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Reasons for the decline of hydraulic motor performance

Reasons for the decline of hydraulic motor performance

Company News
Release time:
2016/04/14 01:03
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(1) Hydraulic motor wear
The WTZ-150 and WTZ-200 series drilling rigs are mainly equipped with 6K-195 and 6K-310 hydraulic motors. After disassembly and inspection, it was found that the friction surface of the hydraulic motor valve disc and the valve disc was seriously worn, and the deepest point of the wear was 0.15 mm; the output shaft oil seal leaked oil.
(2) Reasons for the wear of the valve plate
From the working principle of this hydraulic motor, it can be known that the valve disc and the cycloid rotor are connected and rotated together by a small linkage shaft, and at the same time, the valve disc makes a sliding rotation on the valve disc. The reasons for the excessive wear of this friction pair are as follows:
When the new hydraulic motor is just installed, the hydraulic surface of the motor housing is not filled with hydraulic oil, which causes the friction surface of the friction pair to lack sufficient lubrication and cause wear. Especially at the beginning of the work, a large load is applied, which aggravates the wear of the valve plate.
The failure of the filter element of the hydraulic system makes the hydraulic oil mixed with particulate impurities. Small particles enter the friction surface during the rotation of the valve plate, causing abrasive wear on the friction surface.
The friction surface of the valve disc and the valve disc is deteriorated due to the wear roughness, which increases the storage space for impurities between the friction pairs. The particles entering the friction surface and the ground metal particles rotate with the valve disc, which aggravates the wear.
Due to the wear between the valve disc and the valve disc, the hydraulic oil creates a gap between the inlet and return passages and communicates. Under the action of high pressure, the sealing, cleaning and heat dissipation performance of the hydraulic oil is reduced, and the oil temperature is increased. abrasion.
(3) Reasons for the weakness of the hydraulic motor
According to the analysis of the reasons for the wear of the valve plate, the main reasons for the weakness of the hydraulic motor are as follows:
Due to the wear of the valve plate, the inlet and return oil channels are connected at the valve plate, part of the high-pressure oil is discharged, the oil pressure flowing through the fixed rotor pair drops, the flow rate decreases, and finally the output speed and torque of the motor decrease.
Due to the wear of the valve plate, its relative position in the valve body changes, and the preload and fitting force between the valve plate and the valve plate by the spring on the valve body is reduced, which aggravates the leakage of hydraulic oil and reduces the performance of the hydraulic motor.
As the temperature of the hydraulic oil increases, its comprehensive performance decreases, and its ability to drive the cycloidal rotor to rotate further decreases.
After inspection, it is determined that there is no obvious wear on the joint surface of the rotor pair and the bearing housing and the valve disc matched with both sides thereof. Movement is normal without stagnation and will not cause performance degradation.
(4) The cause of oil leakage of the output shaft oil seal
After the disassembly test, the axial and radial clearances of the output shaft meet the standard, and there is no obvious wear on the matching surface of the output shaft and the oil seal. However, it was found that the aging rubber hardened and the elasticity became poor. After the lip of the oil seal is worn, the preload and the performance of the oil seal decrease. Excessive oil temperature accelerates the wear of the lip of the oil seal. In addition, due to the internal leakage of the hydraulic motor, the back pressure in the casing is too high, which causes the lip of the oil seal And the oil leakage has further intensified.
Repair method
From the above analysis, we can know that as long as the matching relationship between the pair of friction pairs of the valve disc and the valve disc is restored, the performance of the hydraulic motor can be restored. And matching the appropriate output shaft oil seal can eliminate the oil leakage of the hydraulic motor.
(1) Repair of valve plate
After cleaning the valve plate, blow it clean with compressed air. Use the outer diameter micrometer or dial gauge to measure the thickness h1 and the amount of wear of the oil distribution plate where there is no wear (measurement h1 is to provide a basis for adjusting the spring force of the pretension spring of the distribution plate).
Due to severe wear of the valve plate (0.10 mm ~ 0.15 mm), if manual grinding is more laborious, it is decided to use a surface grinder for grinding. When grinding, use the end surface of the oil inlet side of the flow plate as the reference surface, and select 60 # white corundum grinding wheel for grinding.
(2) Repair of valve disc
The grinding requirements of the valve disc and the valve disc are the same, except that the amount of grinding is not large, and there is no need to measure its thickness. When grinding the valve disc and the oil distribution disc to form the coupling surface of the friction pair, the symmetrical surface is the grinding reference plane.
Due to the local paint on the outer surface of the valve disc and the unevenness of the edges caused by external forces, it affects the accuracy requirements of the polished surface. Therefore, it should be cleaned and trimmed before grinding. If possible, the exposed part can be chamfered by 45 ° (width 1 ~ 1.5mm), and then the flatness inspection should be performed. The flatness of the grinding reference surface should be ≤0.01mm. After ensuring that the reference surface meets the requirements, the symmetrical end surface should be ground.
(3) Optional output shaft oil seal
The output shaft oil seal of ETN 6K series hydraulic motor adopts frameless spring seal (VC type). The initial preload of the oil seal is generated by the interference between the rubber material and the shaft. When the lip of the oil seal or the shaft wears, the sealability decreases and oil leakage occurs. This is the main reason for hydraulic motor oil leakage. ETN 6K series hydraulic motors are manufactured according to the product design and manufacturing technology of EATON company in the United States, and the product size adopts the British standard. By measuring the journal, the base hole of the oil seal installation and the thickness of the oil seal, the size of the journal is φ44.43 mm, the size of the base hole of the oil seal installation is φ 63.5 mm, and the thickness of the oil seal is 4 mm.
Oil seals are consumable parts. Oil seals made in British standards are not easy to purchase and have a long lead time. In order to improve the maintenance performance and general performance of the output shaft oil seal, it was decided to follow the principle of no or little change in size, and change it to metric standards to ensure its original performance and strength.
The crude oil seal adopts VC (that is, a single lip outer rubber skeleton without spring oil seal) type, which has poor sealing performance and short service life. According to the working condition and structural size of the hydraulic motor, it can be replaced by SC (single lip with spring outer rubber inner skeleton oil seal) or SB (single lip with spring outer iron shell skeleton oil seal) type oil seal, these two types of oil seals are better than VC type oil seals Good sealing effect and long service life.
The choice of oil seal material is determined by the compatibility of its work, the adaptability of the working temperature range and the follow-up force of the lip on the rotating shaft. Generally, the temperature of the lip is 20 ~ 50 ℃ higher than the temperature of the hydraulic oil, and the linear velocity is less than 15 m / s. Commonly used sealing materials are nitrile rubber, rubber-plastic compound, fluororubber, silicone rubber, polypropylene rubber, ethylene propylene rubber, polytetrafluoroethylene, nylon, polyoxymethylene, neoprene, fluorosilicone rubber and polyurethane.
The maximum speed of 6K-195 hydraulic motor is 866 r / min, the size of the matching surface of the output shaft and the oil seal is φ44.43 mm, and its maximum linear velocity = C × n / 60, where C is the circumference of the journal and n is The maximum speed of the shaft.
Maximum linear speed = C × n / 60 = 44.43 × 3.14 × 866/60
= 2013.6 mm / s
≈ 2 m / s
The normal operating temperature of the hydraulic system is 82 ℃. Due to the decline in the technical performance of the hydraulic system during the later use of the drilling rig, and the impact of hydraulic component failure on the temperature rise of the hydraulic oil, the value of the working oil temperature should be increased by 20 ℃. The temperature of the lip should be higher than the temperature of the working medium by 20 ~ 50 ℃ (the maximum value is 50 ℃), and finally the tolerance temperature of the oil seal lip is determined to be 152 ℃.
Based on the above analysis of the working environment of the oil seal, comparing the performance of various sealing materials, the oil seal material decided to choose fluororubber.
The output shaft journal size is ground from the original φ44.43 mm to φ44 + 0.05 mm, and the diameter of the oil seal seat hole is turned from the original φ63.5 mm to 64 mm. Due to the wide margin of the oil seal installation position, the thickness of the oil seal is set to 8 mm. All data (see the attached table) is selected as an integer, which is conducive to the choice of oil seal.
The whole output shaft is quenched and quenched and tempered. After grinding, the hardness of the sealing oil and the mating surface exceeds 30HRC (generally, the surface hardness of the rotating shaft is required to be 30 ~ 40HRC).
According to the above analysis of oil seal selection, it is decided to choose SC or SB type, φ44 × φ64 × 8 fluororubber oil seal to replace the original VC type oil seal. The interference between the outer diameter of the oil seal and the seat hole and the interference between the lip of the oil seal and the journal are determined by the manufacturer according to relevant standards.
(4) Assembly and test of hydraulic motor
When assembling the 6K-195 cycloid hydraulic motor, in addition to assembling according to regulations and requirements, when installing the valve plate, the thickness Δh (Δh = h1-h2) should be installed in the three preload spring seat holes of the valve plate The steel adjustment gasket ensures the pre-tightening force between the valve disc and the valve disc.
After repairing the hydraulic motor, inject 100 mL of T46 # anti-wear hydraulic oil into the inlet (outlet) ports, and rotate the output shaft several times in both directions. The rotation is smooth without card lag. Keep one port open for air and the other oil Compressed air of 0.6 ~ 0.8 MPa is introduced into the port to drive the hydraulic motor to test run. After the trial operation is normal, the hydraulic motor completes the repair work.
(5) Effects and benefits
Using the above repair methods, a total of 14 hydraulic motors of 6K-195 and 6K-310 types have been repaired. They have been used normally and have been working continuously for more than 3 months, extending the life cycle of old hydraulic motors. The maintenance cost of a single hydraulic motor is less than 300 yuan. If a new hydraulic motor is replaced, it will cost about 6,000 yuan. These 14 hydraulic motors alone will save more than 70,000 yuan, and have achieved obvious economic benefits for the unit.
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