During the operation of the hydraulic press, abnormal cylinder return speed will not only reduce production efficiency, but may also cause equipment failure. In-depth analysis of its influencing factors and formulation of targeted solutions are the key to ensuring the stable operation of the hydraulic press. The following will comprehensively analyze the core reasons affecting the return speed of the cylinder from the dimensions of hydraulic component status, oil characteristics, system pressure, mechanical coordination, etc., and expand detailed investigation and solution methods.
1. Hydraulic reversing valve failure: Abnormal valve core reset causes flow throttling
As the core component of controlling the flow of oil, the reversing valve's valve core reset state directly determines the oil on-off efficiency. When the return spring of the reversing valve suffers from dual problems of insufficient elasticity and structural distortion, a chain reaction will occur: the valve core cannot accurately return to its original position after a power outage, resulting in too small an opening between the slide valve and the valve hole. At this time, the oil is greatly compressed through the passage of the reversing valve, forming a flow-limiting effect similar to a 'throttle valve' - even if the system oil supply is normal, the oil flow entering the cylinder will be significantly reduced, eventually causing the cylinder's return speed to be slow, or even intermittent stuck.
In response to this problem, the investigation and solution need to be carried out in three steps: First, disassemble the reversing valve assembly, visually check whether the appearance of the return spring is deformed or rusted, and use a spring dynamometer to test its elastic force value. If it is lower than 80% of the design standard It needs to be replaced immediately; secondly, check whether the guide hole of the valve core is worn. If there are scratches or steps on the inner wall, it needs to be repaired by precision grinding to ensure smooth movement of the valve core; finally, when reassembling, ensure that the spring installation angle is vertical, and the coaxiality error between the valve core and the valve hole is controlled within 0.02mm to avoid reset failure caused by assembly deviations.
2. Changes in hydraulic oil characteristics: viscosity and contamination affect flow efficiency
The physical properties and cleanliness of oil are the basis for ensuring the circulation efficiency of the hydraulic system. Abnormal changes in oil will affect the return speed of the cylinder from two dimensions: 'fluidity' and 'continuity'.
(1) Oil viscosity increases in low temperature environment: fluidity decreases significantly
The viscosity of hydraulic oil increases exponentially as the temperature decreases. When the ambient temperature is low, the viscosity of ordinary anti-wear hydraulic oil will increase significantly, and the internal friction between oil molecules will increase significantly, resulting in a sharp increase in its flow resistance in pipelines, valve groups and cylinders. At this time, even if the output pressure of the oil pump is normal, it is difficult for the oil to quickly fill the rodless cavity of the oil cylinder, which causes the initial return movement of the oil cylinder to be slow, and the speed does not increase significantly as the stroke progresses.
To solve this problem, we need to start from two aspects: 'active temperature control' and 'oil optimization': on the one hand, an electric heating rod can be installed in the oil tank (the power is selected according to the tank volume), and the temperature controller can be used to preheat the oil temperature to an appropriate range before startup to avoid low-temperature startup; on the other hand, for equipment that has been operating in a low-temperature environment for a long time, it should be replaced with low-temperature anti-wear hydraulic oil. The added pour point depressant and viscosity index improver can ensure stable viscosity at low temperatures and better fluidity than ordinary hydraulic oil. In addition, wrapping thermal insulation cotton on the outside of the fuel tank to reduce the impact of ambient temperature on the oil is also a low-cost and effective auxiliary measure.
(2) Oil pollution and colloid precipitation: valve core stuck or valve hole blocked
During the long-term operation of the hydraulic system, the oil is easily mixed with solid impurities (such as metal chips, seal wear particles) and colloidal sediments (produced by oil oxidation and additive decomposition). These contaminants can have a fatal impact on the valve group: On the one hand, solid impurities may get stuck in the valve core and valve of the flow valve or directional valve. Between the holes, the valve core cannot be fully opened or closed, causing the oil flow to fluctuate and the return speed of the cylinder to fluctuate; on the other hand, the colloidal sediments will adhere to the inner wall of the valve hole, reducing the oil flow cross-section and increasing the movement resistance of the valve core. In severe cases, the valve core may even become stuck and the cylinder cannot return at all.
In response to the oil pollution problem, it is necessary to establish a full-process management and control system of 'prevention + investigation + treatment': at the prevention level, regularly replace the fuel tank air filter (recommended to be replaced every 3 months) to avoid the entry of external dust, and at the same time, install an oil suction filter with a mesh size of more than 100 at the oil pump suction port to reduce the inhalation of impurities; at the inspection level, take samples every 6 months to test the oil contamination level (refer to the NAS 1638 standard, it should be controlled at 8 level), if it exceeds the standard, it needs to be dealt with immediately; at the treatment level, if the valve core is found to be stuck, the valve group needs to be disassembled, the valve core and valve hole should be cleaned with kerosene, and slight scratches on the surface of the valve core should be polished with fine sandpaper. For colloid deposits, a special hydraulic system cleaning agent can be used to circulate and flush, and finally replace with new oil and clean the inner wall of the tank to completely remove residual contaminants.
3. Abnormal system control pressure: Insufficient pressure or fluctuations lead to insufficient power
The control pressure of the hydraulic system is the 'power source' that drives the movement of the cylinder. When the control pressure is low or has poor stability, the cylinder's return power will be significantly insufficient, which is manifested in slow return speed, reduced thrust, and even the inability to return when the load is large.
(1) The control pressure setting is too low: the system design requirements are not met.
When debugging equipment, some users may adjust the pressure value of the control pressure source (such as the relief valve) to a value lower than the design standard in order to avoid 'damaging components due to excessive pressure.' As a result, the oil pressure output by the oil pump cannot effectively push the cylinder piston, resulting in a decrease in the return speed of the cylinder.
The key to solving this problem is to 'accurately calibrate the pressure': first, turn off the main power of the hydraulic press, wait for the system to release pressure, and then connect the pressure gauge to the pressure measuring point of the control pressure source; second, start the equipment, slowly adjust the pressure regulating knob of the relief valve, and observe the pressure gauge reading until it reaches the design pressure value marked in the equipment manual (usually the error needs to be controlled within ±0.5MPa); finally, after the pressure is stable, lock the pressure regulating nut of the relief valve to avoid pressure deviation caused by vibration. In addition, the control pressure needs to be checked regularly (quarterly) to prevent natural pressure drop due to valve group wear.
(2) The pressure source is disturbed: pressure fluctuation causes speed instability
In addition to 'low pressure', the 'stability' of the pressure source will also affect the cylinder return speed. When there is excessive throttling resistance in the control pipeline (such as pipeline bends, pipe diameter is too small), improper adjustment of the flow valve (such as the opening of the throttle opening is suddenly large or small), or there is leakage in the valve group (such as aging sealing ring causing internal oil leakage), the control pressure will fluctuate at high frequencies, causing the pressure in the rodless cavity of the cylinder to be high and low, causing the return speed to be fast and slow, and in severe cases, even 'pause-shock' abnormality will occur.
To check pressure fluctuations, please press 'Pipeline - Valve Group - Seals' The sequence is gradually advanced: first, check whether the control pipeline runs smoothly and whether there is any obvious bending, flattening or blockage. If the pipe diameter is too small, replace the pipe with a matching pipe diameter; secondly, disassemble the flow valve and check whether there are impurities blocking the throttle or valve core wear. If the throttle is severely worn, It is important to replace the valve core and re-adjust the throttle opening to ensure stable flow; finally, check the connection seal between the valve group and the pipeline. If the sealing ring is found to be aging or deformed, the oil-resistant sealing ring (such as nitrile rubber or fluorine rubber material) needs to be replaced in time to avoid pressure loss caused by internal oil leakage.
4. Cylinder mechanical coordination failure: piston stuck or seal failure causing movement to be blocked
As an actuator, the internal mechanical coordination of the oil cylinder directly determines the smoothness of the movement. When 'the piston rod and the cylinder barrel are stuck,' 'the seal is too tight,' or 'the axis is misaligned,' even if the oil supply to the hydraulic system is normal, the oil cylinder may not be able to return normally, or even 'completely motionless' in the extreme case.
(1) The piston rod and the cylinder are stuck: mechanical interference causes the movement to become stuck.
The matching clearance between the piston rod and the cylinder is usually controlled at 0.05-0.1mm If the axis line is misaligned due to installation deviation, or dirt or colloid deposits enter the inner wall of the cylinder, it will cause mechanical interference between the two: on the one hand, the offset of the axis line will cause unilateral friction between the piston rod and the inner wall of the cylinder during movement, resulting in increased local wear and formation of 'steps' that hinder piston movement; on the other hand, dirt and colloid deposits will fill the fitting gap and increase movement resistance. In severe cases, the piston rod and the cylinder barrel will be completely stuck. At this time, no matter how you operate, the cylinder will have no movement or minimal movement.
Solving this problem requires 'disassembly and maintenance + accurate assembly': first, disassemble the cylinder assembly, take out the piston rod and piston, and check whether there are scratches, rust or glue adhesion on the inner wall of the cylinder barrel. If there are slight scratches, use fine honing strips to repair them. If the wear is serious, the cylinder barrel needs to be replaced; secondly, clean the surface of the piston rod and check its straightness error (should be controlled within 0.1mm/m Within), if the bend needs to be corrected by a straightening machine; finally, when reassembling, a dial indicator needs to be used to calibrate the coaxiality of the piston rod and the cylinder barrel to ensure that the error does not exceed 0.03mm. At the same time, apply special grease in the piston sealing groove to reduce motion friction.
(2) The seal is too tight or fails: increased resistance and internal leakage coexist
The seals in the oil cylinder (such as piston seals and piston rod seals) not only play the role of 'preventing oil leakage', but also affect the movement resistance. If the compression amount is too large when the seal is installed (for example, the diameter of the sealing ring is larger than the width of the seal groove), the friction between it and the inner wall of the cylinder or the surface of the piston rod will increase significantly, hindering the piston movement; if the seal ages and fails (such as the elasticity decreases and cracks appear after long-term use), it will cause internal leakage of oil between the rodless chamber and the rod chamber of the oil cylinder. At this time, the oil output by the oil pump will leak into the rod chamber through the sealing gap, causing the pressure in the rodless chamber to be unable to be established and the return speed of the cylinder to be slow.
For seal problems, it is necessary to 'adjust or replace as needed': If the seal is too tight, it is necessary to disassemble the cylinder and check whether the specifications of the seal match the seal groove (for example, the diameter of the seal should be 0.1-0.2mm smaller than the width of the seal groove). If the specifications do not match, replace it with the correct size. Seals; in the case of aging and failure of seals, it is necessary to select seals of appropriate materials according to the operating temperature and pressure of the oil cylinder (such as fluorine rubber seals for high-temperature environments, and combined seals for high-pressure environments). At the same time, the seal groove must be kept clean when replacing it to avoid impurities affecting the sealing effect. In addition, it is recommended to replace the seal every 1-2 years (or 1000 hours of operation) to prevent aging problems in advance.
