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Selection of surface roughness

1.One The influence of surface roughness on the functionality of parts

1.1. Effects of component wear resistance

Due to the micro geometric shape errors on the surface of the parts, when two surfaces move relative to each other, contact can only occur at the peak of the contour, thereby reducing the contact area, increasing the specific pressure, and accelerating the wear rate of the part surface. Generally speaking, the rougher the surface, the greater the frictional resistance, and the lower the wear resistance. However, if the surface is too smooth, it is not conducive to storing lubricating oil, and the two contact surfaces will form dry or semi dry friction, as well as intermolecular adsorption, which will increase the friction coefficient and exacerbate surface wear.

1.2. Effects of Contact Stiffness

The rougher the surface, the smaller the actual contact area between surfaces, and the greater the pressure per unit area, which exacerbates the local plastic deformation at the peak and reduces the contact stiffness, thereby affecting the working accuracy and vibration resistance of the parts.

1.3. The impact of cooperation nature

Surface roughness can affect the stability of the fitting properties. For gap fitting, the peak of micro unevenness will quickly wear off during relative motion, causing the gap to increase; For interference fit, the peak of the surface is flattened during assembly, which reduces the actual interference and lowers the connection strength; For transition fit, surface roughness also has an impact on loosening the fit.

1.4. Effects on fatigue strength

The rougher the surface of the part, the deeper the indentation, and the smaller the curvature radius of the valley, the more sensitive it is to stress concentration, especially when the part is subjected to alternating loads. Due to the influence of stress concentration, the fatigue strength decreases, leading to cracks and damage on the surface of the part.

1.5. Effects of Corrosion Resistance

The rougher the surface, the easier it is for corrosive gases or liquids to accumulate at the valley bottom and infiltrate into the interior of the metal, causing corrosion on the surface of the parts.

In addition, surface roughness also affects the sealing performance of the joint surface and the aesthetics of the parts, so surface roughness is an important indicator for measuring product quality.

2. Surface roughness parameter values and their comparison

The old name for surface roughness is smoothness (previously known as flower 4, flower 5, flower 6, flower 7, and flower 8). The new standard corresponding to the old name is as follows, for example, flower 4 in the old standard corresponds to Ra6.3 (μ m) in the new standard

It can be seen that the higher the smoothness value of the old standard, the higher the surface roughness, while the smaller the value of the new standard, the higher the surface roughness.