Sep.2023 20
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What is Ra & Rz & Ry
Introduction
It's Specific representation of finish symbols on machining drawings and types of representation
Details
The technician said: the surface roughness of a machined part used to be called the surface finish.

Surface roughness symbols are marked on the drawing of the part to indicate the surface characteristics to be achieved when the surface is finished. There are 3 types of surface roughness height parameters:

1, contour arithmetic mean deviation Ra

In the sampling length, along the measurement direction (Y-direction) of the contour line on the absolute value of the distance between the point and the baseline arithmetic mean.

2, micro-uniformity ten-point height Rz

Refers to the sampling length in the five largest contour peak height of the average value and the five largest contour valley depth of the average value of the sum.

3、Maximum contour height Ry

In the sampling length, the contour of the highest peak line and the distance between the lowest valley line.

General mechanical manufacturing industry is mainly used Ra. Ra value is calculated according to the following formula: Ra = 1/l ∫t0|Y (x)|dx or approximate Ra = 1/n ∑ |Yi|. Where Y is the distance between the point on the contour line and the reference line (center line); ι is the sampling length.

Roughness is mostly used to characterize steel plates, because steel plates must have a certain degree of roughness before coating, otherwise the paint does not have enough bite and is easy to peel off.