Grinding Mill Positioning Using Torque-Based Lifting Angle
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Solution Overview
Problem
Accurate positioning of grinding mills is challenging due to the unbalanced position of the charge inside the mill body caused by the lifting angle, leading to oscillations and inefficiencies during maintenance, as existing methods rely on approximations that may not account for varying conditions.
Innovation Solution
Determine a reference lifting angle and driving torque pair during mill rotation, calculate a fill factor that consolidates charge characteristics, and use this to accurately determine the current lifting angle in real-time, allowing for precise positioning by adjusting the mill's rotational position based on the calculated angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the mill is positioned using the conventional method of stopping at a given angle and measuring the cascading angle, then the positioning can be completed with simple operation, but the positioning accuracy is insufficient due to the assumption that the actual lifting angle equals the cascading angle
Solution Approach 1:
The patent implements feedback by continuously measuring the actual lifting angle during mill rotation and using this measured value to adjust the positioning calculation. The control system monitors the relationship between driving torque and lifting angle in real-time, and uses this feedback to determine the precise mill position, eliminating the need to assume the lifting angle equals the cascading angle.
Solution Approach 2:
The patent replaces the conventional mechanical positioning method with an automated control system that uses sensors to measure the lifting angle and a controller to calculate the mill position. This substitution of mechanical measurement and manual positioning with automated sensing and computational control improves accuracy while maintaining operational simplicity.
2Productivity
If the mill body rotates with the charge inside, then the grinding process can proceed, but the center of gravity of the charge is not vertically aligned with the center of the mill body causing counter rotation and oscillations
Solution Approach 1:
The patent applies preliminary action by calculating and compensating for the lifting angle effect before stopping the mill for positioning. The control system determines the precise positioning angle by accounting for the actual lifting angle measured during rotation, and positions the mill accordingly before shutdown, preventing counter rotation and oscillations that would otherwise occur after stopping.
3Ease of repair
If the mill is stopped for maintenance, then the wear liner replacement can be performed, but the mill body oscillates back and forth for several minutes due to the unbalanced charge position
Solution Approach 1:
The patent applies preliminary action by pre-positioning the mill body at the correct maintenance angle before shutdown using the accurate lifting angle measurement. By calculating the precise positioning angle that accounts for the actual lifting angle and setting the mill to this position before stopping, the charge is already in a balanced position when the mill stops, eliminating prolonged oscillations during maintenance operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides more accurate positioning of the grinding mill, reducing oscillations and improving maintenance efficiency by accounting for changing conditions and ensuring the charge is balanced, thus minimizing roll back and shaking during startup.
Implementation Method 1
a reference driving torque M r and a reference lifting angle α r are determined during a rotation of the mill body 1... a current lifting angle α can be calculated for a current point in time... by determining a value for a driving torque M at the current point in time
Implementation Method 2
At a certain lifting angle αc, the gravity force is higher than the friction resulting in the material to cascade
Implementation Method 3
the charge is elevated but does not move due to friction
Data Source
AI summary
The purpose of the invention to provide a method for determining a lifting angle of a charge inside a grinding mill at a specific point in time and a method for positioning a grinding mill which is more accurate. Method for determining a lifting angle of a charge inside a mill body of a grinding mill being rotatable through a drive train, the method comprises the following steps of rotating the mill body; determining a reference lifting angle and a corresponding reference driving torque of the drive train at a reference point in time; calculating a fill factor for the reference point in time based on the reference lifting angle and the reference driving torque; determining a driving torque of the drive train; and calculating the lifting angle based on the driving torque and the fill factor.