TECHNICAL FIELD

[0001] The present invention relates to a roller, The invention is particularly useful construction of rollers for conveyors.

BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] Conveyors are used in many industries to convey material from one location to another for various purposes. Most conveyors employ a conveyor belt that moves over rotatable rollers (or idlers). The rotatable rollers are supported beneath the conveyor belt. The conveyor belt moves over the rotatable rollers, with the underside of the conveyor belt contacting the rollers. The upper side of the Conveyor belt carries the material being conveyed.

[0004] By way of example, in the mining industry such conveyors may be used to carry ore or other material around a site, from site to site, as well as to loading bays and on to ships, trains, trucks and/or other suitable transportation.

[0005] The rollers are supported in roller frames mounted beneath the conveyor belt. Each roller frame typically supports multiple rollers. These rollers, in turn, support the load of the material conveyed on the conveyor belt. For example, the belts in iron ore mining industries carry very large loads, up to 10,000 tonnes per hour; therefore these rollers are under constant heavy load.

[0006] Rollers are generally constructed to have a shaft around which a roller casing is free to rotate. The roller casing is rotatably secured to the shaft by two end caps located adjacent each end of the shaft. The end caps support bearings which allow rotation relative to the shaft. To ensure that the end caps do not restrict the free rotation of the shaft relative to the remaining components of the roller, a recess is provided between the shaft and the end caps. Washers encircle the openings of the recesses at the position of the protruding ends to prevent contaminant particles from entering the recess and damaging the bearings.

[0007] Conveyors also have return rollers which support the conveyor belt on its return journey.

[0008] Over time rollers fail for multiple different reasons. In some instances the bearings seize, the roller disintegrates, or can even explode. A major factor which leads to these failures is the pressure build up and heat generated within the roller when in operation. This is further problematic where dirt has entered into the cavity.

[0009] As the rollers work long hours in extreme conditions and loads they get very hot internally, which in turn creates a lot of pressure inside the roller. The combination of heat and pressure at high speed liquefies the grease in the bearings and push it towards the extreme outside edges of the bearings. This in turn leaves the lower parts of the bearings dry and causes further overheating and pressure build up.

[0010] In order to increase the life of current rollers, holes are often drilled into the end caps of the roller. In some cases a brass filter is installed in the hole to avoid the egress of dust and dirt, and to act as a pressure release valve. However, even a simple small hole, with or without a filter, will be blocked with a combination of dust and moisture in a very short time creating the same scenario as if the hole was not present. Also any dirt that does enter the roller will be pushed into the bearing as a result of the increase in pressure within the roller.

[0011] The temperature of the rollers range between being idle in cold weather to operating continuously in high ambient temperatures. This causes large pressure differences between the cavity inside the roller and the atmosphere outside the roller. In normal operation, this can create a migration of air between the atmosphere and the inside of the roller, or vice versa, if the roller is not sealed. Either direction of air movement is detrimental to the life of the bearings as the entering air will carry dust and the exiting air will deplete the bearing of lubricant.

[0012] Another downside of current rollers is that they are generally manufactured to be disposable once they have failed. Thus, once a component of the roller is damaged or worn out, inevitably the whole roller must be replaced. [0013] When the bearings become worn or damaged, irregularities in the rotation of the roller relative to the shaft occur. This commonly results in damage to the shaft. Once this occurs it is not long before the roller becomes unusable and the whole roller must be replaced.

[0014] Replacement of the bearings, when damaged or worn, is not practical in current rollers. The end caps are fixedly attached to an outer casing. This fixed attachment provides the roller with its integrity and strength. Thus, any attempt to replace bearings in rollers would result in the destruction of the integrity of the roller and a loss of strength.

[0015] Another problem with current rollers is their ability to handle the high stress/forces associated with high tonnage conveyors. As mentioned above, the outer casing is fixedly attached to the end caps. The method of attachment used is primarily stitch welding. However, the use of stitch welding does not create as strong a connection between the outer casing and the end cap assemblies as other methods of attachment. Thus, when these types of rollers are used in high tonnage conveyor belts the stitch welding is prone to separation, resulting in failure of the roller.

SUMMARY OF INVENTION

[0016] The present invention attempts to reduce the prior art problems by producing a roller that better withstands changes in temperature and pressure within the roller. In so doing the roller is also designed such that damaged or worn roller components can be easily replaced.

[0017] It is therefore an object of the invention to provide a roller which ameliorates, mitigates or overcomes, at least one disadvantage of the prior art, or which will at least provides a practical choice.

[0018] The present invention provides a roller comprising: a shaft; an end cap assembly rotatably secured adjacent each end of the shaft; a roller casing extending between the end cap assemblies; a cavity defined between the end cap assemblies, the shaft and the roller casing; a temperature compensating means to minimise temperature differential between the cavity of the roller and that of the environment.

[0019] In contrast to the prior art, the temperature compensating mechanism minimises the range of temperature changes within the roller. This reduces the build up of pressure which, when coupled to the reduction in heat generated, ensures the lubricant in the bearings remains at a relatively constant viscosity so that the lubricant maintains optimum operating conditions for the bearing.

[0020] Preferably the roller is substantially sealed from the outside environment. As there is minimal change in temperature within the roller, and therefore minimal change in pressure, there is no requirement for air to be discharged from or injected into the roller. As such the roller can be substantially sealed from the outside environment, minimising any dirt which can enter the roller and damage the bearings.

[0021] In one aspect of the invention the temperature compensating means comprises a temperature compensating mechanism secured to the shaft at a position between the end cap assemblies. Preferably the temperature compensating mechanism absorbs heat generated within the roller. As the compensating mechanism absorbs heat it expands.

[0022] In another aspect of the invention the temperature compensating means is in the form of a material injected into the cavity of the roller, whereby the material does not expand or contract when exposed to changes in temperature.

[0023] Preferably the material does not absorb heat.

[0024] Preferably the material is polyurethane, but may be any similar material which does not absorb or generate heat. The material may be injected into the cavity such that there is substantially no air in the roller cavity. Preferably the cavity is filled with the material. As there is no air in the cavity there will be no build up of temperature, and therefore no resulting pressure change. As polyurethane will not generate heat, the roller can be sealed, allowing the bearings to work as designed, prolonging the life of the roller. Also, as the cavity is full of the injected material no dirt can pass into the cavity and into the bearings.

[0025] Also, as polyurethane will not generate heat the roller can be used across a large range of temperatures. [0026] Preferably, once the material has been injected into the roller casing, the roller casing and end cap assemblies are rotatably about the shaft whereby the shaft does not damage the injected material.

[0027] Each end cap assembly may comprise an end cap, at least one bearing, and at least one seal.

[0028] Preferably the end cap is machined. The end cap may be of suitable thickness to absorb any heat which may be generated with minimal expansion.

[0029] The at least one bearing may be located in the cavity.

[0030] Preferably the roller casing is mechanically fixed to each end cap assembly. The roller casing may be releasably secured to each end cap. The mechanical fixing may be by crimping the casing to the end cap. Preferably each end cap has a groove or a plurality of dimples machined therein in a symmetrical manner. During assembly an end portion of the roller casing may be crimped such that the roller casing protrudes into each groove or dimple. As a result there is no need to weld the casing to the end caps, which can create an imbalance in the roller. If the roller is balanced the force exerted on the roller is more evenly distributed on its components, prolonging the life of the roller.

[0031] Preferably the roller casing may be removed from the end cap assemblies. This will allow the at least one bearing, or other worn or damaged components to be replaced and the roller re-assembled for continued use.

[0032] Preferably the at least one seal is a labyrinth seal located between the at least one bearing and an external surface of the end cap assembly. The labyrinth seal may comprise a first annular seal part which is press fit on to the shaft, and a second annular seal part which is press fit onto the end cap. The first annular seal part and second annular seal part may have complementary grooves which, when assembled, define a narrow passage which minimises dirt entering the roller. Preferably the labyrinth seal is filled with a high temperature lubricant.

[0033] Each end assembly may comprise a first seal external the end cap, extending between the shaft and the external surface, a second seal being the labyrinth seal located between the first seal and the at least one bearing, and a third seal located between the labyrinth seal and the at least one bearing. [0034] The first seal and third seal may be in the form of a annular shield. The shield of the first seal and the third seal may be different in profile and may be made from zinc.

[0035] The first seal may either be press fit onto the shaft and/or may be held on the shaft by a circlip. An end of the first seal may engage the external surface of the end cap.

[0036] The third seal may be press fit into the end cap. A portion of the third seal may engage the external surface of the at least one bearing.

[0037] The arrangement of the three seals significantly minimises the opportunity for dirt to enter the cavity of the roller and damage the bearings.

[0038] The present invention provides a conveyor having one or more of the rollers as herein before described fitted thereto.

[0039] The present invention provides a device that is incorporated into the construction of the roller body. It uses the basic principle of Boyles law, p1 , V1 / 11 = p2, V2 / 12. As the axle of the roller is stationary, the device is attached to the axle during assembly of the roller and is uninfluenced by any and all of the above negative factors.

However, by the laws of nature, it will adjust the volume occupied by the air trapped inside the roller during manufacture and ensure there is no movement of air between the inside of the roller and the atmosphere, thereby, allowing the seals and lubricant to attend their duties uninterrupted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

Figure 1 is a cross sectional view of a roller according to a first embodiment of the invention; Figure 2 is a cross sectional view of an end cap assembly of figure 1 ;

Figure 3a is a cross sectional view of the seal arrangement of the end cap assembly shown in figure 2;

Figure 3b is a perspective view of a first annular seal part of a labyrinth seal shown in figure 3a;

Figure 3c is a perspective view of a second annular seal part of a labyrinth seal shown in figure 3a;

Figure 4a is a front perspective view of an end cap of the end cap assembly shown in figure 1 ;

Figure 4b is a rear perspective view of the end cap shown in figure 4a;

Figure 4c is a cross sectional view of the end cap shown in figure 4a; and

Figure 5 is a cross sectional view of a roller according to a second embodiment of the invention.

[0041] In the drawings like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention.

DESCRIPTION OF EMBODIMENTS

[0042] Referring to figures 1 to 4c, the invention according to the first embodiment is in the form of a roller 11. One or more rollers 11 is adapted to be supported in roller frames mounted beneath a conveyor belt. These rollers support the load of the material conveyed on the conveyor belt.

[0043] Referring to figure 1 the roller 11 comprises a shaft 13 having ends 15 adapted to be received in a roller cradle of the roller frame. The roller 11 also comprises a first end cap assembly 17 and a second end cap assembly 19, which are both rotatably secured adjacent each end 15 of the shaft 13. [0044] Each end cap assembly 17, 19 comprise an end cap 21 , a bearing 23, a first seal 25, a second seal 27 and a third seal 29.

[0045] Each end cap is machined and is of suitable thickness to provide some heat absorbing qualities. As best shown in figure 4 a,b,c each end cap has three dimples 22 machined therein for reasons which will be described below.

[0046] The first seal 25 is in the form of a zinc shield and extends between the shaft 13 and an external surface 35 of the end cap 21. The first seal in this embodiment is both press fit onto the shaft and held on by a circlip 37.

[0047] The second seal 27 is located between the first seal 25 and the bearing 23 and is in the form of a labyrinth seal. Referring to figures 3a,b,c the labyrinth seal is a two part seal comprising a first annular seal part 39 which is press fit on to the shaft 13, and a second annular seal part 41 which is press fit onto the end cap 21. The first annular seal part and second annular seal part have complementary grooves 43 which, when assembled, define a narrow passage 45 therebetween.

[0048] The third seal 29 is located between the second seal 27 and the bearing 23 and is in the form of a zinc shield. The third seal 29 is press fit into the end cap 21 , with a portion 47 engaging the external surface of the bearing.

[0049] The arrangement of seals 25, 27, 29 make it extremely difficult for any dirt or dust to work its way to the bearing, thus prolonging the life of the roller 11.

[0050] The two end assemblies 17, 19 are joined together by a roller casing 31 such that they rotate simultaneously. The roller casing 31 extends between the end cap assemblies 17, 19 and is held in position relative to the end caps 21 by crimping the ends of the roller casing 31 such that a portion of the roller casing 31 extends into the dimples 22 of the end cap.

[0051] As may be noted by the above construction of the roller 11 , any damaged component may be replaced or repaired by removing the roller casing 31 from the end caps 21 and replacing the damaged component before placing a new roller casing 31 thereon. It is now not necessary to dispose of the whole roller.

[0052] The roller 11 also incorporates a cavity 33 which is defined between the end cap assemblies 17, 19, the shaft 13 and the roller casing 31. In the present embodiment the cavity 33 is filled with a temperature compensating means, in the form of polyurethane 49 which has been injected therein. The polyurethane 49 is injected into the cavity 33 such that the air is expelled from the cavity 33 and there are no pockets of air left therein.

[0053] If the polyurethane 49 was to be injected whilst the shaft 13 was in place the polyurethane would stick to the shaft 13. This will prevent the shaft from rotating freely and will result in damage to the polyurethane. To prevent this from happening, before the polyurethane is injected into the cavity the shaft 13 is removed and a silicon sleeve is positioned in place of the shaft 13. Once the polyurethane is injected and set the silicon sleeve may easily be removed and the shaft re-inserted 13. By following this process the shaft will be free to rotate whilst the integrity of the polyurethane will remain.

[0054] In operation a roller generally heats up, causing an increase in pressure. However, in the roller 11 there is no air in the cavity. As such no heat is generated and the pressure remains relatively constant. Any heat that is generated does not cause the polyurethane to expand and therefore increase pressure. This allows the roller to be sealed, protecting the components within the roller 11 to prolong the life of the roller 11.

[0055] A second embodiment of the roller 111 according to the present invention is illustrated in figure 5. The configuration of this roller 111 is substantially identical to the roller 11 of the first embodiment with the exception that the temperature compensating means is in the form of a temperature compensating mechanism 149 secured to the shaft 13.

[0056] The temperature compensating mechanism 149 absorbs heat as heat builds up in the cavity 33 of the roller 111. This has the same effect as the polyurethane in the first embodiment and assists in maintaining the roller 111 at a relatively steady temperature, and at a relatively steady pressure.

[0057] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

[0058] Reference to positional descriptions, such as lower and upper, are to be taken in context of the embodiments depicted in the figures, and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.

[0059] Throughout this 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