CA1147693A - Idler roller and the manufacture of such idler roller - Google Patents

Abstract

ABSTRACT
The invention relates to an idler roller particularly for conveyor belt support and comprises a prefabricated core member with bearing located at the ends of the core about which core and bearings there is moulded an abrasion and impact resistant load bearing synthetic plastic shell. The shell includes a tubular loud bearing wall and integral side walls having recesses in which are accommodated bearings which receive the idler shaft. By the utilisation of a relatively inexpensive core which does not require to possess load bearing properties, and utilising this core as a former about which the load bearing shell is moulded with bearings in situ, a satisfactory idler roller structure can be constructed relatively inexpensively. The shell should be moulded from a non-foamed polyurethane elastomer material to give high quality abrasion resistance coupled with impact resistance.

Description

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This invention relates to idler rollers particularly for belt conveyors.
Several types of idler rollers are utilised in the conveyor industry including transporting idlers, return idlers and impact idlers. The invention is ap-plicable to all forms of such idlers.
Conventionally idlers for conveyor belt support are constructed of steel or plastic tubular shell material and the ends of the shell are closed by means of separate end plates adapted to carry bearings which are to receive the idler shaft. Tubular shell and end plate cons~ructions have the disadvan-tage of the requirement for an assembly line and i~ is difficult to prevent the ingress of particulate matter into the shell during use. Furthermore steel is a relatively costly structural material for this type of component and has various disadvantages such as its tendency to rust or to fuse to the conveyor belt when the conveyor is shut down in cold weather~ It would be possible to mould a double walled plastic roller body but the tooling and moulding costs would be excessive.
It has been proposed to machine solid roller bodies from plastic material such as polyethylene and polypropylene but the finished article is even more costly than a conventional steel idler roller body. It has also been pro-posed to mould a solid body of plastic material having at least the belt

2~ engaging surface of oamed material but the load bearing properties of the roller body are not suitable for all types of conveyors. Furthermore the entire roller body, including the inner tubular section where a two part body is employed, is constructed to possess load and wearing resistant properties so that the structure is also relatively costly.
It is an object of the invention to provide an idler roller body of plas-tic shell material which has useful advantages over steel shell idler rollers as well as plastic rollers of known construction and which can be constructed with relative ease.
According to the invention there is provided an idler roller comprising a prefabricated core having a bore to accommodate an idler shaft, bearings at each end of the bore, and a shell of synthetic plastic ma~erial moulded around the core and the bearings to provide a tubular load bearing wall and end walls integral therewith the end walls of the shell each including a cavity in which the bearings for receiving the said shaft are located.
The tubular load bearing wall of the shell will normally be elongated and the end walls accommodating the roller bearings in suitable cavities which are co-axial with the shaft accommodating bore in ~he core.
Preferably the core is recessed the bearings being located in the re-cesses c~nd the end walls of the shell including ~ubular zones extencLing axially into the recesses and around the bearings.
Preferably also the end walls of the shell are recessed complementally to the core.
The tubular wall of the shell is a load bearing member the load bearing properties of which are not necessarily assisted by the core. In order to strengthen the shell therefore the core may include a plurality of radial slots therein so that in the moulding of the shell around the core corresponding gussets are formed extending in the slots from the tubular load bearing wall to the tubular zones of the end walls.
The synthetic plastic material used for the formation of the shell may be any hard wearing impact resisting polymer or copolymer composition such as a polyester or polypropylene, but in the preferred embodiments of the invention the shell is formed from a suitable grade of non-foamed polyurethane.

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, Polyurethanes which are hard wearing and impact resistant are well known to persons skilled in the art and suitable grades for the formation of the non-foamed shell should be selected depending upon the type of idler roller manu-factured. Thus for a transportation or return idler selected ratios of poly-etherpolyol and polyisocyanate reactants as well as reinforcement materials such as non-woven fibre glass mat, graphite fibres, polyester fibres and the like may be chosen to obtain a shell hardness not less than 80 shore A and preferably at leas~ 100 shore A with an impact resistance for an unnotched sample of not less than 0, 6 ft x lb/inches based on a Charpy test. The moulding composition preferablyS but not necessarily~ also includes flame retardant and antistatic additives so that the material is self-extinguishing within 5 seconds when subjected to an oxygen, hydrogen welding flame at appro-ximately 1000C. for 15 seconds.
~ or an impact roller the polyurethane moulding composition may be modiied to have a hardness not less than 40 shore ~, preferably 40-60 shore A so that the impact resistance increases and an unnotched sample is unbreakable on a Charpy test. The flammability may be the same as that for a transportation or return idler.
In the preferred embodiment of the invention the polyurethane employed for the formation of the shell is a material in the elast~mer range. Such elastomer provides the required properties of impact and wear resistance coupled with suitable load bearing characteristics.
The core in the idler roller of the invention is not required to enhance the load bearing properties of the hard wearing and impact resistant shell.
Its function is primarily that of an in situ former to enable the shel] to be relatively easily constructed by moulding of a suitable polymer material a-round the core. A secondary function of the core is that it constitutes a space filler within the load bearing shell.
Thus the core may be prefabricated of any suitable material which is preferably lighter than that of the shell so that the mass of the idler roller is not unnecessarily increased. The core could be a prefabricated wooden ele-ment, bonded sand or pulp, a shaped inflated bag or any other desired material, but in preferred embodiments the core is moulded of foamed or expanded polymer material such as expanded polystyrene or preferably foamed polyurethane.
Further according to the invention therefore the core comprises foamed or expanded polymer material and the shell comprises non-foamed polymer materi-al, and in the preferred practical embodiment of the invention the core com-prises foamed polyurethane and the shell non-foamed polyurethane.
During the formation of a non-foamed polyurethane shell about a foamed polyurethane core a strong bond between the two polyurethane materials is formed which is desirable in the end product.
~ he invention includes within its scope a method of manufacturing an idler roller including the steps of mounting a prefabricated annular core with-in a closed circular cylindrical mould to provide a moulding cavity between the cylindrical surfaces of the core and mould as well as between the ends of the core and the ends of the mould, positioning bearings wi~hin the mould at each end of the core~ and introducing a suitable settable plastic material into the moulding cavity to form a shell aro~lnd the core and over the bearings so that the bearings are trapped in position in the moulding operation.
When a polyurethane moulding composition is utilised for the formation of the shell a curing period of at least 2~ hours is required after demoulding of the idler.

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In order to illustrate the invention an example is now described with reference to the accompanying drawings in which :-Figure 1 is a section through portion of an idler roller according to theinvention illustrating the moulding of the roller with the bearing in situ; and Figure 2 is a perspective view of an end zone of the core of an idler roller illustrated in ~igure 1.
Referring to the drawings the idler roller la suitable for location on the transportation side of a conveyor ~not shown) comprises a preformed annular foamed polyurethane core 2 cmd a non-foamed polyure}hane shell extending over the core and including a load bearing tubular wall 3 and end walls ~I which are integral therewith.
The foamed polyurethane core 2 is formed in a mould so that it has re-cessed ends 5, radial slots 6 in the recessed ends and a bore 7 extending there-through.
The shell extending over the core is formed in a mould as will be des-cribed hereunder from a hard wearing and impact resistant non-foamed polyure-thane elastomer composition to have end walls 4 which include tubular zones 4b extending axially into the recesses of the core, which tubular zones are shaped internally complementally to the core and externally to define a bore with circular rebate 8 co-axial with the bore of the core for receiving bearing seals ~not shown). An idler shaft (not shown~ is received within the bore of the core 2 and will carry circlips for proper location of the bearings 11 thereon.
The shell of the idler has gussets 15 which extend from the tubular wall

3 through the slots 6 in the core 2 to the tubular zones 4b of the end walls 4 and serve to strengthen the load bear:ing properties of the shell.

The idler roller la is manufactured by locating the prefabricated core Zon a supporting rod (not shown) with the bearing 11 also on the rod at 0ach end of the bore 7 of the core 2. The core is mounted within a mould comprising a tubular wall 21 and end walls 32 on which the rod is supported so that the core 2 is co-axially disposed in the mould in relation ~o a moulding cavity defined between the mould walls 21 and ~2 and the cylindrical and end walls of the core 2 respectively.
The prefabricated core 2 is itself formed in a mould from a suitable polyurethane foam forming composition in accordance with techniques well known in the art. The physical properties including that of the density of the core ~aterial are not critical since the core is not intended to possess load bea~ing properties but is intended only to act as an internal former and space filler for the shell of the idler roller. Typically the core is made of a rigid po:ly-urethane foam having a density of 20 to 250 Kg per m3, ~he shape of the two ends of the core being chosen so as to permit structural reinforcemen~ of the shell by the shape of the end walls 4 and the formation of gussets 15 formed in the radial slots 6 of the core 2 when the shell is moulded about the core.
The core 2 may be formed in its mould on the rod so that the core need merely be transferred from the core mould to the shell forming mould illustra-ted in figure 1. The rod should be coatcd with a release agent so that afterdemoulding of the idler roller the rod can easily be withdrawn. Alternatively the rod may constitute the shaft of the idler c~nd simply be left in position after demoulding.
Having located the core 2 co-axially with the shell forming mould the shell is then moulded around the core 2 by introclucing a non-foamed polyurethane f~ 7~9t3 elastomer forming composition into the moulding cavity around the core via duct 23 so that the shell configuration illustrated in figure 1 is obtained, the end walls 32 of the mould being profiled as illustrated in figure 1 for this pur-pose. The ~earings 11 in the idler roXler construction are accordingly moulded in position by the end wall portions 4b of the shell formed therearo~md.
Prior to introducing the polyurethane elastomer forming composition into the moulding cavity the mould is preheated and its surfaces are coated with a release agent in accordance with standard practice.
The polyurethane elastomer forming composition is selected for the forma-tion of the non-foamed shell of the idler roller to have high abrasion and impact resistance with flame retardant and preferably also anti-static addi-tives incorporated and also, if desired, reinforcement in the orm of non-woven fibre glass mat, graphite fibres, polyester fibres or fi:Laments throughout the body of the shell or in selected areas thereof.
Further, if desired, metallic add:itives or inserts may be used which would serve to prevent build up of static by draining any charge formed via the bearings and the idler roller shaft.
When the shell has cured sufficiently to be self-s-upporting the roller may be demoulded and left to cure for a further 24 hours. The non-foamed poly-urethane shell bonds intimately with the foamed polyurethane core to providea roller of relatively inexpensive construction which is impact and abrasion resistant and has the advantage of corrosion resistance, a self-cleaning sur-face, belt adhesion resistance and bearing protection.
The idler roller constructed as described above has various material advan-tages over idler rollers of known construction utilised for conveyor belt sup-port. Thus by utilisation of a prefabricated core which is accurately located ~ .

in a cylindrical mould, a moulded shell construction is achieved which does not require subsequent machining or substantial assembly line fabrication since the bearings are moulded in posi~ion. The idleT is thus relatively inexpensive.
The core of the idler roller is itself constructed of an inexpensive ma-terial but which adequately performs its functions as a former about which the load bearing shell is moulded, and a space filler preventing the in~ress of abrasive grit ancl liquids into the shell.
The latter is constructed of polyurethane in the elastomer range and thus has abrasion resistant qualities far in excess of polymer materials of similar cost such as polypropylene and others and, since only a shell and not a solid body is formed, the cost of the materials of construction is maintained at the lowest possible level. The shell is, however, quite capable o wi~hstanding loads placed upon it due to its unitary tubular and end wall construction which can be strengthened by the use of internal gussets or ribs provided by the formation of slots in the core about which the shell is mouldecl.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An idler roller comprising a prefabricated core having a bore to accommodate an idler shaft, bearings at each end of the bore, and a shell of synthetic plastic material moulded around the core and the bearings to provide a tubular load bearing wall and end walls integral therewith, the end walls of the shell each including a cavity in which the bearings for receiving the said shaft are located.

2. The idler roller of claim 1 in which each end of the core is recessed, the bearings being located in the recesses and the end walls of the shell including tubular zones extending axially into the recesses and around the bearings.

3. The idler roller of claim 2 in which the end walls of the shell are recessed complementally to the core.

4. The idler roller of claim 2 in which each end of the core has a plurality of radial slots therein and the end walls of the shell define gussets extending in the slots from the tubular load bearing wall to the tubular zones of the end walls.

5. The idler roller of claim 3 in which each end of the core has a plurality of radial slots therein and the end walls of the shell define gussets extending in the slots from the tubular load bearing wall to the tubular zones of the end walls.

6. The idler roller of any one of claims 1, 2 or 3 in which the core comprises foamed or expanded polymer material and the shell comprises non-foamed polymer material.

7. The idler roller of either of claims 4 or 5 in which the core comprises foamed or expanded polymer material and the shell comprises non-foamed polymer material.

8. The idler roller of any one of claims 1, 2 or 3 in which the core comprises foamed polyurethane and the shell non-foamed polyurethane.

9. The idler roller of either of claims 4 or 5 in which the core comprises foamed polyurethane and the shell non-foamed polyurethane.

10. The idler roller of any one of claims 1, 2 or 3 in which the shell comprises a polyurethane material in the elastomer range.

11. The idler roller of either of claims 4 or 5 in which the shell comprises a polyurethane material in the elastomer range.

12. The idler roller of any one of claims 1, 2 or 3 in which the core comprises foamed or expanded polymer material and the shell comprises a polyurethane material in the elastomer range.

13. The idler roller of either of claims 4 or 5 in which the core comprises foamed or expanded polymer material and the shell comprises a polyurethane material in the elastomer range.

14. A method of manufacturing an idler roller including the steps of mounting a prefabricated annular core within a closed circular cylindrical mould to provide a moulding cavity between the cylindrical surfaces of the core and mould as well as between the ends of the core and the ends of the mould, positioning bearings within the mould at each end of the core, and introducing a suitable settable plastic material into the moulding cavity to form a shell around the core over the bearings so that the bearings are trapped in position in the moulding operation.