Micro morphology of worn surface

The metallographic structure of the wear surface of the high chromium lining plate was observed under the scanning electron microscope. It was found that there are three typical morphologies: (1) furrow. The furrow is wide and shallow, and discontinuous, which is caused by the low stress scratch; (2) pit. The pit is formed by the carbide falling off and the matrix breaking, showing various shapes, Many small pits can be connected into large pits. (3) cracks. Radial cracks are formed around the tongue shaped pits, secondary cracks are formed at the bottom of the pits, and many pits are connected together to form large cracks

Wear mechanism

The proper rotation speed of the ball mill is n = 32D / 2R / min (D is the effective diameter of the mill barrel). During operation, the grinding ball and materials are raised to a certain height by centrifugal force and the effect of the lining plate with the ball, The liner periodically bears the combined action of high stress impact and low stress scratch of grinding ball and material. There are two kinds of wear mechanisms of liner: (1) furrow wear. The liner produces furrow under the action of low stress scratch of grinding ball and material. Because the matrix structure of high chromium cast steel is hard hidden needle martensite, the furrow is shallow and wide, Because of the large amount of eutectic and secondary carbide distributed on the matrix, the furrow is blocked and discontinuous or changed direction, forming discontinuous furrow. (2) brittle peeling. The structure of high chromium lining plate is crypto martensite + eutectic carbide + secondary carbide + residual austenite. Under the high stress impact of grinding ball and material, Micro cracks are produced around the carbides in the lining plate. Under the repeated impact of high stress, the micro cracks continue to expand, forming radial cracks and lamellar cracks around the carbides, and secondary cracks are produced at the bottom of the carbides. The expansion of the cracks makes the carbides loose and peel off, resulting in pits. When the radial cracks and lamellar cracks intersect forward, The wear of the first chamber liner of Φ 2.2m and Φ 2.4m ball mills is mainly ploughing wear and brittle peeling. The impact energy of liner is [3]:

U=Κ⋅Ν⋅G⋅ΗF=Κ⋅Ν⋅G (R1cosα+R1cosβ+V0sinα22g) F.

In the formula, u is the impact energy per unit section of the axial liner (J / cm2); K is the concentrated load coefficient, generally 2; n is the number of abrasives on the liner that can be impacted at the same time; G is the maximum weight of abrasives (kg); h is the maximum falling height of abrasives (m); F is the axial sectional area of each liner (cm2); R is the turning radius of the center of abrasives (m); V0 is the initial velocity of the abrasives thrown out at the breakaway point (M / s)

It can be seen that the load type of lining plate belongs to multiple repeated impact energy. The impact energy is directly proportional to the number of grinding balls simultaneously arranged on the mill diameter and the axial length of lining plate, and inversely proportional to the thickness of lining plate. In large ball mill, the impact energy of lining plate is larger. When the impact energy of lining plate is larger, the wear mechanism is mainly brittle peeling; when the impact energy is smaller, the impact energy of lining plate is mainly brittle peeling, The results are consistent with the test results

(1) High chromium liner is one of the main wear parts of ball mill

(2) According to the analysis of the process conditions and micro morphology of the lining plate, the main characteristics of the wear surface of the high chromium lining plate are furrow, pit and crack. The wear mechanism of the high chromium lining plate is furrow wear and brittle peeling. When the impact energy of the high chromium lining plate is large, the wear is mainly brittle peeling; when the impact energy is small, the wear is mainly ploughing

(3) In order to improve the service life of high chromium lining plate, it is necessary to select the appropriate matrix structure so that the material can obtain excellent mechanical properties, especially to improve the impact toughness, so as to reduce the formation of pits and cracks, enhance the ability to resist brittle peeling and reduce wear

(4) The wear test shows that the service life of high chromium cast steel used in ball mill is longer than that of high manganese steel