SNAP GRIP INDENTER MOUNT USED ON A HARDNESS TESTER

The present disclosure relates to a snap grip indenter mount, used on a hardness tester, particularly a microhardness tester, or similar apparatus. The snap grip indenter mount includes three major components—an indenter ball adapter, an upper housing assembly (or snap-grip male element) and a lower housing assembly (or snap-grip female element). The indenter ball adapter forms a ball-and-socket arrangement with the lower housing assembly. The lower housing assembly includes various set screws for fixing the orientation and symmetry of the indenter ball adapter with the lower housing assembly.

BACKGROUND OF THE DISCLOSURE

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.

OBJECTS AND SUMMARY OF THE DISCLOSURE

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail wherein like numerals refer to like elements throughout the several views, one sees thatFIGS. 1 and 2are exploded views of the snap grip indenter mount10of the present disclosure. The snap grip indenter mount10is made from high grade metal as appropriate for the forces which are expected to be encountered. This high grade metal may be, but is not limited to, stainless steel. The snap grip indenter mount10includes three major components—the upper housing assembly (or snap grip female element)12, the lower housing assembly (or the snap grip male element)14and the indenter ball adapter16.

The upper housing assembly12is shown in further detail inFIGS. 3A-H. The upper housing assembly12includes a generally cylindrical lower base18with first and second V-shaped notches20,22. Cylindrical upper base24extends from cylindrical lower base18and includes first, second and third longitudinal apertures26,28,30. First and third longitudinal apertures26,30are blind apertures which receive respective first and second loadcell pins32,34to a loadcell (not shown) while second longitudinal aperture28is threaded to receive a securing screw from the loadcell and passes through the upper female housing assembly12and is centered on the rotational axis of the snap grip indenter mount10and includes an expanded cylindrical female mounting opening27in the lower planar floor29(seeFIG. 1). As shown inFIGS. 3B and 3F, expanded cylindrical mount opening27further includes an interior annular groove31that receives canted coil spring64. First and second transverse passageways36,38are formed in respective first and second V-shaped notches20,22and lead to respective first and second longitudinally-oriented peripheral passageways40,42. First and second transverse passageways36,38receive respective first and second spring-loaded ball plungers44,46which nest or bear upon the first and second inter-assembly pins48,50extending from lower housing assembly14whereby the first and second spring-loaded ball plungers44,46provide a rotational nesting force. As can be seen fromFIGS. 1 and 2, second inter-assembly pin50has a greater diameter than first inter-assembly pin48, thereby requiring that second longitudinal peripheral passageway42have a greater diameter, giving the pays a “keyed” one-way-only assembly. Further, as can be seen inFIG. 1, second longitudinal peripheral passageway42includes an open lateral portion52.

As shown inFIGS. 1,2and4A-G, the lower housing assembly14includes a generally cylindrical body60with an upper generally planar surface62. A canted coil spring64(seeFIG. 2) serves to draw together the lower planar floor29of the upper housing assembly12and the upper planar surface62of the lower housing assembly14. The upper planar surface62includes first and second lower blind apertures66,68, appropriately sized for receiving respective first and second inter-assembly pins48,50. Male mounting element70extends from the center of upper planar surface62and further includes a distal circumferential lip72. Male mounting element70, including circumferential lip72, is configured to snap detent engage the canted coil spring64. The upper planar surface62is further bounded by a lip74about its periphery.

As seen in FIGS.1and4A-G, the lower housing assembly14further includes lower circumferential wall76defining lower concave cavity77for receiving the indenter ball adapter16. The lower circumferential wall76includes first, second and third radially oriented threaded apertures78,80,82for receiving respective first, second and third symmetry adjusting screws84,86,88which impinge against the indenter ball adapter16and are used to adjust and subsequently lock the two rotational horizontal axes. In other words, the first, second and third symmetry adjusting screws84,86,88are used to adjust the two angles of the indent ball adapter16thereby affecting the symmetry of the indent. In the illustrated embodiment ofFIG. 2, the third radially oriented aperture88is oriented toward the second lower blind aperture68while the first and second radially oriented apertures84,86are oriented 120 degrees on either side of third radially oriented aperture88.

Additionally, lower circumferential wall76includes a fourth radially oriented aperture90, typically unthreaded and, as shown inFIG. 4B, somewhat downwardly inclined, through which the indenter ball orientation adjustment pin116(described below) of indenter ball adapter16extends. The fourth radially oriented aperture90is typically oriented 180 degrees from the third radially oriented aperture82and rotationally equidistant between the first and second radially oriented apertures78,80. Lower transverse threaded passageway92intersects fourth radially oriented aperture90and includes first and second openings94,96which receive respective first and second orientation adjusting screws98,100. The third rotational axis (the vertical Z axis—the indent orientation axis) is adjusted and locked by first and second orientation adjusting screws98,100which are threaded into the lower transverse threaded passageway92and have their flat ends bearing the indenter ball orientation adjustment pin116which protrudes from fourth radially oriented aperture90.

The indenter ball assembly16, illustrated inFIGS. 1,2and5A-E, includes a partially spherical ball-type convex surface110for engaging the interior of lower concave cavity77of lower housing assembly14thereby forming a ball joint or ball and socket arrangement to allow three rotational degrees-of-freedom. The indenter ball assembly16further includes frustoconical wall112extending downwardly from partially spherical ball-type surface110. Frustoconical wall112includes radially oriented pin receiving aperture114for receiving and engaging the indenter ball orientation adjustment pin116. Typically, in assembling the snap grip indenter mount10, the indenter ball orientation adjustment pin116is not inserted into the radially oriented pin receiving aperture114until after the indenter ball assembly16is engaged within the interior of lower concave cavity77of lower housing assembly14. As shown inFIGS. 5A-E, a cylindrical stem118is formed below the frustoconical wall112. Further, central indenter mount passageway120extends through the entire longitudinal axis of indenter ball assembly16forming a first opening122in partially spherical ball-type surface110and a second opening124at the end of cylindrical stem118. As shown inFIG. 2, the second opening124is used to receive upper cylindrical mounting boss128of cylindrical indenter126. As shown inFIG. 2, cylindrical indenter126includes cylindrical wall130further includes a rim138for being face-to-face engaged by the lower lip139formed on cylindrical wall134of the indenter retainer132. The cylindrical indenter126, which may be separately provided, further includes the diamond-shaped protrusions (not shown) to make indents200in the sample which is being hardness tested as illustrated inFIGS. 6A-Dand7A-C. Transverse aperture127is formed in indenter126to indicate the orientation of the protrusion which forms indents200.

The upper and lower housing assemblies12,14can be separated and reconnected with the snap action given by the canted coil spring64as it engages circumferential lip72. The symmetry and orientation of the snap grip indenter mount10will typically always be the same. With this configuration, the user can have multiple indenter/lower housing assemblies140that have each been adjusted to the one upper housing assembly12so the user can at any time remove a lower housing assembly14, typically simply by pulling it down, and replace it with another lower housing assembly14, 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 assembly10, which has yet to be adjusted).

Part 1: Vertical Coarse Rotational Adjustment

1. The user checks that a Knoop Indenter, or similar, is installed as element126or an extension thereof. If not, the user:a. Typically unscrews the indenter retainer132in a counter clockwise direction (when the indenter126is pointing towards the user) or some similar operation.b. The previously installed indenter should drop out. The user replaces with Knoop indenter as indenter126and lines the transverse aperture127in the indenter126up with the front facing pin using a small drill blank or paper clip.c. The user screws back on the indenter retainer132.

2. The user inserts the lower housing assembly14and makes a single indent200in the sample.

3. The user checks that the resulting indent200on the sample is vertical (within a few degrees). If not, the user unscrews the indenter retainer132and moves the indenter126and then tightens again, makes an indent200in the sample and repeats until the indent200is vertical within 5 degrees (see, for example,FIG. 6Das compared toFIGS. 6A-C).

4. Once the indent200is within 5 degrees of being vertical, the user uses the first and second orientation adjusting screws98,100in the lower housing assembly14to 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 below1. If the indent200looks likeFIG. 7A(the rear portion longer than the front portion), then the user should equally loosen the two front symmetry adjusting screws84,86(seeFIG. 2) and then tighten the rear symmetry adjusting screw88.2. If the indent200looks likeFIG. 7B(the rear portion is shorter than the front portion), then the user should loosen the rear symmetry adjusting screw88(seeFIG. 2) and then equally tighten the two front symmetry adjusting screws84,86.3. If the indent200looks likeFIG. 7C(front and rear portions equal), then the vertical symmetry has been adjusted.

Part 3: Horizontal (Left-to-Right) Alignment and Symmetry

1. The user typically unscrews the indenter retainer cap132and rotates the indenter126by 90 degrees to obtain a left-to-right indent. The user typically does not adjust the first and second rotational adjusting screws98,100.

2. The user typically adjusts the two front symmetry adjusting screws84,86. The user typically does not adjust the two front symmetry adjusting screws98,100or the rear symmetry adjusting screw88. The user adjusts screws84,86until the indent200is symmetric about the y-axis.

Part 4: Vertical Fine Rotational Adjustment

The user rotates the indenter126again to give a front-to-back axis orientation and makes an indent200on the sample to check that the indent200has remained symmetric about the x-axis. The user make adjustments to screws98,100to 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.