GB2182584A

GB2182584A - Selective roll crushing apparatus

Info

Publication number: GB2182584A
Application number: GB08626275A
Authority: GB
Inventors: Johannes Duijzers
Original assignee: BEERS MARINE DE
Current assignee: BEERS MARINE DE
Priority date: 1985-11-06
Filing date: 1986-11-04
Publication date: 1987-05-20
Also published as: GB8626275D0; AU6488186A

Abstract

A selective crushing roll apparatus for selectively crushing softer particles in a mixture of softer and harder particles includes a pair of adjacent crushing rolls 10, 12 forming between them a nip 34. The rolls 10, 12 are rotated in opposite directions. The crushing surfaces of the rolls 10, 12 are made of a resilient material such as polyurethane or rubber, so that when the mixture of softer and harder particles is fed into the nip between the rolls 10, 12, the softer particles are crushed and the harder particles pass through without any diminution in size. Rolls 11 and 12 may be forced together and rotated at the same or different speeds. The apparatus is of particular use for crushing marine diamond bearing sediments. <IMAGE>

Description

SPECIFICATION Selective roll crushing apparatus Background to the invention This invention relates two a selective crushing roll apparatus for selectively crushing softer particles in a mixture of softer and harder particles.

One application ofthe invention is in marine diamond prospecting and recovery. In such an application, marine sediments are encountered which are composed of a wide variety of materials including quartzite pebbles and other hard rock particles, stiff and compacted clays and various types of shell, as well as diamondiferous materials. In further diamond separation processes, it is advantageousto reduce the volume occupied by the softer materials such as shell and clay, and this can be achieved by crushing the softer materials. Of course, the dia mondsshould not be crushed. It is therefore desirable to have some apparatus for selectively crushing the softer material without damaging the harder diamondiferous material.

The present invention seeks to provide such an apparatus.

Summary of the invention The present invention provides a selective crushing roll apparatus for selectively crushing softer particles in a mixture of softer and harder particles, the apparatus including at least one pair of adjacent crushing rolls forming a nip between them into which the mixture can be fed and meansforcausing the rolls to rotate in opposite directions, at leastthe crushing surfaces of the rolls being of a resilient mat- erial.

Preferably, the rolls are forced together. The rolls may be caused to rotate at the same, or different, rotational speeds.

Typically, the rolls will have rigid cores with surface linings of a resilient material such as poly urethane or a natural or synthetic rubber.

According to another aspect of the invention there is provided a method of selectively crushing softer particles in a mixture of softer and harder particles, including the step of feeding the mixture into a nip formed between a pair of adjacent crushing rolls rotating in opposite directions, the crushing surfaces of the rolls being of a resilient material sothatthe softer particles are crushed and the harder particles passthroughthe nipwithoutanydiminution in size.

The method of the invention is of particular applic ationforthecrushing of diamond bearing materials comprising softer particles such as particles of clay and shells and the like and harder particles including hard rock particles and diamonds.

Briefdescription ofthe drawings Figure 1 shows a schematic view of apparatus according to a first embodiment of the invention; and Figure 2shows a schematic view of apparatus according to a second embodiment of the invention.

Description of embodiments Referring firstlyto the embodiment of Figure 1, apparatus according to the invention includes first and second crushing rolls 10 and 12 which have round cylindrical cast iron or steel cores 14 carrying resilient linings 16 of polyurethane.

Fixed to the roll 12 is a gear wheel 18 carrying a sprocket 20. A chain 22 extends about the sprocket 20 and another sprocket 24 identical to the sprocket 20.

There is therefore a 1:1 transmission ratio between the sprockets 20 and 24. The sprocket 24 is arranged to be driven by a motor viva a gearbox (notshown).

The gearwheel 18 meshes with a gearwheel 26 which can bave the same, or a different, number of teeth as the gear wheel 18. The gear wheel 26 carries a sprocket 28. A chain 30 passes about the sprocket 28 and about an identical sprocket 32 fixed to the roll 10. There is therefore a 1:1 transmission ratio between the sprockets 28 and 32.

In a prototype constructed according to this embodiment, the motor was rated at 7,5kW and the gearboxwas chosen to have an output speed of 116 RPM.Thustheroll 12 rotated at 116 RPM. Inthe prototype, the numbers of teeth on the gear wheels 18 and 26 were chosen to give a rotational speed of the roll 10 of 126 RPM. Because of the different roll speeds, there was relative shearing movement between the roll surfaces, resulting in a tearing action on material fed to the nip 34 between those surfaces.

In the prototype, the outside diameter of the rolls 10 and 12 was 320mm and the polyurethane lining had a thickness of 28mm.

By fixing the location of the relevantsupporting bearings,therolls lOand l2areforcedtogetherso that the polyurethane linings are in compression against one another. The spacing of the roll axes can, however be varied to suit different conditions.

In use marine sediment is fed to the apparatus buy a chute or vibratory feeder. Check plates are used to direct the sediment accurately to the nip 34 between the rolls 10 and 12.

When the motor is operational,the rolls 10 and 12 are driven in counter-rotation at the same rotational speed or at different rotational speeds (depending on whether the gearwheels have equal or unequal num bers of teeth), as indicated by the arrows 36. Because ofthe resilient nature ofthe roll linings, only softer material in the marine sediment, such as shell and lumps of clay, is crushed in the nip between the rolls, harder particles such as diamondiferous particles passing through the nip without any diminution in size. Further processing is facilitated by the reduction in volume occupied by the crushed softer materials.

The comminuted softer materials may subsequently be subjected to screening to achieve further classification.

Various different drive arrangements are possible.

For instance, a hydraulic drive could be used instead of an electric motor drive. The crushing characteristics of the apparatus can be varied by chan ging the roll spacing, by varying the force with which the rolls are presssed against one another, or by using roll linings of different resiliency.

In the Figure 1 embodiment, both rolls 10 and 12 are driven by the associated sprockets. In the embodiment of Figure 2, only one roll is sprocket driven.

Referring to Figure 2,the first roll 40 rotatesabouta fixed axis and carries a sprocket 42. A chain 44 ex- tends aboutthis sprocket and about another identical sprocket 46 which is motor-driven. There is thus a 1:1 transmission ratio between the sprockets 42 and 46.

The second roll 48 has no associated sprocket and is supported rotationally by a floating bearing 50 which is capabie of sliding movement in an inclined member 52 of a rigid frame 54. In this case, the second roll 48 has a greater mass than the roll 40 and is driven by the roll 40 by friction.

Claims

1. A selective crushing roll apparatusforselec tivelycrushing softer particles in a mixture of softer and harder particles, the apparatus including at least one pair of adjacent crushing rolls forming a nip between therm into which the mixture can be fed and meansforcausingtherollsto rotate in oppositedi- rections, at leastthe crushing surfaces ofthe rolls being of a resilient material.

2. Apparatus according to claim 1 wherein the rolls are forced together.

3. Apparatus accordingto claim 1 orclaim2 wherein the rolls are caused to rotate at the same rotational speed.

4. Apparatus accordingto claim 1 orclaim2 wherein the rolls are caused to rotate at different rotational speeds.

5. Apparatus according to any one of claims 1 to 4 wherein each roll comprises a rigid core with a surface lining of a resilient material.

6. Apparatus according to claim 5 wherein there silient material comprises polyurethane or a natural or synthetic rubber.

7. A method of selectively crushing softer particles in a mixture of softer and harder particles includes the step of feeding the mixture into a nip formed between a pair of adjacent crushing rollers rotating in opposite directions, the crushing surfaces ofthe rolls being of a resilient material so thatthe softer particles are crushed and the harder particles pass through the nip without any diminution in size.

8. Amethod accordingto claim7whereinthe mixture of softer and harder particles comprises a diamond bearing material including softer particles and harder particles including rock particles and diamonds.

9. A seiective crushing roll apparatus forselec- tively crushing softer particles in a mixture of softer and harder particles substantiaily as herein described with referenceto Figure 1 or Figure 2 ofthe accompanying drawings.