GB631034A - Improvements in braking mechanism for oil wells and the like - Google Patents

Abstract

631,034. Winches. WINTHER, M. P. June 27, 1947, No. 16964. Convention date, July 1, 1946. [Class 78 (v)] [Also in Group XXXIV] A brake for hoisting drums of oil well drawworks and like drilling or boring apparatus combines the high retarding torque of an eddy-current brake at high speeds with that of a mechanical friction brake at low speeds. The shaft 29 of the hoisting drum 27 is driven through gearing 25 and has rotatable with it an eddy current inductor drum 37 and a friction brake drum 35. The friction brake drum is applied by a toggle linkage 43 operated by a handlever 45, which is mechanically coupled to a rheostat arm 51. In position A of handlever 45 both eddy current, and friction brakes are released. As the.handlever 45 is moved to the right, the eddy current brake is energised by the closing of the switch 55 and the resistance 61 is progressively short circuited until at the position C the eddy current brake is fully energised and the brake band 39 of the friction brake begins to expand. At position E both brakes are fully applied. The variable resistance 61 is made part of a circuit supplied by a direct current power source 71, or emergency battery 93, through wire 73, eddy current brake coil 67, contactor 81 and a return wire 79. Contactor 81 and another contactor 77, controlling a circuit in parallel with the rheostat 51, 61 are controlled by relay coils 91 and 87 respectively, the two relay coils being energised by switches 55, 89 and 83, 85 respectively, the latter two switches being normally opened and closed by a spring trigger 65 on the handlever 45. The switch 89 is normally open and is closed by a spring loaded reel 7 and its control cable 9 only when the lower block 15 of the hoisting tackle is raised above the level F. This ensures that by bypassing the rheostat 51, 61, the eddy current brake coil is fully energised at the initial operation of lowering the block 15 on to the top of a length of drill pipe 19 and automatically prevents the block 15 from buffing violently against the block 3 when it is desired to insert a new drill section as rapidly as possible. Trigger lever 65 is used to de-energise the eddy current brake coil 67, during the initial operation described above, until the block 15 has dropped below the level F.