Rolling process is widely used to shape tricone bit in China. The advantages of this process are high production efficiency and full use of raw materials; The internal structure of the borehole is characterized by fiber continuity, fine grain, uniform distribution of carbides, and high red hardness. But the rolling process also has obvious defects, that is, the borehole is easy to crack. Under normal circumstances, the bit cracking rate is 5 to 10 percent, sometimes as high as 20 to 40 percent, which can cause companies to lose hundreds of millions of yuan every year just because of the bit cracking.
A number of factors contribute to the tricone bit. A tricone bit can be cracked and used in different ways to reduce bit cracking rates for different reasons. However, the results of the existing methods are not ideal and cannot solve the cracking problem fundamentally. More than 98% of the fractures were found to occur at the intersection of marginal zones and marginal grooves. It can be seen that the crack generation is directly related to the blade band formation. The common rolling process is to roll the edge grooves of the drill bit simultaneously on the four high mills. The edge and edge band, that is, the rolling groove and the rotation are synchronized.
Tricone bit production technology.
During the rolling groove and grinding process, the original four-height mill can still be used, but the cross-sectional shape of the backplate with two blades is changed, that is, the blade without blades. At this point, the function of the fan plate on the back of the double blade is only used to hold the shaped tricone bit. And adjust the charge of the blade. Two rolling processes with four high mill passes are shown below. As can be seen from the image, when the groove rolling and post grinding process is used, cracks in the edge band are avoided because there are no grooves in the fan plate on the edge and the shape of the inset triad bit is simple.
The reasons for cracks are as follows: when rolling slots and rolling back, the width and depth of slots on the blade backplane are different due to the different sizes of the bit frame. Generally, the width is 0.45 ~ 0.95 mm, and the depth is 0.55 ~ 1.15mm. During hot rolling, the drill hole is heated to a near molten state under the action of sector plate rolling, flows along the grinder and extends, and the metal flowing into the groove of the edge band forms a bit edge band. However, the narrow groove of the blade makes it difficult for the metal to flow smoothly, so it is prone to blade defects. Especially when the billet is cooled, narrow and high edge bands are located at the edge of the billet, which is the fastest cooling rate and easy to produce stress concentration. Due to the influence of material, heating temperature, time and speed, machining accuracy of sector plate, it is easy to produce cracks in the edge zone. With groove rolling and post grinding processes, the mill can be avoided by simple, reasonable construction, and satisfying metal flow characteristics.
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