Summary of Surface Finish Parameters Table 1. Primary surface finish parameters.
Figure 1. Measurement of Average Roughness, Ra, and RMS Roughness, Rq.
there being a surface point at a certain height. If one were to draw a line at a particular height the ADF would be proportional to the number of times the surface profile crosses the line. The Material Ratio Curve (also known as the Bearing Ratio Curve, Bearing Area Curve, or the Abbott-Firestone Curve) is the integral of the ADF from above the surface to the height of interest. This is the total percentage of material above a certain height.
Measurement of Material Ratio
This measurement is also known as Bearing Ratio, and its symbol is t p . The Material ratio is usually defined at X% at a slice depth c. Depth c is measured from a reference. This reference can be defined as
T the highest peak
T a lower value that excludes outlying peaks (sometimes this is written as a
reference %, which is the t p at the height C ref ) T the mean, with c being defined as above or below the mean.
If you imagine slicing through the peaks on the surface at a particular depth, t p is the ratio of the total length of the flat “mesas” you would produce to the sampling length. This is illustrated in Figure 3.
1. If you grind to a depth c, t p is the percentage of the surface available to support a
perfectly flat load 2. Ratio of lengths: Add up all lengths with material beneath them in the
measurement length, L; divide the sum of these lengths by L to obtain the ratio. 3. Intersection of the line at height c with the Material Ratio Curve (see also Figure
2).
References
The following have additional information and more details:
1. Surface Metrology Guide , Precision Devices. Inc.
2. Surface Texture Parameters , Mahr
3. ASME B46.1 (1995) specification
mean
C ref
C
t p =19%。