Patent Description:
Single-sided ("blind") fasteners are more prone to outgassing than more conventional double-sided fasteners. The outgassing problem can be solved to some extent by providing an interference fit between the fastener and the bore wall, but in some safety-critical environments (for instance an aircraft fuel tank) it may be necessary to provide an additional degree of protection.

A spark containment cap for a blind fastener is disclosed in <CIT>. A sealed cavity is formed between a cap and a structure. A joint is then assembled by inserting a blind fastener through an aperture from an opposing side of the structure to the cap. The blind fastener is then engaged to form the joint. With such an arrangement, the joint may be formed during final assembly with access to only one side of the structure. Further prior art fasteners are disclosed in <CIT>, <CIT>, <CIT>.

A first aspect of the invention provides a blind fastener which can be installed into a workpiece with access to only one side of the workpiece, according to claim <NUM>, comprising: a head; a shaft with a tail; a tail of the blind fastener comprising the tail of the shaft and a sleeve surrounding the tail of the shaft; and a barrier secured to the tail of the blind fastener, wherein the sleeve is configured to expand away from the tail of the shaft to form an expanded sleeve which is forced against a face of a workpiece to clamp the workpiece between the head and the expanded sleeve, the expanded sleeve comprising a folded bulb or flange, and wherein the barrier is configured to be forced against the face of the workpiece to form a sealed cover around the tail of the blind fastener.

Optionally the barrier comprises a skirt with a skirt rim, and the skirt is configured to force the skirt rim against the face of the workpiece to form a seal between the skirt rim and the face of the workpiece.

Optionally the barrier comprises a cap or sheath with a skirt and an apex, the tail of the blind fastener has sides and an end, the sides of the tail are covered by the skirt, and the end of the tail is covered by the apex.

Optionally the barrier is configured to deform radially towards or away from the tail of the shaft.

Optionally the barrier is configured to expand plastically and/or elastically away from the tail of the shaft to form an expanded barrier.

Optionally the barrier has a skirt with a skirt rim which is separated from the sleeve by a gap, and the skirt is configured to contract towards the sleeve to at least partially close the gap.

Optionally the barrier is secured to the tail of the blind fastener by an interference fit, an adhesive bond, or a snap-fit joint.

Optionally the barrier has an apex, and the blind fastener further comprises an axial cavity between the apex of the barrier and the tail of the blind fastener.

Optionally the blind fastener further comprises a sealant between the barrier and the tail of the blind fastener.

Optionally the barrier comprises a skirt and the blind fastener further comprises a pocket between the skirt and the tail of the blind fastener.

A further aspect of the invention provides a method of installing a blind fastener, according to claim <NUM>, the blind fastener comprising: a head; a shaft with a tail; a tail of the blind fastener comprising the tail of the shaft and a sleeve surrounding the tail of the shaft; and a barrier secured to the tail of the blind fastener, the method comprising the steps of: a) passing the barrier and the tail of the blind fastener through a workpiece; and b) tightening the blind fastener so that: the sleeve expands away from the tail of the shaft to form an expanded sleeve comprising a folded bulb or flange; the expanded sleeve is forced against a face of the workpiece to clamp the workpiece between the head and the expanded sleeve, and the barrier is forced against the face of the workpiece so that the barrier forms a sealed cover around the tail of the blind fastener.

Optionally the barrier comprises a skirt with a skirt rim, and the skirt rim is forced against the face of the workpiece to form a seal between the skirt rim and the workpiece.

Optionally as the sleeve expands away from the tail of the shaft to form the expanded sleeve, the barrier expands elastically or plastically away from the tail of the shaft to form an expanded barrier.

Optionally the barrier is in an expanded state before step a. ; the barrier is in an elastically compressed state as it passes through the workpiece in step a. ; and the barrier springs at least partially back towards its expanded state after it has passed through the workpiece in step a.

Optionally the barrier comprises a skirt and the blind fastener comprises a pocket between the skirt and the tail of the blind fastener, wherein an uncured sealant flows into the pocket as the blind fastener is tightened, and the uncured sealant cures in the pocket to bond the skirt to the tail of the blind fastener and/or to bond the skirt to the workpiece.

A further aspect of the invention provides a joint comprising: a workpiece; a blind fastener comprising: a head; a shaft with a tail; a tail comprising the tail of the shaft and a sleeve surrounding the tail of the shaft; and a barrier secured to the tail of the blind fastener, wherein the sleeve has an expanded part in contact with a face of a workpiece to clamp the workpiece between the head and the sleeve, the expanded part of the sleeve comprising a folded bulb or flange, wherein the barrier comprises a skirt with a skirt rim in contact with the face of the workpiece to form a sealed cover around the tail of the blind fastener, and wherein the skirt rim is held by the tail of the blind fastener in a state of compression which causes the skirt rim to apply a sealing force to the face of the workpiece.

Optionally the joint further comprises a sealed air pocket between the skirt and the tail of the blind fastener.

Optionally the joint further comprises a cured sealant which bonds the skirt to the tail of the blind fastener and/or bonds the skirt to the workpiece.

A further aspect of the invention provides an aircraft fuel tank comprising a joint according to the previous aspect, wherein the aircraft fuel tank has an interior, and the skirt and tail of the blind fastener are within the interior of the aircraft fuel tank.

A further aspect of the invention provides an aircraft comprising an aircraft fuel tank according to the previous aspect.

A blind fastener <NUM> shown in <FIG> comprises a metal shaft <NUM> with an unthreaded body <NUM>, an externally threaded tail <NUM> and a frustoconical head <NUM>. A pin <NUM> is attached to the head <NUM> of the shaft <NUM>. The shaft <NUM> is surrounded by a metal sleeve 3a. The sleeve comprises a frustoconical head 9a surrounding the head <NUM> of the shaft <NUM>, a cylindrical body 5a surrounding the body <NUM> of the shaft <NUM>, and a tail 7a surrounding the tail <NUM> of the shaft <NUM>. The tail 7a of the sleeve 3a has an internal thread which engages with the external thread of the tail <NUM> of the shaft <NUM>. The head 9a and body 5a of the sleeve 3a are unthreaded.

In general terms, the blind fastener <NUM> comprises a head (the head <NUM> of the shaft <NUM> and the head 9a of the sleeve 3a); a body (the body 5a of the sleeve 3a and the body <NUM> of the shaft <NUM>); and a tail (the tail <NUM> of the shaft <NUM> and the tail 7a of the sleeve 3a).

A barrier <NUM> is fitted to the tail of the blind fastener <NUM>, secured to the tail 7a of the sleeve 3a. The barrier <NUM> is an integrated part of the blind fastener <NUM> - carried by the tail <NUM>, 7a of the blind fastener <NUM>.

The barrier <NUM> comprises a sheath with a conical apex <NUM>, a cylindrical sheath body <NUM> and a widened cylindrical skirt <NUM>. The sides of the tail <NUM>, 7a of the blind fastener <NUM> are covered by the skirt <NUM> and the sheath body <NUM>, and the end face <NUM> of the tail <NUM>, 7a of the blind fastener <NUM> is covered by the cap apex <NUM>.

As will now be described below with reference to <FIG>, the sleeve 3a is configured such that a relative rotation between the threads causes the tail 7a of the sleeve 3a to expand away from the tail <NUM> of the shaft <NUM> to form an expanded sleeve with a flange <NUM> which is forced against a reverse face 23a of a workpiece <NUM> to clamp the workpiece between the head <NUM>, 9a of the blind fastener and the expanded sleeve. The barrier <NUM> is also configured to be forced against the reverse face 23a of the workpiece <NUM> by the tail <NUM>, 7a of the blind fastener <NUM> to form a sealed cover around the tail <NUM>, 7a of the blind fastener.

The blind fastener <NUM> is installed by first passing the barrier <NUM> and the tail <NUM>, 7a of the blind fastener <NUM> through a workpiece <NUM>. The blind fastener <NUM> is shown partly inserted in <FIG> and fully inserted in <FIG>.

Next the blind fastener <NUM> is tightened by a tool (not shown). The tool has a first part which grips the pin <NUM>, and a second part which grips the head 9a of the sleeve 3a. The first part of the tool rotates the pin <NUM>, which in turn rotates the shaft <NUM>. The second part of the tool holds the head 9a of the sleeve 3a to prevent the sleeve from rotating. Thus there is a relative rotation between the external threads of the tail <NUM> of the shaft <NUM> and the internal threads of the tail 7a of the sleeve 3a. This relative rotation drives the tail 7a of the sleeve 3a axially towards the workpiece <NUM> so that it deforms plastically and expands radially away from the tail <NUM> of the shaft <NUM> to form an expanded sleeve with a folded flange <NUM> shown in <FIG>. There may be a knurling on the sleeve 3a so it deforms in a predictable way.

As the blind fastener <NUM> is tightened further, the flange <NUM> is forced against the reverse face 23a of the workpiece <NUM> to clamp the workpiece <NUM> between the head <NUM>, 9a and the expanded sleeve.

The barrier <NUM> is configured to expand away from the tail <NUM> of the shaft <NUM> to form an expanded barrier with a flared part <NUM> of the skirt <NUM> as the sleeve 3a expands away from the tail <NUM> of the shaft <NUM>. Thus as the tail 7a of the sleeve 3a expands away from the tail <NUM> of the shaft <NUM> to form the expanded sleeve, the barrier <NUM> is forced by the sleeve 3a so that it also expands radially away from the tail <NUM> of the shaft <NUM> to form an expanded barrier shown in <FIG>. Like the sleeve 3a, the barrier <NUM> deforms plastically as it expands radially away from the tail <NUM> of the shaft <NUM>.

The barrier <NUM> is typically made of a hard electrically insulating (non-conducting) material that can be plastically deformed and has low friction so it can be passed through the workpiece easily. For instance the barrier <NUM> may be made of a polymer (reinforced or not).

The expanded barrier of <FIG> is also pulled axially by the tail 7a of the sleeve 3a so that the flared part <NUM> of the skirt <NUM> is forced against the reverse face 23a of the workpiece <NUM> and the barrier <NUM> forms a sealed cover around the tail <NUM>, 7a of the blind fastener <NUM>, providing a spark containment barrier. The flared part <NUM> of the skirt <NUM> comprises a skirt rim 21a which is forced against the reverse face 23a of the workpiece <NUM> to form an air-tight seal between the skirt rim 21a and the reverse face 23a of the workpiece <NUM>. In this case the rim is an edge of the barrier <NUM>.

The barrier <NUM> may be secured to the tail 7a of the sleeve 3a by an interference fit, an adhesive bond, a thermoplastic weld or a snap-fit joint. Alternatively the barrier <NUM> may be held mechanically in a notch or recess in the tail 7a of the sleeve, or carried by another part (such as a nut) fitted onto the tail 7a of the sleeve. In general the barrier <NUM> may be secured to the tail <NUM>, 7a of the blind fastener <NUM> by any connection which prevents the barrier <NUM> from rotating with the shaft <NUM> and enables the tail <NUM>, 7a of the blind fastener <NUM> to force the skirt rim 21a against the reverse face 23a of the workpiece <NUM>.

Optionally the sheath body <NUM> may have an internal thread which engages with the external thread of the tail <NUM> of the shaft <NUM>. In this case the relative rotation drives the sheath body <NUM> axially towards the workpiece <NUM>. Alternatively the sheath body <NUM> may be unthreaded.

The tool continues to rotate the pin <NUM> until the blind fastener <NUM> is fully tightened, the increased torque causing the pin <NUM> to shear off as shown in <FIG>.

In the fully tightened joint of <FIG>, the sleeve 3a has an expanded flange <NUM> in contact with the reverse face 23a of a workpiece <NUM> to clamp the workpiece <NUM> between the head <NUM>, 9a and the sleeve 3a, and the skirt rim 21a is in contact with the reverse face 23a of the workpiece <NUM> to form a sealed cover around the tail <NUM>, 7a of the blind fastener <NUM>. The majority of the deformation of the barrier <NUM> is a plastic deformation, but there is also an element of elastic deformation as the fastener is tightened, so that the barrier <NUM> in the fully tightened joint is held by the tail <NUM>, 7a of the blind fastener <NUM> in a state of compression. This causes the skirt rim 21a to apply a sealing force to the reverse face 23a of the workpiece <NUM>, inhibiting leakage of gas between the skirt rim 21a and the reverse face 23a of the workpiece <NUM>.

The barrier <NUM> may expand away from the sleeve 3a to form an air pocket between the barrier <NUM> and the sleeve 3a. Alternatively the barrier <NUM> may remain tightly in contact with the sleeve 3a so there is no air pocket, or a minimal air gap may open up towards the skirt rim 21a.

As demonstrated in <FIG> the fastener <NUM> is a "blind" fastener: that is, a fastener which can be installed into a workpiece with access to only one side of the workpiece. The blind fastener <NUM> provides an improvement over the blind fastener is disclosed in <CIT>. In <CIT> the cap must be fixed to the reverse face of the workpiece in a separate cap installation process before the blind fastener is inserted. The blind fastener <NUM> incorporates an integrated spark containment barrier <NUM> which means that access to the reverse face of the workpiece is not required, and the barrier <NUM> can be installed along with the rest of the blind fastener <NUM> in a single installation process.

<FIG> shows a blind fastener 1a with a different barrier <NUM> fitted. The blind fastener has many features in common with the blind fastener <NUM> of <FIG>, and the same features are given the same reference number.

In this case the barrier <NUM> comprises a cap with a flat cap apex <NUM>, and a skirt with a cylindrical part <NUM> and a flared part <NUM>. The skirt <NUM>, <NUM> has an annular skirt rim 37a. The cylindrical part <NUM> of the skirt has an annular seat 39a which contacts the edge of the tail 7a of the sleeve 3a. The sides of the tail <NUM>, 7a of the blind fastener 1a are covered by the skirt <NUM>, <NUM> and the tail <NUM> of the shaft is covered by the cap apex <NUM>. There is an axial air cavity <NUM> between the end face of the tail <NUM> of the shaft and the cap apex <NUM>.

The annular seat 39a of the skirt may be secured to the edge of the tail 7a of the sleeve 3a by an adhesive bond, a thermoplastic weld, or a snap-fit joint. Alternatively the barrier <NUM> may be held mechanically in a notch or recess in the tail <NUM> of the shaft <NUM>, or carried by another part (such as a nut) fitted onto the tail 7a of the sleeve 3a. In general the barrier <NUM> may be secured to the tail <NUM>, 7a of the blind fastener 1a by any connection which prevents the barrier <NUM> from rotating with the shaft <NUM> and enables the tail <NUM>, 7a of the blind fastener 1a to force the skirt rim 37a against the reverse face 23a of the workpiece <NUM> as shown in <FIG>. Optionally a portion of the flared part <NUM> of the skirt <NUM> may be secured to the outer face of the tail 7a of the sleeve 3a.

The skirt rim 37a is separated from the sleeve 3a by a gap 37b to provide an air pocket <NUM> between the skirt and the tail of the blind fastener. The flared part <NUM> of the skirt is configured to contract elastically towards the sleeve 3a to at least partially close the gap 37b to enable the barrier <NUM> to be pushed through a workpiece <NUM> as shown in <FIG>. Thus the barrier <NUM> is configured to contract elastically towards the sleeve 3a to at least partially close the gap as it passes through the workpiece.

As shown in <FIG>, the barrier <NUM> is in an expanded state before being passed through the workpiece <NUM>. As the barrier <NUM> passes through the workpiece <NUM> it is configured to deform radially towards the tail <NUM>, 7a of the fastener, so it is an elastically compressed state as it passes through the workpiece <NUM>. The barrier <NUM> then springs back to its expanded state after it has passed through the workpiece <NUM> as shown in <FIG>, re-opening the gap 37b and associated air pocket <NUM> between the sleeve 3a and the skirt rim 37a.

The barrier <NUM> is typically made of a hard electrically insulating (non-conductive) material that can be elastically deformed and has low friction so it can be passed through the workpiece <NUM> easily. For instance the barrier <NUM> may be made of a polymer (reinforced or not).

In the fully tightened joint of <FIG>, the sleeve 3a has an expanded flange <NUM> in contact with the reverse face 23a of the workpiece <NUM> to clamp the workpiece <NUM> between the head <NUM>, 9a and the sleeve 3a, and the skirt rim 37a is in contact with the reverse face 23a of the workpiece <NUM> to form a sealed cover around the tail <NUM>, 7a of the blind fastener 1a. The majority of the deformation of the barrier <NUM> is an elastic deformation, so that the barrier <NUM> in the fully tightened joint is held by the tail <NUM>, 7a of the blind fastener 1a in a state of compression, and the flared part <NUM> of the skirt has an outwardly bowed shape shown in <FIG>. This causes the skirt rim 37a to apply a sealing force to the reverse face 23a of the workpiece <NUM>, inhibiting leakage of gas between the skirt rim 37a and the reverse face 23a of the workpiece <NUM>. In the fully tightened joint of <FIG> the air pocket <NUM> between the barrier <NUM> and the tail <NUM>, 7a of the blind fastener 1a is sealed.

The axial air cavity <NUM> gives the clearance required to enable the cap to move towards the workpiece <NUM> as shown in <FIG>. In an alternative embodiment shown in <FIG>, a blind fastener 1b is shown with the axial air cavity <NUM> filled with a sealant material <NUM> before the cap <NUM> is installed. As the cap moves towards the workpiece <NUM>, the sealant <NUM> escapes the cavity through grooves in the tail <NUM>, 7a of the fastener, then flows into the air pocket <NUM> between the skirt and the tail <NUM>, 7a of the blind fastener 1b as shown in <FIG>.

Tightening the fastener compresses the sealant in the pocket <NUM> and forces the sealant against the workpiece <NUM> and/or against the tail 7a of the sleeve, providing an enhanced seal. The sealant in the pocket <NUM> then cures to bond the cap <NUM> to the reverse face 23a of the workpiece <NUM> and/or to bond the cap to the tail 7a of the sleeve. A small amount of sealant <NUM> may also remain in the axial cavity <NUM> at the end of the blind fastener, and when this cures it will bond the cap apex <NUM> to the end face <NUM> of the tail <NUM> of the shaft <NUM>.

A blind fastener <NUM> shown in <FIG> is similar to the blind fastener 1a of <FIG>. Identical parts are given the same reference number and will not be described again.

The externally threaded tail <NUM> of the shaft <NUM> is surrounded by a metal sleeve 103a which has an internally threaded tail 107a and an unthreaded body 105a. The internal thread of the tail 107a of the sleeve 103a engages with the external thread of the tail <NUM> of the shaft <NUM>. The head <NUM> and body <NUM> of the shaft <NUM> are surrounded by a collar with a frustoconical head <NUM>, a cylindrical body <NUM> and a tapered tip <NUM> which has axial ridges or grooves (not shown). The tapered tip <NUM> is fitted into the unthreaded body 105a of the sleeve 103a as an interference fit.

Thus the blind fastener <NUM> comprises a head (the head <NUM> of the shaft and the head <NUM> of the collar); a body (the body <NUM> and tip <NUM> of the collar, and the body <NUM> of the shaft <NUM>); and a tail (the tail <NUM> of the shaft <NUM>, and the body 105a and tail 107a of the sleeve 103a).

A barrier <NUM> is fitted to the tail <NUM>, 105a, 107a of the blind fastener <NUM>, secured to the tail 107a of the sleeve 103a. The sides of the tail of the blind fastener <NUM> are covered by the barrier <NUM>. Unlike the previous embodiments, the barrier <NUM> consists only of a flared skirt, so the end face <NUM> of the tail of the shaft is not covered by the barrier <NUM>.

The barrier <NUM> may be secured to the tail 107a of the sleeve 103a by an interference fit, an adhesive bond, a thermoplastic weld or a snap-fit joint. Alternatively the barrier <NUM> may be held mechanically in a notch or recess in the tail 107a of the sleeve 103a, or carried by another part (such as a nut) fitted onto the tail 107a of the sleeve 103a. In general the barrier <NUM> may be secured to the tail of the blind fastener by any connection which prevents the barrier <NUM> from rotating with the shaft <NUM> and enables the tail of the blind fastener to force the skirt rim <NUM> against the reverse face 123a of the workpiece <NUM>.

The sleeve 103a is configured such that a relative rotation between the threads causes the body 105a of the sleeve 103a to expand away from the tail <NUM> of the shaft <NUM> to form an expanded sleeve with a folded flange <NUM> which is forced against the reverse face 23a of the workpiece <NUM> to clamp the workpiece between the head <NUM>, <NUM> and the flange <NUM> of the expanded sleeve. The barrier <NUM> is also configured to be forced against the face of the workpiece <NUM> by the tail of the blind fastener <NUM> to form a sealed cover around the tail of the blind fastener <NUM>.

As shown in <FIG>, the barrier <NUM> is in an expanded state before being passed through the workpiece <NUM>. As the barrier <NUM> passes through the workpiece <NUM> it is configured to deform radially towards the tail <NUM> of the shaft <NUM>, so it is an elastically compressed state as it passes through the workpiece <NUM>. <FIG> shows the barrier <NUM> in such a compressed state, although it has started to spring back since most of it has already passed through. The barrier <NUM> then springs back to its fully expanded state after it has passed through the workpiece <NUM> as shown in <FIG>, re-opening the gap between the sleeve 103a and the skirt rim <NUM>.

In the fully tightened joint, the barrier <NUM> is held by the tail of the blind fastener <NUM> in a state of compression, with a compressed shape shown in <FIG>. This causes the skirt rim <NUM> to apply a sealing force to the reverse face 23a of the workpiece <NUM>, inhibiting leakage of gas between the skirt rim <NUM> and the reverse face 23a of the workpiece <NUM>.

In the fully tightened joint of <FIG> there is a sealed air pocket <NUM> between the barrier <NUM> and the tail of the blind fastener <NUM>. This provides a sealed chamber of compressible gas that can contain any ignition hazard resulting from the fastener <NUM>.

As the fastener <NUM> is tightened, the body 105a of the sleeve 103a rides over the tapered tip <NUM> of the collar, as shown in <FIG>. The ridges or grooves in the tapered tip <NUM> of the collar grip the body 105a of the sleeve 103a and prevent it from rotating with the shaft <NUM>.

In the embodiments above, the blind fastener <NUM>, 1a, <NUM> is tightened by rotating the shaft <NUM>. <FIG> shown an alternative embodiment in which the blind fastener is tightened by pulling the shaft.

The blind fastener <NUM> of <FIG> comprises a metal shaft with a detachable pin <NUM>, a body <NUM>, and a domed mandrel <NUM>. The shaft is surrounded by a metal sleeve with a head 209a, a body 205a and a tail 207a.

The blind fastener <NUM> comprises a head (the head 209a of the sleeve); a body (the body 205a of the sleeve and the body <NUM> of the shaft); and a tail (the mandrel <NUM> and the tail 207a of the sleeve).

A barrier <NUM> is fitted to the tail of the blind fastener <NUM> as shown in <FIG>, secured to the mandrel <NUM>. The barrier <NUM> comprises a cap with a domed cap apex <NUM>, and a flared skirt <NUM> with a skirt rim <NUM>.

The domed cap apex <NUM> may be secured to the mandrel <NUM> by an adhesive bond or a thermoplastic weld. Alternatively the barrier <NUM> may be held mechanically to the mandrel <NUM>, for instance by a snap-fit j oint, or by a clamp or other fastener.

As shown in <FIG>, the sleeve is configured such that as the pin <NUM> is pulled back, the tail 207a of the sleeve is compressed by the mandrel <NUM> which causes the sleeve to expand away from the shaft to form an expanded sleeve with a flange <NUM> which is forced against the reverse face 123a of a workpiece <NUM> to clamp the workpiece between the head 209a of the blind fastener and the flange <NUM> of the expanded sleeve. The skirt <NUM> is also configured to be forced against the reverse face 123a of the workpiece <NUM> by the mandrel <NUM> to form a sealed cover around the tail <NUM>, 207a of the blind fastener.

The skirt <NUM> is in an expanded state before being passed through the workpiece <NUM>. As the skirt <NUM> passes through the workpiece <NUM> it is configured to deform radially towards the tail of the blind fastener, so it is an elastically compressed state as it passes through the workpiece <NUM>. The skirt <NUM> then springs back to its expanded state after it has passed through the workpiece <NUM> as shown in <FIG>, re-opening the gap between the sleeve 207a and the skirt rim <NUM>.

In the fully tightened joint of <FIG>, the sleeve has an expanded flange <NUM> in contact with the reverse face 123a of a workpiece <NUM> to clamp the workpiece between the head 209a and the flange <NUM>, and the skirt rim <NUM> is in contact with the reverse face 123a of the workpiece to form a sealed cover around the tail <NUM>, 207a of the blind fastener <NUM>. The skirt <NUM> in the fully tightened joint is held by the tail of the blind fastener in a state of compression. This causes the skirt rim <NUM> to apply a sealing force to the reverse face 123a of the workpiece <NUM>, inhibiting leakage of gas between the skirt rim <NUM> and the reverse face 123a of the workpiece <NUM>.

In the fully tightened joint of <FIG> there is a sealed air pocket <NUM> between the barrier <NUM> and the tail of the blind fastener. This provides a sealed chamber of compressible gas that can contain any ignition hazard resulting from the fastener.

In the embodiments shown above, the edge of the skirt <NUM>, <NUM>, <NUM>, <NUM> provides the skirt rim which is in contact with the reverse face of the workpiece. <FIG>, by way of example, shows the skirt rim <NUM> of <FIG> in the fully tightened joint.

In other embodiments, the edge of the skirt may be bent back inwardly or outwardly to form a rim with a lip. <FIG> shows an example of an outwardly bent lip 158a and <FIG> shows an example of an inwardly bent lip 158b. In both cases the lip is bent back so that the edge of the skirt is not in contact with the workpiece. The skirt rim in this case is the base 157a, 157b of the lip which is in contact with the reverse face of the workpiece.

In the embodiments of <FIG>, <FIG>, <FIG> and <FIG> the barrier <NUM>, <NUM>, <NUM> springs back to its fully expanded state after passing through the workpiece. However it is not necessary to do so - in other words the barrier <NUM>, <NUM>, <NUM> may only partially spring back. In this case the flange <NUM>, <NUM>, <NUM> will push the skirt out radially as the sleeve expands.

In the embodiments described above, the shaft <NUM>, <NUM>, <NUM>, <NUM> and the sleeve 3a, 103a, 209a, 205a, 207a are typically made of metallic materials. The barrier <NUM>, <NUM>, <NUM>, <NUM> is typically made of a different material to the shaft <NUM>, <NUM>, <NUM> and a different material to the sleeve 3a, 103a, 203a.

The barrier is preferably made from an electrically insulating material, such as a polymer material.

By way of example, the barrier <NUM>, <NUM>, <NUM>, <NUM> may be made from Nylon, acrylonitrile butadiene styrene (ABS), polyethylene, thermoplastic elastomer (TPE or TPE) or another polymer material, optionally fabric reinforced.

In the embodiments described above, the barrier <NUM>, <NUM>, <NUM>, <NUM> forms a sealed cover around the tail of the blind fastener. This enables the barrier <NUM>, <NUM>, <NUM>, <NUM> to contain any ignition hazards (such as sparking or ejection of hot gas/particles) which are generated at the blind fastener. If a sealed air pocket <NUM>, <NUM>, <NUM> is present, then this provides a sealed chamber of compressible gas that can contain any ignition hazards.

The blind fasteners <NUM>, 1a, 1b, <NUM>, <NUM> may be used in any application, but most preferably the blind fastener is used in an aircraft such as the aircraft <NUM> shown in <FIG>. The wings <NUM> of the aircraft contain fuel tanks, one of which is indicated at <NUM> in <FIG>. The upper and lower boundaries of the tank are provided by upper and lower skins of the wing, and the fore and aft boundaries are provided by forward and rear spars of the wing. In the embodiments described above, the barrier and the tail of the blind fastener may be within the interior of the fuel tank <NUM> so that the barrier contains ignition hazards within the full tank. The interior <NUM> of the fuel tank <NUM> is indicated in <FIG>, <FIG>, <FIG>, <FIG> and <FIG>.

The workpiece is illustrated in the <FIG>, <FIG> and <FIG> as a single component <NUM> for ease of illustration, but in practice the workpiece will typically comprise a pair of components which are joined together by the blind fastener as indicated by the two-component workpiece <NUM> in <FIG>. For example the two components of the workpiece may be a wing skin and a wing rib, a wing spar and a wing rib, or a wing spar and a wing skin.

In the embodiments described above, the barrier is secured to the sleeve and/or secured to the tail of the shaft. In other embodiments the barrier may be secured to another part of the tail of the blind fastener.

In the embodiments described above, the barrier is configured to be forced against the face of the workpiece by the tail of the blind fastener to form the sealed cover around the tail of the blind fastener. In other embodiments, the barrier may be forced against the face of the workpiece by another component of the blind fastener.

In the embodiments described above, the head of the blind fastener is part of the shaft or part of the sleeve. In other embodiments, the head of the blind fastener may be provided by another component.

In some of the embodiments described above, the tail of the shaft has an external thread, the sleeve has an internal thread which engages with the external thread of the tail of the shaft, and the sleeve is configured such that a relative rotation between the threads causes the sleeve to expand away from the tail of the shaft to form the expanded sleeve. In other embodiments, such as <FIG>, the sleeve and shaft may be unthreaded.

In the embodiments described above, the barrier comprises a skirt with a skirt rim, and the skirt rim is forced against the reverse face of the workpiece to form a seal between the skirt rim and the reverse face of the workpiece. In other embodiments the skirt may have no rim, or another part of the barrier may be forced against the reverse face of the workpiece.

In some of the embodiments described above, the barrier comprises a cap or sheath which is secured to the tail of the blind fastener. In these embodiments the cap or sheath comprises an apex and a skirt, the tail of the blind fastener has sides and an end, the sides of the tail are covered by the skirt, and the end of the tail is covered by the apex. That is, the cap or sheath fully covers the tail of the blind fastener. In other embodiments (for example <FIG>) the barrier may consist only of a skirt so only part of the tail of the blind fastener is covered by the barrier.

In the embodiments described above, the barrier is configured to expand (plastically and/or elastically) away from the tail of the shaft to form an expanded barrier as the sleeve expands away from the tail of the shaft. In other embodiments, the barrier may not expand during installation.

In the embodiments described above, the barrier is configured to deform (plastically and/or elastically) radially towards or away from the tail of the shaft. In other embodiments, the barrier may not deform during installation.

In the embodiments described above, the barrier has a skirt with a skirt rim which is separated from the sleeve by a gap. Optionally the barrier is configured to contract towards the sleeve to at least partially close the gap. This makes it easier to insert the barrier through a workpiece.

In the embodiments described above, the barrier is secured to the tail of the blind fastener by an interference fit, an adhesive bond, a snap-fit joint, a thermoplastic weld, or a fastener or other mechanical means. In general terms any type of connection may be used which enables the barrier to be pulled by the tail of the blind fastener into sealing engagement with the reverse face of the workpiece.

In some embodiments described above, the blind fastener has an axial cavity, typically an air cavity <NUM>, between an apex <NUM> of the barrier and an end face <NUM> of the tail of the blind fastener. This may provide the clearance required to enable the barrier to move axially during installation.

In one embodiment described above, the blind fastener comprises a sealant, typically an uncured sealant, between the barrier and the tail of the blind fastener. In other embodiments the blind fastener has no sealant.

In some embodiments described above, barrier comprises a skirt and the blind fastener further comprises a pocket <NUM>, <NUM>, <NUM> between the skirt and the tail of the blind fastener. The pocket may be an air pocket, and the air pocket may be sealed in the installed joint.

In the embodiments described above, the blind fastener is tightened by rotating or pulling the shaft. In other embodiments, the blind fastener may be tightened in some other way, for instance by rotating or pulling the sleeve or another part of the blind fastener.

According to the invention, the expanded sleeve comprises a folded bulb or flange.

In the embodiments described above, the barrier is held by the tail of the blind fastener in a state of compression which causes the skirt rim to apply a sealing force to the face of the workpiece. In other embodiments, the skirt rim may be in contact with the workpiece without applying a sealing force.

In some embodiments, the barrier is in an expanded state before it is passed through the workpiece; in an elastically compressed state as it passes through the workpiece; and springs at least partially back towards its expanded state after it has passed through the workpiece. In other embodiments the barrier is not compressed as it passes through the workpiece.

Examples of suitable blind fasteners to which a barrier sheath, barrier cap or barrier skirt can be secured to form a blind fastener according to the present invention include the OSI-Bolt (R) manufactured by Monogram Aerospace Fasteners; Composi-Lok (R) manufactured by Monogram Aerospace Fasteners; Radial-Lok (R) manufactured by Monogram Aerospace Fasteners; Ergotech (R) manufactured by Arconic; and Optiblind (TM) manufactured by Lisi Aerospace.

Claim 1:
A blind fastener (1a) which can be installed into a workpiece with access to only one side of the workpiece, comprising: a head (<NUM>); a shaft (<NUM>) with a tail (<NUM>); a tail of the blind fastener comprising the tail of the shaft and a sleeve (3a) surrounding the tail of the shaft; and a barrier (<NUM>) secured to the tail of the blind fastener,
wherein the sleeve is configured to expand away from the tail of the shaft to form an expanded sleeve which is forced against a face of a workpiece (<NUM>) to clamp the workpiece between the head and the expanded sleeve, the expanded sleeve comprising a folded bulb or flange, and
wherein the barrier is configured to be forced against the face of the workpiece to form a sealed cover around the tail of the blind fastener.