ZA200607077B - Roll crusher - Google Patents

Description

FIELD OF INVENTION | LII)IK - 200 6/70 7077 ® This invention lies in the field of roll crushers, an example of a roll crusher of this general type is described for example in South African patent 1996/3891, granted to Krupp Fordrtechnik GmbH.

BACKGROUND

Crushing Of ores is often done with ball mills or rod mills, in many cases after initial size reduction for example in gyratory crushers or jaw crushers and ball and rod mills may be used to reduce particle sizes to less than 300 micron, for example. However, despite their widespread use ball crushers tend to cost levels in the region of R 35 per ton, they are a very large capital investment, require large footprint area and often several mills are required to handle mine output. Large motors e.g. 400 to 500 kW are typical and efficiencies as low as % are encountered.

Apart from ores encountered in the beneficiation of platinum group metals and gold, crushing is required in many other applications, for example ferro- chrome, where crushing to the region of 7 micron is required, cement production requiring crushing to the region of 20 micron and generally any type of rock.

A problem in the use of roll crushers is the encountering of very hard materials which can cause breakage or severe wear of the rolls and several design proposals focus on regulating of pressure, e.g by hydraulic or spring systems and yielding arrangements to vary the crushing gap; other proposals relate to wear inserts or roll segments, wear monitoring installations and crushing teeth inserts. Other problems relate to undue wear rates, skill and care required for gap setting and other operational aspects.

THE INVENTION :

A roll crusher in accordance with this invention is characterized by a driven roll ® and an idler roll, one roll being of larger diameter than the other; the rolls are held in contact with each other and tensioning means, e.g. springs, holds them in contact at pressures that can be set.

The driven roll may be of larger diameter than the idler roll or vice versa, and an optimum feed angle can be selected for the ore to be fed into the nip between the rolls. The feed angle can be defined as the angle off the vertical of an imaginary tangent to the two rolls at the position where the two rolls touch or nearly touch. The fed angle may be adjusted by providing a difference in height between the axes of rotation of the two rolls, so that the tangent is inclined at an angle to vertical.

Preferably the feed is controlled to a selected size range, which can be selected according to other parameters, such as the ore hardness characteristics, roll diameters, roll speeds and other factors.

A preferred plant would include a sieve arrangement which allows oversize material to be diverted for preliminary preparation suitable for feeding to the rolls and undersize material according to a specified size limit to be fed in a : suitable way to the rolls. This may include a hopper providing feed via a conveyor belt to a spreader chute to feed the material to a width approaching the lengths of the rolls.

The rolls of the invention are preferably not profiled or textured but are smooth.

It is found that the quality of the crushing is a function of the spring (or hydraulic) tension applied between the two rolls and the sizes of the two rolls.

The feed to the rolls may be effected by means of a hopper feed or conveyor belt or other means; a conveyor belt feed may be directed from the side of the small roll or from the side of the large roll.

® THE DRAWINGS

The invention is more fully described by way of examples, with reference to the drawings, in which : -

Figure 1 shows rolls schematically,

And :

Figure 2 shows rolls in isometric view.

THE PREFERRED EMBODIMENTS

As shown in figure 1 the roll crusher 1 includes a driven roll 2, anidler roll 3 and a spring tension structure 4, which applies a pressure between the rolls. A feed conveyor 5 is shown as a conveyor belt which delivers material 6 to be crushed to the nip 7 between the rolls, the rotation direction being shown by the arrows 8 and 9. An initial embodiment of the invention has been produced to give optimum crushing or fracturing of chrome ore; the system functions well in a small to medium driven setup.

Not shown is a ramp for front end a loader to load ore by tipping into a bin.

From the bin the ore is fed through a chute to a conveyor which in turn feeds a vibratory screen that separates the ore. The oversize is fed via a chute onto a second conveyor that stockpiles the oversize that will be crushed to a manageable size for this roll crusher. The undersize is fed via the conveyor 5 and a spreader chute to the rolls. The rolls are in contact with each other and the driven roller is driven through a gearbox.

For example a set of rolls measuring 800 mm diameter and 680 mm diameter and 1,8 m long are driven by a 22 kW motor, crushing chrome ore to 7 micron size 80% efficient and costing in the region of R 4 per ton crushed. Cement can be crushed to 20 micron for example, and indeed any rock. Infeed size ® may be in a range up to 10 mm screen pass. Feed may attain 40 tons per hour. Another example of material that may be processed is building sand.

In the case of chrome ore the infeed is fractured into crystals which themselves are entire or whole, at the size range indicated. It is found that the material tends to crush itself, i.e. the rolls surfaces appear to be insulated from direct wear on them by the material, resulting in efficient comminuting and roll life.

As shown in figure 2, the roll crusher installation 10 comprises a large diameter roll 11 and a small diameter roll 12, the small roll being driven by an electric motor 13, a vee belt 14 on pulleys 15 gnd 16 and a gearbox 17 that reduces the roli speed to a suitable speed. For example a speed of 450 r.p.m. has been found to be suitable. The rolls 11 and 12 are journalled in plummer blocks 18 and 19 respectively and the same on the other side (not seen). The small roll is fixed in position on the frame 20 but the large roll has its plummer blocks able to slide in tracks on the frame (not seen), controlled by hydraulic cylinders 21 and 22. A hydraulic system including a motor 23, pump 24 and control box 25 applies control to the large roll. This can place the large roll at a desired clearance from the small roll and apply a resistance to being displaced that can be set at a required level. A conveyor belt 26 supplies material to the nip 27 between the rolls. The feed angle between the rolls is indicated by the broken line 28.

REFERENCE NUMERALS

1 ROLL MILL 2 DRIVEN ROLL 3 IDLER ROLL 4 SPRING TENSIONER

CONVEYOR BELT

6 MATERIAL

7 NIP AT INFEED TO ROLLS 8 ROTATION DIRECTION - ® 9 ROTATION DIRECTION Mr200 6/07077

ROLL CRUSHER ASSEMBLY

11 LARGE DIAMETER ROLL 12 SMALL DIAMETER ROLL 13 ELECTRIC MOTOR 14 VEE BELT

VEE BELT PULLEY

16 VEE BELT PULLEY 17 GEARBOX 18 PLUMMER BLOCK 19 PLUMMER BLOCK

FRAME

21 HYDRAULIC CYLINDER 22 HYDRAULIC CYLINDER 23 MOTOR 24 HYDRAULIC PUMP

HYDRAULIC CONTROLS BOX

26 CONVEYOR BELT 27 INFEED NIP BETWEEN ROLLS 28 INFEED ANGLE AT NIP BETWEEN ROLLS

SRN Ty S—

Claims (11)

1. CLAIMS : oe
2. ® 1. A roll crusher, which is characterized by a driven roll and an idler roll, one roll being of larger diameter than the other, the rolls are held in contact with or close to each other and tensioning means, which hold them in position at pressures that can be selected. 2, A roll crusher as claimed in claim 1, in which the driven roll is of smaller diameter than the idler roll.
3. 3. A roll crusher as claimed in either one of claims 1 or 2, in which an optimum feed angle can be selected for the ore to be fed into the nip between the rolls.
4. 4. A roll crusher as claimed in claim 3, in which the fed angle is adjusted by providing a difference in height between the axes of rotation of the two rolls.
5. 5. A roll crusher as claimed in any one of claims 1 to 4, which is : included in a plant that has a sieve arrangement which allows oversize material to be diverted for preliminary preparation suitable for feeding to the rolls and undersize material according to a specified size limit to be fed in a suitable way to the rolls.
6. 6. A roll crusher as claimed in claim 5, in which the feed includes a hopper providing feed via a conveyor belt to a spreader chute to feed the material to a width approaching the lengths of the rolls.
7. 7. . Aroll crusher as claimed in claim 6, in which the feed approaches from the side of the small roll.
8. 8. A roll crusher as claimed in claim 6, in which the feed approaches from the side of the large roll.
9. 9. A roll crusher as claimed in any one of claims 1 to 8, in which the ® rolls of the invention are not profiled or textured but are smooth.
10. 10. Arroll crusher as herein described and as illustrated in figure 2 of the drawings.
11. 11. A process of operating a roll crusher as claimed in anyone of claims 1 to 10, in which the feed is controlled to a selected size range, selected according to parameters which include the ore hardness characteristics, roll diameters and roll speeds. DATED THIS 24™ DAY OF AUGUST 2006. {4 Aun APPLICANTS AGENTS