Discharge Grate Assembly Movable Shroud Back Flow Control
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Solution Overview
Problem
In grinding mills, the 'back flow' of slurry from pulp lifter chambers back into the mill shell chamber reduces productivity, especially with inclined discharge end walls, as existing solutions focus on increasing aperture size and number without effectively addressing this issue.
Innovation Solution
A discharge grate assembly with a movable shroud that aligns with apertures to allow slurry flow into pulp lifter chambers while preventing back flow by shifting between open and closed positions as the mill rotates, utilizing stop elements and a motion subassembly to manage the shroud's movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the sizes and/or numbers of apertures in the mill grate are increased to increase slurry flow volume, then the throughput into pulp lifter chamber increases, but back flow of slurry from pulp lifter chamber back into mill shell chamber increases significantly
Solution Approach 1:
The shroud is made movable relative to the body between open and closed positions. The motion subassembly enables the shroud to dynamically adjust its position, covering apertures during the discharge phase to prevent back flow while allowing slurry flow during the intake phase. This dynamic adjustment resolves the contradiction by making the aperture coverage adaptive to the operational cycle.
Solution Approach 2:
The discharge grate assembly is segmented into a body with apertures and a separate movable shroud with cover elements. This segmentation allows the shroud to independently control aperture coverage, enabling selective opening and closing of apertures during different phases of the mill rotation cycle to prevent back flow while maintaining throughput.
2Productivity
If the rotation speed of the mill is increased to achieve optimal throughput, then the processing efficiency increases, but back flow occurs more significantly when pulp lifter chamber is positioned above the charge
Solution Approach 1:
The shroud is positioned to cover apertures before the pulp lifter chamber reaches positions where back flow would occur (between 3 o'clock and 9 o'clock positions). The motion subassembly anticipates the back flow condition and pre-positioned the shroud to block apertures, preventing back flow before it can occur while maintaining high rotation speeds.
Solution Approach 2:
The shroud acts as an intermediary element between the mill shell chamber and the pulp lifter chamber. It mediates the slurry flow by selectively covering or exposing apertures based on the chamber position, allowing slurry flow during intake while blocking back flow during discharge, thus resolving the harmful effect without reducing throughput.
3Loss of substance
If a shroud is added to prevent back flow by covering apertures, then back flow is reduced, but the device complexity increases due to additional moving parts
Solution Approach 1:
The shroud is designed to move automatically based on the mill's rotation and the position of the pulp lifter chamber relative to the charge. The motion subassembly utilizes the existing rotational motion and gravitational forces to drive the shroud's movement, eliminating the need for external power sources or complex control systems. The system serves itself by converting the mill's operational motion into the required shroud positioning.
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
The solution significantly reduces back flow, enhancing mill productivity by ensuring slurry is directed towards the discharge trunnion, even with inclined discharge end walls, without decreasing rotation speed or throughput.
Implementation Method 1
slurry flows from a mill shell chamber into pulp lifter chambers due to charge pressure and gravity
Implementation Method 2
slurry flows from a mill shell chamber into pulp lifter chambers due to charge pressure and gravity
Implementation Method 3
The shroud is movable relative to the body between an open position, in which the openings are at least partially aligned with at least preselected ones of the apertures to permit the slurry to flow therethrough into the pulp lifter chamber, and a closed position, in which the cover elements are at least partially aligned with at least predetermined ones of the apertures, to at least partially prevent the slurry flowing through the apertures back into the mill shell chamber
Data Source
AI summary
A discharge grate assembly for at least partially guiding slurry from a mill shell chamber toward a discharge trunnion thereof via a pulp lifter chamber. The discharge grate assembly includes a body having apertures for permitting the slurry to flow from the mill shell chamber into the pulp lifter chamber, and a shroud having a number of cover elements and a number of openings located at least partially therebetween. The shroud is movable relative to the body between an open position, in which the openings are at least partially aligned with at least preselected ones of the apertures to permit the slurry to flow therethrough into the pulp lifter chamber, and a closed position, in which the cover elements are at least partially aligned with at least predetermined ones of the apertures, to at least partially prevent the slurry flowing through the apertures back into the mill shell chamber.