HEATER FOR HEATING BY INFRA-RED RADIATION

Abstract: The invention concerns a heater (1) for heating and/or curing a substance, such as a putty, filler, primer and top coat material, which substance is applicable onto an object (21), e.g. in the form of a substrate of a thin metallic material, such as Fe and Al sheet-metal. The heater (1) has a body (2) fitted with an IR emitter unit (7) and is adapted to the zone (20) to be heated in the object (21). The adaptation is achieved in that the IR emitter unit (7) has at least one first IR emitter device (9, 10) which is arranged to supply a higher-concentration IR radiation to at least a first part (22, 23) of the zone (20) having satisfactory cooling, and in that the IR emitter unit (7) has at least one second IR emitter device (13, 14) which is arranged to supply a lower-concentration IR radiation to at least a second part (24) of said zone (20) having less satisfactory cooling than the first part (22, 23), in order to produce an essentially even temperature distribution across said zone (20).

Description: HEATER FOR HEATING BY INFRA-RED RADIATION The present invention relates to a heater for heating and/or curing a substance, such as a putty, filler, primer and top coat material. The substance is applied on an object, e.g. in the form of a substrate of a thin metallic material, such as Fe and Al sheet-metal, for instance in the form of motor vehicle sheet. The heater comprises a body fitted with an IR emitter unit arranged to emit IR radiation onto said object in order to effect said drying and/or curing. The IR radiation used in tnis kind of heaters are primarily of short-wave type, the IR radiation causing the substance applied on the object to dry "inside-out" for the purpose of avoiding blisters and other irregularities from forming on the top surface layer of the substance. Heaters of this type are commonly used in e.g. motor vehicle paint finishing shops in which enamelling work is performed on e.g. vehicle body parts. It is important, particularly when heaters are used in paint finishing shops for the repair of damages to the enamel, that the heater dimensions be as small as possible, yet capable of providing the largest possible zone of heating and/or curing on the object. The reason therefor is that particularly in the case of applications of the kind referred to, the heater is often used in narrow spaces, in addi- tion to which it is required that the heater be easy to manage. Different temperature levels in the object are required to heat and/or cure the various substances. To this end, the heater must be constructed to satisfy these demands on differentiated temperatures at a specified distance from the object. In addition, the heating and/or curing of the various substances require that a predetermined time vs temperature curve is followed with respect to the heated surface of the object, if a satisfactory result is to be obtained as concerns surface evenness and smoothness. The time vs. temperature curve may vary from one substance to the next and be achieved e.g. by using a control means to vary the power supplied to the IR unit and/or the distance from the heater to the object. In order to achieve even temperature distribution while satisfying the above-mentioned temperature requirements the IR emitter units of heaters designed in accord- ance with prior-art technology are fitted with a comparatively large number of IR emitters, each one comprising a reflector. The comparatively large number of IR emitters makes the prior-art heaters voluminous and difficult to maneouver in narrow spaces. Another consequence of the use of many IR emitters s the increased costs related to the heater. In addition, prior-art IR emitters are adapted for emission of essentially evenly distributed IR radiation across the heated zone of the object. This is achieved by spacing the IR emitters comparatively densely, by employing identical reflectors for the different IR emitters, and by employing nominal power of equal magnitude in the various IR emitters. The emission of essentially equally distributed IR radiation across the heated zone is disadvantageous inasmuch as parts in the middle of the heated zone are heated to a higher temperature than are the marginal portions of the heated zone of the object. In other words, a temperature peak is generated at the parts located in the middle of the heated zone with the result that the desired even temper- ature distribution across said zone fails to be attained. Said temperature peak generates essentially through thermal conductivity in the object and/or said substances. Since the parts in the middle of the object are surrounded by other parts that are heated by the heater, cooling of the first-mentioned parts is less efficient than in the case of the latter parts. Furthermore, these latter parts could be connected to parts of the object and/or the substance not exposed to the IR radiation from the heater, which further enhances the cooling of said parts . In order to reduce the problem found in connection with such temperature peaks heaters having IR emitters of mutually different nominal power have been suggested lately. In these cases, IR emitters having the lesser nominal power are positioned in a manner ensuring that they radiate the above-mentioned middle parts that are less efficiently cooled whereas the IR emitters having the higher nominal power being positioned to ensure that they radiate the remaining parts that are satisfactorily cooled. The thus configured devices have resulted in some reduction of the temperature peak of the centrally located parts but the temperature peak in the radiated middle parts still may negatively affect surface evenness and the like in the heated/cured substances when these prior-art devices are used. The object of the present invention thus is to suggest a heater that has comparatively small dimensions, that possesses satisfactory maneuverability and that produces a more even temperature distribution across the heated zone of the object than devices m accordance with prior-art technology. These and other objects are achieved in accordance with the present invention in a heater as defined in the appended claims. Presently preferred embodiments of the present invention will be described in the following in more detail with reference to the accompanying drawings. Figs la and lb are two diagrams of schematically represented temperature distribution along an object radiated by a heater, the diagram of Fig. la showing the temperature distribution obtained by means of a prior-art heater and the diagram of Fig. lb showing the temperature distribution obtained by means of the heater in accordance with the present invention. Fig. 2 is a schematic perspective view of one embodiment of an inventive heater. Fig. 3 is a schematic partly sectionalized lateral view of an inventive IR emitter in accordance with one embodiment thereof, said emitter being fitted with an essentially parabolic reflector. Fig. 4 is a schematiac partly sectionalized lateral view of an inventive IR emitter in accordance with one embodiment thereof, said emitter being fitted with an essentially elliptical reflector. Fig. 5 is a perspective view schematically illustrating one example of a stand, shown in dash-and- dot lines, fitted with two inventive heaters in accordance with one embodiment thereof. Fig. 6 is a schematic explosive view, showing the radiation of an object by means of an inventive heater. Fig. la is a schematic diagram of the temperature distribution along an object which is radiated by means of a heater of prior-art design. The X-axis represents a distance along the object and the Y-axis the temperature at the respective point along said distance. The dotted lines symbolize the IR radiation distributed essentially evenly across the surface in accordance with prior-art technology. Fig. lb is a schematic representation of the temperature distribution in the case of a heater in accordance with the invention. The more evenly distributed temperature is achieved by varying the IR radiation intensity across the radiated zone, which is shown schematically by the denser radiation at the marginal portions of said zone. A description will be given in the following with reference to Figs 2-4, explaining the manner in which the referred-to even temperature distribution across the radiated zone of the object is achieved in accordance with the invention. Fig. 2 is a schematic representation of one inventive heater, generally designated by reference 1. The heater has a body 2. In accordance with the shown embodiment, the body 2 comprises two lateral profile sections 3 and 4, respectively positioned in opposed relationship, and a middle profile section 5, positioned intermediate sections 3 and 4. In accordance with the shown embodiment, the ends of the middle profile section 5 are inserted in grooves formed in the lateral sections 3 and 4, respectively. The middle profile section 5 in accordance with this embodiment is formed with a filter element 6 which is received in grooves extending longi- tudmally relative to the middle profile section 5. The middle profile section is fitted with a fan unit (not shown) sucking in air through the filter element and through conduits (not shown) formed in the middle profile section and/or the lateral profile sections, said air serving to cool an IR emitter unit generally designated by reference 7. The IR emitter unit 7 has an essentially rectangular base 30 in the form of a secondary reflector 8 which is connected to the body 1. The secondary reflector 8 is coated with a material possessing good IR radiation reflectivity or else possesses such reflectivity in itself. The base 30 likewise comprises two first IR emitter devices 9 and 10, respectively, arranged in facing relationship, each such device being fitted with an IR emitter 11 (see Fig. 3). The IR emitters 11 have one essentially parabolically shaped reflector 12 each (see Fig. 3), and they are disposed in the vicinity of and along their respective side of a first pair of opposed sides 31, 32 of the base 30. The base 30 also comprises two second IR emitter devices 13 and 14 arranged in facing relationship, each one of said devices comprising an emitter 15 (see Fig.4). The IR emitters 15 have one essentially elliptical reflector 16 each (see Fig. 4) and are disposed in the vicinity of and along their respective side of the other pair of opposed sides 33, 34 of the base (see Fig. 2) . As appears schematically from the embodiment illustrated in Fig.3 the IR emitters 11 having the essentially parabolic reflector 12 emits the major part, approximately 60%, of the IR radiation in a direction straight down- wards whereas a minor part, approximately 20%, of the emitted IR radiation is emitted in a direction diagonally downwards as seen in Fig. 3. The essentially parabolic reflection surface of the reflector 12 in accordance with the preferred embodiment of Fig. 3 at least partly essentially follows a curve that may be mathematically expressed by x 2 = 34.7y, where x and y are expressed in a rectilinear coordinate system. As schematically appears from Fig. 4, the focus of the IR emitters 15 having an essentially elliptical reflector 16 in accordance with this embodiment is disposed at a distance a, which could be e.g. about 16 mm, below the lower edge of the reflector 16. From this focus the IR radiation is spread laterally at an angle which in accordance with the shown example could be about 45°. The essentially elliptical reflection surface of the reflector 16 in accordance with the preferred embodiment of Fig. 4 at least partly essentially follows a curve that may be mathematically expressed as x 2 /30 + y /22.5 = 1.0, wherein x and y are expressed in a rectilinear coordinate system. The IR emitters 11, 15 are attached to their respective reflector 12, 16 which in turn, in accordance with the shown embodiment, are connected to the base 30 in any suitable manner. The IR emitters 11, 15 comprise electrical components which are connected to a source of power (not snown) which in accordance with a preferred embodiment comprises a control means (not shown) to control the power installed in the IR emitters 11, 15. As partly apparent from Fig. 2 but above all from Figs 3 and 4 channels 17 are arranged in accordance with this embodiment between the base 30 and the reflectors 12 and 16, respectively, through which channels air supplied by the above-mentioned fan flows m order to prevent the reflectors 12 and 16 from being fouled by particles emanating from the heated zone of the object, such as e.g. particles containing solvent. Fig. 2 also schematically illustrates one end piece 18. The end pieces 18 are intended to be attached to the respective end walls of the heater 1. In accordance with the preferred embodiment of Fig. 2 the middle profile section 5 and the lateral profile sections 3, 4 are formed with apertures 35 for reception therein of screw means (not shown) and the end pieces 18 are formed with corresponding holes 36 for reception of screw means, the end pieces 18 being intended for attachment to the heater 1 by means of screwing. The screw means then secure the lateral profile sections 3 and 4, respectively, to the middle profile section 5. Fig. 5 illustrates one example of a stand 19 pivotally supporting two heaters 1. In accordance with the shown embodiment the stand 19 comprises four steering wheels, making the stand easy to maneouvre also m narrow spaces. As is easily understood, heaters 1 may be attached individually to stands of the kind shown m Fig. 5 or one or several heaters 1 may be attached to differently designed stands, such as e.g. stands or bracket devices arranged for movement along a ceiling-mounted rail. Fig. 6 illustrates schematically the manner in which the inventive heater radiates an edge-delimited zone 20 of an object 21. By means of the IR emitters having an essentially parabolic reflector, the first IR emitter devices 9 and 10 emit essentially concentrated IR radia- tion to the two first parts 22 and 23, respectively, said parts being disposed at two opposed edges 36, 37 of the radiated zone. The parts 22 and 23 are satisfactorily cooled since they are disposed at the outer marginal portions of the radiated zone 20 and because in accord- ance with the shown embodiment they are positioned m close vicinity to and are contiguous with the non- radiated parts of the object 21. By means of the IR emitters having an essentially elliptical reflector, the second IR emitter device 13 and 14 emit essentially evenly distributed IR radiation to a second part 24 comprising the zone disposed intermediate said first two parts 22 and 23, which part 24 is less well cooled than parts 22 and 23, since it is positioned intermediate the latter parts. The IR emitter devices 13 and 14 are adapted to supply IR radiation of lower concentration to the second part 24 than the IR radiation emitted by the IR emitter devices 9, 10 to parts 22, 23. The IR emitter devices 13 and 14 are likewise arranged to emit IR radiation to two marginal portions 38, 39 of the radiated zone 20, said marginal portions 38, 39 being disposed in facing relationship externally of the zone between said first two parts 22 and 23, and, in accordance with the shown embodiment, being contiguous with non-radiated parts of the ob j ect 21 and thus being satisfactorily cooled. The radiation distribution shown schematically in Fig. 6 results n a considerably more even temperature distribu- tion over the heated zone than in the case of prior-art devices. Fig. 6 likewise shows schematically the manner of arranging the secondary reflector 8 for reflecting back IR radiation emanating from the object 21 towards the zone 20 to be heated. Suitable temperature levels for heating and/or curing such materials as putty, fillers, primers and top coats by means of a heater typically are in the range of about 70-140° C. The supplied effect to the heated surface of the object with respect to the materials putty, fillers, primers and top coats typically are within the range 4 - 8 kW/m 2 . The heating and curing times, respectively, typically vary between about 3 and 15 minutes. Empirical testing using the inventive heater 1 has given the following results under these conditions. It has been found that in the normal case the distance from the heater to the object varies between about 0.5 and 0.7 meters to produce a suitable time vs temperature curve. It is likewise preferable that the mutual centre distance between the essentially elliptical reflectors 16 ranges from about 240 to about 360 mm, and preferably is about 300 mm. Preferably the mutual centre distance between the essentially parabolic reflectors 12 range from 373 to 457 mm, and preferably is about 415 mm. A heater configured in conformity with the above-mentioned preferred values gives a secondary reflector area of about 250 x 350 mm 2 between the reflectors 12, 16. The tests have also shown it to be preferable to arrange for the nominal power of the IR emitters having the essentially elliptical reflector 15 to be about twice the nominal power of the IR emitters having the essentially parabolic reflector 11. It is particularly preferred to arrange for the IR emitters having the essentially elliptical reflector 15 to have one IR lamp each which upon maximum IR radiation of the object, considering the above requirements on temperature, time and so on, has a nominal power ranging from 1.8 to 2.2 kW, and preferably is about 2 kW. It is likewise preferable that the IR emitters having the essentially parabolic reflector 11 have one IR lamp each which upon maximum IR radiation of the object, considering the above requirements on temperature, time, and so on, has a nominal power ranging from 0.9 to 1.1 kW, and preferably is about 1 kW. In the process of the testing, using the above preferred values, a heater has been provided which has a base 30 of 0.4 x 0.5 m 2 and which produces a heated area having an essentially even temperature distribution of 1.0 x 1.1 m 2 . This means that the inventive heater produces a heated area having an essentially even temperature distribution that is about 5 times the area of the base 30, which is a considerable technical improvement over the comparatively large heaters designed in accordance with the prior art. In accordance with the present invention a heater 1 thus is provided which possesses small dimensions compared w th the prior art and therefore is easily maneuverable . In addition thereto, the unique structure of the inventive IR emitter unit 7 produces a more even temperature distribution over the heated zone 20 of the object 21 than is obtainable with prior-art devices. It should be appreciated that some deviations from the described embodiments are possible. For instance, it would be quite possible to achieve essentially the same even temperature distribution by using other combinations of configuration of the essentially elliptical and essentially parabolic reflectors, the centre distances between the reflectors, the distance from the object to the base of the heater, and the nominal power of the IR emitters. All varieties and modification encompassed by the basic inventive idea should, however, be within the scope of the appended claims.

Claims: CLAIMS 1. A heater (1) for heating/and or curing a substance, such as a putty, filler, primer and top coat material, which substance is applicable onto an object (21), e.g. in the form of a substrate of a thin metallic material, such as Fe and Al sheet-metal, said heater (1) comprising a body (2) fitted with an IR emitter unit (7), c h a r a c t e r i z e d in that the heater (1) is adapted to the zone (20) to be heated in the object (21), and in that the IR emitter unit (7) has at least one first IR emitter device (9, 10) which is arranged to supply a higher-concentration IR radiation to at least a first part (22, 23) of the zone (20) having satisfactory cooling, as well as at least one second IR emitter device (13, 14) which is arranged to supply a lower-concentration IR radiation to at least a second part (24) of said zone (20) having less satisfactory cooling than the first part (22, 23), in order to produce an essentially even temperature distribution across said zone (20) . 2. A heater (1) as claimed in claim 1, c h a r a c t e r i z e d in that said first IR emitter device (9, 10) comprises at least one IR emitter (11) having an essentially parabolic reflector (12), which is arranged to emit concentrated IR radiation to said first part (22, 23) . 3. A heater (1) as claimed in claim 1 or 2, c h a ra c t e r i z e d in that said second IR emitter device (13, 14) comprises at least one IR emitter (15) having an essentially elliptical reflector (16), which is arranged to emit essentially evenly distributed IR radiation to said second part (24) . 4. A heater as claimed in claim 2 in combination with claim 3, c h a r a c t e r i z e d in that the heater (1) is arranged to radiate a zone (20) of the object (21), that the object (21) is satisfactorily cooled at least at two marginal opposed portions (36, 37) of said zone (20), and in that the body (2) has an essentially rectangular base (30), which is fitted with at least one IR emitter (11) having an essentially parabolic reflector (12) positioned adjacent and along each side of a first pair of opposed sides (31, 32) of the base (30), said IR emitters (11) being arranged to radiate the surface in the area of each corresponding opposed marginal portion (36, 37) of the zone (20). 5. A heater (1) as claimed in claim 4, c h a r a c - t e r i z e d in that the area positioned between the marginal portions (36, 37) of the zone (20) comprises a second part (24) being less satisfactorily cooled, that the base (30) also has at least one IR emitter (15) comprising an essentially elliptical reflector (16) in the vicinity of and along each side of a second pair of the other opposed sides (33, 34) of the base (30), said IR emitters (15) being arranged to emit essentially evenly distributed IR radiation across said area. 6. A heater (1) as claimed in any one of claims 4-5, c h a r a c t e r i z e d in that it comprises a secondary reflector (8) positioned at the base (30) intermediate the IR emitters (11, 15), said secondary reflector arranged to reflect back to the zone (20) to be heated, IR radiation emanating from the object (21) . 7. A heater (1) as claimed in any one of claims 2-6, c h a r a c t e r i z e d in that the nominal power of the IR emitters (15) having an essentially elliptical reflector (16) is approximately twice the nominal power of the IR emitters (11) having an essentially parabolic reflector (12) . 8. A heater (1) as claimed in any one of claims 1-7, c h a r a c t e r i z e d in that the effect supplied to the heated zone (2o) of the object (21) is between about 4 and 8 kW/m 2 , the heater (1) preferably being adapted for use at a distance from the object (21) of between 0.5 and 0.7 m. 9. A heater (1) as claimed in any one of claims 4-8, c h a r a c t e r i z e d in that the IR emitters (15) having an essentially elliptical reflector (16) has one IR lamp each of a nominal power in the range of 1.8 to 2.2 kW, preferably about 2 kW, that the mutual centre distance between the reflectors (16) of said IR emitters (15) is in the range of 240 to 360 mm, preferably about 300 mm, that the IR emitters (11) having an essentially parabolic reflector (12) has one IR lamp each of a nominal power in the range of 0.9 to 1.1 kW, preferably about 1 kW, and in that the mutual centre distance between the reflectors (12) of the latter IR emitters (11) is in the range of 373 to 457 mm, preferably about 415 mm, the space between the IR emitters (11, 15) being occupied by the secondary reflector (8). 10. A heater (1) as claimed in any one of claims 2-9, c h a r a c t e r i z e d in that the essentially elliptical reflector surface at least partly essentially follows a curve that may be mathematically expressed by x 2 /30 + y 2 /22.5 = 1.0 and in that the essentially parabolic reflector surface at least partly essentially follows a curve that may be mathematically expressed by x 2 = 34.7y, x and y being expressed in a rectilinear coordinate system.

Inventors: LUNDIN KENNETH, LUNDIN, KENNETH
Applicants: INFRAROEDTEKNIK AB, LUNDIN KENNETH, LUNDIN, KENNETH
Application year: 1997
Main classification: F26B23
IPC codes: B05D3, F26B3