What particle size range does ball mill grinding produce?

Ball Mill The ball mill has been around for eons. There are many shapes and sizes and types. There is a single enclosed drum-type where material is placed in the drum along with a charge of grinding media. These can be in various shapes, and typically they are balls. There is a whole science in the size of the starting material versus the ball size, shape material of construction and charge percentage of grinding media. All of these variables affect particle size, shape, and grinding efficiency. This type of grinding is very good for abrasive materials to prevent contamination. The grinding media as well as the interior surfaces of the mill can be lined with abrasion resistant materials suited to the material being ground. In some cases, it can even be the material being ground. However, the batch type system is not a very efficient means of grinding. There is a variety of ball mill that is a continuous process versus a batch process. It has an external classifier which returns the oversized material to the ball mill for further milling. This system is much more efficient in the grinding ability, but it is much more difficult to line the entire system with wear parts to grind an abrasive material. 

Ball mill grinding is one method of crushing ore to an appropriate size fraction. Specifically, ore is put into a large receptacle (a drum) and then it rotates slowly around. Inside the receptacle, there are balls, usually made of metal, that as the ore is rotated around the revolving drum the ore is crushed as the balls rise and fall. The drum has a slight tilt to it, from one end to the other so that the ore slowly works its way to discharging end. The trick or art to all of this is to rotate the drum at a distinct rpm and the balls are harder than the ore so as to efficiently crush the continuous stream of ore to the desired size at the discharge end.

The ball mill is a key piece of equipment for grinding crushed materials, and it is widely used in production lines for powders such as cement, silicates, refractory material, fertilizer, glass ceramics, etc. as well as for ore dressing of both ferrous and non-ferrous metals. The ball mill can grind various ores and other materials either wet or dry. There are two kinds of ball mill, grate type and overfall type due to different ways of discharging material. There are many types of grinding media suitable for use in a ball mill, each material having its own specific properties and advantages. Key properties of grinding media are size, density, hardness, and composition.

• Size: The smaller the media particles, the smaller the particle size of the final product. At the same time, the grinding media particles should be substantially larger than the largest pieces of material to be ground.
• Density: The media should be denser than the material being ground. It becomes a problem if the grinding media floats on top of the material to be ground.
• Hardness: The grinding media needs to be durable enough to grind the material, but where possible should not be so tough that it also wears down the tumbler at a fast pace.
• Composition: Various grinding applications have special requirements. Some of these requirements are based on the fact that some of the grinding media will be in the finished product. Others are based in how the media will react with the material being ground.Where the color of the finished product is important, the color and material of the grinding media must be considered.
• Where low contamination is important, the grinding media may be selected for ease of separation from the finished product (i.e.: steel dust produced from stainless steel media can be magnetically separated from non-ferrous products). An alternative to separation is to use media of the same material as the product being ground.
• Flammable products have a tendency to become explosive in powder form. Steel media may spark, becoming an ignition source for these products. Either wet-grinding, or non-sparking media such as ceramic or lead must be selected.
• Some media, such as iron, may react with corrosive materials. For this reason, stainless steel, ceramic, and flintgrinding media may each be used when corrosive substances are present during grinding.

The grinding chamber can also be filled with an inert shield gas that does not react with the material being ground, to prevent oxidation or explosive reactions that could occur with ambient air inside the mill.

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