Imported hydraulic pump online status monitoring and predictive maintenance

In the metallurgical industry introduced complete sets of equipment, most of its hydraulic station configuration Germany Rexroth, the United States Pike and other countries in Europe, the United States, Japan and other countries to produce high-pressure, high flow hydraulic piston pump unit. After the equipment is put into use, there is no corresponding technical manual of the hydraulic plunger pump when importing, and there is no understanding of the on-line monitoring method and maintenance method of the pump and the soft service life. (Soft life → is the service life limit stipulated in the equipment design). Therefore, some domestic enterprises equipment managers believe that: foreign hydraulic plunger pump performance, long service life, as long as the hydraulic pump is running, the system pressure can be achieved, you do not have to overhaul, there is no establishment of the corresponding hydraulic pump site points Inspection rules and regulations, resulting in the import of hydraulic piston pump management errors. Imports of hydraulic piston pumps and machinery and equipment, are the terms of service. The length of service depends on the cleanliness of the hydraulic medium and the proper monitoring, maintenance and servicing of the equipment during operation. This article mainly discusses pump on-line testing, predictive maintenance, maintenance, replacement and adjustment.

Imported hydraulic piston pump (referred to as pump) three stages of wear

Imports of hydraulic pump wear is divided into initial wear, normal wear and tear, abnormal wear three stages.

1.1 The initial wear stage: pump parts in the manufacturing process, parts of the metal surface has a certain degree of microscopic roughness (surface roughness) of the shaft or hole there is ovality and not straight, the initial relative movement of the metal surface, the pump parts Relatively high-speed movement, this time there will be a slight friction between the friction pair wear and tear, parts in the initial wear stage.

1.2 normal wear stage: After a period of running-in, the friction between the generation of new, higher precision level of roughness, wear slow down. Enter a relatively long period of stable use.

1.3 abnormal wear stage: In this stage, the metal material life cycle fatigue life expectancy, the metal surface will have a fatigue layer, the fatigue layer in the special conditions of the pump high temperature and pressure, the metal surface prone to granular shedding, therefore, abrupt wear Growth, the final failure of the parts.

1.4 Pump in the relative movement of the movement of the three pairs of friction (hydrostatic bearing) wear between parts so that the gap between the parts increases, the pump will increase the amount of leakage, the oil temperature also increased accordingly. Pump soft life is from the initial run-in period to stable use phase and then to the fatigue spalling stage (severe wear stage). The length of time in these three phases mainly depends on the cleanliness of the hydraulic medium used.

1.5 Affect the pump's soft life There is another decisive factor is the pump bearing life. Because the bearing in the pump housing axial load rotation, the three friction within the pump housing (1 cylinder with the flow and face plate; 2 plunger rod and cylinder bore; 3 slipper and swash plate) high-speed friction and rotation parts, metal Surface relative movement, the metal contact friction with the metal, bonding and cutting occurs, and due to local high temperature, causing large-size metal oxide particles fatigue spalling, exfoliated metal particles can not be discharged outside the pump housing and accumulate in the hydraulic pump housing . Due to the pump housing full of hydraulic oil, the deposited metal particles and hydraulic oil mixed together with the rotation of the pump spindle and the cylinder swirl drift in the shell, resulting in increased wear and tear pump bearings. After the bearing wear to a certain extent, the clearance increases. After the bearing clearance increases, the precision of the relative movement between the cylinder and the valve plate can not be guaranteed, so the hydrostatic pressure between the three pairs of friction pairs of the pump is also damaged The balance of the hydrostatic bearing is destroyed (three pairs of friction pair) will accelerate the wear and tear.

The bearings have a basic nominal service life, even when the hydraulic medium used meets the cleanliness standards. Bearing rated life is divided into (1) nominal life rating; (2) revised rated life; (3) in-depth calculation of the rated life.

Pump bearing basic rating life refers to a sufficiently large group of 90% of the same type of bearings in the fatigue symptoms reached or exceeded the first life expectancy. The basis for rating life calculations, consistent with ISO 281, is the fatigue theory of Lundberg and Palmgren, which takes into account many factors including the fatigue limit of the material, the lubrication, the interdependence of the load and lubrication gaps, and the frictional characteristics and load distribution of the bearing, Other factors should be considered in the calculation of the basic rating life, such as the effects of lubrication and contamination. However, if there are more than 10μm metal particles in the fluid wear and tear factors, it can not be accurately calculated. The theory in the case of abrasive wear, usually give a final rated life value. Hydraulic piston pumps use INA Roller Bearings. FZG test to achieve at least wear-resistant grade 10, cleanliness NAS1638 level 8, with β ⒑? 100 filter hydraulic oil bearing soft life.

2, under special circumstances hydraulic plunger pump bearings

2.1 In a hydraulic system operating in a flammable environment at high temperature, a flame-retardant HF (H: Hydraulic fluid: F flame-resistant flame retardant) hydraulic medium is used. For example, the hydraulic medium used in steelworks is HFC "water glycol" working fluid, which has poorer viscosity / temperature characteristics than mineral oil based hydraulic fluid. HF fluids are also less capable of removing air and dirt, and their lubricating properties are far from mineral oil-based hydraulic fluids. Therefore, the technical data of E-series hydraulic piston pumps and motors produced by Rexroth AG in Germany have been adjusted. For the HF working fluid, Features Special bearings with "RR" coating on bearings used in piston pumps. (Bearing Rrcorrotect Corrosion Resistant Coating) However, the service life of this "RR" coated bearing is lower than 50% of mineral oil based hydraulic fluids. (HFD anhydrous oil, phosphate is not in this range)

2.2 on behalf of the SL model is a German company Rexroth for long-term work under high pressure environment and designed a heavy-duty long life pump, SL model is the use of long-life heavy-duty bearings with static pressure balance bearings, and the standard model pump phase Than, "SL" model pump has a longer life, the pump can be long-term work under high pressure. At 31.5MPa, the nominal number of revolutions and the oil viscosity of 36m? / S soft life of 10,000h hours. This pump has a U-port designed to flush the bearings.

3, the factors that affect the pump life

3.1 bearing wear and tear is the impact of soft pump life determinants of pump bearings in the specific operating conditions and the specific axial load friction torque of the special bearings. For example, the German Rexroth A4VSO type straight shaft swash plate pump bearings are Sweden INA Bearing Company Rexroth pump specially designed for such bearing rolling contact area Hertz pressure and bearing surface area with the ordinary bearing a great difference , The difference between it and the ordinary bearing is the special load condition of the pump bearing for the working status of the pump. The logarithm curve of the cylindrical roller bearing is used to modify the roller Special load-bearing roller bearing inner ring and roller contact surface of the symmetrical indexing curve of the special roller bearings.

Piston pump working pressure reaches the peak pressure, which is distributed in the cylinder bore 360 ​​° Cylinder of the nine plungers only four in the discharge port of the pump to compress the high-pressure oil generated partial Load reaction force is applied to the front of the spindle cylindrical roller bearings 160 ° area, this phenomenon so that the spindle bearings to withstand the partial load generated by the deformation and multi-wave peak sudden impact load force, the role of these two external forces , Bearing inevitably there is concentration of the boundary stress that "partial load edge effect", which is bound to reduce the bearing life rating, but also affect the soft life of the pump.

3.2 oil pollution, mainly caused by man-made pollution, when the replacement of the hydraulic filter cartridge did not drain the oil or do not discharge the oil inside the cartridge on the replacement filter, resulting in the cartridge of pollutants From the outlet of the cartridge flows directly into the tank. When a 10μm particles into the pump, it will cause the distribution of a scratch, when the scratches in the high pressure oil for a long time under the erosion, it will evolve into a trench, so a trench will Cause the pump failure.

3.3 suction, the biggest impact on pump soft life is the pump inhalation of oil with air, to correct the hydraulic sector personnel a wrong idea is that the hydraulic pipe does not leak oil does not mean that the air does not leak. When the oil pipe and the joints of the joints are sealed in a small failure range, the pipeline does not leak oil under an atmospheric pressure environment. When the pump displacement increases, the pump suction port S will appear siphon phenomenon, the external atmospheric pressure S pump several times higher than the oil suction port, pump suction port will inhale the air from the failure site. When the air enters the pump distribution area to change from the low pressure area to the high pressure area, the bubble explodes and ruptures under the pressure of the high pressure oil, which will cause cavitation between the distribution surface of the cylinder and the distribution plate. Caustic cavities caused by the distribution of copper layer interval flow channeling. Another pump suction air is due to the small size of the hydraulic tank or the tank interior partition design is unreasonable, when the hydraulic system back to the oil into the oil when the air bubbles have not been completely eliminated when the pump suction port Sucked away, but also according to the above causes.

3.4 Flexible coupling asymmetry, the motor shaft and the pump shaft different axis greater than 0.1mm, the vibration generated by high-speed rotation directly to the pump spindle bearings, affecting the front spindle bearing life.

3.5 Multi-pump work when the resonance: large hydraulic station group pump work, each pump should have its own separate with a shock absorber pump frame, the pump frame and pump frame must be spaced apart to prevent vibration resonance.

3.6 improper maintenance methods, any improper maintenance methods, will cause the pump completely damaged. Pump disassembly and assembly is a delicate and complex work, staff must carefully read the pump repair, motor repair technical parameters, adjust the hydrostatic bearing clearance according to the rules. The best way to do this is by a professional.

4, hydraulic piston pump online monitoring diagnosis and predictive maintenance

4.1 The beginning of this century, modern electronic test technology, computer analysis and other state-of-the-art condition monitoring and diagnostic equipment based on the use of ultrasonic leakage monitoring technology, infrared temperature measurement technology, pump bearing wavelet analysis technology, on-line use of the pump for regular testing Diagnosis, according to the fault signal collected, draw the pump performance curve of online work, make assessment report. According to the monitoring results to decide whether to repair the pump. In order to determine the best pump maintenance, to avoid the maintenance of excess maintenance, greatly reducing costs. Improve the use of soft pump life, reducing downtime loss. Replace the past regular maintenance system with the technical condition monitoring and maintenance system. Also replaced the past, manual tour detection that touch the pump shell temperature and vibration, ear to hear the noise emitted by the pump rotation than before to expand the volume of the old-fashioned method. In particular, equipment maintenance personal experience-based technical maintenance, rather than advanced testing, scientific standards based on the diagnosis of maintenance.

4.2 monitoring and diagnostic device that is the means of fault diagnosis. Fault diagnosis can be divided into two types of portable simple diagnosis and online precision diagnosis. The main parameters of hydraulic pump failure indicator is reduced pressure, flow reduction, temperature rise, variable speed overtime, noise rise and vibration increases, excessive pump leakage and so on. When testing different parameters, different measurement methods, tools and instruments should be chosen according to the actual conditions reflected by the hydraulic pump, the differences between on-site conditions and accuracy requirements. As developed in Japan, the principle of hydraulic pump fault diagnosis is detected by vibration diagnosis, the microcomputer analysis and fault prediction. Can quickly detect the pump from the outside of the internal wear and tear of the pump, thus effectively preventing the pump failure, improve the reliability of the host.

Pump Testing Hydraulic testers can also be used to test the overall pump efficiency. Hydraulic tester is composed of flow, pressure gauge and thermometer, can be connected to the pump outlet, through the adjustment of the various functions of the instrument to detect the pump discharge at all levels of pressure flow, draw the pump total efficiency curve. Pump total efficiency down to 72% must be off the assembly line repair.

Tester and pump drain connection to detect the amount of pump discharge. Pump leakage changes with the use of online time, and in a fixed cycle time, the measured changes in the amount of leakage can be informed of the appropriate changes in the pump operating conditions of the system can work, the amount of leakage over time The curve is called the state curve and can be used for fault prediction and maintenance period determination as an assessment indicator of pump operating conditions.

Drawing and Analysis of Pump Leakage State Curve. Take pump running time as abscissa, internal discharge and volumetric efficiency as ordinate, draw pump leakage curve, the leakage of more than 50% of the normal value must be off-line repair.

4.3 Check the current value, the large metallurgical industry hydraulic station is composed of multiple plunger pump hydraulic system and with a large accumulator package, if one of the pumps within the large amount of leakage or less than the working pressure, The entire hydraulic system pressure and flow hazards can not be immediately apparent, inspectors must work on a daily basis to check the current meter on the current value and make a record. If one of the pumps in the pump group operates at a lower operating pressure than the others, the pump with a lower pressure will show a lower current value than the current value of the pump current in the ammeter. That is, the pump with less work needs to be used than the pump with normal work Low current.

4.4 Measuring pump case temperature. Leakage within the hydraulic piston pump, the pump increases the gap between the friction caused by pressure oil leaks, leakage of pressure oil into heat, it will inevitably cause the pump shell with the normal temperature difference between the shell. If the pump bearing wear and tear, bearing fever and accompanied by noise, the heat pump casing appears at the appearance of the above two kinds of fever phenomenon using "infrared electronic thermometer" test contrast, the problem of pump casing surface temperature than Normal working hydraulic pump housing temperature is high. Inspectors should be used every 4h hours "electronic thermometer" to detect a pump spindle outside the pump housing in the middle of the pump at the back of the lid and other three temperature and pump temperature rise curve in the table marked temperature records, the temperature curve table It can be provided to the technical staff at the same time with the pump monitoring data table so that technicians can make correct judgment on the pump.

5, hydraulic piston pump online washing method

5.1 For the online use of the hydraulic plunger pump housing solid particles can not be discharged and other issues, the German Rexroth hydraulic pump designers in both sides of the hydraulic pump shell designed to install a flushing device for the application of K1`K2 flushing port , For regular flushing of metal particles trapped within the pump housing.

Usually the pump is hydraulic filter from the K1 port into the oil from the K2 port for flushing, if the German Rexroth A2F355 or A2V / A2P355A6V / A7V250 and above the hydraulic pump is equipped with a dedicated U-port for flushing the bearings, while flushing pump operation Another pipe through the U mouth flush spindle bearings. Filter must be used to filter than β10? 100 filter, so get a clean hydraulic oil to flush residual metal particles in the pump. Flushing piston pump must have a variable stroke and load operation, irrigation pump housing should pay attention to the pressure shall not exceed 0.2MPa, because the pump spindle seal the highest pressure 0.3MPa. To ensure that the pump does not overpressure, Rexroth AG produces a low-pressure flush valve dedicated to pump flushing (Flush Valve Order no. 466468 / 503.20.01.16) This valve is installed in line A and B, when the pressure difference between the lines A and B exceeds 0.3-0.5MPa, the flushing valve is opened by the high pressure and the excess oil flows out of the low pressure side to the low pressure circuit B via the pressure relief relief valve (port T) in.

5.2 For "E" series models with "HF" hydraulic medium pumps and motors must be disassembled for up to 5,000 hours of hard life. Special care must be taken to clean the corners. Suitable cleaning materials are listed in VDMA23414. For pumps of the substitute "SL" type, the motor housing must be flushed through port U.

6, the establishment of monitoring and testing and maintenance system

6.1 The pump is the most valuable part of the complete hydraulic system component and it is difficult to predict when the pump will need to be maintained without on-line monitoring and testing of the pump. Without recording and not analyzing the data of the monitored pumps, it is almost impossible to make an accurate judgment as to whether the pumps used online can operate according to the specified service period. If a pump shows signs of detectable deterioration and there is enough time to observe the level of deterioration before the fault occurs, then it is reasonable to have the pump tested online on a regular basis. To enhance maintenance and protection, can improve pump life (utilization). Foreign equipment management has a saying: "Maintenance is to use the equipment for fault management." Therefore, the establishment of a state-based inspection, repair system, on-line use of the pump to do regular daily testing, make a record, draw the pressure, temperature, noise level, current value and other curve table, the state of the pump Identification and status trend analysis, depending on the maintenance of maintenance guidelines. In our Xiaolangdi project and the construction of the Three Gorges Project of foreign contractors for its use of hydraulic pumps, hydraulic motors insist 1500 ~ 2000h hour for a wash, hard life of 8,000h that the pump, motor replacement bearings and adjustments. This is our use of imported hydraulic equipment unit can learn from.

6.2 to establish preventive maintenance. The basic maintenance methods include testing, maintenance, replacement and commissioning. Pump preventive maintenance is a regular on-line pump flushing, pump hard life every 1500 hours for a wash, this method is to improve pump life, one of the most effective way.

6.3 Commonly used maintenance methods are scheduled to be repaired, to give a typical example, the pump bearing soft life is 10,000 hours, but the soft life is only a reference, you can extend this time, but it must be estimated that such an increase will increase the pump Damage risk. Metallurgical hydraulic system site is very complex, especially the impact of pollution, accurate assessment requires a wealth of experience, but we can pump hard life, (hard life --- equipment has been in service time) timely use of computer bearing analyzer In the operation of the three pairs of friction pairs and rolling bearings for testing analysis for the friction pairs and bearings in the working state of the correct judgments and accurate analysis according to the damage trend to estimate the remaining life of the pump and bearings and make timely replacement plan, In order to avoid the economic losses caused by the accident.

6.4 Failure probability of hydraulic pump rises with the age of the pump, corresponding records should be established from the beginning of the service life of the pump, the hard life of the pump and the interval between each flush, the bearing replacement, the maintenance test results, the quality acceptance, etc. should be recorded A set of maintenance process records.

6.5 The establishment of professional equipment supervision personnel, the exercise of equipment operation, maintenance and repair of the entire process of supervision functions, equipment maintenance and management of scientific and digital, to achieve equipment maintenance "zero failure."

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