Cylinder apparatus and method of manufacturing rod for cylinder apparatus

Abstract

A groove processing method capable of smoothly processing a groove on a rod that has been subjected to a hardening treatment without a substantial degradation in strength is provided. A pair of straightening rollers is mounted at each side of rolling rollers mounted on respective rotating shafts of a rolling machine with spacers disposed between the straightening and rolling rollers. A rod is previously subjected to a hardening treatment, for example, high-frequency induction hardening and tempering, or carbulizing & quenching and tempering, so that the surface hardness is not less than 400 Hv. A groove is formed on the rod by rolling using the rolling rollers, thereby allowing a surface hardening layer to be left on the bottom of the groove. At the same time, the rod is held by the straightening rollers to prevent bending of the rod.

What is claimed is:  
     
         1 . A cylinder apparatus comprising: 
 a cylinder having a fluid sealed therein;    a rod inserted in said cylinder, said rod being formed from a circular cylinder-shaped base metal having a circumferential groove formed by rolling after the base metal has been subjected to a hardening treatment; and    an engagement member secured to said rod by engaging in the circumferential groove on said rod.    
     
     
         2 . A cylinder apparatus according to  claim 1 , wherein a surface hardness of said rod when subjected to rolling is not less than 400 in terms of Vickers hardness (Hv).  
     
     
         3 . A cylinder apparatus according to  claim 1 , wherein said rolling is carried out in such a manner that while said circumferential groove is being formed by using rolling rollers, possible axial bending of said rod is corrected with straightening rollers having a flat peripheral surface, which are disposed at both sides of said rolling rollers in an axial direction thereof.  
     
     
         4 . A method of manufacturing a rod for use in a cylinder apparatus wherein said rod is inserted into a cylinder having a fluid sealed therein, said cylinder apparatus having an engagement member that is engaged in a circumferential groove formed on said rod, said method comprising the steps of: 
 performing a hardening treatment on a circular cylinder-shaped base metal to harden said base metal;    forming said circumferential groove on said base metal by rolling; and    performing a surface hardening treatment on said base metal.    
     
     
         5 . A method of manufacturing a rod for use in a cylinder apparatus according to  claim 4 , wherein a surface hardness of said rod obtained by said hardening treatment is not less than 400 in terms of Vickers hardness (Hv).  
     
     
         6 . A method of manufacturing a rod for use in a cylinder apparatus according to  claim 4 , wherein said rolling is carried out in such a manner that while said circumferential groove is being formed by using rolling rollers, possible axial bending of said rod is corrected with straightening rollers having a flat peripheral surface, which are disposed at both sides of said rolling rollers in an axial direction thereof.  
     
     
         7 . A cylinder apparatus according to  claim 2 , wherein said rolling is carried out in such a manner that while said circumferential groove is being formed by using rolling rollers, possible axial bending of said rod is corrected with straightening rollers having a flat peripheral surface, which are disposed at both sides of said rolling rollers in an axial direction thereof.  
     
     
         8 . A method of manufacturing a rod for use in a cylinder apparatus according to  claim 5 , 
 wherein said rolling is carried out in such a manner that while said circumferential groove is being formed by using rolling rollers, possible axial bending of said rod is corrected with straightening rollers having a flat peripheral surface, which are disposed at both sides of said rolling rollers in an axial direction thereof.