GB2513155A

GB2513155A - An arrangement for assessing the clamp load relaxation in a highly-torqued fastener

Info

Publication number: GB2513155A
Application number: GB1306979.4A
Authority: GB
Inventors: Lee Wagstaff; Matthew John Davies; John Marshall
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2013-04-17
Filing date: 2013-04-17
Publication date: 2014-10-22
Anticipated expiration: 2033-04-17
Also published as: GB201306979D0; GB2513155B

Abstract

An arrangement for assessing the clamp load relaxation in a highly torqued fastener clamping two aircraft components together. The fastener comprises a fastening element (1) such as a nut, to which the torque may be applied, and the arrangement comprises a collar (3) being arranged to rotate with the fastening element (1) when the torque is applied and a marker (15). The collar (3) and marker (15) are arranged to enable the extent of the rotation of the fastening element (1) relative to the marker (15), to be evaluated.

Description

AN ARRANGEMENT FOR ASSESSING THE CLAMP LOAP RELAXATION IN

A H IGHLYTOROUE[) FASTENER

Technical Field

The present a.nvennon relates to assessing clamp load.

relaxa Lion and particularly clamp load relaxation in hiqhly-torgued fasteners, Backoround of the invention it is often desirable to know the clamp load of a fastener, in many applications it:5 impractical to measure the clamp load directly, and instead the torque applied to the fastener is measured, and is used to give an indication of what the clamp load is likely to be.

The clamp load of a fastener may reduce over time; often referred to as clamp load relaxation. This is particularly the case where the fastener is clampinq components separated bys ealant or other vIscous material) because the sealant cart seep out over time after the. fastener has initially been Li. ghtened.

Ensur..LLtc. there is suff c;ent and correct. clamp load, is essential in crit.i cal aerosoac:e app.l icat.ion a, such as the connection holding an sn.crine pylon attachment. to an sin' raft wing the engine pylon attachment is the component. rv'n whIch the pylon (holding the engine) hangs) . in. known m5thocJ or.

attaching an engine pylon attachment to an eirc:raft. wing, the nut. of each fastener clamping the two components together is 33 firs tightened by a high torque (e i225Nm) To assess the clamp load relaxation, the. fasteners are then left for two hours and ret.iqhtened usanq that same torouc cf 122.5Mm. If this causes a rotation in the nut of any one of the fasteners,.

of more than 2 degrees, then the fasteners are left again for 2 hours and the re-tightening process is repeated until none of the nuts rotate by more than 2 degrees. The fasteners are then left for 9 hours and re-tightened again (using a torque S of l22SNm). If all the nuts rotate by less than 2 degrees, the clamp load has stabilised and the pylon attachment is correctly attached. If any one of the nuts rotate by more than 2 degrees, they are left for 2 hours and all undergo the re-tightening process described above.

In principle, the high torque can be manually applied using a large torque bar or alike, but manually measuring a small rotation (e.g. around 2 degrees) caused by such a large torque has been found to be problematic. To fit fasteners using the above-mentioned method, including assessing the clamp load relaxation, it is therefore necessary to use a complex machine that automatically both applies the torque and measures the rotation of each nut. A desire has been identified to provide art alternative way of fitting fasteners in critical aerospace applications, and in particular an alternative way of checking the rotation of the fasteners when assessing clamp load relaxation.

Summary of the Invention

According to a first aspect of the present invention there is provided an arrangement according to CLAIM 1. By using a collar and a marker, the position of the fastening element (with which the collar rotates) can be accurately assessed before and after the tightening torque is applied, thereby enabling the clamp load relaxation to be assessed by eye. This means that the fasteners can be fitted manually, providing a simpler and more flexible approach than the prior art.

The collar may comprise an indicator with which the rotation relative to the marker may be assessed. The indicator may be arranged to provide a reference point (for example it may be an arrow, pointer or alike).

In principle, only one marker is necessary to assess the rotation (for example a single marker may be positioned at a fixed angular displacement from the pre-rotation position of the fastening element). However, some embodiments of the invention may comprise a plurality, and more preferably a multiplicity, of markers. The markers may form a scale. Such an arrangement is especially beneficial as the scale may be used to assess multiple rotations of the fastening element.

The above-mentioned arrangement incorporating a scale can be especially useful when the angular rotation is to be measured (i.e. to quantitatively assess how much the fastening element has rotated). However, when assessing clamp load relaxation, it is often necessary to only assess whether the rotation of the fastening element has exceeded a threshold valve, rather that knowing its absolute magnitude of rotation under the applied torque. The marker may denote this threshold value. This means the user only need assess whether or not the collar has rotated past the marker, to determine whether there has been excessive clamp load relaxation.

In a preferred embodiment of the invention, the collar comprises an indicator having a masking portion and a window portion. The indicator and the marker may be such that when the fastening element is in a first rotational position the marker is exposed in the window portion, but when the fastening element is in a second rotational position, the marker is masked by the masking portion. The user preferably need only identify the state' of the marker (i.e. masked or exposed) to identify whether or not the fastening element has undergone at least a threshold value of rotation. Thus, in some embodiments, the user may be able to identify that the fastening element has not undergone at least a threshold value of rotation by virtue of the masking portion masking the marker. For example the masking portion may be downstream of the first window portion, but upstream of a second window portion into which the marker is re-exposed only upon more than a threshold value of rotation.

In other embodiments, the user may be able to identify that the fastening element has not undergone at least a threshold value of rotation by virtue of the marker having remained exposed in the window portion. The collar and the marker may be arranged such that when the fastening element is in the first rotational position the marker is exposed through the window portion, but in the second rotational position the fastening element has been rotated by more than a threshold value of rotation (to the second rotational position), such that the marker is masked by the masking portion. This enables the extent of rotation of the fastening element, relative to the threshold value, to be easily evaluated by observing whether or not the marker remains exposed through the window portion. This provides a clear and unambiguous indication of whether there has been determine excessive clamp load relaxation.

The window portion is preterably sized such that the width of the window portion corresponds to the displacement of the window portion when the fastening element is rotated by the threshold value of rotation. Such an arrangement means that as long as part of the marker is originally at the leading-edge of the window, the marker will not be visible when the threshold rotation has been exceeded. The user does not, therefore need to calculate where to put the marker; it can always be positioned against the leading edge of the window portion (which also has the benefit of being a readily identifiable location at which to place the marker).

The threshold value of rotation is preferably the rotation beyond which excessive clamp load relaxation is deemed to have taken place. The threshold value of rotation may be less than degrees, more preferably less than S degrees. The threshold value of rotation may be 2 degrees.

As described in the introduction above, it may be necessary to assess the clamp load relaxation a number of times (e.g. an intermediate check after a short time period (e.g. 2 hours) and a final check after a longer time period (e.g. 9 hours)).

The collar may comprise a plurality of indicators. Having multiple indicators may enable a different indicator to be used for each assessment of the clamp load relaxation. In principle, each indicator may be provided for only one of a multitude of intermediate checks. However, this is not usually necessary because if such multiple intermediate checks are required, then the indicator of the previous check is likely to be sufficiently distal from the marker used in that previous check, that the indicator can be reused. Therefoxe, in preferred embodiments of the invention, there may be only two indicators: a first indicator for enabling the extent of a first rotation of the fastening element, relative to the marker, to be evaluated, and second indicator for enabling the extent of a subsequent rotation of the fastening element, relative to a second marker, to be evaluated. The second indicator may be remote from the first indicator by at least degrees, and more preferably at least 45 degrees, around the collar. In embodiments in which the collar comprises a plurality of indicators, and each indicator comprise a window portion and a masking portion, the window portions may be the same, or different widths, depending on whether the first and subsequent rotations have different threshold values.

The marker may be pre-printed (for example on a scale).

More preferably the marker is applied manually (for example by marker pen). The marker may be on one of the aircraft components. The marker may be directly on one of the aircraft S components, but more preferably the marker is on a marker-receiving area coupled to one of the aircraft components. The marker-receiving area is preferably detachable from the aircraft component after the fastener has been fitted. For example the marker-receiving area may be an adhesive label on the aircraft component. The marker-receiving area is preferably located radially outward of the fastener. The marker is preferably fixed relative to at least one, and preferably both, the aircraft components.

The collar may be positioned around the fastening element.

The collar may be shaped such that it is rotationally fixed relative to the fastening element. For example, the collar may fit the profile of the fastening element. The collar is preferably located such that torque is not directly applied to the c.llar when the torque is applied to the fastening element. The fastening element may comprise a head for receiving a torquing tool; the collar is preferably below the head.

The present invention is applicable to scenarios in which fasteners are highly-torqued (for example, by a torque of 600Nm or more) The fastener may be suitable for receiving a torque of at least 600Nm. * The fastener may be suitable for receiving a torque of at least lZOONm, The fastener may be suitable for receiving a torque of at least l800Nrn, The fastener comprises a fastening element. The fastener may comprise a bolt and a nut for screw-threaded engagement therewith. The fastening element may be the nut. The fastening element may be part of the bolt (e.g. the bolt head).

The aircraft components are preferably critical aircraft components. For example the components may be an engine pylon attachment and an aircraft wing. The invention is especially beneficial in applications in which sealant is present between the components because such an arrangement tends to suffer from clamp load relaxation as the sealant spreads over time.

The aircraft components may comprise sealant that is compressed by the fastener.

According to another aspect of the invention, there is provided a collar for use in the first aspect of the invention. The collar may comprise an indicator against which the rotation relative to the marker may be assessed. For example, the collar may comprise a masking portion and a window portion. The collar may comprise an opening for fitting over the fastening element.

According to yet another aspect of the invention, there is provided a method according to CLAIM 10. The torque may be manually applied.

The collar may comprise an indicator. The indicator is preferably a masking portion and a window portion. The step of providing a marker may comprise marking a region exposed through the window portion when the fastening element is in the first rotational position, such that by observing whether the marker is masked by the masking portion after applying the torque, the extent of rotation of the fastening element, relative to a threshold value, can be evaluated.

The method may comprise the steps of repeating steps (ii) to (iv) until the marker remains visible through the window portion after the torque has been applied This repetition may be repeated after expiry of a first predetermined time interval from the previous step (iv).

The collar may comprise a plurality of window portions and masking portions. Once the marker remains visible in one of the window portions after the torque is applied, the method may comprise the step of repeating steps (ii) to (iv) for a different window portion in the plurality of window portions.

This repetition may be repeated after expiry of a second S predetermined time interval from the previous step (iv). The second predetermined time interval may be greater than the first predetermined time interval.

The method may involve providing a plurality of markers, one for each repetition of step (ii). The marker(s) may be applied manually.

The method may involve highly-torquing the fastener. The torque applied may be at least l000Nm. The torque may he manually applied.

According to yet another aspect of the invention, there is provided a kit of parts for use in any preceding aspect of the invention, the kit comprising a fastener, and a collar for rotating with the fastening element when the torque is applied.

Any features described with reference to one aspect of the invention ate equally applicable to any other aspect of the invention, and vice versa. For example, any features described with reference to the method of the invention may be equally applicable to the apparatus of the invention and vice versa.

Description of the Drawings

Various embodiments of the invention will now be described, by Hay of example only, with reference to the accompanying schematic drawings of which: Figure la-id show progressive stages in a method of assessing the clamp load relaxation in a highly-torqued fastener according to a first embodiment of the invention; Figure 2 is a perspective view of a collar used in S Figures ia-id; and Figure 3 is a perspective view of a collar in a second embodiment of the invention.

Detailed Description

In known methods of fitting fasteners to attach an engine pylon attachment to a wing, a machine automatically tightens the nut on each fastener using a torque of l22SNm. Since there is sealant present between the structures being clamped by the fastener (pylon attachment, wing skin, wing box etc.) each fastener can be subject to significant clamp load relaxation shortly after it has been tightened. The magnitude of the clamp load relaxation cannot be easily measured directly, so instead the rotation of the nut under a given torque is used to assess the relaxation. More specifically, the fasteners are left for two hours after their initial tightening and then retightened using that same torque of l225Nm. If the torque causes a rotation in any of the nuts, by more than 2 degrees, then the fasteners are left again for 2 hours and the re-tightening process is repeated until none of the nuts rotate by more than 2 degrees. The fasteners are then left for 9 hours and re-tightened again for a final check (using a torque of 1225Nm). If all the nuts rotate by less than 2 degrees, the clamp load has stabilised and the pylon attachment is correctly attached. if any one of the nuts rotate by more than 2 degrees, they are left for 2 hours and all undergo the re-tightening process described above. In known methods, the nut is tightened using a relatively complex -10 -machine which also measures the rotation of the nut. It is desirable to have an alternative way of fitting fasteners in critical aerospace applications, and in particular an alternative way of checking the rotation of the fasteners to S enable the clamp load relaxation to be evaluated.

Figures Ia to lid show progressive stages in a method of assessing the clamp load relaxation according to a first embodiment of the invention. The fastener comprises a size nineteen (i.e. 1. and 3116th inch diameter) bolt 2 (only one end of which is shown in Figure 1W and a nut 1. The fastener is made InconelTM 718 (a nickel-chromium-based superalloy) and is suitable for attaching an engine pylon attachment 12 to a wing box. In other embodiments the fastener may be made from other materials such as titanium, Waspaloytm or MP159Th. The rut 1 is designed to be tightened using a torque of l225Nm, and is capable of withstanding a torque of up to lBOONm.

Referring first to Figure Ia and Figure 2, the nut 1. is first fitted with a plastic collar 3. The collar 3 has an inner profile that matches the profile of the nut 1 such that the collar 3 rotates with the nut I (i.e. without relative rotation between the nut 1 and collar 3). The collar 3 includes a skirt S extending radially outwardly and downwardly towards a circumferential flange 7, The flange 7 defines an indicator in the form of a window portion 9 and adjacent masking portion 11 (discussed in more detail below).

To attach the pylon attachment 12 to a wing box (not shown), the pylon attachment 12 is held in place whilst several fastener bolts 2 (only one of which is shown in Figure ib) are inserted through holes in the wing structure and the pylon attachment 12. A ring-shaped adhesive label 13 is inserted over the shank of the bolt 2 and temporarily stuck to the surface of the pylon attachment 12. As shown in Figure lb each nut 1 is then hand-tightened onto the end of each bolt 2.

-11 -In contrast to the known method of fitting the fastener, the nut is manually tightened using a torque bar (not shown).

The problem of clamp load relaxation does, however, still apply, and the clamp load relaxation must be assessed using broadly the same steps as the prior art: namely leave the fasteners for 2hrs, tighten the fasters, and measure the rotation of each fastening elements under a given torque. In contrast to the prior art however, the rotation of the fastening elements is also measured manually rather than automatically. This provides a simpler way of evaluating the clamp load relaxation. In the first embodiment of the invention, the manual measurement of rotation is enabled by the collar i. as described in more detail below.

After the initial tightening of the nut 1, the user applies a marker 15 onto the label 13 exposed inside the window portion 9 on the flange 7 of the collar 3 (see Figure ic). The user applies the marker using a pen 16 and ensures that the marker 15 extends all the way across the window portion 9, and especially along the leading edge 9a of the window, The window portion 9 is 1.15mm wide at its base (i.e. radially innermost) and 1.27 mm wide at its top (i.e. radially outermost). These distances correspond to the distance travelled by the window portion 9 when subjected to a 2 degree angular rotation of the collar 3. Thus, if the nut 1 (and therefore the collar 3 is rotated under the torque by less than 2 degreas, the part of the marker 15 that was along the leading edge 9a of the window portion 9a remains visible in the window portion 9 after the zotation (see left-hand image in Fig id). This enables the user to readily identify that the nut 1 has not exceeded the threshold rotation and has not suffered excessive clamp load relaxation. In contrast, if the nut 1 is rotated under the torque by more than 2 degrees, all -12 -of the marker is masked by the masking portion 11. This enables the user to readily identify that the nut. I has exceeded the threshold rotation and has therefore suffered excessive clamp load relaxation; repeated tightening of the nut 1 will therefore be required. For such repeated tightening a new marker (not shown) is applied through the window portion 9 and the nut 1 is then retightened (after at least 2 hrs) Figure 2 shows the collar 3 in isolation. As shown in Figure 2, the collar also comprises a second indicator in the form of a second window portion 17 and second masking portion 19 located diametrically opposite the first indicator (these are not shown in Figures la-dJ. The second indicator is used for the final check of clamp load relaxation 9hrs after the previous successful (i.e. < 2 degree rotation) tightening. It is useful to have a second indicator for this purpose because the window portion 9 of the first indicator will, by that stage, have some of the first marker 15 exposed through it.

rigure 3 is a nut 101 and collar 103 according to a second embodiment of the invention. The nut 101 is the same as the nut 101 in the first embodiment but the collar 103 is a different shape. Notably, the collar 103 comprises an indicator in the form of an arrow 121, extending towards the base of the nut 101. The nut 101 is surrounded by an adhesive label 113 on which a multiplicity of markers 115 are printed to form a scale. To measure the rotation of the nut 101, the user notes the starting position of the indicator 121 on the scale (i.e. pre torque being applied) and notes the final position of the marker on the scale (i.e. post torque being applied). The arrangement of the second embodiment of the invention has the advantage that it can be more readily used for several different degrees of rotation (for example in a -13 -.

different application in which the nut must not rotate by more than a threshold angle of, say, 3 degrees).

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will S be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. For example, the torque may be applied to the other end of the fastener (bolt head) and the rotation of the bolt head may be measured. Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents.

It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.

Claims

-14 --Claims 1. An arrangement for assessing the clamp load relaxation in a highly-torqued fastener clamping two aircraft components together, the fastener comprising a fastening element to which the torque may be applied, the arrangement comprising: a collar being arranged to rotate with the fastening element when the torque is applied, and a marker, wherein the collar and marker are arranged to enable the extent of the rotation of the fastening element, relative to the marker, to be evaluated.
2. An arrangement according to claim 1, wherein the collar comprises a masking portion and a window portion, such that when the fastening element is in a first rotational position the marker is exposed through the window portion, but when the fastening element is in a second rotational position, the marker is masked by the masking portion.
3. Art arrangement according to claim 2, wherein the collar is arranged such that in the second rotational position, the fastening element has been rotated by more than a threshold value of rotation, such that the marker is masked by the masking portion.
4. An arrangement according to claim 3, wherein the window portion is sized such that the width of the window corresponds to the displacement of the window when the fastening element is rotated by the threshold value of rotation.-15 -.
5. An arrangement according to claim 4, wherein the threshold value of rotation is 2 degrees.
6. An arrangement according to any of claims 2 to 5, the collar comprising a plurality of window portions and masking portions, each window portion and associated masking portion being arranged to enable the extent of a rotation of the fastening element, relative to a respective marker, to be evaluated.
7. An arrangement according to any preceding claim wherein the fastening element is suitable for receiving a torque of at least l000t4m,
8. An arrangement according to any preceding claim, wherein the fastener comprises a bolt and a nut for screw-threaded engagement with the bolt.
9. An arrangement according to claim 8 wherein the fastening element is the nut.
10. A collar for use as the collar in any preceding claim, the collar comprising an opening foz fitting over the fastening element, and an indicator against which the rotation of the collar relative to a marker may be assessed.
11. A method of assessing the clamp load relaxation in a highly-torqued fastener clamping two aircraft components together1 the method comprising the steps of: (i) providing a collar arranged to rotate with a fastening element of the fastener, (ii) providing a marker; -16 - (iii) applying torque to the fastening element to rotate the fastening element from a first rotational position to a second rotational position: and (iv) evaluating the extent of the rotation of the collar S relative to the marker.
12. A method according to claim 11, wherein the collar comprises a masking portion and a window portion, and the step of providing a marker comprises marking a region exposed through the window portion when the fastening element is in the first rotational position, such that by observing whether the marker is masked by the masking portion after applying the torque, the extent of rotation of the fastening element, relative to a threshold value, can be evaluated.
13. A method according to claim 12, comprising repeating steps (ii) to (iv) until the marker remains visible in the window portion after the torque has been applied.
14. A method according to any precediig claim wherein the torque applied is at least l000Nm.
15. A method according to any preceding claim wherein the torque is manually applied.
16. A kit of parts for use in any of claims 1 to 9 or claims 11 to 15, comprising a fastener, and a collar for rotating with the fastening element when the torque is applied.