Arithmetic average deviation of contour lines? Ra: arithmetic mean of absolute value of contour deviation within sampling length (lr). In actual measurement, the more measuring points, the more accurate Ra. ?
What is the maximum height of the outline? Rz: the distance between the peak line and the valley line of the contour.
Ra is preferred in the common range of amplitude parameters. Before 2006, there was another evaluation parameter in the national standard, that is, the ten-point height of micro-roughness was expressed by Rz, and the maximum height of contour was expressed by Ry. After 2006, the ten-point height of micro-roughness was cancelled, and the maximum height of contour was expressed by Rz.
2. Spacing characteristic parameters
Expressed by the average width Rsm of the contour unit. Within the sampling length, the average value of the micro-roughness spacing of the profile. Microroughness spacing refers to the length of contour peak and adjacent contour valley on the midline.
3. Shape characteristic parameters
It is expressed by the contour support length ratio Rmr(c), which is the ratio of contour support length to sampling length. The length supported by contour lines is the sum of the lengths of line segments parallel to the center line and at a distance c from contour lines and their peak lines.
Extended data
Measurement method of surface roughness
1, comparison method
According to vision and touch, compare the surface roughness comparison sample with the measured surface to determine which value the measured surface roughness is equivalent to, or evaluate the surface roughness by measuring the change of reflected light intensity (see laser length measurement technology). The sample block is a group of metal blocks with a flat or cylindrical surface. Through cutting processes such as grinding, turning, boring, milling and planing, electroforming or other casting processes, the surface has different surface roughness.
Sometimes, samples can be directly selected from the workpiece and used as sample blocks after passing the measurement. Although it is simple and convenient to evaluate the surface roughness with samples according to vision and touch, it will be influenced by subjective factors and often cannot get the correct surface roughness value.
2. Impression method
In actual measurement, we often encounter deep holes, blind holes, grooves, internal threads and so on. , can neither be directly measured with instruments, nor can it be compared with the template surface. This is a common impression method. Impression method is to attach some plastic materials (such as paraffin) with no fluidity and elasticity to the measured surface, copy the outline of the measured surface into the mold, and then measure the impression to evaluate the roughness of the measured surface.
3, touch the needle method
The diamond stylus with a radius of curvature of about 2 microns slides slowly along the measured surface, and the up-and-down displacement of the diamond stylus is converted into an electrical signal by an electrical length sensor. After amplification, filtering and calculation, the surface roughness value is indicated by the display instrument, and the profile curve of the measured section can also be recorded by the recorder.
Generally, the measuring tool that can only display the surface roughness value is called the surface roughness measuring instrument, and the surface roughness profiler that can record the surface contour curve at the same time is called the surface roughness profiler. Both measuring tools have electronic calculation circuits or computers.
It can automatically calculate the evaluation parameters of micro-roughness, such as arithmetic average deviation Rα, ten-point height RZ and maximum height Ry of contour, with high measuring efficiency, and is suitable for measuring surface roughness with Rα of 0.025 ~ 6.3 microns.
4. Interference method
Based on the principle of light wave interference (see flat crystal, laser length measurement technology), the shape error of the measured surface is displayed as an interference fringe diagram, and the microscopic parts of these interference fringes are magnified by a microscope with high magnification (up to 500 times) and then measured to obtain the roughness of the measured surface.
A surface roughness measuring tool using this method is called an interference microscope. This method is suitable for measuring the surface roughness with Rz and Ry of 0.025 ~ 0.8 micron.
5, light cutting method
The light is projected onto the measured surface through the light band formed by the slit, and the surface roughness is measured through the contour curve formed by the intersection of the light and the measured surface. The light emitted by the light source passes through the condenser, the slit and the objective lens 1, and then the slit is projected on the measured surface at an inclination angle of 45 degrees to form a cross-sectional profile figure of the measured surface, which is then amplified by the objective lens 2 and projected on the reticle.
First, use micrometer eyepiece and reading cylinder to read the H value, and then get the H value after calculation. The surface roughness measuring tool using this method is called light cutting microscope. It is suitable for measuring the surface roughness with RZ and Ry of 0.8 ~ 100 micron, which requires manual sampling and has low measurement efficiency.
Baidu encyclopedia-surface roughness measurement
Baidu encyclopedia-surface roughness