Abstract:
A ball-bearing unit for a bearing of a deep-drilling apparatus having bearing races made from steel with balls disposed therebetween. Contaminated drilling medium passes into the space between the bearing races. Load-bearing balls made from ceramic alternate with separating balls of smaller diameter made from steel between the bearing races to extend significantly the service life of the ball-bearing unit.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to the mounting of a hollow shaft between a drilling head and drive turbine in a deep-drilling apparatus.  
         BACKGROUND OF THE INVENTION  
         [0002]    In deep-drilling rigs, drilling heads that are driven in the well have long been in use. Drilling liquid is pumped through a stationary pipe under pressure from outside toward the drilling head. A turbine at the end of the pipe converts the pressure of the drilling liquid into a rotary movement that drives the drilling head. After it has passed the turbine, the drilling liquid runs through a hollow shaft to the drilling head to lubricate and cool the drilling head. Drilling liquid, flows back to the surface outside the drilling head and carries drilled-out rock to the surface. Because of the rough ambient conditions, the drilling liquid, containing impurities, repeatedly penetrates into the roller bearings. One effect is rapid wear of the roller bearings.  
           [0003]    The roller bearing used in the drilling head in DE 25 27 237 C3 is protected by special seals in order to prevent the penetration of water. Despite filtration, the liquid or water still contains a great many impurities. The problem with these seals is that the water can penetrate into the roller bearing despite the seals. Then the impurities in the water damage the roller bearing, so that the service life of the roller bearing is greatly reduced.  
           [0004]    Roller bearings are known which include completely spherical four-point bearings. All roller bearing components of these four-point bearings are made from a wear-resistant roller bearing steel (AISI S2). But an even longer service life of the roller bearing would be desirable, because changing the roller bearing is very expensive for the operator of the deep-drilling apparatus.  
         OBJECT OF THE INVENTION  
         [0005]    It is therefore an object of the present invention to provide a roller bearing for a deep-drilling apparatuses which has a longer service life under operating conditions in which drilling water runs through the bearing.  
           [0006]    Other objects and features of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.  
         DESCRIPTION OF THE INVENTION  
         [0007]    In the invention which concern a ball bearing load-bearing balls are made from ceramic and are spaced a distance apart from each other by slightly smaller separating balls made from steel or an appropriate other metal or material which serves the separating function described herein. The bearing tracks of the bearing races are likewise made from steel or such other material. As a result, the load-bearing roller bodies made only from ceramic make rolling contact with steel surfaces or the other material surfaces.  
           [0008]    In the case there are impurities, e.g., from drilling, in the roller bearing, and in the case of defective lubrication, direct material contact takes place during rolling. In the invention, this direct material contact is always between ceramic and the steel or the other material. It has been found, surprisingly, that in the event of defective lubrication, the wear between bodies in rolling contact (steel and ceramic) is less than in the case of prior art rolling pairings (steel against steel).  
           [0009]    The effect of the rolling pairing of steel and ceramic on the service life of the roller bearing (for example, an axial bearing) is surprising in that, arithmetically, the service life of the roller bearing according to the invention is shorter than that of a completely spherical axial bearing according to the prior art, with steel balls of equal size. But, experiments have shown that the technical disadvantage of the bearing arrangement according to the invention is compensated for by the reduced wear of the bodies in rolling contact. In experiments conducted in realistic ambient conditions, the roller bearings according to the invention last considerably longer than the conventional bearings.  
           [0010]    Before the experiments, it was the predominant opinion that ceramic balls were not particularly durable in a contaminated environment including, inter alia, hard particles of sand. The experiments have shown that the roller bearings made from ceramic withstand this environmental condition without significant damage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows a drilling head with a bearing.  
         [0012]    [0012]FIG. 2 shows the bearing packet in section parallel to the axis of rotation.  
         [0013]    [0013]FIG. 3 shows a plan view of a detail of a bearing. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION  
       [0014]    [0014]FIG. 1 shows a roller bearing of a drive shaft of a drilling head. It is shown in the form of a ball bearing unit  1 . The drive shaft is a hollow shaft  3  and is disposed within the roller bearing. The hollow shaft  3  is rotatably supported by the roller bearing (bearing unit)  1  in a non-rotating housing  2 . The hollow shaft  3  transmits drive torque from a drive turbine (not shown) to a drilling head (not shown). The fluid which operates the drive turbine is passed in direction  4  in the hollow shaft  3 . Upstream of the roller bearing, some fluid is passed through apertures  10  in the ball-bearing unit  1 , to provide liquid to cool and lubricate the roller bearing. The drilling head is then cooled and lubricated by the fluid which emerges at  5  from the hollow shaft. As the fluid is always somewhat contaminated, impurities constantly enter the ball-bearing unit  1 .  
         [0015]    [0015]FIG. 2 shows the ball-bearing unit  1  which mounts the hollow shaft relative to the housing. In this example, a plurality of completely spherical radial/axial ball bearings (4-point bearings) are arranged parallel to one another in a bearing unit  1 . A 4-point bearing includes two outer bearing races  6  and two inner bearing races  7  at each annular row of bearing balls  8 .  
         [0016]    Between the inner and outer bearing races, a load-bearing ceramic ball  8  is followed by a somewhat smaller separating ball  9  in an annular array of alternating types of balls . In FIG. 3, the arrangement of the balls  8 ,  9  is shown in plan view. In each individual bearing of this ball-bearing unit  1 , load-bearing ceramic balls  8  alternating with separating steel balls  9  are used.  
         [0017]    The bearing races  6 ,  7 , are made from a first material steel, and the separating steel balls  9  may be made from a material number to the first material such as roller bearing steel, stainless roller bearing steels or from wear-resistant steels. A preferred embodiment for the race and the separating balls here is AISI S2 steel.  
         [0018]    [0018]FIG. 3 shows a plan view of a series of balls of the ball-bearing unit  1 . The load-bearing ceramic balls  8  and the slightly smaller steel balls  9  are shown. The ceramic balls  8  are in rolling contact only with steel parts i.e., adjacent steel balls  9  or the bearing races  6 ,  7 . The steel balls  9  of smaller diameter  9   a  are smaller sufficiently to ensure that, in maximum loading of the roller bearing, these separating steel balls  9  do not become load-bearing balls.  
         [0019]    The ceramic balls  8  may consist of solid ceramic or may be comprised of a base material that is coated with ceramic. This ceramic material may consist, for example, of silicon nitride or zirconium oxide.  
         [0020]    Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.