What Is a Creeping Eruption?

The crawling phenomenon in mechanics is the phenomenon of the periodic stop and go or slow and fast movement of the follower in the sliding friction pair under uniform driving and certain friction conditions. Creeping is a form of self-excited vibration in mechanical vibration.

Crawling

Crawling in mechanics, which is caused by the follower in the sliding friction pair under uniform driving and certain friction conditions

There are many reasons for crawling: if the normal load is too large, the rigidity of the sliding system elastic element is small, the difference between static and dynamic friction between sliding pairs is large, and the friction coefficient and relative sliding speed curve have declining characteristics. The measures to prevent crawling are mainly to improve the friction characteristics between the sliding pairs, increase the stiffness of the transmission chain of the system, increase the damping of the system and reduce the weight of the sliding parts. The ways to improve the friction characteristics include using a friction pair material with a small friction coefficient, applying better anti-climbing oil and grease, changing pressure lubrication to static pressure lubrication, and changing sliding friction to rolling friction. Creeping and anti-climbing issues are still the subject of research. For example, analyze the influence of the surface morphology of the friction pair on creep, qualitatively and quantitatively discuss the non-linear relationship between friction, relative sliding speed and crawling motion, use the computer to accurately calculate the critical crawling speed and develop better anti-climbing grease. And friction pair materials.

Creep caused by hydraulic system intrusion into air

There are various ways for air to invade the hydraulic system. For example, the hydraulic system is composed of various hydraulic components. To achieve continuous, intermittent and reciprocating movements between parts of various components, a certain amount of clearance is required. It intrudes from the gap, the connection between the components is not tight, and it is affected by vibration. The joint nut is loose, so air enters from it. The components in the component are not coaxial or straight, and the wire pads are not thick. The screws are not evenly grasped evenly and cause leakage. The oil pump suction pipe and the system oil return pipe are not separated or close together in the oil pool. The oil return splashes and stirs into foam. The oil pump suction pipe sucks air, and the filter at the oil pump suction pipe The oiler is blocked by dirt or the oil filter hole is too dense, the oil is insufficient, or the oil suction pipe invades the oil pool too little, resulting in poor oil absorption. A partial vacuum is formed in the oil suction area and a cavity is generated. When the machine is deactivated, the air enters by air, the design is unreasonable, there is no or low back pressure in the oil return path, and the seals are damaged.

When the temperature of the oil is constant, the pressure increases and the volume shrinks, which has a certain compressibility, but this compressibility is extremely small and generally ignored, that is, the oil is considered incompressible, and the air is compressible, and the compressibility is very high. Big. Therefore, when the hydraulic system invades the air, part of the air is dissolved in the pressure oil, and the other part forms bubbles floating in the pressure oil. When the hydraulic system is compressed, the air in the oil is highly compressible, so that the moving part temporarily maintains the original motion state (stopped state). Only when the air is compressed to a certain degree, can there be enough force to overcome the moving part. The inertia force causes the moving part to change the motion state (

1 Improve the friction characteristics between the workpiece and the tool

To improve the friction characteristics between the workpiece and the tool, the following measures can be taken:

(1) Use appropriate tools and workpiece materials. According to different workpiece materials, choose the appropriate material of the tool, so that the mutual friction coefficient between the tool and the workpiece and the difference between the dynamic and static friction coefficient of the tool and the workpiece are as small as possible.

(2) Application of cutting fluid with good performance. The cutting fluid with better performance can better improve the friction characteristics of the tool and the workpiece.

(3) Ball screws are used instead of ordinary threaded screws, liquid friction is used to replace boundary or dry friction, special lubricants are used, etc. By improving the friction characteristics of the machine tool transmission system, the sensitivity of the feed system is improved, and the phenomenon of crawling is reduced. occur.

2 Increase the stiffness of the system

Increasing the stiffness of the entire process system can effectively reduce the occurrence of crawling phenomena.

(1) Reduce the length of the tool protruding from the tool holder, thicken the tool holder, and increase the rigidity of the tool holder.

(2) Reduce the length-to-diameter ratio of the workpiece and use intermediate supports such as a center frame to increase the rigidity of the workpiece.

(3) Appropriately thicken the diameter of the transmission screw in the feed mechanism, shorten the length of the screw, etc., improve the transmission rigidity of the feed mechanism, try to eliminate the gap between the transmission elements in the feed mechanism, and shorten the transmission of the feed mechanism. Chain to improve the rigidity of the machine tool drive system.

3 Increase system damping

To increase the damping of the system, you can choose a material with a large internal damping (such as cast iron) as the support, or you can add high damping materials or press the damping link to the parts to reduce the occurrence of crawling.

4 Reduce the load of cutting

By reducing the number of back-knives and reducing the weight of each transmission component, the load of cutting processing can be reduced, and the crawling phenomenon in cutting processing can be improved.