Solutions to "Drill Deviation" and "Drill Jamming" of Down-the-Hole Drills
2013-07-10
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The KQJ100C down-the-hole drill is an open-air rock drilling equipment featuring a single power source, simple structure, easy operation, short auxiliary time, and light weight. It is most suitable for complex terrain where transport equipment cannot reach. By adjusting the position of the upper and lower support rod groups (fixed with pins after adjustment), different drilling angles can be achieved. The machine can drill holes within a 90-degree range, and with reasonable technical measures, horizontal drilling can also be realized.
I. The first problem encountered in use is the "drill deviation" phenomenon during drilling.
Since the diameter of the drill bit-impactor assembly is larger than that of the drill rod and its length is relatively long, the distance from the drill bit to the rod guide is considerable, and the drill rod has certain elasticity, the "drill deviation" phenomenon is very likely to occur when drilling on irregular rocks, i.e., the rock hole deviates from the axis of the drilling machine. If drilling continues under such circumstances, the drill rod will bend, and even "drill stalling" may occur, making the drilling machine unable to work and causing serious damage to the machine itself.
To solve this problem, we conducted careful research based on the working principle of the drilling machine and designed a drill bucket support positioner, which was installed on the two support legs at the front end of the drilling machine. Practical use has proven that the positioning effect is good, and the "drill deviation" phenomenon has been well resolved.
II. The second problem encountered in use is the "drill jamming" phenomenon.
In relatively broken rock conditions, regardless of the drilling angle, the "drill jamming" phenomenon will be quite serious, especially during drill lifting (or retracting). In severe cases, it may take several days to withdraw the drill bit, seriously affecting construction.
Cause analysis of drill jamming
Since the diameter of the drill rod is smaller than that of the drill bit-impactor assembly, the broken stones on the hole wall, after drilling, collapse under vibration and gravity and settle at the bottom of the hole due to the space created. When lifting (or retracting) the drill, or when the drill bit moves upward (or to the right), it drives the broken stones to move backward together. As the drilling distance increases, the accumulation of broken stones increases, and at the same time, under the action of the conical surface of the connecting rod, an increasing squeezing force is generated, ultimately causing the drill bit to be stuck in the hole.
Treatment methods for drill jamming
The "Operation Manual" of the KQJ100B down-the-hole drill states: "...at this time, only by applying external torque or using auxiliary tools to help lift (or retract) the drill, making the drilling tool rotate, and then lifting the drilling tool while supplying air, until the fault is eliminated." The method described in the manual is only effective when the drill jamming is not too severe; it is difficult to solve when the jamming is severe and consumes a lot of time.
It is known that in severe cases of drill jamming, for a hole 6-7 m deep, the drill lifting time may be as short as three to four days, or as long as six to seven days.
To solve the above problem that seriously affects construction progress, based on careful analysis of the fault causes, we adopted a reverse-thinking approach according to the drilling principle and found an effective solution. That is, inlay hard alloy blocks on the conical surface of the connecting rod between the impactor and the drill rod, and distribute them in a staggered manner, so that when the drilling tool is lifted (or retracted), the lifting force and rotational torque of the drilling tool shear and hone the broken stones into rock powder, achieving reverse drilling. In this way, the drill can be lifted (or retracted) smoothly, and the wear of the broken stones on the impactor casing can be reduced, extending the service life of the impactor by more than two times.
After trial use, this method is practical and feasible. The drill lifting (or retracting) time has been shortened from several days to 15-20 minutes, increasing the efficiency of drilling in broken rock formations by nearly a hundred times.
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