METHOD OF USE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Patent Application Serial No. 62/221,403, filed September 21, 2015, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF INVENTION

[0002] The subject matter disclosed herein generally relates to the design and inspectability of fasteners and in particular to countersunk washers installed under the head of a bolt with a fillet radii.

BACKGROUND

[0003] Many bolts have fillet radii under their bolt head for increased strength. This feature can prevent a straight washer from being positioned directly under the bolt head because of interference between the inner diameter of the straight washer and the under bolt head fillet. Accordingly, countersunk (CS) washers are often used in many products and industries, including the aviation industry, to provide the necessary clearance for fillet radii. Unfortunately, it is possible to install the countersunk washer upside-down such that the clearance is not aligned with the fillet radii. When this occurs, the improper installation can lead to washer and/or bolt damage. Either of which could lead to the concern for reduced fatigue life of the countersunk washer and bolt, and potentially premature failure under the bolt head. In most cases, once the countersunk washer and bolt are fully installed, the upside-down countersunk washer looks like it is correctly installed. This may be due to non-countersunk portion of the washer being forced on the shaft of the bolt and up and around the fillet radii, the washer concaving upward, and/or the introduction of a material failure of the countersunk washer. In any situation, it is exceedingly difficult to inspect this assembly with normal hardware, and it is almost impossible when working in tight or hard to view locations.

[0004] One custom fix to this issue is a double-countersunk washer so it is fully symmetric and cannot be incorrectly installed. Unfortunately, to meet load requirements, such double- countersunk washers generally require an increase of thickness (e.g., two to three times or more), which adds substantial weight and creates the need for increased space. Also, a double- countersunk washer thickness correspondingly requires the use of longer bolts, all of which consumed more space and adds weight and cost. Such a result is particularly problematic in the aviation industry, where weight and space are two concerns that are critical elements of any fixed wing aircraft or helicopter design. Furthermore, the double-countersunk washer changes the load path of the bolt, which increases stress on the part below the bolt and countersunk- washer.

[0005] As a result, there exists a need for a countersunk washer that can easily minimize incorrect installation while also being easily inspected or verified after installation for correct installation. Finally it would be desirable for such a washer to not add thickness or weight to the countersunk washer or the bolt it is being installed with, all while maintaining the designed load path and avoiding changed paths for stress in the part below the bolt head.

SUMMARY

[0006] In one aspect, a countersunk washer is provided. The countersunk washer has an inner diameter, an outer diameter, an upper surface, a lower surface, and an outer edge. The countersunk washer comprises an inner diameter chamfer sloping from the upper surface towards the lower surface and an indicator element on a portion of the outer edge at or near one of the upper surface or the lower surface. In this configuration, the indicator element is configured to distinguish the upper surface from the lower surface as viewed from the outer edge.

[0007] In another aspect, a countersunk washer having an inner diameter, an outer diameter, an upper surface, a lower surface, and an outer edge is provided. The countersunk washer includes an inner diameter chamfer sloping from the upper surface towards the lower surface and an outer diameter chamfer sloping from the upper surface towards the lower surface and intersecting the outer edge. At least a portion of the outer diameter chamfer comprises a visual surface modification. In this configuration, the outer diameter chamfer is configured to distinguish the upper surface from the lower surface as viewed from the outer edge.

[0008] In another aspect, a method of installing a countersunk washer is provided. The method includes the steps of providing a bolt having a bolt head connected to a shaft portion, wherein a fillet radii is provided at the connection between the bolt head and the shaft portion, and providing a countersunk washer, the countersunk washer including an inner diameter and an outer diameter, an upper surface, a lower surface, an outer edge, an inner diameter chamfer, the inner diameter chamfer sloping from the upper surface towards the lower surface, and an indicator element on the outer edge at or near one of the upper surface or the lower surface. The counter sunk washer is installed on the shaft portion such that the inner diameter chamfer is positioned proximate the fillet radii and the upper surface of the countersunk washer is flush with an underside of the bolt head. The countersunk washer is inspected to identify whether the indicator element is in an orientation corresponding with the inner diameter chamfer being positioned proximate the fillet radii. The bolt is then tightened to a desired tightness.

[0009] Although some of the aspects of the subject matter disclosed herein have been stated hereinabove, and which are achieved in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a perspective view of a countersunk washer according to an embodiment of the presently disclosed subject matter.

[0011] FIG. 2 is a plan view of the countersunk washer according to the embodiment of the presently disclosed subject matter shown in FIG. 1.

[0012] FIG. 3 is a side view of the countersunk washer according to the embodiment of the presently disclosed subject matter shown in FIG. 1.

[0013] FIG. 4A is an exploded view of a countersunk washer on the shaft of a bolt immediately below the fillet radii according to an embodiment of the presently disclosed subject matter.

[0014] FIG. 4B is a section view of the countersunk washer on the shaft of the bolt immediately below the fillet radii according to the embodiment of the presently disclosed subject matter shown in FIG. 4A.

[0015] FIG. 4C is a detail view of the countersunk washer on the shaft of the bolt immediately below the fillet radii according to the embodiment of the presently disclosed subject matter shown in FIG. 4B. [0016] FIG. 4D is a perspective view of a countersunk washer the shaft of a bolt immediately below the fillet radii according to an embodiment of the presently disclosed subject matter.

[0017] FIG. 5A is a side view of a countersunk washer installed with a bolt and the outer diameter chamfer facing toward the underside of the bolt head according to an embodiment of the presently disclosed subject matter.

[0018] FIG. 5B is a section view of the countersunk washer installed with bolt and the outer diameter chamfer facing toward the underside of the bolt head according to the embodiment of the presently disclosed subject matter shown in FIG. 5A.

[0019] FIG. 5C is a detail view of the countersunk washer installed with bolt and the outer diameter chamfer facing toward the underside of the bolt head according to the embodiment of the presently disclosed subject matter shown in FIG. 5B.

[0020] FIG. 5D is a perspective view of a countersunk washer installed with a bolt and the outer diameter chamfer facing toward the underside of the bolt head according to an embodiment of the presently disclosed subject matter.

[0021] FIGS. 6 and 7 are side views of countersunk washers according to embodiments of the presently disclosed subject matter.

[0022] FIG. 8 is a perspective view of a countersunk washer installed with a bolt against a mated part in a correct orientation such that an indicator element is visible according to an embodiment of the presently disclosed subject matter.

[0023] FIG. 9 is a perspective view of a countersunk washer installed with a bolt against a mated part in an incorrect orientation such that an indicator element is obscured according to an embodiment of the presently disclosed subject matter.

DETAILED DESCRIPTION

[0024] The presently disclosed subject matter addresses the problems encountered with conventional countersunk washers by introducing improved countersunk washers and methods of installation that can easily minimize incorrect installation. The countersunk washers disclosed can be easily inspected and verified after installation, and they do not add thickness or weight to the countersunk washer or the bolt with which it is being installed, all while maintaining the designed load path and avoid changing the path of stress to and in the part below the bolt head.

[0025] Referring now to FIGS. 1-9 a new countersunk washer, generally designated 10, is provided. As illustrated, countersunk washer 10 defines an upper surface 12, a lower surface 13 substantially opposing upper surface 12, an outer edge 14, and an inner diameter chamfer 11 (e.g., having a slope with an angle of between about 10 degrees and 80 degrees with respect to upper surface 12). Countersunk washer 10 further includes an indicator element, generally designated 15, on a portion of outer edge 14 at or near one of upper surface 12 or lower surface 13. This indicator element 15 provides an external visual indicator of the orientation of countersunk washer 10, even when in an as-installed position. In this way, a user is able to more readily identify whether countersunk washer 10 is installed in the intended configuration or if it is upside-down.

[0026] In the embodiment illustrated in FIGS. 1-5D, indicator element 15 comprises an outer diameter chamfer 16. In some embodiments, outer diameter chamfer 16 has a 30/60 degree angle, although those having ordinary skill in the art will recognize that any of a range of chamfer angles (e.g., between about 20 and 70 degrees with respect to outer edge 14) can be used as long as indicator element 15 is visible in the desired scenario as discussed below. Alternatively, in some embodiments, one or both of inner diameter chamfer 11 and/or outer diameter chamfer 16 is formed as radii rather than as chamfers. In some embodiments, outer diameter chamfer 16 is formed by machining, lathing, or otherwise mechanically modifying countersunk washer 10. In some alternative embodiments, rather than a continuous chamfer about the outer diameter of countersunk washer 10, indicator element 15 is provided as one or more notches, cutouts, or other surface features on one of upper surface 12 or lower surface 13 at or near outer edge 14.

[0027] In any of these configurations, countersunk washer 10 uses less material than a standard washer while maintaining the necessary load carrying capability since the removal of material resulting from the formation of indicator element 15 does not substantially affect the load area for countersunk washer 10 and an associated fastener. Rather, this weight reduction maintains the design load transfer from the fastener and does not introduce stress path changes to the fastener, countersunk washer 10, and the associated part to which the fastener is coupled. [0028] Alternatively or in addition, in some embodiments, indicator element 15 comprises a visual surface modification configured to distinguish upper surface 12 from lower surface 13 as viewed from outer edge 14 before or after installation. In some embodiments, such a visual surface modification includes a surface texture on one or more of a portion of outer edge 14, upper surface 12, and/or lower surface 13 to increase the visibility of indicator element 15. In some embodiments, such a surface texture is applied by other machining steps such as knurling, dot peening, etching, or another form of surface texturing. In some embodiments, such as that illustrated in FIG. 6, indicator element 15 includes outer diameter chamfer 16 that is knurled to improve its visibility and thus provide enhanced contrast between a first portion of outer edge 14 that is proximate upper surface 12 and a second portion of outer edge 14 that is proximate lower surface 13. Alternatively, in some embodiments, such as that illustrated in FIG. 7, indicator element 15 is a textured edge portion 17 that does not have a chamfer. In any configuration, in some embodiments, one benefit of indicator element 15 including a textured surface feature (e.g., knurling, dot peening, etching, notches, cutouts) is the ability to provide a tactile distinction between a first portion of the outer edge proximate the upper surface and a second portion of the outer edge proximate the lower surface. In such embodiments, a user is able to inspect by touch or gage/probe checking for non-smooth surface in the correct location. Such a physical inspection can be performed either instead of or in addition to a visual inspection.

[0029] In yet further alternative embodiments, indicator element 15 comprises a visual surface modification in the form of color instead of or in addition to surface texture. In such embodiments, a colored portion of one or more of inner diameter chamfer 11, upper surface 12, lower surface 13, and/or outer diameter chamfer 16 (if present) is configured to distinguish upper surface 12 from lower surface 13 as viewed from outer edge 14. In some embodiments, this coloration is accomplished through application of a brightly colored molybdenum disulfide lubricant ("moly lube"), by painting, by anodizing, by using dye or stain, or by any of a variety of other known method of changing the color of a metal surface. The use of moly lube is particularly advantageous in some embodiments to reduce the potential for scratch/galling damage to the fillet radii on an associated fastener. In other embodiments in which countersunk washer 10 is composed of a material other than a metal, the coloration is done with a material- appropriate coloration technique(s) known to those skilled in the art. In any form, the use of coloration serves to reduce the likelihood of an incorrect installation, either by itself or in combination with a mechanical modification to washer 10 (e.g., outer diameter chamfer 16). In some embodiments, the coloration used is a bright or sharply contrasting color that is easily visible during installation of countersunk washer 10. In some embodiments, outer edge 14 is not colored or is a significantly different and contrasting color than that used for indicator element 15. In such embodiments, the addition of the bright and/or sharply-contrasting colored portions provides for a visible detection of whether countersunk washer 10 is correctly installed. This visible indicator significantly reduces the opportunity for incorrect installation and greatly enhances the quality inspection conduced by the post assembly inspector.

[0030] Regardless of the particular form, in some embodiments, indicator element 15 is formed or positioned on the same side of countersunk washer 10 as inner diameter chamfer 11 (e.g., at or near upper surface 12). In this arrangement, indicator element 15 is visible both when countersunk washer 10 is positioned to receive a fastener and after the fastener is installed. FIGS. 4 A through 4D illustrate various views of a bolt 20 being aligned with countersunk washer 10. In this configuration, bolt 20 has a fillet radii 21 at the connection between a bolt head 22 of bolt 20 and a shaft portion 23 of bolt 20. When countersunk washer 10 is in the designed alignment with inner diameter chamfer 11 oriented facing fillet radii 21 (See, e.g., FIGS. 4B and 4C), an installer that is inserting bolt 20 in place will see indicator element 13 as bolt head 22 is moved towards upper surface 12 of countersunk washer 10. (See, e.g., FIG. 4D) In this configuration, prior to tightening of bolt 20 to a desired tightness, if countersunk washer 10 is installed upside-down, indicator element 15 is not visible from the perspective looking at bolt head 22, and the installer may quickly correct the orientation of countersunk washer 10.

[0031] Furthermore, in some embodiments, once bolt 20 is engaged with countersunk washer 10 such that inner diameter chamfer 11 is proximate fillet radii 21 of bolt 20 and upper surface 12 is flush with the underside of bolt head 22, indicator element 15 remains visible at the interface between countersunk washer 10 and bolt head 22. (See, e.g., FIGS. 5A through 5D) In such an embodiment, the visibility of indicator element 15 serves as a sign that countersunk washer 10 is properly installed in an orientation in which inner diameter chamfer 11 provides the desired clearance such that countersunk washer 10 does not engage fillet radii 21.

[0032] Referring to FIG. 8, countersunk washer 10 and bolt 20 are shown installed (e.g., upon tightening of bolt 20 to a desired tightness) in a correct orientation with respect to an associated mated part, generally designated 30. As illustrated, indicator element 15 remains visible at the interface between countersunk washer 10 and bolt head 22. In FIG. 9, however, countersunk washer 10 and bolt 20 are shown installed in an incorrect orientation in which countersunk washer 10 is upside-down with respect to bolt head 22, and this installation is not fully clamped down (e.g., because of interference between fillet radii 21 and bottom surface 13 of countersunk washer 10), so bolt head 22 remains offset farther from mated part 30 than in the correct installation illustrated in FIG 8. In this arrangement, indicator element 15 is oriented towards mated part 30 rather than towards bolt head 22 and is thus at least partially obscured by the interface between upper surface 12 and mated part 30. In this way, a person conducting a post-installation inspection is able to readily identify whether countersunk washer 10 is installed in the proper orientation by identifying whether or not indicator element 15 is visible at the interface between countersunk washer 10 and bolt head 22.

[0033] Alternatively, in some embodiments, indicator element 15 is formed or positioned on the opposite side of countersunk washer 10 as inner diameter chamfer 11 (e.g., at or near lower surface 13). In this arrangement, indicator element 15 is designed to face away from the underside of bolt head 22 and will thus be most visible if countersunk washer 10 is improperly positioned to receive a fastener. In such embodiments, indicator element 15 is not visible at the interface between countersunk washer 10 and bolt head 22 after the fastener is installed, and thus identification of indicator element 15 during post-installation inspection indicates improper installation. Those having skill in the art will recognize that it is a design choice as to whether indicator element 15 serves more as a warning of improper installation or as a sign of proper installation.

[0034] Other embodiments of the current invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Thus, the foregoing specification is considered merely exemplary of the current invention with the true scope thereof being defined by the following claims.