Ball mills: design and operating principle
The Samara Strommashina plant has been manufacturing ball mills since the middle of the twentieth century. Hundreds of mills of most diverse modifications have been manufactured over 70 years of the plant operation. Currently the Strommashina manufactures the main types industrial ball mills designed for long trouble-free operation.
Ball mill design is rather simple. This grinding equipment is a drum filled with metal or cast iron balls (grinding media). It is used mostly for production of bulk construction materials, paints, pyrotechnical devices, ceramics and in other industries.
The ball mill patent was sealed more than 180 years ago. It is mentioned in "Industry and engineering" encyclopaedia dated 1896. This mechanism was described as an efficient device for grinding sand in glass production.
The mill was named so due the shape of the chamber in which materials are processed, and also due to the impact element name.
The main classifications
The ball mill is classified based on the properties of the processed raw material:
- device for dry grinding.
- device for wet grinding. Based on the ball type the mills are classified as those
- with steel balls;
- with cast iron balls;
- with balls made of other alloys;
- with ceramic balls.
The Strommashina plant designs and manufactures the both ball types.
Design and operating principle
A ball mill is a hollow drum rotating around its horizontal axis. It is filled with grinding balls (impact elements).
As a result of rotation, balls on the internal drum surface lift and then fall down under the gravity action. The source material is permanently fed through one of spigots. The raw material particles are ground by means of smashing, abrasion and collision. The drum is discharged through other spigot.
If the mill is designed for dry grinding, then the processed raw material is discharged using air flow. Air is delivered by drawing it off from the drum. If wet grinding is carried out, then material is carried by a water flow.
As rotation frequency grows, the drum mill capacity grows first. It is because the balls lift to significant height first. However, soon, if the speed continues to grow, the balls begin to "stick" to the internal drum surface. In this case the crushing plant capacity s drops down abruptly.
Upon expiry of some mill operation time the mill operating elements (grinding balls) get worn. In this case they are just added into the drum together with source material. The maximum filling level of impact elements is 50 mm below the inlet nozzle circumference.
Ball diameter is 30 to 60 mm.
The maximum size of source material particles is 10 to 50 mm.
The drum length is 1500 to 10000 mm
The drum diameter is 900 to 4000 mm
Rotation frequency is 10 to 40 rpm.
Motor power is at least 22 kW.
Capacity is at least 2 t per hour.
Advantages and application
The drum mill is efficient in the following applications:
- coal crushing:
- mineral powder, gypsum grinding;
- marble crushing for microcalcite production;
- grinding of raw material and clinker for cement production.
The main advantages of the ball mill:
- simple design.
- grinding degree control function.
- reliable mechanisms.
Such crushing equipment has its drawbacks which are usually specified as high price, large dimensions and high power consumption. However, the Strommashina has improved the ball mill design over the past decades. It eventually enabled optimising power consumption and reducing the mill manufacture cost. In addition, the plant engineering department is available for calculating the mill dimensions for customised production needs, and for performing all necessary equipment installation and start-up works.