Power tong having cam followers with sliding contact surfaces

Abstract

In a pivoting-jaw power tong having a rotary gear with substantially linear camming surfaces and pivoting jaw members with cam followers for engagement with the camming surfaces upon rotation of the rotary gear relative to the jaw members, each cam follower has at least one contact surface configured for sliding engagement with a primary camming surface. The provision of sliding contact surfaces reduces contact pressures between the cam followers and the camming surfaces, thus reducing wear. The cam followers may be formed integrally with the jaw members, but preferably will be rollers which can swivel relative to their respective jaw members to facilitate substantially uniform sliding contract between the cam follower contact surfaces and the camming surfaces of the rotary gear. In alternative embodiments, the camming surfaces may have a slight concave curvature, with the cam followers' contact surfaces being correspondingly convexly curved.

1 . A power tong having: 
 (a) a gear housing defining a central space, and a perimeter opening into said space; and    (b) a pair of opposing jaw members disposed within said central space, each jaw member having; 
 b.1 a pivot end, a free end, an inner side, and an outer side, with said pivot end pivotably mounted to the gear housing, and said free end oriented toward said perimeter opening;  
 b.2 a pair of dies associated with said inner side; and  
 b.3 a cam follower associated with said outer side;  
   (c) a rotary gear rotatably mounted within the gear housing, and having: 
 c.1 a circular perimeter with a plurality of gear teeth;  
 c.2 an inner surface defining a central space large enough to enclose said jaw members; and  
 c.3 a throat opening in said perimeter;  
 wherein said inner surface defines:  
   (d) a pair of opposed neutral recesses; and    (e) a first pair of opposing primary camming surfaces, each extending substantially linearly in a first direction away from an associated one of the recesses;    and wherein:    (f) the radial distance from the axis of rotation of the rotary gear to a point on any primary camming surface decreases substantially linearly with increased distance from the associated recess; and    (g) each cam follower has at least one contact surface configured for sliding engagement with a primary camming surface.    
   
   
       2 . The power tong of  claim 1 , further comprising a second pair of opposing primary camming surfaces, each extending substantially linearly in a second direction away from an associated one of the recesses.  
   
   
       3 . The power tong of  claim 1  wherein the cam followers are rollers.  
   
   
       4 . The power tong of  claim 3 , further comprising bias means associated with each roller, said bias means being adapted to a facilitate orientation of the cam follower's at least one contact surface with a selected primary camming surface.  
   
   
       5 . The power tong of  claim 1  wherein the cam followers are protuberances formed integrally with their associated jaw members.  
   
   
       6 . The power tong of  claim 1  wherein each primary camming surface is concavely curved, and the contact surface of each cam follower is convexly curved to allow substantially uniform sliding engagement with a corresponding primary camming surface.  
   
   
       7 . In a power tong having: 
 (a) a rotary gear defining substantially linear camming surfaces; and    (b) a pair of pivoting jaw members each having a cam follower for engagement with one of said camming surfaces upon rotation of the rotary gear relative to the jaw members;    the improvement comprising the provision of each cam follower with at least one contact surface configured for sliding engagement with a primary camming surface.    
   
   
       8 . The improvement of  claim 7  wherein the cam followers are rollers.  
   
   
       9 . The improvement of  claim 8 , further comprising the provision of bias means associated with each roller, said bias means being adapted to facilitate orientation of the cam follower's at least one contact surface with a selected primary camming surface.  
   
   
       10 . The improvement of  claim 7 , wherein each primary camming surface is concavely curved, and the contact surface of each cam follower is convexly curved to allow substantially uniform sliding engagement with a corresponding primary camming surface.