EP1667489A2 - CFC radiant heater - Google Patents

Abstract

The heater has a carbon heating component (1) in a housing that is transparent to IR radiation. The component is a carbon fiber-reinforced carbon (CFC) web arranged in a plane and between base and cover plates, where one of the plates being partially transparent to IR radiation. The base plate is made of opaque quartz glass, and welded to the cover plate, where the base plate is reflective for IR radiation. An independent claim is also included for a method for producing an IR radiant heater.

Description

The present invention relates to an IR radiant heater with at least one flat filament made of carbon, in a transparent or at least partially transparent housing for IR radiation.

Such an IR radiator is realized according to EP 0 881 858 with a single filament arranged in a round tube and in DE 44 38 871 and DE 44 19 285 with a plurality of filaments of carbon arranged next to one another. The carbon materials used here consist of parallel carbon fibers, which are connected by means of resin. These structures are graphitized prior to installation in the radiator.

The emitter disclosed in EP 0 881 858 is unsuitable for uniform planar irradiation.

DE 44 38 871 and DE 44 19 285 relate to the use of comparable filaments, but with the aim of achieving a two-dimensional (2D) radiation.

However, the carbon filaments disclosed there can not be combined to any planar heating elements, since the material can only be stretched and arranged with the same width. Although this makes it possible to realize the arrangements shown in DE 44 38 871, they do not give uniform emission intensities nor can curved or round shapes be realized, or even structures shaped in 3D.

Just the arrangement shown in DE 44 38 871, Fig. 5a is in the marginal bands due to the different length of the different fibers a considerable Show variation of the temperature and thus the radiated power per unit length.

Arrangements with a multiplicity of narrow bands, as in DE 44 19 285, require a large number of complex and expensive contacts between the individual bands.

However, such carbon bands can not be arranged in any planar patterns, because the bands allow only slight deviations from a parallel arrangement. Although bands can be designed as desired perpendicular to their areal design. However, such arrangements lack the areal character of a radiation surface.

On the other hand, the present invention also relates to the use of CFC material for radiant heaters.

JP 7-161725 describes cutting a heating pattern of planar material using silicon carbide (SiC). Here, the SiC heating element is located in an open housing made of quartz glass, on which on the side used for heat treatment a graphite disc (see Figure 1, No. (8)) is placed. The graphite disc is heated by the SiC heater and then warms the material secondarily. Such heating elements made of SiC or graphite are brittle and rigid, so that they react very fragile. The heating element is also electrically contacted rigidly by means of screws, so that an additional risk of breakage arises here due to the thermal expansion. To ensure adequate mechanical strength of such heating elements, they must be made massive. Due to the then low electrical resistance very high currents will flow during operation at low voltages. This requires complex power supplies and the electrical leads are very difficult to lead in a vacuum-tight quartz body. For this reason, the quartz glass housing is designed here open.

EP 0 899 777 B1 describes a carbon heater having a heater member of longitudinally stretched interwoven carbon fiber bundles, such as a ribbon or wire form. These woven carbon fiber bundles are expressly not converted by means of graphite into a CFC. These bundles remain so flexible and the risk of brittle fracture is avoided. The described wire or ribbon-shaped heater elements have a high electrical resistance, so that the heater can be designed for operation at common voltages. Due to the very small number of fibers in the band, however, only a very small amount of current flows at maximum power of a few amps, so that overall the performance of such a unit with 30 kW m ² tends to be low.

The heater link is placed in channels that have been milled into a first quartz plate. Subsequently, the heating device is closed by means of a second quartz part that is placed on the first and connected thereto. The connection is made by applying a weight of 10 kg and a hot process in which the entire device is heated to 1450 ° C for 3 h.

The resulting connection of the two quartz parts is not a continuous weld and can gap apart due to mechanical and thermal loads after prolonged operation.

According to US Pat. No. 6,584,279 B2, an IR radiator with a power of up to 28 kW / m ² with braided carbon fibers is available.

In the brake technology, carbon fiber reinforced carbon (CFC) discs made of CFC material or Si impregnated CFC are used.

The aim of the invention is to develop an IR radiator, which can be operated at normal mains voltages, at the same time has high power and lifetime and allows high flexibility in the design options with respect to the required forms of the process.

According to the invention, it has surprisingly been found that, when using complex-shaped filaments for carbon radiators, which were cut out of CFC webs, area outputs of more than 30 kW / m ² , in particular more than 100 kW / m ^{2, can be} produced. Furthermore, it has surprisingly been found that when these filaments are introduced into housings which consist of opaque quartz glass on the underside and clear quartz glass sandblasted or frosted at most on the surface, IR radiation primarily radiates only from the top side. Although the hot quartz glass itself radiates above 5 μm in the region of the long-wave infrared, the radiated power in this wavelength range is independent of the quartz material or the surface used. On the underside of the device according to the invention, however, only this secondary portion of the radiation occurs.

When choosing the appropriate high electrical resistivity CFC material, as it is e.g. When a yarn is used which has been produced from a multiplicity of short fiber sections and has subsequently been woven into a material web, a suitable specific electrical resistance can be set.

Such webs remain flexible and tear-resistant even after impregnation and conversion into a CFC. Even filaments of complex shape cut from CFC sheets remain flexible and tear-resistant.

Since the thickness of the material is low, preferably <1 mm, and more preferably <0.3 mm, it also achieves an electrical resistance of the filaments, which allows operation at normal operating voltages (208 V, 230 V, 400 V, 480 V) , Usual current feedthroughs for IR emitters allow about 25 A, so that considerable power per filament can be realized.

According to the invention it has surprisingly been found that in flat radiant heaters with patterns from a CFC track achievements of over 30 kW / m ^2, in particular over 100 kW can be achieved and emitters with a power of 8-12 KW can be produced and radiate the flat radiator unilaterally, though a planar carbon pattern is arranged between two surfaces, one of which is opaque and the other is clear. The invention can also be realized with a plurality of CFC webs.

This provides a heating technique that is the highest standard for clean applications, as required in the semiconductor industry.

In preferred embodiments of the invention, flat quartz glass elements of the housing are welded together to form a housing. The housing may be made of a high purity material, such as e.g. Quartz glass. The CFC heating filament can be arranged in the housing on brackets, wherein the shape of the brackets is preferably chosen so that the support surface is kept low, ideally limited to one line. Suitable supports are, for example, rods made of quartz glass, aluminum oxide or another non-conductive material of high melting point, which are ideally equipped as a body with a sharp edge on which rests the filament.

The power of the radiant heater is preferably more than 30 kW / m ² , in particular 50 to 250 kW / m ² for radiant heaters with a service life of 5,000 to 10,000 hours.

A further preferred embodiment consists in radiant heaters with a power of over 200 kW / m ² , in particular more than 250 kW / m ² for shorter-lived spotlights.

The particularly preferred field of application are long-lasting radiant heaters with a power of between 100 and 200 kW / m ² .

In the preferred form of a surface radiator, two spatial dimensions are many times larger, preferably one order of magnitude larger, than the third dimension. It has been proven to evacuate the housing or to fill it with inert gas.

The electrical contacting of the filament is preferably carried out via brackets made of molybdenum, with additional layers of suitable carbon materials between the filament and the bracket for an ideal electrical and mechanical contact.

Preferred CFC patterns are disc-shaped, meander-shaped, helical, have the shape of an omega, or a folded-in omega or are circular with a recess. The CFC pattern can be cut out of a CFC sheet with the required accuracy and with gentle treatment of the material of special purity with a laser or water jet.

In the following the invention is illustrated with reference to the figures.

FIG. 1 a shows a plan view of a heating element 1.

FIG. 1b shows a perspective view of a heating element 1.

FIG. 2 a shows a plan view of a base plate 2.

FIG. 2b shows a perspective view of the base plate 2.

FIG. 3 a shows a plan view of a cover plate 3.

FIG. 3b shows a side view of the cover plate 3.

Figure 4 shows a perspective view of the bottom plate 2 with the mounted feeds of the electrical contacts 26 and the mounted pump supports 27th

Figure 5 shows an overall perspective view of the device from below.

A heating element according to FIG. 1a or 1b is cut out of a sheet of CFC material.

The bottom plate 2 according to Figure 2a or 2b is made of opaque quartz glass. In its surface are support webs 22 for the heating tape 1, spacers 23, which are welded to the cover plate and retaining pins 21 for fixing the heating tape 1. Outside, an edge 24 is provided for welding to the cover plate. Further, two holes 25 are provided for the electrical contacts.

Figures 3a and 3b show a cover plate 3 made of quartz glass with recessed openings 31 for welding the cover plate with the spacers 23 of the bottom plate. 2

In Figure 4, the bottom plate 2 is equipped with mounted feeds of the electrical contacts 26 and the mounted pump nozzle 27.

In Figure 5, the electrical leads 28 and base 29 are additionally attached.

The radiant heater according to FIG. 5 has a CFC heating element 1 (FIGS. 1 a and 1 b), which meandering fills the entire surface to be heated. Below the ends of the filament (1) put on the bottom plate 2 (Figure 2a / 2b) made of opaque quartz glass (OM-100 according to Heraeus brochure from 2002) two tubes made of quartz glass for receiving the electrical contacts 26 and the current feedthroughs. The front side 3 is a clear quartz glass pane 3. The panes 2 and 3 are closed to a dense space, which is evacuated via the pipes for the power supply lines. In this embodiment, the carbon belt 1 can be heated at a power of 200 kW / m ² to about 1300 ° C.

In a simple embodiment according to FIGS. 2a and 2b, the opaque disk is designed as a base plate 2, on which spacers 23 are arranged. The bottom plate 2 is of an inner and outer ring 24 limited. The CFC pattern 1 lies loosely on the support webs 22 and a clear quartz glass plate 3 terminates with the rings.

In Figure 2, the current feedthroughs are outside the circular radiation unit and cause for the glass plates 2, 3 and rings a deviation from the disc or ring shape.

In this embodiment, the carbon belt 1 can be heated at a power of 200 kW / m ² to about 1300 ° C.

For highly pure applications, the CFC pattern 1 is cut out of a CFC surface with a laser, the spacers 23 and the rings and the quartz glass plates 2, 3 of highly pure quartz glass, so that in addition to the metallic power supply and the web ends with the Only high-purity quartz glass as a radiator housing and high-purity carbon as the radiation source 1 are used for connecting current feedthrough molybdenum retaining clips.

Preparation example

An opaque quartz glass plate 2 of sufficient thickness is cut into a required shape for the bottom 2, then the depressions are milled and ground. In this case, the edge 24 and the spacers 23 remain at their original height and the support webs 22 for the filament are at a lower level. Finally, the openings at which the pipes for electrical contacting and the current feedthrough are drilled are drilled. Edges may be smoothed or fire polished.

Subsequently, quartz glass tubes are attached to the holes, in each of which a current feedthrough is arranged. In addition, pipes 27 for applying vacuum and for introducing purge gas are located on these pipes.

The cover plate 3 for the top is cut from pure quartz glass and ground. In particular, recesses 31 are introduced for later welding of the plate to the spacers 23 of the opaque plate 2.

The heating element 1 is cut from a CFC sheet material by means of a water jet and then coated in a reactor with pyrocarbon.

Power feedthroughs are made in the form of bruises. At the inner end of the current feedthrough is a molybdenum pin. At this the terminal for receiving the heating element 1 is attached.

The current feedthrough is welded to the tube of the current feedthrough, so that the clamps for receiving the filament are already in the later level of the filament. Subsequently, the tape is inserted into the bottom and the tape ends are connected by clamping the sheet of molybdenum retaining clip with the current feedthrough. In addition, graphite platelets are added for mechanical protection and to improve the electrical contact.

The cover plate 3 is placed and the resulting interior is purged with argon, so that during the welding process no water vapor or oxygen can oxidize the carbon or molybdenum.

Then, the two quartz elements 2, 3 are welded together. In this case, the weld is joined by applying additional quartz glass along the edge and at the recesses 31 in the cover plate, which are opposite the spacers 23 for the cover plate. After completion of the welding, the recesses in the cover plate are completely filled and also the edges between the upper and lower plate are filled to the extent that no recesses are present.

Subsequently, the body is annealed under vacuum or under inert gas. The protective gas is passed directly into the body and rinsed during the entire tempering process.

After tempering, the surface is ground, polished, lobed or sandblasted and finally cleaned by acid. After this process, there is an absolutely flat top.

The interior of the radiator is either evacuated or filled with a protective gas and the radiator deducted.
The electrical contacts are attached externally.

Claims (8)

Infrared radiant heater with at least one planar carbon heating element (1) in a housing which is transparent or at least partially transparent to IR radiation, characterized in that at least one carbon heating element (1) is a CFC web arranged in a planar manner, and between plates (2, 3) is arranged, of which at least one is transparent or partially transparent. IR radiator according to claim 1, characterized in that a plate (2) is reflective for IR radiation. Apparatus according to claim 2, characterized in that the reflective plate (2) comprises opaque quartz glass. Apparatus according to claim 3, characterized in that the opaque quartz glass has a diffuse reflection of more than 90%, preferably more than 95%. Apparatus according to claim 3 or 4, characterized in that a bottom plate (2) made of opaque quartz glass with a transparent cover plate (3) is welded or glued or soldered. Infrared radiant heater according to one of the preceding claims, characterized in that the housing in two dimensions at least by a factor of 5, in particular by 1 to 2 orders of magnitude is more pronounced than in the third dimension. Method for producing an IR radiant heater with at least one planar carbon element (1) which is arranged in a transparent or partially transparent housing, characterized in that the carbon heating element (1) is cut out of a sheet-like CFC material. Method for producing an IR radiant heater with at least one planar carbon element (1), characterized in that the planar carbon element (1) is arranged between a clear (3) and an opaque (2) surface.

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