CA1322031C - Contactless heating of thin filaments - Google Patents
Contactless heating of thin filamentsInfo
- Publication number
- CA1322031C CA1322031C CA000600048A CA600048A CA1322031C CA 1322031 C CA1322031 C CA 1322031C CA 000600048 A CA000600048 A CA 000600048A CA 600048 A CA600048 A CA 600048A CA 1322031 C CA1322031 C CA 1322031C
- Authority
- CA
- Canada
- Prior art keywords
- filament
- heating apparatus
- coil
- thin filaments
- contactless heating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
- C23C16/46—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for heating the substrate
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/46—Dielectric heating
- H05B6/62—Apparatus for specific applications
Abstract
ABSTRACT
A contactless heating apparatus for thin filaments comprises means to linearly support a length of filament, an induction coil provided adjacent to the filament with its axis substantially parallel to the length of filament, a source of alternating current in the frequency range from HF to UHF con-nected to the coil, and a conducting rod connected to one of the end turns of the induction coil and disposed substantially paral-lel to the length of filament; the arrangement being such that heating of the filament occurs adjacent to the conducting rod.
Preferably the filament is run through a vertical cylindrical chamber in which a reducing atmosphere is maintained; the filament and the coil being located in an induction furnace. The coil is preferably non-uniform in diameter, the diameter being larger at the end to which the rod is attached and the end of the coil oppo-site to that to which the rod is attached is earthed. The rod may be shaped such that the separation between rod and filament varies along the length of the rod to thereby vary the temperature pro-file along the heated portion of the filament. The AC power source used 18 a Class C oscillator valve located in the induction furnace. This power source is rich in harmonics.
A contactless heating apparatus for thin filaments comprises means to linearly support a length of filament, an induction coil provided adjacent to the filament with its axis substantially parallel to the length of filament, a source of alternating current in the frequency range from HF to UHF con-nected to the coil, and a conducting rod connected to one of the end turns of the induction coil and disposed substantially paral-lel to the length of filament; the arrangement being such that heating of the filament occurs adjacent to the conducting rod.
Preferably the filament is run through a vertical cylindrical chamber in which a reducing atmosphere is maintained; the filament and the coil being located in an induction furnace. The coil is preferably non-uniform in diameter, the diameter being larger at the end to which the rod is attached and the end of the coil oppo-site to that to which the rod is attached is earthed. The rod may be shaped such that the separation between rod and filament varies along the length of the rod to thereby vary the temperature pro-file along the heated portion of the filament. The AC power source used 18 a Class C oscillator valve located in the induction furnace. This power source is rich in harmonics.
Description
1322~31 l 22762-550 Contactless Heatlnq of Thln Fllaments The lnventlon relates to the heatlng of thln fllaments and ln partlcular to the heating of electrlcally conductive thln f:Llaments for example for chemlcal vapour deposltlon or zone re-finlng to produce lmproved characterlstlcs.
In the area of chemlcal vapour deposltion (CVD), hlgh strength refractory fllaments can be formed by coatlng fine re-fractory fllaments with hlgh strength materlals such as boron and sillcon carblde~ Such composlte fllaments have a high strength t~
welght ratio and are useful as relnforcement materlals for pla~-tlcs, metals and ceramlcs.
The CVD method commonly used relles on heatlng the flla-ment substrate to a tempe~ature sufflclently hlgh to cause reac-tlon and deposltion from raw materlals ln the vapour phase. A
problem encountered ln reslstance heatlng of the fllament sub-strate ls ln malntalnlng good electrlcal contact wlth the fllament to prevent varlatlons ln reslstance durlng the electrlcal heating process. Whlle short lengths of fllament could be flxed between carbon electrodes, lt ls extremely dlfflcult to malntaln good electrlcal connectlon to a movlng fllament.
Dlfflcultles have been found when uslng brass, carbon or other materlals as electrlcal contacts for movlng tungsten fila-ments when slllcon carblde deposlts, for example, begln to bulld up. Thls results partly from the lack of conductlvlty of the slllcon carblde deposlt. Mercury has been used by several prevl-ous lnvestlgators but dlfflcultles due to build up of deposlts remain and there ls the added dlfflculty of worklng wlth a sub-stance havlng a toxlc vapour. Use of mercury contacts ulso has 1322~31 2 2276~-550 the dlsadvantage that lt leads to contamlnatlon of the filament by the mercury. The fllament substrate is normally fed from one reel tc, another and attempts to malntaln electrlcal connectlons at the feed reels rather than between two polnts on the moving fllament has resulted ln temperature fluctuatlons due to the changes whlch occur ln fllament reslstance.
Inductlon heatlng u~lng for example copper colls ln an lnductlon furnace cannot be used to heat flne fllaments, accordlng to accepted theory, slnce the skln effect llmlts the heated volume to a thln layer around the perlphery of the wlre. The thlckness of thls layer ls lnversely dependent on the frequency of the ln-ductlon furnace and ls thlcker than the fllament d~ameter for 60 mlcron dlameter fllaments for hlgh frequency (HF) lnductlon fur-naces; thls means that no net current can flow clrcumferentlally around the wlre to heat lt up. As examplPs, 450 kHz, 13.5 MHz or 430 MHz lnductlon furnaces would have ~kln depths of about 0.05 cm, 0.01 cm or 0.0016 cm respectively, for tungsten wlre at 1200C. It ls thus necessary for the wlre dlameter to be consid-erably greater than the skln depth for successful heatlng. Thls argument elimlnates the possiblllty of uslng the flrst two fre-quencies to heat a 60 mlcron tungsten filament. A further ma~or problem i8 that the gap between the filament surface and the copper inductlon coll must be small for efflclent heatlng but of course thls gap ls very }arge between a thln fllament and even the smallest dlameter water-cooled copper coil. Moreover, in the ca~e of chemlcal vapour deposltlon a reactlon chamber, in which the reactant vapour phase ls enclo~ed, necessltates a large gap be-tween the filament and the copper coll. Thus thls problem also 1322~31 ellmlnates use of the 430 MHz UHF frequency for heatlng a tungsten fllament of 60 mlcron diameter. A plurality of coaxial tuned ln- -ductlon clrcults spaced along the length of a wlre or fllament have been descrlbed by DeBolt ln US patent No. 3754112 and by Douglas et al ln US patent No. 3811940. Such arrangements are compllcated, re~ulrlng lndlvldual lnductlon clrcuits to be tuned -usually ~uarter wave tuned, and rely on the lnteractlon of elec-trlc flelds produced thereby to cause a heating current to flow.
The ob~ect of the present lnventlon is to provide a con-tactless heating system for thln filaments whlch allevlates the above-mentloned dlfflcultles. Applicatlons of uch an inventlon are extremely broad and cover a spectrum of flelds ranglng from CVD to ceramlc slnterlng and heatlng of fllamentary conductlng or semiconductlng extrudates.
The inventlon provldes a contactless heating apparatus for thin fllaments comprlslng, means to llnearly support a length of fllament~
an lnductlon coll provided ad~acent to the fllament with lts axls parallel to the length of fllament;
a source of HF, VHF or UHF alternatlng current connected to the coll~ and a conducting rod connected to the one non-earthed end of the lnductlon coil and disposed substantlally parallel to the length of fllament~
the arrangement belng such that heating of the fllament occurs ad~acent to the conductlng rod.
In the inventlon, as dlstinct from prlor arrangements, the fllament to be heated ls placed outslde the coll and the 1322~31 3a 22762-550 attached rod, preferably copper as with the coll, ls posltloned at a sultable dlstance away, typically about 2cm, and the length of the rod determlnes the length of the heatlng zone. Typlcally the rod ls posltloned parallel to the fllament to provlde unlform heatlng (at red hot temperatures and above~ ln the heatlng zone.
Heatlng by thls method was unexpected and the preclse mechanlsm by whlch energy ls transferred from the coll to the fllament ls not understood. The rod ls preferably connected to the end turn but may be connected to an ad~acent turn near the end of the coll.
Preferably the coll ls non-unlform in dlameter, the dlameter belng larger at the end to whlch the rod ls attached.
Advantageously by earthing the lower end of the fllament at a polnt remote from the coll reglon the power requlred to heat the fllament ls reduced and a longer heated reglon ls posslble.
Advantageously the coll ls the output coll of an lnductlon furnace and thls ls tuned and the AC voltage ralsed untll the re~ulred power 15 reached whereby flrlng occurs le the wlre ls heated.
once this value ls known the furnace can be swltched off and on for almost lnstant heating. Temperatures above red heat can be varled by changlng the power. At the low temperature range, heating is of a vibrating elongated beadllke nature. Reducing the temperature further leads to extinguishing. On the other hand, raising the temperature produces more unlform heatlng. Oxldatlon or coatlng of the wire also leads to more unlform heatlng. By sllghtly changing the posltlon of the rod or alterlng lts shape controlled variatlons in temperature along the thin fllament (red hot or hotter) can also be achleved. Materlals other than copper can be used for the rod. In addition it can be in the form of a 1322~31 3b 22762-550 hollow tube. Typically the coll is made from 0.63 cm dlameter copper tube, wlth 9 turns of lnslde diameter 3.5 cm lncreaslng to 5.2 cm at the non-earthed end (not crltlcal), the coll length belng 8 cm. In one advantageous arrangement the AC power source ls a Class C osclllator valve ln the lnductlon furnace. Thls osclllator is rich in harmonics which could contribute to the observed heatlng effect. More than one conductlng rod connected to a coil may be disposed to heat several filaments.
In the area of chemlcal vapour deposltion (CVD), hlgh strength refractory fllaments can be formed by coatlng fine re-fractory fllaments with hlgh strength materlals such as boron and sillcon carblde~ Such composlte fllaments have a high strength t~
welght ratio and are useful as relnforcement materlals for pla~-tlcs, metals and ceramlcs.
The CVD method commonly used relles on heatlng the flla-ment substrate to a tempe~ature sufflclently hlgh to cause reac-tlon and deposltion from raw materlals ln the vapour phase. A
problem encountered ln reslstance heatlng of the fllament sub-strate ls ln malntalnlng good electrlcal contact wlth the fllament to prevent varlatlons ln reslstance durlng the electrlcal heating process. Whlle short lengths of fllament could be flxed between carbon electrodes, lt ls extremely dlfflcult to malntaln good electrlcal connectlon to a movlng fllament.
Dlfflcultles have been found when uslng brass, carbon or other materlals as electrlcal contacts for movlng tungsten fila-ments when slllcon carblde deposlts, for example, begln to bulld up. Thls results partly from the lack of conductlvlty of the slllcon carblde deposlt. Mercury has been used by several prevl-ous lnvestlgators but dlfflcultles due to build up of deposlts remain and there ls the added dlfflculty of worklng wlth a sub-stance havlng a toxlc vapour. Use of mercury contacts ulso has 1322~31 2 2276~-550 the dlsadvantage that lt leads to contamlnatlon of the filament by the mercury. The fllament substrate is normally fed from one reel tc, another and attempts to malntaln electrlcal connectlons at the feed reels rather than between two polnts on the moving fllament has resulted ln temperature fluctuatlons due to the changes whlch occur ln fllament reslstance.
Inductlon heatlng u~lng for example copper colls ln an lnductlon furnace cannot be used to heat flne fllaments, accordlng to accepted theory, slnce the skln effect llmlts the heated volume to a thln layer around the perlphery of the wlre. The thlckness of thls layer ls lnversely dependent on the frequency of the ln-ductlon furnace and ls thlcker than the fllament d~ameter for 60 mlcron dlameter fllaments for hlgh frequency (HF) lnductlon fur-naces; thls means that no net current can flow clrcumferentlally around the wlre to heat lt up. As examplPs, 450 kHz, 13.5 MHz or 430 MHz lnductlon furnaces would have ~kln depths of about 0.05 cm, 0.01 cm or 0.0016 cm respectively, for tungsten wlre at 1200C. It ls thus necessary for the wlre dlameter to be consid-erably greater than the skln depth for successful heatlng. Thls argument elimlnates the possiblllty of uslng the flrst two fre-quencies to heat a 60 mlcron tungsten filament. A further ma~or problem i8 that the gap between the filament surface and the copper inductlon coll must be small for efflclent heatlng but of course thls gap ls very }arge between a thln fllament and even the smallest dlameter water-cooled copper coil. Moreover, in the ca~e of chemlcal vapour deposltlon a reactlon chamber, in which the reactant vapour phase ls enclo~ed, necessltates a large gap be-tween the filament and the copper coll. Thus thls problem also 1322~31 ellmlnates use of the 430 MHz UHF frequency for heatlng a tungsten fllament of 60 mlcron diameter. A plurality of coaxial tuned ln- -ductlon clrcults spaced along the length of a wlre or fllament have been descrlbed by DeBolt ln US patent No. 3754112 and by Douglas et al ln US patent No. 3811940. Such arrangements are compllcated, re~ulrlng lndlvldual lnductlon clrcuits to be tuned -usually ~uarter wave tuned, and rely on the lnteractlon of elec-trlc flelds produced thereby to cause a heating current to flow.
The ob~ect of the present lnventlon is to provide a con-tactless heating system for thln filaments whlch allevlates the above-mentloned dlfflcultles. Applicatlons of uch an inventlon are extremely broad and cover a spectrum of flelds ranglng from CVD to ceramlc slnterlng and heatlng of fllamentary conductlng or semiconductlng extrudates.
The inventlon provldes a contactless heating apparatus for thin fllaments comprlslng, means to llnearly support a length of fllament~
an lnductlon coll provided ad~acent to the fllament with lts axls parallel to the length of fllament;
a source of HF, VHF or UHF alternatlng current connected to the coll~ and a conducting rod connected to the one non-earthed end of the lnductlon coil and disposed substantlally parallel to the length of fllament~
the arrangement belng such that heating of the fllament occurs ad~acent to the conductlng rod.
In the inventlon, as dlstinct from prlor arrangements, the fllament to be heated ls placed outslde the coll and the 1322~31 3a 22762-550 attached rod, preferably copper as with the coll, ls posltloned at a sultable dlstance away, typically about 2cm, and the length of the rod determlnes the length of the heatlng zone. Typlcally the rod ls posltloned parallel to the fllament to provlde unlform heatlng (at red hot temperatures and above~ ln the heatlng zone.
Heatlng by thls method was unexpected and the preclse mechanlsm by whlch energy ls transferred from the coll to the fllament ls not understood. The rod ls preferably connected to the end turn but may be connected to an ad~acent turn near the end of the coll.
Preferably the coll ls non-unlform in dlameter, the dlameter belng larger at the end to whlch the rod ls attached.
Advantageously by earthing the lower end of the fllament at a polnt remote from the coll reglon the power requlred to heat the fllament ls reduced and a longer heated reglon ls posslble.
Advantageously the coll ls the output coll of an lnductlon furnace and thls ls tuned and the AC voltage ralsed untll the re~ulred power 15 reached whereby flrlng occurs le the wlre ls heated.
once this value ls known the furnace can be swltched off and on for almost lnstant heating. Temperatures above red heat can be varled by changlng the power. At the low temperature range, heating is of a vibrating elongated beadllke nature. Reducing the temperature further leads to extinguishing. On the other hand, raising the temperature produces more unlform heatlng. Oxldatlon or coatlng of the wire also leads to more unlform heatlng. By sllghtly changing the posltlon of the rod or alterlng lts shape controlled variatlons in temperature along the thin fllament (red hot or hotter) can also be achleved. Materlals other than copper can be used for the rod. In addition it can be in the form of a 1322~31 3b 22762-550 hollow tube. Typically the coll is made from 0.63 cm dlameter copper tube, wlth 9 turns of lnslde diameter 3.5 cm lncreaslng to 5.2 cm at the non-earthed end (not crltlcal), the coll length belng 8 cm. In one advantageous arrangement the AC power source ls a Class C osclllator valve ln the lnductlon furnace. Thls osclllator is rich in harmonics which could contribute to the observed heatlng effect. More than one conductlng rod connected to a coil may be disposed to heat several filaments.
4 1322~31 The invention will now be described by way of example only with reference to the accompanylng drawings of which:
Figure 1 illustrates the principle of the inventiQn;
Flgure 2 is a part side elevation of an arrangement of the invention; and Figure 3 shows the output stage of an induction furnace providing power to the coil of the invention.
As shown in Figure 1 a filament 10, of tungsten for example, to be heated is supported vertically. A copper induction coil 11 is placed adjacent to the filament 10 with its axis substantially vertical. The coil 11 is arranged such that its top three turns are of increasingly larger diameter and wider spaced, although this has been found not to be critical. The small diameter end 12 is connected to earth 13 while the large diameter end 14 is connected to a resonating oscillator 15 operated in the frequency range from HF to UHF. A copper rod 16 is attached by a clamp 17 to the end turn of the large diameter end 14 of the coil. The copper rod 16 has a straight portion AB
disposed parallel to the filament 10 and a curved portion BC which is engaged by the clamp 17. The straight length AB of the copper rod determines the length of filament 18 (heating zone) which is heated when resonant AC power is applied to the coil 11. Typically the copper rod 16 is positioned about 2 cm from the filament 10.
Figure 2 shows a part view of a practical arrangement in which a thin filament 20 can be fed through a cylindrical tube 21 containing a reducing gaseous mixture of argon and hydrogen at atomo8pheric pressure. Where chemical vapour deposition is to be ; , ~ 3%2~3~
adopted the appropriate gases are circulated through the cylindrical tube 21. In this arrangement copper tubing is used both for the coil 11 and the straight portion 16. The filament 20 is fed upwardly through the cylindrical tube 21 from a spool and the treated filament is collected by a wooden take-up spool positioned above the tube. Where the filament enters and leaves the tube 21 gas seals are preferably used. These gas seals contain the reaction gases within the tube 21 while permitting frictionless movement of the filament and preventing the ingress of external gases and vapours into the tube. Advantageously, the 1322~31 s 22762-550 take-off spool may be earthed, but the take-up spool is made of wood (or other non-conductor) to avold connectlon or capacltance to earth whlch could cause unwanted RF heatlng of the wlre as lt emerges lnto the alr between the glass apparatus and the take-up spoo 1 .
Flgure 3 shows a conventlonal output stage of a Class C
osclllator inductlon furnace used to provlde the RF output at ter-mlnals 31,32 to the heating coll 11. An HT source ls connected to the anode of a YD 1162 output valve 33 and a 15 - 45 pF varlable tunlng capacitor 34 ls provlded.
For 40 and 60 mlcron dlameter tungsten wlres the power requlred ls of the order of 500 Watts applied to the plate of a Class C osclllator valve ln the lnductlon furnace. The Class C
osclllator ls rlch ln harmonlcs and lt is thought that these har-monlcs may contrlbute to the heatlng effect. Once the furnace ls tuned and the power needed to flre the filament has been deter-mlned then lt has been dlscovered that the flrlng of the fllament can be swltched off and on almost lnstantaneously by swltchlng the power source. A mlnlmum threshold exlsts below whlch flrlng wlll not occur. The lnductlon furnace glves best results when sllghtly off-tune. Certaln condltlon~ produce an elongated beadllke heat-lng effect whlch can be minlmlsed by detunlng. Larger dlameter wires re~ulre hlgher powers to heat them. Heating ls belleved to start at about 800C upwards, wlth no upper llmlt. ~elow about 900C the heatlng 18 sllghtly elon~ated beadlike and below about 800C lt extlngulshes. Although not shown, for radlatlon safety, the apparatus should be located ln an earthed flne mesh screen cablnet.
:
1322~31 The power source may be operated over a frequency ran~e from HF to UHF. In addltlon to heatlng conductin~ fllaments of tungsten, for example to coat them with slllcon carblde, the ln-ventlon can also be used to heat composlte fllaments composed of a conductlng lnner core and an outer semlconductlng coatlng. The rod or tube attached to the coll can be shapsd to glve a predeter-mlned temperature proflle along the fllament, dlfferent from the unlform temperature achleved wlth rod and fllament parallel. The fllament has been found to heat slgnlflcantly only opposlte the rod and thus the heatlng zone ls well deflned. In order to tune the lnductlon furnace lt is necessary to have at lea~t a few turns of the coll for resonance. Although only a slngle heatlng rod has been shown lt may be deslrable to use more than one spaced around the fllament. In addltlon the rod may be attached to a turn of the coll ad~acent to the end turn although thls ls not the prefer-red arrangement. Experlments to date have demonstrated that the lnventlon works wlth tungsten wlres dlameters of 40 to 500 mlcrons. When carbon flbre yarn was heated by thls method, the many very fine fibre end~, of about 5 mlcron dlameter whlch pro-trude profusely from such yarn, were found to become readlly whltehot at a low power settlng at which the bulk of the yarn dld not reach red heat. Thls shows that the method i8 also very ef~lc-lently able to heat flne threads of very small dlameter such as 5 mlcrons.
Mo~t of the work uslng the lnventlon has been done wlth a 6kW lnductlon furnace worklng at 13.56 MHz (an lndustrlally approved frequency) wlth a YD 1162 output valve. When an lnduc-tlon furnace operatlng at a frequency of about l/2 MHz was used, .~.
13221~`3~
below the lower limlt of the HF band heating of fllaments dld not occur. The rf power supply to the coll and attached rod ls pro-vlded vla conductlng rods and these could be coupled to any polnt ln the rf output clrcult. Low gas pressures are not re~ulred slnce the inventlon works at atmospherlc pressure. The lnventlon has also been ~hown to work at pressures other than atmospherlc and also ln a vacuum.
Although the lnventlon has been descrlbed prlnclpally ln relatlon to the heatlng of tunsten wlres the lnventlon has also been demonstrated wlth a 5 mlcron dlameter sllver plated platlnum wlre. Brass or alumlnlum may be used ln place of copper for the coll and rod. ln addltlon the clrcular rod may be replaced by a strlp or sheet. The strlp or ~heet may be stralght or, for example, hellcally or otherwlse wrapped around the cyllndrical contalnlng vessel or the space through whlch the wlre or fllament passes. The strlp or sheet could be arranged so as to wrap sub-stantlally or completely around the fllament. Thls last arrange-ment however ls not so convenlent slnce lt ls not posslble to observe the fllament.
A further posslble appllcatlon of the pre~ent lnventlon 19 the deposltion of insulatlng coatlngs on conductlng wlres. One example would be to coat lron wlth alumlna so as to render the wlre lnert and sultable as a relnforcement materlal.
Although the lnventlon has been descrlbed uslng a con-tinuous rf source lt would be posslble to use a pulsed rf source.
Other modiflcatlons and appllcatlons of the lnventlon wlll be apparent to those skllled ln the art.
~:f'
Figure 1 illustrates the principle of the inventiQn;
Flgure 2 is a part side elevation of an arrangement of the invention; and Figure 3 shows the output stage of an induction furnace providing power to the coil of the invention.
As shown in Figure 1 a filament 10, of tungsten for example, to be heated is supported vertically. A copper induction coil 11 is placed adjacent to the filament 10 with its axis substantially vertical. The coil 11 is arranged such that its top three turns are of increasingly larger diameter and wider spaced, although this has been found not to be critical. The small diameter end 12 is connected to earth 13 while the large diameter end 14 is connected to a resonating oscillator 15 operated in the frequency range from HF to UHF. A copper rod 16 is attached by a clamp 17 to the end turn of the large diameter end 14 of the coil. The copper rod 16 has a straight portion AB
disposed parallel to the filament 10 and a curved portion BC which is engaged by the clamp 17. The straight length AB of the copper rod determines the length of filament 18 (heating zone) which is heated when resonant AC power is applied to the coil 11. Typically the copper rod 16 is positioned about 2 cm from the filament 10.
Figure 2 shows a part view of a practical arrangement in which a thin filament 20 can be fed through a cylindrical tube 21 containing a reducing gaseous mixture of argon and hydrogen at atomo8pheric pressure. Where chemical vapour deposition is to be ; , ~ 3%2~3~
adopted the appropriate gases are circulated through the cylindrical tube 21. In this arrangement copper tubing is used both for the coil 11 and the straight portion 16. The filament 20 is fed upwardly through the cylindrical tube 21 from a spool and the treated filament is collected by a wooden take-up spool positioned above the tube. Where the filament enters and leaves the tube 21 gas seals are preferably used. These gas seals contain the reaction gases within the tube 21 while permitting frictionless movement of the filament and preventing the ingress of external gases and vapours into the tube. Advantageously, the 1322~31 s 22762-550 take-off spool may be earthed, but the take-up spool is made of wood (or other non-conductor) to avold connectlon or capacltance to earth whlch could cause unwanted RF heatlng of the wlre as lt emerges lnto the alr between the glass apparatus and the take-up spoo 1 .
Flgure 3 shows a conventlonal output stage of a Class C
osclllator inductlon furnace used to provlde the RF output at ter-mlnals 31,32 to the heating coll 11. An HT source ls connected to the anode of a YD 1162 output valve 33 and a 15 - 45 pF varlable tunlng capacitor 34 ls provlded.
For 40 and 60 mlcron dlameter tungsten wlres the power requlred ls of the order of 500 Watts applied to the plate of a Class C osclllator valve ln the lnductlon furnace. The Class C
osclllator ls rlch ln harmonlcs and lt is thought that these har-monlcs may contrlbute to the heatlng effect. Once the furnace ls tuned and the power needed to flre the filament has been deter-mlned then lt has been dlscovered that the flrlng of the fllament can be swltched off and on almost lnstantaneously by swltchlng the power source. A mlnlmum threshold exlsts below whlch flrlng wlll not occur. The lnductlon furnace glves best results when sllghtly off-tune. Certaln condltlon~ produce an elongated beadllke heat-lng effect whlch can be minlmlsed by detunlng. Larger dlameter wires re~ulre hlgher powers to heat them. Heating ls belleved to start at about 800C upwards, wlth no upper llmlt. ~elow about 900C the heatlng 18 sllghtly elon~ated beadlike and below about 800C lt extlngulshes. Although not shown, for radlatlon safety, the apparatus should be located ln an earthed flne mesh screen cablnet.
:
1322~31 The power source may be operated over a frequency ran~e from HF to UHF. In addltlon to heatlng conductin~ fllaments of tungsten, for example to coat them with slllcon carblde, the ln-ventlon can also be used to heat composlte fllaments composed of a conductlng lnner core and an outer semlconductlng coatlng. The rod or tube attached to the coll can be shapsd to glve a predeter-mlned temperature proflle along the fllament, dlfferent from the unlform temperature achleved wlth rod and fllament parallel. The fllament has been found to heat slgnlflcantly only opposlte the rod and thus the heatlng zone ls well deflned. In order to tune the lnductlon furnace lt is necessary to have at lea~t a few turns of the coll for resonance. Although only a slngle heatlng rod has been shown lt may be deslrable to use more than one spaced around the fllament. In addltlon the rod may be attached to a turn of the coll ad~acent to the end turn although thls ls not the prefer-red arrangement. Experlments to date have demonstrated that the lnventlon works wlth tungsten wlres dlameters of 40 to 500 mlcrons. When carbon flbre yarn was heated by thls method, the many very fine fibre end~, of about 5 mlcron dlameter whlch pro-trude profusely from such yarn, were found to become readlly whltehot at a low power settlng at which the bulk of the yarn dld not reach red heat. Thls shows that the method i8 also very ef~lc-lently able to heat flne threads of very small dlameter such as 5 mlcrons.
Mo~t of the work uslng the lnventlon has been done wlth a 6kW lnductlon furnace worklng at 13.56 MHz (an lndustrlally approved frequency) wlth a YD 1162 output valve. When an lnduc-tlon furnace operatlng at a frequency of about l/2 MHz was used, .~.
13221~`3~
below the lower limlt of the HF band heating of fllaments dld not occur. The rf power supply to the coll and attached rod ls pro-vlded vla conductlng rods and these could be coupled to any polnt ln the rf output clrcult. Low gas pressures are not re~ulred slnce the inventlon works at atmospherlc pressure. The lnventlon has also been ~hown to work at pressures other than atmospherlc and also ln a vacuum.
Although the lnventlon has been descrlbed prlnclpally ln relatlon to the heatlng of tunsten wlres the lnventlon has also been demonstrated wlth a 5 mlcron dlameter sllver plated platlnum wlre. Brass or alumlnlum may be used ln place of copper for the coll and rod. ln addltlon the clrcular rod may be replaced by a strlp or sheet. The strlp or ~heet may be stralght or, for example, hellcally or otherwlse wrapped around the cyllndrical contalnlng vessel or the space through whlch the wlre or fllament passes. The strlp or sheet could be arranged so as to wrap sub-stantlally or completely around the fllament. Thls last arrange-ment however ls not so convenlent slnce lt ls not posslble to observe the fllament.
A further posslble appllcatlon of the pre~ent lnventlon 19 the deposltion of insulatlng coatlngs on conductlng wlres. One example would be to coat lron wlth alumlna so as to render the wlre lnert and sultable as a relnforcement materlal.
Although the lnventlon has been descrlbed uslng a con-tinuous rf source lt would be posslble to use a pulsed rf source.
Other modiflcatlons and appllcatlons of the lnventlon wlll be apparent to those skllled ln the art.
~:f'
Claims (23)
1. A contactless heating apparatus for thin filaments com-prising means to linearly support a length of filament wherein an induction coil provided adjacent to the filament with its axis parallel to the length of filament;
a source of alternating current in the frequency range from HF to UHF connected to the coil; and a conducting inductor element connected to the one non-earthed end of the induction coil and disposed substantially parallel to the length of filament the arrangement being such that heating of the filament occurs adjacent to the conducting inductor element.
a source of alternating current in the frequency range from HF to UHF connected to the coil; and a conducting inductor element connected to the one non-earthed end of the induction coil and disposed substantially parallel to the length of filament the arrangement being such that heating of the filament occurs adjacent to the conducting inductor element.
2. A contactless heating apparatus for thin filaments as claimed in claim 1 wherein the inductor element is connected to the end turn of said one non-earthed end of the induction coil.
3. A contactless heating apparatus for thin filaments as claimed in claim 2 wherein the coil is non-uniform in diameter, the diameter being larger at the end to which the inductor element is attached.
4. A contactless heating apparatus for thin filaments as claimed in claim 3 wherein the end of the coil opposite to that to which the inductor element is attached is earthed.
5. A contactless heating apparatus for thin filaments as claimed in claim 4 sherein the filament and the coil are located in an induction furnace.
6. A contactless heating apparatus for thin filaments as claimed in claim 5 wherein the inductor element is formed such that the separation between inductor element and filament varies along the length of the inductor element to thereby vary the temperature profile along the heated portion of the filament.
7. A contactless heating apparatus for thin filaments as claimed in claim 6 wherein the inductor element is a metal rod or wire.
8. A contactless heating apparatus for thin filaments as claimed in claim 7 wherein the coil and the inductor element are made of copper tubing.
9. A contactless heating apparatus for thin filaments as claimed in claim 8 wherein the AC power source is a Class C oscil-lator valve located in the induction furnace.
10. A contactless heating apparatus for thin filaments as claimed in claim 9 wherein the frequency is substantially 13.6MHz.
11. A contactless heating apparatus for thin filaments as claimed in claim 10 wherein the filament is located in a cylindrical chamber containing a reducing atmosphere and the coil and inductor element are adjacent to the chamber.
12. A contactless heating apparatus for thin filaments as claimed in claim 11 wherein the end of the coil opposite to that to which the inductor element is attached is earthed.
13. A contactless heating apparatus for thin filaments as claimed in claim 12 wherein the filament and the coil are located in an induction furnace.
14. A contactless heating apparatus for thin filaments as claimed in claim 13 wherein the inductor element is a metal rod or wire.
15. A contactless heating apparatus for thin filaments as claimed in claim 14 wherein the coil and the inductor element are made of copper tubing.
16. A contactless heating apparatus for thin filaments as claimed in claim 15 wherein the AC power source is a Class C
oscillator valve located in the induction furnace.
oscillator valve located in the induction furnace.
17. A contactless heating apparatus for thin filaments as claimed in claim 16 wherein the frequency is substantially 13.6MHz.
18. A contactless heating apparatus for thin filaments as claimed in claim 17 wherein the filament is located in a cylndri-cal chamber containing a reducing atmosphere and the coil and inductor element are adjacent to the chamber.
19. A contactless heating apparatus for thin filaments as claimed in claim 4 wherein the inductor element is a metal rod or wire.
20. A contactless heating apparatus for thin filaments as claimed in claim 19 wherein the coil and the inductor element are made of copper tubing.
21. A contactless heating apparatus for thin filaments as claimed in claim 20 wherein the AC power source is a Class C
oscillator valve located in the induction furnace.
oscillator valve located in the induction furnace.
22. A contactless heating apparatus for thin filaments as claimed in claim 21 wherein the frequency is substantially 13.6MHz.
23. A contactless heating apparatus for thin filaments as claimed in claim 22 wherein the filament is located in a cylindri-cal chamber containing a reducing atmosphere and the coil and inductor element are adjacent in the chamber.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB888811893A GB8811893D0 (en) | 1988-05-19 | 1988-05-19 | Heating of thin filaments |
| GB8811893 | 1988-05-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1322031C true CA1322031C (en) | 1993-09-07 |
Family
ID=10637186
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000600048A Expired - Fee Related CA1322031C (en) | 1988-05-19 | 1989-05-18 | Contactless heating of thin filaments |
Country Status (13)
| Country | Link |
|---|---|
| US (1) | US5183985A (en) |
| EP (1) | EP0414797B1 (en) |
| JP (1) | JPH03504298A (en) |
| AT (1) | ATE140843T1 (en) |
| AU (1) | AU615314B2 (en) |
| BR (1) | BR8907437A (en) |
| CA (1) | CA1322031C (en) |
| DE (1) | DE68926883T2 (en) |
| DK (1) | DK163788C (en) |
| ES (1) | ES2011743A6 (en) |
| GB (1) | GB8811893D0 (en) |
| NZ (1) | NZ229175A (en) |
| WO (1) | WO1989011770A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9002947D0 (en) * | 1990-02-09 | 1990-04-04 | Secr Defence | Radio-frequency heating of thin filaments |
| GB9015921D0 (en) * | 1990-07-19 | 1990-09-05 | Secr Defence | Coreless refractory fibres |
| DE4316964C2 (en) * | 1993-02-27 | 2002-01-31 | Saint Gobain Sekurit D Gmbh | Process for producing a heatable laminated glass pane with metal wires arranged in the thermoplastic intermediate layer and use of an electronic circuit for carrying out the process |
| WO2002049395A2 (en) * | 2000-12-12 | 2002-06-20 | Tokyo Electron Limited | Rapid thermal processing lamp and method for manufacturing the same |
| US7279665B2 (en) * | 2003-07-02 | 2007-10-09 | Itherm Technologies, Lp | Method for delivering harmonic inductive power |
| US7034263B2 (en) | 2003-07-02 | 2006-04-25 | Itherm Technologies, Lp | Apparatus and method for inductive heating |
| US20090191336A1 (en) * | 2008-01-30 | 2009-07-30 | Mohan Chandra | Method and apparatus for simpified startup of chemical vapor deposition of polysilicon |
| US8771481B2 (en) | 2012-01-13 | 2014-07-08 | Harris Corporation | Hydrocarbon resource processing apparatus including a load resonance tracking circuit and related methods |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2668226A (en) * | 1950-06-22 | 1954-02-02 | Du Pont | High-frequency electronic drying apparatus |
| IT713090A (en) * | 1963-01-17 | |||
| GB1136616A (en) * | 1965-12-01 | 1968-12-11 | Aeg Elotherm Gmbh | A method of and apparatus for inductively heating electrically conducting workpieces |
| US3572286A (en) * | 1967-10-09 | 1971-03-23 | Texaco Inc | Controlled heating of filaments |
| US3811940A (en) * | 1969-10-09 | 1974-05-21 | United Aircraft Corp | High frequency heating method for vapor deposition of coatings onto filaments |
| US3694609A (en) * | 1971-02-01 | 1972-09-26 | Owens Illinois Inc | Method and apparatus for inductive heating |
| US3754112A (en) * | 1972-06-14 | 1973-08-21 | Avco Corp | Localized heating filaments by induced currents |
| DE2401170A1 (en) * | 1974-01-11 | 1975-07-24 | Seelemann Baumann Gmbh | Hardening of long steel parts - carbon steel saw strip continuously hardened using induction coil and pulse generator |
-
1988
- 1988-05-19 GB GB888811893A patent/GB8811893D0/en active Pending
-
1989
- 1989-05-11 AU AU37301/89A patent/AU615314B2/en not_active Ceased
- 1989-05-11 JP JP1505598A patent/JPH03504298A/en active Pending
- 1989-05-11 BR BR898907437A patent/BR8907437A/en not_active IP Right Cessation
- 1989-05-11 US US07/623,808 patent/US5183985A/en not_active Expired - Fee Related
- 1989-05-11 AT AT89906393T patent/ATE140843T1/en not_active IP Right Cessation
- 1989-05-11 EP EP89906393A patent/EP0414797B1/en not_active Expired - Lifetime
- 1989-05-11 DE DE68926883T patent/DE68926883T2/en not_active Expired - Fee Related
- 1989-05-11 WO PCT/GB1989/000505 patent/WO1989011770A1/en active IP Right Grant
- 1989-05-17 NZ NZ229175A patent/NZ229175A/en unknown
- 1989-05-18 CA CA000600048A patent/CA1322031C/en not_active Expired - Fee Related
- 1989-05-18 ES ES8901671A patent/ES2011743A6/en not_active Expired - Lifetime
-
1990
- 1990-11-16 DK DK273590A patent/DK163788C/en active
Also Published As
| Publication number | Publication date |
|---|---|
| DE68926883D1 (en) | 1996-08-29 |
| AU615314B2 (en) | 1991-09-26 |
| DE68926883T2 (en) | 1997-03-06 |
| GB8811893D0 (en) | 1988-06-22 |
| ES2011743A6 (en) | 1990-02-01 |
| ATE140843T1 (en) | 1996-08-15 |
| EP0414797A1 (en) | 1991-03-06 |
| NZ229175A (en) | 1991-06-25 |
| BR8907437A (en) | 1991-04-02 |
| WO1989011770A1 (en) | 1989-11-30 |
| AU3730189A (en) | 1989-12-12 |
| US5183985A (en) | 1993-02-02 |
| DK273590D0 (en) | 1990-11-16 |
| DK163788C (en) | 1992-09-07 |
| EP0414797B1 (en) | 1996-07-24 |
| DK273590A (en) | 1990-11-16 |
| DK163788B (en) | 1992-03-30 |
| JPH03504298A (en) | 1991-09-19 |
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| Date | Code | Title | Description |
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