Theoretical reason of reducing ball size of coarse grinding has been found through tests on compressive strength of rock and rupture stress of natural ore lump.

通过岩矿的抗压强度和自然矿块破断力力学试验研究，找到了降低粗磨机钢球尺寸的理论依据。

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Buy a lump of knitting wool to weave a ball of it.

买一团毛线去织一个毛线球。

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The force's police and crime commissioner (PCC) Ron Ball said former officers across the country were facing sometimes huge bills depending on the lump sum claimed.

BBC: Retired police officers face 'huge' pension tax bills