Patent Application
20140331450
This invention relates to wheels for transportation vehicles, and to methods of manufacturing such wheels. In particular it relates to a wheel for a transportation vehicle that may be used in warehouse facilities or automotive or aircraft or marine manufacturing as well in retail premises such as supermarkets, to carry goods.
Such transportation vehicles are generally rectangular in plain view, typically prefabricated from a metal framework, and comprise a wheel, typically a caster wheel, at each of the four corner regions.
Conventionally, wheels for such transportation vehicles are made from polyurethane and aluminum materials, since these materials are hard and provide good wear characteristics. Another reason for the widespread use of polyurethane and aluminum materials is that these materials can be securely hydrogen-bonded together. This enables the wheel to be conveniently manufactured from a plurality of parts bonded together.
Alternatively, or additionally, the plurality of parts may be otherwise chemically or mechanically bonded together, for example by use of an adhesive.
Conventional transportation vehicles do generate an unpleasant level of noise in use.
Considerable development work has been expended in an attempt to reduce this. For example, both resilient spokes and infill's made of an elastomeric material have been incorporated into these types of wheel in the past.
Despite this expenditure and effort, to date only incremental reductions in the level of noise generated have been forthcoming. There is, therefore, a need for a wheel for a transportation vehicle that has a reduced level of noise in use.
This invention provides a wheel for a transportation vehicle comprising:
Characterised in that
A wheel made in accordance with the invention may produce significantly less noise in use than conventionally constructed wheels.
The core is preferably a relatively rigid material such as an aluminum or polyolefin, for example a polypropylene. The ground engaging tread, however, is preferably formed from a material that is softer than the core. A polyurethane material is one example of a material that has good wear and low sound transmission characteristics. Another example would be a rubber material. (see table one)
Preferably the intermediate member has a hardness of less than 75 Shore A, preferably less than 70 Shore A, whilst the core conveniently has a hardness of greater than 90 Shore A, typically being 95 Shore A. Preferably the tread has a hardness greater than 85 Shore A.
The ground engaging tread preferably comprises no more than 50% of the radius of the wheel. Conveniently the ground engaging tread comprises a thin layer of no more than 25%, preferably substantially 15%, of the radius of the wheel. The layer preferably extends circumferentially around the rim of the wheel, and conveniently provides at least substantially the whole of the circumferential surface of the wheel. By use of a suitable material, for example polyurethane or rubber, the ground engaging tread can be relatively thin whilst still providing adequate cushioning.
The core may further comprise a bearing, for example a roller or a ball bearing that interfaces between the axle and the core. The bearing surface may also be a low friction material such as nylon.
The invention is particularly suitable for application to caster wheels, that is wheels which are pilotable on a vertical axis, but it may of course be utilized in other types of wheel.
Preferably the component parts of the wheel, particularly the core and the ground engaging tread, the invention wheel cores have oblong slots to let the liquid cast polyurethane flow through and create a strong mechanical chemical bond. Thus a method of manufacturing a wheel for a transportation vehicle that does not comprise forming a relatively rigid core part, forming a ground engaging tread, and molding an elastomeric infill between the core and the tread. Conveniently the core and the elastomeric infill are directly chemically bonded, whilst preferably the ground engaging tread and the infill are directly mechanically interlocked.
A detailed description of two embodiments of a wheel for a transportation vehicle, which have been selected by way of example, follows. The description is to be read with reference to the accompanying drawings, in which:
A first embodiment of a caster wheel as is shown in
The axle assembly comprises a core-guard, and the inner race of a bearing assembly of the wheel (not shown) may be tightly fitted to an axle assembly when the wheel is assembled.
The core comprises an aluminum or polypropylene (see table one) core and a polypropylene circumferential flange with an extensive outer surface. The outer surface of the circumferential flange forms an extensive interface with the elastomeric infill at.
The polyurethane tread extends circumferentially around the outer surface of the core. It is radial depth compared with the elastomeric infill and the core. The tread is connected to the core via the elastomeric infill, being mechanically interlocked with the infill. The wheel cores have oblong slots to let the liquid cast polyurethane flow through and create a strong mechanical and chemical bond.
The wheel is manufactured by a multi-stage injection or liquid cast molding or hand pour process. The tread and the core are formed separately by injection or liquid cast molding or hand pour molding. The tread is molded with elongate radial channels, which extend through the width of the tread. The tread and the core are then held in place in a mold whilst the elastomeric infill, conveniently of a polypropylene-based material is injection molded or poured between them, and fills the channels. Supporting elements of polyurethane thus extend radially inwards of channels, as shown in
In use, the core, tread and infill rotate about the axle, the core forming a rigid structure that supports the wheel. The polyurethane tread forms the interface between the wheel and the ground, and reduces the amount of noise generated by the wheel.
The tread is mechanically interlocked with the elastomeric infill, as shown in
as shown in Figures and the mechanical interlock in both embodiments is rotationally asymmetrical. This assists in keying the tread securely into the infill.
These wheels have been found to significantly reduce the noise generated by transportation vehicles. When a semi-flexible polyurethane tread is added to the wheel the noise generated has been found to be reduced by around 8-10 dB.
In the present specification “comprise” means “includes or consists of” and “comprising” means “including or consisting of”.
The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilized for realizing the invention in diverse forms thereof.
