MFG Guide

The hazards of crawling on a four-column hydraulic press

Crawling on a four-column Hydraulic Press is very harmful. It damages the surface quality (roughness) and machining accuracy of hydraulic equipment, reduces the service life of hydraulic machine tools and tools, and even produces waste and accidents, so it must be eliminated as soon as possible. In the process of using hydraulic press, there are often some unexpected problems, one of which is crawling. Why does this happen?

The compressibility of the oil will cause two kinds of hydraulic cylinder crawling phenomena, namely:

  • 1. The creeping phenomenon of the hydraulic cylinder in the oil intake throttle speed control system. The working pressure of the oil inlet throttle speed regulating hydraulic cylinder is determined by the external load. Because the flow through the throttle valve changes with the external load resistance, especially in the light load and slow speed conditions, if the fuel inlet throttle speed regulation does not have a back pressure device, it is easy to cause crawling. When the movement inertia is large, forward thrust will occur, but the addition of a back pressure valve may achieve good results.
  • 2. Crawling phenomenon of hydraulic cylinder working in vertical position. In the four-column hydraulic press, the upward movement of the piston type hydraulic cylinder is the working stroke. When the hydraulic cylinder descends and returns by its own weight (a relatively large hydraulic cylinder), its movement energy is absorbed due to the compressibility of the working fluid, which makes the hydraulic cylinder internal pressure rise.

If the movement speed of the piston is greater than the movement speed of the piston determined by the oil displacement of the hydraulic cylinder at a certain time, the pressure in the return cavity of the hydraulic cylinder rises, and the piston stops moving when it is balanced with the downward force of the piston.

Since the hydraulic cylinder continues to return oil, the internal pressure is reduced, and the piston starts to move downwards. Repeated actions like this will result in an increase in static and dynamic friction resistance, which will obviously cause crawling. At this time, a throttle speed regulating device can be added to the oil return line, and the inner diameter of the oil return pipe can be increased to eliminate creeping.

Some four-column hydraulic presses use double rod hydraulic cylinders. When the piston moves downwards, if the piston has a working load, the back pressure change due to the change in kinetic energy accounts for a small proportion of the total back pressure. Therefore, crawling The phenomenon will also be significantly reduced.

The actuator (hydraulic cylinder or hydraulic motor) of the four-column hydraulic equipment often requires a very low speed, such as a few millimeters per minute or even less than 1mm or a few revolutions per minute. At this time, there will often be obvious speed unevenness, intermittent time-sharing, stop and stop, fast and slow, and jump and stop. This phenomenon of hydraulic press becomes a problem of crawling, that is, low-speed stability. The minimum speed at which no crawling phenomenon occurs is called the critical speed of smoothness of motion.

The above content is the hazard caused by the crawling of the four-column hydraulic press. I hope it can be helpful to everyone. If you want to know more about the four-column hydraulic press, please call Dongguan China Machinery Co., Ltd. We will serve you wholeheartedly.

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