5.1 The grinding balls tolerance of the diameter should be accord with Table 1.

5.2 The main chemical composition of each grades should be accord with Table 2.

Name	Grade	Chemical Composition (%)
		C	Si	Mn	Cr	Mo	Cu	Ni	P	S
Alloyed cast iron grinding balls	ZQCr26	2.0-3.3	≤ 1.2	0.3-1.5	>23.0-30.0	0-3.0	0-1.2	0.-1.5	≤1.0	≤0.06
Alloyed cast iron grinding balls	ZQCr20	2.0-3.3	≤ 1.2	0.3-1.5	>18.0-23.0	0-3.0	0-1.2	0.-1.5	≤1.0	≤0.06
Alloyed cast iron grinding balls	ZQCr15	2.0-3.3	≤ 1.2	0.3-1.5	>14.0-18.0	0-3.0	0-1.2	0.-1.5	≤1.0	≤0.06
Alloyed cast iron grinding balls	ZQCr12	2.0-3.3	≤ 1.2	0.3-1.5	>10.0-14.0	0-3.0	0-1.2	0.-1.5	≤1.0	≤0.06
Alloyed cast iron grinding balls	ZQCr8	2.1-3.3	≤ 2.2	0.3-1.5	7.0-10.0	0-1.0	0-0.8	–	≤1.0	≤0.06
Alloyed cast iron grinding balls	ZQCr5	2.1-3.3	≤ 1.5	0.3-1.5	4.0-6.0	0-1.0	0-0.8	–	≤1.0	≤1.0
Alloyed cast iron grinding balls	ZQCr2	2.1-3.6	≤ 1.5	0.3-1.5	1.0-3.0	0-1.0	0-0.8	–	≤1.0	≤1.0
Ductile iron grinding balls	ZQQTB	3.2-3.8	2.0-3.5	2.0-3.0	–	–	–	–	≤1.0	≤0.03
Ductile iron grinding balls	ZQQTM	3.2-3.8	2.0-3.5	0.5-1.5	–	–	–	–	≤1.0	≤0.03

5.3 Mechanical Property

5.3.1 The surface hardness should be accord with Table 3

NAME	GRADE	SURFACE HARDNESS /HRC
Alloyed cast iron grinding balls	ZQCr26	≥58
Alloyed cast iron grinding balls	ZQCr20	≥58
Alloyed cast iron grinding balls	ZQCr15	≥58
Alloyed cast iron grinding balls	ZQCr12	≥58
Alloyed cast iron grinding balls	ZQCr8	≥48
Alloyed cast iron grinding balls	ZQCr5	≥47
Alloyed cast iron grinding balls	ZQCr2	≥45
Ductile iron grinding balls	ZQQTB	≥50
Ductile iron grinding balls	ZQQTM	≥52

5.3.2 The hardness between the casting head surface to the centre of the balls can not be over 3 degrees. Diameter balls size over dia90mm, the grade is ZQCr2 and the other special situation, the hardness differences negotiate between the contracting parties.

5.3.3 The broken rate of the Grade ZQCr26, ZQCr20, ZQCr15, ZQCr12 grinding balls should be less than or equal to 1%. The other grades, the broken rate should be less than or equal to 2%. The special conditions, the requirements need to negotiate between the contracting parties.

5.3.4 Whether regarding the impact value as the acceptance standard depends on the contracting parties.

5.3.5 Casting grinding ball does not allow cracks and the defects, like slag, sand hole, shrinkage hole, shrinkage porosity, gas hole, cold separation, etc. Which will affect the using.

5.3.6 MetallographicStructure

The metallographic structure is the essential quality inspection content in the production process of casting grinding ball. Not as acceptance standard for products. If there is any special need, both parties should agree on it.