Fastener

A fastener, intended for fastening a sandwich panel (b) to a support (a), and including a headed bolt (1) having a break off tail portion, and a flanged tubular body (4) into which the main portion of the shank (3) of the bolt is pulled so as to lockingly interengage the body and set the fastener, includes a deformable tubular spacer (10) disposed on the shank (3) of the bolt (1) between the body (4) and the head (2) of the bolt (1). The spacer (10) is in the form of a sleeve having a tubular central core, and peripheral grooves (12) between which are annular fins (11). The spacer is capable of being deformed to a substantially shorter axial length by axial compression under substantially constant predetermined load. When the fastener is installed and set in work of less than the maximum thickness intended for the fastener, the spacer (10) is deformed by axial compression between the body (4) and the bolt (1), and relieves the work member of the need to bear substantially all of the load required to lockingly interengage the bolt (1) and the body (4), and break the tail portion from the main portion of the bolt (1).

FIELD OF THE INVENTION 
This invention relates to a fastener of the kind generally identified as 
"pull-to-set fasteners" and comprising a headed bolt which can be inserted 
into registering apertures in work members, such as a panel and a support, 
to be fastened, and a flanged tubular body into which the bolt can be 
inserted and pullcd axially, without rotation, the bolt and the body 
having mutually interengageable engaging means whereby the bolt and the 
body can be locked together so as to secure the members to be fastened 
between the head of the bolt and the flange of the body. Such a fastener 
is hereinafter referred to as a "fastener of the kind defined". 
DISCUSSION OF THE BACKGROUND 
In a known fastener of this kind, described in our British Pat. No. 
1538423, the engaging means of the bolt comprises a plurality of annular 
barbs in a suitable position on the shank of the bolt and the engaging 
means of the body comprises a resiliently deformable part into which the 
barbs of the bolt are able to embed so as to resist withdrawal of the bolt 
from the body once they are interengaged. 
The bolt has a tail portion which can pass freely through the body, whereby 
the bolt can be gripped and pulled relative to the body by a suitable tool 
so as to clamp together the members to be fastened and cause 
interengagement of the engaging means, and which portion breaks off from 
the rest of the bolt at a predetermined tensile load, leaving the rest of 
the bolt together with the interengaged body to fasten the members 
together. 
The known fastener has been used extensively in the construction of freight 
containers, in which it has been found satisfactory for securing, to a 
metallic supporting framework, panels of such materials as plywood which 
may have a face-covering skin of plastics material, particularly glass 
fiber reinforced plastics material, which is engaged by the flange of the 
body of the fastener. Such panel materials are sufficiently resistant to 
withstand the pressure with which the flange is forced to bear against the 
face of the panel. 
However, this is not so in the case of panels known as "sandwich panels" or 
"honeycomb board", consisting of a cellular matrix secured by adhesion 
between two sheets of reinforced plastics material, which are less 
resistant to localized compressive loads and which also tend to show 
variations in thickness due to tolerances in manufacture. Such panels can 
suffer damage in or around the zone on which the flange bears, due to the 
compression load applied during setting of the fastener before reaching 
the predetermined load at which the bolt will break. 
SUMMARY OF THE INVENTION 
The present invention aims to provide an improved fastener of the kind 
defined, with a view to avoiding this disadvantage of the known fastener. 
It has been found that by providing the fastener with a deformable spacer 
which is disposed on the shank of the bolt between the bolt head and the 
body of the fastener and which is capable of being deformed b compression 
when the body of the fastener is forced to move towards the head of the 
bolt and into mutually locking interengagement with the bolt, a 
substantial amount of the force which is normally applied to the bolt and 
body during setting of the fastener is absorbed by deformation of the 
spacer, thereby reducing the amount of force which is applied to the 
members to be fastened, and, provided the maximum force which can be 
applied is limited to a predetermined amount, by, for example, the 
breaking of the bolt at a breakneck, the amount of force applied to the 
members to be fastened can be limited so as to avoid damage to the work 
members. 
Thus, it is possible to prevent the flanged body from applying an excessive 
force to the face of a panel of honeycomb board and thus to avoid damaging 
the board. 
According to the invention there is provided a fastener comprising a bolt 
having a shank and a :ead at one end, and a flanged tubular body into 
which the shank of the bolt can be inserted, the bolt and the body having 
mutually interengageable engaging means whereby, on forcing the body along 
the shank and towards the head of the bolt so as to cause the engaging 
means to interengage, the body and bolt can be locked together so as to 
fasten together apertured work members disposed on the bolt between the 
head of the bolt and the flange of the body, the fastener including means 
for limiting to a predetermined maximum the amount of force which can be 
applied to set the fastener, the fastener including a deformable tubular 
spacer which is disposed on the bolt between the head and the body, and 
which is capable of abutting the body and being deformed by compression 
when the body is forced into locking engagement with the bolt, the spacer 
bcing adapted to absorb a substantial amount of the force applied in 
moving the body along the bolt and setting the fastener, and thereby 
reduce the amount of force applied to the work members.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The fastener comprises two essential parts, namely a bolt 1 having an 
enlarged head 2 and an elongate shank 3, and, for the other part, a 
tubular body 4, which is radially enlarged at one end to provide a flange 
5. 
The shank 3 of the bolt has a main portion adjaccnt to the head 2, and a 
tail portion extending to the end remote from the head 2. The main portion 
of the shank 3 comprises a cylindrical neck 6, which adjoins the head 2, 
followed by a cylindrical stem 7, the diameter of which is smaller than 
the neck so as to form a shoulder between the stem 7 and the neck 6. The 
stem 7 is followcd by a zone 8 having engaging means in the form of a 
plurality of annular barbs. Each of the annular barbs extends radially to 
a more or less sharp annular crest having a diameter greater than that of 
the stem 7 and is directed towards the head 2 of the bolt. 
At the end of the zone 8, remote the from the head 2, is a breakneck 9 of 
such a reduced diameter as to forx' the weakest part of the bolt and such 
that when the bolt is subjected to a predetermined tensile load it will 
break at the breakneck rather than elsewhere. Beyond the breakneck is the 
tail portion which may be formed with striations or grooves to facilitate 
gripping of the tail portion and pulling of the bolt by a suitable tool. 
The length of the main portion of the bolt, which comprises the neck 6, the 
stem 7 and the barbed zone 8, is made appropriate to the thickness of the 
work member in which it is intended to use the fastener. The construction 
of the fastener is such as to accommodate some variation over a small 
range in the thickness of the work, but the length of the main portion is 
generally made such that in work members of the intended thickness, with 
the bolt head 3 abutting one face of the work members and the shank 
extending through registering apertures in the work members, the tail 
portion of the shank projects beyond an opposite face of the work and the 
main portion of the shank is entirely within thc work, preferably with the 
breakneck aligned with the said opposite face. 
The tubular body 4 has an internal lining of resiliently deformable 
material, such as a polyamide resin, of such internal diameter that the 
body can be passed along the tail portion of the bolt towards the bolt 
head 2 and then forced over the barbs of the zone 8 which then embed in 
the lining material and resist withdrawal of the body in the direction 
away from the bolt head, as shown in FIG. 3. 
In order to instal the fastener, a gripping and pulling tool is used, 
which, while gripping the tail portion of the bolt shank 3, abuts against 
the flange 5 of the body and pulls the bolt, thereby forcing the body 
along the shank towards the head of the bolt until it becomes mutually and 
lockingly engaged with one or more of the barbs in the zone 8. 
Referring to FIG. 1, the members of the workpiece be fastened by means of 
the fastener are a metal support member (a), such as a frame of a vehicle 
body, and a panel (b) of the kind known as a "sandwich panel" or 
"honeycomb board" having two facing sheets bl and b2 of plastics material 
and a cellular matrix or core b3 between the sheets, the core being 
secured to the sheets by bonding, or adhesively, and spacing them apart in 
parallel relationship. 
The core b3 has a low compressive strength and in order to prevent damage 
to the panel (b) when fastening it to the support member (a), a deformable 
tubular spacer 10 is disposed on the shank of the bolt so as to occupy a 
position between the neck 6 and the barbed zone 8. 
The length of the spacer 10 is made such that when the fastener is 
completely installed in a work member of the maximum intended thickness, 
the body engages and may slightly compress the spacer 10 against the 
shoulder presented by the neck, with the work members being subjected to a 
slight degree of compression between the head 3 of the bolt and the flange 
5 of the body. 
However, when the fastener is installed in a work member having a thickness 
less than the intended maximum, the body 4 engages and begins to compress 
the spacer against the shoulder before the flange 5 engages the near face 
of the adjacent panel. As the tool continues to force the body along the 
shank of the bolt until the flange 5 meets the near face of the panel, the 
spacer is progressively deformed, becoming shorter in its axial length. 
The force required to deform the spacer increases the amount of force 
required to move the body nearer to the head of the bolt to an amount 
approaching that required to cause the bolt to break at the breakneck. 
When the flange 5 then eventually engages the panel, a small amount of 
additional force is required to compress the panel and the total force 
applied therefore increases rapidly to an amount which the breakneck is 
unable to sustain, with the result that the breakneck 10 breaks and thus 
prevents the application of any further compressive force to the 
workmember. Installation of the fastener is then complete. 
The spacer 10 is designed and dimensioned so as to undergo a substantial 
reduction in length by deformation under a load which increases only 
slightly, the load being in a predetermined range of values which, 
together with the load required to force the body along the shank, is 
slightly below that required to break the breakneck. Thus, the panel is 
then only required to bear the slight amount of extra load which is 
required to break the breakneck. 
Referring to FIG. 5, the spacer 10 of this embodiment is made of a ductile 
alloy of aluminum conforming to British Standard 1474, although other 
materials such as annealed low alloy steel have been used with 
satisfactory results. 
The spacer is generally in the form of a tubular cylinder or sleeve, having 
an axial bore of such a diameter as to enable the spacer to be moved along 
the shank 3 of the bolt, passing the barbed zone 8 with slight clearance, 
until it abuts the shoulder provided by the neck 6. 
The peripheral surface of the spacer is formed with a plurality of annular 
fins 11 which are spaced from each other by deep annular grooves 12. 
Peripherally of the bore, and radially inwardly of the fins and grooves, 
is a central tubular core 13 which is continuous from end to end of the 
spacer. 
In use of the fastener, the core 13 acts as a load-bearing column which 
bears the compression load applied between the body 4 and the neck 6, and 
is capable of being compressed, in the axial direction, to a length 
shorter than its original length. 
When the core is sufficiently shortened by compression, all the fins 11 may 
eventually abut each other, and, having done so, increase very greatly the 
rcsistance of the spacer to further shortening. The fins thus serve as 
stops to limit the extent to which the spacer can be shortened, so that, 
in practice, the spacer can only be compressed to a certain minimum length 
which corresponds to the total thickness, in the axial direction, of all 
the fins. This minimum length is a function of the number and thickness of 
the several fins. 
In the absence of the fins, the compression of the core could result in the 
core being deformed so as become increasingly barrel-shaped, in which case 
it would, up to a point become progressively less effective to absorb the 
compression force applied. 
However, the peripheral fins also act as hoops, which by their presence, 
restrain the tendency of the core to become barrel shaped, and thus help 
to preserve the core as a load-supporting column. It is therefore 
desirable, although not essential, that there be several of the fins 
spaced apart along the length of the core, so as to restrain any tendency 
for the core to become barrel-shaped in local regions along its length. 
The fins should also be of sufficient thickness to be able withstand, 
without splitting, the radially outward forces to which they will be 
subjected when the core tends to become barrel-shaped. lf the fins split 
radially they become ineffective as hoops. 
The resistance of the core to axial compression is primarily a function of 
its wall thickness, i.e. the thickness between the root of each peripheral 
grc,ove 12 and the central bore of the spacer. For a given diameter of the 
central bore, this wall thickness will therefore depend on the depth of 
each of the grooves 12. 
By adjusting the depth of the grooves 12, and the number, and relative 
widths, of the grooves a.nd the fins, it is possible to finely adjust the 
degree of 25 resistance of the spacer 10 to axial compression under load, 
and the minimum length to which it can be compressed. 
We have found that four grooves of equal depth, giving five fins, and in 
which the widths of the fins and groves are the same, gives good results. 
However the number of grooves, and also the relative widths and depths of 
the fins and grooves can be varied, so as to provide grooves wider than 
the fins, or fins wider than the grooves. For a given diameter of the 
central bore, the depth of some or all of the grooves 12 can be varied so 
as to enable variation, with close control, of the resistance to 
compression of the core of the spacer according to the amount of 
compressive force which the spacer is required to absorb, in order to 
relieve the panes of the need to bear that amount of the load. 
The invention is not limited to the details of the forgoing example.