Lubricating device

A device for lubricating rotary drill bits of the type comprising a roller cutter (14) which is rotatably carried by means of a bearing system (15, 16, 17, 18). Fluid is supplied to the bearing system for cooling and/or cleaning thereof through a passage (31, 32, 33; 51, 61), and a lubricant is delivered to said passage from a body (31; 39) of porous material, which is soaked in lubricating means. For purposes of controlling the supply of lubricating means the porous member forms a fraction of the inner wall of said passage.

The present invention relates to a device for lubricating rotary drill bits 
of the type comprising at least one roller cutter provided with cutting 
means which is rotatably carried by means of a bearing system. The drill 
bit is provided with at least one first passage means for supplying 
flushing fluid to the hole drilled by the drill bit, and at least one 
second passage means for supplying fluid to the bearing system for cooling 
thereof. Lubricating means is supplied to the fluid in the second passage 
means for simultaneous lubricating of the bearing system. 
The bearing systems in rotary drill bits are designed either sealed or 
unsealed. A sealed design means that the bearing system is sealed and 
supplied with a lubricant, such as grease or oil, from a reservoir which 
is built-in inside the drill bit. The lubricant is supplied to the bearing 
system by means of the difference in pressure inside and outside thereof 
via a membrane. No air or other cooling medium is supplied to the bearing 
system. An unsealed design, of which the present invention is an example, 
means that the bearing system has no sealing means. Impurities are 
prevented from entering into the bearing system due to the fact that air 
is supplied thereto, which air flows outwards for forming an air barrier 
between the roller cutter and the leg associated therewith. 
For purposes of lubricating the bearing system it has been proposed to 
deliver lubricant means to solely that portion of the air which is 
supplied to the bearing system for cooling and cleaning thereof. U.S. Pat. 
No. 2,831,660 discloses a design in which a lubricant reservoir is 
arranged in each of the legs of the drill bit, and the lubricant is 
delivered to the cooling air through a passage in the leg. U.S. Pat. No. 
3,220,496 discloses a design in which lubricant is delivered to the 
bearing system from an adapter which is mounted between the drill bit and 
the forward end of the drill string. The pressure of the flushing fluid 
forces the lubricant to the bearing system via a piston. A similar design 
is disclosed in U.S. Pat. No. 3,749,186. 
A disadvantage of the above-mentioned previously known lubricating devices 
is that the supply of lubricant from the reservoir has been difficult to 
control, which means that too much lubricant often has been supplied 
during the first phase of the drilling operation with the result that all 
lubricant is consumed in a later phase of the drilling operation, which 
decreases the life of the drill bit. 
An object of the present invention is to provide a rotary drill bit in 
which the supply of lubricant can be kept on a predetermined and 
controlled level, thereby making it possible to increase the life of the 
drill bit. Another object of the invention is to provide a rotary drill 
bit in which the risk for break downs is small, thereby increasing the 
reliability of the drill bit. These and other objects are attained by 
giving the invention the characterizing features stated in the appending 
claims. 
The invention is described in detail in the following with reference to the 
accompanying drawings in which two embodiments are shown by way of 
example. 
It is to be understood that these embodiments are only illustrative of the 
invention and that various modifications thereof may be made within the 
scope of the claims.

In the drawings corresponding details on the two embodiments have been 
given the same reference numeral. 
In FIG. 1 a rotary rock drill bit 10 is shown having a support leg 11 on 
which a support or bearing pin 12 is provided. A roller cutter 14 is in 
conventional manner rotatably journalled on the bearing pin 12 over a 
bearing system, which comprises a roller bearing 15, a ball bearing 16, a 
roller bearing 17 and an axial thrust bearing 18. The roller cutter 14 is 
provided with cutting means in form of hard metal inserts 13. The drill 
bit 10 has three legs 11 which together with their associated roller 
cutters 14 are equally circumferentially spaced. For the sake of clarity 
only one leg is shown in FIG. 1. 
The rotary drill bit 10 is provided with a passage 19 for flushing fluid, 
such as compressed air with water added thereto. The flushing fluid is 
intended for flushing the hole drilled by the drill bit. Rearwardly the 
passage 19 turns into a bore 20. A check valve generally denoted by 21 is 
arranged in the rear end of the bore 20. The check valve 21 can be 
considered as consisting of two cooperating valve members, one of which 
being composed by a flat valve plate 22 and a cylindrical strainer body 23 
attached thereto centrally and coaxially therewith. The mantle surface of 
the strainer body 23 is provided with round holes 24 to allow through-flow 
of the flushing fluid. The other valve member forms an insertion which is 
movable relative to the first valve member and comprises a circular cover 
25 supported by three axially extending legs 26. The legs 26 surround the 
strainer body 23 and are attached to the cover 25 and a bottom ring 27. 
The rotary drill bit 10 is provided with three passages 28, 29, 30, one for 
each leg 11, through which fluid, such as compressed air, is supplied to 
the bearing system 15, 16, 17, 18. Normally the fluid is supplied to the 
bearing system on the one hand for cooling thereof, and on the other for 
cleaning thereof and preventing impurities from entering thereinto through 
the annular gap between the roller cutter and the bearing pin. In certain 
cases, however, the fluid might be warmer than the bearing system, which 
means that its primary function is to clean the bearing system. These 
passages are designed as an axially extending tube 31, which over a 
knee-tube 32 turns into a passage 33 in the leg 11 and passages 34, 35 in 
the bearing pin 12. The rear end of the tube 31 terminates within the 
strainer body 23. 
The function of the check valve 21 is in detail described in U.S. Pat. No. 
4,184,554. When flushing fluid containing water reaches the check valve 21 
the water is separated therefrom before the fluid enters the tube 31. 
A reservoir 36 for a lubricant is arranged within the rotary drill bit 10. 
The reservoir 36 is rearwardly closed by a cover 37, which attaches the 
reservoir to the drill bit. The cover 37 is provided with recesses 38 
through which the flushing fluid which passes the bottom ring 27 is 
conducted into the bore 20. 
According to the invention a portion of the inner wall of the passages 28, 
29, 30 is formed by a member of porous material, which is soaked in 
lubricant. When the fluid flows past this member small drops of lubricant 
are brought therewith into the bearing system 15, 16, 17, 18. In the 
embodiment according to FIG. 1 the porous member consists of the tube 31, 
which thus provides a fraction of the passage 28. 
Suitably, the porous material can be a plastic. It has been found that a 
plastic of the type ACLACELL (Trade Mark) is suitable. It is believed that 
other porous materials, such as felt and rubber, can be used. 
The amount of lubricant which can be absorbed by the porous material is 
comparatively limited. For purposes of increasing the available volume of 
lubricant the tube 31 is arranged within the reservoir 36 in the 
embodiment according to FIG. 1. Due to the fact that the supply of 
lubricant is completely depending on the fluid flow through the tube 31 a 
controlled supply of lubricant is achieved. Further, due to the fact that 
the lubricant is delivered from the pores in the porous material there is 
no risk for break downs to occur caused by local clogging of the porous 
material. 
In the illustrated embodiment the tube 31 is arranged to traverse through 
the portion of the flushing fluid passage formed by the bore 20. In FIG. 1 
only one tube 31 is shown. As may be seen in FIG. 2, however, a passage 
28, 29, 30 with an accompanying tube 31 is arranged for each of the three 
legs of the drill bit. 
In the embodiment according to FIG. 3 a tube 39 of porous material and a 
lubricant reservoir 40 are arranged for each of the legs 11 of the drill 
bit. 
In the two illustrated embodiments the lubricant reservoir is accommodated 
within the drill bit. Alternatively, it is believed that the reservoir 
could be arranged in an adapter, which is designed for connection between 
the drill bit and the front end of a drill string which carries the drill 
bit. 
A check valve of the type shown in FIGS. 1 and 3 is then provided in the 
rear end of the adapter. After the check valve the lubricant reservoir 
follows, in which a single tube of porous material common for the legs of 
the drill bit, is located centrally. This adapter is intended to be used 
together with a drill bit of specific design comprising a rearwardly open 
catching means of the type shown in U.S. patent application Ser. No. 
86,436. Fluid containing lubricant is caught by the catching means and 
conducted further to the bearing system through a passage in the drill bit 
via passages in the leg and bearing pin. For a complete description of the 
function reference is made to the above patent application which therefore 
is incorporated in the present specification.