Guide bush and method of forming hard carbon film over the inner surface of the guide bush

Abstract

A hard carbon film ( 15 ) is formed directly or through an intermediate layer for enhancing adhesion over an inner surface ( 11 b ) of a guide bush ( 11 ) for holding a workpiece ( 51 ) rotatably and axially slidable on an automatic lathe at a position near a cutting tool, to be in sliding contact with the workpiece ( 51 ) or directly or through an intermediate layer for enhancing adhesion on the surface of a superhard lining fixed to the inner surface ( 11 b ) The guide bush ( 11 ) has remarkably enhanced durability and prevents damaging the workpiece ( 51 ) and seizing that makes a machining operation impossible even when the guide bush ( 11 ) is used for an extended period of time and when the automatic lathe operates for heavy machining. The hard carbon film ( 15 ) having satisfactory adhesion to the inner surface ( 11 b ) can be efficiently formed in a uniform thickness over the inner surface ( 11 b ) by placing the guide bush ( 11 ) in a vacuum vessel, extending an auxiliary electrode in the center bore of the guide bush ( 11 ) and producing a plasma of a gas containing carbon.

1 . (amended) A guide bush which is in an approximate cylindrical form having a center bore formed along its center including a taper outer surface formed on one longitudinal end portion and provided with slits to make the end portion elastic, a threaded portion formed on another end portion to be mounted on a column of an automatic lathe, and an inner surface for holding a workpiece inside a portion on which the taper outer surface is formed, mounted on an automatic lathe so as to hold a workpiece inserted into the center bore with the inner surface for holding the workpiece rotatably and axially slidable at a position near a cutting tool, and provided with a hard carbon film which is a hydrogenated amorphous carbon film coated on the inner surface for holding the workpiece.  
     
     
         2 . A guide bush according to  claim 1  wherein the hard carbon film is formed on an intermediate layer formed on the inner surface to enhance the adhesion of the hard carbon film to the inner surface.  
     
     
         3 . A guide bush according to  claim 2 , wherein the intermediate layer is a two-layer film comprising: 
 a low layer of titanium, chromium or a compound containing titanium or chromium; and,    an upper layer of silicon, germanium or a compound containing silicon or germanium.    
     
     
         4 . A guide bush according to  claim 1 , wherein the hard carbon film is formed on a superhard lining in the form of a cemented carbide or a sintered member of a ceramic material attached to the inner surface of the guide bush.  
     
     
         5 . A guide bush according to  claim 4 , wherein an intermediate layer for enhancing adhesion is interposed between the superhard lining and the hard carbon film.  
     
     
         6 . A guide bush according to  claim 5 , wherein the intermediate layer is a two-layer film comprising: 
 a lower layer of titanium, chromium or a compound containing titanium or chromium; and,    an upper layer of silicon, germanium or a compound containing silicon or germanium.    
     
     
         7 . A guide bush according to  claim 1 , wherein the guide bush has a substrate, and a portion of the substrate in the vicinity of the inner surface of the same is carburized to form a carburized layer, and the hard carbon film is formed over the carburized layer.  
     
     
         8 . A guide bush according to  claim 7 , wherein an intermediate layer for enhancing adhesion is interposed between the carburized layer of the inner surface and the hard carbon film.  
     
     
         9 . A guide bush according to  claim 8 , wherein the intermediate layer is a two-layer film comprising: 
 a lower layer of titanium, chromium or a compound containing titanium or chromium; and,    an upper layer of silicon, germanium or a compound containing silicon or germanium.    
     
     
         10 . A method of forming a hard carbon film over the inner surface of a guide bush, comprising steps of: 
 placing a guide bush for an automatic lathe in a vacuum vessel having a gas inlet port and a evacuation port, and internally provided with an anode and a filament;    inserting a rodlike or wirelike auxiliary electrode in the center bore of the guide bush having an inner surface to be brought into sliding contact with a workpiece; and    producing a plasma in the vacuum vessel by supplying a gas containing carbon through the gas inlet port into the vacuum vessel after evacuating the vacuum vessel, applying a DC voltage to the guide bush, applying a DC voltage to the anode and applying an AC voltage to the filament to form the hard carbon film over the inner surface of the guide bush.    
     
     
         11 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 10 , wherein the auxiliary electrode is maintained at a ground potential or a positive DC potential, during the hard carbon film formation.  
     
     
         12 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 10 , wherein a ringlike dummy member having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is put on an end face of the guide bush on a side of a portion of the guide bush provided with slits when forming the hard carbon film.  
     
     
         13 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 12 , wherein the auxiliary electrode is disposed so that its extremity is at a distance inside the dummy member from the end face of the dummy member.  
     
     
         14 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 10 , wherein a ringlike jig having a ringlike body having an inside diameter substantially equal to the diameter of the inner surface of the guide bush, and a plurality of projections capable of being inserted in the slits of the guide bush, is put on an end face of the guide bush on a side of a portion of the guide bush provided with the slits with the projections inserted in the slits, respectively, when forming the hard carbon film.  
     
     
         15 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 10 , wherein a cylindrical plug-in jig having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is fitted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.  
     
     
         16 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 10 , wherein a ringlike jig having a ringlike body having an inside diameter substantially equal to the diameter of the inner surface of the guide bush, and a plurality of projections capable of being inserted in the slits of the guide bush is put on an end face of the guide bush on a side of a portion of the guide bush provided with the slits with the projections inserted in the slits, respectively, and 
 a cylindrical plug-in jig having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is fitted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.    
     
     
         17 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 10 , wherein the auxiliary electrode is supported on an insulator inserted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.  
     
     
         18 . A method of forming a hard carbon film over the inner surface of a guide bush, comprising steps of: 
 placing a guide bush for an automatic lathe in a vacuum vessel having a gas inlet port and a evacuation port;    inserting a rodlike or wirelike auxiliary electrode in the center bore of the guide bush having an inner surface to be brought into sliding contact with a workpiece; and    producing a plasma in the vacuum vessel by supplying a gas containing carbon through the gas inlet port into the vacuum vessel after evacuating the vacuum vessel and applying a radio frequency voltage to the guide bush to form the hard carbon film over the inner surface of the guide bush.    
     
     
         19 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 18 , wherein the auxiliary electrode is maintained at a ground potential or a positive DC potential, during the hard carbon film formation.  
     
     
         20 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 18 , wherein a ringlike dummy member having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is put on an end face of the guide bush on the side of a portion of the guide bush provided with slits when forming the hard carbon film.  
     
     
         21 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 20 , wherein the auxiliary electrode is disposed so that its extremity is at a distance inside the dummy member from the end face of the dummy member.  
     
     
         22 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 18 , wherein a ringlike jig having a ringlike body having an inside diameter substantially equal to the diameter of the inner surface of the guide bush, and a plurality of projections capable of being inserted in the slits of the guide bush is put on an end face of the guide bush on a side of a portion of the guide bush provided with the slits with the projections inserted in the slits, respectively, when forming the hard carbon film.  
     
     
         23 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 18 , wherein a cylindrical plug-in jig having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is fitted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.  
     
     
         24 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 18 , wherein a ringlike jig having a ringlike body having an inside diameter substantially equal to the diameter of the inner surface of the guide bush, and a plurality of projections capable of being inserted in the slits of the guide bush is put on an end face of the guide bush on the side of a portion of the guide bush provided with the slits with the projections inserted in the slits, respectively, and 
 a cylindrical plug-in jig having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is fitted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.    
     
     
         25 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 18 , wherein the auxiliary electrode is supported on an insulator inserted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.  
     
     
         26 . A method of forming a hard carbon film over the inner surface of a guide bush, comprising steps of: 
 placing a guide bush for an automatic lathe in a vacuum vessel having a gas inlet port and a evacuation port;    inserting a rodlike or wirelike auxiliary electrode in the center bore of the guide bush having an inner surface to be brought into sliding contact with a workpiece; and    producing a plasma in the vacuum vessel by supplying a gas containing carbon through the gas inlet port into the vacuum vessel after evacuating the vacuum vessel and applying a DC voltage to the guide bush to form the hard carbon film over the inner surface of the guide bush.    
     
     
         27 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 26 , wherein the auxiliary electrode is maintained at a ground potential or a positive DC potential, during the hard carbon film formation.  
     
     
         28 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 26 , wherein a ringlike dummy member having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is put on an end face of the guide bush on the side of a portion of the guide bush provided with slits when forming the hard carbon film, during the hard carbon film formation.  
     
     
         29 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 28 , wherein the auxiliary electrode is disposed so that its extremity is at a distance inside the dummy member from the end face of the dummy member.  
     
     
         30 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 26 , wherein a ringlike jig having a ringlike body having an inside diameter substantially equal to the diameter of the inner surface of the guide bush, and a plurality of projections capable of being inserted in the slits of the guide bush is put on an end face of the guide bush on a side of a portion of the guide bush provided with the slits with the projections inserted in the slits, respectively, when forming the hard carbon film.  
     
     
         31 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 26 , wherein a cylindrical plug-in jig having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is fitted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.  
     
     
         32 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 26 , wherein a ringlike jig having a ringlike body having an inside diameter substantially equal to the diameter of the inner surface of the guide bush, and a plurality of projections capable of being inserted in the slits of the guide bush is put on an end face of the guide bush on a side of a portion of the guide bush provided with the slits with the projections inserted in the slits, respectively, and 
 a cylindrical plug-in jig having an inside diameter substantially equal to the diameter of the inner surface of the guide bush is fitted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.    
     
     
         33 . A method of forming a hard carbon film over the inner surface of a guide bush according to  claim 26 , wherein the auxiliary electrode is supported on an insulator inserted in an expanded section of the center bore of the guide bush, having a diameter greater than that of the inner surface when forming the hard carbon film.