Hydraulic piston pump use and maintenance
The efficiency of the hydraulic system depends mainly on the volumetric efficiency of the hydraulic pump. When the volumetric efficiency drops to 72%, routine maintenance, replacement of bearings and aging seals are required, and friction pairs that exceed the fit clearance are replaced or repaired. Get restored. This article focuses on the swash plate piston pump, which describes its use and maintenance methods.
1. Oil supply form of hydraulic pump Straight-axis swash plate type piston pump is divided into two types: self-suction type of pressure supply type. Pressure-supply type hydraulic pumps mostly use a gas tank with air pressure, and the hydraulic pump itself has a charge pump to supply pressure oil to the oil pump inlet. The self-priming hydraulic pump has a strong self-priming capability and requires no external force to supply oil. The hydraulic fuel tank for pneumatic oil supply must operate the machine after the hydraulic pick-up tank has reached the air pressure after each start of the machine. If the pressure of the hydraulic oil tank is insufficient, it will cause the machine to pull off the slippery whip in the hydraulic pump, which will cause abnormal wear of the returning plate and the pressure plate in the pump body. The plunger pump that uses the oil pump for oil supply, after 3000 hours of use, the operator needs to check the plunger pump 1-2 times a day to check whether the sound of the hydraulic pump is normal. If the speed of the hydraulic cylinder is found to be degraded or boring, the charge pump should be disassembled to check whether there is any scratch on the edge of the impeller, and whether the clearance of the internal gear pump is too large. For self-priming piston pumps, the oil in the hydraulic tank should not be lower than the lower limit of the oil mark, and a sufficient amount of hydraulic oil should be maintained. The higher the cleanliness of the hydraulic fluid, the longer the service life of the hydraulic pump.
2. The most important component of the bearing piston pump for hydraulic pump is the bearing. If there is play in the bearing, the normal clearance of the three pairs of friction pairs inside the hydraulic pump cannot be guaranteed, and the thickness of the hydrostatic bearing oil film of each friction pair is also destroyed. Reduce the life of the piston pump bearings. According to the information provided by the hydraulic pump manufacturer, the average service life of the bearing is 10000h. If this value is exceeded, a new port needs to be replaced.
The disassembled bearing can't detect the clearance of the bearing without professional testing equipment. It can only be visually tested. If it is found that the roller surface has scratches or discoloration, it must be replaced. When replacing the bearing, pay attention to the original letter and type of the original bearing. Most of the piston pump bearings use large load capacity bearings. It is best to buy the original manufacturer and the original specification. If you change another brand, you should consult the bearing. The personnel check the table to change, the purpose is to maintain the bearing's accuracy level and load capacity.
3, three pairs of friction secondary inspection and repair
3.1 Plunger rod and cylinder hole Table 1 is the replacement standard of the piston pump parts (see Figure 1). When the various gaps listed in the table are out of tolerance, it can be repaired as follows:
(1) If the cylinder is fitted with a copper sleeve, it can be repaired by replacing the copper sleeve. First, the diameter of a set of plunger rods is trimmed to a uniform size, and then the outer diameter is polished with a sandpaper of 1000# or more. Three ways to install the copper sleeve in the cylinder:
(a) cylinder heating or copper sleeve low temperature freezing extrusion, interference assembly; (b) mining with Loctite adhesive assembly, this method requires the outer surface of the copper jacket to have grooves; (c) cylinder Hole tapping, copper sleeve outer diameter processing thread, after coating Lok Thai rubber, screw into the assembly.
(2) The cylinder and copper sleeve of the fusion-fired combination method are as follows:
(a) Grinding the cylinder bore by grinding or by manual or mechanical means; (b) Re-squeezing the cylinder bore using a coordinate boring machine; (c) Repairing the cylinder bore with a reamer.
(3) Adopt "surface engineering technology" as follows:
(a) Electroplating technology: plating a layer of hard chrome on the surface of the plunger; (b) brush plating: brushing the surface of the plunger with wear-resistant material; (c) thermal spraying or arc spraying or electric spraying: spraying high carbon horse Austenitic wear resistant material; (d) Laser cladding: A high hardness wear resistant alloy powder is deposited on the surface of the plunger.
(4) The cylinder material of the cylinder hole without copper sleeve is mostly ductile iron, and an amorphous film or coating is prepared on the inner wall of the cylinder. Because of the special material on the inner wall of the cylinder bore, a hard-hard paired friction pair can be formed. If the cylinder hole is blindly ground and the surface material of the inner wall of the cylinder hole is ground, the structural performance of the friction changes. If the friction pair is removed, if it is forcibly used, the friction surface temperature will rise sharply and the plunger rod will be glued to the cylinder hole. In addition, a unique film coating is prepared on the surface of the plunger rod. The coating contains anti-wear + wear + lubrication. This group of friction is actually hard-soft pairing. Once the coating is changed, it will destroy the most. The friction pair of the paired materials, repairing these special plunger pumps, is sent to a professional repair shop.
3.2 Sliding Boots and Swashplates Sliding friction between the sliding shoes and the swashplate is the most complicated pair of three pairs of frictional swashplate piston pumps. Table 1 lists the gap between the plunger rod head and the ball socket of the shoe (see Figure 2). If the gap between the plunger and the shoe is too poor, the high pressure oil in the plunger chamber will be from the gap between the plunger head and the shoe. In the middle, the sliding shoes and the swash plate oil film are thinned. In severe cases, the static pressure bearing will be invalid, the sliding contact between the sliding shoe and the swash plate will be caused by metal contact friction, the sliding shoe will be ablated and the swash plate will be scratched by the plunger ball. When the plunger rod ball head and the shoe ball socket are out of tolerance 1.5 times, they must be replaced in groups. Plunger rod and cylinder bore plunger rod diameter φ16φ20φ25φ30φ35φ40 standard clearance 0.0150.0250.0250.0300.0350.040 limit clearance 0.0400.0500.0600.0700.0800.090 plunger rod ball head and sliding ball ball standard clearance 0.0100.0100.0150.0150.0200.020 limit clearance 0.300.300.300.350.350.35 After a period of swashplate operation, the swash plate plane will appear concave. Before using the platform grinding, the original size and plane hardness should be measured first. After grinding, the amount of grinding is measured. If it is within 0.18, the use of the plunger pump is not harmful. If it exceeds 0.2mm, the original nitride layer thickness should be maintained by nitriding. When the swash plate plane is scraped out of the groove by the plunger ball head, it can be repaired by laser-welding alloy powder. The laser cladding technology not only ensures the bonding strength of the material, but also ensures the hardness of the flux-filling material, and does not completely reduce the hardness of the surrounding structure. The chrome phase electrode is also used for manual surfacing, and the repaired swash plate plane needs to be reheated, preferably by nitriding furnace heat treatment. Regardless of the method used to repair the swashplate, the original dimensional accuracy, hardness and surface roughness must be restored.
3.3 Repair of the distribution plate and the distribution surface of the cylinder The distribution plate has two forms: plane distribution and spherical distribution. The friction pair of the spherical surface distribution is repaired by grinding means when the scratch surface of the cylinder body is relatively shallow; when the groove of the distribution surface of the cylinder body is deep, the surface should be filled with the surface engineering technique before grinding. Do not blindly grind, in order to prevent the copper layer from becoming thinner or leaking out of the steel base. The friction pair in the form of a flat flow can be ground on a platform with a higher precision. Before the cylinder and the valve plate are ground, the total thickness dimension and the size that should be ground should be measured before compensation to the adjustment pad. When the amount of grinding disc is large, it should be reheated after grinding to ensure the hardness of the hardened layer (see Table 2). Table 2 Plunger pump parts hardness standard plunger rod recommended hardware HS84 plunger rod ball head recommended hardness> HS90 swash plate surface recommended hardness> HS90 distribution plate recommended hardness> HS90 After the cylinder and the distribution plate repair, the following methods can be used to check The leakage of the mating surface, that is, the Vaseline oil is applied to the surface of the distribution plate, the oil drain is blocked, the oil distribution plate is placed on the platform or the flat glass, and the cylinder is placed on the distribution plate in the cylinder hole. Inject diesel, it is necessary to interval.