A. Field of the Invention
The present invention is a new and improved device for tensioning cables on a pile driving hammer or the like.
B. Description of the Prior Art
Conventional percussion hammers such as are used for pile driving and the like normally include a ram reciprocally mounted on the hammer body movable between an upper cylinder and a body base. Typically, the base of the body is secured to the upper cylinder assembly by suitable tie means. One such means of tying the hammer base to the upper cylinder assembly is by use of tie cables interconnecting the hammer base and the upper cylinder assembly. Such cable ties must be equally prestressed to provide a hammer body resembling a rigid construction.
In the larger sizes of pile driving percussion hammers, such as those used in offshore operation and weighing in the range of thirty to sixty tons, it may be desired to prestress the cable ties to a final tension in the area of forty tons for each cable tie. Heretofore, difficulty has been experienced in the pretensioning of such cable ties.
Examples of prior art devices for tensioning cables or similar items are disclosed in United States Patent Application Ser. No. 441,027, filed February 11, 1974, now U.S. Pat. No. 3,938,427, and U.S. Pat. No. 2,866,370.
Prior art cable tensioning assemblies include a thread protector cap, a jacking bar assembly, a jacking pedestal, a hydraulic jack, a placement nut, and a locking or retaining nut. To tension or retension a cable on the hammer using the prior art assembly, it is necessary to remove the thread protector cap from the end of the cable fitting. The jacking bar assembly must then be screwed tightly onto the end of the cable fitting. The jack pedestal is then assembled over the jacking bar assembly in a position to abut a support plate mounted on the casing of the hammer.
This procedure is followed by assembling the hydraulic jack over the jacking bar and locking it onto the jacking bar assembly by a locking nut. Hydraulic pressure is applied to the jack thus tensioning the cable.
Once the desired tension is obtained, the retaining nut is rotated downward about the cable fitting locking the cable fitting in position relative to the jacking pedestal thus maintaining the tension on the cable once the pressure in the hydraulic jack is released.
Such prior art cable tensioning assemblies require two men to set up the assembly and tension a cable, since the individual components of the assembly are of considerably weight and require accurate positioning.