GB2402190A

GB2402190A - Threaded wire insert

Info

Publication number: GB2402190A
Application number: GB0312492A
Authority: GB
Inventors: Michael Colin Roberts
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-05-30
Filing date: 2003-05-30
Publication date: 2004-12-01
Also published as: GB0312492D0

Abstract

A helically coiled wire-type threaded insert (10), for installation in a tapped bore (20), comprises engagement means (18) for interlocking engagement with a recess (22) in the bore. The engagement means may comprise at least one detent, protrusion or kink; or the wire may be bent radially outwards at one end. The insert may also comprise tool engagement means for engagement with an insertion and/or extraction tool. The tool engagement means can be in the form of one or more recesses on the inner side of the coil. A method of installing the insert comprises inserting the insert in the opening of the bore and turning the insert until the engagement means engage and lock in a recess in the bore.

Description

1 - 24021 90

THREADED WIRE INSERT

This invention relates to threaded inserts for installation in tapped holes, and in particular concerns helically coiled wire-type threaded inserts and more particularly a tangless helical wire inserts.

Threaded inserts are commonly used in engineering applications where it is desirable to install threaded fasteners such as bolts, studs and the like in components of relatively softer material, for example aluminium or aluminium alloys. Threaded inserts are installed in tapped holes to increase the pull out strength of the installed fastener and protect the tapped hole in the softer material so that the threaded fastener may be repeatedly inserted and extracted from the tapped hole without damaging the component in which the hole is formed.

Helical wire inserts generally comprise a wire helix having a substantially diamond cross-section in the longitudinal direction of the wire. The end of the wire at one end of the inserts is deformed inwards to form a radial tang which provides a turning means for engagement with an insertion/extraction tool for turning the insert into the tapped hole. A notch in the wire enables the tang to be broken off after insertion which allows the bolt or other threaded fastener to protrude beyond the end of the insert when installed. A portion of the helix is deformed from a substantially circular cross-section to a polygonal cross-section for increased frictional engagement with the threaded fastener when inserted into the hole.

Helical wire inserts are usually inserted into tapped holes using an insertion tool which comprises a tube and an internal driving means. The tube has an internal thread at one end and an aperture is provided in one side of the tube for receiving a helical wire insert. The insert is turned by the internal drive means so that it engages the internal thread so that it is compressed radially inwards such that its diameter is reduced to that of the tapped hole. The insert may then be correctly positioned above the tapped hole so that the insert can be wound into the tapped hole by turning the internal drive l - 2 means.

Helical wire inserts of the above mentioned type have a number of advantages in that they are relatively inexpensive components and, they are relatively easy to install in a tapped hole, which is itself relatively inexpensive to manufacture. The inserts can be removed and replaced in-situ, and where appropriate the size of a reinforcement boss around the tapped hole is typically only slightly greater than that a similar size tapped hole with no insert. However, there are various disadvantages associated with helical threaded wire inserts, in particular the tang is usually small and easily lost after it has been removed. This is a particular problem in say engineering production and maintenance environments where the tang can be lost within the interior of an engine block or casing for example. In addition problems can occur if the insert does not grip the tapped thread sufficiently during installation since installation of the threaded fastener in the insert can cause the insert to be wound through the tapped hole. This is a particular problem where tapped holes are provided in components where it is not possible to inspect both sides of the tapped hole after assembly of the threaded fastener in the hole. This problem can occur where helical wire inserts are used in gas turbine engine structural components such as engine casings. Another disadvantage concerns the fact that the positional tolerance of the diamond thread of the insert is not usually as precise as a machined thread and therefore the threaded fastener will not evenly load on all threads of the insert. The maximum tensile load of a bolt is therefore reduced when used with a threaded insert in comparison with the case when a machined thread is engaged by the fastener. A particular concern in high temperature applications such as in gas turbine engines is that known inserts have a limited life.

While helical wire inserts may be reused fifteen times or so in operating temperatures of 20 c, the inserts may be reused maybe five times at operating temperatures of 550 c and the upper operating temperature of these inserts is generally 600 c.

There is a requirement therefore for an improved helical coil wire-type threaded insert which can avoid, at least in part, many of the problems associated with a known wire- type inserts. - 3

According to an aspect of the invention there is provided a helically coiled wire-type threaded insert for installation in a tapped bore, the insert comprising engagement means for interlocking engagement with a recess in a tapped bore.

The insert of the present invention does not rely on its external threaded diameter being greater than the internal thread of the tapped bore it is to be inserted in to provide sufficient friction to prevent wind through of the insert when torque is applied to the insert when a bolt or other threaded fastener is inserted into the tapped hole.

Instead the insert of the present invention is provided with engagement means for positive interlocking engagement of the insert with a recess in the tapped bore.

In preferred embodiments, the engagement means comprises at least one detent on at least one coil of the insert for engagement with a respective recess in the tapped bore.

Preferably, the detent comprises a radial protrusion on a radially outer side of the insert. Thus, as the insert is wound into the tapped bore the radial protrusion is deflected radially inwards when it engages the tapped internal thread by deflection of the coils on which it is formed. The radial protrusion is thus biased radially outwards against the internal thread and therefore when it reaches the position of the recess it moves radially outwards to engage and locate in the recess. The biasing force acting on the radial protrusion holds the protrusion in the recess during insertion and extraction of the threaded fastener. In addition the threaded fastener prevents the protrusion from disengaging the recess as it is being installed. In this way it is possible for the contact forces between the insert and the tapped hole are relatively low over the majority of the length of the insert, thereby ensuring the torque required to install the insert is relatively low.

In preferred embodiments the protrusion is positioned aVor towards one end of the wire insert. Preferably the protrusion is positioned at the trailing end of the insert, that is to say the end of the insert that enters the tapped hole last. This can be advantageous since it readily enables the recess or recesses to be formed in the tapped hole aVor close to the opening of the hole. The protrusion may be in the form of a kink in the wire near the trailing end of the wire. - 4

In one preferred embodiment, the wire of the wire insert is bent radially outwards at one end of the wire to provide the protrusion. The wire is preferably bent outwards at the aforementioned trailing end of the insert. This provides for a relatively simple construction and can result in reduced manufacturing costs when compared with embodiments where the protrusion is formed at a point on the outer surface of the insert at some position along the wire. In this embodiment there is no requirement for the cross-section of the wire to change in the region of the protrusion since all that is required is that the wire is bent at each end.

The insert of the present invention is preferably provided with a tool engagements means for engagement with an insertion and/or extraction tool. In preferred embodiments the tool engagement means comprises at least one tool engagement recess on the radially inner side of the insert. The tool engagement recess may be provided on one coil or on many adjacent coils of the insert. Preferably, the tool engagement recesses are formed along a significant part of the axial length of the insert.

In preferred embodiments, a plurality of tool engagement recesses are circumferentially spaced about the radially inner side of the insert. In one example four such recesses are spaced at equal intervals of 90 around the radially inner side of the insert.

In preferred embodiments, the recess or recesses have a substantially semi-circular cross-section in the plane of the insert perpendicular to the longitudinal axis of the insert.

According to another aspect of the invention there is provided a method of installing a helically coiled wire-type threaded insert in a tapped bore; the said method comprising the steps of: positioning a helically coiled wire-type threaded insert at the opening of a tapped bore, the said insert comprising engagement means for interlocking engagement with a recess in the said bore; inserting the insert in the opening of the bore so that it threadably engages the internal thread of the said bore; and turning the insert in the bore until the said insert engagement means engages a recess in the bore and locks the insert in the bore.

Preferably the insert comprises a plurality of tool engagement recesses circumferentially spaced about the radially inner side of at least one coil; the said method includes the step of inserting an insert installation and extraction tool into the interior of the said insert, the said tool having a radially expansible chuck-type engagement means for engagement with the said recesses, and radially expanding the said chuck so that corresponding parts of the chuck engagement means engage the recesses to lock the said tool with respect to the insert for turning the insert in the bore.

According to another aspect of the invention there is provided a method of extracting a helically coiled wire-type threaded insert in a tapped bore; the insert having a plurality of tool engagement recesses circumferentially spaced about the radially inner side of at least one coil; the said method comprising the steps of: inserting an insert installation and extraction tool into the interior of the said insert, the said tool having a radially expansible chuck-type engagement means for engagement with the said recesses; radially expanding the said chuck so that corresponding parts of the chuck engagement means engage the recesses to lock the said tool with respect to the insert; and turning the insert in the bore in an insert extraction direction to extract the insert from the bore.

The above mentioned methods of the present invention readily enable the insert of the present invention to be inserted and/or extracted to/from a tapped bore. In particular the first mentioned method readily enables an insert of the present invention to be inserted in a tapped bore without using a tang on the insert for engagement with an insert installation tool. In this respect it is to be understood that the same tool may be - 6 used for installation and extraction purposes.

Various embodiments of the invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a helically coiled wire-type threaded insert; Figure 2 is a plan view of an insert according to a first embodiment of the invention; Figure 3 is a plan view of an insert according to a second embodiment of the invention; Figure 4 is a plan view of the insert of Figure 2 installed in a tapped bore; Figure 5 is a plan view of the insert of Figure 3 installed in a tapped bore; Figure 6 is a cross-section view of the insert of Figure 2 installed in a tapped blind bore; and Figure 7 is a cross-section view of an insert according to another embodiment of the invention showing an installation and extraction tool located within the insert.

Referring to Figure 1, there is shown a helically coiled wire-type threaded insert 10 for installation in a tapped hole. The wire of the insert has a generally diamond shaped cross-section along its length and is wound to form a cylindrical-type structure comprising a plurality of adjacent wire coils 12 of substantially the same shape and size such that the insert has a generally constant circular cross-section along its length.

The insert has a leading end 14 and a trailing end 16. The leading end 14 defines the end of the insert that first engages the internal thread of the tapped bore when it is inserted and the trailing end at the other end of the insert is the part of the insert that enters the internally threaded tapped bore last. The structure of the leading end 14 is substantially the same as the trailing end except that the trailing end is provided with one or more radial protrusions 18, as shown in Figures 2 and 3, which constitute engagements means for interlocking engagement with a recess in the tapped bore into which the insert is inserted.

Referring to Figure 2, in this embodiment the radial protrusion 18 is provided towards the end of the wire and is formed as a kink in the wire at a position on the final coil 30 or so from the end of the wire. The protrusion 18 protrudes radially outwards from the radially outer diameter of the insert. In the embodiment of Figure 3 the protrusion 18 is provided at the end of the wire and is formed by bending the end of the wire radially outwards away from the circumferential direction of the coils such that the end part of the wire extends radially outwards of the outer diameter of the insert.

In the embodiments shown in Figures 2 and 3 the insert 10 is provided with a single radial protrusion 18 for interlocking engagement with a recess in a tapped bore in which the insert is to be installed. It is to be understood however that the invention also contemplates embodiments where more than one protrusion is provided on the insert, and also embodiments where a plurality of protrusions are distributed around one or more coils of the insert along the length of the insert.

The inserts of Figures 2 and 3 are shown respectively installed within a tapped bore in Figures 4 and 5. The tapped bore of Figure 4 is identical to that of Figure 5 and comprises an internal thread 20 of substantially similar diameter to the external thread on the outer side of the inserts for loose threaded engagement of the insert in the tapped bore. The tapped bores are each provided with a pair diametrically opposed pilot holes 22 in the surface of the component 24 comprising the tapped bore and which open into the tapped bore to receive and form an interlocking engagement with l the radial protrusion 18.

As can best be seen in the drawing of Figure 6, the holes 22 are formed in the surface of the component 23 in which the tapped bore 20 is formed. In Figure 6 the tapped bore 20 is provided in a boss type structure 25 which extends from a planar structure - 8 27. The holes 22 are shaped and sized to receive the protrusion 18 of the insert as the insert is turned within the tapped bore 20, and to hold the insert in the bore when a torque is applied to the insert by the action of a threaded fastener being inserted into the bore once the insert has been installed, thereby preventing movement of the insert with respect to the tapped bore.

The threaded insert 10 is installed in the bore 20 with minimum interference between the respective internal and external threads since the insert is held in the bore substantially by the inter engagement of the protrusion 18 and hole 22 instead of pressure forces generated by an interference fit between the insert and the bore. In this respect it will be understood that the torque required to install the insert in the bore is significantly less than it would otherwise be if the insert were held within the bore by the action of pressure forces generated by an interference fit. In this respect it is possible to position the insert of the present invention within the bore using an appropriate insert engagement tool, which engages the interior of the insert for turning the insert within the bore. This is described more clearly with respect to Figure 7.

As shown in Figure 7, the insert 10 is provided with a plurality of circumferentially spaced tool engagement recesses 24 on the inner thread of the insert. In the arrangement shown, four recesses 24 are equally spaced at 90 intervals around the internal thread. The recesses 24 do not extend the full length of the insert, and although only one of the wire coils may be provided with recesses 24, it is preferable that the recesses extend along the longitudinal axis of the insert such that they are formed in a plurality of adjacent coils.

Each recess 24 has a semi-circular cross-section in the plane of the insert perpendicular to the longitudinal axis of the insert. The recesses 24 extend radially from the radially inner most point on the wire coil to a radial mid-point position where the diamond cross-section of the wire is greatest. The recesses 24 are provided for engagement with corresponding shaped protrusions 26 that constitute part of an insert installation and extraction tool. The protrusions are movable radially from the retracted position shown in Figure 7 to an insert engagement position where they contact the - 9 - respective recesses 24. The engagement tool protrusions 26 are moved by the action of a tapered mandrel 28 extending in the longitudinal direction of the insert through an aperture defined by the radially inner surfaces of the engagement protrusions 26.

During installation and/or extraction of the insert the installation/extraction tool is inserted into the interior of the insert such that the engagement protrusions 26 occupy the position shown in Figure 6 from where they are moved radially outwards to engage with the respective recesses 24 by movement of the mandrel along its longitudinal axis.

The engagement protrusions 26 and mandrel 28 define a chuck type structure that is capable of being expanded and retracted radially to engage and disengage the insert.

In this position the insert can be turned about its axis in the tapped bore in which it is to be inserted into or extracted from. An applied torque is transferred from the mandrel 28 to the engagement of protrusions 26 to turn the insert in the tapped bore. The applied torque may be sufficient to cause the radial protrusion 18 on the insert to be deflected radially inwards as it is moved from its position within irrespective one of the pilot holes 22. As there is little interference between the insert and tapped bore the torque required to turn the insert within the tapped bore is relatively small. Thus the contract pressure between the engagement protrusions 26 and the recesses 24 can be minimised.

Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be effected without further inventive skill and effort. For example, the invention contemplates embodiments where the insert is provided with more than one protrusion 18 on the radially outer side of the insert, and also embodiments where a plurality of protrusions are distributed around one or more of the wire coils. In addition, it is to be understood that the invention may be applied to blind bores and well as through bores as required. -

Claims

1 A helically coiled wire-type threaded insert for installation in a tapped bore, the insert comprising engagement means for interlocking engagement with a recess in a tapped bore.

2 An insert as claimed in Claim 1 wherein the said engagement means comprises at least one detent on at least one coil of the said insert for engagement with a respective recess in a tapped bore on insertion of the insert in the said bore.

3 An insert as claimed in Claim 2 wherein the said detent comprises a radial protrusion on a radially outer side of the insert.

4 An insert as claimed in Claim 3 wherein the said protrusion is positioned at or towards one end of the wire insert.

An insert as claimed in Claim 4 wherein the wire of the insert is bent radially outwards at one end thereof to provide the said protrusion.

6 An insert as claimed in any preceding claim wherein the said engagement means comprises a single radial protrusion.

7 An insert as claimed in any preceding claim comprising tool engagement means for engagement with an insertion and/or extraction tool.

8 An insert as claimed in Claim 7 wherein the said tool engagement means comprises at least one tool engagement recess on the radially inner side of at least one coil.

9 An insert as claimed in Claim 8 comprising a plurality of tool engagement recesses circumferentially spaced about the said radially inner side of at least - 11 one coil.

An insert as claimed in Claim 8 or Claim 9 wherein the said recess or recesses has/have a substantially semi-circular cross-section in the plane perpendicular to the longitudinal axis of the insert.

11 A method of installing a helically coiled wire-type threaded insert in a tapped bore; the said method comprising the steps of: positioning a helically coiled wire-type threaded insert at the opening of a tapped bore, the said insert comprising engagement means for interlocking engagement with a recess in the said bore; inserting the insert in the opening of the bore so that it threadably engages the internal thread of the said bore; and turning the insert in the bore until the said insert engagement means engages a recess in the bore and locks the insert in the bore.

12 A method as claimed in Claim 11 wherein the insert comprises a plurality of tool engagement recesses circumferentially spaced about the radially inner side of at least one coli; the said method includes the step of inserting an insert installation and extraction tool into the interior of the said insert, the said tool having a radially expansible chuck-type engagement means for engagement with the said recesses, and radially expanding the said chuck so that corresponding parts of the chuck engagement means engage the recesses to lock the said tool with respect to the insert for turning the insert in the bore.

13 A method of extracting a helically coiled wire-type threaded insert in a tapped bore; the insert having a plurality of tool engagement recesses circumferentially spaced about the radially inner side of at least one coil; the said method comprising the steps of: inserting an insert installation and extraction tool into the interior of the said insert, the said tool having a radially expansible chuck-type engagement means for engagement with the said recesses; - 12 radially expanding the said chuck so that corresponding parts of the chuck engagement means engage the recesses to lock the said tool with respect to the insert; and turning the insert in the bore in an insert extraction direction to extract the insert from the bore.

14 An insert substantially as hereinbefore described, and/or with reference to the accompanying drawings.

A method substantially as hereinbefore described, and/or with reference to the accompanying drawings.