Oxidation furnace

An oxidation furnace for the oxidative treatment of fibers having a processing chamber which can be found in the interior of a housing; at least one blowing device; at least one suction device; at least one ventilator that circulates the hot air through the blowing device, the processing chamber, and the suction device; and at least one heating device that lies in the flow path of the hot circulated air. Deviating rollers guide the fibers in a serpentine manner through the processing chamber such that the fibers lie next to one another as a carpet, the fiber carpet being stretched between each opposing deviating roller over one plane. The air in the processing chamber crosses the planes over which the fiber carpet is stretched at an angle that differs from 0° and 90° using special means.

RELATED APPLICATIONS

This application claims the filing benefit of International Patent Application No. PCT/EP2011/004108, filed Aug. 16, 2011, which claims the filing benefit of German Patent Application No. 10 2010 044 296.8 filed Sep. 3, 2010, the contents of both of which are incorporated herein by reference.

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION

The invention relates to an oxidation furnace for the oxidative treatment of fibres, in particular for producing carbon fibres, havinga) a housing, which is gas-tight with the exception of passage regions for the carbon fibres;b) a process chamber located in the interior of the housing;c) at least one blowing device by means of which hot air can be blown into the process chamber;d) at least one suction device, which sucks hot air out of the process chamber;e) at least one ventilator, which circulates the hot air through the blowing device, the process chamber and the suction device;f) at least one heating device located in the flow path of the hot circulated air;g) deflection rollers, which guide the fibres in serpentine manner through the process chamber such that they lie next to one another as a carpet,wherein the fibre carpet stretches over a respective plane between opposing deflection rollers.

In known oxidation furnaces of this type, the different planes of the fibre carpet, which are located above one another, extend horizontally and lie parallel to the flow direction of the hot oxygen-containing air. As a result, the air flow is only involved in the heating and cooling of the fibres in its boundary layers, which are next to the fibre carpet. As a result of the parallel flow, a barrier forms at the surface of the fibres, which reduces the heat transfer. The core of the air flow is not involved in the heat transfer on account of the parallel flow. Substantial differences arise between the air entry and air exit temperature near to the fibres, which in turn leads to substantial temperature differences within the fibre carpet. The fundamental possibility of increasing the heat transfer by increasing the air speed is limited since the increasing movement of the fibres may cause them to become damaged, for example as a result of colliding with one another.

In an alternative construction of the known oxidation furnaces mentioned at the outset, the entire air flow is guided vertically through the different planes of the fibre carpet which are located above one another. This improves the heat transfer. However, the overall height is increased by the air supply system and air suction system.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an oxidation furnace of the type mentioned at the outset, in which, with a low overall height, the heat transfer between the air and the fibres is improved and the temperature of the fibres in the process chamber is further homogenised.

This object may be achieved according to the invention in thath) means are provided, which ensure that the air in the process chamber crosses the planes over which the fibre carpet stretches at an angle which differs from 0° and 90°.

The resultant angled flow of the air relative to the planes of the fibre carpet results in improved temperature constancy since the fibre carpet is acted upon by the same temperature over the entire length between the blowing device and the suction device. This means better process control with a better process result. All of the circulated air is used for the heat absorption and heat supply; there are no air flows between the planes of the fibre carpet which are not involved. A lower volumetric flow rate is sufficient to achieve the same results. This not only saves on energy but also enables the oxidation furnace to be smaller in size.

In an advantageous embodiment of the invention, the means comprise at least two air deflectors. It is particularly favourable to have a plurality of air deflectors, which each extend in the clearances between the planar regions of the serpentine fibre carpet between the blowing device and the suction device. These air deflectors not only result in the desired direction of the air flow. They moreover act as radiation surfaces which contribute to heating the threads and dissipating the exothermic heat produced during oxidation. The temperature difference between the circulated air and the fibres is therefore reduced. At the same time, the air deflectors assume the function of fibre-guiding profiles, which were previously used to prevent fibres from coming into contact or entangling in the event of fibre breakage.

As a means for achieving the desired relative orientations of the air flow and fibre-carpet planes, it is alternatively or additionally possible to provide an additional airflow which has a vertical directional component and is superimposed on the first air flow extending between the blowing device and the suction device in the process chamber. In this embodiment of the invention, the angle at which the “effective” air flow produced by the superimposition crosses the planes over which the fibre carpet stretches can be controlled by the ratio of the flow speeds in the two flows; this implementation is therefore more variable in this respect than one which operates using air deflectors.

It is again alternatively or additionally possible for the said means to comprise deflection rollers which are tilted with respect to the vertical such that the planes over which the fibre carpet extending between them stretches are tilted with respect to the horizontal.

The concept according to the invention can be used both in situations where the main flow direction of the air is that of the longitudinal direction of the oxidation furnace between the inlet region and the outlet region and in situations where the main flow direction of the air is perpendicular to the longitudinal direction of the oxidation furnace. In the first case, the angle at which the air crosses the planes of the fibre carpet should be between 0.8° and 2°, preferably 1°, and in the second case it should be between 2° and 20°, preferably 4°.

It is to be understood that the aspects and objects of the present invention described above may be combinable and that other advantages and aspects of the present invention will become apparent upon reading the following description of the drawing and detailed description of the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

While this invention is susceptible of embodiment in many different forms, there is shown in the drawing and will herein be described in detail one or more embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated.

Reference is firstly made toFIGS. 1 to 3, which show a first exemplary embodiment of an oxidation furnace which is denoted as a whole by the reference numeral1and is used for producing carbon fibres. The oxidation furnace1comprises a housing2which is in turn composed of two vertical longitudinal walls2a,2b, two vertical end walls2c,2d, a top wall2eand a bottom wall2f. The housing is gas-tight with the exception of two regions3,4in the end walls2cand2d, in which the fibres20to be treated are guided in and out and which are provided with special lock assemblies.

As shown in particular inFIG. 2, the interior of the housing2is divided by a vertical partition wall5into the actual process chamber6and air conducting chambers7,8,9,10,11,12located at the side of the process chamber. All in all, the interior of the oxidation furnace1is constructed to be substantially mirror-symmetrical with respect to the central plane S-S indicated inFIG. 2.

Located in the central region of the process chamber6, there is a blowing device which is provided as a whole with the reference numeral13and is explained in more detail below. Suction devices14,15are located in the two outer end regions of the process chamber, respectively adjacent to the passage regions3,4.

Two directionally opposed air circuits are maintained in the interior of the housing2: Starting for example from the suction devices14,15, the air is guided respectively in the direction of the arrows shown inFIG. 2through the air conducting chambers7and12to a filter16and17and then through a heating unit18aand18binto the air conducting chamber8and11. The heated air is sucked out of the air conducting chamber8and11by a ventilator21aand21band blown into the air conducting chambers9and10. From there, the air arrives respectively in one half of the blowing device13, which is described more precisely below, flowing from there in opposite directions into the process chamber6and from there to the suction device14and15in a manner which is explained in more detail below, whereby the two air circuits are closed.

In the wall of the housing2, two outlets30a,30bare provided in the region of the air conducting chambers8,11. By way of these outlets, it is possible to discharge those volumes of gas and air which are either produced during the oxidation process or arrive as fresh air into the process chamber6by way of the passage regions3,4in order to maintain the air balance in the oxidation furnace1. The discharged gases, which can also contain toxic constituents, are supplied for thermal afterburning. The heat obtained thereby can be used at least to preheat the fresh air supplied to the oxidation furnace1.

The blowing device13is constructed in detail as follows:

It comprises two “stacks” of blowing boxes31. Each of these blowing boxes31is in the shape of a hollow cuboid, with the longer dimension extending transversely to the longitudinal direction of the process chamber6over its entire width. The narrow sides of the blowing boxes31, which face the process chamber6in each case, are constructed as perforated plates31a. An exception to this is provided by the bottom-most blowing boxes31, whereof the narrow side facing away from the centre of the oxidation furnace1in each case is closed for reasons which will become clear below.

A respective end face of each blowing box31is in communication with the air conducting chamber9and air conducting chamber10in such a way that the air delivered by the ventilator21aand21bis blown into the interior of the respective blowing box31and can exit from there by way of the perforated plates31a.

The different blowing boxes31in each of the two stacks are arranged at a slight spacing above one another. The two stacks of blowing boxes31are in turn likewise spaced from one another, as seen in the longitudinal direction of the furnace or in the movement direction of the threads20.

The two suction devices14,15are formed substantially by a respective stack of suction boxes19which extend in similar manner to the blowing boxes31in the transverse direction through the entire process chamber6and are constructed as perforated plates19aat their narrow sides extending transversely to the longitudinal extent of the process chamber6. The narrow sides of the respective top-most suction box19in the stack provide an exception here for reasons which will become clear below.

Planar air deflectors33extend in each case between the upper edges of the outwardly facing narrow sides31aof the blowing boxes31and the lower edges of the narrow sides of the suction boxes19which face the centre of the furnace.

The fibres20to be treated are supplied to the oxidation furnace1, extending parallel as a type of “carpet”, by way of a deflection roller32and pass through an air-supply device22here, which is not of interest in this connection and serves to supply the process with preheated fresh air. The fibres20are then guided through the clearances between suction boxes19lying above one another, through the process chamber6, through the clearances between blowing boxes31lying above one another in the blowing device13, through the clearance between suction boxes19lying above one another at opposite ends of the process chamber6and through a further air-supply device23.

The outlined passage of the fibres20through the process chamber6is repeated a plurality of times in serpentine manner, for which a plurality of deflection rollers24,25lying above one another with their axes parallel are provided in both end regions of the oxidation furnace1. The fibre carpet20stretches over a respective plane between the deflection rollers32,25,24,26. After the uppermost passage through the process chamber6, the fibres20exit the oxidation furnace1and are guided during this by way of a further deflection roller26.

During the serpentine passage of the fibres20through the process chamber6, these are surrounded by hot oxygen-containing air and thereby oxidised. This air passes in each case from the narrow sides31aof the blowing boxes31into the clearance between two parallel air deflectors33and arrives in each case at a narrow side19aof a suction box19which faces the centre of the furnace, and more precisely at that narrow side19aof that suction box19which is one “level” lower than the blowing box31.

The flow of hot oxygen-containing air which is produced in this way crosses the plane of the “fibre carpet” on this path, i.e. it is no longer precisely horizontal but has a vertical component of the flow direction. The barrier which occurs as a result of the parallel flow of air and fibres in oxidation furnaces of a known construction is thus prevented. Instead, the air flow penetrates the carpet of fibres20and also reaches the fibres20located in the interior of the fibre carpet20. This results in a better heat transfer, especially to the fibres20located within the carpet, which in turn results in a shorter procedural treatment time, less of a temperature difference between the air temperature and fibre temperature, a homogenisation of the fibre temperature within the fibre carpet20and therefore ultimately an improved fibre quality.

As a result of the angled flow, the fibres20are moreover acted upon by air which comes directly from a blowing box31and therefore has substantially the same temperature over the entire length between the respective blowing box31and the associated suction box19.

The air deflectors33have further functions: On the one hand, they serve as radiation surfaces when the threads are heated and, on the other, dissipate the exothermic heat produced during the oxidation of the fibres20by absorbing the thermal radiation. The temperature difference between the fibres20and the circulated air is thus reduced, which enables the process to be controlled more precisely.

Finally, the air deflectors33assume the function of guide profiles for the fibres. Separate guide profiles of this type were necessary in known oxidation furnaces. In the event of a fibre breaking, they prevent any contact and entanglement with other fibres. All broken fibres are collected by the air deflectors33.

FIG. 4shows an alternative embodiment of that region of an oxidation furnace which is surrounded by a circle on the left inFIG. 1. Corresponding parts of this alternative embodiment are denoted by the same reference numerals as inFIG. 1, but increased by 100, and are not described in further detail. The same applies to the embodiments described below, in which the reference numerals are increased by 100 in each case from embodiment to embodiment.

In the exemplary embodiment ofFIG. 4, the vertical component of the air flow is not achieved by air deflectors but by the additional superimposition of a vertical air flow. To this end, air is blown into the process chamber106in the direction of the arrows134and sucked out in the lower region of the process chamber106in the direction of the arrows135. As it enters the process chamber106and exits the process chamber106, the air can pass through perforated plates136,137which are useful for generating an air flow which extends at an angle with respect to the horizontal.

Whilst, in the exemplary embodiments of an oxidation furnace1and101which are described above with the aid ofFIGS. 1 to 4, the hot oxygen-containing air had a flow whereof the greater directional component pointed in the movement direction of the threads20, this differs in the exemplary embodiments of the invention which are shown inFIGS. 7 to 10. The main flow direction of the air here is substantially transverse to the movement direction of the threads.

Reference is firstly made toFIGS. 5 to 7, which show a first exemplary embodiment of an oxidation furnace201which operates with a transverse air flow.

On comparingFIG. 5withFIG. 1, it is firstly evident that the central blowing device31has been omitted in the exemplary embodiment ofFIG. 5. This is a direct consequence of the fact that the main flow direction of the air does not extend in the longitudinal direction of the oxidation furnace201but in its transverse direction. If suction boxes219are nevertheless provided in both end regions of the housing202, this serves to ensure that air which may contain toxic gases is prevented from escaping by way of the passage regions203,204.

The manner in which the flow of hot oxygen-containing air proceeds in the exemplary embodiment ofFIG. 5is most clearly revealed inFIGS. 6 and 7. To describe the air circuits, the suction device214ais taken as a starting point and will be referred to as “auxiliary suction device” for reasons which shall become clear below. From this, the extracted air firstly arrives in the air conducting chamber207and mixes here with a further air flow as described further below. The unified air flows then pass through a filter216and a heating device218, through which they arrive in the air conducting chamber208. As with the exemplary embodiment ofFIG. 1, some of the air can be discharged through an outlet230a. A ventilator221sucks the air out of the air conducting chamber208and presses it into an air channel209. This latter leads past the process chamber206to a lateral air distributing chamber238which tapers downwards in a wedge-shape and serves as a blowing device213here. The process chamber206is delimited at this side by a perforated plate so that the air guided into the air distributing chamber238can enter the process chamber206.

The process chamber206is divided by a plurality of parallel air deflectors233. Contrary to the air deflectors33of the exemplary embodiment ofFIG. 1, these air deflectors233are not inclined in the longitudinal direction of the oxidation furnace201but in the transverse direction. As a result, the air entering the clearances between the air deflectors233by way of the air distributing chamber238is guided downwards at an angle, upon which it crosses the horizontal carpets of fibres220and thereby ensures a good heat transfer in a manner similar to that of the exemplary embodiment ofFIG. 1. Otherwise the effects linked to the air guidance and the air deflectors233are the same as in the exemplary embodiment ofFIG. 1.

At the opposite side, the clearances between the air deflectors233are in communication via a further perforated plate with the air conducting chamber207, where the air mixes with the air coming from the auxiliary suction devices214a,215aas mentioned above. The air conducting chamber207in turn communicates as above with the suction side of the ventilator221so that the air conducting chamber207forms the “main suction device”214of this exemplary embodiment.

In the exemplary embodiment of an oxidation furnace301which is shown schematically inFIG. 8, angled air deflectors between the different serpentine portions of the fibre carpet320are dispensed with as in the exemplary embodiment ofFIG. 4and an additional air flow is used instead. This additional air is blown into the process chamber306from above in the direction of the arrows334, passes through a perforated plate336here, crosses through a further perforated plate337at the lower end of the process chamber306and is then extracted in the direction of the arrows335. By superimposing the air which is introduced from the air distributing chamber338(representing the blowing device313) into the process chamber306and flows into the suction channel339(representing the main suction device314) on the one hand and the second air flow, which is guided in the direction of the arrows334,335through the process chamber306, an angled air flow is produced which crosses the carpet of fires320with the advantages already mentioned several times above.

A further possibility for generating an air flow which does not flow against the carpet of fibres in a parallel or perpendicular direction is shown inFIG. 9. In the exemplary embodiment described here, air deflectors433are again used although they extend horizontally. It is the carpet of fibres420which is positioned at an angle here, and this can be achieved for example in that the different deflection rollers at the opposing passage regions of the oxidation furnace401are positioned accordingly at an angle.

Finally, the exemplary embodiment ofFIG. 10in turn completely dispenses with air deflectors and replaces these with an additional air flow which is introduced from above into the process chamber506in the direction of the arrows534, passes through a perforated plate536here, passes through the parallel, angled carpets of fibres520and is extracted by way of a further perforated plate537in the direction of the arrows535. The results are similar to those of the exemplary embodiment ofFIG. 8.

It is to be understood that additional embodiments of the present invention described herein may be contemplated by one of ordinary skill in the art and that the scope of the present invention is not limited to the embodiments disclosed. While specific embodiments of the present invention have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims.