Button bits are applied widely in rock drilling fields because of their advantages of free tooth arrangement and high rock-breaking efficiency. Once damage occurs during the rock drilling process, it will seriously affect the project. So the market has higher requirements for the button bit, and its manufacturing process is relatively complicated.
Fixing Tooth Technology of Button Bits
The fixing tooth technology is a critical factor affecting the quality and service life of the button.
The method of fixing the teeth of the button bit refers to how to fix the rock-drilling cemented carbide button on the drill bit so that they can play a supporting role and ensure that the drill bit does not fail due to displacement and dislodgement of the carbide buttons in the process of drilling the rock.
There are three methods of fixing the teeth of the button bit: welding, cold fixing, and hot inserting.
Welding
Welding is the earliest fixed tooth process, and its method is relatively simple. It mainly determines the size of the tooth hole and the carbide button through the welding gap, drills the corresponding tooth hole on the drill bit according to the structure of the drill bit, and then uses the method of brazing or silver welding enough to weld the alloy studs on the drill bit, and the requirements for drilling accuracy and stud size are not high. Its disadvantages are that it is relatively difficult to operate, it is easy to leave welding scars to affect the appearance, and it is prone to lack of welding, the welding strength is not high, and the life of the drill bit is low.
Cold Fixing
The main point of the cold fixing is to calculate the fit gap between the tooth hole and the carbide column according to the yield limit of the steel used for the drill bit and press the column tooth into the tooth hole by an external force using an interference fit. Its characteristics are that the process is easy to master, and the production efficiency is relatively high, but the stability is lacking. When pressing the carbide button into the hole, the drill bit and button are easily damaged under external force. The overall drill bit service life is limited, especially the late life is poor, easy to drop teeth, broken teeth, and other phenomena. It is applied to the threaded button bit with relatively low requirements or without repeated resharpening.
Hot Inserting
For the use of higher requirements of the threaded button bit, can use the hot inserting, that is, choose the thermal expansion and toughness are better carbide steel as drill bit steel, according to the steel and carbide column button in the same heat conditions, the difference in its thermal expansion, choose the appropriate amount of interference, you can easily set the carbide column button into the drill bit tooth hole, wait for its cooling to room temperature steel shrinkage that is to complete the solid tooth.
The hot inserting is not only easy to operate but also has better stability because the force on the carbide button and drill bit is very little during the process of tooth fixing and basically will not be damaged.
Basic Requirements of Steel for Drill Bit in the Hot Inserting
Drill bits are subjected to tremendous impact loads and abrasive wear when they contact and break the rock in the drilling process, and the conditions of use are very harsh, so the requirements for the steel used in drill bits are also particular. The basic requirements are high plasticity, toughness, and hardness in the heat-treated state; high fatigue strength and wear resistance; high air-cooled hardenability; and a simple and low-cost heat treatment process.
If the hot inserting is adopted, the steel for the drill bit must also have the following points:
1. In the heat treatment state, the hardness should reach the requirement of 40 ~50 HRC.
2. It has high-strength physical properties to ensure a high tooth-fixing ability.
3. It has a high-temperature strength and thermal stability to ensure its use of solid tooth strength.
4. High fatigue strength and wear resistance.
5. High coefficient of linear expansion and tempering stability.
6. It is easy to soften and anneal and has good dimensional stability and processability (processability includes cutting performance, hole performance, smoothness, etc.).
