BUSH

Abstract: A bush (10) for installation in easily crushed or marred work material (40) such as apertured honeycomb sheet or fibre reinforced plastics material, enables the work material to be secured to a support (70), by means of a nut and bolt, without damage. The bush (10) has a cylindrical body (12) longer than the thickness of the work (40), and a flange (14) for abutting a face (44) of the work at one end of the body. The other end of the body has an annular boss (30) which projects beyond the other face (46) of the work (40), and, peripherally of the boss (30), an annular skirt (28) which during installation can be deformed to provide a retaining flange (60) for engaging the other face (46) of the work. A bolt (76) can then be passed through the bush (10) and a support (70), and secured with a nut (82). Only the bush (10) directly engages the work (40).

Description: This invention relates to bushes, and more particularly to a bush for installation in apertured work of easily marred or crushed material to receive a bolt or similar headed fastening device, and whereby the bolt can be prevented from damaging the work. Honeycomb structural materials, and composite materials such as plastics material having reinforcement fibres of carbon or glass, particularly in the form of sheets, are used extensively where their light-weight properties and high-tensile strength are advantageous. However, such materials are easily marred or crushed, or otherwise subjected to physical damage, resulting in significant impairment of their desirable properties. Such damage can occur when work made of such materials is assembled and fastened together using fasteners, such as bolts or the like, having a head of small bearing area which bears on a surface of the material adjacent to a hole through which a shank of the fastener passes. Thus, the head of the fastener may crush the material, or may abrade, tear, or otherwise mar the surface of the material, to the considerable detriment of its properties. Furthermore, the shank of the fastener, having a small bearing area, may also damage the material around the hole unless the hole is sleeved or bushed in order to reinforce the material or increase its bearing area. US-A-3765465 discloses a bush in accordance with the prior art portion of claim 1, in the form of a sleeve or grommet for installation in an apertured sheet, and in which the radially enlarged flange presents a frusto-conical surface facing generally towards the body of the sleeve to enable the enlarged flange to be countersunk into a correspondingly frusto-conical recess in the sheet so that the flange lies flush with the face of the sheet. Furthermore, in US-A-3765465, the axial length of the boss is substantially the same as the radial thickness of the skirt, so that, when the skirt is deformed to provide a retaining flange for engaging the other face of the sheet in which the bush is installed, the free end of the boss lies flush with the retaining flange. Thus, the length of the boss is insufficient for the boss to be upstanding above the retaining flange, and is insufficient for the bush to be tolerant of any appreciable variation in thickness of the sheet. Such a bush is neither intended nor adapted to protect a sheet in which the bush is installed from compressive forces applied by, for example, a nut and bolt which extends through the bush. Thus, the flush countersunk radially enlarged flange cannot serve to space a clamping face of the nut and bolt from the adjacent face of the sheet, and the boss is not long enough to project beyond the retaining flange and so will allow compressive force to be applied directly to the retaining flange and, in turn, to the sheet. Furthermore, the frusto-conical shape of the radially enlarged flange renders it susceptible to deformation by the compressive forces applied by a nut and bolt, and the position of the flange relative to the face of the sheet is profoundly affected by the slightest variation in depth of the frusto-conical spot face formed in the sheet to accommodate the flange. Therefore, the radially enlarged flange cannot be relied upon to protect the sheet from contact with, or compressive force applied by, the nut and bolt. We have now devised a bush for installation in an aperture in work which may be easily marred or crushed, and which will afford protection to the work against damage by a bolt used to fasten the work to another structure. According to the invention, there is provided a bush having a generally cylindrical body and a radially enlarged flange at one end of the body for abutting one face of a workpiece, and an axial bore throughout the body and flange, the body having a tail portion remote from the flange, and an intermediate portion between the flange and the tail portion, the tail portion comprising an annular boss periphererally of the bore, and a deformable annular skirt peripherally of the boss, the annular skirt being radially separate from the boss and having an axial length greater than that of the boss, the annular skirt being deformable so that it may be flared outwardly to provide a retaining flange spaced from the flange, characterised in that the radially enlarged flange presents a planar surface facing towards the body, for engaging one face of an apertured sheet, and the annular skirt is deformable progressively to form a retaining flange the position of which may be variable within a predetermined range of distances from the radially enlarged flange, so as to accommodate workpieces having a thickness which varies within said predetermined range, the axial length of the boss being greater than the radial thickness of the skirt by an amount sufficient for the boss to remain upstanding above a retaining flange formed at any position within the predetermined range. The annular skirt may be spaced radially from the annular boss. The annular skirt may extend beyond the boss in the direction axially and away from the flange. The peripheral surface of the body may be splined in a region intermediate between the flange and the skirt. The splined region may be spaced axially from the flange and/or the skirt. Preferred forms of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a side elevation of a bush according to the invention; Figure 2 is a plan view of the bush of Figure 1; Figure 3 is a longitudinal sectional elevation of the bush of Figure 1; Figures 4, 5 and 6 are sectional elevations of a bush, a workpiece in which the bush is to be installed, and tooling for installing the bush, and showing, respectively, initial, immmediate, and final stages in the installation of the bush, and Figure 7 is a sectional view illustrating the use of the bush in the mounting of a sheet on a support. Referring first to Figure 1 of the drawings, a bush 10 comprises a generally cylindrical body 12, and a radially enlarged flange 14 at one end of the body. The flange 14 presents a smooth planar surface 16 facing towards the body, a circular peripheral surface 18, and a flat bearing surface 20 at the end of the bush remote from the body. The flange 14 has a diameter substantially greater than that of the body, so as to present a relatively large bearing area, and has a substantial thickness so as to be robust. A through bore 22 of constant diameter extends axially through the flange and body of the bush. The body 12 has a splined region 24 intermediate between its ends, in which the external surface of the body is provided with splines which extend in the axial direction, and rise slightly above the level of the surface of the body outside the splined region. The splines may be formed by impressing longitudinal grooves into the external surface of the body so as to displace material to form the individual splines between pairs of adjacent grooves. Beyond the splined region 24 in the direction away from the flange, the body has a tail portion 26 extending to the end remote from the flange 14. The tail portion 26 is constituted by two annular parts which are concentric with the bore 22 and with each other. These parts are a radially outer skirt 28 and a radially inner boss 30, and are separated radially from each other by an annular gap 32. The length of the boss 30, in the axial direction of the bush, is made sufficient to accommodate some variation in thickness of the work in which it is intended to install the bush, and is made equal to, or very slightly greater than, the difference between the intended maximum and minimum thicknesses of the work. The length of the skirt 28, in the axial direction, is greater than that of the boss 30 so that the skirt 28 extends beyond the end of the boss 30 in the direction away from the flange 14. The radial thickness of the boss is approximately half the radial thickness of the body in the region between the tail portion 26 and the flange 14. The radially inner surface of the boss forms part of the wall of the bore 22. The skirt 28 peripherally surrounding the boss is spaced radially from the boss, to form the gap 32, by a distance which is equal to less than a quarter of the radial thickness of the body outside the tail portion. Thus, the skirt has a radial thickness less than that of the boss, and is, therefore, relatively thin and more easily deformable than the boss. The skirt is intended to be permanently deformed, by means of a suitable tool during installation, so as to flare outwardly to form a retaining flange. In this embodiment, the bush is made of mild carbon steel. The installation and use of a bush according to the invention will now be described with reference, by way of example, to the installation of the bush 10 in a workpiece in the form of a sheet of carbon fibre reinforced plastics material, and the fastening of the sheet to a support member. Referring first to Figure 4, the bush 10 is installed in a sheet 40 of carbon fibre reinforced plastics material of appropriate thickness and having a through aperture 42 by first inserting the body 12 of the bush through the aperture 42 so that the planar surface 16 of the flange 14 abuts a face 44 of the sheet and the tail portion 26 projects beyond the opposite face 46 of the sheet, and then deforming the skirt 28 so as to abut the face 46, using suitable tooling. The diameter of the aperture 42 and the diameter of the body are related in such a way that, on insertion of the body, the splines embed slightly in the material of the sheet peripherally of the aperture. The axial length of the portion of the body between the flange 14 and the tail portion 26 is made not greater than, but preferable closely similar to the thickness of the sheet 40, so that the tail portion of the inserted bush lies within the sheet and projects substantially beyond the face 46. The tooling used in this example includes a support dolly 48, and an annular anvil 50 which, together with a guide pin 52, is mounted in a suitable press (not shown) for movement towards and away from the dolly. The dolly 48, which in this example is apertured, is then positioned in contact with the bearing surface 20 of the flange 14 and with its aperture in register with the bore 22 of the bush, so as to support the bush against a force applied to the tail-portion and directed axially towards the flange. The annular anvil 50, for deforming the skirt 28, has an annular flat face 54 peripherally of an annular lip 56 which projects forwardly of and tapers away from the face 54. The guide pin 52 is located in the aperture of the anvil, projecting forwardly of the face 54 and the lip 56, and has a diameter such as to be a clearance or sliding fit in the bore 22 of the bush. The internal diameter of the lip 56 is slightly greater than the external diameter of the boss 30, and its narrow forward extremity is of such a thickness as to be able to enter the gap between the boss and the skirt 28. The press is then operated to move the pin and anvil towards the dolly. The pin enters the bore 22, centring the anvil and bush relative to each other as shown in Figure 4, and then the lip 56 engages the inner surface of the skirt and, as the anvil moves forwardly, progressively deforms the skirt as shown in Figure 5, causing the skirt to become outwardly flared so that it encounters the flat face 54 and is thereby flattened and pressed into contact with the face 46 of the sheet to constitute a retaining flange 60 (shown in Figure 6) which opposes the flange 14. The boss 30 is not deformed by the anvil and remains upstanding above the retaining flange 60 and the face 46 of the sheet. Thus, the bush 10 is installed in the sheet and retained therein by the flanges 14 and 60 which abut the two opposing faces of the sheet. Operation of the press during installation of the bush is controlled carefully so as to avoid damaging the sheet by compression between the flanges 14 and 60. The sheet can then be fastened to a support member by means of a conventional fastener, such as a bolt. Thus, in one example, shown in Figure 7, the support member is in the form of an angle bar 70 having a flange 72 formed with an aperture 74. The sheet, with the installed bush 10, is offered to the flange 72 so that the bearing surface 20 of the flange 14 of the bush abuts the flange 72, and the bore of the bush registers with the aperture 74. A bolt 76 having a head 78 and a threaded shank 80 is then inserted through the bore and the aperture 74, so that the head 78 abuts the projecting boss 30, and part of the shank projects beyond the flange 72 of the support. A nut 82 is then engaged with the projecting part of the shank and rotated to draw the head of the bolt towards the flange 72. Thus, the bush can be tightly clamped between the bolt head and the supporting flange 72 so that the sheet is firmly attached to the support, but the tightened bolt does not engage the sheet itself and causes no damage to the sheet. More particularly, the boss spaces the head of the bolt from the face 46 of the sheet by a distance corresponding to the distance through which the boss 30 projects beyond the face 46 of the sheet.

Claims: A bush having a generally cylindrical body (12) and a radially enlarged flange (14) at one end of the body for abutting one face (44) of a workpiece (40), and an axial bore (22) throughout the body (12) and flange (14), the body (12) having a tail portion (26) remote from the flange (14), and an intermediate portion between the flange (14) and the tail portion (26), the tail portion (26) comprising an annular boss (30) peripherally of the bore (22), and a deformable annular skirt (28) peripherally of the boss (30), the annular skirt (28) being radially separate from the boss (30) and having an axial length greater than that of the boss (30), the annular skirt (28) being deformable so that it may be flared outwardly to provide a retaining flange (60) spaced from the flange (14), characterised in that the radially enlarged flange (14) presents a planar surface (16) facing towards the body (12), for engaging one face (44) of an apertured sheet (40), and the annular skirt (28) is deformable progressively to form a retaining flange (60) the position of which may be variable within a predetermined range of distances from the radially enlarged flange (14), so as to accommodate workpieces having a thickness which varies within said predetermined range, the axial length of the boss (30) being greater than the radial thickness of the skirt (28) by an amount sufficient for the boss (30) to remain upstanding above a retaining flange formed at any position within the predetermined range. A bush as claimed in claim 1, characterised in that the annular skirt (28) is spaced radially from the annular boss (30). A bush as claimed in either of claims 1 or 2, characterised in that the peripheral surface (18) of the body (12) is splined in a region (24) intermediate between the flange (14) and the skirt (28). A bush as claimed in claim 3, characterised in that the splined region (24) is spaced axially from the flange (14) and/or the skirt (28). An assembly comprising an apertured workpiece (40) having a bush (10) as claimed in any preceding claim installed therein, the intermediate portion of the bush (10) extending through an aperture (42) in the workpiece (40), and the skirt (28) having been deformed to form a retaining flange (60), the workpiece (40) being held between the said radially enlarged flange (14) and the retaining flange (60), characterised in that the boss (30) is upstanding above the retaining flange (60).

Inventors: LACEY, RAYMOND DENNIS, WOODROW, MICHAEL
Applicants: AVDEL SYSTEMS LIMITED
Application year: 1988
Main classification: F16B5
IPC codes: F16B5, F16B43