Collapsible fastener with plastic sleeve

A collapsible fastener comprises a tubular plastic having a head on one end for bearing against one surface of the work. There is an internally threaded tail portion at the shank end of the sleeve. The shank is slotted to define strips which are notched internally and intermediate the ends. The slots increase in width from their ends to the area of the notches. A screw extends through the sleeve and is devoid of threads intermediate its ends to prevent overtorquing. A radially tapered annulus is positioned atop the sleeve for sealable engagement with the screw head in the assembled condition.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to fasteners, especially fasteners suitable for use 
in mounting panels or sheets of metal, plastics or composition materials 
to supporting structures and/or to each other. Such fasteners are commonly 
used in the construction of metal buildings and the like. Fasteners 
according to the present invention have special utility and advantages in 
attaching plastic sheet or corrugated panels, for example, such as is used 
for connecting a skylight to a supporting structure. Such fasteners can be 
mounted where access to only one side of a panel is possible, so-called 
"blind fasteners". 
2. Brief Description of the Prior Art 
Heretofore, various fasteners have been developed for use in mounting 
panels of sheet metal, plastics or composition materials to supporting 
structures and/or to each other. One such fastener which has gained 
acceptance commercially for plastic sheet and the like is sold by the 
assignee of this application under the trademark "Lap-Lox". The Lap-Lox 
fastener comprises an aluminum or stainless bolt positioned within a 
composite metal-neoprene bonded washer and extending through a grommet 
having an internally bonded threaded brass insert. As the bolt is turned 
in the insert, the grommet is compressed and it collapses against the side 
laps. This fastener has limited clamp-up capability and resistance to 
tensile forces. 
Another fastener sold under the trademark "Fab-Lok" is made entirely of 
metal material and is primarily intended for fastening metal sheets 
together or to heavy or light gauge framing. As shown in U.S. Pat. No. 
3,667,346, it comprises a tubular sleeve which has a head on one end for 
bearing against one side of the work or panel to be mounted and an 
internally threaded tail portion on the opposite end. A metal screw which 
is threaded throughout its entire length is extended through the head and 
sleeve into the tail and is positioned so that the screw head is normally 
initially spaced from the head of the sleeve. The shank of the sleeve is 
slotted and the resulting strips are notched internally at about the 
midpoint between the ends of the shank so that by turning the screw the 
tail portion travels toward the head and the strips are folded against the 
other side of the work or panel to be mounted. Since the fastener has both 
a metal sleeve and a metal screw, in practice it has been necessary to 
provide a neoprene rubber or similar material washer between the head of 
the sleeve and the work to effect a seal therebetween to prevent leakage 
at the point of mounting. 
In addition, since the screw is threaded throughout its entire length in 
the Fab-Lok fastener, as the tail portion travels toward the head portion 
when the screw is turned, there is a danger of overtorquing, thus 
stripping the external threads on the screw or the internal threads in the 
tail portion, loosening or destroying the otherwise secure connection 
between the work and the fastener. 
Thus, it would be desirable to provide an improved fastener for mounting 
panels or sheets of metal, plastics or composition materials to supporting 
structures and/or to each other under circumstances where both sides or 
only one side of the work is accessible to the installer. It would also be 
desirable for such fasteners to be lightweight, inexpensive and to have 
improved corrosion resistance, and to incorporate means to prevent 
overtorquing of the fastener so that a tight, moisture-free connection 
would be virtually guaranteed upon proper installation. The fastener must 
also have a clamp-up capability and ample resistance to tensile forces. 
Prior fasteners have included means for preventing or reducing corrosion 
and for preventing overtorquing. For example, U.S. Pat. No. 3,343,442 
discloses a fastener which includes a resilient sleeve of an elastomeric 
material, for example polyurethane rubber, which is molded over the head 
of a metal bolt. As a nut is tightened onto the bolt threads the sleeve is 
compressed tightly, which is said to effectively seal the aperture in a 
panel on which it is mounted. The shank of the bolt of the disclosed 
fastener has a narrow unthreaded neck portion intermediate the ends of the 
bolt. According to the patent, the nut can only be torqued onto the bolt 
until it reaches the narrow neck portion, at which point application of 
additional torque will only cause the nut to spin freely. It will be 
appreciated, however, that such a fastener requires a separate molding 
operation to effect a bond between the sleeve and the bolt head. It also 
requires available access to both sides of the work so that the nut can be 
tightened. Moreover, the expandable sleeve extends from the outside 
surface of the work when the fastener is installed, whereas it is 
desirable, as in the "Fab-Lok" fastener, that the expandable portion of 
the fastener be hidden from view behind the panel, especially in 
installations where the outside surface is "finished" and the panel is 
attached to supporting structures. 
Means for preventing overtorquing of a screw and tubular sleeve fastener in 
the form of an expansion anchor bolt is disclosed in U.S. Pat. No. 
3,316,796. The fastener disclosed in that patent includes a bolt having a 
shank with a diametrically reduced portion intermediate the ends of the 
shank. The bolt is installed in the sleeve and tightened to pull the end 
of the sleeve toward the head of the bolt. When the reduced portion of the 
bolt is reached, according to the patent the bolt will rotate within the 
thread aperture at the end of the sleeve but the end will not move any 
further toward the opposite or head end of the sleeve. 
The present invention has distinct advantages over each of the foregoing 
known fasteners, as will become apparent from a perusal of the present 
specification. 
SUMMARY OF THE INVENTION 
The present invention is an improved connecting device in the nature of a 
collapsible fastener. The fastening device comprises a tubular sleeve 
having a head on one end for bearing against one surface of the work. 
There is an internally threaded or otherwise disrupted tail portion on the 
sleeve and a shank extending between the sleeve ends. The shank of the 
sleeve is slotted and the resulting strips are notched internally 
intermediate the ends. The slots are double tapered, increasing in width 
from both ends toward the area of the notches. A screw is extended through 
the head and the screw end is threaded into the tail portion such that by 
turning the screw the tail travels toward the head and the strips are 
folded against the other surface of the work. A compressible annulus is 
formed on the opposite side of the head of the sleeve from the shank and 
surrounds the bore of the sleeve. The annulus is radially tapered through 
its periphery toward the longitudinal central axis of the tubular sleeve. 
The screw shank between the top of the screw threads and the screw head 
has a diameter approximately equal to or less than the root diameter of 
the screw threads and is devoid of threads. The length of the sleeve 
between the end opposite the sleeve head and the internal notches is less 
than the length of the screw shank carrying threads. Accordingly, when the 
fastener is set the annulus is tightly engaged by the screw against a 
surface of the work to provide a seal therebetween, and the absence of 
screw threads on the shank prevents overtorquing of the fastener. 
The sleeve is formed of a plastic material of a strong, yet pliable, 
plastic material such as polycarbonate or its equivalent. Thus, when the 
screw is tightened in the sleeve, the annulus is tightly engaged by the 
screw against a surface of the work to prevent moisture from entering the 
space between the head of the sleeve and the shank and contacting the work 
where corrosion could take place. 
The absence of screw threads on the shank between the existing screw 
threads and the head portion of the screw shank prevents overtorquing, 
thus reducing or eliminating the possibility of breaking, cracking or 
otherwise destroying the plastic sleeve as it is folded against the 
surface of the work upon application of torque to the screw. The resultant 
fastener has good clamp-up capability and adequate resistance to tensile 
forces.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
Referring to FIGS. 1 through 6 of the drawings, the fastening device 10 in 
accordance with the invention comprises a tubular sleeve 12 having a head 
14 on one end for bearing against one surface of the work 16 which is to 
be joined to work 18. The sleeve has a tail portion 20 which includes 
internal threads 22. The internal threads can be of a variety of designs 
to accommodate various known fasteners. A shank 24 extends between the 
sleeve ends. The shank of the sleeve includes longitudinal slots 26 which 
define strips 28 along the shank. The strips have internal notches 30 
intermediate the ends of the strips. 
The slots 26 increase in width from their respective ends toward the middle 
so as to have the greatest width in the area of the internal notches 30. 
This assures proper collapsing of the sleeve 12 as will be described 
hereinafter. 
A screw 32 is provided through the head 14 of the sleeve, and the screw end 
is threaded into the tail portion 20 such that by turning the screw, the 
tail travels toward the head and the strips 28 are folded in the area of 
the greatest slot widths and notches 30 and against the surface of the 
workpiece. 
An annulus 34 is formed on the opposite side 36 of the head 14 of the 
sleeve 12 from the shank 24, and surrounds the bore 38 of the sleeve. The 
annulus 34 includes a taper 40 throughout its periphery toward the 
longitudinal central axis of the tubular sleeve 12. 
When the fastening device is assembled, the screw head 42 is initially 
spaced from the head 14 of the sleeve. The screw shank 44, between the top 
of the screw threads 46 and the screw head 42, has a diameter 
approximately equal to or less than the root diameter of the screw threads 
46. This portion of the shank is devoid of threads. 
The length of the sleeve 12, between the end opposite the sleeve head 14 
and the internal notches 30, is less than the length of the screw shank 
carrying threads 46. Accordingly, the annulus 34 is tightly engaged by the 
screw to provide a seal between the work 18 and the annulus 34, and the 
abscence of screw threads on the screw shank 44 prevents overtorquing of 
the fastening device when it is set. 
The sleeve 12 is preferably made of a strong, yet flexible, plastic 
material such as polycarbonate or its equivalent. Thus, when the screw 32 
is tightened in the sleeve 12, the annulus 34 is tightly engaged with the 
surface of work 18, and the screw head 42 approaches the surface of the 
work 16 to prevent moisture from entering the aperture through the work. 
In addition, the collapsed end of the fastener molds itself to the contour 
on the work. This is particularly useful where the work is corrugated or 
nonplanar. 
The absence of screw threads on the screw shank 44 prevents overtorquing, 
thus reduced or eliminating the possibility of breaking, cracking or 
otherwise destroying the plastic sleeve as it is folded against the 
surface of the work upon application of torque to the screw. 
As shown in FIG. 5, wherein the fastening device is in a partially set 
condition and the tail portion has begun to pull up toward the screw head 
42, the strips 28 in the shank 24 of the sleeve 12 have begun to fold at 
the position of the internal notches 30. 
Continued torquing of the screw 32 with respect to the tubular sleeve 12 
results in the strips 28 being folded even further, as shown in FIG. 6, 
and the tail portion is pulled closer to the screw head 42. At the point 
shown in FIG. 6, there are no further screw threads 46 on the screw shank 
44 for the threads 22 in the tail portion to engage. Because of the 
absence of screw threads on the screw shank 44 above this point, the 
continued torquing of the screw with respect to the sleeve will not pull 
the tail portion tighter against the work. Thus, overtorquing is prevented 
by selection of the appropriate length of screw threads 46, fastener 
length, and length of internal threads 22 in the tubular sleeve 12. In 
this connection, it is to be noted that the screw shank 44, between the 
top of the screw threads 46 and the head portion 14 of the sleeve, has a 
diameter approximately equal to or less than the root diameter of the 
screw threads 46 and is devoid of threads, and the length of the sleeve 12 
between the end opposite the sleeve head 14 and the internal notches 30 is 
less than the length of the screw shank which carries screw threads 46. 
The subject fasteners have been utilized in the installation of side laps 
of corrugated translucent fiber glass sheets as a cover for a coal 
conveyor. While this environment is very hostile, the installation has 
been satisfactory. The installation was made from a single access side and 
the sheets were clamped together by the fastener in the area of the sheet 
overlap. 
Tension tests were conducted in 26 gauge sheet steel of single thickness. 
These tests consisted of setting various fasteners and then pulling the 
fastener until either the fastener and/or the material failed. The subject 
fastener with a stainless steel screw failed at an applied average load of 
250 pounds with both the material and fastener failing. The standard 
Lap-Lox fastener described hereinbefore failed at an average load of 90 
pounds with only the fastener failing. A 3/4 inch sheet metal carbon steel 
cadmium plated screw with a hex head installed in a 1/8 inch hole failed 
at an average load of 173 pounds with only the material failing. When the 
subject fastener was installed in thicker material (3/16 inch steel sheet 
and 5/16 inch hole) the average load increased to 318.5 pounds. 
Having described presently preferred embodiments of the invention, it is to 
be understood that it may be otherwise embodied within the scope of the 
appended claims.