Solid material comminution or disintegration – Processes – With application of fluid or lubricant material
Patent
1995-06-08
1996-11-05
Husar, John M.
Solid material comminution or disintegration
Processes
With application of fluid or lubricant material
241 241, 241 29, B02C 2308
Patent
active
055708447
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for tubular rotary ball milling or mill with grinding instruments, comprising at least two grinding compartments separated by a partition, the mill being passed through by a current of sweeping air and working in a closed circuit manner.
The partition which is situated between two of the grinding compartments, makes it possible to control the quantity of material in the compartment situated upstream.
The invention is particularly intended for ball mills, or mills with similar grinding instruments, for cement, in a closed circuit. Generally, these mills have two compartments, namely a preparing compartment with balls with a diameter of 90 to 60 mm and a finishing compartment with balls with a diameter of 40 to 20 mm. In order to avoid dust and excessive heating of the cement during grinding, cement mills are passed through by a current of sweeping air, from upstream to downstream. The partition which separates the first and second compartment of these mills is for this reason called the intermediate partition.
In cement mills, the raw material is supplied at approximately 80% under the size of 20-25 mm, and the work of the first chamber consists of reducing it to approximately 100% under the size of 5 mm, with 95% under the size of 2.5 mm. In fact, to obtain a good grinding efficiency, it is necessary for there to be a large quantity of 20 mm balls in the second compartment. Moreover, these balls work well only insofar as the fineness criteria given above are respected at the inlet of the second chamber, and in particular as there are practically no more particles greater than 5 mm in size.
In a cement mill, the intermediate partition has several functions, it must: compartment downstream;
The above functions can be carried out with single-walled or double-walled partitions. The invention relates to double-walled partitions.
Single-walled partitions are actually practically never used in modern cement grinders; since they wear out on both their faces, they have too short of a lifetime, and in addition their resistance to stresses in the axial direction of the mill is not sufficient. Moreover, with a single partition, the sweeping with air has a very small influence on the filling of the first compartment with material, and an essential characteristic of the invention--using the sweeping of air as a regulating means--could not be produced efficiently.
Patent DE-A-2,133,431 describes a typical embodiment of double-walled partitions used for separating the grinding compartments of modern cement mills. The partition includes a framework consisting of openwork segments, onto which there are bolted, upstream, grilles which allow the cement to enter the partition, and, downstream, shielding plates which make a central discharge opening. The grilles and the rear plates are subjected to strong wear only on one side, and because of this they have better durability than the grilles of single-walled partitions; when they are replaced, the framework is kept.
Slots of approximately 6 mm are provided in the grilles of the upstream wall of the intermediate partitions, the edge of the slots undergoes a small degree of working by the impacts of the balls, the particles larger than 5 mm cannot pass through these slots. If the slots are larger, in the event of disturbance of the operation of the mill, even for a short time, excessively large particles can pass into the second compartment, and they will remain trapped in the balls of 20 mm diameter which are too small to reduce large particles, and this can hamper the running of the mill for several days, with a loss in capacity which can be up to 20%.
Although it is possible, by dimensioning the slots of the upstream wall of the intermediate partition, to fulfil the first fineness criterion at the outlet of the first compartment, i.e. 100% under 5 mm in size, it is impossible to make slots which satisfy the second criterion, i.e. 95% under 2.5 mm in size. In fact, it is not possible to provide sufficiently small op
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Husar John M.
Slegten S.A.
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