Note: Descriptions are shown in the official language in which they were submitted.
~L(345056
COILED' T~BrN~
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''BAC:K~ROUND''OT 'T~:INVE~TI'ON ~'
Field of the :Inve:nt~on
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This invention relates to coiled tubing and in particular
to self-supporting coiled tubing.
Description of t'~e Prior'Art . :.
In the Marvin E. Holmgren United States Letters
Patent 3,454,695, owned by the assignee hereof, an improved
method of forming a coiled plastic hose is di.sclosed for pro-
viding a self-supporting nylon tube. More specifically, as
disclosed in said patent, the tube is formed of nylon 11 (11- .'
amino undecanoic acid).
Such coiled hose has conventionally been formed of
nylon as taught in the Rodgers United States Letters Patent
3,021,871. As pointed out in that patent, it has been conven- ,''
tional.to provide such tubing with normally contacting convolu-
tions, requiring relatively stiff or semirigid plastic materials
thus ruling out plastic materials such as polyvinyl chloride, '
polyethylene, polystyrene, and the like. '~
Prior to the Rodgers development, Ralph E. Smith et
al, in United States Letters Patent 2,905,194, disclosed the
forming of coiled plastic hose of polyvinyl chloride. The
Rodgers patent, in teaching that polyvinyl chloride is, in fact,
unsatisfactory for such coiled hose, indicates that there is
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some ~uestion in the art as to ~hat materials are, in fact,
satisfactory for use. .~
The Rodgers patent teaches the use of the nylon .
famil~ formed by condensation of dibasic acids such as tere- :
phthalic acids, with diamlnes. The Holmgren patent, to the
contrary, teaches the use of nylon 11, which comprises 11
amino undecanoic acid.
SUMMARY OF THE INVENTION
The present invention comprehends an improved flex- .
ible coiled tube having improved cold flow characteristics,
improved resilient memory characteristics, and improved elas-
ticity over a wide temperature range while yet being formed
of a relatively low cost material not heretofore considered ..
suitable for such use.
More specifically, the invention comprehends provid- :
ing such a coiled tube formed of a heat softened reset material
which comprises the polycondensation product of at least one
aromatic dicarboxylic acid having a molecular weight below 300 .
condensed with a polyalkylene ether glycol having a molecular
weight of 400-6000 and at least one diol having a molecular
weight below 250. . ~
Such coiled hose effectively comprises tubing formed .~ ~ .
of a plasticized polyethylene terephthalate in which an effec-
tive small percentage of ethylene diol unit is replaced by .;~
polymer glycols. :~.
Further more specifically~ the illustrated coiled
tube has a Scale D durometer hardness in the range of approxi-
mately 44 to 63. Further more specifically, the illustrated
coiled tube may have an elongation at break in the range of
approximately 500 -to 800.
Still fur-ther more specifically, the illustrated ~:
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- ~ coiled tube may have a flex modulus of 7000 -to 60,000.
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B~ F DES~R~Ip-T,~ON~O~ T~` D~ G
Other ~eatur~s and advanta~es~of the ~nYent~on w;i~ll
be apparent from th~e ~ollowl`ng descx~pti~on taken in connec-
tion w~th the accompany~ng drawing ~here~n: -
FI~RE 1 ~s a schemati~c elevat~on of an apparatus
for forming a coiled plastic tube eT~ody~-`ng the l`nvention; and
FIOEURE 2 is a broken elevation of a coiled tube
embodying the invention having fittings connected to opposite
ends thereof and mounted in an air supply system.
DESCRIPTION OF T~IE PREFERRED EM~O'D'IMENT
In the exemplary embodiment of the invention as
disclosed in the draw~ng, a coiled tube generally designated
10 is shown to comprise a tube which may be formed by a method
similar to that of the above-identified Holmgren patent No.
3,454,695 to have a preselected helical configuration as a
result of setting the tube subsequent to a heat softening
thereof.
Thus, as shown in Figure 1, the tube originally may
be formed as by extrusion from an extruder 11 and a suitable
elevated temperature, such as approximately 500F. The extruded
tubing is firstly passed through a cooling device 12 and drawn
therethrough by a haul off device 13, then coiled and allowed to
cool to ambient temperatures such as for storage.
The tubing may be delivered from the coil to a heating
apparatus 14 to raise the temperature of the tubing to an ,,
annealing temperature suitably for permitting facilitated
formation of the tube in the desired helical configuration
by means of a plurality of guide rollers 15. The helical coil ~',
is then set by cooling thereof while the coil is supported on ,~
suitable rollers 16. The guide xollers 15 and support rollers
16 are driven through suitable gearing 17 from a transmission
18, in turn driven by a drive motor 19.
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50~i~
The present invent~on comprehends ~oxming t~e tube
10 of a polyester el~s-~omer. Polyesters~ haYe long had the dis-
adva~t~ge of shrl`nkage and dropout of res~n after a per~od of
agi~ng as a result of conti~nuous curl`ng. ~mproved polyes-ter
resi~ns-are continuously Be~ng prov~ded but ~eretofore, the use
of polyesters has been generall~ contra~ndi~cated in applications
such as coiled tubi`ng for a number o~ reasons includ~ng those
generally discussed in the above identified Rodgers patent.
It has been found, however, that a polyester resin comprising
a plasti~cized polyethylene terephthalate i`n which an effective
small percentage of ethylene diol unit is replaced by polymer
glycols, provides an i`mproved coi`led hose construction.
More specifically, the improved tube forming material
comprises a coiled flexible tube formed of a heat-softened ~ :
reset material comprising the polycondensation product of at -
least one aromatic dicarboxylic acid having a molecular weight ~ :~
below 300 condensed with a polyalkylene ether glycol having a `
molecular weight of 400-6000 and at least one diol having a
molecular weight below 250. An example of such a polyester
elastomer is that sold by E. I. duPont deNemours & CoO under
the trademark HYTREL. Broadly, the HYTREL polyester material
comp~ises a fully polymerized, high molecular weight, non-
reactive thermoplastic. While such polymers are available
having different hardness characteristics in the preferred
embodi.ment, the scale D durometer hardness is ln the range of
approximately 44 to 63. The polyester elastomer material herein
may be extruded at temperatures in the range of approximately
350 to 700 F. and do not require post-curing to provide full
strength and dimensional stabili`ty.
The polyester elastomer is selected for resistance
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to diss~lution by polar solvents so as to resist s~7elling and
permeation by ~uch solvents and fuels. The polyester eiasto-
mer herein is preferably highly resi.stant to flexing over a
wide tempera-ture range. Preferably, the ela~tomer xemain~ not
brittle at te~peratures down to 90 F . with only a small lncrease
in stiffness at temperatures as low as -65~F. The elastomer
herein may be selected to have relatively high hot strength
at tempexatures of 300D F and above, as desired.
The ela~tomer is highly re~i~tant to flex cut
~rowth over a wide temperature range.
The polyester elastomer herein has a relatively
high l~ad bearing capacity whereby the thickness of the tube
~all may be minimized for a given pressure load. More speci-
fically, the polyester elastomer herein e~shibits high Young's
Moduli in tension, compression, and flexural modes.
The polyestex ela~tomer of the present invention
has a relatively low creep rate, which is defined by the ap-
parent modulus.
The polyester elastomer tubing o~ the presen-t inven-
tion provides a highly desirable improvement o~er tubing, such asnylon ll tubing, in avoiding an increase in the Young's Moduli
as a consequence of los3 o~ plasticixer at high temperatures~
More specifically, the polyester elastomer o the present
invention avoids use of volatile plasticizexs and, thu~,
maintains it elasticity notwlthstanding suhjection of the tu~ing
to relatively high ~emparatures for protracted periods of timeO
The preferred polye~ter elastomer herein has an
elongation at break point in the range o approximately 500
to 800 and a flex modulus in the range of 7000 to 60,000. As
the polymer need not be cured, it is im~ediately available or
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use and does not change in its characteristics over long periods
of time as occurs in conventional nylon polymers and the like.
It has been found that the cold flow and memory
c~aracteristics of such polyester elas~omers are substan-tially
improved ovor that o~ nylon, and as such polyester elastomers
> are relatively low in cost, provide a further advan~age over
the heretofore conventional coiled ~ubing materials. :~
A shown in the drawing, the coiled tube may be pro-
vided with a fitting 20 and a fitting Zl at the opposite end
10 ~or connecti~g a tool, such as an air noæzle 22, to an alr
pressure supply duct 23. As indicated in Flgure 2, ~he poly-
ester elastomeric hose i~ salf-suppoxting in carrying the tool
in an elevatea dispo~ition while yet permitting movement o~
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the tool by the u~er by ex!:~ension of the coilecl tube, as de- ;
si~ed. The improved coiled tube provides a longr trouble-
~xee life o~ such a structure providing the above discussed
highly desira~le advanta~es of previous coiled tube structures
utilizing nylon and the like.
The inventive concept herein may be utilized not only
~0 in the farmation o~ nonrein~orced tubing, as discussecl above,
but also in the formation of reinforced tubing, or hose. Thus,
a suitable braid may be provided about the tube and provided
with an outer cover or shea~h prior to the delivery thereof
to khe heating apparatus 1~. Illustra~ively, the braid may
comprise conventional polyester braid. ~The outer sheakh
may be ~ormed of Hytrel polyester ma~erial, which ~ay be ex- ;
truded about the braid covered core in a conventional manner.
. The ~oregoing disclosure of speci~c embodiments is
illustrative of the broad inventive concepts comprehended by
30 the in~entio~
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