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FIELD OF THE INVENTION 
       [0001]    The present invention relates to components which are resistant to abrasive wear. It has been conceived primarily for use in relation to heel shrouds, arranged to attach to the heel of an excavator bucket, and similar wear parts for excavator buckets such as corner shrouds, wings shrouds, wear bars, lips and wear caps. Aspects of the invention are considered to have wider application than this, and may also be applied to other wear-exposed apparatus, including fixed apparatus. 
       BACKGROUND TO THE INVENTION 
       [0002]    Parts of earth moving machinery and related equipment are subject to significant wear during use, principally due to abrasion. In an attempt to reduce the effects of this abrasion, wear components are often mounted to earth moving buckets and similar machinery. Typical wear components include heel shrouds, wear bars, corner shrouds and wing shrouds. These components are replaceable units, arranged to wear during use while protecting the bucket, and to be replaced before wearing completely through to the bucket. 
         [0003]    It is desirable to make wear components from abrasion resistant materials, in order to extend their working life and to provide an enhanced benefit. It is also necessary to use materials which can withstand substantial impact forces, and the resulting stresses within the material. In general, it has been found that materials with high resistance to abrasive wear, such as chromium white irons and tungsten carbide composites, are generally too brittle to withstand the impact forces to which the heel shrouds are frequently subjected. 
         [0004]    Additional difficulties have been experienced in successfully attaching components made of these materials to earth moving equipment. The materials are generally incapable of being welded, and the provision of holes and the like in the component for mechanical attachment can lead to unacceptable stress concentrations within the material. 
         [0005]    As a result, most wear members are made from quenched and tempered steel, as this provides excellent strength properties along with a degree of resistance to abrasion. 
         [0006]    An alternative type wear member has been proposed in the applicant&#39;s pending PCT application published as WO 2009/086590, the contents of which are incorporated herein by reference. This wear member comprises an outer shell of a tough metal such as a carbon steel, and an inner shell of an abrasion resistant metal such as a white iron. 
         [0007]    This wear member has proved in testing to have many of the stated advantages. Nonetheless, it is considered desirable to provide a wear member having even greater strength than that of WO 2009/086590. 
         [0008]    It has also been observed that the use of an abrasion resistant material within an outer shell can significantly alter the wear rates of different parts of the wear member. It is considered desirable to take advantage of this observation in order to reduce the cost and weight of a wear member without substantially reducing its effectiveness. It is also considered desirable to provide a means of easily determining when a wear member has reached the end of its useful life. 
         [0009]    Different aspects of the present invention seek to achieve these desiderata. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one aspect of the present invention there is provided a wear component formed from at least a first metallic material and a second metallic material, the first material having a toughness greater than that of the second material and the second material being more abrasion resistant than the first material; the component having a shell formed from the first material and an inner body formed from the second material, a metallurgical bond existing between the first material and the second material; wherein the shell includes at least one cross portion extending through the inner body, the cross portion being formed from the first material and having a first side and a second side each of which are bonded to the second material. It is preferred that the cross portion is elongate, with the first side being along one longitudinally extending side of the cross portion and the second side being on an opposite longitudinally extending side of the cross portion. 
         [0011]    The wear component may be for use in conjunction with an excavator bucket. For instance, the wear component may be a heel shroud, a wear bar, a corner shroud, a wear cap or a wing shroud. 
         [0012]    Preferably, the shell includes a plurality of cross portions. These cross portions may be arranged parallel to each other, or may be arranged such that at least one cross portion intersects another cross portion within the inner body. 
         [0013]    In a preferred embodiment, the shell includes opposed end walls and opposed side walls, with at least one cross portion extending between the opposed end walls and at least one cross portion extending between the opposed side walls. 
         [0014]    The shell defines a volume arranged to contain the inner body. This volume has a base, and an upper edge which is defined by upper edges of the end walls and side walls when the wear member is so oriented. It is preferred that at least some of the cross portions are arranged such that the shell includes a space between at least part of these cross portions and the base; that is, that a portion of the inner body is located between the base and the particular cross portion. Preferably, the arrangement is such that the inner body is contiguous. This means that if the second metal is poured in a molten state into the shell, it will fill the shell to the upper edge with no voids remaining. 
         [0015]    It is also preferred that at least some of the cross portions are arranged so as to have an upper edge which is level with the upper edges of the end walls and side walls. 
         [0016]    In accordance with a second aspect of the present invention there is provided a wear component including: 
         [0017]    an inner face for attachment to apparatus subject to wear, the attachment defining a protected surface portion of the apparatus; and 
         [0018]    an outer face which is exposed, in use, to abrasive wear; 
         [0019]    a volume being defined between the protected surface portion of the apparatus and the outer face of the wear component representing the effective volume of the wear component; 
         [0020]    wherein a portion of this volume contains a void. 
         [0021]    The apparatus may be an excavator bucket. In this case, the wear component may be a heel shroud, and the protected surface portion of the bucket part of the bucket heel. Alternatively, the component may be a wear bar, a corner shroud, a wear cap or a wing shroud. 
         [0022]    It is envisaged that the void will contain air, although it will be appreciated that the void may be filled with some material less dense than metal without departing from the scope of the invention. 
         [0023]    It is preferred that the void be open; that is, be located between part of the inner face of the component and part of the protected surface portion of the bucket. It is alternatively considered possible to locate the void entirely within the component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    It will be convenient to further describe the invention with reference to preferred embodiments of the wear member of the present invention. Other embodiments are possible, and indeed other wear components can be formed in a similar fashion, and consequently the particularity of the following discussion is not to be understood as superseding the generality of the preceding description of the invention. In the drawings: 
           [0025]      FIG. 1  is an upper perspective of a heel shroud in accordance with the present invention; 
           [0026]      FIG. 2  is a cut-away upper perspective of a heel shroud in accordance with the present invention; 
           [0027]      FIG. 3  is a cut-away lower perspective of the heel shroud of  FIG. 1 ; 
           [0028]      FIG. 4  is a doubly cut-away upper perspective of the heel shroud of  FIG. 1 ; 
           [0029]      FIG. 5  is an upper perspective of a shell of the heel shroud of  FIG. 1 ; 
           [0030]      FIG. 6  is a doubly cut-away upper perspective of the shell of  FIG. 5 ; 
           [0031]      FIG. 7  is a lower perspective of the shell of  FIG. 5 . 
           [0032]      FIG. 7  is an upper perspective of a wear bar in accordance with the present invention; 
           [0033]      FIG. 8  is a lower perspective of the wear bar of  FIG. 7 ; 
           [0034]      FIG. 9  is an upper perspective of a wear cap in accordance with the present invention; and 
           [0035]      FIG. 10  is a lower perspective of the wear cap of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0036]      FIG. 1  shows a heel shroud  10 , formed of an outer shell  12  and an inner body  14 . The shell  12  is formed from a first metallic material, being one having a relatively high fracture toughness and requiring relatively high impact energy to cause fracture. The first metallic material is one suitable for welding to a heel of an excavator bucket (not shown). The first metallic material may be a mild steel, a higher strength carbon steel or a steel alloy, suitably treated (for instance by case carborising, induction hardening, quenching and/or tempering) to achieve the required properties. 
         [0037]    The inner body is formed from a second metallic material, being one having a high resistance to abrasion. The second metallic material may be an alloy white iron, such as one containing 9-15% chromium; 3.5-4.5% carbon; 0.4-0.7% silicon; 1.0-4.0% manganese; and 0.5-3.0% nickel. Alternatively, the second metallic material may be an alloy chosen from alloys containing carbides of chromium, tungsten, boron, molybdenum, niobium, titanium, vanadium, or the like. 
         [0038]    The shell  12  includes an outer end wall  16 , an inner end wall  18 , a first side wall  20  and a second side wall  22 . The outer end wall  16  has a first portion  24 , which is parallel to and opposite the inner end wall  18 ; and a second portion  26  which extends, in use, along the side wall of an excavator bucket, and which is angled towards the side wall of the excavator bucket. 
         [0039]    Similarly the side walls  20 ,  22 , which are parallel to and opposite each other, each have a first portion  28  which is substantially rectangular, extending between the inner end wall  18  and the first portion  24  of the outer end wall  16 , and a second portion  30  which is substantially right-triangular in shape, and extends in use between the side wall of the excavator bucket and the second portion  26  of the outer end wall  16 . 
         [0040]    The inner end wall  18  and the first portions  24 ,  28  of the outer end wall  16  and side walls  20 ,  22  form an open rectangular prism. When the shell  12  is oriented such that the second portions  26 ,  30  are pointing down, upper edges of the inner end wall  18  and the first portions  24 ,  28  of the outer end wall  16  and side walls  20 ,  22  define an upper edge  32  of the shell  12 . 
         [0041]    The shell  12  defines a volume which is filled by the inner body  14 . The volume is defined by the upper edge  32 ; the end walls  16 ,  18 ; the side walls  20 ,  22 ; and a base  34 . The base  34  broadly follows the shape of the heel of the excavator bucket to which the shroud  10  is to be attached, but is spaced from it as will be discussed below. 
         [0042]    The shell  12  includes one longitudinal cross portion  36  and two transverse cross portions  38 . The longitudinal cross portion  36  extends from the centre of the inner end wall  18  to the centre of the first portion  24  of the outer end wall  16 . The longitudinal cross portion  36  is parallel to, and similar in thickness to, the first portions  28  of the first and second side walls  20 ,  22 , and is located about midway between them. 
         [0043]    The longitudinal cross portion  36  extends from the upper edge  32  of the shell  12  to the base  34  of the shell volume near the inner end wall  18 . The longitudinal cross portion  36  would thus act to divide the shell volume in two, except that where the base  34  follows the curve of a bucket heel around to the bucket side wall the longitudinal cross portion  36  remains of constant depth. There is thus a gap  40  between the longitudinal cross portion  36  and the base  34  near the second portion  26  of the outer end wall  16 . 
         [0044]    Each of the transverse cross portions  38  extends from the first portion  28  of the first side wall  20  to the first portion  28  of the second side wall  22 . The transverse cross portions  38  are parallel to, and similar in thickness to, the inner end wall  18 . They are equally spaced along the side walls  20 ,  22  between the inner end wall  18  and the first portion  24  of the outer end wall  16 . The transverse cross portions  38  extend from the upper edge  32  of the shell  12  towards the base  34  of the shell volume, but do not meet the base  34 . There are gaps  40  between the transverse cross portions  38  and the base  34 . It will be appreciated that the longitudinal cross portion  36  is perpendicular to the transverse cross portions  38 , and intersects each of them. 
         [0045]    The cross portions  36 ,  38  are integral to, and formed of the same material as, the remainder of the shell  12 . 
         [0046]    The heel shroud  10  may be formed using the techniques discussed in WO 2009/086590, whereby a metallurgical bond is created between the shell  12  and the inner body  14 . It will be appreciated that the longitudinal cross portion  36  has two sides, each of which is parallel to the side walls  20 ,  22 . The arrangement is such that the longitudinal cross portion  36  bonds to the second material on each of these sides. Similarly, the transverse cross portions  38  each have two sides parallel to the inner end wall  18 , and the transverse cross portions  38  bond to the second material on each side. 
         [0047]    Where the second material is poured as a liquid, or melted within the shell to be flowable, it will pass beneath the gaps  40  and fill the volume of the shell  12  to the upper edge  32 . The inner body  14  thus formed will have portions extending between the cross members  36 ,  38  and the base  34 , and will be a single contiguous body. 
         [0048]    The heel shroud  10  has the abrasion resistance provided by the inner body  14 , but has a strength reinforced by the cross members  36 ,  38 . 
         [0049]    As noted above, the base  34  is spaced from the bucket heel when the heel shroud  10  is attached. The arrangement is such that the heel shroud  10  includes a plurality of supporting members  42  extending between the base  34  and the bucket heel. These supporting members  42  cooperate with lower edges of the inner end wall  18  and first portions  28  of the side walls  20 ,  22 , and inner edges of the second portions  30  of the side walls  20 ,  22 , to provide a supporting structure for the heel shroud  10  which can be bonded (such as by welding) to the bucket heel. A void in the form of an air gap  44  is maintained in between the supporting members  42 , and the sides walls  20 ,  22  and inner end wall  18 , between the base  34  and the bucket heel. 
         [0050]    The air gap  44  significantly reduces the weight of the heel shroud  10  compared with the same shroud where the gap  44  is filled with metal. It also provides an indication of the remaining heel shroud life. When the inner body  14  is sufficiently worn away to expose the air gap  44 , this will be easily noted by a maintenance worker and provides a ready indication that replacement is required. 
         [0051]      FIGS. 7 and 8  are upper and lower perspectives of a wear bar  50  formed according to similar principles to the heel shroud  10 . The wear bar  50  has an outer shell  52 , and a cavity  54  in which an inner body can be formed. 
         [0052]    In contrast to the heel shroud  10 , the wear bar  50  uses a plurality of transverse cross portions  56  and no longitudinal cross portions. This is a result of the geometry of the wear bar  50 , which is inherently narrow. In the embodiment of the drawings, the wear bar  50  has three spaced transverse cross portions  56 . 
         [0053]    Similarly, the wear bar  50  has five supporting members  58  equally spaced along its underside, as can be seen in  FIG. 8 . The supporting members  58  allow for the creation of air gaps  60  between the wear bar  50  and a bucket to which it is welded. 
         [0054]      FIGS. 9 and 10  are upper and lower perspectives of a wear cap  70  formed according to similar principles to the heel shroud  10 . The wear cap  70  has an outer shell  72 , and a cavity  74  in which an inner body can be formed. 
         [0055]    Similarly to the heel shroud  10 , the wear cap  70  has a single longitudinal cross portion  76  and two transverse cross portions  78 . These are arranged similarly to those of the heel shroud  10 , with the principle difference being that both the longitudinal cross portion  76  and the transverse cross portions  78  are spaced from a base  80  of the cavity  74 , to allow for creation of a contiguous inner body. 
         [0056]    The wear cap  70  has an air gap  82  formed on its under side, as can be seen in  FIG. 10 . The wear cap  70  is sufficiently small that supporting members are not required. Rather, side and end walls of the wear cap  70  extend beyond the base  80  in order to create the air gap  82 . 
         [0057]    It will be appreciated that other wearing parts can be made in a similar fashion to the heel shroud  10 , the wear bar  50  and the wear cap  70  discussed above. Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Summary:
A wear component for use on, for instance, an excavator formed by a shell formed from a tough metal such as carbon steel and an inner body formed from an abrasion resistant metal such as a chromium white iron. The shell includes cross portions extending through the inner body, the cross portions being made of the tough metal. This has the effect of strengthening the overall toughness of the wear component, whilst retaining desirable abrasion resistance.