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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Three parameters are calculated based on this figure.

Root Mean Square Gradient. The functional parameters for characterizing bearing and fluid retention properties are described by six parameters.

The Texture DirectionStdis defined as the angle of the dominating texture in the image. Dominant Radial Wave Length.

These lines are marked Z 0. The amsi bearing area ratio curve, which is also called the Abbott curve, is calculated by accumulation of the height distribution histogram and subsequent inversion.

For an anisotropic surface the correlation length is in the direction perpendicular to the surface lay. The hybrid parameters can be described graphically by the above figure. 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. 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.

The Surfaces Area Ratio, S drexpresses the increment of the interfacial surface area relative to the area of the projected flat x,y plane:. Large values of S ci indicate that the void volume in the core zone is large.


ASME B / ANSI/ASME B – Surface Texture and Gaging for Screw Threads Package

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. Large values of S vi indicate large void volumes in the valley zone. The reported fractal dimension is the average for all directions. If there is a very dominating wavelength, Srwi is close to 0, and if there is no dominating wavelength, it is close to 1.

Roughness Parameters

The fractal dimension can also be evaluated from 2D Fourier spectra by application of the Log Log function. These parameters are the density of summits, the texture direction, the dominating wavelength and two index parameters. For a Gaussian height distribution S ci approaches 1. Mean HeightS mean is the mathematical mean height of all pixels. The amplitude sum, b ralong a semicircle with the radius, ris. It is therefore important to include the measurement conditions when reporting roughness data.

As there are no pixels outside the borders of the image there are no local minimums or local maximums on the borders. Here, a local minimum is defined as a pixel where all eight neighboring pixels are higher and a local maximum as a pixel where all eight neighboring pixels are lower.

Large S bi indicates a good bearing property. The radial spectrum is calculated by the following formula:. For a surface with a dominant lay, the parameters will tend towards 0.

In principle, the texture aspect ratio has a value between 0 and 1. For images consisting of parallel ridges, the texture direction is parallel to the direction of the ridges. Parameters associated with the two-dimensional DIN standard are also calculated based on the bearing area ratio curve. The Dominating Radial Wavelength, Srwcorresponds to the semicircle with radius, r maxhaving the highest amplitude sum, b max: Shw corresponds to the radius r 0.


This parameter is only meaningful if there is a dominating direction on the sample. If the surface is fractal the Log Log graph should be highly linear, with at negative slope. The amplitude sum, A aat a line with the angle, ais defined as:. All six parameters are defined from the surface bearing area ratio curve shown in the figures below. The calculated RMS roughness between cursors corresponds to the square root of the sum of all pixels in the 2D Power Spectrum Image between two concentric circles each with the radius of the inverse wavelength of the cursors in the IAPSD graph.

The Surface Bearing Index, S biis defined as:. 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.

ANSI-ASME B46.1-1985.pdf

The angular spectrum is calculated by the following formula:. Some of the parameters depend on the definition of a local minimum and a local maximum. The first parameter is calculated directly from the image, while the remaining are based on the Fourier spectrum. Area Root Mean Square Slope.