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The rotary gear assembly is a large-diameter gear that has been segmented into
three sections with pivotal hinges and a latching mechanism. The assembly is
shown in Figure 1-3. The smaller rotary gear segments pivot open to encircle the
pipe being worked and then close and latch while working the pipe. The internal
diameter of the gear has a cam insert surface for actuating the jaws.
The complete tong gear train is shown in Figure 1-4. The gear train consists of a
shiftable two-speed gear box in a separate housing mounted on the tong top plate.
The hydraulic motor drives a pinion directly through the high (1:1) or low (1:4.3) ratio
of the gear box. The gear box output drives a pinion within the tong case. Through a
cluster gear the input pinion drives a pair of rotary idlers which in turn drive the
rotary gear.
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Jaw System
Shifting from high to low gear ratios is accomplished by lowering the shift lever
handle.
The model 16 tong uses a three-jaw systemconsisting of two fixed jaws mounted on
the major segment. The jaws are rotated and actuated by the combined action of the
rotary gear, permanent magnets and reversing pin.
During make-up operations, the pipe to be turned is first enclosed in the tong and
the rotary door is closed and latched. Then, with the reversing pin in the make-up
position (as described later), the operator pushes the control lever forward to cause
the jaws to bite and rotate the pipe. To release the jaws and back off fromthe pipe,
the operator pulls the tong control lever outward.
During breakout operations, the reversing pin is placed in the breakout position so
that the jaw bite in the reverse direction. Then the operator pulls the tong control
lever to cause the jaws to bite and break out the pipe. Finally, he pushes the lever
forward to release the jaws and back them off the pipe.
As illustrated in Figure 1-5, the jaw-biting action is a function of the rotary gear
cam. When the rotary gear rotates, the jaw rollers roll up onto the cam surface and force
the jaws to pipe the pipe. Further rotation turns the pipe to make up or break out the
joint.
To provide the restraint necessary for camming to occur, permanent magnets are
added to the jaws. The drag induced by the magnets on a plate within the case body
is sufficient to permit the jaw roller to push the master jaw into engagement with
the pipe. Once the master jaw is engaged, the magnetic drag is overcome,
allowing the jaws to rotate with the rotary gear.
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