Fluid pressure operated devices for radially expanding portions of tubing are known, such devices being disclosed in U.S. Pat. Nos. 1,448,457; 2,479,702; 2,938,562; and 3,200,627. Structures of these patents include fluid conveying mandrels receivable within the tubes, means for expanding the mandrels to hold the tubing, and die elements against which portions of the tubes are flared or otherwise formed by fluid pressure. These expanding devices are customarily used to provide shapped bulges in tubing for coupling purposes and the like. In addition, they are used to expand tubing to fit fins and other apparatus connected to the outer surface of the tubing.
Several hydraulic chucks have been developed which are suitable for tightly gripping one end of the elongated tube while simultaneously delivering a tube expanding fluid. Among these U.S. Pat. Nos. 3,505,846; 3,813,751; 3,962,769; and 4,189,162.
One of the problems which continuously has plagued those users of hydraulic chucks is the inability of such chucks to accomodate relatively large diameter tubes such as those having diameters of from about 2 inches up to about 7 or 8 inches or more. While many of the designs are suitable for gripping the tube satisfactorily, it has not been possible to adequately seal the device. On the other hand, where the sealing may be effective, the device is inadequate for gripping the tube to hold it in position under the substantially high pressure delivered by the hydraulic fluid. In addition, many difficulties with present hydraulic chucks are incurred because the piston which is driven by the fluid to cause activation of the gripping means such as radial collets, forces the piston against the tube. In large diameter operations, the force required to cause the collets to adequately grip the tube often times causes damage to the tube or relative movement of the tube with respect to the collets. In any event, the damage to the tube renders the operation substantially more expensive if the tubes can be salvaged. Repair, or the use of substantially lower pressures prevent wide acceptance of hydraulic chucks for larger diameter tubes.
Accordingly, a hydraulic chuck would be highly desireable that could be employed with large diameter tubes of at least 2 to 8 inches in diameter or larger. The device must be capable of gripping the tube firmly to prevent relative movement thereof during application of hydraulic pressure, while simultaneously be capable of gripping the tube without damaging the tube.