Abstract:
This invention relates to a method of improving the corrosion and wear resistance of a transport trailer surface. More specifically the present invention relates to a method of laser alloying the surface of a transport trailer to enhance the corrosion and wear resistant properties of the surface.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method of improving the corrosion and wear resistance of a transport trailer surface. More specifically the present invention relates to a method of laser alloying the surface of a transport trailer to enhance the corrosion and wear resistant properties of the surface. 
     2. Description of the Prior Art 
     Transport trailer surfaces are used to transport materials that are abrasive and/or corrosive. In many applications materials having abrasive properties, such as gravel or larger rocks, are dumped into, or slid off of, transport trailer surfaces resulting in surface wear and abrasion. Prior art transport trailer surfaces often have short lives as a result of the abrasive and corrosive forces to which they are exposed. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward a method or process for improving the corrosion and wear resistance of a material transport trailer surface. The present invention comprises applying a precursor layer comprising metallic or ceramic powders to a material transport trailer surface. The precursor layer has a thickness in the range of 50-150 microns. 
     The present invention further comprises irradiating the surface of the trailer with a laser at a sufficient energy level and for a sufficient time to melt a portion of the surface while the surface is moving relative to the laser beam. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1A is a block diagram depicting a first method of the present invention. 
     FIG. 1B is a block diagram depicting a second method of the present invention. 
     FIG. 1C is a block diagram depicting a third method of the present invention. 
     FIG. 2 is a top view of a transport trailer surface being processed by a method of the present invention. 
     FIG. 3 is an enlarged top view of the laser beam cross sectional area on the transport trailer surface when practicing the method of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention comprises applying a precursor layer comprising metallic or ceramic powders to a material transport trailer surface, as shown in Block  10  of FIG.  1 A and in FIG.  2 . The precursor layer has a thickness in the range of 50-150 microns. 
     In one embodiment of the present invention, wherein the trailer surface comprises an aluminum alloy, the powder within the precursor, comprises tungsten or silicon carbide, as shown in Block  11  of FIG.  1 B. In another preferred embodiment, wherein the trailer surface comprises steel, the powder within the precursor, comprises chromium and nickel, as shown in Block  13  of FIG.  1 C. 
     The present invention further comprises irradiating the surface of a trailer  20  with a laser beam  22  at a sufficient energy level and for a sufficient time to melt the portion of the trailer surface while the surface is moving relative to the laser beam, as shown in Block  12  of FIG.  1 A. In a preferred embodiment wherein the trailer surface comprises an aluminum alloy, the irradiating uses a laser having a power density in the range of 115-135 kilowatts/cm 2  as shown in Block  15  of FIG.  1 B. In another preferred embodiment, the irradiating is performed at a power density of 125 kilowatts/cm 2 . 
     In another preferred embodiment, the surface and the laser beam are moved relative to each other at a translation rate in the range of 2,500-9,000 millimeters per minute as shown in Block  15  of FIG.  1 B. Such relative movement may be accomplished by moving the laser beam relative to a stationary surface, moving the surface relative to a stationary laser beam, or moving both the surface and the laser beam at different speeds and/or in different directions. 
     In one preferred embodiment, the irradiating is performed with a laser beam  22  having a rectangular cross sectional area, as shown in FIG.  3 . In another preferred embodiment, the longer sides  24  of said rectangular cross sectional area are perpendicular to the translation axis  30  of the laser beam relative to the surface, as shown in FIGS. 2 and 3. 
     In another preferred embodiment, the longer sides of the rectangular cross sectional area  24  of the laser beam have a length of at least 2.8 millimeters. In another preferred embodiment, the shorter sides  26  of the rectangular cross sectional area of the laser beam have a length of at least 0.4 millimeters. A rectangular beam profile having the dimensions described above can be achieved by aligning a spherical lens closest to the beam, a second cylindrical lens closest to the substrate and a first cylindrical lens between the spherical lens and the second cylindrical lens. The spherical lens should have a focal length of 152.4 millimeters. The first cylindrical lens should have a focal length of 203.2 millimeters. The second cylindrical lens should have a focal length of 152.4 millimeters. The spherical lens and the first cylindrical lens should be spaced apart by five millimeters. The first cylindrical lens and second cylindrical lens should be spaced apart by 25 millimeters. 
     In a preferred embodiment, the laser beam is moved along a linear path or track  32  relative to the surface, as shown in FIG.  2 . In a preferred embodiment, the track index, x, is less than or equal to the width of the laser beam, as shown in FIG.  2 . The term “track index”, as used herein, refers to the distance between center lines of adjacent tracks. 
     In another preferred embodiment, the method of the present invention further comprises repeating the irradiating along at least one track  34  adjacent and parallel to the most recently irradiated track, as shown in Block  16  of FIG.  1 A and in FIG.  2 . In another preferred embodiment, the irradiating uses at least two laser beams simultaneously, as shown in FIG.  2 . 
     In a preferred embodiment, the present invention comprises directing a shielding gas at the region of the surface being irradiated, as shown in Block  14  of FIG. 1A In a preferred embodiment, the shielding gas is nitrogen as shown in Block  21  of FIG. 1C, or argon as shown in Block  19  of FIG.  1 B. 
     The foregoing disclosure and description of the invention are illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative construction may be made without departing from the spirit of the invention.