Lubrication – Systems – Machine tools
Reexamination Certificate
1999-06-04
2001-01-09
Lorence, Richard M. (Department: 3681)
Lubrication
Systems
Machine tools
C184S055100, C175S228000
Reexamination Certificate
active
06170611
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method and apparatus for loading lubricant into rolling cutter earth boring bits used for oil and gas drilling and other forms of mineral mining.
DESCRIPTION OF THE RELATED ART
In the manufacture of lubricated, rolling cutter earth boring bits, or commonly referred to as rock bits, or drill bits, the process of filling the bit with lubricant is one of the most critical and, at the same time, most technologically ignored processes in the overall rock bit manufacturing process. The basic steps required to properly load lubricant into a rock bit are: (1) evacuate the air from within the bit; (2) introduce lubricant under pressure into the bit without introducing air; (3) disconnect the lubricant loading device from the drill bit; and (4) purge the lubricant from the passages in the loading device which are used during the evacuation step.
A typical rolling cutter earth boring bit has numerous dead-end passageways and cavities which must be completely filled with lubricant if the bit is to operate properly. Also, care must be taken during loading of the lubricant into the rock bit to prevent damage to its seals or bearing systems within the bit due to the generally high pressure of the lubricant as it is loaded. Because the typical rolling cutter rock bit lubricant is a viscous grease, it is difficult to apply enough pressure to the lubricant to completely fill the bit in a timely manner without harming the seals or bearings.
In operation, rock bits are often immersed in fluid with very high hydrostatic pressures, often exceeding 10,000 PSI. A pressure compensating device is usually provided in the lubrication system to transmit this hydrostatic pressure to the lubrication system. As the hydrostatic pressure increases, the lubricant is forced into any spaces within the bit which had been void of lubricant. The pressure compensating device for the lubrication system must have the capacity to sweep a volume of lubricant from a reservoir into these spaces to maintain pressure balance.
Due to the limited space available in rolling cutter earth boring bits, this reservoir contains a limited amount of the lubricant, or grease. It is important, therefore, that the lubricant loading process be carried out in a manner which minimizes spaces void of lubricant. Ideally, the lubricant is introduced at the highest possible pressure that the bit will tolerate without damage. This assures that the maximum volume of lubricant is loaded into the bit. However, due to the “saw tooth” pressure variations, or pressure spikes, inherent in the design of grease pumps used for lubricant loading, the pressure is rather hard to control, and such pressure spikes might cause pressure to exceed the pressure limits of the seals and/or bearing systems of the rock bit. Consequentially, the pumps are often set at an average pressure much lower than optimal for maximum lubricant fill.
There is an added difficulty caused by the very high viscosity of most rock bit lubricants, or greases. In order to make the lubricant flow at a reasonable rate from the pump to the bit, it is very desirable to have a relatively high pressure setting at the pump. The higher the differential pressure of the lubricant, the faster the lubricant will flow. At the start of the loading process, high differential pressures can be applied to the lubricant and it can flow into the bit at a fairly high rate without building excessive pressure within the bit. As loading progresses, the pressure of the lubricant slowly builds within the bit. Finally, when loading is nearly complete, the pressure of the lubricant within the bit approaches the pressure setting of the pump. To prevent over pressurization of the bit, the pressure of the pump is limited to the maximum pressure allowed at the bit. Since the pump pressure setting is not readily changed during the loading process, the time required to load the lubricant is thus unnecessarily extended.
In recent years, many new rock bit designs have been introduced which have added special requirements on the lubricant loading system due to the use of specials seals, pressure compensation devices, or other components which may be damaged by excessive pressure forces during loading of the bit. Bits with volume compensating metal face seals must have the lubricant loaded carefully, or risk damage to the seal assembly. There are other bit designs that have lubricant vent systems designed to vent at low differential pressures. Finally, very large bits are now manufactured that have 300 square inches or more of “piston” area exposed to the pressure of the lubricant as it is loaded. Even if a modest lubricant loading pressure of 400 PSI is utilized, a staggering 120,000 pounds of force may be applied to the rock bit cutter retention system during the greasing operation. Hidden damage can result within the rock bit due to these excessive forces.
There is a need for a lubricant loading system for rock bits that can much more precisely control the pressure of the lubricant as it is being loaded and assure that the bit is fully loaded with lubricant. This lubricant loading system should have the ability to change the delivery pressure of the lubricant as the loading process proceeds in order to minimize the time required for loading.
SUMMARY OF THE INVENTION
The invention comprises a new type of lubricant loading machine for rock bits, and the bits lubricated by this machine. The new lubricant loading machine utilizes a closed loop pressure controlled lubricant loading system. In its most general form, the machine comprises a vacuum pump, a grease pump with proportional pressure control, a control system, and a pressure sensor. In operation the control device operates the vacuum pump to achieve less than 0.75 PSIA pressure in the cavities of the bit. While maintaining this level of vacuum, the control system operates appropriate valving to introduce lubricant to the bit.
The control system has a set point adjusted to a target lubricant pressure. The control system monitors the pressure signal from the lubricant pressure sensor, compares it to the set point value and sends a appropriate control signal to the proportional pressure controlled grease pump.
In accordance with the invention, the foregoing advantages have been achieved through the method and apparatus for loading lubricant into earth boring bits of the present invention. The apparatus of the present invention for loading lubricant into a bit chamber of an earth boring bit may include a means for removing air from the bit chamber; a means for providing pressurized lubricant to the bit chamber; a means for measuring the pressure of the lubricant at the bit chamber; and a control system for controlling and operating the pressurized lubricant providing means based upon the pressure of the lubricant. A further feature of the present invention is that the means for removing air may be a vacuum pump in fluid communication with the bit chamber. A low pressure transducer may be disposed between the bit chamber and the vacuum pump. An additional feature of the present invention may include a filter disposed between the bit chamber and the vacuum pump. Another feature of the present invention is that the means for providing pressurized lubricant may be a lubricant pump, and the lubricant pump may be a proportional air pressure operated lubricated pump. The lubricant pump may be powered by pressurized air provided by a proportional air regulator.
An additional feature of this aspect of the present invention is that a fluid passageway may be disposed between the means for providing pressurized lubricant and the bit chamber, including a means for purging lubricant from at least a portion of the fluid passageway. The means for measuring the pressure of the lubricant may be a high pressure transducer disposed adjacent to, and in fluid communication with, the bit chamber. An additional feature of the present invention is that the control system may be a closed loop control system, and the closed loop control system may op
Camco International Inc.
Daly Jeffery E.
Lorence Richard M.
LandOfFree
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