Research on Early Failure of Low Chromium Grinding Balls (1)

Abstract: Through the falling test and chiseling-hammering test conducted with the metal-sand composite mould cast low chromium grinding balls, it was concluded that the peeling phenomenon had occurred with many balls before their early failure. The cracking initiated at the area of interface between the metal mould and sand mould, then the debris peeling occurred, and the debris peeled from the area of metal -the sand interface of the composite mould. By analyzing the fracture morphology of the peeled debris, it was considered that the fracture type of ball debris at the metal-sand mould interface was of the grain-through brittle cleavage fracture.

Keywords: low Chromium grinding ball;ball falling test;chiseling test;fracture mechanism

HANG Xiao-bo,YIN Yu-huan,YUAN Yun-she,LIU Gen-sheng,CHEN Wei-ming, Wang Y-chun,LI Li,WEN Mao-dong,ZHANG Song

(1.Shanghai Baoshan Iron & Steel Co. Ltd., Shanghai 201900, China; 2. Materials Science and Engineering College, Tianjin University, Tianjin 300072, China; 3. Machine -Electrical Engineering Department, Jiangsu Information Vocational Technical Institute, Wuxi 214153, China; 4. Materials Science and Engineering College, Hebei University, Tianjin 300130, China)

Among many kinds of grinding balls and their production technology, the grinding balls made of metal-type-sand mold occupy 90% of the grinding ball market. However, in the actual production, many factories that produce low chromium white cast iron grinding balls by using the metal type — sand mold have found that the grinding balls’ early failure is a serious problem, which seriously affects the grinding ability of the grinding machines. Therefore, it has far-reaching theoretical and practical value to study the early failure of low chromium white cast iron grinding ball. The pear-shaped grinding ball is shown in Fig. 1.

low chromium grinding balls picture

1.Test method and content

1.1 Balls falling test

According to the ball mill’s actual working condition, the table-type ball falling test machine is designed to simulate the running form of the ball mill, the main components are the motor, the gearbox, the transmission shaft, and the thick-walled rotating tube. As shown in Fig. 2, the rotating tube’s diameter is 200 mm, the wall thickness is 20 mm, and the revolution is 18 rad/min. The test is carried out by using a bench-type ball-dropping machine. The test is divided into 6 groups, 5 grinding balls in each group, 3 grinding balls of φ80mm, and 2 grinding balls of φ60mm.

2 balls falling test structure

2.2 Gouge test

The grinding balls were divided into 3 groups, 2 in each group, one ball with φ80mm and one ball with φ60mm—each group of grinding balls into the cone-shaped cylinder body, artificial with a hammer chisel.

2.3 Fracture morphology observation

By studying the peeling part’s fracture morphology in the falling ball test, determine the fracture was grinding ball spalling.

2.Test results and analysis

2.1 Analysis of falling ball test results

Put a group of grinding balls into a rotating tube, start recording time, while the test machine is rotating, hear not only the rolling sound of the grinding balls and the sound of impact but also the sound of objects sliding, immediately stop the machine at this time, open the end cover, check the test results as shown in Table 1. As can be seen from table 1,18, grinding balls with a diameter of 80 mm and 12 grinding balls with a diameter of 60 mm were used in the six groups of tests. The most debris produced by the grinding balls was at the junction of the metal mould and the sand mould, see the red arrow in Figure 3. The macro-morphology of the flaked fragments is shown in figure 4. The results show that after working for a period of time, the grinding ball first produces cracks at the boundary of the metal mold, and then begins to flake off, which is the main reason for producing many grinding ball fragments in the ball mill. After the grinding ball spalling at the part of the metal mould, the part is ground into the pear-shaped grinding ball as shown in Fig. 1 in a short time under the abrasion and impact of the material and the grinding ball, which results in the reduction of the grinding ability of the ball mill.

peeling location of the grinding balls
fracture macro-morphology of peeled debris

Next: Research on Early Failure of Low Chromium Cast Grinding Balls (2)