Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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-
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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.
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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
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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
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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.
