Rexroth hydraulic pumps – how to use, repair and assemble gear pumps

1. What should I pay attention to when using a gear pump?

(1) The oil suction height of the gear pump shall generally not be greater than 500mm.

(2) The gear pump should be directly connected with the motor through the flexible coupling, and generally should not be rigidly connected or connected with the power source through the gear pair and belt mechanism, so as to avoid unilateral force, resulting in bending of the pump shaft, unilateral wear and failure of the oil seal of the pump shaft.

(3) The ultimate speed of the gear pump should be limited, and it should not be too high or too low. If it is too high, the oil will not have time to fill the entire interdental space, which will cause cavitation, vibration and noise; If it is too low, it cannot make the pump suction cavity form the necessary vacuum, which will cause poor oil suction. At present, the driving speed of the domestic gear pump is 300-4450r/min, see the gear pump instruction manual for details.

(4) When selected, the gear pump is mostly a unidirectional pump, which is divided into a left pump and a right pump. It is necessary to pay attention when purchasing, otherwise the oil can not be oiled or the oil volume is not enough when used in the opposite direction, and the oil seal of the pump shaft is often overturned and broken. If bidirectional rotary pumps and reversing pumps are required, special orders are required.

(5) The general gear pump is made of YA-N46 (GB 2512-1981) ordinary hydraulic oil, the working oil temperature is controlled at 0-80 °C, and the filtration accuracy is about 25μm.

After the gear pump is used for a long time, the gear will be worn and scratched relative to the sliding surface. The wear of the end face will lead to an increase in axial clearance and an increase in internal leakage. Tooth crest circle wear will lead to an increase in radial clearance; Tooth wear results in increased noise and increased pressure oscillation. When the wear and strain is not serious, it can be slightly ground (grinding) and polished again, and if the wear and strain is serious, it needs to be repaired or replaced according to the situation.

2. How to repair gears and gear shafts?

The wear part of the gear pump shaft (gear shaft) is mainly the journal that is in contact with the needle roller bearing or shaft sleeve. If the wear is slight, it can be repaired by polishing. If the wear is severe, it is necessary to use chrome plating or rework a new shaft, and when remachining, the coaxiality of the two journals is 0.02-0.03mm. The coaxiality of the gears mounted on the shaft or connected to the shaft is 0.01mm.

(1) Tooth shape repair

Use a fine abrasive cloth or oil stone to remove the burrs that have been strained, protrusions or have been ground into a polygonal part, and then install the gear and shaft on the bearing hole of the pump cover for grinding, and use the red pill method to verify the grinding effect. Appropriately change the orientation of the meshing surface, and continue to use it after cleaning. However, the serious wear parts that can be observed by the naked eye should be remade and replaced.

(2) End face repair

For those with slight wear, the two gears can be sanded on a 0# abrasive cloth at the same time, and then placed on the metallographic sandpaper to rub and polish. When the wear and strain are severe, the two gears can be placed on the flat grinder at the same time to grind off a little, and then grind or polish with metallographic sandpaper. At this time, the pump body should also be ground to the same size to ensure the original assembly clearance (0.02-0.03mm). The thickness difference between the two gears should be within 0.005mm, and the perpendicularity between the gear end face and the hole or the runout of the gear axis should be controlled within 0.005mm.

(3) The top of the tooth is round

Due to the radial unbalanced force, external gear pumps generally wear out after a period of use. When the tooth top circle is worn, the radial clearance increases. For low-pressure gear pumps, internal leakage does not increase much. However, for medium and high pressure gear pumps, which will have an impact on the volumetric efficiency, electroplating the outer circle (brush plated tooth top circle) or replacing the gear should be considered.

(4) The gear accuracy of the medium and low pressure gear pump is 7-8 grades, the gear accuracy of the medium and high pressure gear pump is slightly higher by 0.5-1 grade, the coaxiality tolerance between the gear inner hole and the tooth top circle (for the gear shaft, the tooth top circle and the journal outer circle) is <0.02mm, the non-parallelism of the two end faces is <0.007mm, and the surface roughness is.

(5) Gear shaft

For the gear shaft connected to the shaft, if the surface is peeled off or burned and discolored, a new gear shaft should be replaced; If the surface is grayish-white and only the mating clearance increases, the position of the meshing teeth can be adjusted appropriately and the new bearing can be replaced; If the outer surface of the gear is brushed due to sweeping, and there are iron filings on the top of the tooth, the adhesive can be scraped off with an oil stone sand strip, and the joint surface of the pump bore can be sanded, and the radial clearance can continue to be used if the radial clearance is not out of tolerance.

3. How to repair the pump body, front and rear covers, shaft sleeves and side plates?

The wear of the pump body is mainly on the inner cavity surface (the surface in contact with the tooth top circle - G6 surface), and most of them occur on the suction side. If the pump body is symmetrical, the pump body can be flipped 180° for reuse. If it is an asymmetrical type, it is necessary to use electroplating bronze alloy process or brush plating method to trim the wear part of the cavity hole in the pump body.

The front and rear covers and bushings are repaired mainly on the end faces that are in contact with the gears. When the wear is not serious, the end face can be repaired by grinding on the flat plate. When the wear and strain are severe, it can be placed on the surface grinder to grind off the groove first, and then slightly grinded, but it should be noted that the relevant size of the unloading groove should be appropriately deepened and widened.

After the side plate is worn, the two sides of the plate can be placed on the grinding plate or glass plate, and ground and smoothed with 1200# emery, the surface roughness should be lower than Ra0.8, and the thickness difference should not exceed 0.005mm within the whole circle.

4. How to assemble the gear pump?

After repair, the following matters should be paid attention to when assembling the gear pump:

(1) Remove the burrs on each part. The sharp edge of the gear is blunt with a natural oil stone, but it cannot be poured into a rounded corner, and the parts after flat grinding should be demagnetized. All parts are carefully cleaned with kerosene before they can be put into assembly.

(2) Measure and ensure the axial clearance during assembly: the axial clearance of the gear pump δ = pump body thickness L0 - gear width L1, generally to ensure that the δ is 0.02-0.03mm, and at the same time to measure the relevant size and accuracy of other parts.

(3) When the gear pump is assembled, some gear pumps have positioning pin holes. For gear pumps without locating holes, the pump shaft is rotated while the screws are tightened diagonally during assembly. If there is no difference in severity, tighten a few more mounting screws thoroughly. For gear pumps with positioning holes (such as CB-B type), the pin holes are mainly used in the processing process of parts, so there is no positioning datum at the time of assembly, and finally equipped with drilling and hinging two pin holes to drive into the positioning pins.

(4) Pay attention to the parts that are easy to install in reverse, and do not install them in the wrong direction. In particular, it is necessary to confirm whether it is a forward or reverse pump.

(5) The author opposes the use of paper pads between the pump body and the pump cover to solve the problem of leakage, a layer of paper at least 0.06-0.1mm thick, which will seriously affect the axial clearance, increase internal leakage, and in serious cases, the gear pump can not be oiled.

(6) If conditions permit, the gear pump can be tested on the bench according to JB/T 7041-1993 and other standards, and then loaded into the main engine.

Rexroth hydraulic pumps – how to use, repair and assemble gear pumps

Rexroth hydraulic pumps – how to use, repair and assemble gear pumps

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