Method and apparatus for detaching frozen charge from a tube mill

Abstract

A method and associated apparatus for detaching a frozen charge from an inner wall of a grinding pipe of a tube mill such as is used for grinding. The method includes controlling a driving device of the grinding pipe to detach a frozen charge from an inner wall of the grinding pipe, which driving device is operable to apply a driving torque to the grinding pipe. Controlling the driving device includes varying the driving torque applied to the grinding pipe around a predetermined reference level.

What is claimed is: 
     
       1. A method for detaching a frozen charge from an inner wall of a grinding pipe, the method comprising the steps of:
 controlling a driving device of the grinding pipe to detach a frozen charge from an inner wall of the grinding pipe, which driving device is operable to apply a driving torque to the grinding pipe, wherein controlling the driving device comprises: 
 varying the driving torque applied to the grinding pipe, wherein the driving torque is always positive so that the grinding pipe does not change its rotational direction while varying the driving torque. 
 
     
     
       2. The method as claimed in  claim 1 , wherein varying the driving torque comprises varying the driving torque in a stepwise manner about the a predetermined torque reference level. 
     
     
       3. The method as claimed in  claim 1 , wherein varying the driving torque comprises varying the driving torque in any pattern about the a predetermined torque reference level and comprised within a torque range proportional to the predetermined torque reference level. 
     
     
       4. A controller for detaching a frozen charge from an inner wall of a grinding pipe, the controller comprising:
 a controller operable to control a drive device of the grinding pipe to detach a frozen charge from an inner wall of the grinding pipe, which driving device is operable to apply a driving torque to the grinding pipe in one rotation direction so that the grinding pipe does not change its rotational direction, and vary the driving torque applied to the grinding pipe such that the driving torque is always positive so that the grinding pipe does not change its rotational direction about a predetermined and increasing torque reference level. 
 
     
     
       5. The method as claimed in  claim 1 , wherein varying the driving torque comprises varying the driving torque sinusoidally about the a predetermined torque reference level. 
     
     
       6. The method as claimed in  claim 1 , wherein controlling the driving device comprises varying the driving torque applied to the grinding pipe about a predetermined and increasing torque reference level. 
     
     
       7. The method as claimed in claim 1, wherein the driving torque prevents back-lash. 
     
     
       8. The method as claimed in claim 1, wherein the driving torque is always kept in the same direction during the controlling. 
     
     
       9. The method as claimed in claim 1, wherein the driving torque is varied between a minimum torque and a maximum torque, the minimum torque always being positive. 
     
     
       10. The method as claimed in claim 1, wherein the driving torque is varied between a minimum torque and a maximum torque defined by a torque factor, the torque factor being smaller than 1. 
     
     
       11. The method as claimed in claim 1, wherein an oscillation amplitude of the driving torque increases as a predetermined torque reference level increases such that the driving torque does not reach a negative torque. 
     
     
       12. The method as claimed in claim 1, wherein the second derivative of the driving torque with respect to time repeatedly becomes negative while a first derivative of the driving torque remains positive. 
     
     
       13. The method as claimed in claim 1, wherein movement of the grinding pipe is limited to a maximum of 75° while detaching the frozen charge. 
     
     
       14. The method as claimed in claim 1, further comprising bringing the grinding pipe back toward an equilibrium position after the controlling and repeating the controlling again. 
     
     
       15. The method as claimed in claim 14, wherein the repeated controlling is in a same direction. 
     
     
       16. The method as claimed in claim 14, wherein the repeated controlling is in an opposite direction. 
     
     
       17. The method as claimed in claim 1, wherein controlling the driving device comprises varying the driving torque applied to the grinding pipe about a predetermined and increasing torque reference level, the driving torque prevents backlash, the driving torque is always kept in the same direction during the controlling, and the driving torque is varied between a minimum torque and a maximum torque, the minimum torque always being positive. 
     
     
       18. The method as claimed in claim 17, wherein an oscillation amplitude of the driving torque increases as the predetermined torque reference level increases such that the driving torque does not reach a negative torque, and the second derivative of the driving torque with respect to time repeatedly becomes negative while a first derivative of the driving torque remains positive. 
     
     
       19. The method as claimed in claim 18, wherein movement of the grinding pipe is limited to a maximum of 75° while detaching the frozen charge, and further comprising bringing the grinding pipe back toward an equilibrium position after the controlling and repeating the controlling again. 
     
     
       20. A method for detaching a frozen charge from an inner wall of a grinding pipe, the method comprising the steps of:
 controlling a driving device of the grinding pipe to detach a frozen charge from an inner wall of the grinding pipe, which driving device is operable to apply a driving torque to the grinding pipe, wherein controlling the driving device comprises:   varying the driving torque applied to the grinding pipe between a minimum torque and a maximum torque, wherein the minimum torque is always positive, and the driving torque thereby preventing back-lash.