Sheave block with retractable sheave guards

Details Sheave block with retractable sheave guards Sheave block with retractable sheave guards

1998-02-27

2002-05-14

Walsh, Donald P. (Department: 3653)

Implements or apparatus for applying pushing or pulling force

Device or member for contacting and guiding moving cable

Including rotatable, cable contacting, pulley wheel element

C254S403000, C254S405000, C254S404000

Reexamination Certificate

active

06386516

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
FIELD OF THE INVENTION
The present invention relates generally to sheave blocks, such as traveling blocks and crane, or boom, blocks. More particularly, the invention relates to a sheave block having retractable sheave guards.
BACKGROUND OF THE INVENTION
A “sheave block” is an apparatus used in systems for heavy lifting and other weight bearing operations. The sheave block employs numerous “sheaves,” each sheave having a groove in its outer circumference within which a wire rope, or wireline, may be supported. The sheaves are supported and independently rotatable on a common shaft that extends between opposing side plates, or walls, of the sheave block. Each pass (or loop) of the wireline around a sheave in the sheave block is referred to as a “reeve.” By passing the wireline around more than one sheave, thus having numerous reeves, the lifting force of the wireline is multiplied.
Some of the most common forms of sheave blocks include traveling blocks used during oil and gas drilling, crane or boom blocks used on large cranes for various heavy lifting operations and pulley blocks. Lifting systems use a power source to create tension in the wireline, allowing the load to be raised and lowered at a certain velocity. Typically, the power source is capable of supplying power within a certain range; thus the power supply is not unlimited.
In certain instances involving the use of sheave blocks, such as in drilling operations, it is desirable to adjust the weight bearing capability of the wireline as the weight of the load changes so as to maintain, or improve, operational efficiency. A well-known method of adjusting the weight bearing capability of a sheave block system is to change the number of reeves of the wireline. This is know as “rereeving” the wireline. By increasing the number of reeves, the lifting capacity of the system will be increased without additional line tension (or power). At the same time, however, the greater the number of reeves, the slower the lifting operations become at a constant wireline pulling velocity. Thus, while it is sometimes preferred or necessary to increase the number of reeves to lift heavy loads within available power source limits, it is generally desirable to use the smallest number of reeves to lessen the time required for lifting and, thus, to have more time-efficient operation.
During various stages of drilling operations, such as when a heavy drilling string extending deep into the bore hole must be lowered or raised, it is desirable to have a greater number of reeves through the travelling (sheave) block of the drilling rig lifting system to enable the system to support the increased load. At other times, the existence of a relatively light load allows the weight bearing wireline to be reeved over a small number of sheaves in the travelling block, enabling time-efficient operation. The ability to save time by rereeving the travelling block during drilling operations can result in significant cost savings. For example, thousands of dollars per day may be saved when rereeving is used on an offshore drilling rig, where the cost for operating the rig may range between $30,000-$150,000 per day.
Rereeving a sheave block typically involves various design considerations. For example, the sheave block must enable access to the sheaves within the sheave block to allow rereeving. Typically, access is gained by removing or opening safety guards extending at least partially around the sheaves between the side plates. The safety guards are included in the sheave block to prevent the intrusion or entanglement of objects into the sheave block during use and to prevent the wireline from jumping out of the sheave block.
The sheave block design should also allow positioning of the wireline within the sheave block in a load balanced pattern, such as in the center of the sheave block, to assist in maintaining system stability. At the same time, however, it is desirable to minimize the bulkiness and size of the sheave block to enhance handling and installation. Furthermore, because rereeving requires the interruption of the primary operations being performed at the work site, it is highly desirable to minimize the time necessary for rereeving.
Yet another concern is safety. The sheave block should be designed so that the wireline may be rereeved without increasing the risk of equipment damage or human injury.
Sheave block designs that have been proposed in the past have various disadvantages. For example, the increased size and bulkiness of the sheave block disclosed in U.S. Pat. No. 1,577,804 increases its difficulty in use and handling. For another example, the sheave block disclosed in U.S. Pat. No. 2,800,300 must be laid on its side to be rereeved. Rereeving with this block design thus requires substantial time and handling.
Thus, there remains a need for a sheave block that allows speedy rereeving without increasing the risk of safety hazards during rereeving. Especially well received would be a sheave block having sheave guards that generally shield the circumference of the sheaves during lifting operations; that are easily retractable to allow sufficient access to the sheaves for rereeving and positioning of the wireline within the sheave block in a load balanced pattern; that allow rereeving without having to entirely remove the wireline from the sheave block; and that do not add significant mass or size to the sheave block. Preferably, the device should allow the sheave block to perform in a conventional manner. Ideally, existing sheave blocks could be retrofitted, or otherwise adopted, with the new sheave block design.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a sheave block for use with a wireline that includes first and second opposing walls and a shaft extending there between. At least one grooved sheave is disposed on the shaft, each grooved sheave being engageable with the wireline. At least one retractable sheave guard is movably connected to the first and second opposing walls and is moveable between open and closed positions, the open position allowing the wireline to be rereeved around at least one of the sheaves without entirely removing the wireline from the sheave block. The retractable sheave guards may be movable between open and closed positions while the wireline is engaged with at least one of the grooved sheaves. Further, the retractable sheave guards may be moveable between open and closed positions without moving the retractable sheave guards upwardly. At least one of the retractable sheave guards may be pivotably moveable between open and closed positions.
The sheave block may include at least one releasable lock capable of retaining at least one of the retractable sheave guards in its closed position. In one embodiment, the lock includes at least one cam rod. At least one of the sheave guards may include a plurality of fingers and a plurality of wireline passages enabling the guard to be movable between open and closed positions while the wireline is engaged with at least one of the sheaves. The fingers may include eyelets engageable with the releasable lock.
At least two of the sheave guards may be connected and may be cooperatively moveable between open and closed positions. At least one coupler connecting at least two of the sheave guards may be included. In one embodiment, the coupler includes at least one link. The sheave block may include at least one sheave guard stop member capable of supporting at least one of the sheave guards in its open position.
In one embodiment, a first sheave guard includes first and second ends, the first sheave guard being moveable downwardly relative to the sheaves from its closed position to its open position. Further, at least one of the first and second opposing walls may include a guide slot, the first sheave guard including at least one guide member moveable upwardly and downwardly within the guide slot.

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