Patent Description:
Landfill sites are sites where waste material is disposed of by burying the material beneath the ground surface or by simply letting the waste material accumulate over such surface.

Despite recent efforts to recycle more waste material in order to reduce the amount of waste material arriving at landfill sites, a significant proportion of waste material is still disposed of in this way. Whether waste material is not recyclable or if recycling is not available in that locality, landfill is, in some instances, the only option for disposing of waste material.

In order to reduce the cost of operating such landfill sites, it is necessary to compact the waste material. Compacting the waste material reduces the volume of waste material, thereby allowing more waste material to be disposed of in any given volume of space.

Compaction of waste material can occur in a number of different ways. However, the most common way of compacting waste material is to use heavy machinery. Large steel-wheeled vehicles, often referred to as landfill compactor vehicles, traverse landfill sites in order to compact and/or break apart waste material.

Landfill compactor vehicles may have large steel-drum wheels with teeth on their outer surface. These toothed wheels also provide traction for the compactor vehicles. Landfill compactor vehicles are large vehicles with a considerable mass. The teeth of the wheels are therefore placed under considerable stress due to the weight of the vehicle being supported by the teeth as well as the requirement to compact the landfill waste.

It is therefore desirable that the teeth have a high structural strength and that the teeth be securely connected to the landfill compactor vehicle wheels so as to allow the teeth to withstand the high loading forces experienced during operation.

Furthermore, because landfill compactor vehicles spend their operational lives compacting waste material, their teeth are liable to wear down and inevitably require replacing.

It is also therefore desirable that these teeth are also hard wearing such that they do not wear down too quickly in use.

Other varieties of compactor vehicles, which may suffer from similar disadvantages, include soil and rock compactor vehicles.

<CIT> discloses a compaction roller that includes highly wear resistant cleat assemblies which employ readily removable wear caps having bulbous corner portions. Anti-twist projections and corresponding recesses between the wear caps and support bases reduce relative movement between the parts.

<CIT> discloses a base for forming a tooth for a wheel of a landfill compactor vehicle is disclosed. The tooth comprises said base and a cap of a cast metal material formed on said base. The base comprises a block, a core and a lip. The block is adapted to be mounted on said landfill compactor vehicle wheel. The core, which is disposed on a cap-facing side of the base, is for receiving molten metal material during a casting operation and remains embedded in the cap. The lip is disposed around a periphery of the base and is also for receiving said molten metal material, in cooperation with the core. The lip at least partially surrounds the cap-facing side and the core and helps in reducing or preventing imperfections, such as cracks, which could otherwise form at the interface between the base and the cap following the casting operation.

There exists a need to overcome one or more disadvantages associated with prior art arrangements, whether mentioned in this document or otherwise.

According to the invention there is provided a tooth for a compactor vehicle as specified in claim <NUM>.

The tooth may be referred to as a compaction tooth or a compactor tooth. The tooth may be described as a compactor vehicle wheel tooth.

The compactor vehicle may be one of a number of different types of compactor vehicle, such as a: landfill, soil or rock landfill compactor vehicle.

The base may refer to a component which provides an attachment surface, such as the underside, for securing the tooth to a wheel of the compactor vehicle. The base may generally occupy a lower portion of the tooth. The base may be attached to the wheel of the compactor vehicle by welding and/or by one or more fasteners.

The cap refers to a component which provides a tip, of sorts, for, and generally over, the base. In use, it is the cap which provides the majority of the compacting action as the compactor vehicle traverses a surface. The cap may surround at least part of the base such that part of the base is obscured from view once the cap is attached to the base. Part of an outer surface of the base may also provide some compacting action e.g. kneading action.

The base may be made of a material suitable for welding to facilitate attachment of the base to the wheel, an example of such a material being steel. The base may be made of, for example, A3 tool steel.

The base and cap may be cast using one or more metal materials. Non-limiting examples of metal materials include pure metals and alloys. The base is preferably cast using a metal material which is readily weldable. The cap is preferably cast using a comparatively high-wearing material e.g. a material having a high hardness value. The cap may be made from, for example, a variation of white iron and/or high alloy steel.

The body may be generally cuboidal. That is to say the body may generally comprise two pairs of generally parallel sides. The body preferably has a width and depth which is greater than a thickness of the body. The body may be described as block-like. The underside may be the lowermost surface of the body. The underside may be defined by a peripheral edge which surrounds the cavity. The body may comprise one or more features to facilitate welding proximate the underside, such as chamfered edges. The body being configured to engage a wheel of the compactor vehicle wheel may be described as the body being attachable to, or securable to, a wheel of the compactor vehicle. The wheel of the compactor vehicle may be a drum and so the body may be attachable to a drum of the compactor vehicle wheel. The body may be attachable to the wheel of the compactor vehicle wheel by welding and/or by one or more fasteners.

The underside may be at least partly arcuate to facilitate the mating of the underside of the base with the wheel.

The cap-facing side opposing the underside refers to there being a height offset between the underside and the cap-facing side. It will be appreciated that the underside may be arcuate whereas the cap-facing side may be generally planar.

The retention feature of the base may be defined on the body. Alternatively, the retention feature of the base may be defined by an attachment portion which projects from the body. The base may comprise a plurality of retention features (e.g. provided as both part of the body and the attachment portion). The retention feature may be referred to as a base retention feature. The retention feature may take the form of an aperture provided in the attachment portion. The retention feature may take the form of one or more recesses, for example an array of recesses, provided in the body. The retention feature generally refers to a feature which can receive material from the cap so as to lock, secure, or mate, the base and cap together. In preferred embodiments the base comprises a plurality of retention features comprising an array of recesses and an aperture which extends through the attachment portion.

The outer surface of the cap defining a compaction surface may otherwise be described as the cap defining a working surface which, in use, deforms or destroys material underneath the compactor vehicle wheel, and specifically underneath the tooth. The compaction surface of the cap may meet an outer surface of the body at one or more join lines. The combination of the outer surface of the body and the compaction surface of the cap may define a substantially continuous outer surface of the tooth. The compaction surface of the cap may comprise a number of different features including flat faces, arcuate surfaces, arcuate recesses and chamfers. An outer tip of the compaction surface may be dumbbell-shaped or M-shaped. It will be appreciated that a number of other alternative geometries may be defined at the outer tip of the cap.

The retention feature of the cap may refer to a portion of material which extends through an aperture of the base. For example, the retention of the feature of the cap may be a generally tubular body, which may be referred to a portion of material. Alternatively, or in combination, the retention feature of the cap may comprise one or more projections. Said one or more projections may extend outwardly, in cross-section, along a length of the projections. In an outermost position, e.g. at an outer end of the projections, the projections may extend outwardly, or splay outwardly, to anchor the cap to the base. The one or more projections may be said to generally taper outwardly. The outward tapering may define an hourglass-shaped, or C-shaped, projection having wider ends and a narrower middle.

The retention features of the base and cap interlocking with one another is intended to mean that there is an engagement between the features which would secure the features together even in the absence of any metallic bonding between those features. For example, a portion of material (e.g. a loop) extending through an aperture (e.g. of a handle-like projection), or an outwardly tapering projection extending through a corresponding tapering recess, are examples of retention features which interlock with one another. It is the interlocking between the retention features that means the cap remains secured to the base, or attached to the base. The retention features are preferably defined when at least one of the cap and the base is still in a molten metal material form (before said material cools to define a solid component). Using this process, features, such as undercuts, can be incorporated. In preferred embodiments it is the cap which is cast, using a (second) molten metal material, onto a precast base. Put another way, the base is first cast using a (first) molten metal material. Once the base solidifies, the cap is cast onto the base. The cap may be described as being configured to be cast onto the base using a molten metal material, which may be a second molten metal material. For completeness, there is also a metallic bonding which connects the cap to the base. Put another way, the cap is bonded to the base. There may also be an element of 'blending' between the molten metal material of the cap, and the base, during manufacture. The retention features interlock with one another to prevent the cap from separating from the base.

The cavity being defined in the underside of a base refers to a volume which is substantially free of any material. The cavity therefore refers to an open space, or volume. The cavity being defined in the underside of the base may otherwise be described as the underside being a solid surface if not for the incorporation of the cavity. The base may comprise a single cavity. Alternatively, the base may comprise a plurality of cavities. Where the base comprises a plurality of cavities, one or more walls (e.g. ribs) may interpose the cavities. The walls may define a supporting structure. One example of a supporting structure comprises walls which extend between corners of the base in a diagonal manner. Said supporting structure advantageously increases the rigidity of the base. The supporting structure may provide bosses through which fasteners can be attach the base, and so tooth, to the wheel. One example is to drill bores, and tap threads, in the supporting structure. Alternatively, or in combination, pre-cast threads may be incorporated.

Advantageously, the incorporation of the cavity in the underside of the base reduces the amount of material required to cast at least the base. This, in turn, reduces the mass of the base (and so tooth) and the associated cost of manufacture. Furthermore, advantageously the presence of the cavity means that the thermal mass of the base is reduced. During manufacture, the temperature of the base thus increases more readily, in comparison to a base without a cavity. The rate of heat transfer from the molten cap material to the base is thus lower, providing a more steady cooling rate (of the cap material) and reduced risk of chillback (i.e. excessive contraction of the molten metal cap material, which could lead to crack formation). Put another way, there is a reduced thermal shock when introducing the cast metal material, used to manufacture the cap, to the base.

Further advantageously, the incorporation of the cavity, which is free of material, reduces the requirement for further manufacturing processes after the base and cap have been cast. Specifically, in prior art arrangements it may have been necessary to grind a lower surface of the base, to a significant degree, owing to the generally solid nature of the base. In some arrangements, cap material may also have needed to have been ground. Advantageously, the presence of a cavity reduces the amount of grinding which is required because the surface area of the underside of the base is reduced.

Welding the base to the wheel has also been found to be advantageously improved by incorporation of the cavity. This is owing, at least in part, to the lower thermal mass of the base drawing less heat during the welding process.

The cavity may be bound by a peripheral edge which extends around the underside of the base.

The cavity being bound by a peripheral edge may otherwise be described as the cavity being defined by the peripheral edge, or the cavity being surrounded by the peripheral edge. The peripheral edge may be said to define a border, e.g. an outermost lower edge, of the base. It may be a peripheral edge, or at least part thereof, which is welded to the compactor vehicle wheel to secure the tooth to the wheel.

The peripheral edge extending around the underside of the base may be described as the peripheral edge extending entirely around the underside of the base. That is to say, a closed loop of material may be defined.

Advantageously, a single, open cavity can be employed which reduces any grinding or finishing processes required. Furthermore, the amount of material effectively removed from the base, and so the extent to which the mass and cost is reduced, are further increased in comparison to if, for example, the recess was only a comparatively small recess provided at one point in the base.

In embodiments where a plurality of cavities are incorporated, the peripheral edge may be said to bound the plurality of cavities.

The cavity being generally cuboidal refers to the cavity having two pairs of generally parallel sides when viewed in plan. The cross-section of the cavity, taken in plan, may therefore be rectangular or square. In preferred embodiments the heights, or thickness, of the cavity is comparatively less than a width and depth of the cavity. A negative of the cavity may be said to be similar to a thickened plate in geometry.

Advantageously, a generally cuboidal cavity is readily manufactured and defines a significant volume of cavity.

The second portion may be said to extend directly from the first portion. The combined heights of the first and second portions may be equal to a height of the body of the base. The second portion may taper in a linear manner or in an arcuate manner. The second portion tapering in a direction moving away from the underside refers to the second portion having a greater cross-sectional area proximate the underside, and a reduced cross-sectional area distal the underside.

The cavity may extend through at least a majority of the first portion of the base.

The cavity may extend through an entirety of a thickness of the first portion of the base. Alternatively, the cavity may extend through only a portion of the first portion of the base. The cavity extending through at least a majority of the first portion of the base refers to the proportion of a height of the first portion of the base which the cavity extends through. The cavity may extend through at least <NUM>%, preferably at least <NUM>% of a height of the first portion. A widest point of the base may be defined in the first portion, optionally directly between the first and second portions.

The base may further comprise one or more recesses, the one or more recesses extending between the cavity and the cap-facing side.

The base may comprise a plurality of recesses and, in preferred embodiments, comprises four recesses. All of the recesses may be the same geometry, or there may be a mixture.

In preferred embodiments the four recesses can be grouped into two pairs of recesses. The recesses extending between the cavity and the cap-facing side is intended to mean that the recesses place the cavity in fluid communication with the cap-facing side (in the absence of cap material). The recesses may define retention features in that molten metal material of the cap, when the cap is cast onto the base, may flow through the recesses. Once the cap material cools, the cap material may form projections and anchor the cap to the base by engagement with the recesses. To facilitate this, the recesses preferably comprise an anchoring feature, such as an undercut, which anchors the cap in position once the cap material has solidified. The recesses may generally increase in cross-sectional area, towards an outer surface. This may take the form of the recesses splaying outwardly, or extending outwardly, at least at an outer surface. Such geometry improves the interlocking of the projection and the recess, and so the cap and the base.

Advantageously, the one or more recesses extending between the cavity and the cap-facing side provide a secure join between the cap and the base. This can still be achieved whilst the cavity remains free of material, and so the advantages associated with the presence of the cavity can be obtained. Generally speaking, the more retention features which are incorporated, and the stronger the interconnection between the cap and the base and thus the harder wearing the tooth will be.

The one or more recesses may be generally trapezoidal.

The one or more recesses being generally trapezoidal refers to a geometry of the recesses when taken in plan view. Generally trapezoidal refers to the recesses having one pair of generally parallel sides and one pair of non-parallel sides. The one or more recesses may be said to be tapered, or dovetail-shaped, moving from an outer periphery of the base towards the central point.

One of more of the recesses may be described as generally triangular. Where an array of recesses is incorporated, some recesses (e.g. first pair) may be generally trapezoidal whilst some recesses (e.g. a second pair) may be generally triangle.

The base may further comprise an attachment portion which projects from the cap-facing side.

The attachment portion refers to a feature which facilitates attachment of the cap to the base. The attachment portion projecting from the cap-facing side is intended to mean that the attachment portion extends from the cap-facing side, and is preferably provided at a greater height than the cap-facing side. The attachment portion may be generally cuboidal and may be described as tab-shaped. The attachment portion may define a tallest point of the base e.g. at an outer tip of the attachment portion. The attachment portion may be general obscured from view once the cap is cast onto the base.

Advantageously, the attachment portion provides a further feature by which the cap can be secured to the base.

Advantageously, the attachment portion projecting from the cap-facing side means that a reduced amount of cap material is needed, the cap material typically being more expensive than the base material owing to its hardwearing nature.

The attachment portion may define a retention feature of the base, optionally the retention feature of the base.

The attachment portion may define the retention feature introduced in connection with the above aspect of the invention, or may define a further retention feature of the base, i.e. there may be multiple retention features. The attachment portion is preferably incorporated, along with with a plurality of recesses, the combination of the attachment portion and the recesses providing a plurality of retention features of the base.

The retention feature of the base may comprises an aperture which extends through the attachment portion.

The aperture may be said to extend entirely through the attachment portion. The combination of the aperture and the attachment portion may define a handle-like feature. That is to say, the attachment portion may project from the cap-facing side and the aperture may extend therethrough, giving the appearance like a handle.

The attachment portion may comprise a single aperture. The aperture may extend across a majority of the attachment portion. That is to say, a majority of major (e.g. the largest) faces of the attachment portion may be defined by the aperture. Alternatively, the attachment portion may comprise a plurality of apertures.

In embodiments where the cap is cast onto the base, molten metal material used to cast the cap may be poured onto the cap-facing side (of the base) and flow through the aperture. This preferably occurs whilst the molten metal material is at least partly molten. Once the molten metal material solidifies, the material which extends through the aperture, which may be described as a portion of material, preferably defines a retention feature which interlocks with the aperture. The aperture may define a retention feature.

Advantageously, the aperture extending through the attachment portion provides a robust retention feature which can be used to improve the interlock between the base and the cap. The tooth is therefore more robust by virtue of the aperture extending through the attachment portion.

A land of material may be defined between the cap-facing side and a lowermost point of the aperture.

The land of material refers to a solid block of material. Put another way, the land of material refers to a solid volume of material. The land of material may be generally cuboidal. The land of material may be described as generally bar-like. The land of material being defined between the cap-facing side and the lowermost point of the aperture may otherwise be described as the aperture being defined above the land of material. The land of material may be said to interpose the aperture and the cap-facing side.

Advantageously, the land of material being provided between the aperture and the cap-facing side improves the robustness of the base by reducing deflection of the base. Specifically, when the molten metal material, in some embodiments, of the cap is cast onto the base, there is a tendency for the base material to absorb heat from the molten material of the cap and thus thermally expand. Owing to the presence of the cavity in the underside of the base, the thermal expansion, and possibly distortion, may be worsened, due to a reduced amount of material and reduced reinforcement of the base. Advantageously, by incorporating the land of material a rib of sorts may be provided across the base so as to reinforce the base, specifically the body thereof, to reduce the distortion or deflection. Furthermore, the land of material being provided below the aperture reduces the risk that the lack of material, owing to the aperture, could itself result in further deflection by again providing reinforcement in this area.

The aperture may be a generally arcuate aperture.

The aperture being a generally arcuate aperture is intended to mean that a majority of the edges of the aperture are arcuate. Put another way, rather than the aperture being, for example, generally cuboidal and having only relatively sharp fillets at the corners, a generally arcuate aperture refers to an aperture which has at least large fillets in the corners so as to reduce the presence of straight edges and surfaces. Alternatively, the generally arcuate aperture may be entirely arcuate e.g. be circular (i.e. a bore in three dimensions) or elliptical. The generally arcuate aperture may be defined as less than around <NUM>%, preferably less than around <NUM>% or <NUM>%, of a perimeter of the aperture being defined by linear edges. This is another way of describing the majority of the perimeter being defined by arcuate edges.

Advantageously, the presence of a generally arcuate aperture reduces any other comparatively sharper fillets which, given a possible high temperature manufacturing method, could lead to thermal cracks developing in either the base or the cap.

One or more buttresses may extend between the attachment portion and the cap-facing side.

Buttresses is intended to refer to a supporting projection. The buttresses are preferably generally diagonal when the base in viewed in plan. Buttresses may be generally triangular when viewed normal to a major face of the buttresses.

The buttresses may be of the form of a generally right angled triangle wherein one of the perpendicular sides extends from the cap-facing side, and the other of the perpendicular sides extends from the attachment portion.

The buttresses advantageously provide improved attachment, and support, of the attachment portion relative to the body of the base. Specifically, the buttresses provide reinforcement which reduces the risk that the attachment portion become detached from the cap-facing side and/or be deflected relative to the cap-facing side.

In preferred embodiments, the attachment portion is generally cuboidal. In preferred embodiments a buttress extends from each corner of the attachment portion towards a corner of the body of the base. Furthermore, in some embodiments a respective buttress extends between two of a plurality of recesses defined in the cap-facing side.

In some embodiments an array of four recesses may be provided in the cap-facing side, with a respective one of four buttresses extending between two of the four recesses. When viewed in plan such buttresses may therefore define a generally X-shaped geometry.

The base may comprise a lip which extends around a peripheral edge of the cap-facing side.

The lip may be said to extend entirely around a peripheral edge of the cap-facing side. As such, the lip may define an outermost edge of the cap-facing side. The lip may comprise one or more filleted edges. The lip may be said to extend around a second portion of the body of the base, and the second portion may be tapering. The lip may define an uppermost point, or tallest point, of the body of the base.

Advantageously, incorporation of the lip reduces the risk of chill back occurring when the cap is cast onto the base. Specifically, cracks may occur around the join line between the cap and the base, and particularly in the cap, as the molten metal material solidifies more quickly when the relatively hot molten material meets the relatively cool base (the base having a comparatively large thermal inertia). Providing the lip means that the base increases in temperature locally (i.e. at least at the lip) more readily than base would otherwise. This provides for a more even cooling effect, of the molten metal material of the cap, and reduces the risk of unsightly and/or structurally weakening cracks occurring during manufacture.

According to a second aspect of the invention there is provided a method of manufacturing a tooth according to the first aspect of the invention, the method comprising:.

In preferred embodiments the base is cast using the first molten metal material in a first step. In preferred embodiments, in a second step the cap is cast onto the pre-cast (e.g. solidified) base. The base is preferably allowed to cool, and so solidify, before the molten metal material of the cap is introduced. This method of manufacturing may be referred to as a twin-shot casting method. The first and second molten metal materials are preferably different to one another, such that the preferred characteristics associated with the base and cap can be obtained in a single, structurally robust tooth.

The first molten metal material is preferably a readily weldable material, such as a high carbon steel. The second metal material is preferably a comparatively hard wearing material, such as a material having a high hardness value.

The second molten metal material may be introduced, or poured, from above the base (e.g. above the cap-facing side thereof). The cap may be said to be cast onto the base.

The retention features, which interlock with one another, may be formed when the molten metal material of the cap is cast onto the base. For example, the second molten metal material may flow through features of the base, such as recesses and aperture(s), to form projections and/or portions of material which, once solidified, securely interlock the base and cap.

The second molten metal being substantially prevented from entering the cavity is intended to mean that the cavity remains free of material during the manufacturing process. It will be appreciated that a very small amount of the second molten metal material may enter the cavity but that the cavity remains generally free of material.

A mould used to cast the base and/or cap may be stationary whilst the first and/or second molten metal materials are poured and/or whilst they solidify.

Advantageously, the aforementioned method of manufacture reduces the grinding requirement required to finish a manufactured tooth. In prior art arrangements it may be necessary to grind the base, e.g. the entire underside thereof, in order to provide an acceptable finish (e.g. before welding). In contrast, the aforementioned method reduces the area which may be ground because the cavity is defined in the underside and therefore eliminates a significant amount of the surface area which contacts the compactor vehicle wheel.

The method advantageously uses a reduced amount of material owing to the presence of the cavity. It will be understood that the cavity would otherwise be full of material, with the associated increased costs and mass implications, if it wasn't for incorporation of the cavity.

The second molten material being substantially prevented from entering the cavity may otherwise be described as the cavity being sealed from the second molten material. The cavity may be said to be isolated from the second molten metal material.

The first or second molten metal materials may otherwise be described as cast metal materials.

The second molten metal material may be substantially prevented from entering the cavity by a blocking element such as a pattern or core.

The blocking element refers to a device which is able to facilitate the substantial prevention of the second molten metal material from entering the cavity. The blocking element may be described as a seal of sorts, or a baffle or barrier. The blocking element, which may be a pattern, may be said to plug the cavity during casting of the cap.

In this instance pattern refers to a body which generally corresponds to an exterior of the cap. The presence of the pattern may thus substantially prevent the second molten metal material from entering the cavity.

The core may be a destructible core which substantially prevents the second molten metal material from entering the cavity and which is destroyed after use. The core may be a sand core. The cavity may be cleaned out and/or fettled following removal of the core.

Advantageously, the blocking element provides a reliable and repeatable way of substantially preventing the second molten metal material from entering the cavity.

Furthermore, the blocking element is readily useable and does not risk damage to the pre-cast base.

The second molten metal material may flow through the one or more recesses to secure the cap to the base.

The second molten metal material flowing through the one or more recesses to secure the cap to the base will be appreciated to mean that the cap may be secured to the base only after the second molten metal material has solidified.

The recesses preferably incorporate a geometry which defines one or more anchoring features. For example, the recess may splay outwardly at a distal end such that when the second molten metal material solidifies around that feature, the defined feature (e.g. a projection) cannot be withdrawn from the recess (owing to the anchoring effect in that the formed feature generally extends outwardly beyond the recess).

Where a plurality of recesses are incorporated, each of the plurality of recesses may receive the second molten metal material such that the recesses collectively facilitate securing of the cap to the base.

The second molten metal material may flow through the aperture of the attachment portion to secure the cap to the base.

The second molten metal material flowing through the aperture may otherwise be described as the second molten metal penetrating the aperture. As suggested by the name, this occurs whilst the cap material is at least partly molten. Once the second molten material solidifies, a portion of the material present within the aperture defines a retention feature which interlocks the base and the cap.

Securing the cap to the base may otherwise be described as fixing or attaching the cap to the base. Manipulating the tooth by contacting only the cap or the base results in both the cap and the base being moved together.

Advantageously, the second molten metal material flowing through the aperture provides a secure means of attaching the cap to the base. This also allows for the use of different metal materials for the cap and base, which may each have different characteristics depending on their different purposes.

According to a third aspect of the invention there is provided a base for a compactor vehicle tooth, the base comprising:.

The body may further comprise one or more recesses which extend from the cap-facing side to the cavity and generally increase in cross-sectional area from the cap-facing side towards the cavity.

A cavity may be defined in the underside of the base.

A land of material may be defined between the cap-facing side and a lowermost point of the generally arcuate aperture.

According to a fourth aspect of the invention there is provided a tooth for a compactor vehicle, the tooth comprising the base according to the third aspect of the invention, and a cap, wherein a retention feature of the cap interlocks with the generally arcuate aperture of the base to secure the cap to the base.

According to a fifth aspect of the invention there is provided a guard for a compactor vehicle wheel, the guard comprising a base and a cap;.

The guard is a component which protects the compactor vehicle from debris. The guard may be described as a cleat guard. The guard may define a barrier, or shield, of sorts. In preferred embodiments the guard is attached to the wheel of the compactor vehicle at an inner position (i.e. towards a main body of the vehicle). The guard may protect the compactor vehicle by reducing the risk that debris, such as wire and/or strapping, become entangled around, and damage, a main shaft seal provided around an axle which the wheel is mounted to.

The guard may be directly mounted to the wheel (e.g. to the drum). The guard may be mounted to a portion of the wheel which projects outwardly beyond an adjacent portion of the wheel (e.g. on a projecting rim). The projecting rim may define a largest diameter of the wheel (excluding the guard and/or teeth).

According to a sixth aspect of the invention there is provided a compactor vehicle comprising a wheel, wherein one or more of the teeth according to the first or fourth aspects of the invention, and/or one or more of the guards according to the fifth aspect of the invention, are attached to the wheel.

The compactor vehicle may be described as a compaction vehicle. The compactor vehicle may provide functionalities including spreading waste in landfill and compacting the waste in landfill (particularly where the compactor vehicle is a landfill compactor vehicle). The compactor vehicle may be a soil or rock compactor vehicle.

The wheel of the compactor vehicle may be in the form of a drum. The drum may be a steel drum. One or more teeth being attached to the wheel may comprise the one or more teeth being welded to the wheel, such as welded to the drum.

According to a seventh aspect of the invention there is provided a method of manufacturing a guard according to the fifth aspect of the invention, the method comprising:.

The optional and/or preferred features for each aspect of the invention set out herein are also applicable to any other aspects of the invention, where appropriate.

<FIG> is a perspective view of a tooth <NUM> according to an embodiment of the invention. The tooth <NUM> comprises a base <NUM> and a cap <NUM>. The tooth <NUM> is for a compactor vehicle, specifically a compactor vehicle wheel. In use, the tooth <NUM> serves to compact, and break up, material.

The compactor vehicle may be one of a number of different types of compactor vehicle, such as a: landfill, soil or rock compactor vehicle. The material which is compacted and/or broken up by the tooth <NUM>, in use, may therefore include landfill waste, soil (e.g. dirt) and/or rocks (e.g. aggregate). In preferred embodiments the tooth <NUM> is mounted to a wheel of a landfill compactor vehicle, and is used to compact, and break up, landfill waste.

The tooth <NUM> is manufactured in a two-part casting process, which may be referred to as a twin-shot casting process. In the process, the base <NUM> is initially cast using a (first) molten metal material and allowed to cool. With the base <NUM> set (e.g. solidified), the base <NUM> then forms part of a mould into which a (second) molten metal material, which forms the cap <NUM>, is poured and allowed to set. The tooth <NUM> can therefore be manufactured to have a weldable base <NUM> and a hard-wearing cap <NUM> in a single body (with the two parts secured together). This is achieved by manufacturing the base <NUM> and the cap <NUM> from two different materials.

Although not visible in <FIG>, the base <NUM> and cap <NUM> are interconnected by way of one or more retention features which will be described in connection with later figures (and are shown in, for example, <FIG>.

Returning to <FIG>, the base <NUM> comprises a body <NUM>. The body <NUM> defines the bulk of the base <NUM>. The body <NUM> defines an underside <NUM> which, in use, is configured to engage a wheel of the compactor vehicle. As will be appreciated from <FIG>, in combination with, for example, <FIG>, the underside <NUM> may be at least partly arcuate. Providing an at least partly arcuate underside <NUM> is advantageous in providing a more secure fix, or engagement, of the base <NUM>, and so tooth <NUM>, to a wheel (e.g. a drum) of the compactor vehicle.

Returning to <FIG>, the body <NUM> of the base <NUM> comprises two portions: first and second portions <NUM>, <NUM>. The first portion <NUM> is a portion which defines the underside <NUM>. The second portion <NUM> extends from the first portion <NUM>. The second portion <NUM> generally tapers so as to define a narrowing cross-section of the base <NUM>. The uppermost point of the second portion <NUM> of the body <NUM> the base <NUM> meets the cap <NUM> at four outer join lines <NUM>, <NUM> (only two of which are visible in <FIG>). As will be appreciated from <FIG>, the join lines <NUM>, <NUM> define a generally uninterrupted surface between the cap <NUM> and the base <NUM>, specifically outer surfaces thereof. During manufacture, the molten metal material used to manufacture the cap <NUM> may outwardly overhang the base <NUM> (e.g. by between around <NUM> to around <NUM>). Said overhang may be ground, or fettled, back to leave the generally uninterrupted, or flush, surface and to define the outer join lines <NUM>, <NUM>. This has been found to improve the casting process by reducing chillback (e.g. reducing the formation of cracks, proximate the join lines <NUM>, <NUM>, owing to the cap <NUM> material cooling too quickly during casting).

One distinction of the illustrated tooth <NUM>, over prior art teeth, is that the second portion <NUM> of the body <NUM> of the base <NUM> was previously occupied by material used to manufacture the cap <NUM>. The base <NUM> has therefore effectively increased in height. This reduces the amount of comparatively expensive molten metal material used to cast the cap.

The first portion <NUM> further comprises chamfers <NUM>, <NUM> which facilitate the welding of the base <NUM> to the wheel of the compactor vehicle. As will be appreciated from <FIG>, the chamfers <NUM>, <NUM> extend across an entire width of the base <NUM>. The base <NUM>, and so tooth <NUM>, may only be welded to the wheel at the chamfers <NUM>, <NUM> (e.g. at two edges of the underside <NUM>). Alternatively, the base <NUM> may be welded to the wheel at all four edges of the underside <NUM> (e.g. at chamfers <NUM>, <NUM> and at the edges which extend between the chamfers <NUM>, <NUM>). Attachment at all sides (e.g. so as to form a seal, of sorts, between the underside <NUM> and the wheel) advantageously reduces the risk of ingress of material (e.g. debris, fluid etc.) underneath the base <NUM>.

For reasons that will be explained in more detail in connection with <FIG>, it is the base <NUM> of the tooth <NUM> which is a particular focus of the present application.

Returning to <FIG>, to briefly discuss the cap <NUM>, the cap <NUM> comprises an outer surface <NUM> which defines a compaction surface. That is to say, in use, it is the outer surface <NUM> of the cap <NUM> which provides a majority of the compacting action, or functionality. The outer surface <NUM> of the cap <NUM> defines a number of different features including flat faces <NUM> (only one which is visible in <FIG>), arcuate surfaces <NUM> (only one of which is visible in <FIG>) and arcuate recesses <NUM>, <NUM> (only two of which are visible in <FIG>).

The cap <NUM>, in the outer surface <NUM> thereof, defines an outer tip <NUM>. The outer tip <NUM> refers to an uppermost surface of the tooth <NUM>. The outermost tip <NUM> is M-shaped illustrated embodiment, but other profiles of outer tip <NUM> are possible. Indeed, a dumbbell-shaped outer tip is shown in <FIG>, which will be described later in this document.

Turning now to <FIG>, a perspective view of the tooth <NUM> is provided generally from an underside thereof. The <FIG> view shows, more clearly, a cavity <NUM> which is defined in the underside <NUM> of the base <NUM>. The cavity <NUM> is a volume which is free of any material. That is to say, the cavity <NUM> is not occupied by either base <NUM> material or cap <NUM> material. Instead, the cavity <NUM> exists as a free volume within the base <NUM>.

Advantageously, incorporation of the cavity <NUM> provides savings in the amount of material required to cast the base <NUM>. Specifically, the amount of a first molten metal material, used to cast the base <NUM>, is reduced. It will therefore be appreciated that there are associated costs, and weight, savings due to the reduction in material which would otherwise be present in place of the cavity <NUM>. The weight savings are particularly advantageous in reducing the loading requirement placed on the transmission of the vehicle (to which the tooth <NUM> is mounted).

A further advantage of incorporating the cavity <NUM> is that, in previous arrangements, it may have been necessary to carry out a final manufacturing process on the underside of the base before it be welded to the compactor wheel. For example, a grinding process may have been carried out after both the base and cap had been cast. It may have been necessary to grind a significant amount of material in order to ready the underside for attachment to the compactor vehicle wheel. In the illustrated embodiment, the presence of the cavity <NUM> reduces the surface area of the underside <NUM> if the base <NUM>. It will therefore be appreciated that this reduction of surface area provides a corresponding reduction in any grinding process which may be carried out after the tooth <NUM> has been cast. There are therefore associated time, labour and material cost savings with the reduction, or avoidance, of the further process. Furthermore, should any cap material enter the cavity <NUM> inadvertently, during the casting process, said material does not need to be ground.

A further advantage of the cavity <NUM> is that the thermal inertia of the base <NUM> is reduced. Put another way, the base <NUM> can more readily increase in temperature in comparison to if the cavity <NUM> was filled with material (to define a solid block-like base). Generally speaking, the base <NUM> will be cast first, using a first molten metal material which is then allowed to cool (to solidify the base <NUM>). Once the base <NUM> has been cast, the cap <NUM> is generally cast onto the base <NUM> by using a second molten metal material. The base <NUM> may therefore form part of the mould which is used to cast the cap <NUM>. When the comparatively hot molten metal material of the cap <NUM> contacts the comparatively cool precast base, heat is transferred from the molten metal material of the cap <NUM> to the base <NUM>. In certain zones, particularly around edges of the base <NUM>, the comparatively large thermal mass of the base <NUM> (and associated high thermal inertia e.g. resistance to temperature change) can lead to excessive cooling and shrinkage, referred to as chill back, of the material used to form the cap <NUM>. This can lead to unsightly and structurally weakening cracks, particularly around the join lines between the base <NUM> and the cap <NUM>. By incorporating the cavity <NUM>, the thermal inertia of the base <NUM> is reduced such that the base <NUM> more readily heats during the casting process when the cap <NUM> is cast onto the base <NUM>. Advantageously, this reduces the thermal shock experienced by the molten material used to manufacture the cap <NUM>, resulting in a more even cooling process.

A further associated advantage is that less heat is required to weld the base <NUM> of the tooth <NUM> to the wheel of the compactor vehicle. Owing to the reduced thermal inertia of the base <NUM>, welds have been found to have improved penetration into the base <NUM> and the wheel. This is owing, at least in part, to less heat being drawn out of the weld, during the welding process, by an otherwise solid base (which could act as a heat sink of sorts). Put another way, it is walls of the base, forming a peripheral edge of the underside <NUM>, which are welded, rather than an otherwise solid cuboidal base. Cracking associated with the weld(s) may therefore be alleviated.

Although the illustrated embodiment comprises a single cavity <NUM>, in other embodiments a plurality of cavities may be incorporated. Said plurality of cavities may be defined, at least in part, by a supporting structure (e.g. comprising a plurality of walls) define in the underside <NUM> of the base <NUM>.

Also visible in <FIG> are outer ends <NUM>, <NUM>, <NUM>, <NUM> of projections forming part of the cap <NUM>. These projections are more clearly visible in <FIG> (labelled <NUM>, <NUM>, <NUM>, <NUM>) and will be described in detail later in this document. Briefly, the projections of the cap <NUM> are formed when the second molten metal material is cast onto the base <NUM>. The projections are formed by virtue of the molten material flowing through the recesses <NUM>, <NUM>, <NUM>, <NUM> defined in the base <NUM>. The recesses <NUM>, <NUM>, <NUM>, <NUM> are more clearly visible in <FIG>.

Returning to <FIG>, an outer end of the recesses <NUM>, <NUM>, <NUM>, <NUM> extends outwardly proximate the recess <NUM>, as shown in <FIG>. Returning to <FIG>, by allowing the second molten metal material of the cap <NUM> to occupy the outwardly extending portions of the recesses <NUM>, <NUM>, <NUM>, <NUM>, the corresponding outer ends <NUM>, <NUM>, <NUM>, <NUM> of the projections share the same geometry. The resulting geometry of the projections, shown also in <FIG>, thus defines retention features which interlock the cap <NUM> and the base <NUM>.

Returning to <FIG>, it will be appreciated that the cavity <NUM> is generally cuboidal. That is to say the cavity <NUM> is generally defined by two pairs of parallel sides, and has an associated thickness. The cavity <NUM> is also bound by a peripheral edge <NUM> which extends around the underside <NUM> of the base.

Turning to <FIG>, a perspective view, generally from above, of the base <NUM> is provided in isolation. <FIG> more clearly shows a number of features of the base <NUM> which are used to interconnect the cap <NUM> to the base <NUM>.

As previously described in connection with <FIG>, the base <NUM> comprises the body <NUM> which, in turn, comprises first and second portions <NUM>, <NUM>. The first portion <NUM> defines the underside <NUM> and chamfers <NUM>, <NUM>. Also shown in <FIG> are recesses <NUM>, <NUM>, <NUM>, (<NUM> not being visible in <FIG>). For ease of reference, the recesses are herein referred to as first recess <NUM>, second recess <NUM>, third recess <NUM> and fourth recess <NUM>.

<FIG> also shows the body <NUM> of the base <NUM> defining a cap-facing side <NUM>. As suggested by the name, when the tooth is assembled it is the cap-facing side <NUM> of the base <NUM> which faces the cap. The cap-facing side <NUM> is generally planar and is generally rectangular. The cap-facing side <NUM> may be said to generally oppose the underside <NUM> of the base <NUM>. This is owing to the fact that the underside <NUM> and cap-facing side <NUM> are generally provided at different ends of the body <NUM> of the base <NUM>.

The base <NUM> further comprises a lip <NUM>. The lip <NUM> extends around a peripheral edge of the cap-facing side <NUM>. The lip <NUM> may be said to project from the cap-facing side <NUM>.

Advantageously, in use the lip <NUM> reduces a thermal mass/inertia imbalance between molten metal cap material and the base <NUM> by more readily heating up than the bulk mass of base <NUM>. Said warming reduces distortion and shrinkage of the cap associated with the cooling of the molten metal material.

In the illustrated embodiment the lip <NUM> projects by around <NUM> (upwardly) from the cap-facing side <NUM>. The lip <NUM> preferably projects by between around <NUM> and around <NUM>. In the illustrated embodiment the lip <NUM> is around <NUM> in thickness when viewed in plan (i.e. in width or depth). The lip <NUM> is preferably between around <NUM> and around <NUM> in thickness when viewed in plan.

As will be appreciated from <FIG>, the recesses <NUM>, <NUM>, <NUM> (and <NUM>, not visible in <FIG>) extend through at least the cap-facing side <NUM> of the base <NUM>. Furthermore, each of the recesses <NUM>, <NUM>, <NUM> comprises filleted edges where said recesses <NUM>, <NUM>, <NUM> open out into the cap-facing side <NUM>. As will be appreciated from <FIG>, a corresponding filleted edge is provided around the recesses <NUM>, <NUM>, <NUM> where they open out into the cavity <NUM> of the opposing side.

Returning to <FIG>, the base <NUM> further comprises an attachment portion <NUM>. The attachment portion <NUM> extends from a cap-facing side <NUM>. The attachment portion <NUM> defines an uppermost point of the base <NUM> at an outer tip <NUM> of the attachment portion <NUM>. Attachment portion <NUM> facilitates attachment of the cap to the base <NUM>. The attachment portion <NUM> is generally cuboidal and maybe described as tab-shaped.

The attachment portion <NUM> defines a retention feature in the form of an aperture <NUM>. The aperture <NUM> is a feature which molten metal material, of the cap, flows through when the cap is cast onto the base <NUM>. The features interlock to secure the cap to the base <NUM> (as shown in, for example, <FIG>).

In the illustrated embodiment, the aperture <NUM> is a generally arcuate aperture. Generally arcuate aperture is intended to mean that less than around <NUM>%, preferably less than around <NUM>% or <NUM>%, of a perimeter of the aperture <NUM> is defined by linear edges. Instead, the majority of the perimeter of the aperture <NUM> is defined by arcuate edges.

Advantageously, incorporating a generally arcuate aperture <NUM> reduces any comparatively sharp fillets which could otherwise lead to cracks propagating in the attachment portion <NUM> as part of the manufacturing (casting) process.

Provided between the aperture <NUM> and the cap-facing side <NUM> is a land <NUM> of material. The land of material <NUM> refers to a solid block of material. Advantageously, the presence of the land <NUM> of material provides structural reinforcement, and robustness, to the base <NUM> despite the incorporation of the aperture <NUM>. The aperture <NUM> may be said to be offset from the cap-facing side <NUM> by the land <NUM> of material.

Four buttresses <NUM>, <NUM>, <NUM> (<NUM> not visible in <FIG>) extend between the attachment portion <NUM> and the cap-facing side <NUM>. The buttresses <NUM>, <NUM>, <NUM> are supporting projections of sorts which extend in a generally diagonal direction when viewed in plan (see, for example, <FIG>). The buttresses <NUM>, <NUM>, <NUM> are generally triangular projections. Advantageously, the presence of the buttresses <NUM>, <NUM>, <NUM> reduces the risk of distortion occurring to the attachment portion <NUM>, particularly between the attachment portion <NUM> and the cap-facing side <NUM>. This is of particular importance where the attachment portion <NUM> is used to secure the cap to the base <NUM>. The presence of the buttresses <NUM>, <NUM>, <NUM> also reduces the risk of torsional distortion, or twisting, of the attachment portion <NUM> about the cap-facing side <NUM>.

As will be appreciated from <FIG>, each of the buttresses <NUM>, <NUM>, <NUM> extends between a respective two recesses <NUM>, <NUM>, <NUM>. Again, this is more clearly visible in <FIG>.

Turning to <FIG>, a perspective view of the base <NUM> is provided shown generally from the underside. <FIG> thus shows the cavity <NUM> defined in the underside <NUM> of the base <NUM>.

<FIG> shows how the recesses <NUM>, <NUM>, <NUM>, <NUM> open out into the cavity <NUM>. Put another way, the recesses <NUM>, <NUM>, <NUM>, <NUM> extend to the recess <NUM>. When <FIG> is viewed in combination with <FIG> it will be appreciated that each of the recesses <NUM>, <NUM>, <NUM>, <NUM> extends between the cap-facing side <NUM> and the recess <NUM>. <FIG> also illustrates how lower ends of the recesses <NUM>, <NUM>, <NUM>, <NUM> have filleted edges like that described in connection with the upper edges in connection with <FIG>.

<FIG> also shows a generally X-shaped geometry which defines an uppermost point of the recess <NUM>. Said X-shaped geometry is defined at least partly by a surface <NUM> provided between the cavity <NUM> and the aperture <NUM> (in the attachment portion <NUM>). The recess <NUM> may therefore be said to extend between the surface <NUM> and the underside <NUM>. The surface <NUM> defines an uppermost point of the cavity <NUM>.

For completeness, <FIG> also shows the first and second portions <NUM>, <NUM> of the body <NUM> of the base <NUM>. Chamfers <NUM>, <NUM> defined in the front and rear edges of the first portion <NUM> are also visible in <FIG>.

Turning to <FIG>, a plan view of the base <NUM> is provided. In <FIG>, generally only a second portion <NUM> of the body <NUM> is visible, along with the attachment portion <NUM> and buttresses <NUM>, <NUM>, <NUM>, <NUM>.

<FIG> more clearly shows the arrangement of the four recesses <NUM>, <NUM>, <NUM>, <NUM> extending between the cap-facing side <NUM> and the recess (provided beneath the indicated recesses in <FIG>). Each of the recesses <NUM>, <NUM>, <NUM>, <NUM> are generally trapezoidal in that they have one pair of parallel sides. The shapes of the recesses <NUM>, <NUM>, <NUM>, <NUM> may otherwise be described as dovetail-like or tapering. Third and fourth recesses <NUM>, <NUM> are smaller in cross-section than the first and second recesses <NUM>, <NUM>. The recesses can be grouped into two pairs of recesses <NUM>, <NUM> and <NUM>, <NUM>. Recesses belonging to a given pair may each be said to generally oppose one another in that they mirror each other across a central plane of the base <NUM>. Two such planes are indicated schematically in <FIG> as <NUM>, <NUM>.

Taking a first plane <NUM>, the plane <NUM> bisects the base <NUM> between front and rear sides thereof. The first plane <NUM> may therefore be said to define a mid-point of a depth of the tooth. First and second recesses <NUM>, <NUM> are provided equidistant from, and opposing one another about, the first plane <NUM>.

Turning to the second plane <NUM>, the second plane <NUM> bisects the base <NUM> between left and right sides thereof. The second plane <NUM> may therefore be said to define a mid-point of a width of the base <NUM>. Third and fourth recesses <NUM>, <NUM> are provided equidistant from, and oppose one another about, the second plane <NUM>.

It will also be appreciated that the base <NUM> has two planes of symmetry about both the first and second planes <NUM>, <NUM>. More uniform cooling, and being able to insert the base <NUM> into the mould in multiple orientations, are benefits stemming from the symmetry of the base <NUM>. The symmetry also provides the possibility of being able to rotate the cap, relative to the base <NUM>, when the tooth is manufactured, to provide a 'lateral' tooth.

<FIG> illustrates each of the buttresses <NUM>, <NUM>, <NUM>, <NUM> extending between the attachment portion <NUM> and the cap-facing side <NUM>. Each of the buttresses <NUM>, <NUM>, <NUM>, <NUM> generally extends from a corner of the cuboidal attachment portion <NUM> when viewed from above. Each of the buttresses <NUM>, <NUM>, <NUM>, <NUM> also extends in a direction between a respective two recesses <NUM>, <NUM>, <NUM>, <NUM>. For example, the first buttress <NUM> extends between the first recess <NUM> and fourth recess <NUM>. The buttresses <NUM>, <NUM>, <NUM>, <NUM> extend generally diagonally across the cap-facing surface <NUM>.

The base <NUM> has an aspect ratio (i.e. a ratio of width to depth) of around <NUM> when viewed in plan The base <NUM> preferably has an aspect ratio of between around <NUM> and around <NUM> when viewed in plan. Put another way, the base <NUM> is preferably generally square.

Turning to <FIG>, a view of the base <NUM> from underneath is provided. <FIG> shows the underside <NUM> generally defined by the peripheral edge <NUM> which extends around the cavity <NUM>. The cavity <NUM> can therefore be said to be defined by the peripheral edge <NUM> and/or the underside <NUM>.

<FIG> shows the layout of the recesses <NUM>, <NUM>, <NUM>, <NUM> from underneath. The recesses <NUM>, <NUM>, <NUM>, <NUM> may be collectively referred to as an array, or arrangement, of recesses. The generally X-shaped surface <NUM>, which defines an upper limit of the recess <NUM>, is also shown. Chamfers <NUM>, <NUM> are also visible in <FIG>.

<FIG> is a front view of the base <NUM>.

A vertical extent of the first and second portions <NUM>, <NUM> of the body <NUM> of the base <NUM> are indicated in <FIG>. Chamfer <NUM> is also visible.

The attachment portion <NUM> is shown projecting from the body <NUM> (specifically a cap-facing side thereof, not visible in <FIG>). Similarly, first and second buttresses <NUM>, <NUM> are shown extending between the attachment portion <NUM> and the body <NUM>. The generally arcuate aperture <NUM>, extending entirely through the attachment portion <NUM>, can also be seen. The land <NUM> of material provided underneath the aperture <NUM>, between the aperture <NUM> and the body <NUM>, is also visible. As previously mentioned, the outer tip <NUM> of the attachment portion <NUM> defines the tallest or uppermost point of the base <NUM>.

As mentioned above, generally arcuate aperture is intended to mean that less than around <NUM>%, preferably less than around <NUM>% or <NUM>%, of a perimeter of the aperture <NUM> is defined by linear edges. Instead, the majority of the perimeter of the aperture <NUM> is defined by arcuate edges. In the illustrated embodiment, the aperture <NUM> has a perimeter defined by three linear edges <NUM>, <NUM>, <NUM> and three arcuate edges <NUM>, <NUM>, <NUM>. The linear edges <NUM>, <NUM>, <NUM> interpose the arcuate edges <NUM>, <NUM>, <NUM>. The total perimeter of the aperture <NUM> is around <NUM> in the illustrated embodiment. The sum of the extent of the linear edges <NUM>, <NUM>, <NUM> is around <NUM>. The extent of the perimeter which is linear is therefore only around <NUM>% (~<NUM>%). The majority of the perimeter of the aperture <NUM> is defined by arcuate edges. Also of note, a single arcuate edge <NUM> extends between two generally parallel linear edges <NUM>, <NUM>. Put another way, the arcuate edge <NUM> is generally U-shaped. No linear edges are provided between outer ends of the arcuate edge <NUM>.

The aperture <NUM> is around <NUM> wide in the illustrated embodiment (i.e. the distance between the linear edges <NUM>, <NUM>). The aperture <NUM> is preferably between around <NUM> and around <NUM> wide. The aperture <NUM> is around <NUM> in height in the illustrated embodiment. The aperture is preferably between around <NUM> and around <NUM> in height. The radius of the arcuate edges <NUM>, <NUM> is around <NUM> in the illustrated embodiment, and is preferably between around <NUM> and around <NUM>. The radius of the arcuate edge <NUM> is around <NUM> in the illustrated embodiment, and is preferably between around <NUM> and around <NUM>.

Incorporation of a generally arcuate aperture reduces the risk of stress-induced cracks being formed at otherwise comparatively sharp corners of the aperture. This concept can be utilised in isolation or, or in combination with, the incorporation of the cavity (<NUM> in <FIG>) in the base <NUM>.

Returning to <FIG>, a width <NUM> of the base <NUM> is around <NUM> in the illustrated embodiment. The width <NUM> is preferably between around <NUM> and around <NUM>. Given that the base <NUM> defines the widest part of the overall tooth in the illustrated embodiment, the aforementioned width dimensions also apply to the tooth more generally (i.e. the width of the tooth is around <NUM> in the illustrated embodiment). The base <NUM> having widths falling within the aforementioned ranges have been found to be advantageously compatible with machinery associated with compactor vehicles. An example of such machinery is a scraper used to remove debris from the wheel, between teeth mounted to the wheel.

A height <NUM> of the base <NUM> is around <NUM> in the illustrated embodiment. The height <NUM> is preferably between around <NUM> and around <NUM>.

As shown in <FIG>, the outer sides <NUM>, <NUM> of the first portion <NUM> are generally planar and extend in a vertical direction. Outer sides <NUM>, <NUM> of the second portion <NUM> are also planar but incorporate a shallow draft, of around <NUM>°, away from the vertical. A vertical height of the first portion <NUM> is around <NUM> in the illustrated embodiment. The vertical height of the first portion <NUM> is preferably between around <NUM> and around <NUM>. A vertical height of the second portion <NUM> is also around <NUM> in the illustrated embodiment. The vertical height of the second portion <NUM> is preferably between around <NUM> and around <NUM>. The combined heights of the first and second portions <NUM>, <NUM>, and so an overall height of the body <NUM>, is therefore around <NUM> in the illustrated embodiment. The combined heights of the first and second portions <NUM>, <NUM>, and so an overall height of the body <NUM>, is preferably between around <NUM> and around <NUM>. However, it will be appreciated that a range of other dimensions, and geometries, may otherwise be used.

As mentioned above, one distinction of the illustrated tooth <NUM>, in comparison to existing teeth, is the presence of the second portion <NUM> of the body <NUM> of the base <NUM>. Advantageously, increasing the height of the body <NUM> of the base <NUM>, by incorporating the second portion <NUM>, avoids using the (comparatively expensive) second molten metal material, used to manufacture the cap, in regions which generally experience low wear in use. It has been found that below around <NUM>, of an overall height of the tooth <NUM>, the wear is considerably lower than in the region above it. The illustrated tooth <NUM> therefore provides a desirable balance of cost saving and durability by increasing the height of the body <NUM> of the base <NUM>.

<FIG> shows the arcuate nature of the underside <NUM>, or specifically a portion thereof. The underside <NUM> being at least partly arcuate is advantageous in providing a more secure engagement of the base <NUM>, and so the overall tooth, to a wheel of the compactor vehicle. An at least partly arcuate underside <NUM> therefore provides an improved conformance of the underside <NUM> of the base <NUM> to the wheel of the compactor vehicle. In the illustrated embodiment, the radius of curvature of the underside <NUM> is around <NUM>. However, and as mentioned above, other dimensions may otherwise be used.

<FIG> also shows first and fourth buttresses <NUM>, <NUM> extending from the attachment portion <NUM> to the body <NUM> to the base <NUM>. Like in <FIG>, the outer tip <NUM> of the attachment portion defines an uppermost point, or outer tip <NUM>, of the base <NUM>.

A depth <NUM> of the base <NUM> is around <NUM> in the illustrated embodiment. The depth <NUM> is preferably between around <NUM> and around <NUM>. Given that the base <NUM> defines the deepest part of the overall tooth in the illustrated embodiment, the aforementioned depth dimensions also apply to the tooth more generally (i.e. the depth of the tooth is around <NUM> in the illustrated embodiment).

Turning to <FIG>, a cross-section front view of the base <NUM> is provided as indicated by the cross-section marker <NUM> shown in <FIG>. Returning to <FIG>, the cross-section front view indicates the relative depths of various internal features of the base <NUM> previously introduced in this document.

<FIG> shows the body <NUM> of the base <NUM> comprising the first and second portions <NUM>, <NUM>. Attachment portion <NUM> is shown extending from the cap-facing side <NUM>, the attachment portion <NUM> defining the generally arcuate aperture <NUM> therethrough. Third and fourth buttresses <NUM>, <NUM> extend between the attachment portion <NUM> and the cap-facing side <NUM>. The lip <NUM> extends around a periphery of the cap-facing side <NUM>. The land <NUM> of material provided between the cap-facing side <NUM> and the aperture <NUM> is also indicated, along with the vertical height of the same.

Third and fourth recesses <NUM>, <NUM>, which extend between the cap-facing side <NUM> and the cavity <NUM>, are also shown. A vertical height, depth or extent, of the third and fourth recesses <NUM>, <NUM> is labelled <NUM> in <FIG>. The vertical height <NUM> of the third and fourth recesses <NUM>, <NUM> is substantially the same as the vertical height of the recesses <NUM>, <NUM> (not shown in <FIG>). As previously mentioned, a height, or depth, of the recesses is defined between the cap-facing side <NUM> and the surface <NUM>. The recesses <NUM>, <NUM> open out into the cavity <NUM>. A vertical extent of the cavity <NUM> is also labelled in <FIG>. For completeness, an indicated plane <NUM> corresponds with the surface <NUM>, which defines an end point of both the cavity <NUM> and the recesses <NUM>, <NUM>.

<FIG> also indicates the undercut nature of the recesses <NUM>, <NUM>. Described only in connection with the fourth recess <NUM>, but equally applicable to the third recess <NUM> (and first and second recesses <NUM>, <NUM>), the fourth recess <NUM> has a narrowest width <NUM> and a width <NUM> at a lowermost point of the recess <NUM>. It will be appreciated that along the depth of the recess <NUM>, moving from the narrowest point <NUM> towards the lowermost end width <NUM>, the recess <NUM> generally increases in width. This may otherwise be described as the generally undercut feature. This is particularly evident at the width <NUM> defined at the lowermost point of the recess <NUM>. When molten metal material of the cap is poured onto the cap-facing side <NUM> of the base <NUM>, as part of the manufacturing process, the second molten metal material runs along the cap-facing side <NUM> and down into the recesses <NUM>, <NUM>. The second molten metal material is substantially prevented from entering the cavity <NUM> and its flow is therefore limited to approximately the plane indicated by <NUM> in <FIG> (i.e. in line with the surface <NUM>). The second molten metal material, which goes on to form the cap, therefore only extends down to a lowermost point of the recesses <NUM>, <NUM>, as indicated by a lowermost point of the height indicator <NUM>. The second molten metal material therefore entirely fills the recesses <NUM>, <NUM>, including at both narrowest, and end, points <NUM>, <NUM>.

Once the second molten metal material solidifies, the outwardly tapering, or undercut, nature of the recesses <NUM>, <NUM>, in combination with the solidified cap material (e.g. projections), interlock the base <NUM> with the cap. Put another way, the cap is anchored to the base <NUM>. Each of the cap and base <NUM>, specifically projections (not shown in <FIG>) and the recesses <NUM>, <NUM> thereof, thus define retention features which secure the base to the cap.

As will be appreciated from <FIG>, and as will be described later in the document, it is a combination of the recesses <NUM>, <NUM> (and <NUM>, <NUM>, not shown in <FIG>) and the aperture <NUM>, these being the retention features of the base <NUM>, which receive molten metal material of the cap and interlock the cap to the base <NUM>.

In some embodiments, the attachment portion <NUM>, and so aperture <NUM>, may be omitted. However, the recesses <NUM>, <NUM> (and <NUM>, <NUM>, not shown in <FIG>) still define retention features which, after the cap has been cast onto the base <NUM>, interlock the cap with the base <NUM>. Any attempt at separating the cap from the base is substantially prevented by the interference of cap material with the narrowing recesses <NUM>, <NUM>. It will be appreciated that once the second molten metal material is poured onto the cap-facing side <NUM>, and flows into the recesses <NUM>, <NUM>, the resulting cap material generally conforms, or corresponds to, the geometry of the recesses <NUM>, <NUM> (and <NUM>, <NUM>, not shown in <FIG>). This is owing to the fact that the base <NUM> forms at least part of a mould used to cast the cap, and so overall tooth.

<FIG> also illustrates how the cavity <NUM> extends through a majority of the first portion <NUM> of the base <NUM>. As will be appreciated from the plane <NUM>, corresponding to the surface <NUM> and so an uppermost point of the cavity <NUM>, the plane <NUM> lies at a lower position than a lowermost point of the second portion <NUM>. As such, the illustrated cavity <NUM> does not extend through an entirety of the first portion <NUM>, but in some embodiments the cavity may extend through an entirety of the first portion <NUM>. Similarly, in some embodiments the cavity may extend through an entirety of the first portion <NUM>, and at least part of the second portion <NUM>.

Turning to <FIG>, a cross-section side view of the base <NUM> is provided as indicated by the cross-section marking labelled <NUM> in <FIG>.

Many features of <FIG> have already been described in detail in connection with <FIG> more clearly shows the arcuate nature of at least part of the underside <NUM> of the base <NUM>.

The attachment portion <NUM> is again shown extending from the cap-facing side <NUM>, and defining the generally arcuate aperture <NUM> therethrough. The land of material <NUM> provided between the cap-facing side <NUM> and the aperture <NUM> is also labelled. The lip <NUM> extends around the periphery of the cap-facing side <NUM>.

The land of material <NUM> is around <NUM> in height in the illustrated embodiment, and is preferably between around <NUM> and <NUM>.

First and second recesses <NUM>, <NUM> are visible in <FIG>. Like the third and fourth recesses <NUM>, <NUM> described in connection with <FIG>, the first and second recesses <NUM>, <NUM> generally increase in cross-section moving from an uppermost point of the recesses towards a lowermost point of the recesses. As such, and again like the recesses <NUM>, <NUM> described in connection with <FIG>, the recesses <NUM>, <NUM> are generally undercut in that their cross-section towards a lowermost point of the recesses is greater than a cross-section at an uppermost point. When a molten metal material of the cap is cast into the recesses <NUM>, <NUM>, and the material solidifies, each of the recesses <NUM>, <NUM> and corresponding projections of the cap (not shown in <FIG>), define retention features which interlock with one another to secure the cap to the base <NUM>.

<FIG> is a front cross-section view of the tooth <NUM> taken about a cross-section line as indicated by the cross-section markers <NUM> in <FIG>.

As will be appreciated from <FIG>, the tooth <NUM> is shown in an assembled state and with both the base <NUM> and the cap <NUM> present. Retention features of the base <NUM> and the cap <NUM>, as will be described in detail below, interlock with one another to interlock the base <NUM> to the cap <NUM>.

In <FIG> it will be appreciated that the outer surface <NUM> of the cap <NUM> forms a generally continuous exterior with an outer surface of the base <NUM>. Specifically, flat faces <NUM>, <NUM> of the cap <NUM> are generally flush with outer surfaces <NUM>, <NUM> of the second portion <NUM> of the base <NUM>. These surfaces meet at join lines <NUM>, <NUM>.

<FIG> indicates how the molten metal material used to cast the cap <NUM> generally flows over the cap-facing side <NUM> of the base <NUM>. Furthermore, the molten metal material flows into the third and fourth recesses <NUM>, <NUM> (and first and second recesses - not shown in <FIG>).

By virtue of the molten metal material, used to cast the cap <NUM>, flowing into the recesses <NUM>, <NUM> (among others), a plurality of projections <NUM>, <NUM> (<NUM>, <NUM> not visible in <FIG>) are defined in the cap <NUM>. The projections <NUM>, <NUM>, <NUM>, <NUM> are also shown in <FIG>, whereat the cap <NUM> is shown in isolation of the base <NUM>.

Returning to <FIG>, third and fourth projections <NUM>, <NUM> extend through third and fourth recesses <NUM>, <NUM>. As such, the volumes, e.g. geometries, of the third and fourth projections <NUM>, <NUM> generally match those of the third and fourth recesses <NUM>, <NUM>. This is to be expected given that the recesses <NUM>, <NUM> effectively form part of the mould used to cast the cap <NUM>. <FIG> illustrates how the outer ends <NUM>, <NUM> of the third and fourth projections <NUM>, <NUM> splay outwardly relative to a body of the projections <NUM>, <NUM>. Put another way, the projections <NUM>, <NUM> extend outwardly at outer ends <NUM>, <NUM> thereof. This provides an anchoring functionality in that the projected cap <NUM> is thus securely interlocked with, and secured to, the base <NUM>.

The outer ends <NUM>, <NUM> of the projections <NUM>, <NUM> are generally flush with the surface <NUM> which also defines the uppermost surface of the cavity <NUM>. As such, the molten metal material used to cast the cap <NUM> only extends down to the point where the outer ends <NUM>, <NUM> of the projections <NUM>, <NUM> are defined. Substantially no molten metal material, used to manufacture the cap <NUM>, thus enters the cavity <NUM>. This effect may be achieved by sealing, or blocking, the cavity <NUM> whilst the molten metal material, used to manufacture the cap <NUM>, is poured. A blocking element may be used as a way of preventing the molten metal material flowing into the cavity <NUM>. The blocking element may also advantageously define a lowermost surface of the recesses <NUM>, <NUM> during the moulding process.

<FIG> also indicates that a portion <NUM> of molten metal material of the cap <NUM> flows through the aperture <NUM> of the base <NUM>. Once the molten metal material of the cap <NUM> solidifies, the portion <NUM> and the aperture <NUM> thus define retention features which interlock with one another to also secure the cap <NUM> to the base <NUM>. It will be appreciated from <FIG> that the attachment portion <NUM> is generally obscured from view once the cap <NUM> has been cast onto the base <NUM>.

A height <NUM> of the tooth <NUM> is around <NUM> (e.g. <NUM>) in the illustrated embodiment. The height <NUM> is preferably between around <NUM> and around <NUM>.

Turning to <FIG>, a cross-section side view of the tooth <NUM> is provided as indicated by the cross-section markings labelled <NUM> in <FIG>.

<FIG> shows the portion <NUM> of material of the cap <NUM> which extends through the aperture <NUM>. Of note, because of the cross-section view provided, the attachment portion <NUM> appears disjointed owing to the presence of the aperture <NUM>. The land <NUM> of material between the aperture <NUM> and the cap-facing side <NUM> is also more clearly visible in <FIG>.

<FIG> shows first and second recesses <NUM>, <NUM> defined in the base <NUM>. First and second projections <NUM>, <NUM> of the cap <NUM> extend through the first and second recesses <NUM>, <NUM> respectively. Like that described in connection with <FIG>, outer ends <NUM>, <NUM> of the first and second projections <NUM>, <NUM> lie substantially flush with surface <NUM>, or an uppermost surface of the cavity <NUM>. Furthermore, the recesses <NUM>, <NUM> generally taper outwards moving from the cap-facing side <NUM> towards the cavity <NUM>. Similarly, the projections <NUM>, <NUM> therefore also generally taper outwardly moving from the cap-facing side <NUM> towards the cavity <NUM>. The recesses <NUM>, <NUM>, and projections <NUM>, <NUM>, thus again define retention features which interlock with one another and interlock the cap <NUM> to the base <NUM>.

For completeness, the outer surface <NUM> of the cap <NUM> meets the second portion <NUM> of the base <NUM> at join lines <NUM>, <NUM>.

<FIG> is a perspective view of the cap <NUM>, generally from above, in isolation of the base. It will be appreciated that, in practice, it is generally not possible to obtain the geometry of the cap <NUM> shown in <FIG>, in isolation of the base, without destroying the base <NUM> from around the cap <NUM>.

<FIG> shows the first projection <NUM>, second projection <NUM>, and fourth projection <NUM> of the cap <NUM>. As will be appreciated from <FIG>, the projections <NUM>, <NUM>, <NUM> generally extend downwardly from the cap <NUM>. Outer ends <NUM>, <NUM>, <NUM> of projections <NUM>, <NUM>, <NUM> are shown to generally extend outwardly towards the lowermost position of the projections. The extension, or outwardly splaying, nature of the projections outer ends <NUM>, <NUM>, <NUM> also provides an anchoring effect and secures the cap <NUM> to the base. Each of the projections <NUM>, <NUM>, <NUM> (and <NUM>, not visible in <FIG>) thus define retention features which secure the cap <NUM> to the base <NUM>.

Turning to <FIG>, an perspective view of the cap <NUM> is provided generally from beneath. <FIG> clearly shows each of first to fourth projections <NUM>, <NUM>, <NUM>, <NUM>, and associated outer ends <NUM>, <NUM>, <NUM>, <NUM> thereof. Like that described above in connection with <FIG>, the outer ends <NUM>, <NUM>, <NUM>, <NUM> of each of the projections <NUM>, <NUM>, <NUM>, <NUM> generally extend outwardly towards the lowermost point of the projections <NUM>, <NUM>, <NUM>, <NUM>. In the illustrated embodiment the outer ends <NUM>, <NUM>, <NUM>, <NUM> of each of the projections <NUM>, <NUM>, <NUM>, <NUM> extend around <NUM> (downwardly) from the cap-facing side <NUM>. The projections preferably extend by between around <NUM> and around <NUM> from the cap-facing side. As will be appreciated from <FIG>, the array of projections <NUM>, <NUM>, <NUM>, <NUM> generally matches the array of recesses (see <FIG>) <NUM>, <NUM>, <NUM>, <NUM>. The respective arrays generally correspond with one another and define retention features which interlock with one another to secure the cap <NUM> to the base.

For completeness, <FIG> also shows a base-facing surface <NUM> of the cap <NUM>. A recess <NUM> extends around a peripheral edge of the base-facing surface <NUM> and is created by virtue of the lip <NUM> (see <FIG>).

<FIG> shows the underside of the cap <NUM> in isolation of the base. The view is taken normal to the base-facing side <NUM>. Outer ends <NUM>, <NUM>, <NUM>, <NUM> of each of the projections <NUM>, <NUM>, <NUM>, <NUM> (not labelled in <FIG>) are shown in <FIG>, along with part of a recess <NUM> which corresponds to the shape of the attachment portion and buttresses of the base (e.g. see <FIG> and <FIG>). The portion <NUM> of material which extends through the aperture of the attachment portion, to define a retention feature, is also shown in <FIG>.

<FIG> is a cross-section front view of the cap <NUM> in isolation. The <FIG> view corresponds with that shown in <FIG>, but with the base <NUM> omitted.

<FIG> shows the third and fourth projections <NUM>, <NUM> of the cap <NUM>, along with outer ends <NUM>, <NUM> thereof. Part of the recess <NUM>, corresponding with the attachment portion and buttresses of the base, is also visible. Finally, the portion of material <NUM> which extends through the aperture of the base is also shown.

<FIG> is a cross-section side view of the cap <NUM> in isolation of the base. The <FIG> view generally corresponds with that shown in <FIG>, but with the base <NUM> omitted.

First and second projections <NUM>, <NUM> of cap <NUM> are visible, along with outer ends <NUM>, <NUM> thereof. Part of the recess <NUM>, generally corresponding with the attachment portion and buttresses of the base, is also visible.

Turning to <FIG>, a tooth <NUM> according to another embodiment is illustrated. <FIG> is a perspective view of the tooth <NUM> generally from above.

The tooth <NUM> comprises the base <NUM> and a cap <NUM>. The base <NUM> is identical to the base <NUM> described in connection with earlier figures, and will therefore not be described in detail here.

The cap <NUM> is different, in some aspects, to the cap <NUM> described previously. An outer tip <NUM> of the cap <NUM> is generally dumbbell-shaped. The cap <NUM> generally has two planes of symmetry.

The cap <NUM> comprises flat surfaces (e.g. <NUM>), arcuate surfaces (e.g. <NUM>) and a plurality of generally arcuate recesses (<NUM>, <NUM>).

As indicated by comparing <FIG> and <FIG>, the same base <NUM> can be used to manufacture teeth having different cap geometries for different purposes. The way in which the cap <NUM> is manufactured, and attached to the base <NUM>, is the same as that described in connection with the earlier embodiment.

<FIG> shows a perspective view of the tooth <NUM> generally from below. As mentioned above, the tooth <NUM> comprises the base <NUM> and the cap <NUM>.

<FIG> is a perspective view of a guard <NUM> according to another embodiment. The guard <NUM> incorporates a number of features described in connection with the tooth <NUM>, and so the guard <NUM> will only be described briefly.

The guard <NUM> is a component which protects the compactor vehicle from debris. The guard may protect the compactor vehicle by reducing the risk that debris, such as wire and/or strapping, become entangled around, and damage, a main shaft seal provided around an axle which the wheel is mounted to.

In preferred embodiments, a circumferential array of multiple guards <NUM> is provided around the wheel of a landfill compactor vehicle (e.g. as shown in <FIG>).

Returning to <FIG>, the guard <NUM> comprises a base <NUM> and a cap <NUM>. Like the earlier embodiments, the cap <NUM> is preferably cast onto the base <NUM>, the overall guard <NUM> being manufactured using a twin-shot casting process.

The base <NUM>, specifically an underside <NUM> thereof, is configured to engage a wheel of a compactor vehicle. Although not visible in <FIG>, the underside <NUM> comprises a cavity similar to the cavity <NUM> described in connection with the base <NUM>.

The cap <NUM> defines an outer surface <NUM>. Although not visible, the cap <NUM> comprises one or more retention features which interlock with corresponding retention features in the base <NUM> to secure the cap <NUM> to the base <NUM>.

<FIG> is a perspective view of the base <NUM> in isolation. From <FIG> the similarities between the base <NUM> and the base <NUM> (see <FIG>) will be appreciated. The base <NUM> comprises an attachment portion <NUM>, recesses <NUM>, <NUM> and a number of other features like that of the base <NUM> shown in <FIG>. The base <NUM> comprises a plurality of retention features (e.g. an aperture <NUM> of the attachment portion <NUM>, and recesses <NUM>, <NUM>). The base <NUM> comprises a cap-facing side <NUM>.

Owing to the similarities between the base <NUM> and the base <NUM>, it will be appreciated that incorporation of the cavity in the underside <NUM> of the base <NUM> (not visible in <FIG>) is beneficial for the same reasons described in connection with the base <NUM>. Examples of advantages include weight and cost savings, reduced process requirement, easier welding of the base to the wheel, and reduced thermal inertia of the base.

<FIG> is a perspective view of a compactor vehicle wheel <NUM> with a plurality of teeth <NUM> and guards <NUM> mounted thereto.

A circumferential array <NUM> of guards <NUM> (only one of which is labelled) is incorporated. Each of the guards <NUM> are mounted to the wheel <NUM> at a portion <NUM> of the wheel <NUM> which projects radially outwardly beyond an adjacent portion <NUM> of the wheel <NUM>. The portion <NUM> may be referred to as a projecting rim. The adjacent portion <NUM> may be described as a main rim of the wheel <NUM>, and extends across a majority of the axial length of the wheel <NUM>. The teeth <NUM> (only one of which is labelled in <FIG>) are mounted to the adjacent portion <NUM> (otherwise referred to as the main rim).

The array <NUM> of guards <NUM> is provided at an inner position <NUM> of the wheel <NUM>. Said inner position <NUM> of the wheel <NUM> is the end of the wheel <NUM> adjacent a main body of the compactor vehicle in use. The inner portion <NUM> may be referred to as an inner end of the wheel <NUM>. An opposing outer (i.e. exposed) end <NUM> of the wheel <NUM> is the end which is distal the main body of the compactor vehicle in use.

As described above, the guard <NUM>, and so array <NUM>, protects the compactor vehicle by reducing the risk that debris, such as wire and/or strapping, become entangled around, and damage, a main shaft seal provided around an axle which the wheel <NUM> is mounted to.

Claim 1:
A tooth (<NUM>) for a compactor vehicle, the tooth comprising a base (<NUM>) and a cap (<NUM>);
wherein the base comprises:
a body (<NUM>) defining an underside (<NUM>), configured to engage a wheel (<NUM>) of the compactor vehicle, and an opposing cap-facing side (<NUM>); and
a retention feature (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in which material of the cap is received;
wherein the cap comprises:
an outer surface (<NUM>) defining a compaction surface; and
a retention feature (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>);
wherein the retention features of the base and cap interlock with one another to fix the cap to the base and prevent the cap from separating from the base;
characterised in that a cavity (<NUM>) is defined in the underside of the base.