Grinding Media Material Used In Ball Mill

Release time：2021-10-12

The grinding body of a ball mill  

Four, grinding body  

(-) type and material of grinding body (1) type of grinding body  

Different shapes and sizes of grinding bodies have different grinding effects in the grinding process.  The grinding body used by the ball mill in cement factory is classified as follows according to its shape:  

1. Steel ball Steel ball is a kind of grinding body widely used in ball mill.  According to the milling process requirements, usually choose various specifications of Q20-120mm steel ball;  For the coarse grinding bin of the ball mill, various steel balls of Q50-100mm are generally selected, and various steel balls of G20-50mm are selected for fine grinding bin.  Steel forgings Steel forgings are short cylindrical in shape and their specifications are expressed in millimeters of length multiplied by diameter.  Steel forging is generally used in the fine mill bin of the open circuit ball mill and also in the fine mill bin of the closed circuit ball mill.  

Of the specifications of the commonly used steel forging o15mmx20mm, p18mmx22mm, p20mmx25mm, p25mmx30mm, etc.  The diameter of steel forging in small mills is as small as o12mm or less.  

3. Steel bar Steel bar is an abrasive body used in rod mills.  Bar specifications are expressed in millimeters of length multiplied by diameter.  Steel rod diameter is generally selected  

40-90mm, the rod length should be 50-100mm shorter than the length of the mill rod bin.  For example: O2.4 ×13mm wet baseball mill, the effective length of the first chamber is 2.75m, the specification of steel rod used is O60 ×2650mm, P65x2650mm and O70x2650mm.  

(2) material selection of grinding body  

The abrasive body should have high wear resistance and impact resistance.  Require its material hard, wear-resistant and not easy to crack.  Burrs and cracks are not allowed on the surface of the grinding body, and the roundness of the steel ball shall not exceed 2% of its diameter.  

In cement industry, the consumption of grinding body and lining plate is quite large. The quality of grinding body material not only affects the grinding efficiency of the mill, but also relates to the operation rate of the mill.  Countries around the world have made achievements in improving the wear resistance of abrasives. From the 1960s to the 1970s, high chromium cast iron (steel) balls have been widely used.  Japan mainly has high chromium steel ball, low chromium steel ball and alloy white cast iron ball;  Germany mainly has high chromium cast iron ball and low alloy steel ball;  Alloy steel balls commonly used in the United States and Canada.  In recent years, in China's cement industry, ball mill grinding body materials are as follows  

1. High chromium cast iron high chromium cast iron is a kind of high chromium content of alloy white cast iron, its characteristics are wear resistance, heat resistance, corrosion resistance, and has a considerable toughness.  The surface hardness of high chromium cast iron ball with Martensite as matrix can reach 54-66 HRC.  The wear resistance of high chromium cast iron ball is 8-12 times that of ordinary carbon steel ball.  2. Low chromium cast iron low chromium cast iron contains a small amount of chromium, can maintain the white cast iron to obtain martensitic metallography.  Low chromium cast iron has lower toughness than chromium cast iron, but has better wear resistance, so it is suitable to be used as lining plate in pellet, iron forging and fine run-in.  

3. Forged bearing steel Forged bearing steel can be used to manufacture steel balls of various diameters, with carbon content of about 1.0%, chromium content of about 1.5%, and other elements of conventional content.  The consumption of the ball is higher than that of the high chromium cast iron ball, but because of the low alloying element content.  There is still a wider use of the market.  

Baseball mill steel rod material requirements of high hardness, wear resistance, constantly broken, not bending, commonly used 4OMn steel or 70 high carbon steel rolled.  (2) Reasonable loading capacity of grinding body  

(1) Calculation formula of filling rate  

The percentage of the filling volume of the grinding body to the effective volume of the mill is called the filling rate of the grinding body.  

100%  

Type in the  

- Grinding Grinding body filling rate, %;  

V, -- Grinding volume of grinding body filling, ms;  V -- Effective volume of mill (bin), m3.  (2) The filling rate is calculated by measuring the grinding surface height  

When it is necessary to verify whether the filling rate of the mill is consistent with the value specified in the ball matching scheme after loading the grinding body, or when it is necessary to supplement some steel balls and steel forging due to the wear of the grinding body during the operation of the mill, the filling amount of the grinding body is usually calculated by measuring and looking up tables.  The method is to measure the effective diameter D of the mill with a ruler when there is no material or only a small amount of material in the mill.  The vertical distance from the grinding surface to the top liner is measured through the center of the mill.  , and then calculate the value of H/D. The relationship is as follows (Figure 7-11).  

.__sin;  '  

Cloud = 360-2  

D is the same thing as h is equal to 2 cosine of 5  

H = Di book, cos5  

Where, α -- filling rate of the grinding body of the mill;  

β -- the central Angle of the filling surface of the grinding body to the center of the mill;  H -- Distance from the center of the mill to the filling surface of the grinding body, m;  Dt -- effective diameter of mill. M;  

H -- Grinding grinding body filling surface height, M.  

Figure 7-11 Grinding center height of the filling surface of the grinding body H/D values are listed in Table 7-2.  Table 7-Relationship between 2H/D value and filling rate  

H/D.  

0.72  

0.71  

0.70  

0.69  

0.68  

0.67  

p(%)  

22.9  

24.1  

25.2  

26.4  

27.6  

28.8  

H/D,  

0.66  

0.65  

0.64  

0.63  

0.62  

0.61  

p(%)  

30.0  

31.2  

32.4  

33.7  

34.9  

36.2  

Grinding machine with filling rate greater than 32%.  The filling rate can also be calculated directly using the following empirical formula  

o= 113 -126 D  

In the formula, pO -- grinding grinding body filling rate, %.  

When measuring the filling surface height of grinding body, attention should be paid to the filling condition of grinding material.  If the material surface is 15-20mm higher than the abrasive surface, the error of 2%-4% should be deducted from the calculated filling rate.  

The filling rate of the grinding body has a great influence on the grinding efficiency of the mill. If the filling rate is too high or too low, the grinding efficiency will decrease.  There are many factors affecting the optimal filling rate of the grinding body, such as the form of the mill, specifications, part of the structural characteristics and the performance of the grinding material.  Therefore, the best filling rate should be determined by production test and adjusted appropriately according to the varying degree of influencing factors.  Table 7-3 shows the general abrasive filling rate of various mills in Cement factories in China.  

Table 7-3 Filling rate of grinding bodies of various mills in cement factories  

Mill form  

Fill rate p (%)  

Mill form  

Fill rate p (%)  

Middle discharge or tail discharge dryer mill  

25 to 28  

- Class CLOSED circuit long mill  

30-36  

Open circuit long mill  

25 to 30  

Select powder to dry short ball mill  

35-38  

The barn of a baseball mill  

20-25  

Two stage closed circuit short ball mill  

40-45