Abstract:
A prespray processing method includes preparing a work surface for spray coating, roughing the work surface by pressing a tool against the work surface, having a material of the work surface displaced thereon to form a depression thereinto, and keeping the material of the work surface unremoved therefrom.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a prespray processing method in which a base material surface is roughed prior to a spray coating process, and a prespray processed engine cylinder block. 
     2. Description of Related Art 
     As a preliminary process for a formation of a coating layer of iron-based material to be sprayed onto an inner surface of a cylinder bore of a linerless aluminum cylinder block that is advantageous for weight reduction and exhaust processing of an automobile engine, a roughing of the inner surface of the cylinder bore is needed to achieve an enhanced adhesion of the sprayed coating layer. 
     Japanese Patent Application. Laid-open Publication No. 11-320414 discloses a shot-blasting as a roughing method. Japanese Patent Application Laid-open Publications No. 10-77807 and No. 2002-155350 disclose a cutting as a roughing method. 
     SUMMARY OF THE INVENTION 
     However, the shot-blasting results in the powder of the abrasive material remaining on the roughed surface. The cutting results in cut chips remaining on the roughed surface. 
     If a spray coating is performed on the roughed surface with foreign particles such as the powder of the abrasive material of the shot-blasting or the cut chips remaining thereon, these foreign particles may remain exposed on the surface of the sprayed coating, or adhesion strength of the sprayed coating layer becomes lowered, leading to unstable formation of the sprayed coating layer and lowering reliability thereof. 
     An object of the present invention is to provide a prespray processing method that achieves a stable formation of a sprayed coating layer, improving the reliability thereof. 
     An aspect of the present invention is a prespray processing method comprising: preparing a work surface for spray coating, roughing the work surface by pressing a tool against the work surface, having a material of the work surface displaced thereon to form a depression thereinto, and keeping the material of the work surface unremoved therefrom. 
     Another aspect of the present invention is a prespray processed engine cylinder block comprising: a cylindrical surface prepared for spray coating and roughed with a depression formed thereinto by displacement of a material of the cylindrical surface thereon without removal of the material of the cylindrical surface therefrom. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings wherein: 
         FIG. 1A  is a schematic cross-sectional view showing an essential portion of a cylinder block having a cylindrical inner surface thereof being processed by a tool in a prespray processing method according to a first embodiment of the present invention and  FIG. 1B  is a plan view of a roller wheel of the tool for use in the method of the first embodiment taken along line IB-IB in  FIG. 1A . 
         FIG. 2A  is a cross-sectional view of a cylindrical section formed with a spiral groove on the cylindrical inner surface thereof and  FIG. 2B  is an enlarged cross-sectional view taken along line IIB-IIB in  FIG. 2A . 
         FIG. 3  is a plan view showing a part of an outer periphery of a modified form of the roller wheel shown in  FIG. 1A . 
         FIG. 4  is a plan view showing an essential portion of a cylinder block having a cylindrical inner surface thereof being processed by a tool in a prespray processing method according to a second embodiment of the present invention. 
         FIG. 5  is a schematic showing a spray coating to be implemented when forming a coating layer on the roughed inner surface. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiments of the present invention will be explained below with reference to the drawings, wherein like members are designated by like reference characters. 
     As shown in  FIG. 1A , a cylindrical inner surface  1  such as an inner surface of a cylinder bore formed in a cylinder block of an engine is a base material surface on which a coating layer is to be formed by spray coating. A cylindrical section  11  is made of die-cast aluminum alloy (metal classification ADC 12 ) inside of which the cylindrical inner surface  1  is provided in a processed condition with a certain precision. The cylindrical inner surface  1  is formed in a rough surface, before spray coating material composed of iron-based material is sprayed thereonto to form a sprayed coating layer. 
     A roller wheel  3  is brought into pressure contact with the cylindrical inner surface  1 , and forced to roll thereon to conduct component rolling for thereby forming a spiral groove  1   a  (depression) in a threaded form as shown in  FIGS. 2A and 2B . 
     A processing device  5  supporting the roller wheel  3  thereon has a body section  7  supporting rotatably relative thereto a central shaft  9  which is to be inserted into the cylindrical section  11 . The central shaft  9  has on a lower lateral side thereof a pair of guide rods  13  and  15  whose base ends are supported on the central shaft  9  movably in the radial direction of the cylindrical inner surface  1 . To the distal ends of the guide rods  13  and  15 , a roller wheel support shaft  17  is fixed. The roller wheel support shaft  17  has on a lower end thereof the roller wheel  13  rotatably mounted thereonto. 
     The roller wheel support shaft  17  has on a lateral side thereof closer to the central shaft  9 , a connecting arm  19  which has one end fixed to the roller wheel support shaft  17  while the other end thereof is movably inserted into a horizontal guide hole  9   a  provided on the lower lateral side of the central shaft  9 . The connecting arm  19  has an end portion inserted to the guide hole  9   a  formed with a slant face  19   a  that is inclined such that a lower end of the slant face  19   a  protrudes rightward with respect to an associated upper end as shown in  FIG. 1A . 
     In contrast, an actuation rod  21  is inserted into a vertical guide hole  9   b  provided through the central shaft  9  to be movable in an axial direction thereof. The actuation rod  21  has a lower end formed with a slant face  21   a  held in sliding contact with the slant face  19   a  of the connecting arm  19 . 
     With such a structure, the actuation rod  21  is axially moved downward by a drive mechanism (not shown) to cause the slant face  21   a  to slide on the slant face  19   a , allowing the connecting arm  19  and the roller wheel support shaft  17  to move outward in the radial direction of the cylindrical inner surface  1  (leftward as viewed in  FIG. 1A ), thereby forcing the roller wheel  3  to move in the same direction to have it in pressure contact with the cylindrical inner surface  1 . 
     Further, a resilient member such as a spring (not shown) is disposed between the central shaft  9  and the roller wheel support shaft  17  for urging the roller wheel support shaft  17  toward the central shaft  9 . This allows the roller wheel  3  to be released from the cylindrical inner surface  1  in a condition where the connecting arm  19  is not pressed by the actuation rod  21 . 
     When roughing the cylindrical inner surface  1  with the processing device  5 , a whole of the processing device  5  is fed downward in the axial direction of the cylindrical inner surface  1  with the central shaft  9  being rotated about the center axis of the cylindrical inner surface  1  and the roller wheel  3  rolling on the cylindrical inner surface  1  in pressure contact therewith, whereby the spiral groove  1   a  is formed on the inner cylindrical surface  1  as shown in  FIGS. 2A and 2B . 
     Component rolling is conducted with the roller wheel  3  rolling on the cylindrical inner surface  1  in pressure contact therewith to cause plastic deformation to occur on the cylindrical inner surface  1 , wherein the base material on the cylindrical inner surface  1  is displaced thereon without being removed therefrom, to thereby form the spiral groove  1   a  thereon. This does not generate cutting chips which would be generated when roughing a surface with a generally used cutting tool, while preventing foreign particles from remaining on a roughed surface, whereby the subsequent treatment to form a sprayed coating layer (represented as at  23  in  FIG. 2B ) is performed in a stable condition, thereby enabling the sprayed coating layer  23  to have improved reliability. 
     Further, in a case that the cylinder bore inner surface of the cylinder block of the engine is a cylindrical inner surface  1  processed in the roughing process mentioned above, the cylinder bore inner surface is formed with the sprayed coating layer with high reliability, whereby defects such as biting or seizing during sliding motions of a piston can be prevented. 
     The prespray roughing process mentioned above is performed in the following conditions. 
     Material of Tool (Roller wheel  3 ): Sintered Hard Alloy 
     Rotational Speed of Central shaft  9  of Processing Device  5 : 60 rpm 
     Feed Speed of Processing Device  5 : 0.5 mm/rev 
     Pressing force: 100N 
     Further, a shape of the groove  1   a  resulting from the roughing process mentioned above is measured by a profile measuring tool of a non-contact type such as one using a laser, whereby precision of the shape of the groove  1   a  is guaranteed. 
     The roller wheel  30  in  FIGS. 1A and 1B  can be formed to have on its outer periphery a serrated edge  30   a  as shown in  FIG. 3 . 
     By having the roller wheel  30  formed with the serrated edge  30   a  rolling on the cylindrical inner surface  1  in pressure contact with the cylindrical inner surface  1 , the cylindrical inner surface  1  is formed in a spiral groove like the spiral groove la as shown in  FIG. 2A  with a transferred pattern of the serrated edge  30   a  (not shown). 
     This allows the produced spiral groove to have a finer undulation than the spiral groove lain  FIGS. 2A and 2B , enabling a sprayed coating layer to have further improved adhesion. 
     A second embodiment of the present invention will be explained with reference to  FIG. 4 . In this embodiment, a processing device  50  has a plurality of connecting arms  190  each corresponding to the connecting arm  19  of  FIG. 1 , and pluralities of roller wheel shafts  170  and roller wheels  300  associated with the connecting arms  190 . The connecting arms  190  are connected to a central shaft  90  corresponding to the central shaft  9  of  FIG. 1  at equidistantly and circumferentially spaced positions on the lower lateral side thereof. 
     Like the first embodiment, the connecting arms  190  are caused to move with the roller wheel support shafts  170  toward the cylindrical inner surface  1  and pressed outward in the radial direction of the cylindrical inner surface  1 , such that the roller wheels  300  are brought into pressure contact with the cylindrical inner surface  1 . Here, an actuation rod is formed to have a slant faces on a lower end thereof at circumferentially spaced four positions in face-to-face relationship with the connecting arms  190 . 
     With the second embodiment, the central shaft  90  is rotated and fed in the axial direction of the cylindrical inner surface  1 , with the plurality of roller wheels  300  rolling on the cylindrical inner surface  1  in pressure contact therewith to form a plurality of spiral grooves thereon. The use of the plurality of roller wheels  300  provides the spiral grooves formed in a smaller pitch than that of the first embodiment of  FIG. 1 . Accordingly, a sprayed coating layer can be formed in further improved adhesion than that achieved in the first embodiment. 
     Further, using appropriate binders, powder of nickel-based material is adhered onto the roller wheels  3 ,  30 ,  300  of the embodiments set forth above at contact areas thereof to come into contact with the cylindrical inner surface  1 . The nickel-based material on the roller wheels is to be left in and adhere onto the grooves la when the roller wheels  3 ,  30 ,  300  roll on the cylindrical inner surface  1  in pressure contact therewith to form the groove  1   a.    
     Nickel-based material has higher adhesion strength to iron-based material to be used as a spray coating material than aluminum-based material of which the cylindrical inner surface  1  is made. Therefore, the provision of nickel-based material adhered onto the cylindrical inner surface  1  enhances the adhesion of the sprayed coating layer thereto. Furthermore, when spray coating material is sprayed onto the cylindrical inner surface  1 , powder of nickel-based material adhered onto the grooves  1   a  on the cylindrical inner surface  1  is caused to melt due to heat of the sprayed material, thereby providing a further increase in adhesion strength of the sprayed coating layer onto the cylindrical inner surface  1 . 
       FIG. 5  is a view illustrating how a spray coating is carried out for forming the sprayed coating layer  23 . A wire flame spray coating gun  61  is inserted into a center of a cylinder bore. An iron-based metal is melted as spray coating material and sprayed through a spray coating port  61   a  onto the cylindrical inner surface  1  (inner surface of the cylinder bore), whereby the sprayed coating layer  23  is formed. 
     In the spray coating process, the spray coating gun  61  is supplied with a flame wire  65  of iron-based material as spray coating material from a flame wire supplier  63 , fuel gas from a fuel gas container  67  storing fuel gas for ignition such as acetylene, propane or ethylene through a delivery tubing  71 , and oxygen gas from oxygen gas container  69  storing oxygen gas through a delivery tubing  73 . The spray coating gun  61  is further supplied with compressed air from a compressor (not shown). The compressed air is used to spray melt droplets of coating material  75  resulting from thermal melting due to ignition onto the cylindrical inner surface  1 , while the spray coating gun  61  is rotated and fed in an axial direction of the cylinder bore. 
     The preferred embodiments described herein are illustrative and not restrictive, and the invention may be practiced or embodied in other ways without departing from the spirit or essential character thereof. For example, the base material surface is not limited to the inner surface of the cylinder bore of the cylinder block of the engine. The present invention may have application to other cylindrical inner surfaces. In a further alternative, the present invention is not limited to the cylindrical surface, and may be applied to other contoured surface profiles. 
     The scope of the invention being indicated by the claims, and all variations which come within the meaning of claims are intended to be embraced herein. 
     The present disclosure relates to subject matters contained in Japanese Patent Application No. 2004-271743, filed on Sep. 17, 2004, the disclosure of which is expressly incorporated herein by reference in its entirety.