Note: Descriptions are shown in the official language in which they were submitted.
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STEEL PIPE WITH INTEGRALLY FORMED LINER AND METHOD
OF FABRICATING THE SAME
Related Applications
This is a continuation in part patent application of
United States Serial Number 08/225,440, filed April 8,
1994 and entitled STEEL PIPE WITH INTEGRALLY FORMED LINER
AND METHOD OF FABRICATING THE SAME, which is a
continuation in part of United States Serial Number
10 07/736,108, filed July 26, 1991 and entitled METAL PIPE
WITH INTEGRALLY FORMED LINER AND METHOD OF FABRICATING
THE SAME, the contents of both which are hereby
incorporated by reference.
Field of the Invention
The present invention relates generally to buried
pipe for use in sewers, storm drains, pen stocks,
culverts and other low head applications, and more
particularly to metal pipe with an integrally formed
liner for use in corrosive and abrasive environments and
a method of fabricating the same.
Background of the Invention
Metal pipe of both corrugated and spiral rib design
is widely used for drainage, culverts and other similar
fluid conduits. Although susceptible to abrasion, steel
pipe has advantages over concrete pipe and the like due
to its comparatively high strength and low weight. These
characteristics render metal pipe comparatively
inexpensive to manufacture, ship and handle while
permitting its use in applications requiring it to
support substantial soil overburden. Further, in recent
years a particular spiral ribbed steel pipe has been
introduced by W.E. Hall Co., of Newport Beach,
California, the assignee of the subject application, that
possesses hydraulic efficiency comparable to more costly
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concrete pipe as well as possesses superior structural
capabilities for prolonged use in buried storm drain
applications.
Since metal pipe is susceptible to corrosion and
excessive abrasion, its use has heretofore been
restricted primarily to culvert and storm drain
applications. In sanitary applications, i.e. sewer
systems, corrosion causing sulfuric acid is formed from
hydrogen sulfide gas generated by waste products. Such
waste products and/or acid has rendered the use of steel
pipe in sanitary applications impractical since it
rapidly deteriorates in the corrosive environment. As
such, much heavier and more expensive concrete, lined
concrete and/or vitreous clay pipe has traditionally been
utilized for sanitary applications. Thus, although metal
pipe is generally preferred because of its high strength
and comparatively low weight and cost, metal pipe has
heretofore not been widely used in sanitary applications
due to its susceptibility to corrosion.
In storm drain applications, such metal pipe is
particularly susceptible to extensive abrasion caused by
the movement of gravel, dirt, sand, etc. therethrough.
Such excessive abrasion frequently degrades metal pipe to
a point where leakage of the contents of the pipe
therefrom becomes a major concern. Additionally, such
abrasion may, in some instances be sufficient to
adversely affect the structural integrity of the pipe,
and consequently result in structural failure of the pipe
wherein the overburden crushes a portion of the pipe,
thereby effectively plugging the pipe and substantially
reducing or eliminating flow therethrough.
In recognition of these deficiencies, prior art
attempts to allow the use of concrete pipe as opposed to
vitreous clay pipe for large size sewer applications
while reducing the susceptibility to corrosion of
concrete pipe have included: the installation of a thick
corrosive-resistant plastic liner, and/or forming the
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inside of a concrete pipe with an additional sacrificial
concrete in the crown portion of the pipe.
Such prior art corrosion-resistant liners typically
~ comprise plastic inserts sized to be received within each
s concrete pipe section. Such liners are commonly cast
within each pipe section. Subsequently after the pipe
sections have been laid in place, adjacent liners are
bonded together with the intention of forming a seal to
prevent corrosive fluids and gases from contacting the
concrete pipe. Although such prior art concrete
pipe/plastic liner solutions have proven generally
suitable for large size sewer applications, the inherent
high cost of such solutions has posed a severe impediment
in construction products and projects. Further the
useful life of such prior art sacrificial concrete pipe
solutions is finite, which requires widespread
rehabilitation over time thereby mandating tremendous
expense in down line rehabilitation costs.
In recognition of the general inability of metal
pipe and concrete pipe for sewer applications, in recent
years plastic pipe has been introduced into the
marketplace. Although such plastic pipe withstands
degradation caused by the corrosive environment found in
sewer applications, its use has heretofore been primarily
limited to small size sewer applications. In this
regard, the structural integrity of plastic pipe is
extremely limited such that in large size applications,
the sidewall of such plastic pipe must be fabricated
extremely thick or profiled to enable such plastic pipe
to withstand compressive forces exerted in burial
applications. Due to the high cost of such plastic
material, the use of such plastic pipe in large scale
sewer applications has been economically impractical.
Therefore, in view of the specific factors encountered in
large scale sanitary sewer applications, nearly all such
applications have utilized costly concrete pipe having a
sacrificial wall formed therein which significantly decay
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over prolonged use and thus will require costly
rehabilitation and/or replacement over time or separately
affixed liners which are typically cost ineffective.
In contrast to the waste product and/or acid
environment encountered in sanitary applications, metal
pipe utilized for burial storm drain applications
additionally encounters substantial problems associated
with its operational environment. In relation to burial
storm drain applications, long term exposure of the
exterior of the metal pipe within the burial environment
serves to corrode the exterior of the pipe while water
and debris flowing through the interior of the metal pipe
degrades the pipe through abrasion.
In an effort to prevent such corrosion effects, the
interior of metal pipe has been lined with concrete in
the hopes that a thicker lining would be more abrasion
resistant and thereby resist deterioration and corrosion.
However, there fails to exist any cost effective means
for anchoring concrete to the interior wall of metal
pipe.
An alternative prior art approach to solving the
corrosion and abrasion deficiencies of metal pipe for
storm drain applications has been to fabricate the metal
pipe from plastic laminated steel film material. One
such prior art product is known as Black-Klad~, a product
of Inland Steel Company of Chicago, Illinois. Prior to
rolling the steel sheet into a pipe section, one surface,
i.e. that surface which forms the inner pipe surface, is
laminated with a polymer material. The thickness of such
lamination is limited to approximately 0.0l0 inch and is
intended to resist degradation caused by corrosion and
some abrasion. However, due to the comparatively thin
thickness layer of plastic lAm;n~nt, the l~mi n~nt tends
to wear through due to abrasion from sand, rocks, etc.
and thereby expose the metal surface below. Further,
during the pipe formation process, the thin laminant
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oftentimes is damaged due to metal cold roll forming
procedures.
Attempts to apply thicker laminations to such prior
art products have heretofore resulted in greater
5 blistering and separation of the polymer compound from
L the metal pipe. As such, the application of a protective
polymer layer to metal pipe has heretofore been rendered
ineffective.
Therefore, because the prior art interior lining of
10 metal pipes have proven susceptible to abrasion and
corrosion, and since abrasion resistant inert linings
such as those constructed of concrete or an inert polymer
material have failed to remain effectively anchored to
the metal pipe walls, metal pipe has heretofore been
15 unacceptable for use in sanitary applications such as
sanitary sewers.
As such, there exists a substantial need in the art
for a sufficiently thick polymer liner which may be
securely applied to metal surfaces to maintain the
20 integrity thereof when the metal pipe is placed in a
corrosive environment and to remain thereon without
blistering during the pipe formation process. Further,
there exists a substantial need in the art for an
improved metal pipe with an inert protective lining
25 constructed of a polymer material such as polyethylene
which would resist the attack of sulfuric acid as well as
resist other forms of corrosion encountered in sewer
applications.
Summary of the Invention
The present invention specifically addresses and
alleviates the above referenced deficiencies associated
in the prior art. ~ ~More particularly, the present
35 invention comprises a metal pipe with an integrally
formed polymer liner for use in corrosive and abrasive
environments. In the preferred embodiment of the present
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invention, the polymer liner is comprised of .050 to .125
inch thick polyethylene, preferably a low density
polyethylene (LDPE), linear low density polyethylene
(LLDPE), or a blend of both which is securely bonded to
the metal pipe during fabrication of the metal pipe. As
used herein, the term "low density polyethylene/linear
low density polyethylene blend is defined to include a
blend having from 0 to 100% low density polyethylene and
from 0 to 100% linear low density polyethylene. Thus,
this term includes low density polyethylene with no
linear low density polyethylene added and also includes
linear low density polyethylene with no low density
polyethylene added. However, other polymers having
corrosion resistant properties similar to polyethylene
are likewise contemplated herein.
The liner is formed by first applying a
comparatively thin monolayer or multilayer
polymer/adhesive film to the metal pipe surface during a
pre-treatment process in order to facilitate bonding of
the subsequently extruded, comparatively thick, layer of
low density polyethylene/ linear low density polyethylene
blend. When the thin film is formed as a multilayer
film, the sublayers are preferably co-extruded.
However, the sublayers of the thin film may alternatively
be formed completely independent of one another, i.e., at
different times. While the comparatively thin film is
preferably applied via extrusion or co-extrusion, those
skilled in the art will appreciate that the comparatively
thin film may be applied via various different well known
techniques, including cast and blown-film techniques.
The thin film is preferably applied in a pre-treatment
process to the sheet metal, preferably prior to roll
forming corrugations or ribs in the sheet steel. The
comparatively thick low density polyethylene/linear low
density polyethylene layer blend is preferably applied
a~ter the corrugations or ribs are formed in the sheet
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metal, preferably su~sequent to helically winding and
forming the sheet steel into a pipe product.
The thin film is specifically formed to securely
adhere to the surface of the sheet metal and provide a
polymer constituent layer suitable for subsequent
thermal/chemical bonding of the comparatively thick layer
of polyethylene, preferably a low density
polyethylene/linear low density polyethylene blend. As
such, the thin film serves as a strong bonding agent or
interface which adhesively bonds to the metal pipe and
additionally forms a base material suitable to enable the
subsequent application of the comparatively thick layer
of polyethylene, preferably low density
polyethylene/linear low density polyethylene blend
thereto.
The present invention provides a smooth,
hydraulically efficient interior surface which is
resistent to the corrosive action of sulfuric acid and
the like as is typically encountered in sanitary
applications. It is also highly resistant to abrasion
caused by the flow of water-born debris such as dirt and
gravel as is encountered in culvert and storm drain
applications.
The comparatively thin film applied in the pre-
treatment process to facilitate bonding of the laterapplied comparatively thick layer of low density
polyethylene/linear low density polyethylene blend
comprises either a monolayer or multilayer film. The
monolayer film defines a single layer and the multilayer
film defines two sublayers.
The monolayer is preferably comprised of
polyolefin/maleic anhydride (MA), ethylene acrylic acid
(EAA), ethylene methacrylic acid (EMAA), or a blend of
these polymers, or another metal adhesive.
Those skilled in the art will appreciate that
various other metal adhesives are likewise suitable for
use as the monolayer film. Optionally, the monolayer may
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--8--
be corona treated prior to applying the comparatively
thick layer of low density polyethylene/linear low
density polyethylene blend.
When a monolayer of polyolefin/maleic anhydride is
utilized, the concentration of maleic anhydride is
preferably maintained between approximately 0-10%,
preferably less than 1%, by weight.
The monolayer adhesively bonds to the metal surface,
thereby providing a securely attached substrate to which
the later applied comparatively thick low density
polyethylene/linear low density polyethylene blend bonds,
so as to provide secure and reliable attachment of the
low density polyethylene/linear low density polyethylene
blend to the metal pipe.
When a multilayer thin film is utilized, the first
sublayer, i.e., that sublayer next to the metal pipe
wall, is preferably formed the same as the monolayer
discussed above, i.e., polyolefin/maleic anhydride,
ethylene acrylic acid, ethylene methacrylic acid, a blend
of these polymers, or another metal adhesive.
The second sublayer of the multilayer thin film,
i.e., that sublayer formed on top of the first sublayer,
to which the later applied layer of low density
polyethylene/linear low density polyethylene blend is
bonded, preferably comprises a polymer
adhesive/polyethylene blend, i.e., a carboxy-modified
polyethylene such as either ethylene acrylic acid,
ethylene methacrylic acid, low density polyethylene with
a 0-10% concentration, by weight, of maleic anhydride,
linear low density polyethylene with a 0-10%
concentration, by weight, of maleic anhydride, high
density polyethylene with a 0-10% concentration, by
weight, of maleic anhydride, or some combination of these
materials. Again, those skilled in the art will
appreciate that various other metal adhesives are
likewise suitable.
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_g _
Those skilled in the art will further appreciate
that various additives such as antiblocks, antioxidants,
pigments, ultraviolet stabilizers, etc., may be added to
the second sublayer, as desired. Corona treatment may
also be utilized to facilitate application of the first
~ and second sublayers, as desired.
It has been found that the use of the 0-10
concentration of maleic anhydride, as discussed above,
increases the adhesion o~ the polyethylene monolayer or
the second layer of the multilayer film by a factor of
approximately 5 as compared to such layers lacking maleic
anhydride.
The process of forming the metal pipe of the present
invention commences with the steps of pre-washing G-210
(2 oz.) galvanized coil strip in the gauge range o~ 0.048
inches thick thru 0.138 inches thick to initially remove
any residual oil and dirt. The metal is subsequently
processed in a high pressure hot alkaline spray bath to
remove any residual dirt or oils and then rinsed with
high pressure hot water sprayed upon both surfaces of the
metal. An optional mechanical brushing device may be
employed to further condition the surfaces or to remove
any residual chromates or surface oxides. A secondary
high pressure hot alkaline spray and hot, fresh water
rinse is then repeated. The strip is then treated with
a suitable etchant and then dried. An optional oxygen
barrier primer may be applied to the strip or the strip
may be prime coated with an adhesive and then heated to
the appropriate temperature to cure the coating with the
subsequent lamination of the monolayer or multilayer
film. Subsequently, this laminated strip is then water
quenched and cooled to the appropriate ambient
temperature and then recoiled into coil form again.
Subsequently, the laminated coil may then be formed by
conventional techniques to include corrugations or ribs
and formed into a pipe length via a conventional pipe
mill.
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Subsequently, the pre-treated and
corrugated/profiled sheet metal strip is optionally
heated and a comparatively thick, typically having a
thickness of approximately .050 to .125 of an inch,
molten layer of polyethylene preferably a low density
polyethylene/linear low density polyethylene blend, for
example, is extruded unto the interior of the pipe
length. Due to the comparatively thick layer being
applied at an elevated plasticized temperature, it
securely thermally and chemically bonds to the monolayer
or multilayer thin film previously applied to the sheet
metal to provide a composite corrosion and abrasive
resistant pipe.
In the preferred embodiment of the present
invention, application of the comparatively thick, low
density polyethylene/linear low density polyethylene
blend occurs subsequent to forming the sheet metal into
a pipe product. After this, the pipe sections are cooled
and cut into desired lengths using conventional
techni~ues. In addition to being thermally/chemically
bonded to the comparatively thin film layer, the
comparatively thick, low density polyethylene/linear low
density polyethylene blend may optionally be further
secured to the sheet metal via extruding the same
polyethylene material into the ribs or channels of the
pipe to form anchors which attach to the low density
polyethylene/liner low density polyethylene blend layer.
Preferably, the anchor is extruded directly into the
channel. The comparatively thick, low density poly-
ethylene/linear low density polyethylene blend is thenimmediately applied thereover such that the anchor and
the low density polyethylene/linear low density
polyethylene blend layer firmly bond to one another.
Such thermal/ chemical bonding is facilitated by
positioning both the anchor extruder die and the low
density polyethylene/linear low density polyethylene
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blend layer extruder die in close proximity to one
another and in close proximity to the formed pipe.
Thus, the anchor conforms precisely to the
configuration of the channel, i.e., substantially fills
the channel, and additionally thermally bonds thereto.
- Extrusion of the anchor into the channel preferably
occurs after the pipe has been formed, i.e., after
interlocking of the seams attaching adjacent wall
sections to one another.
10Extrusion of the anchor into the channels may occur
as a single extrusion, or alternatively, may comprise a
plurality of extrusions. For example, in a double
extrusion process approximately one half of the anchor is
first formed by extruding into the lower portion of the
channel and the remainder of the anchor is subsequently
- formed by applying a second extrusion upon the previously
extruded portion of the anchor. Those skilled in the art
will recognize that various numbers of extrusions may be
so utilized in such multiple extrusion processes, as
desired. A plurality of channels may be filled
simultaneously or each channel may be filled
individually, as desired.
Alternatively, the anchor and the low density
polyethylene/linear low density polyethylene blend layer
may be commonly extruded from a single extruder such that
the channel is filled so as to form the anchor and the
low density polyethylene/linear low density polyethylene
blend layer applied upon the inner surface of the pipe
simultaneously. The extruder is thus configured such
that a quantity of low density polyethylene/linear low
density polyethylene blend is initially provided in those
areas of the pipe where the channel is formed and a
further layered quantity of low density
polyethylene/linear low density polyethylene blend is
provided on the inner surface of the pipe, and extending
over the channels. Thus, the fabrication process is
simplified by reducing the number of extruders required
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-12-
and by el; m; n~ting the requirement for bonding between
the anchor and the low density polyethylene/linear low
density polyethylene blend layer since the two are
integrally extruded.
Although disclosed in relation to specific
application to pipe forming applications, the present
invention is additionally applicable to other metal
forming applications wherein chemical resistance of the
fabricated metal product is required.
These, as well as other advantages of the prese~nt
invention will be more apparent from the following
description and drawings. It is understood that changes
in the specific structure shown and described may be made
within the scope of the claims without departing from the
spirit of the invention.
Brief Description of the Drawings _ _
Figure l is a perspective view of the exterior of a
length of pipe constructed in accordance to the present
invention;
Figure 2 is an enlarged cross-sectional view of the
pipe wall of Figure l taken about lines 2-2 of Figure l;
Figure 3 is a flow diagram of the method of forming
metal pipe with an integral liner of the present
invention; Figure 4 is a perspective view of the
apparatus for forming the metal pipe with an integrally
formed liner for the present invention;
Figure 5 is an enlarged perspective view of the pipe
mill former of Figure 4;
Figure 6 is an enlarged sectional view of the sheet
metal after the ribs and edge portions have been cold
formed but prior to crimping;
Figure 7 is a sectional view depicting the crimping
lock seam process;
Figure 8 is a sectional side view depicting the
optional roller blending of the monolayer/co-extruded
layer over the crimped lock seam;
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Figure 9 is a flow chart of the pre-treatment, pre-
coating process for bonding the thin mono/multi-film
layer to the sheet metal;
Figure lO is an enlarged cross-sectional view of a
portion of the liner and steel pipe showing the resultant
thin film layer and the comparatively thick low density
polyethylene layer formed on the interior of the pipe
layer.
Figure ll is a perspective view of an apparatus for
applying both the integral liner to the inner surface of
the metal pipe and forming the anchor within a channel
thereof;
Figure 12 is an enlarged perspective view of the
extruder for applying the integral liner and the extruder
for forming the anchor of Figure ll;
Figure 13 is an enlarged perspective view of the
liner extruder and anchor extruder of Figures ll and 12;
and
Figure 14 is an enlarged cross sectional side view
of a tapered channel having an anchor extruded directly
therein and also having the integral liner formed upon
the inner surface of the pipe.
Detailed Description of the Preferred Embodiment
The detailed description set forth below in
connection with the appended drawings is intended as a
description of the presently preferred embodiment of the
invention, and is not intended to represent the only form
in which the present invention may be instructed or
utilized. The description sets forth the functions and
sequence of steps for constructing and utilizing the
invention in connection with the illustrated embodiments.
It is to be understood, however, that the same or
equivalent functions and sequences may be accomplished by
different embodiments that are also intended to be
encompassed within the spirit and scope of the invention.
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Although not by way of limitation, the process and
apparatus of the present invention is well suited for use
on helical spiral ribbed metal pipe such as that
disclosed in United States Letters Patent No. 4,838,317
issued to Andre et al. and assigned to the subject
assignee W.E. Hall Co., the disclosure of which is
expressly incorporated herein by reference. In this
regard, the process and apparatus of the present
invention shall be described in relation to the
fabrication of such helical spiral ribbed metal pipe.
However, those skilled in the art will recognize that the
teachings of this invention are applicable to other metal
pipe structures, as well as other metal products, such as
sheet products, such as sheet products, which are desired
to withstand corrosive environments.
Referring now to Figures 1 and 2, the improved
spiral ribbed pipe of the present invention is depicted
as being generally comprised of a metal pipe wall
material, preferably steel. Spiral ribbed pipe 10 has
externally extending ribs 12 and lock seams 14 formed
thereon, and also has an integrally formed polyethylene
liner 16 formed upon the inner surface thereof. Spiral
channels 18 are preferably formed in the sheet steel 11
of which the pipe 10 is formed, and are preferably filled
with a polymer such as polyethylene, as will be explained
in more detail infra.
Referring now to Figure 3, an overview of the
process of forming the metal pipe 10 with an integrally
formed liner 16 of the present invention is provided.
The process generally comprises pre-treating sheet metal
such as steel to have a comparatively thin,
polymer/adhesive layer formed thereon and coiling the
same for later pipe fabrication. The pre-treated sheet
metal 11 is then subsequently uncoiled via an uncoiler
20, and ribs and/or corrugations and seams 14 (as shown
in Figures 1 and 2) are formed thereon with a profile
roll former 22 (as shown in Figure 4). Subsequently, the
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-15-
pretreated and preformed sheet metal 11 may be cleaned
and optionally heated 24. A seam roller and pipe mill
former 30 forms the preformed sheet metal into a helical
pipe section and crimps the lock seams 14 together to
~orm a pipe product. A sheet extruder with a suitable
die and laminator 31 provides hot extrudate polymer such
as polyethylene and preferably low density and/or linear
low density polyethylene or a blend thereof, to the upper
or inside surface of the sheet metal. The laminator
applies presses the hot extrudate into contact with the
upper pre-treated surface of the sheet metal, thermally
and chemically bonding it to the comparatively thin
polymer/adhesive film layer. The pipe and liner are
preferably cooled 32 after the extrusion process and
cutter 33 then cuts sections of pipe to a desired length.
The steps of ~orming the ribs 12 and seams 14 with
the profile roll former 22 and of forming the preformed
sheet metal into a helical pipe section with pipe former
30 are thoroughly disclosed in United States Letters
Patent No. 4,838,317, issued to Andre et. al., the
disclosure of which is expressly incorporated herein by
re~erence. However, other conventional metal pipe
fabrication techniques as well as other fabricated metal
products are contemplated herein.
As best shown in Figures 1 and 2, the metal pipe
having an integrally formed liner of the present
invention includes a channeled wall defining a plurality
of outwardly projecting structural ribs 12 and a
hydraulically efficient interior surface. The ribs 12
are preferably formed in a helical configuration. The
channels 14, which are formed interiorly thereof, are
generally fabricated having either a square, rectangular
or deltoid configuration, and are open along the interior
surface of the pipe. In the preferred embodiment of the
present invention, the channels 14 are tapered to define
a deltoid shape so as to mechanically capture an anchor
therein, as shown in Figure 14.
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-16-
Referring now to Figure 9, the detailed steps of the
pre-treatment process l9 (of Figure 3) utilized prior to
forming the sheet metal ll into pipe sections lO is
described. Those skilled in the art will recognize that
as conventional practice, the sheet metal ll is
fabricated in elongate lengths that are coiled for ease
in subsequent forming processes.
The initial pre-treatment process l9 is initiated by
un-coiling the coiled galvanized metal strip 6l and then
pre-washing 62 the strip to remove any residual oil
and/or dirt from the upper and lower surfaces of the
strip ll. This step may consist of processes weIl known
in the art such as the application of a detergent
solution. The sheet metal ll is then preferably
subjected to a high pressure hot alkaline spray bath 64
to further loosen and remove any oil and dirt r~;ning
upon the surfaces. The alkaline spray 64 is followed by
a high pressure hot water/fresh water rinse 66. The
strip ll may optionally be brushed with a mechanical
rotary brushing device 67 to remove any residual
chromates and to further condition the surfaces of the
metal or to remove any oxides The strip ll is then
further conditioned and cleaned with another high
pressure hot alkaline wash 68 to ensure adequate removal
of any residual chromates or surface contaminants. Strip
ll is then rinsed with a buffered high pressure hot
water/fresh water rinse to neutralize the surface and
prepare same for the application of the etchant.
Following the treatment of the pre-wash 62, alkaline
cleaning 64, hot water/fresh water rinse 66, optional
mechanical brushing 67, alkaline cleaning 68, and
buffered hot water/fresh water rinse 70, the sheet metal
is subsequently subjected to a chemical treatment or
etchant 72, such as Parker Bonderite 1303, or Betz
Metchem Permatreat 1500 etchant to roughen the surface
and prepare it for the optional application of a primer
or adhesive. Next the sheet steel is dried 74, and an
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--17--
optional oxygen barrier primer or adhesive 76, may be
applied to the etched strip 11. In most instances
however, the oxygen barrier primer or adhesive may be
eliminated. Subsequently, the etched strip 11 is cured
or heated 78, to an exit metal temperature of
- approximately 400~F and a comparatively thin, continuous,
planar, preferably co-extruded polymer/adhesive layer is
laminated to the sheet metal 11.
As best shown in Figure 10, the polymer/adhesive
layer 80 is applied to the sheet metal to have a
laminated thickness of 10 mils min. and is preferably
manufactured as a monolayer or alternatively as a
multilayer film having two distinct layers, i.e., the
lower laminate layer 81 and upper laminate layer 82. As
a monolayer film, the comparatively thin layer preferably
comprises a polymer/adhesive material such as
polyolefin/maleic anhydride, ethylene acrylic acid,
ethylene methacrylic acid, or a blend of these. Those
skilled in the art will appreciate that various other
polymer metal adhesives are likewise suitable.
Optionally, corona treatment may be utilized prior to
application of the comparatively thin layer so as to
enhance a fusion thereof.
As a multilayer film, the first sublayer thereof,
i.e., that layer immediately adjacent the metal surface,
is preferably formed as the same polymer/adhesive
material as the monolayer discussed above and the second
sublayer, is preferably formed upon the first layer, and
comprises a carboxy-modified polyethylene such as an
ethylene acrylic acid, low density polyethylene blend
having a 0-10% concentration, by weight, of maleic
anhydride, linear low density polyethylene having a 0-10%
concentration, by weight, of maleic anhydride, high
density polyethylene having a 0-10% concentration, by
weight, of maleic anhydride, or ethylene methacrylic
acid. Those skilled in the art will appreciate that
various other metal adhesives are likewise suitable.
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-18-
Further, those skilled in the art will appreciate
that various different additives such as antiblocks,
antioxidants, pigments, and UV stabilizers may be
utilized, as desired. Both the first and second layers
are optionally treated to facilitate adhesion of
subsequently applied layers.
The first and second sublayers of the comparatively
thin film are fabricated by any of the various techniques
well known in the art, including cast and blown film
techniques.
Preferably, the first sublayer of the thin film
comprises ethylene acrylic acid and the second layer of
the thin film comprises linear low density polyethylene
having a 0-10% concentration of maleic anhydride, by
weight.
Thus, in the preferred embodiment, the lower
l~mi n~nt 81 is formed of an ethylene acrylic acid which
comprises an adhesive which securely bonds the co-
extruded l~mi n~nt 80 to the sheet metal ll via direct
contact with the sheet metal ll or contact with the prime
coat 76 applied to the sheet metal ll. As will be
explained in more detail infra, the monolayer or
multilayer co-extruded film 80 therefore provides a lower
adhesive/polymer layer 8l adapted to securely bond the
co-extruded layer 80 to the sheet metal ll and an upper
polymer containing layer 82 which serves as a base
material to allow thermal bonding of a subsequent polymer
to the upper layer 82 of the co-extruded layer 80.
In the preferred embodiment, the preferably co-
extruded polymer layer 80 is applied to the sheet metalll at an elevated temperature of approximately 425~ to
630~F, and is pressed tightly thereupon by way of a
conventional roller 316. Subsequently, the sheet metal
ll having the co-extruded polymer layer 80 applied
thereto is cooled 84 and subsequently recoiled 85 for
later use in the pipe fabrication process. In the
preferred embodiment it is contemplated that the pre-
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--19--
treatment process is facilitated on both the upper and
lower surfaces of the sheet metal 11 with the lower
surface treatment providing additional corrosion
protection for the soil side of the resultant pipe.
However the lower side may alternatively be coated with
~ conventional thermoplastic films such as vinyls or
acrylics.
Referring now to Figures 4 and 5 and 11 through 13,
the additional process steps of actually forming the
metal pipe 10 and applying the integrally formed liner 16
of the present invention are illustrated. As shown, the
pre-treated sheet metal 11 previously disposed in a coil
30 is mounted upon a conventional uncoiler 20. The
uncoiler 20 facilitates the uncoiling of the pre-treated
sheet metal 11, having the polymer/adhesive layer 80
disposed upon the upper surface thereof. The pre-treated
sheet metal 11 passes through a profile roll former 22
having a plurality of form rolls 32 which progressively
form the ribs 12 (as shown in Figure 1) and edge seam
members 54 and 56 (as shown in Figure 6) within the sheet
metal 11. It should be noted that the formation of the
ribs 12 comprises the major cold forming procedures for
the pipe 10 and is facilitated on the pre-treated sheet
metal. As such, the substantial tensile and compressive
forces exerted in the cold forming process are
accommodated by the comparatively thin, preferably co-
extruded, polymer/adhesive layer 80 without cracking
and/or blistering. Upon exiting the profile roll former
22, the sheet metal 11 may optionally be subjected to a
cleaner/heater 24 which prepares the upper
polymer/adhesive surface of the sheet metal 11 for the
subsequent pipe length forming process and the thermal/
chemical bonding of the comparatively thick polymer
layer, preferably low density polyethylene thereto.
The thermally bonded metal/ polyethylene sheet 44 is
then passed into a conventional pipe mill having a
crimp/forming roller 50 which helically winds and crimps
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the male and female edge seams 56 and 54 into a lock seam
which forms the resultant pipe length 46. The action of
the crimping/forming roller 50 is depicted in Figure 7.
As shown in Figure 7, the crimping/forming rollers 50
crimps adjacent edge seam members s6 of the
polymer/adhesive laminated sheet metal 44 together by
forcing male seam members 56 into the adjacent female
seam member 54 as the sheet steel 44 is rolled helically
and then bending both male 56 and female 54 seam members
into laminar juxtaposition with the adjacent laminated
steel sheet 11.
As the pipe mill progressively forms the length of
pipe 46, the comparatively thick polymer layer preferably
formed of a low density polyethylene is subsequently
applied within the interior of the pipe length 46 by way
of an extrusion process. In the preferred embodiment,
the extrusion process is utilized to simultaneously fill
the interior of the channel or rib 18 formed on the pipe
wall while simultaneously applying the comparatively
thick polymer layer over the interior of the pipe
section. In this regard, by filling the channel 18 of
the ribs 12, a mechanical anchor is provided which
further secures the resultant polymer layer 16 to the
interior of the pipe length 46.
Referring now to Figures 16-18, the preferred
apparatus for applying the layer of comparatively thick
low density polyethylene and filling the channel 18 of
the rib 12 to yield the anchor structure is shown. With
particular reference to Figures 11 through 13, the
apparatus preferably comprises a hopper 300 cont~;n;ng a
granular polymer preferably polyethylene 302. A lead
screw assembly 304 extends from the bottom of the hopper
300 and into the interior of the pipe 46 axially downline
of crimping roller 50 by way of an extension 303. As
will be recognized, as the sheet metal 11, 44 is crimped
by the roller 50, the resultant pipe 46 extends axially
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-21-
away from the roller 50, i.e., from left to right as
viewed in Figure 11.
As in contemporary extrusion systems, a lead screw
- assembly 304 heats and plasticizes the granular polymer
302 as it travels via lead screw 308 throughout the
length of the lead screw assembly 304. The lead screw
assembly 304 transports the polymer 302 to an extrusion
head assembly or die 310 located axially down line from
the crimp roller 50 which both fills the channel 18 to
form an anchor 200 (Figure 14) of the pipe section 46 and
applies a liner 16 to the inner surface thereof.
With particular reference to Figures 12 and 13 the
extrusion assembly die 310 comprises an anchor extruder
die 312 and a liner extruder die 314. The anchor
extruder die 312 deposits a quantity of polymer material
directly into the channel 18 such that the channel 18 is
substantially filled with polymer material, thereby
forming an anchor 200 directly therein. Due to the
interior of the channel 18 having the comparatively thin
polymer/adhesive layer 80 previously applied thereto, the
quantity of polymer firmly bonds to the polymer
constituent of the previously applied comparatively thin
layer. The liner extruder die 314 subsequently lays down
a sheet of polymer material over the anchor 200 as well
as upon the interior of the pipe wall such that the
heated polymer material of the anchor 200 and the hot
polymer material of the liner 16 adhere to one another,
as well as to the previously applied comparatively thin
polymer/adhesive layer 80 upon the pipe wall.
Preferably, each newly added section of liner 16
slightly overlaps the previously applied layer thereof,
so as to assure adequate bonding thereto as well as
desired coverage of the interior of the pipe 46.
As can be best seen in Figures 12 and 13, a roller
316 is preferably utilized to firmly press the extruded
sheet 16 of polymer material into contact with the inner
polymer/adhesive surface layer 80 of the pipe 46, thereby
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-22-
assuring adequate contact pressure to bond the layer 16
to the polymer/adhesive layer of the pipe wall. It has
been found that a roller 316 comprised of aluminum and
cooled with air allows the liner 16 to be firmly pressed
into place while inhibiting adhesion of the liner 16 to
the roller 316 itself. The roller 316 is preferably
adjustable in height so as to vary the thickness of the
liner 16 applied to the interior of the pipe section 46,
as well as the application pressure. Those skilled in
the art will recognize that alternative roller
configurations are contemplated herein.
Although numerous polyethylene materials are
suitable for use as the liner 16, a preferred material
candidate for the comparatively thick polymer layer is
a low density/ linear low density polyethylene material
known as DOWLEX 3010 or DPT 14S0 (trademarks of Dow
Chemical Company, Midland, Michigan), which are known to
exhibit superior abrasion resistance. Preferably in the
application process, the cleaner/heater 24 elevates the
temperature of the sheet metal 11 and the
polymer/adhesive layer 80 disposed thereon to
approximately 100-225~ F. and not to exceed 300~ F. such
that the polyethylene layer 16 will more readily
thermally bond thereto.
The extruder head or die 310 forms the polyethylene
into a continuous planar layer 40 (shown in Figure 10)
having a thickness of approximately .050 to .125 of an
inch, and preferably approximately .100 inch, which is
applied to the upper surface of the comparatively thin
polymer/adhesive layer 80 disposed upon the sheet steel
11. In the preferred embodiment the polyethylene
layer 40 is extruded onto the comparatively thin polymer
layer 80 at a temperature between approximately 425~-
630~F, preferably approximately 525~F. In the absence of
preheating, the preferred process and temperature for
extruding DOWLEX 3010 is approximately 500~F.
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--23--
Due to the polyethylene layer 40 being applied to
the upper surface of the pre-treated sheet metal 11 at an
elevated plasticized temperature, a strong
- thermal/chemical bond is facilitated between the
5 polyethylene layer 40 and the polymer constituent
existing in the upper layer 82 of the polymer/adhesive
layer 80 disposed upon the sheet metal 11. As such, a
polymer to polymer bond is achieved which securely
affixes the low density polyethylene layer 40 to the pre-
treated and pre-formed sheet metal 11. The resulting
laminated sheet metal 11 may then be further cooled with
blown air or water prior to being formed into a helical
pipe section 46.
After application of the low density polyethylene or
linear low density polyethylene layer 40 to the pre-
- treated sheet metal 11, the resultant metal/polyethylene
laminate possesses a cross-sectional configuration
depicted in Figure 14. As shown, the low density
polyethylene layer 40 extends in a thermally/chemically
20 bonded generally contiguous orientation over the upper
surface of the sheet metal 11 and preferably overlaps at
the rib or channel 18 to maintain a consistently smooth
diameter through the pipe length.
As should be recognized, the resultant pipe section
25 46 having the channels 18 filled with the anchor has
structural strength greater than conventional spiral
ribbed metal pipe. Further, as shown in Figure 10, the
pipe 10 includes an integrally formed substantially pure
low density polyethylene liner 16 having sufficient
thickness (i.e. approximately .100 of an inch) which is
capable of withstanding corrosion caused by contAm;nAnt
acids encountered in sewer applications. Additionally,
since the low density polyethylene liner 16 is applied
integrally to the pipe during the fabrication process and
thermally bonded to the polymer/adhesive layer 80 adhered
to the steel pipe 11, delamination, blistering or
cracking of the low density polyethylene layer 16 is
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W097/04265 PCT~S96111933
-24-
eliminated. Further upon installation of the pipe 10 in
sewer applications, adjacent pipe sections may be easily
abutted and joined at their interfaces by utilizing high
density polyethylene wraps which may be thermally
welded/bonded to the low density polyethylene liner
affixed to the interior of the pipe.
Referring now to Figure 14, a cross section of the
anchor 200 formed within a channel 18 and a liner 16, 40
formed upon the interior of a pipe section 46 is
provided. The anchor 200 bonds to the liner 16 at the
interface 320 thereof. Additionally, the anchor 200 is
both mechanically captured and chemically bonded to the
previously applied comparatively thin polymer/adhesive
layer 80 within the channel 18. The anchor 200 is bonded
within the channel 18 since it is applied thereon while
in the plastic state and thus bonds to the previously
applied comparatively thin layer 80 disposed within the
channel 18. The anchor 200 is mechanically captured
within the channel 18 due to the deltoid or upwardly
tapered construction thereof, which mechanically prevents
the anchor from being pulled therefrom. Additionally,
the liner 16 adhesively bonds to the previously applied
comparatively thin layer 80 applied on the interior of
the pipe 46 since it is likewise applied in a heated or
molten state.
Further, the helical shape of the anchor 200 itself
tends to prevent its being pulled from the channel 18,
since such pulling from the channel would require that
the helical anchor be twisted to facilitate its removal.
Thus, the present invention provides both an
adhesive/chemical bond of the liner to the metal pipe as
well as a mechanical bond via the deltoid shape anchor.
Thus, if for any reason the adhesive/chemical bond should
fail over time, the mechanical bond positively insures
maintenance of the liner within the interior of the pipe.
It will be understood that the exemplary steel pipe
with integrally formed liner described herein and shown
CA 0222~8~4 1997-12-29
W097t04265 PCT~S96/11933
-25-
in the drawings represents only a presently preferred
embodiment of the invention. Indeed, various
modifications and additions may be made to such
embodiment without departing from the spirit and scope of
the invention. For example, various polymer materials
having properties similar to polyethylene and ethylene
acrylic acid may be used. In this regard, Applicant has
additionally found that low density polyethylene or
linear low density polyethylene is a preferred material
candidate for the liner 16 and use of such material is
clearly contemplated herein. Disclosure and scope of the
present invention is not limited to the use of low
density polyethylene. In this regard, in its broad
sense, the present invention facilitates the use of a
relatively thick polymer liner to be disposed upon a
metal surface, which polymer is adhered to the metal
surface by way of a previously applied comparatively thin
layer having an adhesive component and a polymer/adhesive
component which enables the subsequent thermal bonding of
the comparatively thick substantially pure similar
polymer layer via the constituent polymer layer found in
the previously applied comparatively thin layer.
Additionally, the present invention contemplates the
use of affixing a protective polymer layer to a
fabricated product after pre-forming and/or completely
forming the fabricated product by pre-treatment of the
metal utilized in the fabricated product for subsequent
deposition of the polymer layer thereto. Also, various
metals and alloys having sufficient structural strength
may be utilized as the pipe metal.
Furthermore, the polymer laminated metal and method
for forming the same need not be limited to the
fabrication of pipe, but rather may find application in
many diverse areas such as automotive body sheet metal
applications and the like. Thus, these and other
modifications and additions may be obvious to those
skilled in the art and may be implemented to adapt the
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W097/04265 PCT~S96/11933
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present invention for use in a variety of different
applications.
