EP0495770B1 - Infrared radiant heater - Google Patents

Abstract

The novel infrared radiator comprises a supporting panel (1, 2) made of sheet steel which is coated at least partially with a dielectric, preferably a ceramic-base one, or of enamel, or is made of aluminium oxide on which at least one metal-oxide conductor track (4, 8, 9) is deposited. Said infrared radiators (1, 2), which have a high efficiency and produce a very uniform radiation level distribution, can be assembled in a simple way to produce an infrared radiator array. <IMAGE>

Description

The invention relates to an infrared radiator with a carrier plate, on which at least one conductor track made of a material that generates heat by electrical energy is arranged.

The use of infrared radiation instead of known methods, which work almost exclusively with warm or hot air, is very rapidly spread in all areas of technology which require heating, drying and / or curing processes.

Drying and / or hardening processes, which are carried out with infrared emitters, work with a considerably better efficiency, since thermal energy is transmitted directly to the object to be heated or irradiated by electromagnetic wave radiation, without material carrier.

The use of infrared emitters instead of conventional drying devices is particularly advantageous for those drying or curing processes that require precise observance of temperature and / or heat quantities, since infrared emitters can react particularly quickly, with low inertia feedback systems for temperature and heat control.

The use of infrared radiators is also of great advantage compared to conventional heating and drying processes if, in addition to curing due to the evaporation of solvents by the application of heat, the macromolecule formation of the paint or coating binder is to be accelerated.

Various embodiments of infrared radiators have therefore already been proposed, for example in FR-A 2 558 579, which describes an infrared radiator with rod-shaped infrared emitters mounted in channels provided with reflectors and in US Pat. No. 2,500,872 an infrared radiator is known which has several infrared emitters, which are each assigned a reflector. Furthermore, from DE-C 850 573 an infrared emitter designed like a light bulb is known.

From FR-A 1 104 164 an infrared radiator unit is known which consists of several parts which can be pivoted relative to one another. Each of these parts has a substantially U-shaped channel, in which sockets, which hold infrared emitters designed like incandescent lamps, are fastened.

US Pat. No. 2,387,804 describes a module for infrared radiators in which the infrared emitters are arranged in two rows next to one another in a housing. Finally, a tunnel-shaped drying oven is described in US Pat. No. 2,439,005, which is equipped with several infrared emitters similar to incandescent lamps.

All known infrared radiation fields have the disadvantage that emitters with linear or quasi-point incandescent filaments are used, attempts being made to keep the radiation intensity distribution on the surface to be treated as uniform as possible with the aid of reflector mirror surfaces and lenses and by coordinating the spacing between the radiators . Despite all the measures, differences in radiant intensity of up to 1: 3 are common.

Infrared radiation sources, e.g. those according to DE-A 24 42 892 are for the formation of large infrared radiation sources, such as e.g. are not suitable for curing paints in the automotive industry.

The radiation source for infrared radiation described in DE-A 34 37 397 is also a very small radiation source which is intended to enable the intensity of the radiation source to be modulated with sufficiently high frequencies. According to page 2, last paragraph of this document, gas analysis devices form an area of application of such infrared radiation sources. The carrier substrate of the radiation source according to DE-A 34 37 397 consists of silicon of about 300 »thick, which is coated on its top with an insulating oxide layer. Below the conductor track, the carrier substrate has a thickness of only about 20 ».

Particularly when drying and / or curing foils and thin layers, which are made of lacquers and pastes, the most uniform possible beam field strength over the entire surface to be treated is of crucial importance, since the appearance of peak values of the beam strength is too fast or mainly due to the Solvent evaporation taking place on the surface, or also excessive crosslinking, with corresponding brittleness. On the other hand, too low values or even "gaps" in the beam intensity distribution lead to insufficiently hardened or cross-linked foils and layers.

According to the current state of the art, an approximately uniform distribution of the beam intensity can only be achieved by directly stringing together so-called infrared surface radiators. Infrared emitter fields of this type are designed for power densities from 16 to 45 kW / m². However, these heater fields cannot be used economically for drying and curing foils and thin layers, since only 4 to 8 kW / m² are required in these application areas.

It is an object of the invention to provide an infrared radiator which avoids the shortcomings of the known radiators and which is preferably designed for a power density of up to approximately 8 kW / m² and is inexpensive in the process.

This object is achieved with an infrared radiator of the type mentioned at the outset, which is characterized in that the carrier plate consists of sheet metal which is at least partially coated with a non-conductor (dielectric), preferably on a ceramic basis or from enamel.

Materials that convert electrical energy (electricity) into heat include, for example, heat conductor alloys according to DIN 17470, such as CrAl 20 5, NiCr 30 20, NiCr 60 15 or NiCr 80 20, resistance alloys according to DIN 17 471, such as CuMn 12 Ni, CuNi 30 Mn or CuNi 44 or so-called resistance-forming metal oxides such as bismuth-ruthenium oxide, from which the conductor track can be produced by methods known in the art. An essential property of the material of the conductor track must therefore be that it emits heat, preferably heat radiation in the infrared range, when current flows through the conductor track. The fact that the carrier plate consists of sheet metal, which is at least partially coated with a non-conductor (dielectric), preferably on a ceramic basis or made of enamel, has made it possible to produce carrier plates up to a size of 400 x 400 mm or larger at low cost in this way to form surface emitters that ensure a very uniform distribution of the radiant intensity on the surface to be treated.

For example, the electrical resistance of the conductor tracks of the flat radiators intended for drying film and lacquer layers is designed such that a radiator temperature of at least 240 ° C. is not exceeded and not exceeded by 280 ° C. and that a power consumption of approximately 6 kW / m² is achieved. Flat radiators with this dimensioning of the heating conductors emit long-wave infrared radiation with a maximum of the spectral energy distribution at 5400 nm. Experiments have shown that all color tones reflect the performance of long-wave infrared radiation above 4000 nm much less, i.e. absorb better than that of the short-wave under 2000 nm lying. For example, a white, glossy lacquered surface reflects about 75% of the power of infrared radiation with a wavelength of 1300 nm, but only about 10% of that with 5400 nm. For example, test specimens coated in glossy black, green, red, light blue, ivory, yellow and white are illuminated comparable conditions with infrared radiation of 5400 nm wavelength, the mean value of the surface temperature is 20% higher than that which is achieved with infrared radiation of 1300 nm. Furthermore, it can be seen in these series of measurements that the difference in the surface temperature of the black to the white test specimen is 72% for infrared radiation of 1300 nm, but only 12% for infrared radiation of 5400 nm.

The infrared radiator according to the invention has several essentials Advantages on.

The entire working area of the emitter field emits with very little difference in the beam intensity distribution.

The heating conductors cover a very large proportion of the radiator field area. This results in an above average level of conversion of electrical energy into electromagnetic radiation power.

The emission of long-wave infrared radiation from the radiators with a maximum of the spectral energy distribution at 5400 nm improves the power transmission e.g. on film and lacquer layers significantly compared to power transmission with short-wave infrared radiation.

With flat radiators, the radiation distribution is achieved without additional optical aids, such as mirrors and reflector surfaces or lenses, by means of radiation directed directly at the object. This avoids the clogging of these aids by paint mist and dusts, a fact that adheres to all known radiation fields.

A particularly suitable metal for the carrier plate is e.g. Stole.

Another advantage of the infrared radiator according to the invention is that e.g. Enameled steel sheets can be used instead of ceramic-coated as a carrier for the heating conductors, especially if large infrared radiators are to be produced. While ceramic-coated carrier plates can only be produced with known production facilities up to a size of approximately 400 x 400 mm, the systems for enamelling enable the production of much larger carrier plates for infrared radiators.

When producing small and very small radiator fields, it has proven to be advantageous if the carrier plate consists of a non-conductor, such as aluminum oxide.

The simple electrical and mechanical construction, in particular the possibility of the all-metal construction, results in a hitherto unknown insensitivity to shocks and vibrations.

The flatness and the metallic or ceramic working surface of the emitter field according to the invention enables it to be easily cleaned.

At a selected working temperature of max. 280 ° C of the infrared radiator enables a simple and inexpensive construction of the radiator.

In one embodiment according to the invention, plug-in tabs connected to the conductor track for connecting electrical lines or the like are attached to the carrier plate by means of conductive adhesive or soft solder connections. This is a very simple and effective way of attachment. All inner conductor connections of the radiator fields can be carried out with standard silicone-coated conductors.

The infrared radiator according to the invention enables the construction of inexpensive infrared fields in that one or more infrared radiators is (are) held in a frame and that advantageously a rear cover is held in the frame on the back of the infrared radiator (s) and in the space between the (the) infrared radiator (s), the rear cover and the frame an insulating layer and preferably the electrical connection lines are arranged.

Another simple and inexpensive construction of infrared radiation fields with infrared radiators is that one or more infrared radiators are attached to a frame, e.g. screwed or glued, that a cover is attached to the rear of the frame and that in the space between the (the ) Infrared radiator (s), the cover and the frame an insulating layer and preferably the electrical connection lines are arranged.

If the space between the emitter (s), the cover and the frame is filled with quartz sand, then explosion-proof emitter fields can be produced.

The implementation of gas-tight radiator fields in the two types described above is e.g. possible because the frame is sealed on all sides by means of silicone rubber.

In a particularly simple embodiment, the infrared radiator (s) are screwed or glued to a mounting plate. Such a mounting plate can e.g. consist of aluminum sheet.

In order to produce application-related infrared radiator fields in a simple manner, the mounting plate or the frame can be flat or, in sections, curved or bent.

Further details, advantages and features of the invention result from the subclaims and the description of exemplary embodiments of infrared radiators according to the invention with reference to the drawings.

• Fig. 1 und Fig. 2 Ausführungsformen erfindungsgemäßer Infrarotstrahler,
• Fig. 3 zu einem Strahlerfeld zusammengesetzte erfindungsgemäße Infrarotstrahler,
• Fig. 4 einen Teilschnitt durch das Strahlerfeld von Fig. 3 entlang der Linie IV-IV,
• Fig. 5 eine Ansicht des Gegenstandes von Fig. 4 von unten,
• Fig. 6 eine weitere Ausführungsform eines Strahlerfeldes,
• Fig. 7 einen Teilschnitt durch das Strahlerfeld von Fig. 6 entlang der Linie VII-VII und
• Fig. 8 eine weitere Ausführungsform eines erfindungsgemäßen Strahlerfeldes.

Show it:

• 1 and FIG. 2 embodiments of infrared radiators according to the invention,
• 3 is an infrared radiator according to the invention assembled to form a radiator field,
• 4 shows a partial section through the radiator field of FIG. 3 along the line IV-IV,
• 5 is a bottom view of the object of FIG. 4,
• 6 shows a further embodiment of a radiator field,
• Fig. 7 is a partial section through the radiator field of Fig. 6 along the line VII-VII and
• 8 shows a further embodiment of a radiator field according to the invention.

In Fig. 1, an infrared radiator 1 is shown, which consists of a carrier plate 3 made of sheet steel, which is coated with a dielectric on a ceramic basis. There is a conductor track 4, e.g. Made of metal oxide, applied in the so-called thick film technique in the screen printing process. At both ends of the conductor track 4 there is a pin 5 or 6 for connecting electrical lines. These plug-in lugs 5, 6 are soldered to the carrier plate 3 or the ends of the conductor track 4.

At the corners of the carrier plate 3 there are four holes 7, by means of which the carrier plate 3 can be fastened to any mounting plate or mounting frame.

In Fig. 2, a carrier plate 2 made of aluminum oxide is shown, which carries two conductor tracks 8, 9, the ends of which are connected in pairs with plug-in tabs 10, 11 for connecting electrical lines. This infrared radiator 2, which has, for example, an edge length of 100 x 100 mm, is advantageously fastened according to the respective requirements by gluing by means of heat-resistant and heat-conducting adhesive to mounting plates or by fastening in suitable frames.

3 shows a radiator field which is equipped with four schematically illustrated infrared radiators 1 or 2. The infrared emitters 1 or 2 (flat radiators) are held in a frame 15 which consists of multi-grooved profiles 16, 17, 18 and 19, e.g. made of plastic or aluminum.

4 and 5, for example, options for connecting these profiles are shown, the flat radiators 1 or 2 being omitted in these representations. The profiles 16 and 17 have the same cross-sectional shape and meet at right angles. They have a substantially U-shaped profile, with the legs 20 and 21 each outwardly facing grooves 22, 23 and 24 are such that there are three circumferential grooves 22, 23 and 24 when the frame 15 is assembled.

The groove 22 serves for receiving an infrared radiator 1 or 2, the groove 23 for receiving an insulating layer and the groove 24 for receiving rear cover plates.

The frame 15 is further divided by profiles 18 and 19 like window rungs, these profiles 18, 19 also having mutually opposite pairs of grooves 25, 26 and 27, which cooperate with the corresponding grooves 22, 23 and 24 of the profiles 16 and 17. So that the infrared emitters 1 or 2 are as close as possible to one another, the profiles 18 and 19 are narrower than the profiles 16 and 17.

The corner connection of the profiles 16 and 17 shown in FIGS. 4 and 5 consists essentially of a cross bolt 28 which is inserted through two holes 29 in the legs 20, 21 of the profile 17 and two screws or threaded bolts 30. These screws 30 are located each in the opposite central grooves 23 of the profile 17 and protrude through holes in the leg 21 of the profile 16 or are received in threaded holes in the cross bolt 28. The screws 30 protrude through the leg 21 into the central recess 31 of the U-shaped profile 16 and have nuts 32. By tightening the nuts 32, the profile 17 is pulled over the cross bolt 28 against the profile 16, thus creating a firm connection between the profiles 16 and 17.

4 and 5, the fastening of the profile 18, which is received between two profiles 17, consists essentially of two cross bolts 35, one of which is received in bores 38 in the legs 20 and 21 of the profiles 17.

The cross bolts 35 have in their center transverse to the longitudinal axis bores, which are penetrated by a screw 36. This screw also passes through a hole in the central web of the profile 18 and lies in the central recess 31 of the profiles 17. If the nut 37 of the screw 36 is tightened, the profiles 17, between which the profile 18 is received, are pulled towards one another via the transverse bolts 35, and thus a firm connection between the profiles 17 and 18 is established.

The frame 15 of FIG. 3 can in this way be composed of any number of profiles 16 to 19 and accommodate a certain number of infrared radiators 1 or 2, as required.

The sealing of the joint between the infrared radiators 1 or 2 and the profiles 16 to 19 can e.g. as shown with an infrared radiator 1 or 2 in Fig. 3, by a bead 39 made of appropriate silicone rubber.

The radiator field shown in Fig. 6 has a frame 40, e.g. made of aluminum on which two infrared radiators 1, only shown schematically, are fastened by means of screws passing through the holes 7. The frame 40 of the radiator field of FIG. 6, shown in partial section in FIG. 7, has a U-shaped profile, the infrared radiators 1 being screwed to a leg 41 of the frame profile. A rear cover plate 43 is attached to the second leg 42, e.g. glued on. In the space 44 thus formed between the infrared radiator 1, the rear cover plate 43 and the frame 40, e.g. an insulating layer is arranged or it is filled with quartz sand. In addition, the electrical lines can also be arranged in this space 44. The seal between the infrared radiators 1 or 2 and the frame 40 can, as can be seen from FIG. 7, be made by beads 50 made of silicone rubber or the like.

In Fig. 8, an infrared radiator array 45 is shown schematically, which consists of three mutually inclined plates 46, 47 and 48, on each of which two infrared radiators 1 or 2 are attached. The plates 46 to 48 can of course also be units formed by frames 15 (FIG. 3) or 40 (FIG. 6) and connected to one another in a fixed or movable manner, for example via joints. In this way, the respective Corresponding emitter fields can be assembled, which are characterized by a very high strength and a very high ease of maintenance at low manufacturing costs.

If the plates 46 to 48 shown in FIG. 8 consist of a thermally highly conductive material, then the infrared radiators 1, 2 are well protected with a beam direction indicated by the arrows 49. The infrared radiators 1 or 2 are with their back on the plates 46 to 48 e.g. glued or screwed on.

Claims (12)

1. Infrared radiator with a support plate (1, 2), on which at least one conductor strip (4, 8, 9) made of a material, which generates heat through electrical energy, is arranged, characterised in that the support plate (1) is made of sheet metal, which is at least partially coated with a non-conductor (dielectric), preferably ceramic based or enamel.
2. Infrared radiator according to Claim 1, characterised in that the support plate (1) is made of sheet steel.
3. Infrared radiator according to Claim 1, characterised in that the support plate (2) is made of a non-conductor such as aluminium oxide, for example.
4. Infrared radiator according to one of Claims 1 to 3, characterised in that connector lugs (5, 6, 10, 11) connected to the conductor strip (4, 8, 9) are attached to the support plate (1, 2) for the connection of electrical conductors or similar by means of conductive adhesive or soft solder joints.
5. Infrared radiator according to one of Claims 1 to 4, characterised in that at least two infrared radiators (1, 2) are combined to form an infrared radiator array.
6. Infrared radiator according to one of Claims 1 to 5, characterised in that one or more radiators (1, 2) is (are) held in a frame (15).
7. Infrared radiator according to Claim 6, characterised in that a rear cover is held in the frame (15) on the rear side of the infrared radiator(s) (1, 2); and that an insulating layer and preferably the electrical connection lines are arranged in the space between the infrared radiator(s) (1, 2), the rear cover and the frame.
8. Infrared radiator according to one of Claims 1 to 5, characterised in that one or more infrared radiator(s) (1, 2) is (are) fastened to a frame (40), e.g. by screw or adhesive joint; that a cover (43) is fastened to the rear side of the frame (40); and that an insulating layer and preferably the electrical connection lines are arranged in the space (44) between the infrared radiator(s) (1, 2), the cover (43) and the frame (40).
9. Infrared radiator according to Claim 7 or 8, characterised in that the space (44) between the radiator(s) (1, 2), the cover (43) and the frame (40) is filled with quartz sand.
10. Infrared radiator according to one of Claims 6 to 9, characterised in that the frame (15, 40) is sealed on all sides by means of silicon rubber.
11. Infrared radiator according to one of Claims 1 to 5, characterised in that the infrared radiator(s) (1, 2) is (are) screwed or adhered to an assembly plate (46, 47, 48).
12. Infrared radiator according to one of Claims 6 to 11, characterised in that the assembly plate (45) or the frame (15, 40) is flat or curved stepwise or bent stepwise.

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