"Crawling" is an abnormal movement state that often occurs in hydraulic transmission. Slight "creeping" causes weak vibrations of moving parts, and significant "creeping" causes moving parts to jump a large distance. The harm of the phenomenon of "creeping" is great, and the elimination of the phenomenon of "creeping" is very important for improving the stability of the hydraulic system and improving the machining accuracy of the machine tool.
(1) "Crawling" caused by poor driving rigidity
After the air enters the oil, part of it is dissolved in the pressure oil (hydraulic oil), and part of it forms bubbles to float in the pressure oil. Because the air is compressible, the hydraulic oil has obvious elasticity, which causes poor driving rigidity and causes "creeping air to be mixed into the hydraulic system:
① Between reciprocating parts, there needs to be a certain fit gap, and air is easily mixed from these gaps.
②The hydraulic pipe joint is loose or the seal is not tight, and air enters the system.
③The accuracy of hydraulic components is poor, and the performance of seals is poor, causing leakage.
④The suction pipe is improperly installed to draw in air, or it is blocked by dirt to form a partial vacuum.
⑤ Insufficient oil in the oil tank or insufficient insertion depth of the oil suction pipe causes air to be sucked in.
⑥ The partial pressure in the hydraulic system of the excavator is lower than the separation pressure of air, so that the air dissolved in the oil is separated.
⑦ The system design is unreasonable. When the machine stops working, the left and right chambers of the hydraulic cylinder communicate with each other and pass through the oil return path. Under the action of potential energy, the oil flows back to the oil tank to form a partial vacuum in the system.
For the above reasons, take measures as follows:
①When manufacturing and repairing parts, the tolerance requirements should be strictly met, and the fit clearance should be ensured during assembly.
②Tighten the connection of each pipe to prevent leakage.
③Tighten the connecting screws at each joint evenly, and the gaskets should be even. Multi-layer paper pads are not allowed.
④ The inlet and outlet pipes in the tank should be kept at a certain distance, and partitions can be added to separate them.
⑤ To remove the dirt attached to the oil filter, an oil filter with sufficient capacity should be used.
⑥ The oil tank must have enough oil so that it is not lower than the oil mark indicating line.
⑦ In order to ensure that all parts of the system can always be filled with oil, a check valve should be installed at the pump outlet, and a back pressure valve should be installed on the return line.
⑧Improve the hydraulic system, try to prevent the partial vacuum in the system, and set the necessary exhaust plug or air release valve.
(2) "Crawling" caused by large clearance of hydraulic components
①When the crawling moving parts move at low speed due to the low-speed movement of the moving parts, the resistance increases once the dry friction occurs. At this time, the hydraulic pump is required to increase the pressure, but due to the large gap of the hydraulic pump, the oil leakage is serious and cannot adapt to the actuator due to the resistance The resulting pressure changes result in "crawling should repair or replace parts in the hydraulic pump at this time to ensure the clearance required for assembly to reduce leakage of the hydraulic pump.
② "Crawling damping holes and orifices of various regulating valves are blocked by dirt, inflexible movement of the spool, etc. caused by the failure of the regulating valve, which causes large pressure fluctuations, resulting in" creeping "when the thrust or flow is large and small. Always keep the oil clean, regularly clean and replace, and strengthen the maintenance of components to prevent hydraulic oil pollution.
③ "Crawling caused by component wear increases the matching clearance due to the wear of valve parts, and some high-pressure oil and low-pressure oil communicate with each other, resulting in insufficient pressure. In addition, the clearance between the hydraulic cylinder piston and the bore of the cylinder body increases due to wear, which occurs Leakage reduces the pressure difference between the two chambers of the hydraulic cylinder and the thrust, resulting in "creeping" due to changes in friction at low speeds. The specific measures are to carefully check the fit gap, research or rework the components to ensure the fit gap, And replace damaged seals.
(3) "Crawling" caused by changes in frictional resistance
This phenomenon occurs more frequently in hydraulic cylinders, mainly because: the center line of the hydraulic cylinder is not parallel to the piston rod, the piston rod is partially or full-length bent, the inner circle of the cylinder barrel is scratched by shaving, and the piston and the piston rod are not on the same axis. The accuracy of the cylinder does not meet the technical requirements, and the oil seals at both ends of the piston rod are adjusted too tight. The measures taken are to check the accuracy and damage of the hydraulic cylinder one by one and repair it. The installation accuracy of the hydraulic cylinder should meet the technical requirements.
