Solid material comminution or disintegration – Processes – By utilizing kinetic energy of projected or suspended material
Patent
1988-10-31
1990-04-24
Rosenbaum, Mark
Solid material comminution or disintegration
Processes
By utilizing kinetic energy of projected or suspended material
241 29, 241 39, 241152A, B02C 1906
Patent
active
049193392
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with a method and an apparatus for improving the grinding result of a pressure chamber grinder. In the method finely divided material to be ground is fed by means of a mechanical feeder device into a pressurized equalizing tank, in the equalizing tank the possibly clodded material is made loose by means of a rotor, and the material thus made loose is transferred into a pre-grinder, wherein several grinding-gas jets are applied to the material to be ground so that the material to be ground is fluidized, the fluidized material-gas flow is passed into a bisecting device, wherein it is divided into two component flows of equivalent magnitude and composition, each component flow is passed into the main grinding chamber through a long accelerating nozzle of its own, which said nozzle is directed so that a collision zone for the two component flows is formed in the centre point of the said main grinding chamber.
It is an advantage of such a pressure chamber grinder that, as regards its energy economy, it is by far superior to conventional jet grinders, wherein ejectors are usually used as the feeder or accelerating device. Since in principle the material particles to be ground are subjected to the grinding effect only once, it is necessary to resort to a separate classifier in which the coarser particles are separated from the material-gas flow and returned, in one way or another, into the main grinding chamber for regrinding. In practice this mode of operation is usable when in the ground material the fraction having the final particle size is relatively small, and the unground material to be returned to the grinding, is high.
If instead the material fraction returned to the grinding is relatively small it is questionable whether the use of a separate classifier is motivated. The Finnish patent application No. 854671 discloses a solution for this kind of cases, according to which a pressure chamber grinder and a so called free-flow grinder a coupled in series. This system has proven to be especially suitable when the material ground in the pressure chamber grinder contains a very small fraction of unground material and when the material is of a very small particle size.
In practice it has been noticed that all such systems based on grinding the material solely using jet grinding techniques suffer from relatively high operating costs. Especially the grinding of a material containing after the pressure chamber grinder more than about 50% of a product of the final particle size involves unnecessary high costs if the previously mentioned equipment is applied. Among such materials can be named, for instance, paper fillers, such as talc, as well as various foodstuffs, such as for instance corn and cocoa.
The object of the present invention is to eliminate these problems. This has been achieved by means of a method which is characterized in that the material-gas mixture ground in the main grinding chamber is passed through an acceleration tube into a mechanical grinder in a direction corresponding to the rotation direction of the grinder rotor driven by an electric motor, whereby the pivotably mounted grinding hammers of the grinder are arranged to break up coarser particles, moved to the outer periphery of the grinder, before their exit through a central outflow of the grinder.
By using such a solution, the desired final result is obtained without a separate classifier or a secondary grinder of free-flow type, and in addition with essentially better energy economy. In the mechanical grinder the grinding conditions are chosen so that only the oversize particles are ground and the finer particles pass through this subsequent grinder almost without delay. The method and apparatus according to the invention is especially advantageous when an unusually high degree of fineness in the final product is not required and when the hardness of the material to be ground is not high. Thus, especially soft minerals and foodstuffs are suitable.
In the following, we will describe the invention in mor
REFERENCES:
patent: 3860184 (1975-01-01), Acton
patent: 4586661 (1986-05-01), Niemi
patent: 4811907 (1989-03-01), Niemi et al.
Machines and Equipment for Ceramics and Refractory Producing Plants, Mashinostroenie, Moscow, 1968; pp. 62-63.
Oy Finnpulva AB
Rosenbaum Mark
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