Is there crawling in the hydraulic system? Noise? "Technical sharing to solve your worries!"

"Crawling" in Hydraulic systems

"Crawling" is an abnormal motion state that often occurs in hydraulic transmission. A slight "crawling" causes the moving part to vibrate imperceptibly to the naked eye, while a significant "crawling" causes the moving part to jump over a long distance. The crawling phenomenon is very harmful. Therefore, eliminating the "crawling" phenomenon is of great significance for improving the stability of the hydraulic system and enhancing the machining accuracy of machine tools.

"Crawling" caused by poor driving rigidity

Cause of malfunction

After air enters the oil, part of it dissolves in the pressure oil, while the rest forms bubbles and floats in the pressure oil. Due to the compressibility of air, the hydraulic oil acquires obvious elasticity, resulting in poor driving rigidity and causing "crawling".

Countermeasures

When manufacturing and repairing parts, the tolerance requirements should be strictly met, and the fit clearance should be ensured during assembly. Tighten the connections of all pipes to prevent leakage. Evenly tighten the connecting screws at each joint surface. The sealing gaskets should be uniform and multi-layer paper gaskets are not allowed. To remove the dirt adhering to the oil filter, a filter with sufficient capacity should be used. Improve the hydraulic system, try to prevent local vacuum in the system, and install necessary vent plugs or vent valves.

"Crawling" caused by large clearance in hydraulic components

Cause of malfunction One

When a moving part moves at a low speed, once dry friction occurs, the resistance increases. At this point, the hydraulic pump was required to increase the pressure. However, due to the large clearance of the hydraulic pump, it suffered from severe oil leakage and could not adapt to the pressure changes caused by the variation in resistance of the actuator, resulting in "crawling".

Countermeasures

Repair or replace the internal parts of the hydraulic pump to ensure the required clearance for assembly and reduce the leakage of the hydraulic pump.

Cause of Failure Two

"Crawling" caused by control valve failure: The damping holes and throttle ports of various control valves are blocked by dirt, and the valve core does not move flexibly, etc., which cause large pressure fluctuations, resulting in the thrust or flow being sometimes large and sometimes small, thus causing "crawling".

Countermeasures

Keep the oil clean, clean and replace it regularly, and strengthen the maintenance of components to prevent hydraulic oil contamination.

"Crawling" caused by changes in frictional resistance

Cause of malfunction

This phenomenon occurs more frequently in hydraulic cylinders. The main reasons are that the centerline of the hydraulic cylinder is not parallel to the piston rod, the piston rod is partially or fully bent, the inner circle of the cylinder barrel is scratched or roughened, the precision of the cylinder barrel does not meet the technical requirements, and the oil seals at both ends of the piston rod are adjusted too tightly, all of which can cause "crawling".

Countermeasures

Check the accuracy and damage conditions of the hydraulic cylinder item by item, and carry out repairs or replacements. The installation accuracy of the hydraulic cylinder should comply with the technical requirements.

"Noise" in the hydraulic system

There are many causes of noise, and they need to be identified and judged based on specific circumstances.

Noise caused by cavitation

Cause of malfunction

When the resistance in the suction pipeline is very high, the oil cannot fill the pipeline and the pump cavity in time, generating a local vacuum and forming a low pressure. When the pressure drops to the "air separation pressure", a large amount of air dissolved in the working fluid decomposes out, forming cavitation bubbles. When bubbles reach the high-pressure area, they are compressed and burst, generating high-frequency impacts. The pressure value can sometimes be more than ten times the system pressure. At this time, not only will the system experience "cavitation", but it will also be accompanied by impact vibration, noise and high temperature.

Countermeasures

① Increase the diameter of the oil suction pipe, reduce or avoid the bending of the oil suction pipe, and reduce pipe resistance;

② Clean the oil filter frequently;

③ The suction height of the hydraulic pump should be as small as possible.

Noise caused by the control valve

Cause of malfunction One

The valve seat is poorly sealed.

Countermeasures

Replace the steel ball or grind the valve seat sealing joint surface of the cone valve to ensure good contact between the steel ball and the valve seat joint surface.

Cause of Failure Two

The spool valve does not move flexibly inside the valve body.

Countermeasures

Polish the slide valve with metallographic sandpaper and remove any dirt.

Fault Cause three

If the throttle valve opening is too small, a high flow rate will cause a jet flow.

Countermeasures

Reduce the hydraulic difference between the inlet and outlet of the throttle valve, or use a small-sized throttle valve to make the opening of the throttle valve larger when the flow rate is very low.

Fault Cause Four

The electromagnetic directional control valve switches rapidly, generating hydraulic shock.

Countermeasures

A buffer device is set in the oil circuit of the electromagnetic directional control valve.

Mechanical noise of the hydraulic system

Cause of malfunction One

The coaxiality error or loosening of the coupling between the prime mover and the pump or the damage of the bearing.

Countermeasures

Increase the coaxiality of the coupling within 0.1mm and replace the damaged bearings.

Cause of Failure Two

The pipeline installation is improper, and the distance between the oil inlet pipe and the oil return pipe is too close.

Countermeasures

Appropriately increase the distance between the oil inlet pipe and the oil return pipe, and position the main pipes with pipe clamps.