GB2187657A

GB2187657A - Method and device for influencing the finished product during the crushing operation in a roller mill

Info

Publication number: GB2187657A
Application number: GB08705466A
Authority: GB
Inventors: Paul Clemens; Kirsten Winkelmann; Hubert Beyer; Heinrich Schubert; Roland Bissot; Jens Hanisch
Original assignee: ZEMENTKOMBINAT VEB
Current assignee: ZEMENTKOMBINAT VEB
Priority date: 1986-03-10
Filing date: 1987-03-09
Publication date: 1987-09-16
Anticipated expiration: 2007-03-09
Also published as: GB2187657B; DK110987A; GB8705466D0; DE3704974A1; CS153187A1; DD258325A3; DK110987D0

Abstract

A method for influencing the grain-size distribution of the finished product produced in roller mills with an internal or external material circuit in which, with constant operating parameters, the grinding stock is either conveyed outwards over the grinding disk edge (3) or inwards under a roller element (1), according to the position and geometry of a rearranging device (2) and the particular transport speed. The rearranging device (2) which is preferably formed like a plough share, is associated with at least one, although usually each roller element (1). The transport speed of the disc may also be altered. <IMAGE>

Description

SPECIFICATION Method and device for influencing the finished product during the crushing operation in a roller mill This invention relates two a method for influencing the grain-size distribution ofthe finished product produced in roller mills with an internal or external material circuit, and to a device for carrying outthe method.

It is known that the properties relating to thefunctional value of ground substances are essentiallydetermined bytheirgranulometricproperties.

In currently known roller mills with an internal material circuit, the desired properties are essenti ally obtained by varying the contact pressure ofthe grinding rolls, the orifice height, the throughput, the grinding disk speed, the sorting airstream and the sorter speed. In roller mills with an external material circuit, the essential factors which affect the grainsize distribution ofthe crushed product are the contact pressure of the grinding rolls, the orifice height, the throughput, the grinding diskspeed and the set- ting of the classifying device.This means that with constant operating parameters (i.e. contact pressure, grinding diskspeed,throughput), on which the crushing process essentially depends, the grain-size distribution is determined by the classifying device in both the above variants. The object of the separating device known from DDR Patent Specification No.

205079 isto breakupthe packing structureofthe compressed grinding stock after each roller element, and to rearrange and mix the grinding stock without having any purposeful or necessary influence on the grain-size distribution.

In DE Patent Specification No. 1 507 579, a device is described which is used as a control memberfor controlling the output of roller mills witch a constant throughput. Reference is made to a marked increase in output, without an increase in power requirements, owing to the described sorting effects.

Although the arrangement of the device does achieve sorting effects to a degree, it cannot be used foroperationsto influencethesize range in itsillust- rated form.

The aim ofthe present invention is to influence the desired grain-size distribution of the crushed products of roller mills with constant operating parameters while simultaneously minimizing power requirements.

It is an object of the invention to provide a method and a device for influencing the grain-sizedistribu- tion ofthefinished product during crushing operations in roller mills.

According to one aspect of the invention, there is provided a method of influencing the grain-size distribution of a finished product during the crushing operation in a roller mill comprising two or more roller elements rotating in a fixed position, a horizontally rotating grinding disk onto which the grinding stock is supplied, and at least one device for rearranging and mixing up the grinding stock, the method comprising conveying the grinding stock which is crushed in the rolling process at a predetermined variable transport speed via the or each rearranging device to achieve a variable partial sorting operation, and/ortransporting unsorted yet rearranged stockto the next roller element to be acted upon again.

According to another aspect ofthe invention there is provided a device comprising two or more roller elements rotatable in a fixed position, a horizontally rotatable grinding disk, means for feeding grinding stock onto the centre of said disk or in front of the roller elements, the grinding stock which is crushed in the rolling process being conveyed art a predetermined variable transport speed via at least one rearranging device to achieve a variable partial sorting operation, unsorted yet rearranged stock being transported to the next roller element to be acted upon again.

With the preferred method of the invention, with constant operating parameters, the grinding stock is either conveyed outwards over the grinding disk edge or inwards under the following roller element, according to the position and geometry of the rearranging device and the particular transport speed.

The rearranging device, which is preferably formed like a plough share, is associated with at least one, although usually each roller element.

If the grinding stock is transported outwards and dispersed in the process, the sorting air stream carries the sufficiently fine grinding stock out. In this way, a ground product with an essentially lower pro- portion of fine grains can be produced with low power requirements.

If ground product is conveyed inwards, the grinding stock is acted upon again underfavourable crushing conditions and fine grains can be produced with low power requirements.

The grinding stock is delivered either centrally onto the disk or in front of the roller elements. With a given position and geometry ofthe rearranging de vice,thesame result can be obtained byvaryingthe transport speed ofthe grinding stock bed which has been acted upon.

As roller mills are usually designed to have a constant grinding disk speed, three-phase squirrel-cage motors are generally used. The present drive solutions enable an infinitely variable speed control to be retrofitted in the required area by using frequency control without having to change the motors.

Examples of the invention will now be described, for illustrative purposes only, with reference to the accompanying drawing.

Example 1 Limestone is crushed in a semi-industrial roller mill with an internal material circuit. The roller mill operates with a throughput of 50 kg h-1.With constant operating parameters (contact pressure, grinding disk speed, throughput, sorting air stream, etc.), the installation of a rearranging device with a specific geometry and in a specific position enables a crushed productwith a low number of fines to be produced when the grinding stock is transported at the appropriate speed. If the largest grain size of the crushed product is 355 pm, the portions which are smailerthan 30 Fm and 90 Fm can in each case be reduced by 10%.

The specific power requirements in this case dec rease by 60%.

Example 2 An extremely fine limestone dust is to be produced underfavourable power conditions in the same roller mill as that described in Example 1. With the same operating parameters, the installation of a rearranging device of a specific geometry and in a specific position enables the portion which issmallerthan 30 m to be increased from 66% to 73% and the portion which is smallerthan 10 pwm to be increased from 35% to 48%, with the same residue of size 90 Fm of 20%, when the grinding stock is transported at an appropriate speed.

By installing a specific rearranging device,the specific power requirements can be reduced by 45%, while a finer end product can be obtained.

Example 3 Referring to the drawing, there is shown a rearranging device 2 located directly behind one or more roller elements 1 of a roller mill (only part of which is shown). With a constant grinding disk speed (i.e,.

transport speed), it is possible to minimise the separation ofthefine stock from the granular mass and to convey the rearranged stock to the next roller element (not shown) to be acted upon by turning the device 2 about its axis 3 in the direction a. By turning the rearranging device 2 about it axis 3 in the direction b, grinding stock which has been acted upon is intensively sorted in the area of the nozzle ring (not shown) before being acted upon again when free of the fine stock.

If the position of rearranging device 2, which is preferably formed like a plough share, is constantly adjusted, it is possible to minimisethe sorting ofthe granular mass and increase the supply to be acted upon bythe next roller element by reducing the speed ofthe grinding disk e.g. by means ofafrequ- ency-controlled three-phase squirrel-cage motor (not shown). If the speed is increased, the supply of already acted on grinding stock to the area ofthe nozzle ring is increased and, free ofthe fine stock, is acted upon again.

The portion of rearranged grinding stock can be further influenced by moving the plough share-like device 2 in a vertical direction in relation to the horizontally rotating grinding disk.

Claims

1. A method of influencing the grain-size distribution of a finished product during the crushing operation in a roller mill comprising two or more roller elements rotating in a fixed position, a horizontally rotating grinding disk onto which the grinding stock is supplied, and at least one device for rearranging and mixing upthegrindingstock,themethod comprising conveying the grinding stockwhich is crushed in the rolling process at a predetermined variable transport speed via the or each rearranging device to achieve a variable partial sorting operation, and/ortransporting unsorted yet rearranged stock to the next roller element to be acted upon again.

2. A method according to claim 1, wherein with a constanttransport speed of the grinding stockwhich has been acted upon, the position and/or geometry of the or each rearranging device is altered.

3. A method according to claim 1, wherein with a constant position and/or geometry of the or each rearranging device, the transport speed is altered.

4. A method of influencing the grain-size distribution of a finished product during the crushing operation in a roller mill substantially as herein described with reference to the accompanying drawing.

5. Arollermill comprisingtwoormore rollerel- ements rotatable in a fixed position, a horizontally rotatable grinding disk, means forfeeding grinding stock onto the centre of said disk or in front ofthe roller elements, the grinding stock which is crushed in the rolling process being conveyed ata predetermined variable transport speed via at least one rearranging device to achieve a variable partial sorting operation, unsorted yet rearranged stock being transported to the next roller element to be acted upon again.

6. A roller mill according to claim 1 including means to alterthe position and/or geometry of the or each rearranging device.

7. A roller mill according to claim 1 including means to alterthe transport speed of the disk.

8. Arearranging deviceforfittingtoa rollermill as claimed in any of claims 5 to 7 substantially as herein described with reference to the accompanying drawing.

9. A roller mill substantially as herein described with reference to the accompanying drawing.