Crawling is an abnormal motion state which often occurs in hydraulic transmission. The slight "crawling" causes the movement parts to produce the eye not easy to perceive the vibration, the remarkable "crawling" causes the movement piece to produce the big distance jumps. Crawling is very harmful, so eliminating the "crawling" phenomenon is very important for improving the stability of the hydraulic system and the machining accuracy of the equipment.
1. "Crawling" caused by the change of friction resistance
Cause of failure: this phenomenon occurs more in the hydraulic cylinder, mainly because the center line of the hydraulic cylinder is not parallel to the piston rod, the piston rod is partially or fully bending, the cylinder inside is scratched and scratched, the cylinder barrel precision can not reach the technical requirements, and the oil seal adjustment at both ends of the piston rod will cause "crawling".
Countermeasures: one by one check the accuracy and damage of the hydraulic cylinder, and repair or update it. The installation accuracy of the hydraulic cylinder should be in accordance with the technical requirements.
2. "Crawl" caused by the large gap between hydraulic components
One reason for failure is: when moving parts are moving at low speed, resistance will increase if dry friction occurs. At this time, the hydraulic pump is required to increase the pressure, but because of the heavy oil leakage of the hydraulic pump gap, it can not adapt to the pressure change caused by the change of the resistance of the actuator and produce "crawl".
Countermeasures: repair or replace parts in the hydraulic pump to ensure the clearance of assembly requirements, so as to reduce the leakage of hydraulic pumps.
The cause of failure two: "crawl" caused by control valve failure: the damping holes and throttle of various control valves are blocked by dirt, the movement of the valve core is not flexible and so on, which makes the pressure fluctuate greatly and causes the "crawl" when the thrust or flow is large.
Countermeasures: keep the oil clean, regularly clean and replace, and strengthen the maintenance of components, so as to prevent the pollution of hydraulic oil.
3, "crawl" caused by driving stiffness difference
Fault reason: after the air enters the oil, part of it is dissolved in the pressure oil, and the rest bubbles form in the pressure oil. Because of the compressibility of the air, the hydraulic oil produces obvious elasticity, resulting in poor rigidity caused by "crawling".
Countermeasures: when manufacturing and repairing parts, the tolerance requirements should be strictly met, and the fit clearance should be ensured during assembly. Fasten the joint of each pipe to prevent leakage. Tighten the connecting screws evenly at each joint. The gasket should be even and no multilayer paper pad is allowed. Remove the dirt attached to the oil filter. Adequate oil filters should be used. Improve the hydraulic system, try to prevent partial vacuum in the system, and set the necessary exhaust plug or bleed valve.
There are many reasons for "noise" in the hydraulic system, so we need to identify and judge according to specific conditions.
1. Noise caused by cavitation
Fault reason: when the suction line is very resistant, the oil will not fill the pipeline and pump chamber, causing partial vacuum to form a low pressure. When the pressure is low to the "air separation pressure", the air dissolved in the working fluid is decomposed to form cavitation bubbles. When the bubble is compressed and broken in the high pressure area, it will produce high frequency shock. The pressure value can be as high as 10 times of the system pressure. This will not only make the system "cavitation", but also be accompanied by shock vibration, noise and high temperature.
Countermeasures: (1) increasing the diameter of the oil suction pipe, reducing or avoiding the bending of the oil suction pipe, reducing the pipe resistance and cleaning the oil filter often.
2. The mechanical noise of the hydraulic system
One reason for failure is: the coaxality error of prime mover and pump coupling or loosening or bearing damage.
Countermeasures: increase the coaxality of the coupling in 0.1mm, replace the damaged bearing.
The cause of failure is two: poor installation of pipeline, too close oil inlet and return oil.
Countermeasures: properly open the distance between the oil inlet pipe and the oil return pipe, and the main pipe is clamped by the pipe clamping device.
3, the noise caused by the control valve
Cause of fault one: seat seal is bad.
Countermeasures: replace the steel ball or repair the cone valve seat seal joint, so that the contact between the ball and the valve seat is good.
Fault reason two: slide valve moves inflexible in valve body.
Countermeasures: use spool valve to polish and remove dirt with metallographic sandpaper.
Fault reason three: throttle valve opening too small, high flow rate produces jet.
Countermeasures: reduce the hydraulic difference between inlet and outlet of throttle valve, or adopt small size throttle valve, so that the opening of throttle valve is larger when the flow rate is small.
The cause of failure is four: the electromagnetic reversing valve is switched quickly, resulting in hydraulic impact.
Countermeasures: set up buffer device in the electromagnetic reversing valve oil circuit.
