Because the hydraulic system of the molding machine uses more cylinders, and the load of each station is different, it makes sense to apply a variable pump in the system.
I. Working principle: The axial piston pump with sliding shoe structure is currently the most widely used axial piston pump. The plunger placed in the cylinder body contacts the swash plate through the sliding shoe. When the transmission shaft drives the cylinder body When rotating, the swash plate pulls the plunger out of the cylinder or pushes it back to complete the suction and discharge process. The oil in the working volume cavity composed of the plunger and the cylinder bore communicates with the suction and discharge chambers of the pump through oil distribution plates, respectively. The variable mechanism is used to change the inclination of the swash plate. The displacement of the pump can be changed by adjusting the inclination of the swash plate.
2. Maintenance of the plunger pump: The swash plate type axial plunger pump generally adopts the form of cylinder rotation and end flow distribution. A friction pair consisting of a bi-metal plate and a steel oil distribution plate is inlaid on the end surface of the cylinder body, and most of them adopt a plane flow distribution method, so maintenance is relatively convenient. The oil distribution plate is one of the key components of the axial piston pump. When the pump works, on the one hand, the high-pressure oil in the working chamber pushes the cylinder to the oil distribution plate, and on the other hand, the oil film pressure between the oil distribution plate and the cylinder body forms a pair. The hydraulic back thrust of the cylinder block makes the cylinder block away from the oil distribution plate. The designed hydraulic pressure force Fn of the cylinder to the oil distribution plate is slightly larger than the hydraulic reverse thrust Ff of the oil distribution plate to the cylinder, that is, Fn / Ff = 1.05 ~ 1.1, so that the pump works normally and maintains a high volumetric efficiency.
In fact, due to the pollution of the oil, there is often slight wear between the oil distribution plate and the cylinder block. Especially at high pressure, even slight wear can increase the hydraulic reverse thrust force Ff and destroy Fn.
1. Insufficient or no oil output from the hydraulic pump
(1) Insufficient intake: The reason is that the resistance on the suction pipe is too large or the replenishment amount is insufficient. If the speed of the pump is too large, the liquid level in the fuel tank is too low, air leaks from the oil inlet pipe, and the oil filter is blocked.
(2) Excessive leakage: The reason is that the gap of the pump is too large and the seal is bad. For example, the oil distribution plate is scratched by metal fragments, iron filings, etc., and the end face leaks oil; the check surface of the check valve in the variable mechanism does not fit well, and the supporting surface of the pump body and the oil distribution plate has trachoma or grind marks. The damaged part of the pump can be identified by checking the foreign matter in the hydraulic oil in the pump body.
(3) The tilt angle of the swash plate is too small, and the displacement of the pump is small. This requires adjusting the variable piston to increase the tilt angle of the swash plate.
2. In the neutral position, the oil displacement is not zero. When the swash plate inclination angle of the variable displacement axial piston pump is zero, it is called the neutral position. At this time, the output flow of the pump should be zero. However, sometimes the phenomenon that the center position deviates from the center point of the adjustment mechanism, and there is still a flow output at the center point. The reason is that the position of the controller is deviated, loosened or damaged and needs to be re-zeroed, tightened or replaced. This phenomenon can also occur due to insufficient angle maintenance of the pump and wear of the tilted trunnion.
3. Output flow fluctuations Output flow fluctuations are related to many factors. The variable pump can be considered to be caused by poor control of the variable mechanism. For example, foreign matter enters the variable mechanism and marks step marks, abrasions, scars, etc. on the control piston, resulting in unstable movement of the control piston. Insufficient energy or damaged parts of the amplifier, and the poor performance of the damper of the control piston containing the spring will cause the control piston to move unstable. Unstable flow is often accompanied by pressure fluctuations. Such failures generally require dismantling the hydraulic pump, replacing damaged parts, increasing damping, increasing spring stiffness and controlling pressure.
4. Abnormal output pressure: The output pressure of the pump is determined by the load and is approximately proportional to the input torque. There are two kinds of faults in abnormal output pressure.
(1) The output pressure is too low. When the pump is in the self-priming state, if there is a leak in the oil inlet pipe or there is a large leak in the hydraulic cylinder, check valve, and directional valve in the system, the pressure will not rise. This requires finding leaks, tightening and replacing seals to increase pressure. The relief valve is faulty or the adjustment pressure is low, and the system pressure cannot go up. You should readjust the pressure or repair the relief valve. If the cylinder of the hydraulic pump deviates from the flow plate and causes a large amount of leakage, in serious cases, the cylinder may rupture. The mating surface should be reground or the hydraulic pump replaced.
(2) The output pressure is too high: if the circuit load continues to rise, the pump pressure also continues to rise, which is normal. If the load is constant and the pressure of the pump exceeds the pressure required by the load, check the hydraulic components other than the pump, such as directional valves, pressure valves, transmissions and oil return pipes. If the maximum pressure is too high, adjust the relief valve. 5. Vibration and noise: Vibration and noise occur simultaneously. They not only cause harm to the operator of the machine, but also cause pollution to the environment. (1) Mechanical vibration and noise: If the pump shaft and the motor shaft are not concentric or top dead, the bearings and couplings of the rotating shaft are damaged, the elastic pads are damaged, and the mounting bolts are loose. For pumps running at high speeds or transmitting large amounts of energy, periodic inspections should be performed to record the amplitude, frequency, and noise of each component. If the rotation frequency of the pump is the same as the natural frequency of the pressure valve, resonance will be caused, and the speed of the pump can be changed to eliminate resonance.
(2) Noise caused by liquid flow in the pipeline The oil inlet pipeline is too thin, the flow capacity of the oil inlet filter is too small or clogged, the air is sucked in by the oil inlet pipe, the oil is too high, the oil level is too low, the oil is insufficient, and the high pressure pipeline Noise will be generated when liquid impact occurs in the process. Therefore, the fuel tank must be properly designed, and the oil filter, oil pipe and directional valve must be correctly selected.
6.Hydraulic pump overheating: There are two reasons for the excessive heating of the hydraulic pump. One is the heat generated by mechanical friction. Because the moving surface is in a dry or semi-dry friction state, the moving parts generate heat by friction with each other. The second is that liquid friction generates heat. High-pressure oil leaks into the low-pressure chamber through various gaps, and a large amount of hydraulic energy loss is converted into heat energy. Therefore, the correct selection of the gap between the moving parts, the volume of the fuel tank and the cooler can prevent excessive heat generation and excessive oil temperature of the pump. In addition, clogging the oil return filter causes the oil return back pressure to be too high, which will also cause the oil temperature to be too high and the pump body to overheat.
7. Oil leakage: The main reason for the oil leakage of the plunger pump is: (1) the main shaft oil seal is damaged or the shaft is defective or scratched; (2) the internal leakage is too large, which causes the pressure at the oil seal to increase, and the oil seal is damaged or washed. (3) The drain pipe is too thin and too long to leak oil at the seal; (4) The external oil pipe of the pump is loose, the pipe joint is damaged, the seal is aging or cracks occur; (5) The variable adjustment mechanism bolt is loose, and the seal is broken; 6) Cast iron pump casing has trachoma or poor welding.
At present, there are many manufacturers producing plunger pumps. The structure of imported and domestic parts is different. Each pump should be used strictly in accordance with its factory instructions. When repairing the pump, you should first check whether the pump is properly installed and used in the system to facilitate the timely detection of the cause of damage, eliminate hidden dangers, and ensure the normal operation of the system. The repaired hydraulic pump should be used only after it has been tested by certain testing equipment. If there is no detection condition, it should also be repeatedly debugged in the system to make it work normally.