GB2030483A

GB2030483A - Method of making a seal nut

Info

Publication number: GB2030483A
Application number: GB7848952A
Authority: GB
Original assignee: Microdot Inc
Current assignee: Microdot Inc
Priority date: 1978-10-02
Filing date: 1978-12-18
Publication date: 1980-04-10
Also published as: GB2030483B; DE2855712C2; FR2437892B3; JPS5548447A; FR2437892A1; IT7831067A0; IT1192308B; CA1105661A; DE2855712A1

Abstract

An aluminium seal nut (10) having a sealing ring insert (34) is formed from a nut blank which is cold formed with a counterbore (26) leaving a predetermined amount of excess material protruding around the periphery of the counterbore. A bearing surface (16) is subsequently flattened by an additional cold forming step to force the excess material radially inwardly to form a lip (32) for retaining the plastics sealing ring insert (34). Driving surfaces (20) are formed on the torque receiving end (14) during formation of the excess material. The central bore (22) is drilled through and threaded. The metal flow lines at the top of the counterbore follow the contour of the lip (32). The initial step of forming the nut blank may be accomplished by cold forming. <IMAGE>

Description

SPECIFICATION Method of making a seal nut The present invention relates to an improved method of making a seal nut, that is a nut incorporating a sealing means for making the nut fluid tight when tightened down against a member.

Seal nuts are commonly used in the aircraft industry wherein many aircraft are designed with "wet" wings which require that the fasteners utilized in the wings form a fluid-tight seal. Currently, the most widely used type of seal nut in the aircraft industry comprises a nut having an annular deformable sealing ring inserted into a counterbore cut into the bearing surface of the nut. Typically, the sealing ring is designed to protrude above the bearing surface of the nut so that when the nut is tightened down against the workpiece member, the sealing ring is deformed inwardly into the threads on the shank of the bolt thereby forming a fluid tight seal.

Such seal nuts are generally made by a process whereby a counterbore is cold formed into the bearing surface of the nut and then an undercut is machined into the side walls of the counterbore to provide a means for retaining the sealing ring in place. The disadvantage of this process is that the undercut requires a separate machining operation which slows the production rate of the sealing nuts and hence significantly increases cost. Moreover, as with all cutting operations, the undercut surface creates a weakened stress point in the nut which restricts the torque and load limits of the nut.

According to the present invention there is provided a method of making a seal nut comprising a body and a sealing ring disposed within a counterbore in the bearing surface of the body, the method comprising the steps of: forming the body of the nut; cold forming the counterbore in the bearing surface of the body so as to retain some excess material protruding above the bearing surface adjacent the periphery of the counterbore; cold forming said bearing surface to flatten it and to force said excess material radially inwardly; and thereafter inserting the sealing ring into the counterbore to be retained by the inwardly forced material. In particular, utilizing this method a means for retaining the sealing ring insert is created without requiring a separate machining operation and without weakening the structure of the nut.In fact, as will subsequently be explained in greater detail, the cold forming process of the present invention actually strengthens the load bearing surface of the nut.

Thus, the resulting sealing nut produced is not only less costly to manufacture than the prior art nuts but is also a better quality nut.

The present invention will become further apparent from a reading of the detailed description of a preferred embodiment with reference to the accompanying drawings, in which: Figures 1 to 4 illustrate the various stages in the manufacture of a sealing nut according to the teachings of the present invention, Figures 1 and 2 being elevational views and Figures 3 and 4 being cross-sectional views; Figure 5 is a partly cutaway view of a complete sealing nut manufactured according to the present invention; Figure 6 is an enlarged sectional view of a detail of the counterbore of a nut blank made according to conventional practice; and Figure 7 is a view similar to Figure 6 but showing a detail of the counterbore of a nut blank made according to the teachings of the present invention.

A complete sealing nut 10 made according to the present invention is illustrated in Figure 5. The sealing nut 10 includes a body comprising a base section 12 and a torque receiving section or "wrench pad" 14. The torque-receiving section 14 typically bears a plurality of driving surfaces 20 which are adapted to be engaged by a conventional wrench.

The base section 12 of the nut 10 includes a flat annular bearing surface 16 of greater diameter than the torque-receiving section 14, a tapered portion 18 joining the base section 12 to the torque-receiving section 14.

The sealing nut 10 has formed therein a central bore 22 having an internal thread 24. The threaded portion 24 of the central bore 22 is substantially limited to the torque-receiving section 14 of the sealing nut 10, with the central bore 22 being enlarged by a counterbore 26 at the base end 12 of the nut 10. The counterbore 26 is actually a two-step counterbore with the diameter of the central bore 22 being increased initially from the diameter of the thread 24 to a first enlarged diameter portion 28 and then further increased to a second enlarged diameter portion 30 at the base end 12 of the nut 10.

Importantly, it will be noted that the final enlarged counterbore diameter portion 30 is reduced slightly at the bearing surface 16 of the nut 10 to form a lip 32. The purpose of the lip 32, as noted previously, is to provide a means for retaining a sealing ring 34 in place.

The sealing ring 34 comprises an annular-shaped deformable plastics material, for example polytetraf luoroethylene, that has an inner surface 36 that has a diameter slightly larger than the diameter of the thread 24 of the central bore 22 and an outer surface 38 the diameter of which is substantially equivalent to that of the second enlarged counterbore 30. In this manner, the sealing ring 34 is adapted to be press-fitted into the second enlarged counterbore 30 so that it seats against the ledge 40 and is frictionally secured in place by the lip 32.

In addition, it will be noted that the thickness of the sealing ring 34 is substantially greater then the depth of the second enlarged counterbore 30 so that the sealing ring 34 protrudes above the bearing surface 16 of the nut 10 when properly secured within the counterbore 30. In this manner, when the nut 10 is tightened down in use to the point where the bearing surface 16 contacts the workpiece, the protruding portion of the sealing ring 34 is deformed inwardly into the threads of the bolt on which the nut 10 is fastened, thereby forming a fluid-tight seal along the shank of the bolt. The deformation of the sealing ring 34 also serves the added purpose of locking the nut 10 to the bold to resist loosening due to vibration.

Referring now to Figures 1 to 4, the preferred method of making the above described sealing nut 10 will now be explained. A metal slug 40, herein comprised of aluminium is initially cold formed into the basic configuration of a nut blank 44 as illustrated in Figure 2 with a torque-receiving end 14 and a flanged base section 12. The nut blank 44 is then cold formed a second time to form the counterbore 26 in the base end 12 of the nut. The bearing surface 16 of the nut is also formed during the step so as to leave an annular ring or axial lip 42 of excess material protruding above the bearing surface 16 around the periphery of the counterbore 26. Typically, the driving surfaces 20 on the torque-receiving end 14 (Figure 5) are formed during this step as well.

The nut blank 44 is then cold formed a third time to flatten the bearing surface 16 of the nut, thereby causing the excess material in the axial lip 42 to flow radially inwardly to form the radial lip 32, thereby reducing slightly the diameter of the counterbore 26 at the bearing surface 16 of the nut. The central bore 22 is then machined through the torque-receiving end 14 of the nut and an appropriate internal thread formed therein. The annular sealing ring 36 is subsequently snap-fitted into the counterbore 26 to complete the sealing nut 10 illustrated in Figure 5.

Referring to Figures 6 and 7, the advantages of the described method of producing the sealing nut 10 will now be explained. In Figure 6, an enlarged view of a section of the counterbore 26 of a nut blank 44 formed according to conventional practice is shown.

An initial cold forming process has created metal flow lines 48' in the nut blank 44' which substantially follow the contour of the cold formed counterbore 26'. However, when the undercut 46 is machined into the counterbore 26' according to prior art practice, flow lines 48' are broken by the machining operation, thus creating a stress point or stress "riser" 50 in the vicinity of the bend at the base of the undercut 46. The effect of the stress riser 50 is to concentrate stress forces at this point, thereby reducing the integrity of the nut and restricting the torque and load limits of the nut.

In Figure 7, however it can be seen that a nut blank 44 made pursuant to the present teachings results in metal flow lines which substantially follow the contour of the lip 32. Specifically, when the lip 32 is bent over from the position indicated by the dotted line 42, the cold forming process causes the flow lines 48 to follow the movement of metal radially inwardly creating the slightly reduced diameter in the counterbore 26 at the bearing surface 16. Thus, the disadvantage of an undercutting operation breaking flow lines is eliminated.

Accordingly, the nut blank 44 made according to the presently described process possesses superior load bearing characteristics as compared with a nut manufactured pursuant to prior known methods.

Moreover, because the lip 32 is cold formed rather than undercut by a separate machining operation, the cost of manufacturing the present nut is significantly reduced.

Claims

1. A method of making a seal nut comprising a body and a sealing ring disposed within a counterbore in the bearing surface of the body, the method comprising the steps of: forming the body of the nut; cold forming the counterbore in the bearing surface of the body so as to retain some excess material protruding above the bearing surface adjacent the periphery of the counterbore; cold forming said bearing surface to flatten it and to force said excess material radially inwardly; and thereafter inserting the sealing ring into the counterbore to be retained by the inwardly forced material.

2. A method according to claim 1, wherein the counterbore is cold formed so as to retain a circular ridge of excess material protruding axially above said bearing surface around the periphery of the counterbore.

3. A method according to claim 1 or 2, wherein a threaded central bore is formed in the nut with a diameter less than the diameter of the counterbore.

4. A method according to claim 3, wherein said sealing ring is annular and has an internal diameter slightly larger than the diameter of the central bore and an external diameter substantially equal to the diameter of the counterbore.

5. A method according to any preceding claim, wherein the counterbore is cold formed to a depth less than the thickness of the sealing ring so that the sealing ring protrudes above the bearing surface when inserted within the counterbore.

6. A method according to any preceding claim, wherein said sealing ring is snap-fitted into the counterbore.

7. A method according to any preceding claim, wherein the initial step of forming said body is accomplished by cold forming.

8. A method according to any preceding claim, wherein said body is made of aluminium.

9. A method of making a seal nut substantially as herein described with reference to and as illustrated in Figures 1 to 5 and 7 of the accompanying drawings.

10. A seal nut when made by the method of any preceding claim.