Wear resistant wheel for track laying vehicle

An aluminum or aluminum alloy wheel is disclosed for use in a back-to-back support wheel assembly in a track laying vehicle. Studs are embedded in the wheel rim edges 30 to reduce wear at the point of contact by the horns 34 of the track 36.

BACKGROUND OF THE INVENTION 
This invention relates to the manufacture of articles by the technique 
known variously as squeeze forming, squeeze casting or extrusion casting 
which, for the sake of convenience, throughout this specification the 
claims will be referred to as "squeeze forming". Basically the technique 
of squeeze forming comprises introducing liquid metal into a first part of 
a mould, closing the mould under pressure so that the liquid metal is 
displaced by the mould closure to fill a cavity within the mould without 
entrapping air, maintaining the metal under pressure whilst solidification 
takes place so as to ensure that any shrinkage cavities which may form are 
closed and filled, and then opening the mould and removing the formed 
article. 
Metals most conveniently employed to produce squeeze formed articles are 
aluminium and aluminium alloys and although such squeeze formed aluminium 
or aluminium alloy articles are of sound metallurgical structure and 
strength, they can sometimes be subject to unacceptably severe wear 
conditions. For example, a support wheel for a track-laying vehicle of the 
type described in European Patent Application 79,300,842.6 (published as 
No. 0,005,937) is produceable by squeeze forming in aluminium or aluminium 
alloy but that part of the wheel which is engaged by the steel horns of 
the track is subject to extreme wear conditions. 
It will be understood that many differing squeeze formed articles can be 
subject to severe wear conditions, and it is an object of the present 
invention to provide a squeeze formed article, and method of producing 
such article, wherein wear-resistant means are incorporated. 
SUMMARY 
In accordance with one aspect of the invention there is provided a method 
of manufacturing a metal article by squeeze forming characterised by the 
steps of locating a set of hard metal wear-resistant elements in a mould 
at a position corresponding to the position at which it is desired to 
produce a wear-resistant area in the formed article, the hardness of the 
metal elements being greater than the hardness of the metal being formed; 
introducing molten metal into the mould; closing the mould under pressure 
so that the molten metal is displaced by the mould closure to fill a 
cavity in the mould within which the hard metal elements are located; 
maintaining the metal under pressure whilst solidification thereof takes 
place and the hard metal elements become embedded therein, and opening of 
mould and extracting the formed article. 
Conveniently the hard metal elements are initially located in a first part 
of the mould which provides at least part of the die cavity whereby, when 
the molten metal is introduced to said first part of the mould and the 
mould is closed under pressure, the metal is displaced to fill the cavity 
and to flow on to and around the hard metal elements. 
Alternatively the hard metal elements may be initially located in that part 
of the die cavity wherein the molten metal is introduced so that the 
liquid metal flows at least partially on to and around the hard metal 
elements before the mould is closed under pressure and the metal is 
displaced to fill the cavity. 
As a further alternative the hard metal elements may be releasably carried 
by a second part of the mould providing part of the die cavity which is 
brought towards said first part of the mould when the mould is closed 
under pressure, the molten metal then being displaced to fill the cavity 
and to flow on to and around the hard metal elements. 
In accordance with a further aspect of the invention there is provided a 
squeeze formed metal article having a plurality of hard metal 
wear-resistant elements embedded therein during the forming operation, the 
hardness of said elements being greater than the hardness of the metal of 
the article. 
The metal to be formed is a light metal such as magnesium or aluminium or 
an alloy thereof and the hard metal elements are conveniently formed of 
hardened steel; the metal being formed having a hardness within the range 
60-200 VPN and the hard metal elements having a hardness within the range 
350-1000 VPN. 
Conveniently the hard metal elements comprise a set of spaced apart metal 
studs carried on a support member which may be a flexible member for 
enabling it and the studs carried thereon to be located in the mould or 
may be a rigid member configured to be positively located in the mould. 
The article may comprise a one piece support wheel for a track laying 
vehicle comprising a disc and a rim, the disc being of dished 
configuration with the centre part of the disc extending axially of the 
wheel beyond one of the edges of the rim, and the set of hard metal 
elements being embedded in said rim edge for resisting wear imparted 
thereto by the horns of a track supported by said wheel. It will be 
appreciated that, in a track laying vehicle, a pair of such wheels would 
be arranged to be secured together in back-to-back configuration so that a 
continuous circumferential groove is provided between each pair of wheels 
into which the track horns project to guide the movement of the track 
beneath the wheels.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIG. 1 of the drawings there is illustrated a mould having an 
upper mould part 10 and a lower mould part 12 configured to provide, when 
closed together, a die cavity in the shape of a wheel. The wheel is 
produced by the squeeze forming technique out of an aluminium or aluminium 
alloy material which is introduced in molten liquid form (by means of a 
suitable inlet nozzle) to that part of the die cavity provided in the 
lower mould portion. 
To provide a wear-resistant surface to the rim of the wheel, a set of a 
hard metal wear resistant elements 14 is located in the die cavity in the 
lower mould part 12 at a position corresponding to that which will 
provide, in the formed article, the rim thereof. Thus, referring to FIG. 
1, a ring of cylindrical steel studs on a support member is located around 
the periphery of the die cavity in the lower mould part 12 before the 
liquid aluminium or aluminium alloy is introduced to the mould. After a 
predetermined quantity of liquid metal has been introduced to the die 
cavity the mould is closed by downward movement of the upper mould part 
10. Such closure of the mould under pressure forces the liquid metal 
within the die cavity to flow radially outwardly and upwardly of the 
cavity defined between the upper and lower mould parts 10 and 12 whereby 
the liquid metal also flows on to and around the stud set 14 as is clearly 
shown in FIG. 2. 
The mould is held closed under pressure whilst solidification of the metal 
takes place so as to ensure that any shrinkage cavities which may form are 
closed and filled and during which time the stud set 14 becomes embedded 
in the metal. After a predetermined time the upper mould part 10 is 
withdrawn upwardly away from the lower mould portion, as shown in FIG. 3, 
and the formed wheel 16 is ejected from the die cavity by means of 
suitable ejector rods 18. 
Referring to FIG. 3, it will be seen that the squeeze formed wheel 16 is 
thus provided with the wear-resistant stud set 14 around the lower edge of 
its rim and such a wheel is conveniently used as part of a back-to-back 
support wheel arrangement for the track of a track-laying vehicle 
substantially of the type described and illustrated in European Patent 
Application No. 79 300 842.6 (published as No. 0005937). 
Referring now to FIGS. 4 to 13 there will be described various alternative 
forms of stud sets 14 suitable for location in the mould as hereinbefore 
described for providing a wear resistant surface to the edge of a wheel 
rim. In all of these embodiments the actual wear resistance is afforded by 
a set of cylindrical hardened steel studs conveniently having a hardness 
within the range 350-1000 VPN as compared with the hardness of the 
aluminium forming the wheel itself which has a hardness within the range 
60-200 VPN. Thus referring to FIGS. 4 and 5, the studs 14a are provided in 
a roller chain assembly, each stud having a spigot 14b projecting from 
either side of the stud and the spigots being connected to adjacent studs 
by means of plate-like support links 14c to provide a completely flexible 
assembly. Thus a single length of such a roller chain, or a plurality of 
lengths thereof, can be arranged in the mould prior to the introduction of 
molten aluminium for the squeeze forming operation. 
FIGS. 6 and 7 show an alternative form of flexible stud set assembly 14 
wherein a set of cylindrical studs 14d are each provided with a spigot 14e 
at the rear face only and are interconnected by means of plate-like 
support links 14f having a force fit on the spigots and links 14ff having 
a free fit on the spigots. Again a single length of such an assembly, or 
plurality of individual lengths, can be located in the mould prior to the 
introduction of the molten aluminium. 
FIGS. 8 and 9 show a very similar stud set arrangement 14 to that shown in 
FIGS. 6 and 7 with the exception that the rear ends of the spigots 14e of 
the studs 14d are upset whereby the studs are rivetted to the support 
links to provide a flexible assembly for location in the mould. 
FIGS. 10 and 11 show a yet further variation wherein the studs 14d are 
retained on the support links 14f by means of a star washer 14g engaging 
over each spigot 14e with a friction fit. 
FIGS. 12 and 13 show an arrangement wherein a plurality of studs 14d are 
each spot welded at their rear face to a single steel wire 14h which, as 
will be clearly seen from FIG. 13, is of convoluted shape. This convoluted 
shape of the support wire enables the stud set 14 to be located more 
positively in the mould whereby there is less likelihood of its position 
being disturbed during the squeeze forming operation prior to 
solidification of the molten aluminium. 
Each stud of the stud set 14 in the arrangement of FIGS. 12 and 13 is 
formed from a through-hardened steel to SAE 51100/52100 specification and 
is of cylindrical form with radiused ends, the provision of which lowers 
the stresses in the stud. Such a steel stud has good weldability, good 
wear resistance and good impact resistance to the conditions encountered 
in use and is further described herein. 
It will be appreciated that, in all of the arrangements shown in FIGS. 4 to 
13, the actual stud length may be varied as between adjacent studs to 
provide for the possibility of differential wear life at the wheel rim 
edge. Thus, after the wheel has been formed, some of the studs may be 
visible at the rim edge surface whilst other studs may be totally embedded 
within the aluminium and be located beneath the rim edge surface. However 
in all of the variations in design of the stud assembly, it will be 
appreciated that, after the wheel has been formed, the studs will be 
effectively mechanically locked into the wheel rim edge due to the 
penetration of the molten aluminium around the studs and support members 
during the forming operation. Furthermore an intermetallic bond will be 
established between the steel studs, the support member and the aluminium. 
Referring now to FIGS. 14 to 16, there is shown squeeze formed aluminium 
wheels 20 with wear-resistant steel studs 14 at the rim edges produced in 
accordance with the invention as used in a support wheel assembly of a 
track laying vehicle. Referring particularly to FIGS. 14 and 15, each 
wheel 20 comprises a dished disc portion 22 and a rim portion 24 wherein 
the disc merges into the rim substantially in the axially central zone 26 
of the rim so that the adjacent portion of the disc and rim together are 
of T-shape. 
The centre portion 28 of the disc 22 extends axially beyond the edge 30 of 
the rim 24 so that, when a pair of similar wheels 20 are secured to the 
hub 32, the wheels are in back-to-back configuration and a continuous 
circumferentially extending groove is defined between the two wheels into 
which the horns 34 of the track 36 are arranged to extend and to guide the 
track beneath the wheels. Appropriate bolt holes 38 are formed in the 
centre portion 28 for securing the two wheels 20 together and also for 
securing the wheels to a vehicle hub 32. 
It will be seen that the hardened steel stud set 14 extends 
circumferentially around the wheel rim edges 30 between which the track 
horns 34 project so as to afford the required wear resistance. In the 
particular arrangement shown in FIGS. 14 and 15 the cylindrical steel 
studs are spot welded at their rear faces to a single length of steel 
wire. The single length of steel wire may be of the convoluted form for 
initial location purposes as previously described with reference to FIGS. 
12 and 13 or, alternatively, the single length of steel wire may be 
non-convoluted and may be initially located in the mould, together with 
its welded-on studs, by means of circumferentially spaced washers on, for 
example, every sixth stud. 
The provision of studs 14 welded onto a single steel support wire which is 
convoluted or non-convoluted and which is in accordance with the general 
constructional principles of the embodiments described with reference to 
FIGS. 12 and 13 offers many advantages in use. It will be appreciated that 
a support wheel for a track-laying vehicle is subject to extremely violent 
wear and impact conditions from the horns of the track. Thus although the 
re-enforced rim edges 30 on which the track horns 34 bear have to be 
extremely wear resistant against the continuous "chatter" of the horns it 
is also necessary that such rim edges 30 are able to offer good impact 
resistance against the extremely violent impacts from the horns 34 due to 
the continued predisposition of the horns to jump out of and then re-enter 
the groove between the rim edges in use. 
Steel studs having good weldability, good wear resistance and good impact 
resistance enable the studs to be securely welded to the length of steel 
support wire; the wire and the studs then being mechanically locked into 
the wheel rim edge during the forming of the wheel as previously 
described. The retention of the studs and wire in the wheel is further 
enhanced by the inter-metallic bond established between the steel studs, 
the support wire and the aluminium. The retention of the studs welded onto 
the support wire enable the studs to resist displacement out of the wheel 
material during the violent conditions of use referred to above whilst at 
the same time the studs offer good wear resistance and good impact 
resistance during such conditions of use. 
It will also be seen that the outer peripheral surfaces 40 of the wheel 
element rims 24 are cylindrical for locating a solid rubber tyre 42 on 
each rim; the tyre being conveniently moulded in situ on the rim. 
Although the foregoing specific description has been with reference to a 
support wheel for use in a track-laying vehicle, it will be appreciated 
that the invention, in its broadest terms, envisages the production of 
squeeze formed articles for any suitable purpose wherein it is desirable 
to provide a wear resistant area by the incorporation of a set of hard 
metal wear resistant elements.