Poor quality grinding media influence the whole grinding system, including that grinding media consumption, effectiveness of grinding, power consumption and so forth. However good quality grinding media helps you improve production and energy efficiency and minimize operating costs. 

Taking the common failure modes of grinding balls, we show you Allstar’s solution and quality assurance.

Common casting defects & Allstar solution

The casting ball must be free from casting defects such as shrinkage cavity and gas porosity. As shown in Figure 1, the ball of US(Allstar) is free from any casting defects. Comparatively, the ball of OTHERS(competitors) shows obvious casting defects. 

Figure 1. Photograph of OTHERS casting balls showing casting defects such as shrinkage and gas porosity 

Casting defects will lead to premature failure of the grinding media during mill operation, as shown in Figure 2. 

Figure 2. Photograph of OTHERS casting balls showing Fracture in the mill

The casting defects will also have detrimental effects on both impact and abrasion resistance of the grinding ball. The impact fatigue resistance is very important and needs to be controlled by a proper heat treatment step. Or else the repeated impact of the grinding balls may cause one (or more) of the following to happen to the ball:

• Small pieces of the surface may spall off (micro-spalling as shown in Figure 3)
• Large pieces of the surface may spall off (macro-spalling as shown in Figure 4)
  
• The ball may fracture through the centre (see a typical example in Figure 5)

Figure 3. Photograph of OTHERS casting balls showing Micro Spalling 

Figure 4. Photograph of OTHERS casting balls showing Macro Spalling

Figure 5. Photograph of OTHERS casting balls showing fracture through the centre 

US (Allstar) casting ball is produced by metal mould that can be faster cooling the smelted metal plus strict time and temperature control at smelted metal make structure finer and more uniform. The metal mold and the Allstar advanced heat treatment technology make the Allstar casting ball with good impact fatigue resistance the least abrasive wear. 

Common forged defects & Allstar solution

The forged grinding balls need to be free of defects such as flats, pits, soft spots and cuts. The surface should be smooth. The mean diameter between two parallel planes on the ball surface, sphericity or the deviation from a true spherical form (out-of-round condition) is also an important step in quality control. A typical example of the defects found in OTHERS forged grinding balls is shown as Figure 6. 

Figure 6. Photograph of OTHERS forged balls showing obvious forged defects 

For forged ball, the most important to quality is the raw material-round steel. Allstar purchases round steel from national large scale steel mills. Quality is fully assured.

Nonuniform hardness throughout & Allstar solution

The hardness influences the abrasion resistance of the grinding balls. The uniform hardness gradient yields a grinding ball with good abrasive wear resistance. A steep hardness gradient is usually viewed as undesirable because of faster wear of softer constituents.

Below is a hardness comparison US VS OTHERS. 

OTHERS ball has the same AVH figure as US ball. But after three quarters of the radius, the hardness of OTHERS ball dips below that of US ball. Once the ball has worn down to approximately 2/3 diameter, the remainder will wear away very quickly. The rapidly wearing grinding ball will give rise to an unstable and imbalanced ball charge.

Allstar heat treatment production line is computerized giving uniform surface hardness and comtrolled cross-sectional harness essential for very even wear. Comparatively, the cross sectional hardness profile shows US ball will wear evenly throughout its life. This will give a better size distribution in the mill, and avoid ‘dead zone grinding’. The shape of the ball will be preserved for much longer, giving a far more efficient grind.
High quality such as Allstar offer always saves money in the long run.