WO2009016484A1

WO2009016484A1 - Training idler roller assembly for a heavy duty conveyor belt

Info

Publication number: WO2009016484A1
Application number: PCT/IB2008/001999
Authority: WO
Inventors: John Pear Cumberlege
Original assignee: John Pear Cumberlege
Priority date: 2007-07-31
Filing date: 2008-07-31
Publication date: 2009-02-05

Abstract

A training idler roller assembly (1) for a heavy duty conveyor belt (5) is provided. The assembly comprises one or more idler rollers (2) mounted for free rotation on one or more axles (3) operatively mounted relative to a heavy duty belt conveyor to extend transversely relative thereto. Guide structure selected from at least one guide roller (8) and a flange is carried by the idler roller assembly at each side of the conveyor belt such that a spacing between opposite guide rollers or flanges exceeds the width of the conveyor belt. The guide structure is spaced from the idler roller in a direction of belt travel and each has a contact surface for operatively contacting an edge region of the belt upon lateral drift thereof. Such contact urges the edge of the conveyor belt out of the otherwise natural plane of the belt towards firmer engagement with the idler roller with the result that the conveyor belt is urged laterally to release contact with the said contact surface and thus return towards a central position.

Description

TRAINING IDLER ROLLER ASSEMBLY FOR A HEAVY DUTY CONVEYOR BELT

FIELD OF THE INVENTION

This invention relates to a conveyor belt training idler roller assembly for a heavy duty conveyor belt that is adapted to operate to return the conveyor belt to a generally central desired path of travel when the belt drifts laterally to one or other side of its intended path of movement.

BACKGROUND TO THE INVENTION

A training idler roller assembly is typically positioned between adjacent ordinary idler rollers at one or more predetermined positions along the length of a belt conveyor assembly. It is to be noted that the same considerations apply to both the upper load bearing pass of the endless conveyor belt and the lower return pass thereof.

It is well known in the art that a conveyor belt, whatever it's nature, generally requires some form of facility for returning it to a central position on its support rollers whenever it tends to drift laterally to one or other side of a desired path of movement during operation. Various expedients have been proposed and implemented in order to achieve this and in this regard generally vary according to the type of conveyor belt and the service it is rendering.

In the instance of generally light duty food type of conveyor belts (with which this invention is not concerned) training of the belt can be achieved by rather simple structure as a result of the generally short runs, light weight and physical properties of the conveyor belt material. Thus, for example, British patent number GB2077683 describes a food conveyor in which the belt is typically 0.25 to 1 mm thick (with an upper limit of 4 mm being mentioned) in which a low friction belt is passed around a low friction rod at a terminal end of the conveyor remote from a driven end. The low friction belt is disclosed as having a coating of PTFE on its surface that engages the roller or alternatively being a metal belt. Neither of these belt constructions would be practical for heavy duty applications as contemplated herein.

Turning now to some of the expedients that have been proposed, and possibly used in relation to heavy duty conveyor belts, some of these employ complex and costly arrangements that detect the positions of the edges of the conveyor belt and engage them in order to forcefully urge the conveyor belt inwards to a central position whenever it drifts away from such a central position. These are considered by applicant to be undesirable as a result of the fact that the edges of the conveyor belt can become frayed or damaged relatively rapidly.

Other devices tend to fall into one of two general categories. The first is that of relatively complex devices in which the position of the edge of a conveyor belt is employed to activate a power steering mechanism for positively steering a conveyor belt idler roller in a direction so that the belt returns to the centre of the roller. In this case sophisticated pneumatic, hydraulic, or electrical steering mechanisms may be activated to impart movement to the training idler roller to counteract the lateral drift of the conveyor belt.

Alternatively, a somewhat more simple mechanical arrangement may be utilized in which sensor rollers are activated by the edge of a belt as it drifts towards one side or the other and the contact between the edge of the belt and the sensor rollers translates into a positive mechanical steering action of the training idler roller. All of these devices that are known to applicant are typically mechanically complicated; are generally costly; and often require significant maintenance in view of their complexity and additional components.

The other general category of training idler rollers is one in which the training idler roller is free to rotate about a generally central axis transverse to the plane of the conveyor belt in order to allow the roller to slew about the axis and steer the belt back towards a central position on the idler roller. In this instance lateral movement of the belt itself is arranged to achieve the steering effect by virtue of increased drag exerted on the roller that is occasioned when the belt moves towards one side of its desired path. Such drag operated training idler rollers have, as far as applicant is aware, given rise to considerable difficulties in the mechanical mounting of the idler rollers so that they can slew about a central axis and in the way in which the conveyor belt activates the roller to in fact slew about the axis and thereby cause the conveyor belt to move back towards a central position.

The two latter categories of training idler rollers both depend for their operation on the provision on the outer surface of the roller of a friction affording layer that is typically a rubber material so that a positive frictional force can be used to move the conveyor belt back to a central position.

On the other hand, the use of low friction contact surfaces on standard idler rollers has been gaining in popularity. Of particular note, there have been idler rollers having at least a contact surface of ultra high molecular weight polyethylene that has a coefficient friction not very different from that of polytetrafluoroethylene (TEFLON™), an acknowledged leader in low friction materials.

It is to be noted that in this specification the term "low friction" is intended to mean low friction as would normally be understood by someone skilled in the heavy duty belt conveyor art. Nevertheless, in order to provide more guidance for the benefit of the addressee, the term low friction is intended to apply to conveyor belt training idler roller systems in which the coefficient of friction is significantly less than that existing between steel or rubber or polymer coated training idler rollers and a rubber coated or polymer coated conveyor belt.

It is also to be noted that there is a substantial difference between the centering of a belt relative to a drive roller that a driven conveyor belt would normally contact over about 180° of the generally cylindrical surface of the drive roller. Thus it would not be helpful to one of ordinary skill and knowledge in the art to look to devices used for centering a conveyor belt relative to a drive roller therefor.

Thus, one would not consider apparatus such as that described in United States patent number US6053832 in which guide rollers having a surface inclined towards the belt surface are in constant engagement with the edges of the belt to differing degrees according to lateral movement of the belt. In heavy duty applications such an arrangement would lead to serious and rapid abrasive action on the edges of the belt with a consequent unacceptable degree of wear. It is to be noted that such a drive arrangement is apparently aimed at lightweight applications that are outside the ambit of heavy duty conveyor belts and it is doubtful that such an arrangement would even be effective as a drive roller in a heavy duty conveyor belt application. The wear in an abrasive atmosphere, such as in a mining application, would simply be too great. One would therefore steer totally clear of such an arrangement for training idler rollers in a heavy duty application.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a training idler roller assembly for use in heavy duty conveyor belt applications that avoids complexities and at least alleviates one or more of the disadvantages of prior art training idler roller assemblies whilst nevertheless being effective in operation.

It is to be understood that, in this specification, the term heavy duty conveyor belt is intended to mean a conveyor belt designed to transport bulk material from one place to another, typically mined or excavated material such as coal and ore both before and after any crushing, milling, purification or extraction procedures have been carried out on it. Typically such conveyor belts have a width ranging between about a half a meter (2 feet) and about 3 meters (8 feet) with a thickness of from about 5 mm (2/10 of an inch) to about 35mm (1 and 4/10 inches). Such a conveyor belt may have a length of as little as 20 meters (22 yards) and may extend over substantial distances ranging from one or several hundred meters or yards to one or more kilometers (0.6 miles or more). Such conveyor belts are of generally rigid construction and have either or both of a fabric and steel reinforcing encased in a rubber material or a plastic such as polyvinyl chloride (PVC) or a suitable polyurethane (PTFE). In the instance of a fabric reinforcing, the reinforcing will typically comprise from 2 plies to about 8 plies.

In accordance with this invention there is provided a training idler roller assembly for a heavy duty conveyor belt comprising one or more idler rollers mounted for free rotation on one or more axles operatively mounted relative to a heavy duty belt conveyor to extend transversely relative to the travel direction thereof and to support a region of the belt in a manner such that lateral drift of the belt from a central desired position on the idler roller assembly towards one or other end thereof (side edge of the conveyor belt) automatically gives rise to corrective influence being imposed on the conveyor belt, and wherein guide structure selected from at least one guide roller and a flange is carried by the idler roller assembly and is associated with each side of the conveyor belt such that the spacing between opposite guide rollers or flanges exceeds the width of the conveyor belt thereby resulting in the conveyor belt, in a central desired position, not being in contact with either guide roller or flange, and wherein the guide structure is spaced from the idler roller in a direction of belt travel, the training idler roller assembly being characterized in that each of the guide structures has a contact surface associated therewith for operatively contacting an edge region of the belt upon lateral drift thereof to an appropriate extent in a manner that urges such edge of the conveyor belt out of the otherwise natural plane of the belt towards firmer engagement with the idler roller where the edge region of the belt contacts same such that the conveyor belt is urged laterally to release contact with the said contact surface of the guide structure and thereby give rise to said corrective influence being imposed on the conveyor belt.

It is noteworthy that heavy duty conveyor belts are often provided with a troughed configuration with side edge portions that are raised at an incline from a central portion of the belt so as to keep transported material on the belt against falling off the side edge portions therof. The side edges of conveyor belts naturally tend to curl upwardly or "cup" during belt travel. With troughed belts, loading tends to be concentrated on the central, more flat portion of the belt thus exacerbating the belt cupping problem. If the idler roller of the training idler roller assembly herein is an inclined wing roller configured to roll about a fixed, inclined axle and used to support a side edge portion of a troughed belt, it has been found that cupping of the corresponding belt edge is undesirable. Normally, wing rollers will each carry approximately 15% of the load on the belt while 70% of the load is carried by the center roller. With belt cupping, the wing rollers may only carry 10% of the load which is insufficient to properly influence the tracking or steering of the belt. Accordingly the guide structure described above is configured and arranged so that when the belt drifts laterally toward the guide structure, the raised side edge of the cupped belt side edge portion, will engage the guide structure so that the contact between them generates a generally downward force on the raised edge of the belt to push the cupped side edge portion back down onto the wing roller.

This allows the wing roller, which preferably is towed-in oriented from its inner end under the belt to its outer end in the belt travel direction, to exercise a corrective influence on the otherwise misaligned belt urging it back toward its proper centered position on the rollers.

In a preferred form, the guide structure comprises a guide roller having an enlarged upper head portion at the upper end of the roller shaft. Either surfaces of the shaft or head portion of the roller can engage the raised side edge of the cupped belt portion and urge it back downwardly. Preferably, the roller shaft is rotatable about an upstanding fixed axle mounted to a frame of the training idler roller assembly unit so as to extend at an acute angle to the fixed axle of the wing roller. In this manner, a confined pocket is formed between the guide roller and the adjacent idler roller with the surfaces of the shaft and any head portion oriented to push the raised belt edge back down toward the idler roller.

As a general rule, but not essentially, the idler roller assembly is formed as a modular idler roller unit adapted to be attached to an existing conveyor belt installation.

In a first variation of the invention the said one or more idler rollers are mounted, in plan view, on a line at right angles to the desired path of travel of the conveyor belt and in this instance, each idler roller has a low friction outer surface and each of the guide structure is a guide roller having its axis of rotation inclined inwardly towards the conveyor belt relative to the axis of rotation of the adjacent idler roller with the guide roller being located either on the approach side of the idler roller or on the exit side thereof, or both in the event there are two guide rollers on each side of the conveyor belt. In a second variation of the invention the training idler roller assembly comprises a plurality of idler rollers mounted for free rotation on two or more axles have their axes extending transversely across the desired path of travel of the conveyor belt over the idler rollers in use so as to support the conveyor belt over at least a substantial part of the width thereof wherein two control idler rollers are arranged symmetrically about a centre line of the desired path of movement of the conveyor belt so as to effectively support the conveyor belt over a part of its width and wherein the axis of rotation of each of the control idler rollers is, in plan view, inclined to a line extending at right angles to said centre line such that a component of force directed inwardly towards said centre line is exerted on the conveyor belt from each side of the centre line by the two control idler rollers in use to thereby give rise to a corrective influence being imposed on the conveyor belt.

In this second variation of the invention the control idler rollers are preferably arranged to operatively extend outwards from a position beneath a conveyor belt to a position beyond the edge thereof. In such an instance the guide structure may be either a guide roller having its axis of rotation inclined inwardly towards the conveyor belt relative to the axis of the adjacent control idler roller or it may be a flange rotatable in unison with the outer end region of the control idler roller such that the periphery of the flange contacts an edge of a belt that drifts into contact with it downstream of the axis of the control idler roller to urge the belt out of the otherwise natural plane of the belt and towards the roller and thereby give rise to said corrective influence being imposed on the conveyor belt.

In the second variation of the invention, the plurality of idler rollers may comprise either a control idler roller extending outwards from a central region beneath a conveyor belt towards each side thereof, or a single central idler roller located between the operatively inner ends of the control idler rollers to support the central region of a conveyor belt in use. The plurality of idler rollers, in elevational view, may define a composite flat support idler roller assembly for supporting a conveyor belt in a substantially flat condition or, alternatively, the plurality of idler rollers may be arranged to support a conveyor belt in a generally troughed condition. Still further in the second variation of the invention, each of the individual idler rollers could have a low friction outer surface or the outer surface may be of a standard type of friction afforded by materials such as rubber and some plastics materials. In the latter instance, the friction can be used as a belt cleaning facility as the limited lateral slip of the belt relative to the control idler rollers inherently performs a scraping type of effect.

In either variation of the invention, the angle between the axis of any guide roller and the axis of the adjacent idler roller is preferably greater than 45° and more preferably between 60 and 89° and most preferably between 75 and 89°. It has been found that this acute angle is effective to prevent the edge of the belt moving up and down in an uncontrolled manner when an edge contacts the guide roller or even moving away from the relevant region of the idler roller to thereby exacerbate the situation. The angle selected will depend largely on the properties of the belt and its natural tendencies in operation, particularly, its tendency to cup as described above.

In the instance of a low friction outer surface, the coefficient of friction with a conveyor belt in use is preferably at most 0.5, more preferably a less than about 0.2, and most preferably less than about 0.1. The low friction outer surface may be selected from a surface of a high density polyethylene material, preferably ultra high density polyethylene material and a polytetrafluoroethylene (TEFLON™) material. The contact surface of any guide roller and the outer end region of any idler roller may have a contact surface presenting a hard wearing surface having a preferred hardness of about 65 to 70 HRC Rockwell.

The invention also provides a conveyor belt installation in which a training idler roller assembly as defined above is included and the training idler roller is positioned to lift the conveyor belt off adjacent standard idler rollers in order to ensure proper contact with the training idler roller assembly. More specifically, in a preferred arrangement according to the invention, prefabricated training idler roller assemblies according to the invention are installed between adjacent standard idler rollers by attaching a frame of the training idler roller assembly to the longitudinally extending support stringers of the belt conveyor installation. Preferably the prefabricated assemblies are configured so that they can be attached to any one or a number of different conveyor belt installations and need only to be simply bolted to the stringers.

Clearly, the exact configuration of a training idler roller according to the invention will depend on the size, nature and speed of operation of the conveyor belt to be supported and, most significantly, on the material and surface characteristics of the idler roller and surface of the belt in contact therewith.

In order that the above and other features of the invention may be more fully understood, various embodiments of the invention will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is a schematic part sectional elevation taken across the width of a belt conveyor and illustrating a simple embodiment of training idler roller of the first variation of the invention;

Figure 1a is an enlarged view of one end of the roller illustrated in Figure 1 ;

Figure 2 is a schematic side elevation of a short length of the conveyor belt assembly thereof;

Figure 3 is a schematic plan view thereof;

Figure 4 is an elevation taken across the width of a belt conveyor similarly to Figure 1 but illustrating application of the first variation of the invention to a two roller trough training idler roller assembly;

Figure 5 is a similar elevation illustrating application of the first variation of the invention to a three roller trough training idler roller assembly; Figure 6 illustrates an arrangement similar to Figure 1 in which the idler roller has somewhat flared ends;

Figure 7 is a schematic plan view illustrating a short length of a conveyor including a simple embodiment of training idler roller assembly of the second variation of the invention;

Figure 8 illustrates schematically, in elevation, a straight (generally horizontal) arrangement of the control idler rollers illustrated in plan view in Figure 7;

Figure 9 illustrates schematically, in elevation, a troughed arrangement of control idler rollers for supporting a conveyor belt in a troughed condition;

Figure 10 is the same as Figure 7 but illustrates a different shape of control idler roller;

Figure 11 is a schematic plan view similar to Figure 7 but showing a three roller idler assembly;

Figure 12 is a similar schematic plan view illustrating an alternative form of guide structure in the form of a flange rotatable in unison with each of the control rollers;

Figure 13 illustrates schematically, in side elevation, the way in which the guide structure illustrated in Figure 12 operates;

Figure 14 illustrates schematically, in side elevation, an installation showing one general form of positioning of a training idler roller assembly of the type provided by this invention; Figure 15 illustrates one form of modular training idler roller assembly according to the invention separately from any conveyor components;

Figure 16 illustrates schematically an inclined conveyor belt; and,

Figure 17 illustrates one form of modular training idler roller assembly according to the invention that is configured to act also as a belt arrestor in applications in which a belt conveyor traverses a significant incline as illustrated in Figure 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the embodiment of the first variation of the invention illustrated in Figures 1 to 3 of the drawings, a training idler roller assembly in the form of a unit, generally indicated by numeral (1), comprises a simple, single, generally horizontal idler roller (2) mounted for free rotation on an axle (3) that itself is provided with a mounting bracket (4) at each end thereof whereby the unit can be operatively attached to a support structure for a belt conveyor with the idler roller unit extending transversely across the belt (5).

The outer surface of the idler roller provides a low friction surface with a heavy duty conveyor belt (5) to be supported thereon and, in this instance, the idler roller comprises a steel core (6) over which a tubular sleeve (7) of ultra high density polyethylene has been installed. The coefficient of friction of such a system will, it is estimated, in the instance of a conventional belt having a rubber or other elastomeric surface, be somewhere in the range of 0.04 to 0.5, and more probably in the range of 0.05 to 0.2, but will in any event depend on all relevant variables. In this regard, reference may be had to a conventional fixed idler roller marketed by the company NYLOCOMP (PTY) LTD of South Africa.

The low coefficient of friction results in very little drag being created between the training idler roller and conveyor belt and such a simple idler roller would accordingly be considered to be totally unsuitable for use as a training idler roller in which drag between the belt and idler roller is typically of paramount importance in instances in which no outside forces are used to return a conveyor belt to its desired generally central position.

It has now, rather surprisingly, been found that, as provided by this invention, the provision of suitable guide structure, in this instance in the form of a guide roller (8) associated with each end of the idler roller, results in the rather simple low friction idler roller becoming a training idler roller that imposes a corrective influence on a belt supported on it to return it towards a central position simply consequent on contact between the guide roller and adjacent edge region of the belt.

It is to be noted that the spacing between the two opposite guide rollers is such that when the conveyor belt is located in a central desired position, it is not in contact with either guide roller. This is important in order to minimise wear and tear on both the guide rollers and the belt in the generally abrasive conditions in which such heavy duty conveyor belts operate.

The low friction outer surface may be selected, for example, from a surface of a high density polyethylene material, preferably ultra high density polyethylene material and a polytetrafluoroethylene (TEFLON™) material.

The guide rollers may be located either on the approach side of the idler roller or on the exit side thereof, or there may be a guide roller on each of the approach and exit sides of the idler roller. In any event, the guide roller is spaced in the direction of travel of the belt relative to the training idler roller.

As shown most clearly in Figure 1a, the axis of rotation (9) of each of the guide rollers is inclined inwardly towards the conveyor belt relative to the axis (10) of the adjacent idler roller, thereby forming an acute angle between the two axes of rotation. This acute angle is preferably greater than 45° so that a predominantly lateral force is imposed on the edge of the belt and, still more preferably, the angle is very much larger than 45° and is preferably between 80 and 89°. The angle is indicated by the symbol "b" in the accompanying drawings, in particular in Figure 1a bag is chosen according to the belt characteristics. The contact surface of any guide roller and the surface of the outer end region (11) of any idler roller (see Figure 4) may be of a hard wearing material. Thus, in the instance of a steel surface, a preferred hardness of about 65 to 70 HRC Rockwell may be employed. In the instance of a plastic surface, such as a polyurethane surface of the material may have about a 90 Shore hardness. This hard wearing surface operatively contacts an edge region of the belt upon lateral drift thereof.

The arrangement is such that when an edge of the belt moves into engagement with the contact surface of a guide roller it is urged in a direction out of the natural plane of the conveyor belt and towards more firm engagement of the edge region with the idler roller, as will be apparent from numeral (12) in Figure 1a. It has been found that this combination of a low friction surface on the idler roller and the inclined contact surface of the guide roller immediately causes the belt to move towards its central position in which it is disengaged from both of the guide rollers. The conveyor belt is thus urged laterally to release contact with the said guide roller and thereby give rise to a corrective influence being imposed on the conveyor belt.

It is to be noted that the guide rollers are illustrated in Figures 1 and 2 as having a headed configuration in which the head (8a) is located at the terminal end of the right circular cylindrical guide roller (8b) and this construction may be preferred in order to control the conveyor belt should a catastrophic condition develop. However, as illustrated in Figures 1a and 3, the head may be omitted.

In either case, the guide roller, which has its axis inclined at an acute angle to the axis of the adjacent roller, cooperates with the adjacent idler roller to form a confined, generally V-shaped, pocket (13) (see Figure 1a) therebetween into which the raised side edge of the belt (5) fits when the belt drifts laterally in the direction of the roller (8). With the head portion (8a), the confinement becomes more pronounced since a three sided pocket is provided with the roller head portion (8a) inclined toward the idler roller due to the acute angle formed between the guide roller (8b) and the idler roller, as previously described. Figure 4 illustrates application of the first variation of the invention to a trough idler roller unit having two idler rollers (14) on diverging from a central position whilst Figure 5 illustrates its application to a trough idler roller unit having three idler rollers (15) wherein two idler rollers diverge from opposite ends of a generally horizontal central roller. Figure 5 also illustrates, at numeral (5a) the cupping effect referred to above.

Figure 6 illustrates the variation that the ends of the idler roller could be flared outwards, as indicated by numeral (16), provided that the inclination of the surface of the flared end makes an acute angle with the axis (17) of the guide rollers (18).

Turning now to the first embodiment of the second variation of the invention that is illustrated in Figure 7, the structure for automatically imposing a corrective influence on the conveyor belt (20) by a training idler roller assembly is constituted by the arrangement of a pair of control idler rollers (21 ) that are arranged symmetrically with one on each side of a desired centre line (22) extending along the desired direction of travel indicated by arrow "A" of the conveyor belt (20). The control idler rollers extend over the major part of the width of the conveyor belt, in use, so that only a small band (23) extending along the centre of the conveyor belt is not directly supported by the training idler roller assembly. The conveyor belt is thus supported over at least a substantial part of the width thereof

The control idler rollers are freely rotatable about their own axes (24) that extend at an incline, in plan view (that is in a direction at right angles to the surface of a conveyor belt operatively supported on the training idler roller assembly), to a line (25) extending across the conveyor belt at right angles to the centre line, the angle of inclination being indicated by angle "a". The control idler rollers thus have their inner ends (26) slightly closer to the approach side of the conveyor belt than the outer ends (27). The result is that a component of force indicated by arrow "F" is directed inwardly towards said centre line is exerted on the conveyor belt from each side of the centre line by the two control idler rollers.

The actual value of the angle "a" will vary according to the physical properties of the surfaces of the control idler rollers and the conveyor belt and also on the strength of the central region of the conveyor belt. It is generally expected that the angle "a" will be between about 1 ° and about 5°. It will be noted that the control idler rollers extend outwards from a central position beneath a conveyor belt to a position beyond the edge (28) thereof. This ensures that the entire lateral regions of the conveyor belt are in contact with the control idler rollers at all times.

Preferably, the training idler roller assembly is made as a complete unit for installation between the side support stringers (29) of a conveyor belt installation. To this end, the control idler rollers are preferably mounted by way of mounting plates (30) to a transverse frame member (31 ) that can be provided with mounting bracket assemblies (32) at its ends for direct attachment to the stringers (29) on opposite sides of the conveyor installation.

One form of modular unit without any associated components of the conveyor belt itself is illustrated in Figure 15. It will be seen that the guide rollers (33) are supported by the bracket assemblies (32) through adjustable support arms (37). Indeed, a modular unit is preferably configured so that any adjustments necessary can be made to suit a particular conveyor belt at the time of installation thereof.

It is important to note that the inclination of the control idler rollers to each other in plan view is independent of their inclination to each other in elevation taken across the direction of travel of the conveyor belt in a plane at right angles to the plane of the conveyor belt. Thus the control idler rollers may, in elevation, have their axes substantially coplanar, as illustrated in Figure 8, so that the belt is supported on a generally flat condition. Alternatively, as illustrated in Figure 9, they could be inclined to each other so as to support the conveyor belt in a generally trough condition. The ^"arrangement of the idler rollers in elevation is not material to the operation of the second aspect of invention that is concerned with the arrangement of the rollers in plan view, a view in which plural rollers have, in the past, invariably been arranged with their axes in one or more planes at right angles to the direction of travel of the conveyor belt.

As indicated above, with the two control idler rollers being symmetrically arranged with their axes at an incline, as described, two generally equal and opposite forces "F" are imposed on the conveyor belt from the two sides regions thereof. The result is a positive force urging the conveyor to its substantially central position on the idler roller assembly from both sides. Nevertheless, in a system in which the balance between wear and tear and the training aspect of the training idler roller assembly is considered, it has been found that this "toe-in" arrangement of the control idler rollers relative to each other is not entirely effective.

Thus, as described above, a guide roller (33) is provided at each side of the belt with the guide roller axis inclined in the manner described above. Thus, any lateral drift of the conveyor belt such that a guide roller is contacted will result in a correction as has already been described and the "toe-in" effect will then resume its function.

It will be understood that the arrangement of the control idler rollers will give rise to a slight amount of slippage between the roller surface and the belt surface. This slippage can be put to good use when the idler roller unit is appropriately positioned in a conveyor assembly to effectively clean the belt and act as a belt scraper on the return pass of a belt conveyor.

In the event that this attribute of the control idler rollers is to be employed, applicant believes that the effect is most significant in the event that the control idler rollers have a normal rubber outer surface rather than the low friction surface described above in relation to the first variation of the invention. Of course, if this attribute is not required, a low friction surfaces can nevertheless be used on the control idler rollers in view of the fact that the guide rollers will act to return the conveyor belt to a central path, in any event. In the event that this feature is required, applicant has noted that tapered rollers (34), as illustrated in Figure 10, apparently operate particularly well as belt cleaning elements.

Of course, one or more idler rollers (35) may be installed between two control idler rollers (36) associated with the edges of a conveyor belt, as illustrated in Figure 11.

Referring now to Figure 12, as an alternative to the guide roller in the particular case of the second variation of the invention in which the control idler rollers are inclined in the direction of travel of the conveyor belt, the guide structure may assume the form of a terminal flange (40) located at, and rotatable in unison with, the outer end of each control idler roller (41 ). Provided that the face of the flange is at generally right angles to the surface of the control idler roller, the outer periphery of the flange will always be nearer the edge of the belt (42) and will, by the nature of things, have a higher peripheral velocity than the surface of the roller. Because of the "toe-in" nature of the control idler rollers, the periphery of the flange on the exit side of the control idler roller will first contact the edge of a belt that drifts laterally into contact with it and, because of the higher peripheral velocity, the edge will be urged towards greater engagement with the idler roller in the same manner as is described above in relation to the guide roller and as indicated by numeral (43) in Figure 13.

Figure 14 illustrates a preferred installation in which a training idler roller assembly (44) according to the invention is installed between two adjacent standard idler rollers (45) such that the belt (46) is lifted off the two standard idler rollers so that the training idler roller supports sufficient weight of the belt to have the desired effect on training it towards a central position.

As indicated above, the idler roller assembly of the invention may be configured for use as a belt arrester in applications in which a belt conveyor has an inclined section (60), as illustrated in Figure 16. In such an instance, a series of belt arresters (61) may be located at spaced intervals, typically about 60 meters (66 yards) at the inclined so that the weight of the load on the belt (indicated by numeral (62)) does not cause the belt is to reverse in the event of a belt breaking or otherwise ceasing to be driven in the upward direction.

Referring now to Figure 17, such a conveyor belt arrester idler roller assembly may have a pair of parallel spaced horizontal support idler rollers (63) that could be crowned or of any other required configuration, and a pair of laterally extending upwardly inclined wing rollers (64). A pair of guide rollers (65) is associated with each outer end of each wing roller so that one is positioned on the approach side to the wing roller and the other is positioned on the exit side thereof. Each of the guide rollers is configured as described above so that it is inclined over the belt where it passes over the wing roller. The wing rollers unidirectional so that are at their rotates only in the required direction of travel of the associated conveyor belt, as indicated by arrow "B" in figure 17. In the event of the belt commencing a reverse movement, the guide rollers serve to keep the belt centralised and urge the belt into contact with the wing rollers to enhance the braking effect that the nonreversible wing rollers applied to the conveyor belt. The wing rollers may also be crowned to enhance the contact between the belt and the wing roller.

Claims

CLAIMS:

1. A training idler roller assembly (1 , 44) for a heavy duty conveyor belt (5, 42) comprising one or more idler rollers (2, 14, 15, 21 , 34, 35, 36, 41 ) mounted for free rotation on one or more axles (3) operatively mounted relative to a heavy duty belt conveyor to extend transversely relative thereto and to support a region of the belt in a manner such that lateral drift of the belt from a central desired position on the idler roller assembly towards one or other end thereof (side edge of the conveyor belt) automatically gives rise to corrective influence being imposed on the conveyor belt, and wherein guide structure selected from at least one guide roller (8,18, 33) and a flange (40) is carried by the idler roller assembly and is associated with each side of the conveyor belt such that a spacing between opposite guide rollers or flanges exceeds the width of the conveyor belt thereby resulting in the conveyor belt, in a central desired position, not being in contact with either guide roller or flange, and wherein the guide structure is spaced from the idler roller in a direction of belt travel, the training idler roller assembly being characterized in that each of the guide structures has a contact surface associated therewith for operatively contacting an edge region (12, 43) of the belt upon lateral drift thereof to an appropriate extent in a manner that urges such edge of the conveyor belt out of the otherwise natural plane of the belt towards firmer engagement with the idler roller where said edge region of the belt contacts same such that the conveyor belt is urged laterally to release contact with the said contact surface of the guide structure and thereby give rise to said corrective influence being imposed on the conveyor belt.

2. A training idler roller assembly as claimed in claim 1 in which the idler roller assembly is formed as an idler roller unit adapted to be attached to an existing conveyor belt installation.

3. A training idler roller assembly as claimed in either one of claims 1 or 2 in which said one or more idler rollers are mounted, in plan view, on a line at generally right angles to the desired path of travel of the conveyor belt and each idler roller has a low friction outer surface (7) and each of the guide structure is a guide roller having its axis of rotation (9) inclined inwardly towards the conveyor belt relative to the axis of rotation (10) of the adjacent idler roller with the guide roller being located either on the approach side of the idler roller or on the exit side thereof, or both in the event there are two guide rollers on each side of the conveyor belt.

4. A training idler roller assembly as claimed in claim 3 in which the training idler roller assembly comprises a single idler roller extending across the width of the assembly.

5. A training idler roller assembly as claimed in either one of claims 1 or 2 in which the training idler roller assembly comprises a plurality of idler rollers (21 , 34, 35, 36, 41 ) mounted for free rotation on two or more axles with their axes extending transversely across the desired path of travel of the conveyor belt over the idler rollers in use so as to support the conveyor belt over at least a substantial part of the width thereof wherein two control idler rollers (21 , 34, 36, 41 ) are arranged symmetrically about a centre line (22) of the desired path of movement of the conveyor belt so as to effectively support the conveyor belt over a part of its width and wherein the axis of rotation (24) of each of the control idler rollers is, in plan view, inclined to a line (25) extending at right angles to said centre line such that a component of force directed inwardly towards said centre line is exerted on the conveyor belt from each side of the centre line by the two control idler rollers in use to thereby impose a corrective influence on the conveyor belt.

6. A training idler roller assembly as claimed in claim 5 in which the control idler rollers are arranged to operatively extend outwards from a position beneath a conveyor belt to a position beyond the edge thereof.

7. A training idler roller assembly as claimed in either one of claims 5 or 6 in which the guide structure is a guide roller (33) having its axis of rotation inclined inwardly towards the conveyor belt relative to the axis of the adjacent control idler roller.

8. A training idler roller assembly as claimed in either one of claims 5 or 6 in which the guide structure is a flange (40) rotatable in unison with the outer end region of the control idler roller (41 ) such that the periphery of the flange contacts an edge of a belt (42) that drifts into contact with it downstream of the axis of the control idler roller to urge the belt out of the otherwise natural plane of the belt towards the roller and thereby give rise to said corrective influence being imposed on the conveyor belt.

9. A training idler roller assembly as claimed in any one of claims 5 to 8 in which the control idler rollers have an outer surface of a standard type of friction affording material such taht friction and limited lateral slip of the belt relative to the control idler roller surface inherently perform a belt cleaning effect.

10. A training idler roller assembly as claimed in any one of claims 5 to 8 in which the control idler rollers have an outer surface exhibiting a low coefficient of friction.

11. A training idler roller assembly as claimed in any one of the preceding claims in which any guide roller has an axis extending at an angle of from 60 to 89° relative to the axis of the adjacent idler roller of the idler roller assembly.

12. A training idler roller assembly as claimed in claim 11 in which any guide roller has an axis extending at an angle of from 75 to 89° relative to the axis of the adjacent idler roller of the idler roller assembly.

13. A training idler roller assembly as claimed in any one of the preceding claims in which the contact surface of any guide roller is a hard wearing surface.

14. A training idler roller assembly as claimed in any one of the preceding claims in which the contact surface of an outer end region of any idler roller is a hard wearing surface.

15. A training idler roller assembly as claimed in any one of the preceding claims in which the guide structure is, in each instance, a guide roller and the assembly is configured as an arrester idler roller assembly provided with at least one unidirectional rotatable idler roller and a guide roller on both the approach and exit sides of the idler roller assembly in respect of each side of the idler roller assembly.

16. A conveyor belt installation in which a training idler roller assembly as claimed in any one of the preceding claims is included and the training idler roller is positioned to lift the conveyor belt off adjacent standard idler rollers in order to ensure proper contact with the training idler roller assembly.