IR-SOURCE WITH HELICALLY SHAPED HEATING ELEMENT

Abstract: An infrared radiation lamp that includes an electrically heated filament and a reflector. The invention is characterised in that the filament (1) is comprised of a high temperature element that is wound to a helical configuration (2), such that the helix will be free-standing at operating temperatures; and in that the helix (2) is placed in an open reflector (3) made of ceramic material.

Description: IR-source with Helically Shaped Heating Element. The present invention relates to an infrared radiation lamp. Different types of infrared radiation lamps are known to the art. These lamps are based on a tungsten filament or tungsten wire enclosed in a light bulb. This filament emits a large amount of infrared radiation when heated by an electric current. Such lamps, however, deliver a relatively low radiation power, for instance a power of about 1.5-2 W/cm 2 . There is a need to generate much higher power concentrations, and then particularly on small surfaces. For instance, there is a need to produce a power concentration of 80-90 W/m 2 on a surface of only some few square centimetres in area. It has not earlier been possible to achieve such power concentrations . There is also a need to reach such high power concentrations over larger surfaces of different configurations, such as round surfaces and elongated, rectangular surfaces, for instance. In addition to obtaining a high power concentration, there is also a need to be able to vary the power concentration over the surface concerned. The reason why a high concentration is required is often because it is desired to heat a product rapidly during manufacture. An example of needing to rapidly heat small surfaces is found in the application of plastic caps on packaging units, where only the surface of the caps shall be quickly heated to melting temperature, for instance to a temperature of 300-400°C. An example of larger surfaces is found in the heating of wafers in electronic manufacturing processes, where the higher power shall be delivered to the peripheral parts of the wafer as opposed to the central part thereof. The present invention satisfies the requirement of a high power concentration in respect of infrared radiation lamps. The present invention is not restricted to any particular use, and can be applied in many different fields. The present invention thus relates to an infrared radiation lamp which includes a reflector and an electrically heated filament, and which is characterised in that the filament is comprised of a high temperature element which is wound to a helical configuration such that the helix will be freestanding at operating temperatures, and in that the helix is placed in an open reflector made of ceramic material. The invention will now be described in more detail with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawings, in which - Figure 1 illustrates a lamp which is shown in section below the line A-A; - Figure 2 is a sectional view taken on the line B-B in Figure 1; and Figure 3 is a view corresponding to the view of Figure 1, but showing three lamps mutually combined to form a unit. The illustrated infrared radiation lamp includes a reflector and an electrically heated filament. According to the invention, the filament 1 is comprised of a high temperature element which has been wound into a helical configuration 2, such that the helix is free-standing at operating temperatures. The helix 2 is placed in an open reflector 3 made of ceramic material. The fact that the reflector is open means that no wall will be present at the reflector opening. The helix is thus surrounded by air. The high temperature element is a known resistor element. Examples of such elements are those marketed by Kanthal AB under the trade name Kanthal Super 1800 and Kanthal Super Excel respectively. Such electrical resistor elements are of the molybdenum suicide type and have long been known. They are primarily intended for use in so-called high temperature applications, primarily in conjunction with furnaces, ovens, that operate at temperatures of about 1700°C. Swedish Patent Specification 458 646 describes the resistor element Kanthal Super 1900. The material is an homogenous material with the chemical formula Mo x Wι- x Si 2 . The molybdenum and tungsten are isomorphous in this chemical formula, and can thus replace each other in the same structure. It is preferred that the filament, or wire, has the form of a resistor element comprised of molybdenum suicide MoSi 2 or of a material having the chemical formula Mo x ι_ x Si2. As before mentioned, an important feature of the invention is that the helix 2 is free-standing. This enables the lamp to be directed in any desired direction. In order for the helix to be free-standing, the number of turns in the helix must be limited so as to prevent the helix from becoming too heavy, e.g. top heavy. If the helix is too heavy, the straight parts 4, 5 of the filament will bend when a certain temperature is reached, unless the lamp is directed vertically downwards. According to one preferred embodiment, the helix 2 will have at most 3.5 turns. According to one preferred embodiment, the element has a diameter of 1-3 mm. The element will preferably have an operating temperature of about 1700-1800°C. This is achieved with a known power unit that delivers 5-10 volts and a power of 300-600 W, for instance. The lead-in wires 6, 7 may be of a molybdenum silicide type with a diameter three times larger than the diameter of said element. The lead-ins may alternatively have the form of aluminium rods that have been moulded directly on the element 1. The reference numeral 12 in Figure 1 identifies a holder made of a material marketed under the name Duratec. Reference numerals 13, 14 identify cable grips. According to one preferred embodiment, the reflector is made of a ceramic fibre material, such as A1 2 0 3 . However, the reflector may, alternatively, be made of any appropriate material capable of withstanding the temperatures in question. The outer surface 15 of the reflector will preferably be coated with a reflective material, so as to reduce radiation losses from the lamp. In the case of the embodiment shown in Figures 1 and 2, only one helix 2 is present in the reflector. However, two or more helices 8, 9, 10 may be mounted in one and the same reflector 11, as illustrated in Figure 3. The reflector may, of course, be given different designs to suit different lamp applications. The number of helices may also be varied in accordance with lamp application. It can be mentioned by way of example that a lamp intended to heat small surfaces to a high temperature, as mentioned in the introduction, may include a reflector that has an opening diameter of 30 mm. The reflector may therewith have a wall thickness of 20 mm. The reflector may, of course, be much larger in the case of other applications. It will be obvious that the inventive lamp satisfies the need for high power concentration mentioned in the introduction. Although the invention has been described with reference to a number of exemplifying embodiments thereof, it will be understood that the person skilled in this art will be capable of modifying the described embodiments in accordance with the use range of the lamp. The present invention shall not therefore be considered to be restricted to the aforedescribed embodiments, since modifications and variations can be made within the scope of the following Claims.

Claims: CLAIMS 1. An infrared radiation lamp that includes an electrically heated filament and a reflector, characterised in that the filament (1) is comprised of a high temperature element that is wound to a helical configuration (2) , such that the helix will be free-standing at operating temperatures; and in that the helix (2) is placed in an open reflector (3) made of ceramic material. 2. An infrared radiation lamp according to Claim 1, characterised in that the element (1, 2) is of the molybdenum silicide type (MoSi 2 ) . 3. An infrared radiation lamp according to Claim 1, characterised in that the element (1, 2) is made of a material having the chemical formula Mo x Wι_ x Si 2 . 4. An infrared radiation lamp according to Claims 1, 2 or 3, characterised in that the helix (2) includes at most 3.5 turns . 5. An infrared radiation lamp according to Claims 1, 2, 3 or 4, characterised in that the reflector (3) is made of a ceramic fibre material, such as A1 2 0 3 . 6. An infrared radiation lamp according to Claims 1, 2, 3, 4 or 5, characterised in that the element has a diameter of 1-3 mm. 7. An infrared radiation lamp according to Claims 1, 2, 3, 4, 5 or 6, characterised in that the element (1, 2) is adapted to have an operating temperature of about 1700- 1800°C. 8. An infrared radiation lamp according to any one of the preceding Claims, characterised in that the outer surface (15) of the reflector is covered with a reflective material, so as to thereby reduce lamp radiation losses. 9. An infrared radiation lamp according to any one of the preceding Claims, characterised in that two or more helices (8, 9, 10) are provided in one and the same reflector.

Inventors: ANDERSSON JAN, JOHANSSON LARS-GOERAN, ANDERSSON, JAN, JOHANSSON, LARS-GOERAN
Applicants: ANDERSSON JAN, JOHANSSON LARS GOERAN, KANTHAL AB, ANDERSSON, JAN, JOHANSSON, LARS-GOERAN
Application year: 1998
Main classification: H05B3
IPC codes: H01K1, H01K7, H05B3