GB1569388A

GB1569388A - Method of and an apparatus for sifting ground material

Info

Publication number: GB1569388A
Application number: GB3113877A
Authority: GB
Original assignee: DESSAU ZEMENTANLAGENBAU VEB
Current assignee: DESSAU ZEMENTANLAGENBAU VEB
Priority date: 1976-07-30
Filing date: 1977-07-25
Publication date: 1980-06-11
Also published as: DK309277A; FR2359651A1; DD127112A1; ATA500777A; DE2730497A1; AT353722B; CS195506B1

Description

(54) A METHOD OF AND AN APPARATUS FOR SIFTING GROUND MATERIAL (71) We, VEB ZEMENTANLAGEN BAU DESSAU, a body corporate organised and existing under the laws of the Gennan Democratic Republic, of 13 Brauereistrasse, 43 Dessau, German Democratic Republic, do Lj declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, tohe pardculatiy described in and by the foltrpping statement::-- This stion relates to a method of and an apparatus for the sifting of ground material, for example minaals, pulverised in a rolling miu by means of grinding bodies rolling on a grinding plate.

A method of grinding and sifting minerals has already been suggested wherein the ground -crial emerges from the grinding process under centrifugal force and immediately passes through a current of sifting gas flowing around a for grinding out this method The apparatus for carryitrg out ts method courts of a grinding plate rotating at high and and upon which roll a relatively large number of small grinding bodies. Goaxially disposed around the grinding plate is the flow duct of a transverse flow sifter, in turn sur rounded by the container which catches the coarse material. The grinding plate rotating 9t a high speed throws the ground material tito the flow duct located coaxially around flie grinding plate, and in which the sifting * separates the fines from the coarse mat erial, while the coarse material is collected in the catching container and recycled back to the mill.A disadvantage in this respect is that the high grinding speed is not variable and therefore cannot be adapted to the op timum conditions which suit diferert mat erials. The high grinding speed means that in spite of the grinding path being provided with a large number of grinding bodies of snail diameter, the centrifugal force causes coarse material to pass through the interstices between the grinding bodies and leave the grinding plate unpulverised. For the fine material, though, the grinding speed is still too low. By reason of its low actual mass and its adhesion in the grinding bed, this fine material is only inadequately thrown into the sifting chamber.The large number of grinding bodies of small diameter creates problerns in respect of storage and the generation of the pressing force. Since each grinding body must be individually mounted and pressed onto the grinding track, in addition to the high cost of materials, considerable space is required, so that the rolling mill becomes large and heavy.

In addition, the reduction of the grinding body diameter means that by reason of the poorer intake conditions of small grinding bodies of the mill, a finer or more intensely connninuted material must be fed to them.

Having regard to the disclosed state of the art, the grinding plate has the function of a discharge device for the crossflow sifter disposed around it. However, this presupposes that the grinding plate runs at a sufficiently high speed to impart the necessary centrifugal force to the comminuted material. This high grinding plate speed is the cause of the shortcomings nherent in the state of the art.

The technical problern on which the invention is based lies in reducing the grinding plate speed and in nevertheless permitting of the favourable disposition of the cross-flow sifter around the grinding plate without the provision of intermediate transport paths.

According to the present invention in one aspect there is provided a method of sifting ground material, ground in a rolling mill having a grinding plate and which is discharged from the grinding plate under the action of centrifugal force and gravity, in which the ground material after being discharged from the grinding plate falls onto a rotating inpeller ring disposed below the grinding plate and under the effect of centrifugal force is accelerated and passed through a flow of sifting gas which flows linearly around the grinding plate and impeller ring.

According to the present invention in another aspect there is provided apparatus for sifting ground material ground in a rolling mill having a rotatable grinding plate, comprising a crossflow sifter surrounding the rotatable grinding plate of a rolling mill, the grinding plate also forming a means of feeding the crossflow sifter, said sifter comprising an axial duct surrounding the grinding plate, an impeller ring disposed below the grinding plate and having its outer edge protruding into an opening provided in the inner wall of the flow duct, the inner edge of the impeller ring having a smaller diameter than the diameter of the grinding plate and means for supplying gas to the sifter.

The impeller ring is mounted on the mill housing, its outer rim protruding into an annular slotted aperture in the flow duct of a crossflow sifter which is disposed around the pulverising apparatus. The inside diameter of the impeller ring is preferably smaller than that of the grinding plate, so that grinding plate and impeller ring partly overlap.

The impeller ring on which straight, circular or spiral blades provided with wearing elements may he located to enhance the scattering effect, has its own regulable speed motor drive.

In order to produce the twisting flow of the sifting air, the sifting air connections, discharge tangentially into the flow duct in the direction of notation of the impeller.

An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 is a section through the sifting apparatus provided on a rolling mill; Figure 2 shows a plan view of the impeller ring on which various types of impeller blades are only partially indicated; and Figure 3 shows a plan view of the convergence of the sifting air connectors into the flow duct.

As shown in Figure 1, the material is pulverised by grinding bodes rolling on a rotating grinding plate 1 of a rolling mill and pours over a retaining ring 2 as the result of gravity and emerges from the grinding process.

Located directly below the grinding plate 1 is an impeller ring 3. This impeller ring 3, the inside diameter of which is smaller than the diameter of the grinding plate 1, is mounted on the mill housing and has its outer edge protruding into an opening 5 provided in the inner wall of a flow duct 6 of a crossflow sifter, the said duct 6 extending coaxially around and at a radial distance from the grinding plate 1. The ground material is caught by the impeller ring 3. The impeller ring 3 is caused, by its own drive, to rotate at high speed, and imparts to the picked-up ground material such high radial acceleration that the said material is thrown at high velocity tangentially through the slotted opening 5 into the free cross-section of the flow duct 6.In order to prevent the particles of ground material slipping on the surface of the impeller ring at the high speed of the impeller ring 3, straight or circular or spirally curved blades 4 are provided on the said surface, as can be seen in Figure 2 and in order to prolong the working life of the blades 4, they are provided with wear resistant elements.

So that the rotary speed of the impeller ring 3 can be adapted to the opumum conditions for the different materials, the impeller drive speed is regulable. A strong jet of sifting air, preferably consisting of hot gases, and which, according to Figure 3, enters the flow duct 6 in the direction of rotation of the impeller ring 3 through connectors 7 located tangentially on the flow duct 6 moves spirally upwardly therein, separating the fine material from the coarse material, while the coarse material is thrown across the flow duct 6 and through an opening in its outer wall and recycled back to the rolling mill through suitable (hut not shown) catching and conveying means.

The invention makes is possible for the grinding plate on rolling mills, in combination with a crossflow sifter, to continue to rotate at optimum speed, so that an undisturbed pulverising process coresponding to the relevant loading conditions can be achieved. By the reduction of the grinding plate speed, the drive selected may be substantially smaller, so saving on energy and material, and making the sifting apparatus lighter in weight and easy to assemble.

WHAT WE CLAIM IS: 1. A method of sifting ground material, ground in a rolling mill having a grinding plate and which is discharged from the grinding plate under the action of centrifugal force and gravity, in which the ground material after being discharged from the grinding plate falls onto a rotating impeller ring disposed below the grinding plate and under the effect of centrifugal force is accelerated and passed through a flow of sifting gas which flows linearly around the grinding plate and impeller ring.

2. The method claimed in claim 1, in which the current of sifting gas follows a helical path.

3. Apparatus for sifting ground material ground in a rolling mill having a rotatable grinding plate, comprising a crossflow sifter surrounding the rotatable grinding plate of a rolling mill, the grinding plate also forming a means of feeding the crossflow sifter, said sifter comprising an axial duct surrounding the grinding plate, an impeller ring disposed

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. a flow of sifting gas which flows linearly around the grinding plate and impeller ring. According to the present invention in another aspect there is provided apparatus for sifting ground material ground in a rolling mill having a rotatable grinding plate, comprising a crossflow sifter surrounding the rotatable grinding plate of a rolling mill, the grinding plate also forming a means of feeding the crossflow sifter, said sifter comprising an axial duct surrounding the grinding plate, an impeller ring disposed below the grinding plate and having its outer edge protruding into an opening provided in the inner wall of the flow duct, the inner edge of the impeller ring having a smaller diameter than the diameter of the grinding plate and means for supplying gas to the sifter. The impeller ring is mounted on the mill housing, its outer rim protruding into an annular slotted aperture in the flow duct of a crossflow sifter which is disposed around the pulverising apparatus. The inside diameter of the impeller ring is preferably smaller than that of the grinding plate, so that grinding plate and impeller ring partly overlap. The impeller ring on which straight, circular or spiral blades provided with wearing elements may he located to enhance the scattering effect, has its own regulable speed motor drive. In order to produce the twisting flow of the sifting air, the sifting air connections, discharge tangentially into the flow duct in the direction of notation of the impeller. An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 is a section through the sifting apparatus provided on a rolling mill; Figure 2 shows a plan view of the impeller ring on which various types of impeller blades are only partially indicated; and Figure 3 shows a plan view of the convergence of the sifting air connectors into the flow duct. As shown in Figure 1, the material is pulverised by grinding bodes rolling on a rotating grinding plate 1 of a rolling mill and pours over a retaining ring 2 as the result of gravity and emerges from the grinding process. Located directly below the grinding plate 1 is an impeller ring 3. This impeller ring 3, the inside diameter of which is smaller than the diameter of the grinding plate 1, is mounted on the mill housing and has its outer edge protruding into an opening 5 provided in the inner wall of a flow duct 6 of a crossflow sifter, the said duct 6 extending coaxially around and at a radial distance from the grinding plate 1. The ground material is caught by the impeller ring 3. The impeller ring 3 is caused, by its own drive, to rotate at high speed, and imparts to the picked-up ground material such high radial acceleration that the said material is thrown at high velocity tangentially through the slotted opening 5 into the free cross-section of the flow duct 6.In order to prevent the particles of ground material slipping on the surface of the impeller ring at the high speed of the impeller ring 3, straight or circular or spirally curved blades 4 are provided on the said surface, as can be seen in Figure 2 and in order to prolong the working life of the blades 4, they are provided with wear resistant elements. So that the rotary speed of the impeller ring 3 can be adapted to the opumum conditions for the different materials, the impeller drive speed is regulable. A strong jet of sifting air, preferably consisting of hot gases, and which, according to Figure 3, enters the flow duct 6 in the direction of rotation of the impeller ring 3 through connectors 7 located tangentially on the flow duct 6 moves spirally upwardly therein, separating the fine material from the coarse material, while the coarse material is thrown across the flow duct 6 and through an opening in its outer wall and recycled back to the rolling mill through suitable (hut not shown) catching and conveying means. The invention makes is possible for the grinding plate on rolling mills, in combination with a crossflow sifter, to continue to rotate at optimum speed, so that an undisturbed pulverising process coresponding to the relevant loading conditions can be achieved. By the reduction of the grinding plate speed, the drive selected may be substantially smaller, so saving on energy and material, and making the sifting apparatus lighter in weight and easy to assemble. WHAT WE CLAIM IS:

1. A method of sifting ground material, ground in a rolling mill having a grinding plate and which is discharged from the grinding plate under the action of centrifugal force and gravity, in which the ground material after being discharged from the grinding plate falls onto a rotating impeller ring disposed below the grinding plate and under the effect of centrifugal force is accelerated and passed through a flow of sifting gas which flows linearly around the grinding plate and impeller ring.

below the grinding plate and having its outer edge protruding into an opening provided in the inner wall of the flow duct, the inner edge of the impeller ring having a smaller dia- meter than the diameter of the grinding plate, and means for supplying gas to the sifter.

4. Apparatus as claimed in claim 3, in which the impeller ring is provided with blades prwided with wear resistant elements.

5. Apparatus as claimed in claim 4, in which the blades are straight, circular or

6. Apparatus as claimed in any one of claims 3 to 5, in which the impeller ring lss its own variable speed drive.

7. Apparatus as claimed in any one of claims 3 to 6, in which the sifter axial duct is provided with air inlet connectors disposed tangentially of the duct for directing the incoming air flow in the direction of rotation of the impeller plate.

8. A method of sifting ground material, substantially as hereinbefore described with reference to the accompanying drawings.

9. Apparatus for sifting ground material, substantially as hereindescribed with reference to and as illustrated in the accompanying drawings.