Note: Descriptions are shown in the official language in which they were submitted.
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MULTI-LAYER PIPE WIT~I
SINGLE CORRUGATION IN INNER WALL
SUMMARY OF THE INVENTION
The Bac~round
This invention relates to spirally wound pipe products, and
more particularly to a helical pipe having two or more pipe wall
thicknesses, the inner wall of the pipe being generally smooth
~\ and the outer wall of the pipe being corrugated.
- It is well known to form spiral pipe from an elongated sheet
of metal or other ductile material. Such pipe products are illus-
trated, for example, in United States Patent Nos. 1,179,577;
2,337,374; 3,106,177 and 3,132,616. Multi-layer spiral pipe is
illustrated in United States Patent No. 3,340,901.
In the conventional apparatus for producing a helical pipe
product, an elongated sheet of metal is impressed with longitudinal
corrugations and then spiralled into adjacent, helical convolutions
which are joined either by welding or by formation of a continuous
lock seam. One apparatus for forming a spirally wound pipe product
is illustrated in the applicant's Canadian application entitled
"Spiral Pipe Formincl Machine With Device For Aligning Spiralling
Rolls", Serial No. 273,181, filed March 4, 1977.
Many pipe products of the prior art, although exhibiting suffi-
cient load bearing capacity to be used as a drainage culvert for
highways and the like, suffer the disadvantage of having a non-
smooth inner wall. For example, helically corrugated pipe producedby the apparatus of the applicant's above-identified patent or
Freeze U.S. Patent No. 2,136,943 has helical corrugations in the
inner wall as well. The result of a non-smooth inner wall is in~i-
bition to fiow of liquids through the pipe, forcing the pipe user to
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select a larger diameter pipe than would be needed were the
wall of the pipe smooth.
The prior art has recognized that the strength of a
corrugated pipe in combination with a smooth inner wall is a
favourable material combination. For example, Lombardi U.S.
Patent No. 3,340,901 has disclosed a pipe product formed from
at least two layers of metal including a corrugated pipe outer
shell and a smooth pipe inner shell.
However, prior art pipe of this nature generally suffers -~
the disadvantage of having a relatively weak juncture of adjacent
convolutions of the pipe shell. Stressive forces inherent
in a spirally wound pipe and experienced by a spirally wound
pipe when buried beneath the earth tend to weaken the seam
of the Lombardi pipe, requiring the pipe maker to employ greater
thickness pipe material than otherwise would be necessary in
order to obtain sufficient strength for the pipe seam.
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The Invention
The above disadvantages of the prior art and others are
overcome by the present invention which provides a multi-layer,
spirally wound pipe having a smooth inner wall and corrugated
outer wall which has a single corrugation in the inner wall
of the pipe in which the helical seam of adjacent pipe convolutions
is located.
Thus, according to the present invention, there is
provided a multi-layer, spirally wound pipe with a substantially
smooth interior wall having a single, helical corrugation
in the inner wall and a corrugated exterior wall. The pipe
comprises an inner pipe layer consisting of an elongated sheet
of material curled into adjacent, helical convolutions, with the
inner pipe layer convolutions being joined by a helical seam.
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A single, continuous helical corrugation is located in the
inner pipe layer and has the same helix angle as the helical
convolutions. The helical seam is located within the single
corrugation on a neutral axis of the single corrugation. An
outer pipe layer consisting of an elongated sheet of corrugated
material is curled into adjacent, helical convolutions about
the inner pipe layer, and the outer pipe layer convolutions
are joined by a helical seam which is located on a neutral axis
of a corrugation of the outer pipe layer. The helix angle of
the helical convolutions of the outer pipe layer is substantially
the same as the helix angle of the single corrugation, whereby
the single corrugation lies within one of the corrugations of the
outer pipe layer. ~ means joins the inner and outer pipe layers.
~ The invention also encompasses the novel method of
forming a multi-layer, spirally wound pipe which has a single,
helical corrugation located in the inner pipe wall, wherein
the inner pipe wall is generally smooth between adjacent
convolutions of the single corrugation. The process comprises
longitudinally corrugating an elongated sheet of material,
forming a multi-layer sheet by positioning a flat sheet in a
contiguous layer upon the corrùgated sheet, with the edges of
the sheets being generally coextensive, shaping a first portion
of the single corrugation in one marginal edge of the multi-
layer sheet, and shaping a second portion of the single corrugat-
ion complementary to the first portion in the other marginal
edge of the multi-layer sheet. The multi-layer sheet is
spiralled into adjacent, helical convolutions having the first
and second portions abutting to form the single corrugation,
and the adjacent convolutions are joined along the corrugation
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portions to form the multi-layer pipe and complete the single
corrugation. The joining of the adjacent convolutions includes
the step of forming the juncture of the corrugation portions
on a neutral axis of the single corrugation.
Preferably, and in order to obtain a sufficiently strong
helical seam, the helical seams of the inner and outer pipe convo-
lution are formed as a common double lock seam located within the
single corrugation in the inner pipe layer convolutions. The
lock seam is normally located on a neutral axis of the single
corrugation in order to reduce to a minimum the stressive forces
which tend to cause the pipe to unravel or weaken along the
lock seam.
With the lock seam located in the single helical con-
volution, i~ is located beneath the "sight-line" of the inner
surface of the pipe, out of the path of liquids which may flow
through the pipe. Additionally, the lock seam fills a portion
of the inner corrugation, thereby reducing the turbulent flow
which would otherwise be expected from an inner corrugation in
the pipe.
The distance between adjacent convolutions of the inner
corrugation vary depending on the width of the elongated sheets
used to manufacture the pipe. The wall of the pipe between
such corrugation convolutions is normally smooth, so that the inner
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pipe wall presents a generally smooth surface to liquids and
reduces turbulent flow characteristics to the least possible
minimum.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described in greater detail with
reference to the drawing, in which:
Figure 1 is a schematic representation of a portion of
a pipe product according to the invention, and
Figure 2 is a broken section taken along lines 2-2 of
Figure 1.
DETAILED DESCRIPTION OF THE INVENTION
.
Turning now to the drawing, a tube or pipe according to
the invention is generally designated 10. The pipe illustrated
is composed of a pair of elongated sheets of ductile material,
such as galvanized steel, which are formed into adjacent, helical
convolutions. As illustrated, the inner wall of the pipe is
formed from a generally flat sheet 12, while the outer wall
of the pipe is composed of a corrugated sheet 14. Adjacent
convolutions of the sheets 12 and 14 are joined in a common
double lock seam 16.
In a first embodiment of the invention,as shown in
greater detail in Figure 2, the inner wall of the pipe 10 is
generally smooth along the surface of the sheet 12, excepting
a single helical corrugation 18 formed in the pipe at the juncture
of adjacent helical convolutions. The lock seam 16 is formed
on a neutral axis of the single corrugation 18, that portion
of the corrugation between a hill 20 and a valley 22. If desired,
and although not illustrated, the lock seam 16 can as easily be
located between the valley 22 and a second hill 24 of the cor-
rugation 18, so long as the lock seam 16 is located on theneutral axis.
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The purpose of the single corrugation 18 is to assur~
that the lock seam 16 is located on a neutral axis. When the
pipe 10 is buried in use, stressive forces act along a line
running between the hill 20 and ~alley 22, tending to compress
or extend the lock seam 16 at its strongest point, across
the folded-over portions of the lock seam. Were the single
corrugation 18 omitted and the lock seam 16 formed along
the inner surface of the flat sheet 12, stressive forces would
tend to bow the seam 16, helping cause failure of the pipe 10
along the seam.
As further illustrated in Figure 2, all portions of
the sheet 12 between adjacent convolutions of the corrugation
18 are generally flat, and rest upon hills 26 of the corrugated
sheet 14. Therefore, the inner surface of the pipe 10, with
the exception of the single corrugation 18, is smooth.
The lock seam 16 is formed as illustrated with a heel
28 and a heel 30 located adjacent opposite ends of the seam
16 to strengthen the seam. Also, as illustrated, the material
of the seam 16, aLthough below the "sight-line" of the inner
surface of the pipe 10, occupies and fills a portion of the
corrugation 18. Therefore, the seam 16 aids in reducing tur-
bulent flow characteristics caused by pro~ision of the single
corrugation 18 in an otherwise smooth inner wall of the pipe 10.
One method for construction of the pipe 10 is described
in the applicant's co-pending Canadian Patent Application No.
311,688, entitled "Method and Apparatus for Making Multi-Layer
Spiral Pipe", filed September 20, 1978. The pipe 10 may be
made by first impressing corrugations in a flat sheet of material
to form the corrugated sheet 14, lying the flat sheet 12 upon
the corrugated sheet 14, and then forming portions of the single
corrugation 18 in opposite marginal edges of the multi-layer
sheet. At the same time, portions of the seam 16 may be formed
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in the sheet along the portions of the corrugation 18.
After the layered sheets are suitably prepared, the
sheets are curled into adjacent, helical convolutions and lock
seam portions interengaged and formation of the double lock
seam 16 completed. The pipe is then cut to desired lengths
by a suitable severance mechanism. Preferably, and as illus-
trated in the applicant's United States Patent No. 3,815,455,
severance of succeeding pipe sections is accomplished by a flying
saw.
Changes may be made to the foregoing multi-layer pipe
without departing from the spirit thereof. For example, the
lock seam 16 may be omitted and a welded seam formed in its
place along a neutral axis of the corrugation 18. The scope
of the invention is defined by the following claims.
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SUPPLEMENTARY DISCLOSURE
A further description of the details of the invention will
be observed with reference to the additionaI drawing, wherein:
Figure 3 is a broken section of a modification of
the pipe shown in Figure 2.
Figure 3 illustrates a second embodiment of the invention
modified somewhat from that shown in Figure 2 and being parti-
cularly useful for pipe having deep corrugations in the outer
wall, such as that having corrugations on the order of one
inch deep, which consequentially have a large neutral axis.
As shown in Figure 3, the inner wall of the pipe 10 is composed
of curled convolutions of a sheet 12 which is generally
smooth with the exception of a single helical corrugation 32
formed in the inner wall at the juncture of adjacent helical
convolutions. In this embodiment of the invention, the single
hèlical corrugation 32 is not fully coextensive with the external
corrugation 34 of the corrugated sheet 14 forming the outer
wall of the pipe in which the corrugation 32 is located.
As shown, a common double lock seam 16' joins adjacent
convolutions of the sheets 12 and 14. In this embodiment,
due to the depth of the external corrugation 34, and due to
the relatively shallow depth of the single corrugation 32,
the lock seam 16', while formed on a neutral axis of both
the single corrugation 32 and the external corrugation 34,
is adjacent a common hill 38 shared by the corrugations 32 and
34. Hence, the neutral axis of the corrugation 32 in which
the seam 16' is located is coextensive with a portion of
the neutral axis of the corrugation 34 of the outer layer which
shares the seam 16'. The remaining portions of the corrugation
32 are located within but not coextensive with the corrugation
34. The result is a single corrugation 32 in the inner wall
of the pipe 10 having approximately the same depth as the single
corrugation 18 shown in Figure 2, but the outer wall of the
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. - pipe having a deeper corrugation profile for added strength and
rigidity.
In the same manner as shown in Figure 2, the material
of the lock seam 16' is below the "sight line" of the inner
surface of the pipe 10. Since the seam occupies and fills a
portion of the single corrugation 32, the seam aids in reducing
turbulent flow characteristics caused by the provision of
the single corrugation 32 in an otherwise smooth inner wall
of the pipe 10.
It should be recognized that although the neutral
axis of the corrugation 32, opposite the neutral axis in
which the seam 16' is located, is shown to be of the same
general pitch as that in which the seam is located, the pitch
of the opposite neutral axis can be substantially steepened,
and even vertical or greater, so long as the common seam 16'
~ remains located on a neutral axis of both the corrugations
32 and 34. Thus, the pitch of the right-hand portion of the
corrugation 32 (as shown in Figure 3) may be changed from that
shown without altering pipe strength, but with the possible
benefit of reduced turbulent flow through the pipe 10.
By providing a relatively shallow single corrugation
32 in the inner wall of the pipe 10 with the outer wall of
the pipe having substantially deeper external corrugations,
turbulent flow characteristics caused by the provision of
the single corrugation 32 are reduced to a minimum, yet the
strength of the pipe is not at all compromised from that shown
in Figure 2, since the lock seam 16' is located on a neutral axis,
and therefore stressive forces act along the common neutral axis
shared by the corrugations 32 and 34, tending to compress or
extend the lock seam 16' at its strongest point, along the
folded-over portions of the seam.
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