Power tong

DETAILED DESCRIPTION In accordance with the present invention there is provided a novel power pipe tong having a pipe-gripping assembly for holding the pipe concentric with the rotary gear.
In a particular embodiment the tong includes a frame having a throat at its front; a power driven rotary gear having a mouth adapted for alignment with the throat, the rotary gear being rotatably mounted on the frame; a pair of pivotally mounted jaws located on opposite sides of the centerline of the tong and having their pivot points rearward of the center of rotation of the rotary gear; a cam follower associated with each jaw; pipe gripping elements carried by the jaws; and at least one pair of opposed cam surfaces on the interior surface of the rotary gear, the cam surfaces of the pair being cooperatively shaped such that when the cam followers are cammed at points along the opposed cam surfaces the jaws are positioned so that a pipe section gripped therebetween is centered within the rotary gear.
In accordance with the invention there is also provided a novel rotary gear comprising means for being rotatably driven about a central gear axis by a suitable drive train; a central opening for housing a pipe section being gripped for rotation, the opening defining a gear interior surface; an aperture for aligning with the open-mouth of the tong during pipe loading and unloading; and at least one pair of diametrically opposed cam surfaces on the interior surface of the rotary gear, the cam surfaces being asymmetric with respect to the diametric line connecting the cam surfaces to compensate for the differferent angles at which the respective cam followers attack the two opposed cam surfaces during make up or break out operations.
Accordingly, a primary feature of the present invention is the provision of a power tong having means for bringing the gripping elements into secure and uniform engagement with the pipe so that the pipe may be rotated evenly about its axis to prevent dangerous vibrations.
One aspect of this feature is the provision of opposed cam surfaces presenting different curvatures in order to compensate for the different angles at which the cam followers attack their respective cam surfaces during make up and break out operations