The Foremost Floating Cushion Sub has been designed specifically to fit all mid range and large blast hole rotary drills which are utilized to drill in soft to medium hard rock formations. When mounted into the drive spindle of the gear box it will provide a minimum of two and one half inches of free travel between the top of the drill string and the rotary drive. The extended travel capacity built into the cushion sub enables the drill operators to quickly and easily make-up and breakout connections on the drill pipe with minimal thread damage. When the rotary drive is lowered to pick up on the threads of the drill pipe, the piston component in the cushion sub will move up into the housing of the sub when the threads come in contact which will considerably lessen the impact not only on the threads of the drill pipe but also the bearings and gears retained within the rotary drive.
The unique configuration of the housing assembly will not only provide direct drive forces from the rotary drive to the drill string but due to its design also absorb torsional vibration from the rotary bit or DTH hammer assembly through the use of polymers incorporated in the drive system. Whether using pull-down or holdback methods of drilling, urethane cushions located on both the top and bottom ends of the piston stroke as well as some hydraulic dampening from within the housing cavity, the shock and vibration from the rock bit will be greatly reduced and therefore enhance the drills performance and decrease maintenance.
The Foremost Cushion Sub will accommodate drill string combinations up to and including nine and one quarter inches in diameter. Typically, the assembly is supplied with a pin up / box down thread combination cut to customer specifications as per the drill application. The cushion sub assembly has been configured to fit into mid range and large rotary drills so as not to interfere with the operation of the carousel and to allow the operator to install the unit without any modifications to the drill.
In most cases, there will be room in the mast to install a short saver sub below the cushion sub to make up the required length as per the original extended sub supplied by the drill manufacturer. Seals, cushions and other wear parts can be easily replaced in your own facility as no special tools or equipment are necessary for dismantling and rebuilding the complete assembly. Lubrication of internal components to reduce wear and prevent corrosion within the housing is accomplished by means of a grease fitting conveniently located on the bottom surface of the lower cover plate.