Coated article, manufacturing method therefor and coating apparatus

Abstract

After forming a primary powder bed at a toothed portion of an article, such as a gear or a spline shaft, by electrostatic powder coating process, the powder bed is removed from crests of teeth in the toothed portion by a specified thickness by scraping it off while sucking up the scraped powder. Next, the electrostatic powder coating process is performed again to form a secondary powder bed over the entire surface of the toothed portion. Then, the primary and secondary powder beds are melted or fused by induction heating to thereby form a coating film of a substantially uniform thickness.

What is claimed is:  
     
         1 . A method for manufacturing a coated article, comprising the steps of: 
 performing electrostatic powder coating process to form a primary powder bed in at least a region of an article to be coated, said region having projections and depressions defined by or defining said projections;    removing the primary powder bed from a tip portion of each projection by a specified thickness;    performing electrostatic powder coating process to form a secondary powder bed over said region from which the primary powder bed at the tip portions of the projections has been removed by the specified thickness; and    melting the primary and secondary powder beds by induction heating to form a coating film on the article.    
     
     
         2 . The manufacturing method according to  claim 1 , wherein the step of removing the primary powder bed includes scraping the primary powder bed while removing the scraped powder by suction.  
     
     
         3 . The method according to  claim 1 , wherein in the steps of performing electrostatic powder coating process, a powder coating material having a mean particle size of 5 μm to 100 μm is used.  
     
     
         4 . The method according to  claim 1 , wherein in the steps of performing electrostatic powder coating, a thermoplastic resin-based powder coating material is used.  
     
     
         5 . The method according to  claim 4 , wherein the thermoplastic resin is a nylon resin.  
     
     
         6 . The method according to  claim 1 , wherein in the step of removing the primary powder bed, the thickness by which the powder bed is removed is set such that the coating film to be formed has a substantially uniform film thickness at any portion thereof.  
     
     
         7 . The method according to  claim 6 , wherein the film thickness is within a range of from 100 μm to 300 μm.  
     
     
         8 . The method according to  claim 1 , wherein a ratio of a coating weight A (g/m 2 ) of the primary powder bed to a coating weight B (g/m 2 ) of the secondary powder bed falls within a range of A/B=20/80 to 80/20.  
     
     
         9 . A method for manufacturing a coated gear, comprising the steps of: 
 depositing a powder coating material having a particle size of 10 to 70 μm onto a gear by electrostatic powder coating process to form a primary powder bed on a surface of the gear;    removing the powder bed from crests of teeth of the gear by a specified thickness by scraping the powder bed with a scraper while sucking up the scraped powder;    further depositing a powder coating material having a particle size of 10 μm to 70 μm over the surface of the gear by electrostatic powder coating process to form a secondary powder bed; and    melting the primary and secondary powder beds by electromagnetic induction heating to form a coating film having a thickness of 150 μm to 200 μm.    
     
     
         10 . A method for manufacturing a coated spline shaft, comprising the steps of: 
 forming a thermoplastic resin-based primary powder bed on a surface of a toothed portion of a spline shaft by electrostatic powder coating process;    removing the powder bed from crests of teeth in the toothed portion of the spline shaft by a specified thickness by scraping the powder bed with a scraper movable in an axial direction of the spline shaft while sucking up the scraped powder by a suction means;    further coating the toothed portion of the spline shaft with a thermoplastic resin-based secondary powder bed by electrostatic powder coating process; and    melting the primary and secondary powder beds by electromagnetic induction heating to form a coating film.    
     
     
         11 . A method for forming a coating film on an article to be coated, said article having a region containing projections and depressions defined by or defining the projections, comprising the steps of: 
 performing electrostatic powder coating process to form a primary powder bed in said region of the article to be coated;    removing the primary powder bed from a tip portion of each projection by a specified thickness;    performing electrostatic powder coating process to form a secondary powder bed over said region from which the primary powder bed at the tip portions of the projections has been removed by the specified thickness; and    melting the primary and secondary powder beds by induction heating to form a coating film in said region of the article, said coating film having a substantially uniform film thickness at any portion thereof.    
     
     
         12 . A coating apparatus comprising: 
 coating means performing electrostatic powder coating on an article to be coated having a region containing projections and depressions defined by or defining the projections, to form a primary powder bed on a surface of the article in said region;    scraper means removing the powder bed from a tip portion of each projection of the article;    coating means performing electrostatic powder coating on the article from which the powder bed at the tip portions of the projections has been removed by the scraper means, to form a secondary powder bed over the entire surface of the article in said region; and    induction heating means melting the primary and secondary powder beds.    
     
     
         13 . The coating apparatus according to  claim 12 , further comprising means for sucking up powder scraped off the powder bed.  
     
     
         14 . A method for manufacturing a coated article, comprising the steps of: 
 electrostatically depositing powder onto an article to be coated, said article having projections and depressions defined by or defining the projections; and    melting the powder by induction heating the article to thereby make a coating film adhere to the article.    
     
     
         15 . The method according to  claim 14 , wherein the powder deposit on the article has different thicknesses, and dimensions of the article are previously set according to the thicknesses of the powder deposit so that the resulting coated article has a desired outer dimension.  
     
     
         16 . The method according to  claim 14 , further comprising a step of cutting tips of the projections of the article to be coated before the step of electrostatically depositing powder.  
     
     
         17 . The method according to  claim 14 , wherein thickness of the coating film is set to be 100 μm to 250 μm.  
     
     
         18 . A coated article having a specified outer dimension and having a coating film, wherein substantially no air bubbles are present in the coating film.  
     
     
         19 . The coated article according to  claim 18 , wherein the thickness of the coating film is substantially same in all portions thereof.  
     
     
         20 . The coated article according to  claim 19 , wherein a difference between a film thickness of the coating film at a thickest portion and a film thickness thereof at a thinnest portion is within a range of from 0 μm to 40 μm.  
     
     
         21 . The coated article according to  claim 19 , wherein said film thickness is 100 μm to 300 μm.  
     
     
         22 . The coated article according to  claim 18 , wherein the coating film has different film thicknesses, and the article before being coated has dimensions set according to the film thicknesses of the coating film.  
     
     
         23 . The coated article according to  claim 22 , wherein the film thicknesses are 100 μm to 250 μm.  
     
     
         24 . The coated article according to  claim 18 , further comprising an undercoat under the coating film.  
     
     
         25 . The coated article according to  claim 18 , wherein the article is a gear.  
     
     
         26 . The coated article according to  claim 18 , wherein the article is a spline shaft.