EP0162941B1 - Process for monitoring the burning temperature of a firing kiln in the laquered -thread production, and kiln therefor - Google Patents

Abstract

1. Method for controlling the enamelling temperature of an enamelling stove (5) for producing enamelled wire with an enamelling retort (7) for several wires, with which the enamel-coated wire is dried and stoved by a current of hot air circulated in the single-circuit reverse current, which is carried in the recirculation shaft (12) of the enamelling retort (7) by a catalyzer (18), wherein a partial current of hot air is always branched-off in the recirculation shaft (12) behind the catalyzer (18) and admitted to the recirculation shaft (12) in front of the catalyzer (18).

Description

The invention relates to a method according to the preamble of claim 1 and a baking oven according to the preamble of claim 7.

In a known system for the production of enamelled wire from one or more wires running in parallel (DE-C 3118830), the wire, previously annealed in a stress-free annealing, passes through a lacquer application device and finally through a drying and stoving zone in a stoving retort, in which hot air is circulated in countercurrent to the wire feed . The solvent vapors and fission products generated when the paint is baked on are removed from the drying zone by recirculation via a return shaft. In the return duct, the vapors extracted from the stoving retort, including the fresh air drawn in, pass through a mixing zone, a heating system and a catalyst and are heated by the heating system and the catalyst which burns the solvent vapors. If there is a sufficient amount of solvent heat, the known system can be operated in a self-sustaining manner after the heating process, that is to say without the supply of external energy.

The production of enamelled wire has to be based on high quality requirements determined by standards, whereby the enamelled wire manufacturers are increasingly working on a quality standard that in some cases goes far beyond the requirements stipulated by the standards. In order to be able to meet such high quality requirements, compliance with constant process conditions in the stoving furnace with regard to supply and exhaust air quantities, temperature, air and wire speed is an essential requirement.

Ideally, comparatively narrow tolerances can be maintained with the previously known system. Difficulties arise, however, if, for example, one of the wires running in parallel breaks because the lacquer application is interrupted, as a result of which the amount of solvent present in the catalyst for combustion is reduced and the heat balance required to maintain a uniform temperature is thereby disturbed. For example, the temperature rise of the hot air passed through the catalyst caused by the combustion of the solvents in the catalyst in the previously known system is in the order of magnitude of 80-200 ° K. In a system with, for example, six wire draws, this means that if a wire fails, for example due to a wire break, the temperature rise due to combustion on the catalytic converter is reduced by a sixth. If the temperature of the catalytic converter rose as a result of the combustion of solvent vapors, for example, 120 ° K, the temperature rise would decrease by a sixth to 100 ° K as a result of the fault. However, this would lead to a drop in temperature of the hot air after the catalytic converter of 20 ° K. The same problem also occurs when wires have to be stopped, for example when the wire cross-section has to be changed. On the other hand, when new wires are started up, the temperature increases considerably.

The drop in temperature that occurs when the wire is at a standstill, or the increase in temperature after the catalytic converter that occurs during wire start-up, is intended to influence the constancy of the temperature in the retort retort as little as possible. The control required for this takes place via the heating system. However, practice has shown that this regulation is sluggish, so that there are still fluctuating stoving conditions and thus fluctuating enamelled wire quality. In the event of a malfunction, the fresh air supply at the wire inlet or at the wire outlet of the stoving retort could be reduced or increased, which would be a less sluggish control than via, for example, an electrical heating device, but this leads to a change in the longitudinal temperature profile and a reduction in the drying and Burning zone of available hot air, which in turn leads to fluctuations in the enamelled wire quality.

The object of the invention is to ensure, by simple measures, that the process conditions are kept as constant as possible, even if, as a result of disruptions in the wire feed, for example wire breakage, or shutdown or start-up of individual wire pulls when changing the wire size, the temperature of the non-circulated hot air is forced and so that the baking temperature changes.

Starting from the known method and the known stoving oven, the object is achieved by the characterizing features of claims 1 and 7, respectively.

Because, according to the invention, a partial stream of the hot air passed through the catalyst is continuously branched off and fed back to the catalyst, the amount of hot air flowing through the catalyst increases, while the amount of solvent introduced into the catalyst and therefore also the amount of the introduced Solvent energy does not change in normal operation. As a result of this increase in the air flow rate through the catalyst, the temperature difference between the catalyst inlet and the catalyst outlet also decreases. If, for example, the amount of air passed through the catalyst is doubled, the temperature difference is halved. In this way, temperature fluctuations can be considerably reduced in the event of fluctuations in the amount of solvent introduced, for example in the case of wire breaks, so that substantially more constant process conditions and thus a more uniform wire quality also result in the event of a malfunction or when individual wire pulls are shut down.

The partial air stream branched off behind the catalytic converter can be introduced into the return duct immediately before the catalytic converter. Since experience has shown that some of the solvent vapors are burned as soon as they pass the electrical heating device, it is also expedient to enter the branched-off partial air flow before the glow in the return duct of the stoving retort. However, it is particularly advantageous to introduce the branched-off partial air flow into the return shaft before the mixing zone, because this is to achieve an optimal uniformity of air temperature and air speed in the return shaft.

A further equalization of the stoving conditions can be achieved if the circulation of the partial air flow is also used to regulate the temperature in the drying and stoving zone in the stoving retort. As a result, the temperature can be kept almost constant even when the number of wires passed through the baking oven changes, for example in the event of a wire break, the circulated air quantity is reduced in order to compensate for the reduction in the quantity of solvent and thus the reduced temperature rise on the catalytic converter. If, on the other hand, the number of wire draws is increased, a constant temperature is guaranteed by a corresponding increase in the circulated partial air flow.

The circulating partial air flow is expediently regulated by changing the speed of the circulating air blower provided in the circulating line. The control can expediently also be carried out by a flap or a slide provided in the circulation line. The control can be carried out depending on the temperature determined by a temperature sensor in the drying or baking zone or depending on the temperature determined by a temperature sensor in the drying or baking zone or depending on the amount of solvent by a solvent measuring device, such as a flame ionization detector , respectively. Another possibility is that the regulation is effected depending on the number of wires passing through the furnace.

• Fig. 1 eine schematische Ansicht einer Anlage zur Lackdrahtherstellung,
• Fig.2 eine schematische Schnittdarstellung durch das Ofengehäuse,
• Fig. 3 eine Schemadarstellung der Anordnung einer Umwälzleitung eines Rückführschachtes,
• Fig.4 eine Schemadarstellung einer anderen Anordnung der Umwälzleitung sowie
• Fig. eine Schemadarstellung einer weiteren Anordnung der Umwälzleitung gemäss den Fig. 3 und 4.

Exemplary embodiments of the invention are described below with reference to the drawing. Show in it

• 1 is a schematic view of a system for the production of enamelled wire,
• 2 shows a schematic sectional view through the furnace housing,
• 3 shows a schematic representation of the arrangement of a circulation line of a return shaft,
• 4 shows a schematic representation of another arrangement of the circulation line as well
• 3 shows a schematic representation of a further arrangement of the circulation line according to FIGS. 3 and 4.

The total length shown schematically in FIG. 1 is used for the production of enamelled wire, preferably several wires, and essentially comprises a wire outlet 1 with bare wire coils 2, from which the wire is drawn off by a subsequent wire pulling device 3. With the interposition of deflection rollers, the wire finally runs into a glow 19 of the lacquer kiln, generally designated by the reference number 5, is deflected at the end thereof and arrives at a lacquer application device 6 arranged at the front end of the lacquer kiln 5, from where the wire or the parallel wire draws a burn-in retort designated 7. After passing through the stoving retort 7, the wires pass through a wire cooling device designated 8. Depending on the desired coating application, the wires pass through the work stations 6, 7 and 8 several times, that is, coating application device, baking retort and wire cooling device, until they are finally wound onto spools on a coating wire winding device 9.

2 shows further details of the lacquer kiln 5. Thereafter, the stoving retort 7 is subdivided into a drying chamber 10 and a curing or stoving chamber 11, in which the lacquer applied to the wire by the upstream lacquer application device 6 and dried in the drying chamber 10 is stoved. Furthermore, the burn-in retort 7 is assigned a return shaft, designated 12, at the left end of which a circulating air blower 13 is provided, by means of which the air is circulated in the single-circuit counterflow principle in the direction of the arrow 14, specifically in the drying chamber 10 and in the baking chamber 11 in counterflow to that in the direction of the arrow 15 transported wire.

Specifically, the circulating air blower 13 sucks in solvent vapors and fission products of the lacquer applied to the wire and fresh air in the drying chamber 10 via the wire inlet 16, the mixing of the gases taking place in a mixing zone 17 downstream of the circulating air blower 13. Arranged in the return shaft 12 are the glow 19, by means of which the wires guided through glow tubes of the glow 19 are annealed without stress, as well as the mixing zone 17, the heating system 4 and a catalytic converter 18 in which the solvent vapors and fission products of the lacquer are burned. The air circulated in the return shaft 12 is heated both when passing through the heating system and when passing through the catalytic converter 18, and the hot air is then introduced into the baking chamber 11 of the baking retort 7 via a perforated sheet metal bushing 20 of a known type. The air flow and the fresh air drawn in through the wire inlet 16 can be regulated by a flap in front of the circulating air blower 13.

A part of the exhaust gases circulated in the return shaft 12 is passed through an exhaust pipe 22 coaxially arranged with the glow 19 and an exhaust pipe 23 discharged into the open with a further catalyst 24 located therein. The fan indicated at 25 indicates that this is a forced discharge, which may be regulated by a flap 26 arranged in the exhaust pipe 23.

An inert gas source formed by a steam generator 27, which is heated by the exhaust pipe 22, requires that steam serving as inert gas is introduced at 29 at the inlet end of the glow tube 19 via a steam line 28.

To the right of the exhaust pipe is a wire cooler 30, from which the wire is led to the coating device 6. In the downstream direction of the wire, the perforated sheet metal bushing 20 is followed by the wire cooling device 8, which has a pressure blower 31 and a suction blower 32, by means of which a differential pressure in the wire cooler 8 can be set, such that an overpressure is generated in the area of the wire outlet 33, so that fresh air can enter the burn-in chamber 11 through the wire outlet without harmful substances getting into the free atmosphere.

The wires running through the annealing line 19 reach the lacquer application device 6 and pass through the stoving retort 7, where the lacquer applied is stoved and the resulting solvent vapors are drawn off into the return duct 12 by means of the circulating air blower 13. The wire then enters the wire cooler 8 and, depending on the lacquer application required, is repeatedly returned to the lacquer application device 6 until it is finally discharged to the enamel wire winding device 9. In this way, if the amount of solvent is sufficiently large, self-sustaining operation without the supply of external energy can be ensured due to the hot air generated in the return shaft 12 because the heat of the solvent is used with the aid of the catalyst 18 to operate the drying and baking process. In order to maintain the combustion process and also to prevent the explosion limit from being exceeded, fresh air is drawn in via the wire inlet 16 and the wire outlet 33, which at the same time essentially prevents the escape of toxic unburned solvent vapors into the environment.

Under normal production conditions, such a system can maintain uniform process conditions due to the use of solvent energy and with the help of the heating system, as are required for a constant quality level of the enamelled wire.

In order to largely avoid fluctuations in the process conditions as a result of a wire break or when a wire is drawn in, a separate circulation line 35 is assigned to the return shaft 12 according to FIGS. 3 to 5, through which a partial flow of the hot air circulated in the return shaft 12 branches off behind the catalytic converter 8 and before the catalyst is fed back into the return shaft 12. A circulating air blower 36 is arranged in the circulation line 35. Due to the branched and reintroduced hot air, the amount of hot air flowing through the catalyst 18 is increased, which causes the temperature difference between the hot air before and after the catalyst 18 to decrease while the amount of solvent remains unchanged and the solvent energy in the process remains constant.

In the exemplary embodiment according to FIG. 3, the branched partial flow is fed into the return shaft 12 directly upstream of the catalytic converter 18. In the alternative shown in FIG. 4, the branched partial flow of the hot air is fed before the heating system 4, whereas in the embodiment according to FIG 5 the branched-off partial stream is introduced into the return shaft 12 upstream of the mixing zone 17. The embodiment according to FIG. 4, i.e. introduction of the partial flow upstream of the heating system 4, takes into account the fact that part of the solvent vapors is burned as soon as it passes through the heating system, so that it is then expedient to direct the circulating air upstream of the heating system into the return duct 12 of the branding retort. The embodiment according to FIG. 5 is particularly expedient for introducing the partial flow upstream of the mixing zone, as a result of which the best equalization of air temperature and air speed in the return shaft 12 is achieved.

As can also be seen in FIGS. 3 to 5, a flap 37 is arranged in the circulation line 35, a slider being alternatively provided for this purpose. The air circulation and thus the temperature in the drying and stoving zone of the stoving retort 7 can thus be regulated. Instead of regulation by the flap 37 or by a slide, the amount of circulated air can also be achieved by changing the speed of the circulating air blower 36. In both cases, regulation takes place either as a function of the temperature recorded by a temperature sensor (not shown) in the drying or stoving zone or by means of a solvent device, such as a flame ionization detector.

Claims (12)

1. Method for controlling the enamelling temperature of an enamelling stove (5) for producing enamelled wire with an enamelling retort (7) for several wires, with which the enamel-coated wire is dried and stoved by a current of hot air circulated in the single-circuit reverse current, which is carried in the recirculation shaft (12) of the enamelling retort (7) by a catalyzer (18), wherein a partial current of hot air is always branched-off in the recirculation shaft (12) behind the catalyzer (18) and admitted to the recirculation shaft (12) in front of the catalyzer (18).

2. Method according to Claim 1, whereby a mixed zone (17) and a heating system (4) are laid out in the recirculation shaft (12) behind each other in front of the catalyzer (18), wherein the branched-off and circulated partial current of hot air is admitted directly front of the catalyzer (18), the heating system (4) or the mixed zone (17).

3. Method according to Claim 1 or 2, wherein the volume of the partial current circulating is adjusted according to the enamelling temperature.

4. Method according to Claim 1 or 2, wherein the volume of the partial current circulating is adjusted according to the concentration of solvent vapours in the drying zone (10) of the enamelling retort (7).

5. Method according to Claim 1 or 2, wherein the volume of the partial current circulating is adjusted according to the number of wires fed through the enamelling retort (7).

6. Method according to one of the above Claims, wherein the volume of the partial current circulating is adjusted by modifying the speed of a circulation fan (36) for the partial current or by a butterfly valve (37) fitted in the circulation pipe.

7. Enamelling stove for implementing the method according to Claim 1 for a device for producing enamelled wire with an enamelling retort (7) showing a drying zone (10) and an ana- melling zone (11) for several wires, which is laid out in connection with a device for distributing enamel (6), and with a recirculation shaft (12) for circulating a hot air current by means of a fan (13) in the single-circuit reverse current for feeding wire through the enamelling retort (7), in which a mixed zone (17), a heating system (4) and a catalyzer (18) are laid out for burning solvent vapours and cleavage products from the enamelling retort (7) entrained in the hot air current, wherein a circulation pipe (35) is fitted, which branches off from the recirculation shaft (12) behind the catalyzer (18) and joins the recirculation shaft again in front of the catalyzer.

8. Enamelling stove according to Claim 7, wherein a circulation fan (36) is laid out in the circulation pipe (35).

9. Enameling store according to Claim 7, wherein a device is fitted for adjusting the partial current circulated, which shows at least one temperature probe in the drying or enamelling zone or a solvent gauge in the drying zone of the enamelling retort (7).

10. Enamelling stove according to Claim 9, wherein the control device influences a speed-changing motor of a circulation fan (36) laid out in the circulation pipe (35).

11. Enamelling stove according to Claim 9, wherein the control device influences a butterfly waive (37) laid out in the circulation pipe (35) or a slide valve for adjusting the branched-off partial current.

12. Enamelling stove according to one of Claims 7 to 11, wherein the circulation pipe (35) joins the recirculation shaft (12) immediately before the catalyzer (18), the annealing (19) or the mixed zone (17).

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