Patent Application
20060243494
This invention relates in general to earth boring bits, having rotating cones, and in particular to barrier members such as seals for the lubricant system.
An earth boring bit of the type concerned herein has a body with at least one bearing pin depending from it. Typically, there are three bearing pins, and a cone mounts rotatably to each of the bearing pins. The cones have cutting elements on the exterior that engage the earth formation as the bit body rotates. Drilling fluid pumped from the surface discharges out nozzles of the bit body and returns up the exterior of the drill string along with cuttings.
A lubricant system supplies lubricant to the clearances between the bearing pin and the cone. The lubricant system includes a cavity in the bit body that connects by passages to the clearances between the bearing pin and the cone cavity. Barrier members prevent entry of debris and cuttings into the lubricant.
One of the barrier members comprises a seal located between the bearing pin and cone cavity. The seal may be of a variety of types, including an O-ring seal or a metal face seal assembly. In the case of metal face seals, elastomeric energizing rings are employed to urge the metal face seals into contact with each other. In one type, the metal face seal assembly includes an elastomeric excluder ring that blocks drilling fluid from contact with the energizing ring.
Another barrier member comprises a pressure compensator diaphragm. The diaphragm is an elastomeric member located in the lubricant cavity. One side of the diaphragm is exposed to the exterior of the drill bit and the other side is in contact with the lubricant. The diaphragm reduces pressure differential between the exterior of the bit and the lubricant in the lubricant chamber.
The barrier members, being elastomeric and exposed to drilling fluid, are subject to being cut or torn by drilling cuttings. In the case of an O-ring seal serving as the barrier member, one side is in dynamic sliding contact, thus is subject to wear. If worn excessively, drilling fluid can enter. Tears or cuts on the barrier member can cause drilling fluid to enter. If the drilling fluid enters the lubricant chamber, the cuttings will damage the bearing surfaces, lubricant will leak out, and the life of the bit will soon be over.
One prior art approach to reducing wear on elastomeric seal surfaces of earth boring bits is to place a fabric of woven fibers on the side of the seal that is in dynamic sliding engagement. In applications other than earth boring bits, chopped fiber material has been dispersed in the rubber material of brake bands, clutch plates, and sheet gaskets. Also, chopped fiber material has been dispersed in adhesives and sealants to vary the viscosity of the material.
The bit of this invention is a rotating cone type having a lubricant chamber for supplying lubricant to bearing surfaces between the cone and a bearing pin. The lubricant chamber has at least one barrier with one side exposed to the exterior of the bit for contact by drilling fluid in the well bore. This barrier prevents entry of drilling fluid into the lubricant chamber. The barrier comprises an elastomeric compound containing non-woven, non-cellulose, fibers dispersed therein.
The barrier may comprise an O-ring seal deformed between an inner diameter portion of the cone and an outer diameter portion of the bearing pin. The barrier may comprise a pressure compensator diaphragm that flexes to reduce pressure differential between the drilling fluid in the well bore and the lubricant in the lubricant chamber. The barrier could also be an excluder ring or a metal seal assembly.
The chopped fibers are preferably formed from a polymer in the group consisting essentially of aromatic polyamide, non-aromatic polyamide, polyimide, polyurethane and polyester. The fibers are randomly oriented and uniformly dispersed throughout the material of the barrier. Preferably the volume of the fibers is less than 5% that of the elastomeric material of the barrier.
Referring to
Body 13 has a separate lubricant chamber for each of the bearing pins 15. Each lubricant chamber supplies lubricant to bearing surfaces of bearing pin 15 and cone 17. Each lubricant chamber includes a lubricant cavity 21 in body 13 and a plurality of passages 23 extending from cavity 21 to the exterior of bearing pin 15. Two elastomeric barriers prevent entry of drilling fluid on the exterior of bit 11 into the lubricant chamber. One of the barriers comprises a seal assembly 27 located at the base of bearing pin 15. The other barrier comprises a pressure compensator diaphragm 29 located in lubricant cavity 21.
Compensator diaphragm 29 has one side exposed to drilling fluid through a port 31 formed in body 13. The inner side of compensator diaphragm 29 is in contact with lubricant in lubricant cavity 21. Compensator diaphragm 29 flexes on the axis of lubricant cavity 21 to reduce pressure differential between the exterior drilling fluid pressure and the pressure of the lubricant in lubricant cavity 21. In this example, a rigid shell 33 in lubricant cavity 21 provides a stop against deformation of compensator diaphragm 29 when the lubricant is depleted. A cap 35 secures the opposite side of lubricant cavity 21. Compensator diaphragm 29 is formed of an elastomeric or rubber material, such as nitrile butadiene, or hydrogenated nitrile butadiene.
A variety of seal assemblies 27 exist for sealing between cone 17 and bearing pin 15. In the embodiment of
Seal assembly 27 includes an elastomeric or rubber energizer ring 41 deformed between a groove or seal gland 43 on the exterior of bearing pin 15 and an outer diameter portion 45 of non-rotating ring 39. The outer diameter 45 of non-rotating ring 39 is inclined so that a spring force caused by energizer ring 41 urges non-rotating ring 39 into sealing engagement with rotating ring 37. Seal assembly 27 may also include an elastomeric excluder ring 47, which is an elastomeric or rubber member, such as nitrile butadiene or hydrogenated nitrile butadiene, located between the outer end of non-rotating ring 39 and part of seal gland 43. Excluder 47 serves to prevent drilling fluid from contacting energizing ring 41.
Excluder 47 is formed of a rubber or elastomeric compound that contains a uniform disbursement of fibers 48. Fibers 48 are short randomly oriented non-cellulose members. Rather than a cellulose material, such as cotton, fibers 48 are formed of a material that is preferably a polymer from a group consisting essentially of aromatic polyamide, polyimide, non-aromatic polyamide, polyurethane and polyester. One preferred type of fiber 48 is an organic polymer fiber manufactured by DuPont with the trademark Kevlar. These fibers are formed from Kevlar yarn that is cut and refined to produce a short fibrillated fiber. DuPont offers product, referred to as Kevlar Engineer Elastomer, that comprises a Kevlar fiber pulp suitable for dispersion in rubber products. The amount of fibers 48 dispersed into the elastomeric compound of excluder 47 is small, preferably less than five percent by volume. The hardness of excluder 47 is preferably in the range from 40-50 Shore A.
Energizer ring 41 is not exposed to drilling fluid, thus in the preferred embodiment, it is of conventional elastomeric material and contains no chopped fibers 48. Compensator diaphragm 29, however, is exposed to drilling fluid, thus fibers 48 may be dispersed throughout the elastomeric material of diaphragm 29 of the same type and in the same proportion to those in excluder 47. Compensator diaphragm 29 may be formed of the same type of rubber material as excluder 47, but would typically have a hardness of about 75 Shore A.
The embodiment of
The invention has significant advantages. The chopped dispersed fibers increase the wear resistance of the barrier members of earth boring bits that are engaged in dynamic contact. The fibers increase the resistance of the barrier members to tearing and cutting from drilling cuttings as well.
While the invention has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.
