Local eddy current and worst speed of low speed and heavy load gears

The existence of the worst speed in the boundary lubricated gears has not been discussed in the literature. There is not only adsorption layer but also flow layer in the boundary lubricating oil film. The adsorption layer is determined by the adsorption of the lubricating oil and the surface activity of the friction pair, and the flow layer is determined by the relative sliding speed of the friction surface and the viscosity of the lubricating oil. With the increase of the relative sliding velocity, the oil film of the flow layer also thickens continuously. When the oil film completely submerges the convex peaks of the two friction surfaces, it will enter the state of fluid lubrication. If the sliding speed is not large enough, the oil film in the flow layer is relatively thin, which is not enough to submerge all the convex peaks. Therefore, the tooth surface is worn by the collision and friction of the convex peaks. At the same time, the oil film in the flow layer near the convex peak and in the concave Valley is stirred to form a local vortex.

As shown in the figure. Although the local eddy current is discontinuous, it has a local dynamic effect, which weakens the rubbing effect and reduces the wear. When the sliding speed further decreases, the local eddy current also weakens, the rubbing effect between the convex peaks is relatively enhanced, and the wear rate gradually increases. When most of the local eddy current disappears and almost does not work, the wear rate also reaches the maximum, and the corresponding sliding speed is the worst speed. If the sliding speed continues to decrease, the rubbing speed and wear rate will decrease.

It can be seen that the collision friction between local eddy current and convex peak exists simultaneously under the condition of boundary lubrication, and the effect of local eddy current reduces the wear, and the collision friction between convex peaks increases the wear rate, and the wear rate depends on the comprehensive action of both. The worst velocity phenomenon is the phenomenon that the local eddy current begins to disappear.

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