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Use and Maintenance of Hydraulic Piston Pump for Construction Machinery

2018-04-27

The efficiency of the hydraulic system of construction machinery mainly depends on the volumetric efficiency of the hydraulic pump. When the volumetric efficiency drops to 72%, it is necessary to carry out regular maintenance, replace bearings and aging seals, and replace or repair friction pairs that exceed the fit clearance. Its performance is restored.
The efficiency of the hydraulic system of construction machinery mainly depends on the volumetric efficiency of the hydraulic pump. When the volumetric efficiency drops to 72%, it is necessary to carry out regular maintenance, replace bearings and aging seals, and replace or repair friction pairs that exceed the fit clearance. Its performance is restored.
This paper mainly introduces the use and maintenance methods of the straight shaft swash plate piston pump.
 
1 oil supply form of hydraulic pump
Straight shaft swash plate piston pump is divided into two kinds of pressure oil supply type self-oil type. Most of the pressure oil type hydraulic pumps use air pressure oil tanks, and some hydraulic pumps have their own oil supplement pumps to provide pressure oil to the hydraulic pump oil inlet. The self-oil-absorbing hydraulic pump has a strong self-oil absorption capacity and does not require external oil supply.
The hydraulic oil tank supplied by air pressure must wait for the hydraulic stain tank to reach the air pressure before operating the machine every time the machine is started. If the hydraulic oil tank is used as a machine when the air pressure is insufficient, it will pull off the sliding whip in the hydraulic pump and cause abnormal wear of the return plate and pressure plate in the pump body. After 3000h of use, the operator shall check the plunger pump 1-2 times a day to check whether the running sound of the hydraulic pump is normal. If it is found that the speed of the hydraulic cylinder drops or the car is stuffy, it should be disassembled and inspected to check whether there is a scratch on the edge of the impeller and whether the gap of the internal gear pump is too large.
For self-priming plunger pumps, the oil in the hydraulic oil tank shall not be lower than the lower limit of the oil standard, and a sufficient amount of hydraulic oil shall be maintained. The higher the cleanliness of the hydraulic oil, the longer the service life of the hydraulic pump.
 
2 Bearing for hydraulic pump
The most important part of the plunger pump is the bearing. If the bearing has clearance, the normal clearance of the three pairs of friction pairs inside the hydraulic pump cannot be guaranteed. At the same time, the thickness of the hydrostatic bearing oil film of each friction pair will be destroyed and the service life of the plunger pump bearing will be reduced. According to the information provided by the hydraulic pump manufacturer, the average service life of the bearing is 10000h, beyond which a new port needs to be replaced.
The clearance of the disassembled bearing cannot be detected without professional testing instruments, and can only be visually inspected. If scratches or discoloration are found on the surface of the roller, it must be replaced.
When replacing the bearing, attention should be paid to the English letters and models of the original bearing. Most of the piston pump bearings use large load capacity bearings. It is best to buy products of the original manufacturer and original specifications. If you replace another brand, you should consult the experienced personnel of the bearing. The purpose is to maintain the accuracy level and load capacity of the bearing.
 
3 Three pairs of friction pair inspection and repair
 
3.1 plunger rod and cylinder hole
Table 1 is the replacement standard of plunger pump parts (see fig. 1). when the clearance listed in the table is out of tolerance, it can be repaired by the following methods:
(1) If the cylinder body is inlaid with a copper sleeve, it can be repaired by replacing the copper sleeve. First, the diameter of a group of plunger rods is trimmed to a uniform size, and then the outer diameter is polished with sandpaper above 1000.
Cylinder installation copper sleeve of three methods:
(a) Cylinder body heating and hot fitting or copper sleeve low-temperature freezing and extrusion, interference fitting; (B) Adopting Le Thai glue for adhesive assembly, which requires grooves on the outer diameter surface of the copper outer sleeve;(c) Tapping the cylinder hole, processing the thread on the outer diameter of the copper sleeve, coating Le Thai glue, and screwing into assembly.
(2) The cylinder block and copper sleeve of the melting and burning combination method are as follows:
(a) Grind and repair the cylinder bore manually or mechanically with a grinding rod; (B) Re-bore the cylinder bore with a coordinate boring machine; and (c) Repair the cylinder bore with a reamer.
(3) The use of "surface engineering technology", the method is as follows:
(a) electroplating technology: plating a layer of hard chromium on the surface of the plunger; (B) brush plating technology: brush plating wear-resistant material on the surface of the plunger;(c) thermal spraying or arc spraying or electric spraying: spraying high carbon martensite wear-resistant material;(d) laser cladding: high hardness wear-resistant alloy powder is deposited on the surface of the plunger.
(4) The cylinder block material without copper sleeve is mostly ductile iron, and amorphous film or coating is prepared on the inner wall of the cylinder. Because the inner wall of the cylinder hole has this special substance, it can form a hard-hard pair of friction pairs. If you blindly grind the cylinder hole and grind off the surface material of the inner wall of the cylinder hole, the structural performance of the friction will be changed. If the friction pair with the coating removed is used forcibly, the temperature of the friction surface will rise sharply, and the plunger rod and the cylinder hole will be glued.
In addition, a unique thin film coating is prepared on the surface of the plunger rod. The coating contains the function of reducing wear-resistant lubrication. This group of friction pairs is actually hard-soft pairing. Once the coating is changed, the friction pairs of the best matching materials will be destroyed. Repair these special plunger pumps and send them to a professional repair shop.
 
3.2 shoe and swash plate
The sliding friction between the sliding shoe and the swash plate is the most complex of the three pairs of the swash plate piston pump.
Table 1 lists the gap between the ball head of the plunger rod and the ball socket of the sliding shoe (see fig. 2). if the gap between the plunger and the sliding shoe is too poor, the high-pressure oil in the plunger cavity will leak out from the gap between the ball head of the plunger and the sliding shoe, and the oil film between the sliding shoe and the swash plate will be thinned. in severe cases, the static pressure support will fail. When the ball head of the plunger rod and the ball socket of the sliding shoe exceed the tolerance by 1.5 times, they must be replaced in groups.
Diameter of plunger rod and cylinder hole plunger rod φ16φ20φ25φ30φ35φ40
Standard clearance 0.0150.0250.0250.0300.0350.040
Limit clearance 0.0400.0500.0600.0700.0800.090
Ball joint of plunger rod
Standard clearance with shoe ball socket 0.0100.0100.0150.0150.0200.020
Limit clearance 0.300.300.300.350.350.35
After the swash plate acts for a period of time, the swash plate plane will appear concave phenomenon. Before using the platform for grinding, the original size and plane hardness should be measured first. After grinding, and then measure the amount of grinding is how much, such as within 0.18mm, the use of piston pump without hindrance; if more than 0.2mm, you should use the method of nitriding to maintain the original nitride layer thickness.
When the plane of the swash plate is scraped by the plunger ball head, the groove can be repaired by laser cladding alloy powder. Laser cladding technology can not only ensure the bonding strength of the material, but also ensure the hardness of the melting material, and not all reduce the hardness of the surrounding tissue.
Also in line with the use of chromium phase welding rod for manual welding, repair welding swash plate plane needs to be re-heat treatment, the best use of nitride furnace heat treatment. No matter which method is adopted to repair the swash plate, the original dimensional accuracy, hardness and surface roughness must be restored.
 
Repair of 3.3 distribution plate and cylinder block distribution surface
The distribution plate has two forms of plane distribution and spherical distribution.
The friction pair of spherical flow distribution shall be repaired by grinding when the scratch on the flow distribution surface of the cylinder body is relatively shallow. When the groove of the flow distribution surface of the cylinder body is deep, the groove shall be filled with "surface engineering technology" before grinding. Blind grinding is not allowed to prevent the copper layer from thinning or oil leaking out of the steel base.
The friction pair in the form of plane distribution can be ground on a platform with high precision.
Before grinding the cylinder body and the valve plate, the total thickness size and the size that should be ground should be measured first, and then compensated on the adjusting pad. When the amount of grinding of the distribution disk is large, the heat treatment should be re-treated after grinding to ensure the hardness of the hardened layer (see Table 2).
Table 2 Hardness standard of plunger pump parts
Plunger Rod recommend Hardware HS84
Plunger rod ball head recommend hardness> HS90
Swash plate surface recommend hardness> HS90
recommend hardness of valve plate> HS90
After the cylinder body and the distribution plate are repaired, the following methods can be used to check the leakage of the mating surface, that is, apply vaseline oil to the surface of the distribution plate, block the drain passage, lay the oil distribution plate flat on the platform or flat glass, then place the cylinder body on the distribution plate, inject diesel oil into the cylinder hole, and inject oil at intervals, that is, inject oil into one hole, and observe for more than 4 hours, there is no leakage and collusion of diesel oil in the plunger hole, indicating that the cylinder body and the valve plate are qualified for grinding.
 
4 Conclusion
The length of the service life of the plunger pump is related to the usual maintenance, the quantity and quality of the hydraulic oil, and the cleanliness of the oil. It is also an effective way to prolong the life of the plunger pump by avoiding the friction pair caused by the particles in the oil.
In the maintenance of replacement parts should try to use the original production of parts, these parts are sometimes more expensive than other imitation parts, but the quality and stability is better, if the purchase price of cheap imitation parts, in the short term seems to save the cost, but the resulting hidden dangers, may also cause greater harm to the use of plunger pump