Impact pulverizers are known, is machines used in the grinding industry for exerting a grinding action by impact between the product and fixed or rotating surfaces.

A known type of pulverizer consists of a cylindrical body of vertical azis housing in its upper part an electric motor, on the shaft of which a disc is keyed. Said disc is housed in a pulverizing chamber and comprises on its upper surface a plurality of teeth cooperating with corresponding teeth provided on a disc facing it from above.

To achieve a final product particle size variable as a function of the starting substance, it is known either to vary the speed of the lower disc by changing the motor pulleys or using a frequency regulator, or to vary the number of teeth on the disc.

A drawback of such pulverizers is that varying the speed by changing the pulleys involves time loss, while the use of a frequency regulator involves high cost.

In addition, changing the pulleys or varying the number of teeth cannot be done automatically, hence such pulverizers are never suitable for a highly automated plant.

An object of the invention is to eliminate these drawbacks by providing a pulverizer which enables the particle size of the final product to be easily, comfortably and possibly automatically regulated on the basis of the quantity and type of starting substance.

This and further objects which will be apparent from the ensuing description are attained according to the invention by an intensive pulverizer as described in claim 1.

The invention is described in detail hereinafter with reference to the accompanying drawings, on which: Figure 1 is a longitudinal section through a pulverizer of the invention shown in the configuration in which its teeth are spaced apart; Figure 2 is a longitudinal section therethrough shown in the configuration in which the teeth are in their position of maximum mutual approach; Figure 3 is a plan view thereof from above.

As can be seen from the figures, the pulverizer of the invention comprises substantially a cylindrical casing 2 divided into two overlying chambers 4,6, one of which, namely the lower chamber 4, houses an electric motor 8 of verticla axis, whereas the upper chamber 6 houses two mutually facing pulverizing discs 10,12. The disc 10 is keyed onto the shaft of the electric motor 8 and comprises a plurality of teeth 14 arranged along circumferences concentric with the motor shaft. Said teeth 14 cooperate with corresponding teeth 16 arranged along concentric circumferences and rigid with the disc 12, which is movable vertically.

Said movable disc 12 is provided with a perimetral rim 18 housing seal gaskets 20, and which together with a lower half-shell 22 forms the pulverizing chamber 6.

The lower half-shell 22 comprises an annular rim 24 in which there are provided three threaded seats for engaging corresponding threaded pins 28 having their shank rigid with the disc 12 and being provided upperly with sprocket wheels 30.

The three sprocket wheels 30 are connected together by a ring chain 32 also provided with a tensioning device 34 mounted on a plate 36 adjustable atong slotted holes 38.

The pulverizing chamber 6 is provided upperly with an entry opening and laterally with an exit conduit 42, downstream of which there is provided a compressed air injector (not shown on the drawings).

In correspondence with the entry opening there is provided a conical member 44 which, in combination with a vertically movable cylindrical member 46, forms an annular aperture 48 the cross-section of which varies according to the position of the cylindrical member 46 relative to the conical member 44.

The height of the cylindrical member 46 is adjusted by operating handwheels 50.

The pulverizer is used in the same manner as traditional pulverizers in which the substance to be processed is fed through the opening 40 into the pulverizing chamber 6 in which the lower disc 10 is rotating and, drawn by vacuum, is passed through the interstices formed between the mutually engaged facing teeth. The interstices between the teeth 14,16 and consequently the distance between the discs 10,12 must be varied in accordance with the particle size of the starting substance, which can be achieved by operating one of the pins 28 either manually or automatically (for example by using a motor with position setting by remote control) in order to raise or lower the disc 12 relative to the fixed disc 10. In this respect, as the sprocket wheels are connected together by the chain 32, rotating one pin also results in rotation of the other pins.

From the aforegoing it is apparent that the pulverizer of the invention enables a variable particle size to be obtained depending on the starting substance, by easy adjustment of the distance between the discs, which can also be done automatically.