Patent Application
20150260624
1. Field of the Disclosure
The present disclosure relates to a snap grip indenter mount, used on a hardness tester, particularly a microhardness tester, or similar apparatus.
2. Description of the Prior Art
Hardness, a material's resistance to permanent deformation, is generally measured on either a Brinell, a Rockwell or a Microhardness testing machine. In a microhardness test, a four-sided pyramidal diamond indenter is pressed into the sample's surface with a controlled force. The indenter is removed and the lengths of the diagonals of the indentation left in the surface of the sample are measured using a microscope. The hardness is calculated (usually by the software) using the test force and the area of indentation.
A microhardness tester can be fitted with at least two indenter types, including a Vickers indenter and Knoop indenter. A Vickers indenter is a symmetrical four-sided pyramid; it makes a square-shaped indent. Both diagonals are measured to calculate the hardness. A Knoop indenter is highly asymmetrical in that it makes an elongated (7:1) rhomboidal indent. Only the long diagonal is measured and used for the hardness calculation.
Microhardness testers are generally equipped with multiple indenters and multiple microscope objectives all mounted on a multi-position rotatable turret. To run tests, the turret rotates to position the indenter above the test sample, the indent is made and the turret rotates to an objective position so the user (and the software) can view and measure the indent.
To make symmetrical indents on a test sample, the diamond indenter must contact the surface with a precise angular orientation. That is, the indenter axis and the surface of the test sample must be mutually perpendicular in both axes within 3 arc-minutes. Two adjustable horizontal axes are required because such a tight angular tolerance is not achievable with fixed parts, even with the most precise machining.
A third indent orientation—rotation of the indent about the viewing axis must also be controlled. Opposite indent corners need to be oriented left-to-right and front-to-back within a half degree or so. This rotational alignment is needed mostly because users typically expect the indents to be visually aligned with the primary axes—a crooked indent is a sign of poor machine quality. In addition, because indent length is measured automatically by two pairs of software filars (one pair is exactly vertical and one pair is exactly horizontal), many users would assume that an indent with a visually perceptible angle would be inaccurately measured by the software filars—even though an indent with a very apparent 2.5 degree angle would be measured accurately, typically within 0.1 percent, by the filars.
To achieve “indent symmetry”, Wilson Tukon 2100 and Tukon 2500 testers use an arrangement of thin shims (0.001″ & 0.003″ thick sheet metal washers) to adjust the angle of the X-Y stage. Two Knoop indents (one horizontal and one vertical) are made with the unshimmed tester, indent asymmetry is measured and the measurements are used to calculate the thicknesses of the shims needed to correct the asymmetry. The X-Y stage is removed from the tester, the shims are placed around the four screws that clamp the X-Y stage to the loadframe and the X-Y stage is refitted to the machine. Finally, two more Knoop indents are made to verify the results of shimming
The TU2500 does not have a fine rotation adjustment of the indent orientation. The user must manually rotate the indenter with a one millimeter tommy-bar temporarily placed through the transverse hole in the indenter.
Various companies manufacture devices which adjust their indenter symmetry, probably through an adjustment mechanism of some sort. Similarly, a four axis (two translations and two rotations) alignment device exists for adjusting the alignment of tensile test specimens. It is manufactured by the Interlaken Company, see U.S. Pat. No. 5,377,549, issued on Jan. 3, 1995.
In commonly-owned U.S. Pat. No. 7,004,017, issued Feb. 28, 2006, a canted-coil spring serves to center the indenter and draw its shoulder into firm compressive contact with the end face of the coupling.
Additionally, commonly-owned PCT/US2012/053750 entitled, “Apparatus for Microscopic Detection of Hardness”, filed on Sep. 5, 2012, while well-suited for its intended purposes, does not include a snap grip feature.
Generally, the prior art “shimming-at-the-stage” symmetry adjustment method is acceptable (i.e., the indent can be made symmetric) but the method is time consuming and requires temporary removal of the X-Y stage so the shims can be installed. The heavy weight of the stage and its proximity to the microscope objectives and indenters makes stage removal and installation a risky task—there is a big risk of jerking the heavy X-Y stage up and into the microscope and loadcell components as the thread that holds the stage down suddenly releases.
Another disadvantage of shimming-at-the-stage is that because the sample surface is tipped by shimming, the focus plane of the microscope changes and some part of the view will lose focus.
A further deficiency of the prior art method is that the “before-shimming indent” cannot be found for comparison against the “after-shimming indent” because the stage is removed from the machine and replaced (not in exactly the same position) after shimming.
Vickers and Knoop indenters are machined with such accuracy that an indenter can usually be removed from the machine mount and replaced with another indenter and indent symmetry will be retained. However, indent rotational orientation will always be lost when changing an indenter. This is a big problem because indent rotational orientation is a tedious, hit-or-miss task with the prior art method where the operator will usually overshoot or undershoot the position with each rotational adjustment of the indenter with the not-so-controllable tommy-bar rotational adjustment. The adjustment of indent rotational orientation is frequently thought to be the single most difficult thing to do on the TU2500 machine.
It is therefore an object of the present disclosure to provide for simplified adjustment of the indenter in hardness tester or similar materials testing apparatus.
This and other objects are attained by providing a ball joint that is set-screw-adjusted. Because symmetry adjustment is done at the indenter, the stage stays in place during adjustment and the focus plane is unaffected by the adjustments. The center of the ball joint is at the tip of the diamond indenter, so the indenter tip does not translate as the angle is adjusted. This means the adjusted indent can be placed adjacent to the “before-shimming indent” for visual verification of the adjusting action.
The combination of the snap grip coupling and the two-pin rotational orientation mechanism allow a user to change out an indenter/lower housing assembly without needing to redo any alignment adjustment. The user can remove a Knoop indenter and install a Vickers indenter and continue testing without interruption.
This disclosure addresses the ease of adjusting the indent orientation by using two opposing set screws to make the adjustment—fine adjustment of the set screws is easy and tightening both screws offers a secure locked position. This disclosure also provides a way to snap the lower housing assembly into a repeatable position every time it is installed—there is typically no need to adjust symmetry or indent orientation.
Further objects and advantages of the disclosure will become apparent from the following description and from the accompanying drawings, wherein:
Referring now to the drawings in detail wherein like numerals refer to like elements throughout the several views, one sees that
The upper housing assembly 12 is shown in further detail in
As shown in
As seen in FIGS. 1 and 4A-G, the lower housing assembly 14 further includes lower circumferential wall 76 defining lower concave cavity 77 for receiving the indenter ball adapter 16. The lower circumferential wall 76 includes first, second and third radially oriented threaded apertures 78, 80, 82 for receiving respective first, second and third symmetry adjusting screws 84, 86, 88 which impinge against the indenter ball adapter 16 and are used to adjust and subsequently lock the two rotational horizontal axes. In other words, the first, second and third symmetry adjusting screws 84, 86, 88 are used to adjust the two angles of the indent ball adapter 16 thereby affecting the symmetry of the indent. In the illustrated embodiment of
Additionally, lower circumferential wall 76 includes a fourth radially oriented aperture 90, typically unthreaded and, as shown in
The indenter ball assembly 16, illustrated in
The upper and lower housing assemblies 12, 14 can be separated and reconnected with the snap action given by the canted coil spring 64 as it engages circumferential lip 72. The symmetry and orientation of the snap grip indenter mount 10 will typically always be the same. With this configuration, the user can have multiple indenter/lower housing assemblies 140 that have each been adjusted to the one upper housing assembly 12 so the user can at any time remove a lower housing assembly 14, typically simply by pulling it down, and replace it with another lower housing assembly 14, and not have to make any symmetry or orientation adjustments. Typically, this embodiment of the disclosure is used in compression only.
The typical operation of the embodiment of the disclosure is as follows (assuming the starting point of an assembled lubricated indenter mount assembly 10, which has yet to be adjusted).
1. The user checks that a Knoop Indenter, or similar, is installed as element 126 or an extension thereof. If not, the user:
2. The user inserts the lower housing assembly 14 and makes a single indent 200 in the sample.
3. The user checks that the resulting indent 200 on the sample is vertical (within a few degrees). If not, the user unscrews the indenter retainer 132 and moves the indenter 126 and then tightens again, makes an indent 200 in the sample and repeats until the indent 200 is vertical within 5 degrees (see, for example,
4. Once the indent 200 is within 5 degrees of being vertical, the user uses the first and second orientation adjusting screws 98, 100 in the lower housing assembly 14 to adjust the vertical alignment of the indents.
5. Once the indents are vertically aligned, the symmetry is adjusted.
Once the indents are vertically aligned, the symmetry is adjusted as described below
1. The user typically unscrews the indenter retainer cap 132 and rotates the indenter 126 by 90 degrees to obtain a left-to-right indent. The user typically does not adjust the first and second rotational adjusting screws 98, 100.
2. The user typically adjusts the two front symmetry adjusting screws 84, 86. The user typically does not adjust the two front symmetry adjusting screws 98, 100 or the rear symmetry adjusting screw 88. The user adjusts screws 84, 86 until the indent 200 is symmetric about the y-axis.
The user rotates the indenter 126 again to give a front-to-back axis orientation and makes an indent 200 on the sample to check that the indent 200 has remained symmetric about the x-axis. The user make adjustments to screws 98, 100 to adjust the rotational orientation of the indent within 0.5 degrees.
The user is then ready to perform microhardness or similar testing.
Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.
This application claims priority under 35 U.S.C. 119(e) of U.S. provisional patent application Ser. No. 61/733,548, filed on Dec. 5, 2012, the disclosure of which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US13/69306 | 11/8/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61733548 | Dec 2012 | US |
