CA2208166A1

CA2208166A1 - Re-forming thermoplastic materials

Info

Publication number: CA2208166A1
Application number: CA002208166A
Authority: CA
Inventors: John Wood
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-12-17
Filing date: 1995-12-18
Publication date: 1996-06-20
Also published as: AU4266896A; WO1996018493A1; EP0797500A1; GB9425503D0

Abstract

Method and apparatus for re-forming walled thermoplastics members including pipe (12) as re-lining of worn-out pipeline (20) by heating (14) to soften throughout wall thickness without melting, and re-sizing/re-shaping by fluid pressure (16). Infrared heating radiation (14) and progressive change of thermoplastics (polyethylene) from absorptive to useful transparency at or near crystalline melt (below full melt) temperature allows self-regulation of heating, as well as replacement of original thermoplastic memory of geometry. Preferred compact machine (10) combines heating elements array (22), pressurising gas turbine (18) and electric power generator (30) in coaxial/concentric arrangement.

Description

W 096/18493 PCT/~55h~5S4 TITLE: RE-FORMING THERMOPI~ASTTC MEMBERS
Technical Field The in~ention relates to re-~orming thermoplastics members, including method and apparatus ~or re-sizing and re-shaping re-lining pipes for damaged or worn-out under-ground pipelines to avoid the need for excavation.
Such pipelines typically carry gas or water under head or pressure, or sewage ~ervices, in urban areas. Some existing pipe lines are over 100 years old and are in a sad state of disrepair due to various factors including damage due to ground Illvve--le~Lt, corrosion and crumbling.
~echnical Bach~l~u~.d The idea of "no-dig~' repairs of pipelines is not new.
For more than 25 years, the so-called "Insituform" (RTM) process has been used to re-line sewer pipelines. This process was the first of what are now called soft-lining methods of pipeline rehabilitation. A long tube of wo~en ~elt serves as the lining ma~erial and is impregnated with epoxy or polyester resin. This tube is installed in the host pipeline using an inversion process and is then cured n situ to form a structural repair.
Slip-lining is a simple alternative method ~or thermo-plastic re-lining. An undersized, extruded thermoplastics pipe is dragged through the original pipeline and gaps left ~etween the undersized pipe and the host pipeline are filled using a grout, at least to stop sewage etc int~n~ly entrant ~rom lateral connections from flowing into/through such gaps. E~en for repairs without lateral connections, grouting is often needed to stabilise the under-size slip-lining in position. Whether or not limited to positions of lateral connec~ions, e~cav~tion is required at intervals for grouting, necessitating host pipeline run location being accurately determined from of ten old site-plans.
Swage-down systems can assist meeting annular gap problems of slip-lining, by t~ki n~ a full-size re-lining thermoplastics pipe and s~lARhing, or swaging, it undersize SUBSTITUTE SHEFr (RULE 26) WO96118493 PCT/GD~S~95~

using hydraulic rams to fit it into the host pipeline.
High pressure air is used to re-expand the new pipe when it is in position, and thermoplastic memory ~rom the pipe extrusion process as to full-size geometry assists system stability over time. Gaps are, however, not fully eliminated by th~s system since the match between the diameters of the old pipeline and the pre-swaged plastic pipe will only rarely b~ perfect. Often, within the any length o~ re-lined host pipeline, some sections of re-lining pipe will be loose, and some parts the plastic pipeneed to take on a distorted shape in order to fit. Swage-down systems cannot produce a ~dimple' for use by robot hole-cutters, which means that each lateral connection position usually has to be excavated to re-connect it.
So-called U-liner systems are alternative to swage-down with two main differences. The re-lining th~r~_ plastic pipe is extruded round then folded into a "U" shape in cross-section at the pipe manufacturing plant, so as to facilitate fitting inside a host pipeline. The temperature at which the pipe is ~ormed into the U shape is critical because of the way that temperature affects the pipe's ~h~r~plastic memory. Also, steam is blown through the central ch~nn~l o~ the ~olded re-lining pipe to soften it sufficiently for it to be inserted through a st~n~d man-hole access tO the host pipeline. Once dragged into place,the re-lining pipe is inflated against the host pipeline usir.g air pressure. It has been claim~d that the stc-~ n~
will induce a new thermoplastic memory for the pipe at this sta~e. However, the close-fit tends to be short-lived, which is not surprising as simple st~m; ng is limited to 100~C, thus below typical crystalline melt temperatures, e.g. 120~C for polyethylene, to be ~ree~e~ for erasing/
replacement of thenmoplastic memory. Thus, there is a t~n~ncy for the pipe to revert or creep back over time ~o the extruded diameter, which means results are no better than for Swage-down. At worst, the pipe can seek to revert co the U shape because of imperfect temperature control SU~STITUTE SHEET (~IJLE 26) during forming of the "U" shape off the extrusion line.
Another problem with U-bending arises from dragging the fold re-lining pipe into position while very soft.
The Youngs modulus of polyethylene at 100°C is low and the pipe stretches easily, even with just friction to overcome in dragging into position. Because no new thermoplastic memory is set, residual stress can appear in the re-lining pipe as it cools and tries to revert to its original geometry, including as to length. This can cause longitudinal creep movement, including as to intended positions of any lateral holes that have been cut in the pipe.
It is one particular object of this invention to mitigate such problem(s), through other applications arise.
Disclosure of Invention According to one particular aspect of this invention, there is provided a method of re-sizing or re-shaping a hollow thermo-plastics member, conveniently elongate, say tubular, comprising the steps of heating the thermoplastics material of the member to soften it, and applying fluid pressure, conveniently pressurised gas, to alter its size and/or shape, wherein the heating is by electromagnetic radiation to which the thermoplastics material both develops a degree of transparency without melting that at least reduces further heating up an softens enough to be re-sized and/or re-shaped as desired by said fluid pressure application. Advantageously, re-forming is at or above a temperature at which thermoplastic memory as to original geometry becomes at least partially erased and usefully replaced by the re-formed goemetry.
According to another particular aspect of this invention, there is provided apparatus for re-sizing or ' re-shaping a hollow or thermoplastics member, conveniently elongate, say tubular, comprising means for heating the thermoplastics material of the member to soften it, and means for applying fluid pressure, conveniently pressurised gas, to alter the size and/or shape of the hollow member after its thermo-plastic material is softened by said -W 096/18493 P~ 9~ 9S4 heating, wherein the means for heating serves to provide electromagnetic radiation to which said thermoplastics material is absorptive before developing a degree of transparency without melting that at least r~ c~c further heating up and is then soft eno~gh to be re-sized and/or re-shaped as desired by said ~luid pressure, preferably at or above a temperature at which thermoplastic memory as to original geometry becomes at least partially erased and replaced.
Conceptually, including as to the original motivating context of improv~ng lining/re-lining pipes, particularly underground pipelines, or other conduits, this invention can be seen as seeking to modify known production processes blowing gas into soft, often near-molten, material to stretch and expand that material into a desired actual product. Such processes are widely used, with or without external product-related form-imposing constraint or moulds, for producing such things as plastics film whether to be substantially for~n-sus~r~;nin~ or to be s~retchable, inflatable elastomeric balloons, various hollow-ware often of nec~ed bottle or flask type, etc. In themselves, of course, such production processes can ~e seen as derivative from, indeed include, age-old forming o~ hollow glassware.
Initially, apparent absence of proposed application of such processes to re-forming, i.e. going from an initial already-made product form to a modified product ~orm, with particular re~erence tO th~ plastics products, seemed surprising.
Eowever, pro~ound dif~iculties quickly came to light, particularly ~or polyethylene or other typical or ~easible thermoplastics re-lining pipe material. Thus, melt temper-atures and other thermal properties of such materials, particularly low heat con~l~ctivity and high specific heat (le~ing to very steep temperature gradients in normal wall thic~nesses, typically 25mm and more, of re-l ;ning pipe, that deleterious surface melting occurs be~ore the whole is soft enough to ~ n~ satisfactorily, particularly when SUBSTITUTE SHEET (PIULE 26) WO 96/18493 P~ /~b~S1~95 1 heating from one side only as is only practical from the interior of a re-lining pipe. These problems are drastically exacerbated by the further highly desirable objective o~ achieving so~tness throughout wall thickness that effectively erases as-produced pre-reformed thermo-plastic memory and replaces it by post-reformed thermo-plastic memory. Crystallinity inevitable at envisaged wall thicknesses, and complexi~y of pre-full-melt phases of thermoplastics materials, contribute.
General method and apparatus aspects o~ this invention arise from solYing these pro~lems/di~iculties, basically by adaptation of conventional thermoplastics materials for re-lining pipes, or other hollow or walled ~embers that inherently present similar problems ~or any desired re-forming, so that heating means utilised achieves a suf ~iciently uniform softening of the thermoplastics material throughout i~s wall thickness ~or desired re-forming by applied ~luid pressure, further preferably (as a~ove) achieving so~tness (believed to correspond to what is known as ~rystalline melt occurring be~ore going ~ully molten) su~ficient for at least partial erasure/rerl~rPmQnt of thermoplastic memory for subse~uent re-~ormed product stability.
It will be appreciated that, as well as P~r~ncion as en~isaged ~or re-lining pipes, contraction down, say onto a former, could be done where there is exterior access to the thermoplastics mP~Pr to be re-formed.
Thermoplastics material adaptations can involve inclusions of other materials, for example con~l~otive if contact heating is to be used, say by super-heated steam;
or electrical reactance responsi~e if electrical induction hP~t; ng is to be used; or other releYantly suitable suitably energy-absorptive, say for mi~Lo~dve heating.
Such inclusions could be of particulate or filamentary type, or be as sheets, such as of mesh or other PYr~n~P~
~orms, say corrugated longit~;n~lly if not otherwise P~r~n~ible with desired re-forming o~ the thermoplastics SUBSTITUTE SHEET (P~ULE 26) W 096/18493 PCT/~ 5S4 material itself.
The aforementioned effective transparency together with re-formability, prefera~ly with geometric memory replacement, i.e. at or close to crystalline melt or above up to full melt temperatures of thermoplastic materials, has ~reat advantages by way of capability for self-regulation in relation to effects, including srattering, of applied electro-magneti~ heating radiation capable of required heat intensity. Inclusions in the thermoplastics material may also assist in relation to internal heat retention and/or transparency/opaqueness adjustment, e.g.
fine particles (typically 45 n~nnmptres nomin~l) of c~rh~n black in small quantities (typically 100 - 1000 ppm).
For typical polyethylene re-lining pipe materials, and heating radiation in infra-red extending into visible light spectrum, it was found that the desired ef~ective transparency ef~ect does not occur in its ~ or normal black, yellow and blue pigmentations, but does happen ~or so-called "natural" polythene, as readily available with a creamy white hue. Other infra-red transparent colouration of a~ least surfaces could, of coùrse, be used.
For conductive, inductive or mi~-u~J~v~ assisting inclusions in appropriate content/form for suitably even or satis~actorily low temperature gradient through wall thick-ness o~ the member concerned, and satisfactorily high heatintensity achieved (say c ,-~able with that for in~ra-red/visible light), temperature sensing and heating control means will ordinarily be required. Hc~_v~, for electro-magnetic radiation heating accomr~n;ed by transition to effective transparency, there will be a simple and automatic p~oy~essive softPn;n~ from ;nC~Pnt to opposite surface, with little or no further in-material heating at such transparency. This is particularly attractive ~or a re-lining pipe re-fonming machine that may simply be towed at a rate known to be ef~ective, preferably with compressed gas applied ;mme~i~tely, co--v~--iently from a turbine associated with the heating means, further pre_erably SUBSTITUTE SHEET (RULE 26) -W 096~18493 pcTl~3s/~95~

serving for any necessary or desired cooling, whether of P~r~n~e~ re-lining pipe or of the heating means itself.
Any suitable compressed gas may be used, e.g. air or inert (such as carbon dioxide) ~or safety ayainst explosion risks; and, at least for re-lining a host pipeline, means can ~e provided for creating bac~ pressure in the re-lining pipe downstream o~ the pre~erably mo~able heater to cause the softened pipe to re-size. Suitable apparatus could include means for creating a pressure rh~mh~r sealed agains~ the sur~ace of the member, means for pressurizing the chamber and means for detecting a pressure drop in the chamber indicati~e, for ~mple, of a rupture in the member. The pressurizing means may apply pressure pulses to such chamber or against other suitable back-pressure.
Brief Descri~tion of Drawings Specific imple~entation for this invention will now be described, by way of example, with reference to the accomp-anying dia~Ldl,~..atic drawings, in which:-Figure 1 is an overall longitll~; n~l seceional view o~
one apparatus;
Figure 2 is a longit~l~i n~l sectional view of heating means;
Figure 3 is an overall longitn~i n~l sectional view of another apparatus;
Figure 4 is a schematic view of a device for detecting bursts in the wall of re-lining pipe;
Figure 5 is a diagra~ showing heating re-lining pipe wall locally in restoring a lateral connection; and Figure 6 shows a further stage in restoring a lateral connection, after the heating stage o~ Figure 5.
Modes of Carryinq Out Invention In Figures 1 and 2, heating ~-rhi n~ 10 iS pulled through undersized thermoplastics re-lining pipe 12 to soften it by its absorption o~ at least infra-red radiation 14. Fluid pressure, specifically compressed gas 16, is used to Q~r~n~ the softened re-lining pipe 12 at 16A into contact with host pipeline 20 to exclude ~nn~ r gaps, SUSS~lrU~E SHEE~ (RULE 26) WO96/18~93 PCT/~,S~5~4 ideally give general closely intima~e fit. The fluid flow 16 is also shown at 16B cooling the ~xp~n~ re-lining pipe 12. The process can be continuous, with the heater 12 shown integrated with gas flow tllrhi n~ 18 .
Evacuated Halogen lamps or Ni-Chrome wire can serve as heating elements 22 and source of radiant infra-red heat, typically accompanied by visible light to which preferred thermo-plastics material~ also become transparent. Chromed or polished aluminium reflector(s) 24 usefully ser~e to direct the radiation from the heating el.- -nrs Z2, with forced cooling at 16C on its way to turbine drive nozzle 18N, to ensure that the heaters 22 and the reflectors 24 do not overheat within preferred transparent glass cont~;n;
tube 23.
Electricity for driving preferred elongate, advantage-ously ~nn~ r, arrays of h~t~n~ lamps/elements 22 could be taken directly ~rom electrical cables put into the pipe, but, as preferred on safety and logistical grounds, use is shown of a further integration into the heating r~h;n~ 10 of a generator 30 shown having, inside and concentric with the array 22, wi n~i ngS 32 and rotating magnet assembly 34 in bearings 36, and also sharing cooling by incoming gas supply.
Input cold gas ~low 16C to the eurbo-generator 18/30 is shown coming through re-lining pipe end sealing gland 21 from an a~ove-ground compressor 27 through an upstream manhole also acco~mo~ting haulage cable 29C from winch 29 through stabilising pulley pro~isions 29P and the gland 21.
The gas, con~eniently air, goes past elastomeric wiping seal 26 to the re-lining pipe 12 and is shown ~h~nn~l led at 27 to flow o~er the lamps/elements 22 and reflector(s) 24 to keep them cool in the glass tube 23. Cooling air-speeds o~ up to lO0 meters/second can be used without incurring too much turbulent energy loss. Not all of the heat L~...ov~d by cooling the lamps/elements 22 and re~lector(s) 24 is wasted because it effectively gets transferred to the input gas to the turbine 18, thus raising the temperature SVBSTITUTE SHEET (RULE 26) wo96lls493 PCT/~b~S~9S4 and therefore the gas pressure. Much of the ~emov~d heat energy is ehere~ore recovered due to the increased work that can be extracted by the tur~ine wheel ~rom the hotter, higher pressure gas. High pressure gas goes from end 40 of the re-lining pipe 12 through ~lexible ~on~ t 42 to a back-pressure regulating valve 44 shown at a downstream manhole, and ser~ing to assure desired expansion/cooling.
Alternatively, bac~-pressuring means might be towed along behind the machine 10.
Towing the pressure regulator behind the re-sizing machine means that only one lateral hole need be coped with at any one time. Also, it means that the holes will not become pressurised, since air is ~ree to escape. This allows the possibility o~ putting an inflation sock bag, say of PTFE, to seal the laterals, at least behind though feasibly wholly o~er the entire machine.
Rather than atmospheric air as the pressurised and cooling gas, for which the ~mho~m~nt of Figures 1 and 2 is particularly designed, some other and safer gas could be used, usually inert, ~or ~mrle r~rh~n dioxide, see Figure 3. The same re~erences are used advanced by one hundred ~or the same or functionally similar items. Dif~erences mainly concern external gas supply bottle 150, above-ground turbo-compressor 152 ~or its pressurising to high re-lining pipe llZ P~r~n~ing pressure, high and low pressure ~lexible gas ~low lines 154 and 156 to and from seals to heating machine 110 for int~r~l cooling flow therethrough, and intercooler 158 for low pressure gas return to the turbo-compressor 152. ~ ge line 129P to winch 129 is shown passing through a high pressure seal in gas ~low line 154, but any practical arra,y_.~.c"t is ~easible, including remotely controlled self-propulsion for the heater machine 110 .
Combination heater/generator or heater/turbine or heater/generator/turbine m~ch;nPs ~or tra~ersing pipes etc constitute another aspect of this in~ention by way of such combination(s) together, pre~erably with plural heating SUBSTITUTE SHEET (RULE 26) CA 02208ï66 1997-06-18 W 096/18493 P~l/~b9S/02954 elements, conveniently in an annular preferably elongate array; and further preferably with trailing end turbine and/or inner reflector means and/or electric generator provision, conveniently either or both concentric with heating element array; and/or suitably transparent cnnt~in-ment of heating element(s~ etc and~or defining a heating element~s) and reflector(s) cooling path for turbine gas supply; and/or (see be~ow) control means for unwanted radiation components from the heater by suppression and/or filtering.
Preferred embodiments of such m~chine, e.g. as at lO/18 etc ~or 110/118) can be ad~antageously compact, particularly that can be winch~ through a 7-inch (ca.
175mm) re-lining pipe, including being no more than about 18~ (ca. 450mm) long in order to negotiate normal bends.
Moreover, thermal characteristics, including high latent heat, o~ most thermoplastics, perhaps particularly polyethylene, lead to a joule-heat requirement for st~n~rd re-lining pipes o~ at least 25 kW of power to re-fonm a lOOm length of pipe in one hour, which can be met by compact ~A~h;nes hereof capable of (non-limiting) projected practical mi ni ~-m process speed to suit. Turbo-generator requirements need be only four-pole, as frequency of operation is relatively unimportant for a generator so long as the load can be altered to suit the voltage that it outputs. A 40kW, 40,000 RPM brushless motor could be driven in re~erse by a turbine wheel to produce the required power.
With thermoplastics, typically polyethylene, re-l; n;ng pipe material soft, see Figure 4, the ~r~ncion pressure will stretch the material into any unsupported ~oid, particularly of a lateral connection 60, at least to form a ~dimple~ 62, if not a burst 64 (dimple formation omitted) if inflation pressure is high enough and/or the material soft enough. An unburst dimple 62 facilitates ftn~;n~
lateral connections 60 for later cutting, con~eniently by a con~entional cutter robot. A blow-out hole 62 may self-SUBSTITUTE SHEET (RULE 26) W 096118493 PCT/~5~55~1 heal to some extent, because, as soon as a hole forms, gas will rush out o~ it, cooling the thermoplastics material down and consolidating it. Loss of gas flow through small holes may not ~e significant, even int lateral connections, at the expansion pressure~s) envisaged. ~omr~red to the very high ~low through downstream back-pressure regulation valve 44, loss of air into laterals may not significantly a~fect the inflation pressure regulation.
I~ e~fects o~ burst-outs are not desired and cannot be prevented any other way, a pre-liner could be used. A thin sock of high strength, transparent, higher melt temperature plastic (e.g polypropylene) could be gas-inverted into the host pipeline prior to re-lining.
Detecting positions of burst-outs 64 might be simply by monitoring gas pressure changes at the back-pressure valve 4~. Alternatively, a simple pressurised gas machine 66 could be dragged through the re-formed re-lining pipe 12 (or 112) with end sealing provisions 68A,B and pressure loss detection signalled over line 69. However, ~nc;~n~e of re-lining pipe blow-outs 64 is turned to advantage herein at lateral connections, see Figures 5 and 6. A
machine 70 (which could include position detection of Figure 4) dragged through the re-formed re-lining pipe 12 (or 112), is also shown with end sealing provisions 72A,B
to define a cham~er 74 which can be pressurized. Reduction in pressure in the chamber 74 again indicates the presence of a blow-hole as an increase in gas-~low above the nonmal leakage rate of the seal provisions 72A,B. Pulses of air could be used to avoid pressurising lateral connection 76 associated with the blow-hole 78.
Reinstating good lateral connection at 78 involves heating to so~tening the thermoplastics material locally, much as was done at installation. An infra-red heat source 80 and directional reflector 84 on a rotatable carrier 86 serves to soften the area around the blow-hole 78/lateral SUBSTITUTE SHEET ~RULE 26) WO96/l8493 PCTIGB9S/02954 connection 76, this time typically using an external electric source if allowed by the low power requirement.
Then, the carrier 86 is rotated a half turn and a balloon 88 is inflated to push so~tened thermoplastics material into the lateral connection 76. This machine 70 could be towed along behind the basic P~An~ion machines 10 and 110 o~ Figures 1 to 3, and serve in desired back-pressuring.
Reverting to basic desired softening etc action, heating in the thermoplastics of the pipe 12 (or 112) should not be uneven and thus lead to local melting and cold spots. using infra-red, heat absorption is virtually only in whatever is its instant penetration depth, and falling exponentially through it. The penetration depth is low ~or opaque polyethylene due to intrinsic low thermal co2~t~ctivity and high specific heat, which would cause surface melting, with r~A~ning thickness staying cold.
For a ~ully transparent material, there would, of course, be virtually no heat absorption at all. For an idealised material otherwise with the thermal characteristics of Z0 polyethylene, but a particular degree o~ transparency such that all incident infra-red radiation was captured in the thickness of the wall o~ the pipe 12 (or 112), the temperature gradient through that thickness would be very steep, and the material could not soften towards the outer sur~ace before the inner sur~ace melted. Inter~;Ate degrees of transparency might take off enough energy as heat on all ;nC;~nt radiation eventually to heat up to desired temperature, but efficiency would be very low SUBSTITUTE SHEET (RULE 2B) wos6lls493 PCT/~9S~ 554 (leading to excessive heating of the host pipe) without good reflection provisions for multiple wall thickness traversals by the radiation (addiny greatly to complexity and processing time).
So-called "natural" creamy-white polyethylene (due to crystallinity though free of normal pigments) discloses the property o~ going ~rom opaque enough ~or absorption, including internal scattering effects, typically up to about 70~ o~ incident infra-red radiation, to heat up to the desired temperature at which it goes transparent enough (or perhaps change of refractive index is involved, the exact mechanism not being fully understood at this stage, see below regarding optical transparency having been noted) to limit ~urther heating below ~ull melting; and to do so progressi~ely through the thickness from incident to other surface, see idealised in sloping line 28.
Further ref; n~m~nt can include taking steps to reduce radiation content at certain frequencies/wa~e-lengths related C-H resonance to which particular thermoplastics materials are or may be particularly susceptible, including as to surface burning, e.g. f~n~m~ntals peaking at 0.9, 1.2 and 1.74 micrometre and odd (or co~ nC; ~Pnt, e.g. 3.5 micrometre) harmonics for polyethylene, This is readily done in various ways using generally known filter and/or suppression techniques readily tailored specifically to the purposes hereof. For example, suitable dielectric material can be installed on the glass tube 23, often a combination of materials and layers, say at 23A on its inner surface SlJBSTITlJTE SHEET (~llLE 26) CA 02iO8166 1997-06-18 WO 96/18493 PCTJ~29S4 where re~lection is involved in discrimination and unwanted radiation components eventually dissipate between the filter and the reflector 24. Alternatively the hea~ing elements may be coated with ~requency selective suppressive ma~erials, such as various oxides on Ni-Chrome heating elements Perhaps even more simply, an appropriate sample of the thermoplastics material concerned could be used on a sacrificial basis as a filter.
As a non-limiting postulation of self-regulating action in such as polye~hylene, noted sudden increase is optical transparency appears Accom~ ed by pronounced softening, at a particular temperature close to and through crystalline melt, perhaps attri~utable to random re-orientation of its long polymer molecule ~h~; nc and associated loss of geometric memory, ultimately in favour of the new shape. ~n any event, in practice, procedures hereo~ will e~en allow for re-sizing ~-~hin~ becoming stuck in one position, i.e. without melting the re-lining pipe even if infra-red radiation continues (then merely ~oing into the host pipe structure, o~ten cast iron so harmlessly heat conducting), tho~gh it would o~viously make best sense to stop heating temporarily i~ release of the machine is going to be long delayed.
Although in~ra-red is a preferred energy source, any frequency, or spectrum of fre~l~nc; s which are absorbed by and heats the thermoplastic will wor~. White-light halogen lamps are certainly feasible sources o~ power. They are understood to output about 40~ of their energy in the SUESTITUTE SHEET (P~ULE 26) wos6/1s493 PCT/GB95/029S4 visible spectrum, the rest being infra-red. Having at least some output energy in the visible spectrum has one ad~antage in allowing ready optical monitoring of progress.
Also, optical clarity of the material when it softens may S be better in the visible region than in the in~ra-red. So, at least signi~icant (i~ not all should that be desired) visible spectrum heating could mean that, once softened, the heat take-up rate would be so low as to give indefinite time ~or the machine to be stopped in one place with the lamps running, but without melting the plastic. A possible disad~antage in using prP~o~n~ntly white light could be reflecti~ity of whitish cold polyethylene slowing heating up, and requiring plural traversals over the lamps between the pipe and the reflector(s) in being ahsorbed in the polyethylene. ThiS increases the heat loss in the reflector and may also mean that the lamps run hotter.
Lamp output frequencies could be tailored to some extene to suit any pre~erential colour absorption pattern o~ the particular plastics material to be heated. Heat intensity from such as Ni-Chrome wires can be adjusted by controlling the current density, and therefore heat intensity in the wires, though Ni-Chrome wires should not be run white hot because they would either n~ ~; Re or melt a~ these temperatures. For white light, tungsten ele~ents in an inert atmosphere could be used, but probably not with significant operational advantage co~r~ed with generally more efficient halogen lamps.
Whatever the source of the light energy, the output SUBSTITUTE SHEET (RULE 26) will be spread out from infra-red into the visible. All that can be controlled is frequency where the peak output intensity will exist.
Gi~en present underst~n~;ng that so-called crystalline melt (breaking chain interlocking?), say for polyethylene, is energetically rather similar to any other melting process, but precedes full melt (_reaking to ~ree molecules?), the high speci~ic/latent heat of melting and solidi~ication for the latter gives a good energy margin, even above crystalline mel~, without onset of full melt.
It appears not to be necessary to go to ~ull melt, only to crystalline melt, suf~iciently to e...~v~ the first-made geometric ~ ...o-~ and thus ~L~V~t the pipe from ever creeping back to the previous undersize geometry. The exact speed of towing the de~ice through the re-lining pipe is thus not too critical. In~ep~l the m~ch~np can always be moved below theoretical m~Y;tml~ speed, but the extra heat ener~y transferred, above what is required to so~ten, will never cause melting, even discounting the primary heat self-regulation o~ the transparency e~fect, but could remain important to avoid surface melting on the leading edge and/or ; n~ nt sur~ace o~ the heated area.
Industrial A~ h;lity Pre~erred PmhO~m~ntS of this invention afford clean and dry, low cost, 100~ no-dig, fast operation with progressive one-stage c~nr~rrent heating, fonming and cooling; and no possibility of thermoplastic recovery either radial or longitnA~n~l in a low residual stress true SUBSTITUTE SHEET (~ULE 26) WO96tl8493 P~--/~9S/029S4 close-fit system not requiring grouting. Preferred transparency onset ~eatures gi~e intrinsic temperature regulation. No resins need be used, so storage life is indefinite; and plant requirement is small size and 5 minim~l . No lead-in trenrhing is needed, nor modifications to existing manholes; and good dimples make lateral connections easy without excavation. Small heated volume/
area lead to low losses, and application is seen beyond polyethylene, basically only limited as to thermoplastic materials meeting requirements hereo~, including as to inclusions for controlled heating alternatively to infra-red.

SUBSTITUTE SHEET (RULE 26)

Claims

181A Method of re-forming a walled thermoplastics member, the method comprising the steps of heating the member to soften its thermoplastics material sufficiently uniformly through its thickness (but without full melting) for desired re-forming by fluid pressure, and applying pressurised fluid to so re-form the member in size and shape as desired, characterised in that said heating is by electromagnetic radiation to extent sufficient to cause in said thermoplastics material a change or transparency contributory to achieving said desired re-forming.

1B Method of re-forming a walled thermoplastics member, the method comprising the steps of heating the member to soften its thermoplastics material sufficiently uniformly through its thickness (but without full melting) for desired re-forming by fluid pressure, and applying pressurised fluid to so re-form the member in size and shape as desired, characterised in that said thermoplastics material has inclusions of nature cooperative with application for heating to aid even-ness of heating and softening throughout its wall thickness for said desired re-forming.

2. Method according to claim 1, wherein the member is elongate tubular for re-lining a pipeline relative to which it is cross-sectionally undersize until in situ by said re-forming from its interior.
3. Method according to claim 1 or claim 2, wherein the member is of natural polythene.

4A' Apparatus for re-forming a walled thermoplastics member, comprising means for heating the member to soften its thermoplastics material sufficiently uniformly through its thickness (but without full melting) for desired re-forming by fluid pressure, and means for applying pressurised fluid to so re-form the member in size and shape as desired, characterised in that the heating means operates by production of electromagnetic radiation to extent sufficient to cause in said thermoplastics material a change of transparency contributory to achieving said desired re-forming at temperatures corresponding to where inclusion-free said thermoplastics material does or would go highly transparent approaching but before full melting.

4B' Apparatus for re-forming a walled thermoplastics member, comprising means for heating the member to soften its thermoplastics material sufficiently uniformly through its thickness (but without full melting) for desired re-forming by fluid pressure, and means for applying pressurised fluid to so re-form the member in size and shape as desired, characterised in that the heating means operates in cooperation with predetermined inclusions in said thermoplastics material to aid even-ness of heating and softening throughout its wall thickness for said desired reforming at temperatures corresponding to where inclusion-free said thermoplastics material does or would go highly transparent approaching but before full melting.

6. Method or apparatus according to any preceding claim, wherein the heating is enough for at least partial erasure and replacement of thermoplastic memory as to geometry before re-forming.

8. Method or apparatus according to claim 7, wherein the radiation is or includes infra-red.
9. Method or apparatus according to claim 8, wherein the heating is via selective filtering and/or suppressing means for removing frequencies to which the thermoplastics material is undesirably responsive.

10. Apparatus for heating within a tubular member, comprising a machine towable through the member, the towable machine having an elongate and/or annular array of electric heating elements operative electrically to supply infra-red radiation and an electrical generator for operating the heating elements.

11. Apparatus according to claim 10, wherein annular said array has associated radially inner reflector means.
12. Apparatus according to claim 10 or claim 11, wherein the machine has a turbine driven by pressurised gas or for desirably pressurising gas and operating the electrical generator 13. Apparatus according to claim 12, wherein elongated and annular said array of heating elements is concentric about said electrical generator with said turbine at one end serving to draw gas over other components for cooling purposes.
14. Apparatus according to claim 14, comprising tubular transparent means about the array of heating elements.
15. Apparatus according to claim 14 with claim 9, wherein the transparent means has associated dielectric frequency selective filter means.
16. Apparatus according to claim 13 with claim 9, wherein the heating elements have associated frequency selective suppression means.