Note: Descriptions are shown in the official language in which they were submitted.
CA 02221679 1997-11-20
FIELD OF THE INVENTION
The invention relates to a screw with threads and with reamer
formations between the threads and the screw head, for reaming an
oversized hole in a workpiece, to allow for thermal expansion and
contraction, and to a wall construction using panels erected with such
reamer screws.
BACKGROUND OF THE INVENTION
Building construction commonly requires the erection of a building
framework, which is then covered in, both on the exterior and the interior,
with various forms of panelling.
Typically the framework will be of wooden studs, but may also be of
steel framing. The same is also true of roof construction in many cases.
Lower cost buildings such as storage buildings, warehouses, some
military buildings and in particular, agricultural buildings, are often erected
using panelling which is simply screwed directly onto the wooden studs or
steel framework with screws. Where the panelling, and the framework of
the building, were compatible in terms of thermal expansion and contraction
rates, this system worked relatively satisfactorily. Forms of panelling include
reinforced fibre glass, vinyl sheet, honeycomb vinyl panelling, and non-
combustible fibre cement board to name only a few. In these cases, the
thermal expansion and contraction of panelling may vary substantially from
the thermal expansion and contraction of the studs. Where this is the case,
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the panelling, when it is erected on the studs, will look neat and flat, but
after one or two seasons of thermal variation (fatigue and/or expansion), the
panelling may begin to wrinkle, warp, or stress and some of the fastenings
may become loosened, or it may become torn around the fastening.
These factors are regarded as unsatisfactory in the industry, and
various efforts have been made in the past to overcome the problem. One
system is simply to pre-drill the panelling with holes which are oversized
relative to the screws. However, this requires careful location of the screw
holes, so that they register with the studs, and it is well known and indeed is
common experience that the registering of such pre-drilled holes using typical
on-site labour is, at best, unreliable as there is no guarantee that the
fasteners will be placed in the centre of the hole. The holes may be drilled
where there are no studs, and this will require a final filling operation, which
is costly and time consuming and also unsightly.
Where this system could be carried out accurately however, the
oversized holes were found to be adequate to allow for thermal expansion
and contraction to take place without damage to the panels, but such cases
were rare.
A simpler and more attractive solution is to provide a self-drilling
screw which will drill through the panelling, and into the stud, without the
requirement for pre-drilling. However, in this case the problems of thermal
expansion and contraction have not been solved, and the unsatisfactory
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results described above will show up in a year or two or as early as one
season (winter to spring).
One of the problems facing any solution to this dilemma is that the
screw must first enter the panelling and pass through it and secure itself
firmly in the stud. Accordingly while the screw threads formed on the body
of the screw are of one size, a portion of the screw shank close to the head
of the screw must be left unthreaded. If this is not done, then as the screw
tightens up it will tend to lift the panelling off the stud, and then it is no
longer possible to tighten up the screw.
Another factor particularly applicable in the case of agricultural
buildings used for housing livestock, is that the building interior must be
frequently washed down and disinfected, as each batch of livestock is
moved through the building. High pressure hoses and washers are used for
this purpose, and the high pressure spray tends to enter around the current
fasteners of choice and may damage the panelling.
It is also of importance especially in the housing of livestock, that such
fastening heads will have a low profile, so that they will not be liable to
scratch the skin of livestock, or cause any other harm.
BRIEF SUMMARY OF THE INVENTION
With a view to overcoming the foregoing problems the invention
comprises a reamer screw having an elongated shank, with a leading end and
a trailing end, at opposite ends, a self-drilling threaded portion at the leading
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end, and a torque formation at the trailing end, and a smooth shank portion
extending between said threaded portion and said trailing end, and reamer
formations formed by outwardly extending portions of said smooth shank,
located between said threaded portion and said trailing end, whereby said
reamer portions will ream an enlarged opening in said workpiece, defining a
thermal expansion/contraction space between said workpiece and said shank,
and wherein the reamer portions are sufficiently strong and are located in
relation to the threads, so that while they are capable of entering the surface
of the substrate or stud, they will not penetrate too far.
The invention provides, on the underside of said torque formations,
adjacent said sealing washer, a generally trumpet shaped transition between
said shank and said torque formations, and including a sealing washer
located on said smooth shank, adjacent said torque formations, consisting of
a steel washer and a compressible seal whereby to engage and centre said
sealing washer as said screw is driven home, and to ensure that the
compressible seal is compressed evenly all around the screw head, and the
opening in the panel workpiece.
Preferably, a screw in accordance with the invention will comprise the
following identified components:
Definitions
PT = Panel/Substrate Thickness
SW = Sealing Washer
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SWID = Sealing Washer inside Diameter
WL = Wing Location
WT = Wing Thickness
WS = Wing Span
TS = Trumpet Dimension
CT = Clearance Height
WH = Wing Height
TP = Thread Pitch
BD = Blank Diameter
TD = Trumpet Diameter
M B = Washer Thickness
and will follow the design formula as follows:
Design Formula
TS equal to or greater than 1.2MB
CT equal to or greater than .4 WH
WL equal to PT + CT + SW
WH equal to 4 PT
WT equal to or greater than .1 BD
TD equal to .9 SWID
WS equal to .9 SWID
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The reamer screw is designed with various dimensions to accept
various thicknesses of workpiece. The objective is to provide a space
between the reamer formations and the underside of the torque formations,
which is at least equal to the thickness of the workpiece, so that the reamer
formations pass completely through the workpiece, and enter a slight
distance into the substrate such as a stud or the like, leaving the workpiece
on a smooth portion of the shank between the reamer formations and the
torque formations.
The torque formations may be a hexagonal head, or a recess or any
other form of driving engagement suitable for the purpose.
Preferably an annular flange is formed around the torque formations,
so as to securely engage the sealing washer, and also so as to provide a
positive stop for any drive in-tool which is used for driving the screw into the
workpiece and substrate.
The reamer formations are preferably two generally flattened flanges
or wings struck out from opposite sides of the shank, and extending a
sufficient distance along the shank to ream out a clear hole through the
workpiece, the precise dimensions and length of such reamer formations
being related to the expansion clearance required in the workpiece, and at
the same time, being related to the dimensions of the sealing washer,
according to a predetermined formula.
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The screws in accordance with the invention may also be provided
with self-starting cutting formations in the tip of the screw, such as a
shallow groove extending along the length of between two and three
threads, so as to expose edges of said threads for increased self-starting and
cutting ability.
The invention also comprises the combination of a plurality of such
reamer screws, and a panel of material, secured to a plurality of substrates or
studs or the like, forming a wall covering. Such wall covering may be interior
or exterior, or both, and may also comprise a covering for a ceiling or roof.
The clearance defined by the reamer formation passing through the
workpiece will preferably be in the region of 0.05 of an inch radially around
the smooth shank, between the shank and the workpiece.
The various features of novelty which characterize the invention are
pointed out with more particularity in the claims annexed to and forming a
part of this disclosure. For a better understanding of the invention, its
operating advantages and specific objects attained by its use, reference
should be made to the accompanying drawings and descriptive matter in
which there are illustrated and described preferred embodiments of the
Invention.
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IN THE DRAWINGS
Figure 1 is a side elevational view of a screw illustrating features of
the invention;
Figure 2 is a section along the line 2-2 of Figure 1;
Figure 3 is a side elevational view of a screw at a stage in
manufacture of the screw of Figure 2;
Figure 4 is a top plan view showing the torque head of the screw of
Figures 2 and 3;
Figures 5 and 6 illustrate reamer screws similar to Figure 1, but with
varying spacings between the reamer formations and the torque head as well
as different sizes of reamer formations;
Figure 7 is a side elevational view corresponding to Figure 1 and
showing a modified form of reamer formation;
Figure 8 is a schematic side elevation of a typical wall panel secured to
structural members or studs, by means of reamer screws illustrating the
invention;
Figure 9 is a section along the line 9-9 of Figure 8, showing the reamer
screw of Figure 1 being used with a wall panel of a predetermined thickness;
Figure 10 is a side elevational view, corresponding to Figure 9, but
illustrating the screw of Figure 5 used in a somewhat thicker wall panel or
workpiece;
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Figure 11 is a side elevational view showing the screw of Figure 6
used in a somewhat thicker wall panel or workpiece;
Figure 12 is a side elevational view showing the screw of Figure 7
used in conjunction with a workpiece;
Figure 13 is a section through an alternate form of honeycomb
workpiece;
Figure 14 is a schematic illustration of a reamer screw, with the
various critical dimensions identified by acronyms;
Figure 15 is section through a sealing washer; and,
Figure 16 is a section of a screw in a workpiece.
DESCRIPTION OF A SPECIFIC EMBODIMENT
Referring now to Figure 1, it will be seen that this illustrates a reamer
screw showing certain features of the invention. As explained above, the
reamer screw is designed for securing a panel or workpiece to a structural
member or stud ~Figure 8) in a particularly advantageous manner. In the
past, securing of studs by means of pre-drilled holes was unsatisfactory for
the reasons described above. Securing panels by means of self-drilling
screws was also unsatisfactory for reasons described above, due to thermal
expansion and contraction.
The reamer screw illustrated in Figure 1 is designed as a self-drilling
screw requiring only a single act for insertion through the workpiece, and
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into the stud, and at the same time reaming out its own oversize opening in
the workpiece or panel.
This screw therefore does away with the need for pre-drilling the work
piece, and the problems associated with pre-drilling such as centre alignment
to the predrilled hole and the excessive labour involved at the work site.
The screw in Figure 1, is indicated generally as 10 and comprises a
leading end 12 and a trailing end 14. The leading end 12 is formed with a
point 16, and a self-tapping thread 18. At the trailing end there is a torque
head 20 indicated in this case by the hexagonal surfaces 22. Screws having
torque heads of this type are particularly suitable for use with powered
screwdrivers and powered insertion devices. However, the invention is not
specifically limited to this form of torque head, but is also applicable to
screws having driving recesses (not shown) or other forms of torque surfaces
such as are well known in the art and require no special description.
An annular stop flange 24 extends around torque head 20, and acts as
a stop for the chuck of the insertion tool (not shown) so that a workman
using an insertion tool can apply considerable pressure, and also angular
direction, to the screw while it is being inserted.
The self drilling threads 18 terminate at the point 26. Between the
termination of the threads at point 26, and the torque head 20, there is a
substantially smooth, cylindrical screw shank 30.
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The shank 30 adjacent its junction with the head 20, has a trumpet
shaped formation 32, flaring outwardly, to self align the screw and the
washer, as set out below.
In order to ream out an oversized hole in a workpiece (Figures 8, 9, 10
and 1 1 ) reamer formations 34-34 are formed on either side of the shank 30.
The reamer formations 34 (Figure 2) are simply formed by squeezing out
wing portions of the shank 30 on opposite sides, in this case being radially
opposed to one another along a 180 degree axis. However, the precise
orientation of the reamer formations is not of importance, the one shown
being simply a matter of convenience for manufacturing. It will of course be
appreciated that while the invention is illustrated as having two such wing
portions 34, it could equally well have four or six such wing portions, for use
in special cases, the illustration of two such wing portions being merely for
the sake of explanation and without limitation.
The reamer formations 34 will be seen to comprise relatively thin, flat
portions of metal, which extend outwardly relative to the shank 30 so as to
ream out a hole in the workpiece, which is oversized relative to the shank,
without interfering with the secure hold of the threads 18 in the substrate or
stud.
Simply for the sake of completeness, Figure 3 illustrates a screw
blank, having a straight cylindrical body 30, and on which the torque head
20 has already been formed in known manner, and upon which the threads
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18 will be formed by thread rolling techniques such as are well known in the
art and require no special description.
As explained above the spacing indicated by the distance D1 (Figure 1 )
between the trumpet formation 32 and the reamer formations 34 is a
predetermined distance calculated to permit the reamer formations 34 to
pass completely through a workpiece of a predetermined thickness. The
predetermined workpiece thickness will be less than the distance D1 of
Figure 1. The relationship of the various dimensions to one another is
illustrated and described in more detail in relation to Figures 14, 15 and 16
1 0 below.
The screws of Figures 4 and 5 are substantially identical to the screw
of Figure 1, except that the distance D between the reamer formations 34
and the trumpet formation 32 is progressively greater and is indicated as D2
(Figure 5) and D3 (Figure 6).
These distances are calculated for use with workpieces of increasing
thickness, so that for any particular workpiece of a predetermined thickness,
a screw can be provided in which the reamer formations 34 will pass
completely through the workpiece, reaming out an oversized hole and at the
same time leaving the workpiece loose on the shank portion defined by the
length D1, D2 or D3, respectively and thus providing a suitable space for
thermal expansion-contraction of the workpiece around the screw shank.
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Figure 7 illustrates a modified form of screw 10, the modification
consisting of the lengthening or extending of the reamer formations 34A
which in this case have a distance indicated as L, which is greater than the
length of the reamer formations 34 in Figures 1, 5 and 6. Such extended
length reamer formations will be of assistance in use with certain types of
workpiece materials, where it is desired to completely clean out the oversized
hole so as to relieve the workpiece of any restriction around the shank, and
ensure adequate spacing for thermal expansion and contraction.
Figure 8 illustrates a typical arrangement showing the erection of a
panel on structural members such as studs 40. The studs may typically be
on sixteen inch centres although this is not critical for the invention. The
panel or workpiece indicated as W is of rectangular shape and may be
erected length wise as shown, or may be erected with its length extending
vertically upwardly, depending upon the desire and design of the wall
construction .
Screws indicated as 10 are shown at intervals securing the workpiece
W to the studs 40. The workpiece W is typically a flat planar panel often a
composite panel, having a surface material of thermo plastic bonded in place
on a substrate which may be another form of plastic, or chipboard, wood,
plywood, or other form of plastic product. In any event, it will be seen that
the action of the screw is such that the insertion of the screw and the
reamers leaves an oversized reamed out hole in the panel. This allows the
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screw to be tightened up, so that the panel is securely held flat against the
stud 40, without the panel lifting off, or becoming jammed in threads of the
screw, which was often the case in the past.
It will be apparent that during variations in weather conditions, the
workpiece W will expand and contract due to thermal forces, and, as
mentioned in the past this has caused problems of wrinkling and rupturing of
the workpiece.
By means of the reamer formations 34 of the invention, each of the
screws 10 reams out its own oversized hole through the workpiece, thereby
allowing a space around each screw for expansion and or contraction of the
workpiece due to thermal forces, and/or changes in weather conditions. It
will of course be noted that even though the holes are oversized, they are
completely sealed against the entry of moisture by the compressible seals
44, held by the sealing washers 42.
Typical examples of screws in accordance with the invention shown in
various thicknesses of panel are shown in Figures 9, 10, 1 1 and 12. It will
be seen that in each case the reaming formations have passed through the
workpiece W and have left an oversized hole indicated as H. The thickness
of the workpiece W in each case is such that the reamer formations 34 have
passed completely through the workpiece, and are in fact entering into the
surface of the structural member or stud 40.
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In accordance with a further advantageous feature of the invention,
the screws 10 are preferably used in conjunction with sealing washers
indicated as 42.
The washers 42 are of generally saucer shape, having a central
somewhat oversized opening so that they are loose on the shank of the
screw. A suitable compressible washer liner seal 44 is provided, which is
typically adhesively bonded and/or vulcanized to the washer 42.
As the screw is tightened up into the stud 40, the trumpet shaped
formation 32 wedges into the centre of the washer 42 causing it to be
centred and to flatten and spread the liner 44 tightly against the surface of
the workpiece W. The compressible material 44 will be squeezed, and
provides a good liquid tight seal.
The use of the washers 42 and the seals 44, in combination with the
reamer formations 34, enables a simple assembly operation of the washers
onto the screws after the reamer formations have been formed, the washers
defining openings 46 which are sized to admit the reamer formations 34.
The relationship of the various dimensions of the washer and the size and
span of the reamer formations will be described in more detail in relation to
Figures 14,15 and 16.
The fact that the washer holes 46 make only a loose fit on the shank
30 of the screw is no problem. The trumpet formations 32 squeeze into the
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openings 46, and provide a centering action, as the screw is tightened up to
hold the washers centred on the screw axis.
Finally, as illustrated in Figure 12, the screw threads 18 may be cut
away as at 48 by means of a shallow groove. This exposes the side edges of
two or three of the threads so as to provide a better thread cutting action for
providing a quicker self-drilling entry of the screw.
Various different forms of work piece can be fastened using features
of the invention. The work pieces W illustrated in Figures 9, 10, 1 1 and 12
are all solid work pieces of different thicknesses.
They may be laminates or they may be wood panelling or they may be
metal, but usually they will be laminates of vinyl on top of some form of
substrate, such as is well known in the art.
However, one particularly suitable form of work piece is shown in
Figure 13 illustrated as 50. This is a honeycomb structure having an outer
surface 52 formed of a semi-rigid vinyl material, preferably pigmented such
as white pigment, and an under surface 54.
Between 52 and 54, there are spaced apart transverse walls 56
formed integrally with the panels 52 and 54. This structure is light weight
and easy to handle even in large size panels, and is found to be particularly
suitable for use in accordance with screws having features of the inventions,
which ream out oversized holes through the work piece and allow the work
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piece room for thermal expansion and contraction without disruption of the
screw fastening, or the panel.
In order to perform satisfactorily, in the relatively hostile environment
for which they are intended, particularly for example in agricultural barns,
housing livestock, although this is merely one example, it is desirable to
maintain certain critical relationships between the various components of the
reamer screw described.
Accordingly, reference may be made to Figures 14,15 and 16. These
illustrate the reamer screw with the various dimensions shown by letter
combinations or acronyms. The acronyms are defined as follows:
Definitions
PT = Panel/Substrate Thickness
SW = Sealing Washer
SWID = Sealing Washer inside Diameter
WL = Wing Location
WT = Wing Thickness
WS = Wing Span
TS = Trumpet Dimension
CT = Clearance Height
WH = Wing Height
TP = Thread Pitch
BD = Blan k Diameter
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TD = Trumpet Diameter MB = Washer Thickness
The relationship between the various dimensions identified by the
acronyms will preferably be as follows:
Design Formula
TS equal to or greater than 1 .2MB
CT equal to or greater than .4 WH
WL equal to PT + CT + SW
WH equal to 4 PT
WT equal to or greater than .1 BD
TD equal to .9 SWID
WS equal to .9 SWID
Preferably the radial clearance between the screw shank, and the
workpiece is about 0.05 of an inch, this dimension being found to be
adequate for most panel materials, and studl materials. It will be appreciated
that given a spacing between screws, in a panel, of about sixteen inches, by
twelve inches, the cumulative spacing across or along any one panel is
adequate to handle the normal thermal expansion/contraction stresses.
The foregoing is a description of a preferred embodiment of the
invention which is given here by way of example only. The invention is not
to be taken as limited to any of the specific features as described, but
comprehends all such variations thereof as come within the scope of the
appended claims.
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