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Introduction
The Brinell Hardness Test is prescribed in ASTM E
10. The standard requires precise measurement of the diameter of an
indentation made with hardened balls of various diameters under various
loads. The MPM measurement system provides the optics and analysis
software for the required diameter measurement and subsequent
calculation of the Brinell hardness in accordance with the requirements
of ASTM E 10.
System Features
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Figure 1 - Digital Optical Comparator System |
The MPM digital imaging system consists of a camera, a
telecentric lens, an opaque lighting source, an infrared back lighting source,
a rack and pinion stand, data acquisition software, and image analysis
software. The 7200 System can be provided with fixed zoom detents (that is,
pre-defined magnification points), or the 7200 can be upgraded to the 7300
which is provided with a motorized system for continuous zoom. It is
desirable to use the detents so that the calibration at each magnification can
be used. These calibrations only need to be updated annually. For the 7300
System, the software returns to precisely the magnification specified by the
user.
In a typical measurement, the system will automatically
capture the image and use the Brinell software tools to make the required
diameter measurements. The user can save the measurement in a data table
which can be printed or stored on the computer.
Calibration
The software has the capability to calibrate distances
and areas in real-world coordinates. The calibration can be performed in one
dimension (1D) or in two dimensions (2D). The 1D calibration is achieved
using a precision reticle as shown in Figure 2.
While the telecentric lens greatly reduces parallax
distortion and other optics problems such as lens axis perpendicularity, a
recently developed two-dimensional calibration technology eliminates residual
errors in the optics. With this technology, it is possible to re-map the
pixel grid to yield a nearly undistorted image. An example 2D calibration
grid is shown in Figure3. The 2D calibration approach is the most accurate
and is recommended by MPM.
Figure 2 - Example 1D Calibration using a Precision Reticle |
Figure 3 - Example 2D Dot-Matrix Distance Calibration
using Precision Grid
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Example Measurements
Several example measurement are shown in Figures 4
and 5. In accordance with ASTM E 10, the user places a box (at any
angle) around the Brinell indentation and the software measures the two
orthogonal diameters and calculates the hardness.
Figure 4 - Auto Measure Indent Example |
Figure 5 - Manual Indent Analysis Window
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Other Measurements
Please refer to the
Percent Shear, Lateral Expansion,
Notch Verification and the
Digital Optical Comparator pages for a description of other features that
are included with these systems.
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