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Why does DTH hammer malfunction

Feb 29, 2024
DTH hammer can be divided into valve type DTH hammer and valveless DTH hammer according to the air distribution method. The main manifestations of DTH hammer failure are DTH hammer non-impact, weak impact and intermittent impact.

Reason 1: Processing Defects

The match between the DTH hammer piston and the cylinder liner is relatively tight, and the matching length is long, and the machining accuracy and surface smoothness are required to be high, which requires very high cylindricity of the piston and the cylinder liner. If the cylindricity is not guaranteed, the piston will have directional or intermittent sticking, and eventually the drill rod may have to be lifted and unloaded frequently for DTH hammer maintenance.
In addition, the rigidity of the outer casing of the DTH hammer is also an important factor restricting the service life of the DTH hammer. If its rigidity is poor, the DTH hammer will be deformed due to frequent collision with the borehole wall during the drilling process; when the DTH hammer is not working, it is often necessary to vibrate, disassemble and clean the DTH hammer, which will aggravate the damage of the outer casing of the DTH hammer. Deformation; and the deformation of the outer casing will cause the internal parts of the DTH hammer to be stuck and cannot be disassembled, which will eventually directly cause the DTH hammer to be scrapped.

Reason 2: The Backstop Seal of the DTH Hammer Tail is Unreliable

At present, the tail of DTH hammer is equipped with a check valve, and its structure is shown in the figure. The sealing form mainly relies on the compression deformation of the spherical rubber cap or the O-ring installed on the metal conical cap to carry out the backstop sealing. Its backstop function is realized by an elastic body, and the elastic body generally has a guiding device.

This sealing method has the following problems:
(1) There is friction between the spring and the guide device, which will affect the cut-off speed of the check valve;
(2) The frequent compression and friction of the rubber sealing material for a long time will cause excessive wear; (3) The spring is fatigued and damaged, resulting in the failure of the backstop seal;
(4) When the gas is stopped, the air pressure inside the DTH hammer suddenly decreases, causing the rock powder or liquid-solid mixture to flow back into the inner cavity of the DTH hammer, which will cause the piston to be stuck;
 (5) What is more serious is that the water carries the cuttings into the valve position (valve type DTH hammer), so that the valve plate can not close the gas distribution normally, resulting in the failure of the DTH hammer only to discharge the chips without impacting the work.

Reason 3: DTH Hammer Head Has No Seal

The dill bits on the head of the DTH hammer are all provided with an exhaust hole to communicate with the bottom of the well, and the dill bits and the DTH hammer are connected by splines, and the fit gap is large.
When a diving surface is encountered during the drilling process or cementing fluid needs to be added due to difficulties in well formation, there are a large amount of liquid and solid mixtures in the bottom hole and the gap between the well wall and the drill pipe. When the cementing fluid is used, the gas supply will be stopped again, so that the check valve at the end of the DTH hammer will be quickly closed. Clearance of spline sleeve. Then, the DTH hammer is like an empty water cup upside down in the liquid. The gas enclosed in the inner cavity of the DTH hammer will inevitably be compressed by the external liquid. More fluid in the hammer cavity. However, if too much water enters the inner cavity of the DTH hammer, some cuttings will be brought into the piston motion pair of the inner cavity, which greatly increases the stuck frequency of the piston.
At the same time, if the cuttings deposited between the piston and the contact end face of the dill bit cannot be removed for a long time, most of the impact energy of the piston will be absorbed by the cuttings and cannot be effectively transmitted down, that is, the impact is weak.

Reason 4: Dill Bit Stuck

The dill bit and the DTH hammer are spline fit, and the fit gap is relatively large, and the tail of many types of DTH hammerdill bit splines can expose the matched spline sleeve. If the debris is wet, it is easy to form a mud bag and stick to the dill bit. If this state is not improved in time, the mud bag will enter the spline fitting gap, which will affect the effective transmission of the impact power of the DTH hammer piston; more seriously, the dill bit and the spline sleeve may be stuck together.


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