Rotary Table – Drilling Equipment – Readyzone

Rotary Table

Rotary - table

Rotary table

The primary function of the rotary table is to transmit torque and impart a rotary motion to the Kelly and drill string. The top of the housing of the rotary table customarily forms a portion of the derrick floor and is provided with a non-skid treads. The exposed top of the rotating table, as well as the exposed upper part of the rotary or Kelly bushing, should be free of projections which might be hazardous to personnel. The rotating table is usually cast of alloy steel and fitted underneath with a ring gear which is shrunk onto the table proper. The table is supported either by ball or tapered roller bearing capable of supporting the dead load of the string of drill pipe or casing which may be run into the well. Provision in the form of suitable bearings must also be made for holding the table in place against any possible tendency to upward movement imparted during rig operation. Suitable guards are arranged so that mud or water cannot get into the oil bath provided for the gears and bearings. The ring gear and its driving pinion gear are customarily of spiral bevel construction, which provides for smoother operation than straight bevel gears. The speed reduction from the pinion shaft to the table is of the order of 3 or 4 to 1. The pinion shaft is customarily furnished with antifriction bearings, often of tapered roller design. It is also equipped with oil seals and guards to prevent entry of mud or water into the interior of the equipment.

Power for driving the rotary table is most often taken from the draw works and transmitted to the rotary table by a chain and sprocket drive. In this arrangement the excess power available, as well as the momentum of the heavy moving parts, presents a hazard to twisting off the drill pipe if the bit should become stuck. The hazard is reduced where a single internal combustion engine can be used for driving the rotary. Independent drives are also used for the rotary tables; and these employ a steam engine, an internal combustion engine, or an electric motor, according to the type of power used in the drilling rig. Also, a hydraulically driven table has been developed. In common, all such drives rotate the horizontal pinion shaft, the spiral bevel pinion gear rotates the ring gear, which in turn rotates the vertical drill string.

Rotary tables are rated according to the size of the opening through the table, such as twenty inches, and the dead-load capacity of the table, such as 7,00,000 pounds.

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Reference : Mc Cray & Cole, Oil Well drilling Technology, New India Publication.

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