size 5 ?m to 1 2 ?m and a copper-tin alloy consisting of 80 % copper (Cu) and 20 % tin (Sn). The concentration shall be 1 5, corresponding to 0,66 carat/cm 3 (= 0,1 32 g/cm 3 ). In order to obtain reproducible grindability test results, it is considered necessary that all laboratories use only standard diamond pellets from the same producer. 1 ) 4.2 Dressing tool, of cast iron, about 280 mm in diameter. 4.3 Abrasion blocking tool as used in 6.3, of flat cast iron, about 250 mm in diameter. 4.4 Abrasive grains, of fused aluminium oxide with a mean grain size of 1 1 ,5 ?m to 1 4,5 µm. 5 Apparatus Usual laboratory equipment, together with the following. 5.1 Grinding test apparatus (see Figure 1 ), consisting essentially of: 5.1.1 Diamond pellet tool (see Figure 2), having a diameter of 1 1 5 mm and constructed of cast iron. The tool shall rotate horizontally at a constant speed. The flat tool...