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Title:
IMPROVEMENTS IN ROLL CRUSHERS
Document Type and Number:
WIPO Patent Application WO/1999/047263
Kind Code:
A1
Abstract:
An improved roll crusher (10, 60) characterised by at least a pair of substantially opposed rolls (12, 14) between which feed particles (30) may be fed, the roll face of at least one of the pair comprising a roll surface across a substantial portion of which are provided continuous slope discontinuities.

Inventors:
VELLETRI MARIO (AU)
VELLETRI PIERO (AU)
Application Number:
PCT/AU1999/000148
Publication Date:
September 23, 1999
Filing Date:
March 12, 1999
Export Citation:
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Assignee:
CVR HOLDINGS PTY LTD (AU)
VELLETRI MARIO (AU)
VELLETRI PIERO (AU)
International Classes:
B02C4/08; B02C4/30; (IPC1-7): B02C4/30; B02C4/08; B02C4/28
Foreign References:
US4410144A1983-10-18
US4906419A1990-03-06
GB2146919A1985-05-01
DE4332782A11995-03-30
Other References:
DERWENT ABSTRACT, Accession No. 79-13828B/07, Class D16, P41; & SU 600177 A (MAGARACH) 20 April 1978.
DERWENT ABSTRACT, Accession No. 82-C5674E/10, Class P41; & FR 2487698 A (MILLE L) 5 February 1982.
DERWENT ABSTRACT, Accession No. 95-307675/40, Class D14; & JP 07204896 A (TOKYO MENKI KK) 8 August 1995.
DERWENT ABSTRACT, Accession No. 97-449198/42, Class A35, (A95); & CA 2193334 A (TIREX AMERICA INC) 20 June 1997.
DERWENT ABSTRACT, Accession No. 85-123963/21, Class P41; & EP 142162 A (ABLA CONSULT INT) 22 May 1985.
Attorney, Agent or Firm:
WRAY & ASSOCIATES (W.A. 6000, AU)
Download PDF:
Claims:
THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS
1. An improved roll crusher characterised by at least a pair of substantially opposed rolls between which feed particles may be fed, the roll face of at least one of the pair comprising a roll surface across a substantial portion of which are provided slope discontinuities.
2. An improved roll crusher according to claim 1, in which the slope discontinuities comprise an alternating arrangement of convex surfaces interspersed with alternating surfaces of a differing profile.
3. An improved roll crusher according to claim 2, in which the alternating surfaces of a differing profile are provided with a substantially plane surface.
4. An improved roll crusher according to any one of claims 1 to 3, in which the roll face of one roller comprises slope discontinuities whilst the roll face of the remaining roller is adapted to allow a substantially uniform gap therebetween during rotation.
5. An improved roll crusher according to any one of claims 1 to 4, in which the roll face of one roll of the pair comprises an alternating arrangement of convex and plane surfaces, the roll face of the remaining roll of the pair comprising an alternating arrangement of concave and plane surfaces.
6. An improved roll crusher according to claim 4 or 5, in which the pair of rolls are arranged such that during rotation of the rolls the concave or convex surfaces of each roll are substantially opposed.
7. An improved roll crusher according to any one of claims 4 to 6, in which the pair of rolls rotate at the same speed and maintain a generally constant or substantially uniform gap between the roll faces.
8. An improved roll crusher according to any one of the claims 5 to 7, wherein the plane surfaces and the convex or concave surfaces of each roll alternate on a regular basis and define points of transition between the plane surfaces and the convex or concave surfaces.
9. An improved roll crusher according to claim 8, wherein the points of transition on the rolls decrease the angle of nip between the surfaces of the rolls relative to prior art roll crushers employing rolls of the same diameter, thereby increasing the reduction ratio of the improved roll crusher.
10. An improved roll crusher according to claim 9, wherein the feed particles are drawn into the rolls with a smallest angle of nip defined between the tangents described by the point of transition between the convex surface and plane surface on one roll, and the plane surface of the other roll.
11. An improved roll crusher according to claim 5, in which ratio of the radii describing the concave surfaces of one roll to the radii describing the convex surfaces of the other roll is about 2.83: 1.
12. A method of comminuting materials, the method characterised by the method steps of : feeding particles of the material to be comminuted to a double roll crusher; the double roll crusher comprising a pair of rolls, the roll face of at least one of the pair comprising a roll surface across a substantial portion of which are provided slope discontinuities, the roll face of the remaining roll being adapted to allow a minimal variation in the gap therebetween; rotating the rolls at the same speed whereby a generally constant or subsantially uniform gap is maintained therebetween; and wherein the discontinuities of slope on the roll face of at least one roll acts to provide a generally small angle of nip and a consequently large reduction ratio.
13. A method according to claim 12, in which the slope discontinuities of at least one roll face comprise an alternating arrangement of convex surfaces interspersed with alternating surfaces of a differing profile.
14. A method according to claim 13, in which the alternating surfaces of a differing profile are provided with a substantially plane surface.
15. An improved roll crusher substantially hereinbefore described with reference to any of Figures 1 and 3 to 7.
16. A method of comminuting materials substantially as hereinbefore described with reference to the Figures 1 and 3 to 7.
Description:
TITLE Improvements in Roll Crushers FIELD OF THE INVENTION The present invention relates to improvements in roll crushers. The improvement of the present invention is particularly intended for use with double roll crushers.

Still more particularly, the roll crusher of the present invention is intended to provide an improved or smaller angle of nip.

BACKGROUND ART Size reduction or comminution equipment is commonly available in a variety of forms. These include for example hammer mills, rolling compression mills, attrition mills, revolving mills, ultrafine grinders, cutting machines and crushers.

Crushers are commonly defined as either coarse, intermediate or fine. The roll crusher is generally referred to and used as either a primary or secondary crusher.

Typically, a double roll crusher comprises a pair of rolls rotatable in opposite directions and inwardly toward each other. One of the rolls is provided in ajustable bearings and is spring loaded so as to allow very hard material passage through the crusher. One or both of the rolls may be driven. If only one roll is driven the other will be driven by friction.

Double roll crushers are generally provided in either smooth or toothed configurations. Toothed roll crushers tend to be more versatile than smooth roll crushers although they typically cannot handle very hard solids. The smooth roll crusher produces few fines and almost no oversize product. However, they are known to operate most efficiently when set to give a reduction ratio of feed to product of 3 or 4: 1. A greater reduction ratio, up to 8: 1, can be generated if the rolls are kept full of feed as crushing is achieved not only by the action of the rolls

but by attrition between the particles of feed also. This process is referred to as choke crushing. The serious draw back associated with this method is a consequent increase in power consumption.

It is seen as desirable to increase the reduction ratio of roll crushers to a ratio perhaps more typical of the cone crusher, being about 10: 1. However, the cone crusher has associated problems of low throughput and high wear.

At present, smooth roll crushers are most commonly used for secondary crushing applications on reasonably friable materials, including oil shale, coal and phosphate. It is considered desirable to improve the application of roll crushers to harder material, including gold ores and the like.

Smooth roll crushers are limited as to the size of feed particle they can process because of the angle of nip between rollers of a given diameter. The angle of nip is defined as the angle between the roll faces at the level where they are just able to take hold of a feed particle and draw it into the crusher's crushing zone.

Typically, very large diameter rolls are required to nip small particles, resulting in very high capital costs. It is considered desirable to decrease the angle of nip for a given feed particle size as this increases the likelihood of that given feed particle size being drawn into the crushing zone. Alternatively, an angle of nip comparable with that provided by the prior art may be achieved with rolls of a smaller diameter, and consequently with lower capital cost.

Whilst the toothed roll crushers of the prior art may be argued to reduce the angle of nip through the presence of the teeth on the faces of the rolls, they are unable to provide a substantially uniform or constant gap between the rolls. This leads to poor control of product size.

The improved roll crusher of the present invention has as one object thereof to substantially overcome the above-mentioned problems associated with the prior art.

Throughout the specification, unless the context requires otherwise, the word "comprise"or variations such as"comprises"or"comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

DISCLOSURE OF THE INVENTION In accordance with the present invention there is provided an improved roll crusher characterised by at least a pair of substantially opposed rolls between which feed particles may be fed, the roll face of at least one of the pair comprising a roll surface across a substantial portion of which are provided slope discontinuites.

Preferably, the slope discontinuities comprise an alternating arrangement of convex surfaces interspersed with alternating surfaces of a differing profile. The alternating surfaces of a differing profile may be provided with a substantially plane surface.

Still preferably, the roll face of one roller comprises slope discontinuities whilst the roll face of the remaining roller is adapted to allow a minimal variation in the gap therebetween.

The roll face of one roll of the pair may preferably comprise an alternating arrangement of convex and plane surfaces, the roll face of the remaining roll of the pair comprising an alternating arrangement of concave and plane surfaces.

The pair of rolls may preferably be arranged such that during rotation of the rolls the concave or convex surfaces of each roll are substantially opposed.

In one form of the invention, the pair of rolls rotate at the same speed and maintain a generally constant or substantially uniform gap between the roll faces.

The plane surfaces and the convex or concave surfaces of each roll alternate on a regular basis and define points of transition between the plane surfaces and the

convex or concave surfaces. The points of transition on the rolls decrease the angle of nip between the surfaces of the rolls relative to prior art roll crushers employing rolls of the same diameter, thereby increasing the reduction ratio of the improved roll crusher. The feed particles are drawn into the rolls with a smallest angle of nip defined between the tangents described by the point of transition between the convex surface and plane surface on one roll, and the plane surface of the other roll.

In accordance with the present invention there is further provided a method of comminuting materials, the method characterised by the method steps of : -feeding particles of the material to be comminuted to a double roll crusher; -the double roll crusher comprising a pair of rolls, the roll face of at least one of the pair comprising a roll surface across a substantial portion of which are provided slope discontinuites, the roll face of the remaining roll being adapted to allow a minimal variation in the gap therebetween; -rotating the rolls at the same speed whereby a generally constant or subsantially uniform gap is maintained therebetween; and wherein the discontinuities of slope on the roll face of at least one roll acts to provide a generally small angle of nip and a consequently large reduction ratio.

The slope discontinuities of at least one roll face preferably comprise an alternating arrangement of convex surfaces interspersed with alternating surfaces of a differing profile. In one form of the invention the alternating surfaces of a differing profile are provided with a substantially plane surface.

BRIEF DESCRIPTION OF THE DRAWINGS The improved roll crusher of the present invention will now be described by way of example only, with reference to two embodiments thereof and the accompanying drawings, in which: Figure 1 is a diagrammatic cross-sectional view of an improved roll crusher in accordance with a first embodiment of the present invention; Figure 2 is a diagrammatic cross-sectional view of a smooth roll crusher of the prior art and showing calculation of the angle of nip; Figure 3 is a cut-away view of the improved roll crusher of Fig. 1 showing calculation of the angle of nip therein; Figure 4 is a diagrammatic cross-sectional view of the improved roll crusher of Figure 1 showing the rolls with the gap therebetween set at Omm; Figure 5 is a graphical representation of the variation in horizontal roll gap through a 60° rotation of the rolls from the position shown in Figure 4; Figure 6 is an upper perspective view of an improved roll crusher in accordance with a second embodiment of the present invention; and Figure 7 is a side elevational view of the improved roll crusher of Figure 4.

BEST MODE (S) FOR CARRYING OUT THE INVENTION In Figure 1 there is shown in part a diagrammatic representation of an improved roll crusher 10 comprising a first roll 12 and a second roll 14 mounted horizontally and in a generally opposed and parallel manner along their length. The rolls 12 and 14 are mounted so as to be rotatable about axes 12a and 14a respectively.

The roll 12 has provided at its periphery a roll face comprising an alternating but regular arrangement of concave surfaces 16 and plane surfaces 18. The meeting of the surfaces 16 and 18 define slope discontinuities extending across either the entire width/length of the roll 12 or a substantial portion thereof. The points at which the surfaces 16 and 18 meet define points of transition 20 along the width/length of the roll 12.

The roll 14 has provided at its periphery a roll face comprising an alternating but regular arrangement of convex surfaces 22 and plane surfaces 24. The meeting of the surfaces 22 and 24 defines slope discontinuities extending across either the entire width/length of the roll 14 or a substantial portion thereof. The points at which the surfaces 22 and 24 meet define points of transition 26 along the width/length of the roll 12.

The rolls 12 and 14 are arranged to rotate inwardly or towards each other, as generally indicated by arrows 28. Rotation of the rolls 12 and 14 in this manner acts to draw feed particles, for example feed particle 30, downwardly between the rolls 12 and 14. The distance or gap 32 between the rolls 12 and 14 is set by a user (not shown) and is typically limited by a stop means (not shown).

In Figure 2 there is shown a diagrammatic representation of a smooth roll crusher 34 comprising smooth rolls 36 and 38, and showing a feed particle 40 being fed therebetween. The angle of nip is the angle formed by the tangents 42 to the faces 44 of the rolls 36 and 38 at the point of contact with the feed particle 40. As shown in Figure 2, the angle of nip is 2a. The geometry of this arrangement is such that the angle of nip may be calculated as follows: r, + b Equation 1: = cosa r2 + r1 For smooth roll crushers typical of the prior art the angle of nip is generally not greater than 30° to 32°. However, as is evident from the above calculation,

factors such as the particle size and the radius of the rolls have an impact on the angle of nip.

In Figure 3 there is shown a portion of the improved roll crusher 10 of Figure 1 and feed particle 30. The convex surface 22 is in effect the exposed surface of a nominal cylinder 46 passing along the length of the roll 14. A tangent line 48 for the point of particle 30 in contact with the surface 22 is described, as is a "tangent"line 50 for the point of particle 30 in contact with the plane surface 18.

The tangents 48 and 50 define an angle of nip 52.

The angle of nip 52 is less than that provided by smooth rolls 36 and 38 for the same size feed particle and for rolls of substantially equivalent diameter. This smaller angle of nip is generated through the specific interaction of the surfaces of the rolls 12 and 14. Specifically, it is the relative positioning of the alternating convex or concave surfaces and the plane surfaces. It is only this arrangement that provides a tangent line of the nature of tangent 48 to be effective, thereby providing a smaller angle of nip. As a result there is a greater likelihood of "nipping"larger feed particles and which in turn increases the reduction ratio of the improved roll crusher 10.

It can be seen from Figure 3 that the particle 30 contacts the roll face of the roll 14 at two points, one on the convex surface 22 and one on the plane surface 18.

This action, made possible through the slope discontinuities of the roll face of roll 14, contributes to the ability of the roll crusher 10 to"nip"or grab a theoretical spherical feed particle, as depicted by feed particle 30.

In Figure 4 there is shown the improved roll crusher 10 with the gap 32 set at Omm. The measurements provided in Figure 4 are in millimetres and it is envisaged that the roll crusher 10 when used will be four timas as large. The preferred radius defining the concave surfaces 16 is shown at reference numeral 54 as 119.45mm, whereas the preferred radius defining the convex surfaces 22 is shown at reference numeral 56 as 42.19mm. Whilst the exact measurements of the radii will vary depending upon the size of the rolls the invention is applied to,

the ratio therebetween will not. Accordingly, the ratio of the radii 54 to 56 is about 2.83: 1. This ratio has been calculated in an attempt to minimise fluctuations in the gap 32 during rotation of the rolls 12 and 14.

In Figure 5 there is shown a graphical representation of the fluctuation in roll gap 32 through a 60° rotation of the rolls 12 and 14 from the point shown in Figure 4.

The minimum theoretical gap of Omm is achieved when the convex and concave surfaces 22 and 16 are directly opposed as shown in Figure 4, and as represented by the lateral extremities of the x axis of the graph of Figure 5. The dips 58 in the graph of Figure 5 represent the points at which the points of transition 20 and 26 come closest together during rotation, whilst the peak 59 depicts the point at which the plane surfaces 18 and 24 are directly opposed.

The inventors have found the profile of the rolls 12 and 14 as discussed above to provide the most advantageous compromise between maintaining a substantially uniform gap 32 and yet providing a minimal angle of nip 52.

In use, the rolls 12 and 14 are caused to rotate in a synchronised manner, at the same speed and in the direction of arrows 28, as is shown in Figure 1. Feed particles 30 are directed between the rolls 12 and 14 by known means. The rolls 12 and 14 are synchronised such that the plane surfaces 18 and 24 of each roll are substantially opposed as are the concave surfaces 16 of the roll 12 and the convex surfaces 22 of the roll 14. Such an arrangement is again shown in Figure 3. The gap 32 between the rolls 12 and 14 is maintained at a generally constant distance through rotation of the rolls 12 and 14.

The discontinuity between the convex surfaces 22 and the plane surfaces 24 of the roll 14 substantially increases the probability that the particle 30 will be "nipped"between the rolls 12 and 14. As discussed hereinbefore, it is the co- operation between the points of transition 26 on the roll 14 and the plane surfaces 18 of the roll 12 that provide a smaller angle of nip 52, as seen in Figure 3, when compared with comparable prior art roll crushers.

A comparison may be made between the roll crusher 10 of the present invention and a smooth roll crusher of the prior art on the basis of, inter alia, either the nip angle created when rolls of the same diameter are used to nip a particle of a given size, or the roll diameter required to nip a particle of a given size if a given angle of nip is assumed. Please refer to the following examples: Example 1 Assuming a common roll diameter of 850mm, a spherical particle of 100mm diameter and a gap of 7mm, the comparison is as follows using Equation 1 as set out hereinabove : Prior Art Spherical Roll Crusher 10 Rolls ri 425mm 425mm r2 50mm 50mm b 7mm 0-7mm (assume worst case of 7mm) a 24.5° 10.2° 2a (angle of nip) 49° 20.4°

Example 2 Assuming a desire to achieve a nip angle in a prior art spherical roll crusher equivalent to that shown in Example 1, the necessary roll diameter can be calculated, again using Equation 1, as follows:

r, + 3.5mm = cos 10.2° r, = 2900mm 50mm + r, Consequently, the diameter of the smooth rolls necessary to provide a nip angle equivalent to that of the roll crusher 10 of the present invention with 850mm rolls, is 5800mm or 5.8m.

Both Examples 1 and 2 have been calculated assuming a desired gap of 7mm.

As is evident from the foregoing description, the gap 32 of the roll crusher 10 will actually vary during rotation of the rolls 12 and 14 between 0 and 7mm.

In Figures 6 and 7 there is shown a roll crusher 60 compising a support frame 62 and two roll assemblies 64. The support frame 62 comprises four legs 66, each with bracing members 68, and two elongate members 70 extending between them. The elongate members 70 each have provided on an upper surface thereof a skid 72 arranged to support the roll assemblies 64.

The roll assemblies 64 each comprise a motor 74 and a gear box 76, a drive shaft 78 and drive sprocket 80 being provided with each gear box 76. Each roll assembly further comprises either a first roll 12 or a second roll 14, the rolls 12 and 14 being as described with reference to the roll crusher 10, like numerals denoting like parts.

The rolls 12 and 14 are linked by way of a sprocket 82 and drive chain 84 to their respective drive sprockets 80, gear boxes 76 and motor 74 in an operable manner. As such, drive from the motors 74 can be transferred as required to the rolls 12 and 14. The rolls 12 and 14 are additionally mounted by way of roller bearings (not shown), in known manner, within the roll assemblies.

Each roll assembly 64 is supported by way of four skid members 86, the skid members resting upon the skid members 72 provided on the elongate members 70 of the support frame. Dustcovers or guards 87 may be provided for the

bearings, sprockets and chains of the roll assemblies. A dustcover may similarly be provided for the skids 86.

One of the roll assemblies 64 has associated therewith a spring assembly 88, the spring assembly 88 comprising two coaxially mounted springs 90 and a roll force adjusting crank 92. The crank 92 is threadedly engaged with a portion of the support frame 62 in a manner allowing operation of the crank 92 to adjust the tension in the spring assembly 88. The provision of the spring assembly acts to resiliently bias the one roll assembly 64 towards the other. The other or remaining roll assembly 64 is fixedly attached to the support frame 62, as can be best seen in Figure 7.

The gap 32 between the rolls 12 and 14, shown in Figure 1, is able to be set and adjusted through manipulation of a bolt 94 abutting the adjustably mounted roll assembly 64. The bolt 94 is threadedly mounted within a locating block 96 fixedly located on the elongate member 70. A further bolt 94 and mounting block 96 may be provided on the remaining elongate member 70 also.

The operation of the roll crusher 60 is substantially similar to that described for the roll crusher 10 hereinabove.

It is further envisaged that alterations in the arrangement and mounting of the roll assemblies 64 may be made without departing from the scope of the present invention. For example, a hydraulic ram, rather than the spring assembly 88, may be used to resiliently bias one of the rolls with respect to the other.

The improved roll crushers 10 and 60 of the present invention can be seen from the above description to lead to a higher reduction ratio than that provided by prior art roll crushers as larger particles may be"nipped"and this in turn leads to a greater reduction ratio. It is envisaged that such may be accomplished without significant increases in power consumption as compared to similar smooth roll crushers.

Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.