NATIONAL STANDARD OF THE GRINDING BALLS IN CHINA (6)
6.1 The diameter of the casting grinding ball is measured by a tool with an accuracy of not less than 0.01 mm.
6.2 The analysis method of the chemical composition should be according with the standards of GB/T 223. 3, GB/T 223. 4, GB/T 223.11, GB/T 223. 18, GB/T 223. 23, GB/T 223. 26, GB/T 223. 28, GB/T 223. 60, GB/T 223. 63, GB/T 223. 67.GB/T, 69 and GB/T 223. 72. Spectral analysis, x-ray analysis and other analytical methods can also be used.
6.3 Rockwell Hardness test should be accord with the requirements of GB/T230.1 – 230.3. The surface hardness shall be measured within 3 mm below the surface of the grinding ball. The grinding ball hardness test surface shall be made by mechanical machining, wire cutting or electric spark technology. However, wire cutting or Electrical discharge machining must be machined to remove at least the 0.5mm thickness to avoid the heat affected zone.
6.4 The impact fatigue test of grinding balls shall be carried out according to the method specified in Appendix A.
6.5 The determination and calculation of the broken ball rate shall be carried out in accordance with the provisions of Appendix B.
6.6 The metallographic examination methods, including Matrix structure, morphology of carbide or graphite and amount of eutectic phosphorus, were performed according to GB / T 13298, GB / T 8263, GB / T 7216 and GB / T 9441 The spheroidizing grade of nodular cast iron is according to GB / T 1318.
6.7 The calculation of wear rate shall be carried out in accordance with the provisions of Appendix C.
7.1 The casting grinding ball shall be inspected by the supplier’s quality inspection department.
7.2 Chemical composition inspection shall be conducted in batches. If melt by induction furnace, each furnace as batch; if melt by cupola furnace, every 2hours as batch. Get one example to inspect the composition for each batch. If the test result is unqualified, then double sampling re-inspection, which still has 1 sample is unqualified, then the batch of grinding ball is unqualified.
7.3 The diameter and hardness of grinding balls are inspected in batches. The same-grade of the balls under the condition of stable melting process, melt by using the same melting furnace and the same heat treatment process (if heat treatment is needed), the certainquantity and the same size of grinding balls shall be called as the batc Three grinding balls were randomly selected from each batch for inspection. If one ball is unqualified, the same number of ball is randomly selected for re-inspection. The quantity of unqualified ball is more than or equal to 2. Then the batch of grinding ball is not qualified. If the hardness of the grinding ball is not qualified, repeated heat treatment is allowed.