ASME B / ANSI/ASME B – Surface Texture and Gaging for Screw Threads Package ASME B and ANSI/ASME B The ASME B46 1 ANSI ASME. Find the most up-to-date version of ANSI B at Engineering The American Standard for Surface Texture in ANSI B gives Ra as the standard surface finish designation. In most applications where RMS is called.

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### Roughness Parameters

Values numerically greater than 1. The angle measured, is the angle difference between the two most dominant angles found in the image by analyzing its autocorrelation function. We calculate Std from the Fourier spectrum. Maximum Peak Height Sp: The Radial Wave IndexSrwiis a measure of how dominant the dominating radial wavelength is, and is defined as the average amplitude sum divided by the amplitude sum of the dominating wavelength:.

These parameters reflect slope gradients and their calculations are based on local z-slopes.

Area Root Mean Square Slope. The advantage of this is that deviations from the bearing plane can be quantified better when setting the bearing plane to zero see how this is done in the Plane Correction Dialog section.

This may be the case for image containing well organized linear structures. The result is called the angular spectrum. For Gaussian height distributions S ku approaches 3. The Reduced Summit Height, Spkis the height of the upper left triangle. Each point in the graph corresponds to the normalized power in a circle one frequency pixel wide in the squared FFT image the Power Spectrum Image.

Surfaces with very dominant directions will have Stdi values close to zero and if the amplitude sum of all direction are similar, Stdi is close to 1. The angular spectrum is calculated by the following formula:. The Texture DirectionStdis defined as the angle of the dominating texture in the image. For a surface with a dominant lay, the parameters will tend towards 0. The Roughness Average, S ais defined as:. The table lists the roughness parameters by their symbol, name, corresponding 2D standard and unit.

They are defined as the height difference between the highest and lowest pixel in the image. For images consisting of parallel ridges, the texture direction is parallel to the direction of the ridges.

The Fractal Dimension, Sfd is calculated for the different angles by analyzing the Fourier amplitude spectrum; for different angles the amplitude Fourier profile is extracted and the logarithm of the frequency and amplitude coordinates calculated.

If the surface is fractal the Log Log graph should be highly linear, with at negative slope. For a Gaussian height distribution S ci approaches 1.

Large values of S ci indicate that the void volume in the core zone is asi. For non-integer values of andthe value of F u pv q is found by linear interpolation between the values of F u pv q in the 2×2 neighboring pixels. The Projected Area, S2Aexpresses the area of the flat x,y plane as given in the denominator of R The spatial properties are described by five parameters. The Mean Summit Curvature, S scis the average of the principal curvature of the local maximums on the ansk, and is defined as:.

The fractal dimension, D, for each direction is then calculated as. All the parameters are based on two-dimensional standards that are extended to three dimensions. The Core Roughness Depth, Skis the height difference between the intersection points of qnsi found least mean square line. If there is a very aansi wavelength, Srwi is close to 0, and if there is no dominating wavelength, it is close to 1.

The hybrid parameters can be described graphically by the above figure. The line having the angle, awith the highest amplitude sum, Amaxis the dominating direction in the Fourier transformed image and is perpendicular to the texture direction on the image.

The Surfaces Area Ratio, S drexpresses the increment of the interfacial surface area relative to the area of the projected flat x,y plane:. The functional parameters for characterizing bearing and fluid retention properties are described by six parameters. The Ten Point Height, S10 zis defined as the average height of the five highest local maximums plus the average height of the five lowest local minimums:. For all surfaces S ci is between 0 and 0. Smaller values indicate broader height distributions and visa versa for values greater than 3.

With this definition the Stdi value is always between 0 and 1. If the angle of the ridges is turned clockwise, the angle is positive and if the angle of the ridges is turned anti-clockwise, the angle becomes negative.

The first parameter is calculated directly from the image, while the remaining are based on the Fourier spectrum. In principle, the texture aspect ratio has a value between 0 and 1.

## ANSI-ASME B46.1-1985.pdf

These parameters are the density of summits, the texture direction, the dominating wavelength and two index parameters. The radial spectrum is calculated by the following formula:.

Note, also that roughness values depends strongly on measurement conditions especially scan range and sample density. The amplitude xnsi, A aat a line with the angle, ais defined as:. For a Gaussian height distribution S vi approaches 0.

The Dominating Radial Wavelength, Srwcorresponds to the semicircle with radius, r maxhaving the highest amplitude sum, b max: Before the calculation of the roughness parameters we recommend carrying out a slope correction by a 2 nd or 3 rd order polynomial plane fit. The surface bearing area ratio curve, which is also called the Abbott curve, is calculated by accumulation of the height distribution histogram and subsequent inversion. Maximum Valley Depth Sv: