Button bits demonstrate their unique superiority in mining, quarrying, water wells, construction, and other areas. The carbide buttons inserting of button bit is crucial, being a significant factor affecting the quality and lifespan of the button bit.

There are three methods for inserting carbide buttons: copper brazing, cold press, and hot press.

1. Copper Brazing:

Copper brazing is the earliest way of inserting carbide buttons, primarily determining the size of the hole and the carbide button based on the gap during brazing. According to the bit skirt structure, corresponding button holes are drilled into the bit skirt, and then the carbide buttons are welded into the bit skirt using copper or silver welding techniques.

This method does not require high precision for the drilling or button size. During brazing, the brazing material is placed at the bottom of the carbide button, with some flux sprinkled on the carbide button surface. The brazing material diffuses fully in an oxygen-free condition, forming a dense, uniform, and full weld. The hole only bears the radial and tangential stresses caused by the condensation shrinkage of the weld, with no axial tensile or compressive stress. Additionally, this layer of brazing material can delay the impact during rock drilling, thus avoiding the disadvantages of interference fit.

However, the high temperatures during welding impose thermal stresses, potentially causing defects and micro-crack propagation in the low cobalt alloy, as well as reduced hardness  (by HRC  0.5-0.8 ) and bending strength (by 8%-20%) of the carbide. The formation of an oxide layer on the surface of the alloy button makes the carbide button prone to fracture.

Currently, this method is mainly used for single used button bits, such as blast furnace tapping bits and anchor bits.

2.  Cold Press V.S Hot Press

Cold press and hot press both utilize interference fit to fix the carbide buttons, and the interference is generally between 0.04mm and 0.08mm. Factors influencing the interference include, but are not limited to:

1. Drill bit skirt material;

2. Heat treatment process of the skirt;

3. Diameter of the carbide buttons;

4. The equipment for inserting carbide buttons into the bit skirt.

Cold press is done at room temperature, without the need to heat the button bit, directly using a hydraulic hammer to press the carbide buttons firmly into the button bit.

This process has a lower production cost but lacks stability.

Improper selection of interference can significantly increase the pressing force, sometimes causing the carbide and the hole to be damaged. Even with appropriate interference, the tangential, axial, and radial stresses experienced by the carbide button under heavy loads can accelerate the expansion of existing defects, leading to premature damage to the carbide buttons.

The overall lifespan of cold pressed button bits is limited, particularly in the late drilling stage of button bits, and issues such as buttons popping out or breakage are common.

Cold pressed button bit is generally used for softer, less abrasive rock formation, and higher-end anchor bits often utilize this method.

Unlike cold press, the hot press process takes advantage of the principle of thermal expansion and contraction. It involves heating the bit skirt to a certain temperature, typically between 200°C and 500°C, to expand the diameter of the button holes. Then, the carbide button is inserted into the hole and physically contracted to tightly integrate the buttons with the bit skirt.

This method does not necessitate pressure, or only minimal pressure, thereby avoiding or reducing the impact on the performance of the carbide buttons, making it more effective in maintaining the original properties of the carbide buttons.

Hot press is currently the best and mainstream method for inserting carbide buttons. Hot pressed button bits have better wear resistance, higher hardness, and superior stability, suitable for very hard and highly abrasive rock formation.

As the leading exporter of rock drilling tools in China, Sinodrills’ threaded button bits and down-the-hole button bits are all hot pressed, offering long service life, greater wear resistance, and excellent stability!