Centrifugal Tube Mills – What They Are and How They Work
A Tube Mill is a type of mill that consists of a large number of balls or cylindrical shaped material in its rotating shaft. The spinning of these balls is an essential component of the working of a mill as it is the means through which materials are fed through the mill. Tube Mills also is known as Tube Cylinder or Pit Mill is a type of mill that uses centrifugal force to spin the balls. This forces the material to be drawn into the grinding chamber from a distance. In fact, Tube Mills can be described as combining the function of two machines – that of anvil and a scroll mill.
Tube Mill work mainly in two ways: Centrifugal or Rotary and Ascentive or Vacuum. Centrifugal tube mills work on the principle of applying a force, usually by means of a roller, on the moving medium through the mill. These are generally considered to be the most efficient and least expensive of all working machines, as they require a relatively low force for performing the operation, and they have a high reproducibility.
On the other hand, tube mills that use the induction method use the concept of an electromagnetic induction, whereby a permanent magnet attracts the outside of a plate. This attracts the material that is inside the magnet, causing it to be drawn towards the field. With this method, there is no need for force or grinding of raw materials, and hence it is a cost-effective solution. However, even with the efficiency of this technology, it is expensive when compared to other methods. It has been found that because the power required for spinning the balls is inversely proportional to the size of the cavity, the power consumed is approximately the same for both types of milling.
Centrifugal tube mills grind the material using the concept of radial stream pressure, where the balls are accelerated to a high velocity. The large area of contact gives the operator a lot of scope for precise grinding. The balls are made of a hard metal that is subject to high stress while in use. The force with which the balls travel against the force of gravity results in grinding to a fine finish, as the small contact areas are large in relation to the diameter of the balls. This leaves the material of a finer quality than that obtained from vacuum grinding.
As the name implies, vacuum grinding uses no water or any gas to act between the grinding balls and the mesh, which is the component that catches the ball and crushes it into powder form. With this type of milling, the operator places the balls on the mesh and manually crushes them. This type of operation has a sturdier disadvantage because the water used is drawn into the mill from the vicinity around the grinding operation, reducing the viscosity of the balls. This makes it necessary for operators to periodically wipe the blades with water or other liquids. Forcing or propelling the balls in this mill is quite an operation, requiring manual labor for many operators.
Centrifugal tube mills are also used for formation testing purposes because they can rapidly cycle thousands of balls of different sizes and compositions. The operator places the balls inside the housing and cycles the machine through the variety of sizes and compositions until the desired formation occurs. This allows the operator to see very quickly whether the batch size and composition require changes to be made.