GB2093786A - Idler roller assemblies for troughed conveyor belts - Google Patents

Abstract

An idler roller assembly consists of an odd number of e.g. three rollers extending transversely of a conveyor belt to provide support therefor in which the centre roller, supporting the lowermost middle portion of the belt, has an axial length shorter than e.g. 50-70% of the axial length of the adjacent wing rollers that support the remainder of the belt. The arrangement provides improved tracking of the conveyor belt and a longer life for the bearings supporting the said centre roller. <IMAGE>

Description

SPECIFICATION Improvements in or relating to idler roller assemblies The present invention relates to improvements in continuous belt conveyor systems and in particular the idler roller assemblies that support loaded conveyor belts.

It is standard practice for idler roller assemblies used to support loaded conveyor belts to consist of 3 or 5 rollers of equal length. The rollers are mounted with the outermost or wing rollers at an angle to the horizontal so that the belt is supported in a trough-like configuration, the centre roller of the assembly being parallel to the ground and supporting the middle and lowermost part of the conveyor belt.

The angle at which the wing rollers are mounted is, to some extent at least, governed by the need for them to maintain accurate belt tracking i.e. maintain the belt substantially symmetrical with respect to the lengthwise axis of the conveyor system.

Heavy duty conveyors using high horse power drives require belts of high tensile strength, which strength is achieved at the expense of a heavy carcass construction with consequential reduced transverse flexibility. As a result when using idler roller configurations as described above, the line contact between the surface of the belt and the surface of the rollers is progressively reduced as the weight of the carcass increases owing to the increase in length of the bend in the belt at the intersection between the roller surface angles.

The above mentioned condition is more pronounced with the 5 roller configuration. On heavy belts contact with the wing rollers is at the belt edge only and the centre and intermediate rollers are in contact only in the centre of each roller face. Lack of linear contact with the roller face means that tracking influence of the roller on the belt is lost with the result that problems are experienced in tracking the belt when unloaded.

Conversely when the same belt is supported on a two roll VEE type idler very little belt contact is lost at the intersection between the roller faces, this is due to the total belt weight lying in two planes only with the resultant forces creating a smaller arc length at the single intersection of the rollers. Whilst being ideal for tracking the unloaded belt, this arrangement creates problems with a loaded belt due to the load sharply deforming the belt into the total angle of the roller intersection at the centre and is therefore unsuitable for supporting loaded conveyor belts.

We have now found that significantly improved line contact between the belt and the rollers, with resultant improvement in tracking, can be achieved by making the centre roller shorter than the wing rollers, which arrangement requires an equivalent increase in the length of the wing rollers in order to maintain a total surface length greater than the belt width.

The present invention, therefore, provides an idler roller assembly for supporting a continuous conveyor belt wherein the said assembly comprises an odd number of rollers and includes a centre roller supporting the centre of the belt and adjacent wing rollers supporting the remainder of the belt wherein the said centre roller has a shorter axial length than the said wing rollers.

Preferably the length of the centre roller is in the range 50 to 75% of the length of the wing rollers.

The invention will now be more fully described with reference to the accompanying drawings.

In the drawings: Figure 1 is a diagrammatic representation of an idler roller assembly of the prior art.

Figure 2 is a diagrammatic illustration of an idler roller assembly according to the present invention.

In figure 1 an idler roller assembly comprises three equal length rollers 1,2 and 3 supporting a heavy duty conveyor belt 4, having a width of 122cm. The rollers are each 43cm long. Each roller is mounted on axles carried on bearings located in each end thereof, the outer axles of wing rollers 1 and 3 being supported in the conveyor frame (not shown) and the inner axles thereof being coupled to each end of the axle of middle roller 2, so that the middle roller is supported between the ends of the wing rollers.

As a result of the lack of transverse flexibility in the heavy duty conveyor belt 4, the line contact between belt 4 and the surface of rollers 1 and 3 is shorter than that normally achieved with lighter weight belts, with consequent deterioration in tracking of the unloaded belt.

In this arrangement it is generally accepted, for the purpose of calculating bearing life, that 60% of the total load is taken at the centre roller 2, i.e.

30% per bearing. Thus approximately 15% of load is taken at the lower bearing of the inclined wing rollers 1 and 3 and 5% at the upper bearings thereof. Taking fixed load and speed for calculating estimated bearing life, a typical result is as follows: life of centre roller bearings = 1 6,000 hours, life of wing roller bottom bearing = 130,000 hours.

Although the bearings in the wing rollers 1 and 3 have a considerably longer life than those of the centre roller 2, the whole assembly has to be dismantled at the end of useful life of latter bearings.

In figure 2 rollers 21,22 and 23 are mounted in a conveyor frame (not shown) in the same manner as the rollers of figure 1 and support the same heavy duty conveyor belt 4.

The centre roller 22 in this arrangement, is however, 30.5cm long and the wing rollers 21 and 24 are each 48cm long. Thus the middle roller 22 is about 63% of the length of the wing rollers 21 and 23.

The line contact between the surface of rollers 21 and 23 with the surface of belt 4 is significantly increased providing improved tracking of the unloaded belt.

Also in this arrangement the total loading of the two bearings of the middle roller 22 and the bottom bearings of the wing rollers 21 and 23 is approximately the same at 45% but more equally proportioned at approximately 222% per bearing.

Again taking a fixed load and speed for calculating estimated bearing life, a typical result is as follows: Centre roller bearing life = 40,000 hours; Bottom wing bearing life = 40,000 hours; Thus in addition to the improved tracking, bearing life of the centre roller is considerably increased providing a longer expected working life for the assembly before it has to be removed following bearing failure.

Similarly with 5 roller configurations in which the middle roller is shorter than the wing rollers, the line contact between the conveyor belt and the surface of the wing rollers is significantly improved and, additionally, the load on the bearings supporting the rollers is of a more uniform nature with the result that there is significantly increased working life for the bearings supporting the centre loader with consequential improved life for the total assembly.

Claims (4)

1. An idler roller assembly for supporting a continuous conveyor belt, the said assembly comprising an odd number of rollers extending transversely of the said belt and including a centre roller supporting the middle lowermost portion of the belt and adjacent wing rollers supporting the remainder of the belt, wherein the said centre roller has a shorter axial length than the said wing rollers.

2. An idler roller assembly according to claim 1 wherein the axial length of the centre roller is in the range 50 to 70% of the length of the adjacent wing rollers, said wing rollers being of equal length.

3. An idler roller assembly according to claim 1 or 2 wherein the assembly consists of the two wing rollers and one centre roller.

4. An idler roller assembly according to claim 1 substantially as herein described with reference to figure 2 of the drawings.