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Analysis of the damage causes of the main parts of the hydraulic rock drill

From： Hunan ZEGA Date：2019-04-24 15:27:35 Hits：784 Belong to：Company News

First, the accumulator end cover crack

Cracks generated by accumulator end covers, cracks are caused by the following three aspects:

First, the method of checking the pressure of the accumulator is improper. The pressure of the accumulator should not be checked too frequently, because it is easy to cause nitrogen leakage in the accumulator air bag during inspection. The accumulator operating at low charging pressure will result in excessive impact from the hydraulic oil. This impact force acts on the accumulator end cap, which can cause cracks in the accumulator end cap.

Second, the nitrogen-filled pressure valve has not been replaced. When the accumulator is overhauled, the nitrogen-filled pressure valve should be replaced. This is because the sealing surface of the old nitrogen-filled pressure valve will wear out after frequent opening and closing for a long time. Wear of the sealing surface of the nitrogen-filled pressure valve can cause nitrogen leakage in the accumulator air bag, which in turn causes cracks in the accumulator end cover.

Third, the tightening force of the accumulator end cover is too large. Failure to tighten the accumulator end cover according to the specified torque can cause additional stress inside it, resulting in early cracks.

Second, the rinse head is ruptured

The flushing head is made of high-strength, corrosion-resistant steel and its role is to keep the water seal in place and support the stop ring. The reasons for its rupture are as follows:

The first is a missteering. After analyzing a number of cases of flushing head rupture, it was concluded that the main reason for the rupture of the flushing head was that the hydraulic rock drill manipulated the impact action without propulsion, especially when the high impact or reverse propulsion (counterattack) was easy to cause the flushing head to rupture.

Second, the rinsing head is corroded. Since the material used to make the flushing head cannot combine high strength and good corrosion resistance, if the flushing water used is acid-alkali corrosive, the flushing head will be corroded. This corrosive action can cause cracks in the rinse head.

Third, the front end is corroded. A flushing head is installed inside the rock drill front end, and if the front end is corroded, the flushing head moves forward. After the flushing head is displaced, the reaction impact force generated by the rock drill is transmitted to the connecting plate through the stop ring, causing the stress to be concentrated around the orifice at the front-end connecting plate. Because the connecting plate is the part that connects the flushing head, stress concentration is easy to cause cracks in the flushing head.

Third, the front end crack

The

front end of the hydraulic rock drill is equipped with a precursor sleeve and a flushing head to withstand all the loads transmitted by the brazing tail. The reasons for its rupture are as follows:

First, operational errors. The rock drill maneuvers the rock drill for a long time to impact the machine in the case of low propulsion, no propulsion or reverse propulsion (counter-fight). At this time, the impact force of the impact piston is transmitted to the front end through the stop ring and the flushing head, which can cause cracks in the front end.

The second is internal corrosion of the front end. If corrosion occurs inside the front end, the hydraulic rock drill will cause stress concentration in the corrosion part during operation, resulting in cracks at the front end. This crack extends over time until it breaks completely.

The third is flushing water corrosion. If the hydraulic rock drill uses corrosive flushing water, corrosion will occur at the front end, and stress concentration will form in the corrosion area, resulting in cracks at the front end.

Fourth, the impact piston guide area is damaged

The most common problem with impact pistons is damage to the guide area, causing the piston and guide sleeve to jam. The causes of its damage are as follows:

First, there are pollutants. The damage caused by contaminants in the impact piston guide area includes: after the hydraulic oil is contaminated, the contact between the impact piston and the guide sleeve is not good; There are contaminants between the sealing chamber and the rear end cover or impact piston guide sleeve, resulting in poor neutralization of the impact piston. The above damage causes the local surface temperature of the piston to rise sharply, resulting in microscopic thermal cracks on the surface of the impact piston. This crack continues to propagate inside the impact piston, eventually causing the impact piston to break.

Second, the bolt tightening force is unbalanced. The bolts on both sides of the rock drill are damaged or the tension force is unbalanced, and the tightening force of the rear cover bolt is unbalanced (the bolt is not re-tightened during the specified maintenance period), which can cause the coaxiality of the connection of the rock drill components to decrease, and the impact piston impact force is not transmitted along the straight line, which can eventually lead to the jamming or damage of the impact piston guide area and the guide sleeve.

The third is the corrosion of the meshing surface. The meshing surface of the guide sleeve and the piston corrodes, resulting in increased friction during piston impact operation, resulting in premature damage of the impact piston guide area and guide sleeve.

5. Impact piston cavitation

The

pistons of hydraulic rock drills are subjected to impulse forces, which often cause cavitation when impacting the surface of the piston front and rear drive areas, as well as in the piston sealing area. The causes of cavitation are as follows:

First, the propulsion pressure is too low. Hydraulic rock drills operate at low propulsion pressures for long periods of time, which can lead to cavitation of impact pistons. When the propulsion pressure is too low, the buffer piston is forced to move forward, and the impact position of the impact piston is forward, so that the stroke of the impact piston becomes longer and the impact frequency is reduced. Because the reversing time of the reversing valve has not changed, the reversing time of the impact piston does not match the reversing time of the reversing valve, resulting in instantaneous high pressure, which can lead to cavitation of the impact piston.

Second, frequent reverse propulsion (counter-fighting) of the hydraulic rock drill, too low or too high nitrogen pressure in the accumulator air bag and damage to the accumulator will accelerate the cavitation wear of the impact piston. For example, when the nitrogen pressure of the accumulator is too low, the buffer capacity of the buffer piston is reduced, and the impact piston pulse is not buffered, which increases the hydraulic oil pressure sharply, which can cause the impact piston gas candle.

6. The sealing surface of the impact piston is damaged

Damage to the sealing surface of the impact piston

is usually caused by the seizure between the piston sealing area and the cylinder block. Since the bite between the steel parts in this part can cause the impact piston to get stuck, the impact is stopped before the impact piston breaks completely. There may be two reasons for the impact piston to die: First, there are impurities in the hydraulic oil, or the impurities enter from the outside of the rock drill to the impact piston and the cylinder block. The second is that the tightening torque of the side bolt is wrong, resulting in poor neutrality, or the impact piston guide sleeve is worn.

7. The impact end face of the impact piston is damaged

Impact piston impact end face damage is usually caused by:

(1) Salt corrosion: If the hydraulic rock drill is placed in a salty environment for a period of time, even if it is not running, the metal will be attacked by salt, the fatigue strength will be reduced by two-thirds than normal, and the piston will be damaged after a few hours of normal impact. Impact pistons cannot withstand salt moisture, and the only way to extend piston life is not to allow saline moisture to enter the rock drill.

(2) Corrosion damage: If corrosive liquid enters the piston surface and tail when the rock drill is running, the piston impact end face will form a corrosion groove. Grooves can cause fatigue cracks that eventually lead to piston breakage. If the damage to the piston is not very serious, the piston can be ground.

8. The rotating bearing is seriously worn

The preload of rotating bearings should be appropriate, if the preload is too small, the bearing balls will deviate from the raceway and cause bearing damage. Rock drills with simple cushioned pistons, such as the COP1032/1238/1440 rock drills, are particularly sensitive to low preload of rotating bearings. The buffer piston of these rock drills strikes on the rotating bushing, causing vibrations that cause the bearing balls to deviate from their raceways and cause the housing to be deformed and, in the circumference, to rupture the rotating bearing. Excessive preload force causes excessive friction on the bearing, which can lead to premature bearing wear. When assembling rotating bearings, bearing preload tests must be performed.

9. The rotating bushing is damaged

The rotating bushing transmits the reaction force of the impact from the brazing tail to the cushioned piston. There are usually 2 reasons for damage to rotating bushings:

(1) Insufficient lubrication, adequate lubrication is a necessary condition for the rotating bushing to maintain good performance. High propulsion and large bore drills require enhanced lubrication. Discoloration around the end face of the rotating bushing is caused by insufficient lubrication, which can lead to rupture of the rotating bushing and damage to other parts of the rock drill.

(2) Fatigue damage rotating bushing is a wearing part, generally under impact conditions after working for 400h should be replaced to prevent damage to other parts due to fatigue damage of rotating bushing.

10. The side bolts are damaged

Side bolts are

used to assemble the individual parts of the rock drill together, and the side bolts are subjected to the impact forces caused by severe vibration during the rock drilling process. In order to avoid fatigue failure, the side bolts must be tightened according to the process requirements. There are two reasons for the damage of the side bolts: First, the bolt tightening torque is not checked within the specified interval. Second, there are impurities between the nut and the bolt, or thread corrosion leads to seizure. In the case of thread corrosion, even if the side bolts are tightened according to the tightening torque, insufficient tightening force will not be generated. Indentations, corrosion points on threads can lead to cracks, which can lead to fatigue failure of side bolts. The side bolts are severely rusted or cracked and should be replaced. Side bolts, nuts, and gaskets should be replaced with each overhaul to prevent secondary damage. Do not mix old and new bolts.

11. The stop ring is damaged

Common

causes of damage to rock drills are caused by severe backlash, low propulsion or no propulsion. When the piston drives the brazing tail to its front position, the piston will have some residual impact force, and these residual impact forces will act on the stop ring. Backfighting, low propulsion or no propulsion force can cause accelerated wear of the stop ring. The stop ring must be checked when replacing the brazing tail, and must be replaced if it is damaged or worn by more than 1mm. The stop ring is a wearing part, in order to avoid damage to related parts (such as buffer pistons, brazing tails) caused by fatigue damage of the stop ring, it is generally necessary to replace the new stop ring every 400h impact.

12. The drive sleeve is worn

The most common fault symptom of drive sleeves (triangular sleeves, quadrangular sleeves) is premature wear. Drive sleeve wear is usually caused by the following 4 reasons: First, there is no lubrication or insufficient lubrication. Second, the model of the lubricating oil is not correct. Third, the borehole diameter of the borehole is larger than the size designed by the rock drill. Fourth, the drive sleeve is overheated. Overheating of the drive sleeve can cause the brazing spline area to break. In addition, the internal rack of the drive sleeve is damaged and the front guide sleeve is seriously worn, which will cause the drive sleeve to crack, and the excessive gap between the drive sleeve and the rotating bushing will also cause the drive sleeve to crack.

13. Buffer piston cavitation

Sometimes cavitation of the buffer piston is usually due to damage to the accumulator diaphragm or incorrect nitrogen filling pressure. The resulting flow wave creates cavitation on the buffer piston.

Cavitation of the buffer piston is usually due to a broken accumulator diaphragm or incorrect nitrogen filling pressure. The resulting flow fluctuations create cavitation on the buffer piston.

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