Note: Descriptions are shown in the official language in which they were submitted.
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FABRICATION O~ A FLAN OE ArAPTER FOR PLASTIC PIPE
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This invention relates to flaring the end of a thermoplastic pipe
to form a flange.
Flanged connections for joining sections of plastic conduit have
been proposed and utilized to a limited extent. In one method for provid-
ing a flanged end on a plastic pipe, flanges are molded, then welded or
fused to the end of the plastic pipe, as required. This method is gener-
ally unsatisfactory because a variety of sizes of flanges must be main-
tained in stock in order to have the required size when needed. This
method is economically unsatisfactory because of the variety of molds re-
quired to mold the various sizes of flanges. In another method, the end of
a plastic pipe is flared with a heated flaring tool. This method is gener-
ally unacceptable for flaring the end of a plastic pipe having a relatively
thick wall. This method is also unacceptable because expansion of the pipe
to the flange shape reduces the wall thickness of the expanded portion.
Accordingly, it is an object of this invention to provide a process
for forming a radial flange on a plastic pipe.
Other objects and advantages of the i~vention will be apparent to
one skilled in the art upon study of this disclosure and the appended draw-
ing, of which:
FIGURES 1-6, inclusive, are views schematically illustrating vari-
ous stages during the formation of a flange on a thermoplastic pipe.
In accordance with the present invention, there is provided a method
of forming an annular flange on the end of a plastic pipe which comprises
folding a first section of the end portion of a plastic pipe back upon the
next succeeding section and compressing the turned-back section to form a
flange.
The method of this invention is applicable to any size of plastic
pipe. It is particularly applicable to large-diameter pipe having a rela-
tively thick wall, i.e., pipe having an inside diameter of at least 6 inches
and a wall thickness of at least ~ inch.
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It is necessary tha~ the material in the end portion of the pipe
have sufficient plasticity to allow the first section to be folded back on
the next succeeding section. The required plasticity can be obtained by
heating the pipe to a temperature substantially above ambient temperature.
Due to the relatively thick wall of large-diameter pipe, it is preferred
that the pipe wall be heated on its inner and outer sides simultaneously.
This can be accomplished by heating at least a portion of the pipe in a
heated oil bath or a heated glycol bath.
It is preferred that the material in the pipe have a mechanical
memory, i~e., the material has a tendency to return to its original config-
uration. This allows the first section of the end portion to be folded
back on itself.
The polymer materials from which the pipes or pipe in sections are
made are polymers of ethylene or copolymers of ethylene and a small quan-
tity of a mono-l-olefin having 3 to 8 carbon atoms per lecule, i.e., up
to about 10 weight percent~ Such polymers and copolymers have a weight
average molecular weight in the approximate range of 200,000 to 1,000,000,
preferably from 250,000 to 500,000~ It is presently preferred that the
plastlc pipe be formed from a copolymer of ethylene and a mono-l-olefin,
containing at least about 90 weight percent of ethylene. In a presently
preferred embodiment, the plastic pipe is formed fron an ethylene/butene-l
copolymer containing from 90 to 98 weight percent ethylene and from 2 to 10
weight percent butene-l~
Referring now to the drawing and particularly to FICURE l, the end
portion 2 of a plastic pipe 4 is heated to a temperature substantially above
ambient temperature. The axial extremity 6 of conduit 4 is positioned over
a male plug 8 ha~ing a surface contour 10 adapted to fold the axial extrem-
ity 6 and a first section 12 back upon the next succeedin~ section 14.
As shown in FIGURES 2-4, a force is applied to the pipe 4 moving it
toward the plug 8 so that the first section 12 follows the contour 10 and
folds back on the next succeeding section 14.
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,~ ~emale plllg assist 16 having a flat radial surface 18 is then
positioned concentrically over the pipe 4 and placed in contact with the
axial extremity 6. As shown in FIGURE 5, a force is applied to the plug
assist 16, moving it toward the plug 8. As the plug assist 16 is moved
toward the plug 8, the folded first section 12 is c~mpressed and generally
follows the contour 10 of the plug 8~ The force applied to plug assist 16
is continued until the first section has assumed a radial flange configura-
tion, as shown in FI~nR~ 6.
The thus-flanged pipe is maintained under pressure between the male
plug 8 and the plug assist 16 until it cools sufficiently to hold its shape
without reverting to its former shape~ The section can be cooled by water
spray to accelerate such cooling.
The width of the flange, and concomitantly, the amount of first
section 12 folded back on the next succeeding section 14, is dependent upon
the pipe diameter and its wall thickness and the size of the bolt circle on
the metal backup flange which is used to join two flanged pipes together~
Accordingly, flange size is a matter of preference. Similarly, the dimen-
sions of contour 10 of the male plug 8 and the radial surface 18 of the
female plug assist 16 are dependent upon the desired flange size.
While it is preferred that the male plug 8 be a single unit, it is
within the scope of this invention to utilize a first mandrel, not shown,
having a surface contour adapted to turn the first section back on the next
succeeding section, and a second mandrel, not shown, having a surface con-
tour ada~ted to turn the folded section radially outward.
The following example is given better to facilitate the understand-
ing of this invention.
EXAMPLE
A 2~-inch section of pipe, having an inside diameter of 8 inches
and a wall thickness of ~ inch, made of high density polyethylene was used.
This section was made from an ethylene/butene-l copolymer containing 95
weight percent ethylene and 5 weight percent butene-l, having a molecular
3-
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weight of about 250,000, a density of 0.941 grams/cc and a high load melt
index of 2 g/10 minutes (ASTM D-1238-70, Condition F); the resin contained
2 weight percent carbon black, 0~1 weight percent glycerine and 0.1 weight
percent 4,4'-thio-bis~6-tert-butyl m-cresol).
About 6 inches of one end of the pipe section was heated in a bath
of ethylene glycol at 275 F (135 C) until it was soft enough to be de-
formed but not melted. It was then placed on a male plug and hydraulic
pressure of about 2000 psi was applied until the pipe end had bent past 90
and generally conformed to the shape of the plug. On partial cooling, the
end section folded back on itself.
A female mandrel assist was then placed o~er the pipe and hydraulic
pressure at about 2000 psi was applied to form the flange and to maintain
the flanged shape until the pipe had cooled sufficiently to maintain the
shape.
Reasonable modifications are possible within the scope of this dis-
closure without departing from the scope and spirit thereof
