The button series bit has developed rapidly and evolved from the large-diameter button roller cone bit, which was born mainly to achieve the goal of fast drilling of hydraulic rock drills, saving auxiliary work time, and increasing industrial speed. Compared with other drill bits, the button bit has the characteristics of fast drilling speed, free tooth arrangement, unlimited diameter, and small regrinding workload.
The button bit is just like its name, its working surface is a spherical metal, and it is distributed on the entire surface of the bit like human teeth. That is to say, the button bit is composed of cemented carbide inlaid on the bit body. According to the connection form of the button bit with the drill rod, it can be divided into three types: taper button bit, threaded button bit, and down-the-hole drill bit.
Button bits are widely used, but in actual rock drilling, if the cemented carbide button embedded in the bit body falls off, its working performance and service life will be seriously affected, and this has a relationship with its fixing technology.
The fixing process of button bit refers to how to fix the rock-drilling cemented carbide button on the bit body so that it can play a supporting role to ensure that the carbide buttons won’t shift and fall off during the process of drilling the rock.
The fixing technology of button bit includes welding, cold pressing, hot pressing, cold inserting and hot inserting.
Welding
This is the earliest used fixing process. It is relatively simple, mainly determining the size of the perforation and the alloy button through the welding gap. According to the structure form of the drill bit, the corresponding perforation is drilled on the drill bit body, and then the alloy button is welded to the drill bit body by brazing or silver welding. At present, this process does not require high drilling accuracy and button size.
The disadvantages of this process are below:
A. Relatively difficult operation/The operation is relatively difficult.
B. Easily leave welding scars/It is easy to leave welding scars.
C. Prone to lack of welding, weak welding strength.
D. Shorter service life of drill bit.
E. It is mostly used in the production of taper holes to connect small-diameter button bits, which have now been phased out.
Cold pressing
Determine the processing size of the buttonhole according to the size of the carbide column buttons and the amount of interference, and drill and ream the corresponding buttonhole on the bit body. At room temperature, in the cold pressed fixing equipment by external force with interference fit method to force the carbide buttons into the buttonhole, using the force generated by the elastic deformation of the shell steel to fasten the carbide buttons.
Hot pressing
Determine the buttonhole processing size of the bit body according to the size and interference of the carbide column button, and drill and ream the corresponding buttonholes; when fixing the button, first heat the bit body to a suitable temperature (must be lower than that of the shell steel) annealing temperature to ensure that the bit body will not undergo softening annealing), and then press the carbide post button into the corresponding buttonholes by external force on the special fixing buttons tool, and cool to room temperature. The hot pressing buttons fixing method uses the elastic deformation force of the shell metal material to fasten the carbide buttons.
Cold inserting
This process is currently adopted by most enterprises. The main point of the process is to calculate the matching gap between the perforation and the alloy column according to the yield limit of the steel used for the drill bit body and use the method of interference fit to press the button into the perforation by an external force.
The characteristic of this process is below:
A. The process is easy to master and the production efficiency is relatively high, but the stability is lacking.
B. When the alloy button is pressed into the perforation, the bit body and the button are easy to be damaged under the action of external force, and the button bit life is limited.
C. It is easy to insert detached from the slot and insert shattered after a period of use.
D. It is mainly used to fix threaded button bits which are not required or repeated grinding now.
Hot inserting
Heat the bit body first and keep it warm for a period to allow the buttonholes to expand. The carbide button can be inserted into the corresponding holes by a slight external force and then cooled to room temperature on a slow cooling table.
The hot insert process is mainly used for the threaded button bit with higher requirements. Select the alloy steel with good thermal expansion and toughness as the steel for the drill bit body. According to the difference in thermal expansion between the steel body and the alloy button under the same heating conditions, it is easy to select the appropriate amount of interference. The alloy button is inserted into the perforation of the drill bit body, and the fixing process is completed after the steel body shrinks at room temperature after cooling. The hot insert fixing process is not only easy to operate but also has better stability because the force on the alloy button and the bit shell is very small during the fixing process, and it is not damaged.
The medium and large-diameter button bits are new products that were gradually developed and matured in the 1970s at home and abroad. Its fixing process, like some famous drilling tool companies, all use the “hot-clamping button” or “hot-pressing-fixing button” and the former Soviet Union adopts the “welding fixing button”, but the details of the process are unknown.
The submerged bottom induction brazing button fixing process is to ensure the welding quality, using the favorable conditions of perforation and capillary brazing, the groove bottom plate brazing method of the flake alloy drill bit has been evolved into the submerged bottom type of the button bit. Brazing button bits in this way is even more successful than brazing sheet-alloy bits.
Features:
A. The fixed button is firm. Soldering liquid fully diffuses under anaerobic conditions, which can form dense, uniform, and plump weeds;
B. The stress state of the alloy and steel body is good. The alloy cylinder only bears the small radial and tangential compressive stress generated by the condensation and shrinkage of the solder liquid, and there is no axial tensile and compressive stress. However, the cold-pressed button has huge radial, tangential, and axial stress states, and their distribution is uneven.
C. The properties of the alloy are unaffected.
D. Convenient operation, good quality stability, and high production efficiency.
E. It is easy to promote and has a quick effect.
For medium and large diameter button bits, Compared with the use of submerged bottom induction brazing fixing buttons, hot-clamping fixing technology has more advantages. Threaded medium and large diameter button bits are mainly used for heavy-duty rock drilling rigs to drill deep holes in hard and brittle or medium-hard rock layers. In this case, the button diameter is larger, the button pitch is larger, the steel body of the button wall is thicker, the button distribution is easier, the slag discharge condition is better, the abrasion of the steel body and the button is slower, and the button regrinding condition is better.
The advantages of the hot-clamping fixing technology:
A. The quality of the fixed button is better, and the phenomenon of a broken button is less likely to occur.
B. It eliminates the threat of the button surface being oxidized and subjected to excessive thermal stress or mechanical force that may be generated by the alloy button in other fixing methods.
C. It can calmly implement the best heat treatment specifications for the steel body and give full play to the use potential of the steel.
D. There is no flux flowing, and the appearance quality of the drill bit is good.
Disadvantages: Machining, heat treatment, testing, and gear matching processes are complex, the requirement is stricter, the quality of fixed buttons is not stable and the production efficiency is low.
Conclusion
The fixing technology and interference of the button bit influence its service life. The manufacturers of rock drill bits can reasonably choose one or two kinds of rock drill bits according to the rock drilling conditions, drill bit diameter, equipment conditions, and management level to improve the quality of rock drill bits and obtain excellent economic benefits.
