Solid material comminution or disintegration – Processes – Plural successive comminuting operations
Patent
1997-10-28
1999-05-04
Hail, III, Joseph J.
Solid material comminution or disintegration
Processes
Plural successive comminuting operations
241 30, 241103, 241122, 241181, B02C 1900, B02C 1718
Patent
active
058993940
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for grinding of material in a ring roller mill which mill comprises at least one grinding ring, at least one roller fitted inside the grinding ring and at least one unit fitted between the roller and the grinding ring.
Such a mill can, for example, be used in connection with the manufacture of cement for grinding of mineral clinker materials, slag, and similar materials.
In the published European patent application No. 486371 a ring roller mill is described. In this mill the feed material is charged to a space before the grinding path where it is subjected to centrifuging action. Hereafter the material and the air are carried axially through the mill. The grinding ring in this mill operates at grinding pressure between 10-40 MPa and at supercritical speed, which means that the material subjected to grinding action is retained on the grinding ring all the way round. It is, therefore, possible and necessary to fit scrapers and guiding plates internally in the ring in order to release the material during the passage transversely to the grinding ring and to guide the material forward along the roller in the flow direction.
In a ring roller mill which is operated at subcritical speed, the ground material will only be retained on a part of the grinding ring. In an area on the grinding ring, dependent on the rotational speed of the ring, the surface roughness of the ring and the characteristics of the processed material, the ground material will be detached from the ring, continuing to fall along a downward path towards a draw-in zone in front of the roller.
An even distribution of the material in the draw-in zone and in the grinding bed is of major significance for the operation of the mill. Major variations in the thickness of the grinding bed will cause irregular operation or vibrations in the mill and substantial fluctuations in the torque of the drive arrangement. An uneven loading of the roller may also cause the wear segments which protect the surface of the grinding ring and the roller to be damaged.
The intensity of grinding pressure applied and the type of material being ground are determining factors in regard to the form that the compacted material will have after its passage under the roller in the mill. A high grinding pressure and/or sticky material will lead to formation of agglomerates which retain their form after the material is discharged from the grinding ring, whereas a lower grinding pressure will result in the dropping material being a relatively loose, crumbling material. Both the size and hardness of the agglomerates will have an effect on the evening-out of the bed of material which is deposited in the draw-in zone and in the grinding bed proper.
A ring roller mill operating at subcritical speed has a lower rate of rotation than a ring roller mill operating at supercritical speed. In order to increase the production in a mill operating at subcritical speed to the same level as in a similar mill operating at supercritical speed it is necessary to increase the grinding pressure. Normally the grinding pressure in a mill operated at subcritical speed will be higher than 50 MPa.
It is the objective of the present invention to provide a method for grinding of material in a ring roller mill where the agglomerates formed during operation are crushed and distributed along the draw-in zone and the roller in such a way that no undesirable vibrations or skew placement of the roller occur during operation.
This is achieved according to the invention in a surprisingly simple way by mounting a unit at a certain distance from a point P on the ring. The unit is placed in the path where the compacted material falls off the ring, descending towards the draw-in zone in such a way that the unit is hit by agglomerates formed during operation at an angle .alpha. between 60.degree. and 120.degree., where .alpha. is the angle between the surface of the unit and the direction of incidence of the material.
During the grinding process the impact and distribution units will
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F. L. Smidth & Co. A/S
Hail III Joseph J.
Kingsbury Susan
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