Self-cleaning roller screen

Abstract

A method for cleaning of a roller screen transporting and screening particles by means of at least three rotating rollers. The rollers are installed in succession at given clearances and arranged transversally in relation to the transport direction of the particles to screen a desired range of particle sizes. At least one roller changes its circumferential velocity and/or its rotational direction over time at defined time intervals for defined time periods such that for this defined time period for at least one pair of neighbored rollers one roller has a higher circumferential velocity than the other and/or both rollers roll in opposite rotational directions.

Claims

1. A method for cleaning of a roller screen transporting and screening particles by means of a plurality of rotating rollers, the method comprising: installing in succession the plurality of rotating rollers at given clearances and arranged transversally in relation to a transport direction of the particles to screen a desired range of particle sizes, wherein the plurality of rotating rollers are divided into at least two groups, a first group of the at least two groups including at least two rotating rollers of the plurality of rotating rollers, and a second group of the at least two groups including at least one rotating roller of the plurality of rotating rollers; providing a separate frequency converter for each group of the at least two groups to which all rotating rollers of the respective group of the at least two groups are connected, at least one group of the at least two groups of rotating rollers changes: its circumferential velocity such that for defined time periods for at least one pair of neighbored rollers of the plurality of rotating rollers a first roller of the at least one pair of neighbored rollers has a higher circumferential velocity than a second rotating roller of the at least one pair of neighbored rollers; and/or its rotational direction for the defined time periods such that for the defined time periods the at least one pair of neighbored rollers roll in opposite rotational directions, wherein all of the plurality of rollers are driven with the same circumferential velocity and the same rotating direction between the defined time periods.

2. The method according to claim 1, wherein every other roller of the plurality of rollers changes its circumferential velocity and/or its rotational direction.

3. The method according to claim 1, wherein the defined time periods are periodic or random.

4. The method according to claim 1, wherein the length of each of the defined time periods is from 0.1 to 3000 sec.

5. The method according to claim 1, wherein the ratio between the changed circumferential velocity and the unchanged circumferential velocity is between 50 to 200%.

6. The method according to claim 1, wherein the length of each of the defined time periods is from 0.1 to 30 sec.

Description

IN THE FIGURES

(1) FIG. 1 shows an X-Y view for a first embodiment of a roller screen according to the invention,

(2) FIG. 2 shows an X-Z view for a first embodiment of a roller screen according to the invention.

(3) FIG. 1 shows a preferred embodiment of the invention in a partial side view cross-section of the roller screen 1 belonging to a roller screen for pellets. The roller screen 1 is installed with respect to an apparatus for the agglomeration of pellets 2 so that the pellets discharged from there fall on the roller screen 1. Any other feeding device for another form of pellets or particles is possible.

(4) Preferably, the roller screen 1 is essentially arranged in an inclined position to improve the particle transport in the transport direction 11. The transport direction 11 is also determined by the typical direction of the roller rotation 12 which is typically identical for all rollers. The roller screen 1 is supported via a supporting structure 3 on which the frame 4 of the roller screen 1 is installed.

(5) The frame 4 is further provided with rollers 5, so that the rollers 5 are located underneath the frame 4. Between the rollers 5, given clearances 6 with a defined dimension are foreseen. Next to the agglomeration apparatus 2 the pellets will move downwards onto the rollers 5. The pellets are screened by means of the roller screen in order to separate such pellets that are too small in diameter and unsuitable for the hardening process. Pellets that are too small drop through the clearances 6 between the rollers 5 into the funnel 9 from where they are returned in a not shown way to the agglomeration apparatus 2. The funnel 9 can be replaced by a belt conveyor, which is also not shown in the figure.

(6) According to the invention at least every second roller has a separate means 7 to vary the circumferential velocity so a difference of circumferential velocity of neighboring rollers 5 can be induced. Thereby, relative circumferential velocity as well as different rotational direction can be changed individually. Thereby, particles respectively pellets which have been lodged in the clearance 6 between two rollers 5 can be flipped out of the clearance, either upward or downward, and, therefore, by periodically changing the circumferential velocities in defined time intervals for defined periods enables a cleaning of the roller screen without any manpower. The means 7 to vary the circumferential velocity can be electric motors connected to a frequency converter or hydraulic motors or mechanical or electrical brakes or an electrical switch to shut off an electric motor for short time periods or to switch it to a different pole pair number, i.e. different circumferential velocity, or a switch to change the rotational direction.

(7) It is preferred that respective means 7 are electrical motors coupled to frequency converters 8, preferably, several electrical motors are connected to the same frequency converter. FIG. 1 shows an example according to which 14 rollers 5 have 14 individual drive motors, arranged in 3 groups of 4 to 5 rollers, where the 1.sup.st and 4.sup.th and 7.sup.th and 10.sup.th and 13.sup.th roller are connected to a first frequency converter 8, the 2.sup.nd and 5.sup.th and 11.sup.th and 14.sup.th roller are connected to a second frequency converter 8′ and the 3.sup.rd and 6.sup.th and 9.sup.th and 12.sup.th roller are connected to a third frequency converter 8″.

(8) The same effect can also be generated in an embodiment as shown in FIG. 2. Thereby, at least each second roller 5 in the roller screen 1 shows a mechanical brake 10. By braking certain rollers 5, e.g. every second roller, the circumferential velocity of said rollers 5 can be reduced. Thereby, the complex use of a high number of separate motors and additional frequency converters can be avoided. Further, an upgrade of an existing roller screen 1 by adding additional brakes is quite easy and comparably cheap.

(9) Naturally, the concept of FIGS. 1 and 2, which is explained in connection with plants for pelletizing iron ore can be operated with any other form of particles like in the food or mining industry, etc.

(10) The variation of the circumferential velocity or of the rotational direction of an individual roller 5 always helps cleaning the two gaps 6 on both sides of this roller 5 since the changed circumferential velocity in the roller 5 frees both clearances 6 from pellets getting stuck in these clearances 6 by flipping them upwards or downwards.

REFERENCE NUMBERS

(11) 1 roller screen

(12) 2 agglomeration apparatus

(13) 3 supporting structure

(14) 4 frame

(15) 5 roller

(16) 6 clearance

(17) 7 means to vary the circumferential velocity

(18) 8 frequency converter

(19) 9 funnel

(20) 10 brake

(21) 11 transport direction

(22) 12 typical direction of roller rotation