Abstract:
Wear-resistant and abrasion-resistant assemblies can be affixed to surfaces of various pieces of equipment to extend the life of the equipment and increase its effectiveness. The assembly is a multi-layer composition of two harder materials that provide wear-resistance surrounding a material that provides strength and flexibility, as well as providing a means of attaching the assembly to the piece of equipment. When one or more assemblies does incur wear, assemblies can be replaced easily to further extend the life of the equipment.

Description:
CROSS-REFERENCE TO RELATED APPICATIONS  
       [0001]     This application claims priority to U.S. Provisional Patent Application No. 60/604,560 entitled “LAMINATED WEAR-RESISTANT ASSEMBLIES,” filed on Aug. 26, 2004 on behalf of Edward Williams, which is hereby incorporated by reference for all purposes. 
     
    
     TECHNICAL FIELD  
       [0002]     The invention relates generally to wear-resistant and abrasion-resistant assemblies that can be affixed to a surface to extend the life of the equipment and increase the effectiveness of the equipment.  
       BACKGROUND  
       [0003]     The use of wear-resistant material affixed to the working surfaces of equipment that is subject to high wear or abrasion from materials being processed is well known. Various ceramics, tungsten, or tungsten-carbide are some of the more commonly used materials. While wear-resistant materials are very hard, they tend to be expensive, brittle, and difficult to work with. For these reasons, equipment is rarely made from these materials. Depending on the arrangement and material used, such materials can be sprayed on in a thin coating, or sheets or tiles of such wear-resistant material can be affixed to working surfaces of equipment made from materials such as steel, aluminum or other metallic or non-metallic substances. Such wear-resistant materials have been used to prolong the life of a variety of equipment, such as drill bits, rotating fans, centrifuge conveyors, to name a few.  
         [0004]     For example, U.S. Pat. No. 4,003,115 to Fisher discloses a system whereby wear resistant-material is sprayed into a cavity created along the leading edge of a conveyor screw. However, in use, the amount of hardened material that can be secured to the surface of such equipment by spraying yields a thin coating of harder material on working surfaces. While this is satisfactory for some uses, many other uses require a thicker layer of wear-resistant material. For example, U.S. Pat. No. 6,648,601 also owned by the same assignee as the present invention, discloses affixing patterns of tiles of a wear-resistant material to rotating fan assemblies used for processing coal dust, which is highly abrasive, and would wear off a thin coating of hardened material in a very short time. Similarly, U.S. Pat. No. 5,380,434 to Paschedag discloses a system for affixing flat, wear-resistant tiles to the leading edge of a centrifuge conveyor screw, and U.S. Pat. No. 6,739,411, owned by the same assignee as the present application discloses affixing tiles of a wear-resistant material to the areas of drill bits that are subject to high wear.  
         [0005]     Because such wear-resistant materials tend to be very brittle, they are prone to fractures or cracking. Thus they can be difficult to work with. Additionally, depending on the equipment on which the wear-resistant materials are being used, and the product being processed in the equipment, cracked or chipped materials could contaminate the product, or cause damage in the equipment.  
         [0006]     One solution has been to affix them to a carrier, or backing, made of a material that is easier to work with, such as steel. However, there can be difficulties with securing the wear-resistant materials to the carrier, just as there are difficulties in securing the wear-resistant materials directly to the equipment. Because the wear-resistant materials are prone to fracturing or breaking, drilling holes through the materials to secure them to a carrier or other surface with fastening devices can be difficult, and result in a high incident of fracturing, cracking or chipping. One solution has been to solder, or braze the wear-resistant materials to the carrier. However, depending on the material characteristics of the carrier and the wear-resistant materials, it is necessary to heat the materials to a high temperature to perform the soldering or brazing. Because the materials expand and contract at different rates, after being secured, they contract at different rates. If the differences are great enough, the carrier will torque or shear as it cools, and the attached wear-resistant material can also bend, or will crack or fracture, or in some situations, the secure itself will fail and the two materials will detach from each other.  
         [0007]     Therefore, what is needed is a system and method for affixing wear-resistant members to equipment that is simple, cost-effective and easy to use. Such systems should provide for a method of securely fastening wear-resistant members to equipment, as wear-resistant materials are typically hard and can be brittle and break easily under certain circumstances. Such systems and methods should, among other things, reduce or eliminate instances of fracturing or cracking of the wear-resistant materials. Such systems should also reduce the possibility of the attached wear-resistant members becoming detached and contaminating product or damaging equipment.  
       SUMMARY  
       [0008]     The present invention, accordingly, provides a multi-layer laminated wear-resistant assembly. The assembly comprises a bracket, typically made of steel or some similar material, which can be welded, soldered or glued and can be machined or manipulated. The bracket is layered between a plate wear-resistant material, such as tungsten-carbide on the front, and a third layer at the rear of the bracket, which can be made of the same material as the front layer, or of a different material having similar characteristics of expansion and contraction as the plate of wear-resistant material. The layers of the assembly are secured together by soldering, brazing or some other method.  
         [0009]     Because the bracket material is trapped between two layers of harder materials with similar characteristics, it does not warp or shear when the materials begin to cool after brazing, but stays “stretched” between the two layers of harder materials. This “stretched” state is due to the shrinkage differentials of the materials used in the layers of the assembly that occur after brazing when the assembly is cooling. When the entire laminated assembly has cooled, a stronger mechanism is achieved that is more resistant to cracking or fracturing because of the more flexible material that comprises the middle layer of the assembly providing a support structure.  
         [0010]     By creating a laminate of a bracket made of a more flexible material, such as steel or other material, with wear-resistant material as the top layer of the laminate, and a third layer of material on the rear side of the steel, a much stronger, more useful product is achieved than would be if only one of the materials was used alone. The face of hardened material prolongs the life of the equipment and increases the effective time of operation before repair or replacement is necessary. Additionally, the individual assemblies can be easily removed and replaced as assemblies wear over time, further increasing the life of the mechanism.  
         [0011]     In one preferred embodiment of the present invention, a laminated wear assembly is provided. A core member having a first and an opposite second face and having an attaching member extending substantially perpendicular from the second face to substantially form an “L” shape is included in the laminated wear assembly. Moreover, the core member further comprises a first coefficient of thermal expansion. Additionally, a first wear member is also included having a second coefficient of thermal expansion secured to a substantial portion of the first face, wherein the first coefficient of thermal expansion is greater than the second coefficient of thermal expansion. In addition to having a first wear member, there is also a second wear member having a third coefficient of thermal expansion secured to a substantial portion of the second face, wherein the second coefficient of thermal expansion is approximately equal the third coefficient of thermal expansion. The laminated wear assembly, too, is formed such that the core member remains substantially stretched at approximately room temperature.  
         [0012]     In another preferred embodiment of the present invention, the core member comprises a material selected from the group consisting of stainless steel, carbon steel, aluminum, and NiCroMoly.  
         [0013]     In yet another preferred embodiment of the present invention, the first wear member and/or the second wear member are made from a composition comprising at least tungsten-carbide.  
         [0014]     In another preferred embodiment of the present invention, the core member, the first wear member, and the second wear member are secured to one another by brazing, soldering, welding, or gluing.  
         [0015]     In an alternative embodiment of the present invention, a method of forming a laminated wear assembly is provided. A core member is formed having a first and a second opposing face with an attaching member extending substantially perpendicular from the second face to form an “L” shape, and having a first coefficient of thermal expansion. A first wear member is also formed having a second coefficient of thermal expansion, wherein the second coefficient of thermal expansion is less than the first coefficient of thermal expansion. Additionally, a second wear member is formed having a third coefficient of thermal expansion, wherein the second coefficient of thermal expansion is approximately equal to the third coefficient of thermal expansion. Onced formed, the core member, the first wear member, and the second wear member are heated to a sufficient temperature that causes the core member, the first wear member, and the second wear member to secure with one another and to form the laminated wear assembly. After heating, the laminated wear assembly is cooled to approximately room temperature so that the core member remains in tension in a tensile state of stress at approximately room temperature.  
         [0016]     Another alternative embodiment of the present invention provides a method of forming a laminated assembly. With this alternative embodiment, a core member, having a first and a second opposing face, a first wear member, and a second wear member are formed. Once formed, each of the core member, the first wear member, and the second wear member are elongated. Once elongated, the first wear member is secured to the first face, and the second wear member is secured to the second opposing face. The first wear member and the second wear member are then reduced, while the elongation of the core member is maintained.  
         [0017]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0019]      FIG. 1  is an exploded side view of an assembly embodying features of the present invention;  
         [0020]      FIG. 2  is a rear perspective view of an assembly of the present invention;  
         [0021]      FIG. 3  is a rear exploded view of an assembly embodying the features of the present invention;  
         [0022]      FIG. 4  is a front view showing several assemblies secured to the leading edge of a piece of equipment; and  
         [0023]      FIG. 5  is a side view of a secured assembly of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0024]     In the discussion of the FIGURES, the same reference numerals will be used throughout to refer to the same or similar components. In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without such specific details.  
         [0025]     Referring to  FIGS. 1-3  of the drawings, the reference numeral  10  generally designates a laminated assembly of the present invention. The assembly  10  comprises a first wear member  30 , a core member  20 , and a second wear member or backing element  40 .  
         [0026]     The assembly  10  is essentially a bracket that can be affixed to machinery to protect wear surfaces. For example, assembly  10  can be affixed to driving faces of an extrusion screw, as shown in  FIG. 4 . The assembly  10  is formed by sandwiching the core member  20  made of a workable material, such as steel, between the first wear member  30  and the second wear member  40 , where the core member  20 , the first wear member  30  and the second wear member  40  are secured to one another, such as by brazing, gluing, soldering, or welding. Typically, the first wear member  30  and the second wear member  40  are comprised of a hard material, such as tungsten-carbide.  
         [0027]     Specifically, each of the core member  20  and the first wear member  30  have first faces  20   b  and  30   b  and second faces  20   a  and  30   a,  respectively. In forming the assembly  10 , the second face  30   a  of the first wear member  30  is secured to the first face  20   b  of the core member  20 , and the second wear member  40  is secured to the second face  20   a  of the core member  20  in slot  24 . However, as it can be seen in  FIGS. 1-3 , second wear member  40  does not completely cover the second face  20   a  of the core member  20 . There is an attaching member  22  extending substantially perpendicular from the second face  20   b  of the core member  20  such that the core member  20  forms an “L” shape. The attaching member  26  would thus allow for a portion of the workable material, such as steel, to be exposed so as to attach to machinery, as shown in  FIG. 4 , while the first face  30   b  of the first wear member  30  faces outward and comes in contact with the admixture being processed.  
         [0028]     In the process of securing the layers of the assembly together, heating is commonly employed; moreover, it is not uncommon to utilize assembly  10  in heated environments. One of the reasons for employing the multiple layers of wear members is due to differing coefficients of thermal expansion of the dissimilar metals. Typically, the hard protective metals, such as tungsten-carbide, have a lower coefficient of thermal expansion than the more workable core materials, such as steel. The relative differential expansions/contractions usually cause bending or bowing, resulting in torsion, compression, and tension that can cause failure. Thus, as stated above, the second wear member  40  does not cover the entire second face  20   a  of the core member  20 ; it covers enough area of the second face  20   a  of the core member  20  to prevent the core member  20  from bending or bowing as the assembly  10  is heated or cools. Reduction in the relative size of the second wear member  40  can reduce costs because less material can be used to cover the rear side of the assembly  10 .  
         [0029]     Additionally, if the assembly  10  is to be secured to the underlying equipment by means of soldering or welding, in many cases, it is easier to weld the exposed material of the core member  20  on the rear side of the assembly  10  to the underlying equipment or machinery than having to weld the types of harder materials that typically comprise the second wear member  40  to standard equipment or machinery. In some cases, depending on the harder materials used, welding of those materials may not even be possible.  
         [0030]     Furthermore, as stated above, the layers of the assembly  10  are typically laminated together by soldering, brazing or other means that utilize heat. After they have been heated during one of these processes (or heated independently of the joining process), the dissimilar metals are secured together. As the assembly cools, the core layer  30  remains in an expanded or “stretched” state between the two outer layers  30  and  40 . In other words, once at room temperature, the core member  20  is in tension or in a tensile stress state in its major direction. Thus, additional, intentional residual stresses are added to any inherent residual stresses present in the assembly  10 . As an example, consider that core member  20  and second face  30   a  are 1.5 inches in the major (longest) direction before heating, while second wear member  40  is 0.925 inches before heating. After lamination and cooling to ambient temperature, second face  30   a  and the second wear member  40  return to 1.5 inches and 0.925 inches, respectively, but the core member  30  remains partially extended. Therefore, the assembly  10  has a dominant or major tensile stress, resulting from differential expansion (contraction) along the major dimension of the assembly  10 .  
         [0031]     Moreover, it is also possible to form each of the first wear member  30  and the second wear member  40  of multiple pieces. Depending on the conditions and circumstances of the particular application for the assembly  10 , flexibility may be desirable, which would be provided by replacing a single piece of hard material with multiple pieces of material. Specifically, as can be seen in  FIG. 3 , the second wear member  40  is formed of two pieces. However, any number of pieces can be utilized.  
         [0032]     Additionally, the core member  20  may also have a variety of configurations. As shown in  FIGS. 1-3 , a portion of the second face  20   a  of the core member  20  is exposed. This type of configuration allows for additional welds to underlying machinery. However, it is also possible to completely cover both the first face  20   b  and the second face  20   a  of the core member  20 .  
         [0033]     As seen in  FIGS. 4 and 5 , in operation, the core member  20  hangs over and is secured to the outer edge  102  of the equipment  100 , such as an extrusion screw, by means of spot welding of the attachment member  26  of the core member  20  to the outer edge  102  of the equipment  100 . Additionally, the bottom of the assembly  10  is spot-welded to the leading edge  104  of the equipment  100 . With this configuration, the core member  20 , is made of a material such as steel, which can be welded to the extrusion screw  100 . However, it can be appreciated that the assembly  10  can be secured to the equipment  100  by a variety of methods, including gluing, brazing, soldering or other securing methods. Another benefit of the present invention is that when an assembly  10  does wear and need replacing, this can be done easily in the field by soldering, welding or gluing a new assembly  10  to the equipment  100 . Because wear-resistant materials such as tungsten-carbide can be brazed, but cannot be welded, replacing surfacing material made only of tungsten-carbide in situ would be difficult, as brazing in typical ambient environments is difficult and does not always produce a strong bond.  
         [0034]     The front face  30   b  of the first wear member  30  faces outward from the equipment  100  and comes in contact with the material being processed in the equipment  100 . As can be seen, a series of assemblies  10  are placed adjacent to each other and to provide a smooth continuous covering along the leading edge  104  of the extrusion screw  100 . As can be understood, the size and shape of assemblies used can vary in accordance with the size and shape of the equipment  100 .  
         [0035]     Thus, the arrangement of the present invention yields an assembly  10  of greater strength and resistance to cracking than use of a single layer of tungsten-carbide, and achieves rigidity from having a layer of more flexible material between two layers of harder material.  
         [0036]     It is understood that the present invention can take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or the scope of the invention. Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.