The present invention broadly relates to a drilling bit, and, more specifically pertains to a new and improved crenellated drilling bit for the fluid-jet supported drilling of rock.
Generally speaking, the drilling bit of the present invention is for liquid-jet supported, especially rotary, drilling in rock and comprises hard-metal tipped cutting edges, pins or the like with at least one means of supply for a fluid pressure medium having a pressure between 500 and 4,000 bar which opens into at least one nozzle releasably installed in the drilling bit body.
In other words, the present invention relates to a drilling bit, such as a crenellated drilling bit for fluid-jet supported rotary drilling in rock which comprises a drilling bit body having cutting elements tipped with hard-metal, at least one nozzle member releasably installed in the drilling bit body, at least one supply channel for a fluid pressure medium provided in the drilling bit body and opening into the nozzle member, and the fluid pressure medium having a pressure of between 500 and 4,000 bar.
Drilling bits, whether for impact or pure rotary drilling in rock, must fulfill diverse objectives. The rock can be subject to relatively high pressure-loading, while on the other hand the tensile strength of rock is usually low. The drilling bit serves as a force-transmitting element between the drilling machine and the rock. The rock is initially elastically deformed by the effect of the forces of the drilling bit, especially of the cutting edges, while compressive cracks and shear cracks simultaneously arise in the rock. Rock particles must simultaneously be dislodged from the crystal structure of the rock and transported away from the immediate effective region of the cutting edges. Such elimination must be performed in order that the energy supplied by the boring machine not be employed to further reduce the drilling chips, which would build up a cushion between the rock to be removed and the drill cutting edges.
It is known to employ fluids, especially gases or liquids, to transport the drilling chips away. The liquids can also comprise suspension materials, in order that specifically denser substances can be transported out of the bore hole. Such flushing fluids, however, do not serve to support the removal of solid rock.
In water-jet supported cutting, the water-jet enters into cracks, fissures and the like, which already exist or which arise due to the effect of the forces of the drilling bit upon the rock, and loosens the rock structure, so that a supplemental material-removal effect can be attributed to the liquid jet, which is most commonly a water-jet. This effect arises as a rule at a pressure between 500 and 4,000 bar.
It is important for the effect of the high-pressure-medium jets that the jet can cooperate with the cutting edges of the drilling bit, i.e. that the jets be directed to those locations or regions of the rock where the cracks arise. Upon considering that there is an intimate interaction between crack growth and the arrangement of cutting edges on the drilling bit, then the great importance of exact orientation of the liquid jet or jets becomes particularly clear.
The liquid jets exit from the drilling bits through nozzles which may, for instance, be constructed of corundum and comprise an exit aperture which is only a fraction of a millimeter. Since the jets, as a rule, have a lower service life than the drilling bits per se, these jets are preferably removably attached to the drilling bit.
It is already known to fasten a disc-shaped nozzle in a drilling bit for fluid-jet supported drilling by a union nut which has a slot for turning with a screwdriver. This permits performing the replacement of the delicate nozzles with coarse tools, but an exact positioning of the nozzle as well as an optimum sealing, which would avoid a corresponding pressure loss, is usually no longer guaranteed after replacement of the nozzles.