GB2485352A

GB2485352A - Infra-red heating apparatus

Info

Publication number: GB2485352A
Application number: GB201018903A
Authority: GB
Inventors: Matthew Grossett
Original assignee: IGNIS RED Ltd
Current assignee: IGNIS RED Ltd
Priority date: 2010-11-09
Filing date: 2010-11-09
Publication date: 2012-05-16
Also published as: GB201018903D0

Abstract

Infra-red heating apparatus includes an infra-red emitter formed of a plurality of filaments electrically connected in series. An input voltage may be selectively applied across any number of filaments. The input voltage can be applied between the ends of the series or to one end and to a selected voltage taps A,B,C,D located between adjacent filaments. The filaments can be identical or dissimilar so that when applied to plural filaments the voltage is divided either equally or unequally between them. The filaments can have identical infrared emission characteristics issuing an identical emission spectrum or have dissimilar spectral emission characteristics. The input voltage can be selectively applied in order to adjust an infra red spectrum to longer or shorter wavelengths. The voltage applied to an individual filament can thus be varied with a consequential shift in the emission spectrum of the filament while retaining a useful power output from the emitter as a whole. The infra-red emitter can be used to dry paint and can comprise a support (fig 4, 3) and a controller (fig 4, 5) to select the filaments to which the input voltage is applied.

Description

I

Infra-red Heating Apparatus

Field of the invention

This invention relates to an infra-red heating apparatus and to an infra-red emitter forming part of such an apparatus.

Background of the invention

Infra-red emitters are used in infra-red heating apparatus and have many advantages over conventional heating methods such as warm air convection heating. With the infra-red emitter converting nearly all the supplied electrical energy to infra-red the item * to be heated receives nearly all of the energy used without requiring recirculation fans * and inefficient burners or heating systems.

* A particular advantage, of infra-red heaters is that they allow the heat energy to be targeted and therefore they are used in a wide range of applications where localised heating of a target area is required. For example, infra-red heaters may be used for drying a painted surface, heat-treating or curing a surface where only a part of the surface requires heating. A simple example of such a case is in the automotive industry where only a part of a car is being painted -for example following a repair -where S...

heat is provided only where it is needed and only for as long as is necessary. Similar uses for infra-red emitters may be foynd in aerospace and other industries.

* Infra-red heaters may also b,e used where localised heating is preferred in order to avoid thermal damage to other part's that do not require heating.

* *. 25 :.: Conventionally an infra-red emitter comprises a filament received within a tube. A * voltage is applied across the filament in order to generate infra-red emissions. Typical * materials for the filament include carbon and various metals. Normally the filament will be encased within a tube for protection, and quartz glass is often used as it provides low thermal resistance. A reflective surface may be provided -either within the tube or outside -which serves to. provide greater directionality to the emitted infra-red energy and allows the heat to be better targeted.

It is important to note that the filament does not of course emit infra-red radiation at a single wavelength but that there is a spectrum of wavelengths. The shape of this spectrum -and the part of the spectrum where the major part of the emitted infra-red energy is located -will depend on the chosen design characteristics of the infra-red emitter including in particular the choice of filament material, the physical dimensions of the filament and the applied voltage. Conventionally therefore infra-red emitters are designed and sold as being suited for emitting in particular wavelengths: notably short wave infra-red emitters where most of the energy (greater than 60%) is provided at wavelengths less than 2 microns, and medium wave emitters where the major part of the energy is emitted at wavelengths between 2 and 4 microns.

The frequency at which the major part of the energy is emitted is important because some applications require the energy to be at particular ranges of wavelengths. For example, the absorption spectrum of water peaks at around 3 microns so if the infra-red emitter is being used for example to dry water based paints then it is better to use a medium wave emitter than a short wave emitter. For other applications short wave * 15 * infra-red radiation may be preferred. Generally, it is necessary to have a range of emitters available each designed to generate peak emissions in a different part of the spectrum. However, this is costly as it requires a user to have multiple emitters.

Prior art

To provide a single infra-red emitter capable of emitfing either short wave or medium wave infra-red radiation it is known simply to provide two (or more) separate quartz 0**�e* * tubes each provided with a filament designed to generate infra-red radiation with a desired, spectrum and then a user simply switches between tubes depending on whether they want short wave or medium wave radiation. W02004/049760A1 and US * 25 2001/0046379A1 describe examples of such designs. While effective in achieving the abilityto switch between short and medium wave radiation requiring separate emitters increases the cost.

One method of switching the frequency of the infra-red radiation without changing the physical characteristics of the filament and tube is simply to change the applied voltage. Reducing the voltage applied to the filament shifts the infra-red emission spectrum towards medium wavelengths (ie to lower frequencies and less energy), increasing, the voltage applied shifts the infra-red emission spectrum to shorter wavelengths (higher frequency, higher energy).

35, * . However, the problem with simply reducing the applied voltage to shift to longer wavelengths is that in doing so there is a disproportionate loss in output power. For example, with a 10% reduction in input voltage there is typically a 15% reduction in output power. A 50% reduction in input voltage results in a 70% reduction of output power -in other words 50% of the original input voltage results in only 30% of the original output* power. Simply changing the input voltage to change the emission spectrum is therefore an inefficient option.

Summary of the invention

According to the present invention there is provided an infra-red.emitter comprising a plurality of filaments connected in series, wherein an input voltage may be selectively applied across any ntimber of said filaments.

In preferred embodiments of the invention a first filament in said series and a last filament in said series are each provided at one end with means for applying an input * voltage, and wherein voltage taps are provided between at least some adjacent filaments, whereby the input voltage may be applied either to the said ends of the first and last filaments, or may be applied to the said end of the first or the said end pf the last filament and to a selected voltage tap. Preferably there are n filaments where n is an integer that is 2 or.greater, and there are n-I voltage taps.

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* Preferably the filaments are electrically identical such that if a voltage is applied across a plurality of said filaments the voltage is divided equally between them. Alternatively at * least some of the filaments may be electrically dissimilar such that if a voltage is ****** * 25 applied across a plurality of the filaments the voltage is divided unequally between * ** +1*.

* * * tiuem. **. * *.***

* Preferably the filaments have identical infra-red emission characteristics such that when a given voltage is applied to a plurality of the filaments each filament emits an identical infra-red spectrum. Alternatively at least some of the filaments have dissimilar * infra-red emission characteristics such that when a given voltage is applied to a plurality of said filaments said filaments emit dissimilar infra-red spectra.

The invention also extends to an infra-red heating apparatus including an infra-red emitter as defined above. * Such an infra-red heating apparatus may further comprise control means for controlling operation of said emitter, the control means including selector means for selecting the filaments of the emitter to which the input voltage is to be applied. Means for supporting the infra-red emitter in a desired position may also be provided.

According to the present invention there is also provided a method of heating a surface using infra-red radiation, comprising: providing an infra-red heating apparatus including an infra-red emitter comprising a plurality of filaments connected in series, positioning * said emitter such that infra-red radiation emitted by said emitter is directed towards the surface to be heated, and selectively applying an input voltage across any number of * said filaments to adjust an infra-red emission spectrum to longer or shorter wavelengths.

According to the present invention there is further provided a method of adjusting the emission spectrum of an infra-red emitter, comprising providing a plurality of filaments connected in series, and selectively applying an input voltage across any number of said filaments to adjust an infra-red emission spectra to longer or shorter wavelengths.

Brief description of the drawings

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- * Fig.1 is a perspective general view of an infra-red emitter, Fig.2 is a circuit diagram of the emitter filaments according to a first embodiment of the * invention, S.....

* 25 Fig.3 is a circuit diagram of the emitter filaments according to a second embodiment of 1:'> the invention, and Fig.4 is a circuit diagram of the emitter filaments according to a second embodiment of the invention. *

Detailed description of preferred embodiments

Referring firstly to Fig.1 there is shown therein an example of a typical infra-red heating apparatus that may be used to provide localised heating. In Fig.1 the apparatus I is shown providing localised heating to the front wing of a car 2 for example for drying paint following a repair to the front wing but it will be understood that this is purely exemplary and the heating apparatus could be used for many other purposes. The * heating apparatus I includes an emitter unit 3 that is supported on a vertical support member 4 50 that the vertical position of the emitter unit 3 óan be adjusted. The emitter * unit 3 is mounted on the support member 4 by an adjustable bracket so that the angle of the emitter unit 3 may also be adjusted. Also connected to the support member 4 -though it may also be provided elsewhere -is a control unit 5 provided with the operational controls for the heating apparatus.

The emitter unit 3 will comprise an elongate infra-red emitter 6 that will be described in more detail below. The emitter 6 is located within a housing 7 such that the emitter may be generally parallel to a surface on which the infra-red heating apparatus stands, or it may be vertical to such a surface, or the emitter unit 3 may be adjustable so that the axis of the elongate infra-red erhitter 6 may be moved between horizontal and vertical configurations as required. An inner rear surface of the housing 7 may be provided with a reflective surface such that infra-red radiation emitted may be directed in a. particular direction. + As described the infra-red heating apparatus is generally conventional. However, in a conventional infra-red heating apparatus there will be either a single infra-red emitter or a number of independent emitters that can be selectively activated by a user. In contrast Fig.2 shows an embodiment of the invention with reference to a schematic circuit diagram of the infra-red emitter. en*s* * *

As can be seen from Fig.2 in an embodiment of the invention the emitter 6 comprises two filaments 20, 21 that are electrically connected in series. The filaments may be * 25 * made of any conventional material and in any conventional manner. They may be provided together within a single quartz tube S or may be provided in separate tubes.

Each filament 20, 21 has a respective end A, C which may form one terminal to which an input voltage may be connected, and a voltage tap B is provided between the two filaments 20, 21. * * This single emitter 6 may be operated in two different modes to produce different * output infra-red spectra.

* Firstly, the full input voltage (eg a 240V mains supply) can be applied across A-B. In * 35 * this configuration filament 21 is not used and instead filament 20 emits infra-red radiation at near 100% power with a frequency spectrum that will depend on the particular characteristics of the filament. For the sake of illustration in this embodiment it is assumed that filament 20 is designed such that when operated at full power it emits predominantly at short wavelengths.

Alternatively, the full input voltage V1, can be applied across A-C so that both filaments 20, 21 are energised. Assuming that the two filaments are identical -or at least have identical electrical properties -then the voltage applied across each filament will be VI2. This reduction in the voltage applied to a particular filament will mean that the emission spectrum for that filament is shifted towards longer wavelengths so that there is a higher content of medium wavelengths.

As is known when the voltage applied to a filament is reduced then the power output from that filament is also reduced. In particular as indicated above a 50% reduction in 15:the applied voltage means that the power output from a single filament may be reduced to 30% of the power emitted by a single emitter when the full applied voltage is applied across that emitter. However, in the embodiment of Fig.2 because there are two filaments the total power output is approximately 60% (experimental results suggest nearer to 70%) of the output from a single filament to which the full input voltage is applied. I...

* Fig.3 illustrat!s an embodiment in which three identical filaments 30, 31, and 32 are provided connected electrically in series. The first and last filaments in the series - * filaments 30 and 32 -are provided with respective ends A, D which may form ** * * ** * . 25 respective terminals to which an input voltage may be connected,.and voltage taps B and C are provided respectively between the two filaments 30, 31 and 31., 32. In this embodiment there are three alternate modes of operation: V1, may be applied across (1) A-B, (2) A-C and (3) A-D. The first and second modes correspond to the two modes of the embodiment of Fig.2 since in neither case is filament 32 energised and thus will.

not be described fUrther. in the third mode, however, all three filaments are energised and assuming again that they are identical the voltage applied to each individual filament is V1d3 then compared with the first and second modes where respectively 100% and 50% of the applied voltage is provided to an individual filament, the emitted infra-red spectrum is shifted still further towards medium to long wavelengths but at the price of each filament having an output power of only about 15% compared with the first moda However because all three filaments are energised the total power output is about 45%.

Fig.4 illustrates an embodiment in which four identical filaments 40, 41, 42 and 43 are provided connected electrically in series. The first and last filaments in the series -filaments 40 and 43 -are provided with respective ends A, E which may form * respective terminals to which an input voltage may be connected, and voltage taps B, C and D are provided respectively between the two filaments 40, 41, the two filaments 41, 42 and the two filaments 42, 43. In this embodiment there are four alternate modes * 10 of operation: V may be applied across (1) A-B, (2) A-C, (3) A-D and (4) A-E. The first, second and third modes correspond to three modes of the embodiment of Fig.3 since in none of these modes is filament 43 energised and thus will not be described further.

In the fourth mode, however, all four filaments are energised and assuming again that they are identical the voltage applied to each individual filament is V1I4 and compared with the first, second and third modes where respectively 100%, 50% and 33% of the applied voltage is provided to an individual filament, the emitted infra-red spectrum is shifted still further towards medium to long wavelengths but at the price of each filament having an output power of only about 9% compared with the first mode.

However because all four filaments are energised the total power output is about 36%.

It will be understood that in any of the above embodiments the control unit 5 may be * provided with a selector switch that may be operated by a user to select which mode is operated by applying the input voltage between selected points. The switch may have settings labelled -for example -"short wavelengths", "short/medium wavelengths", ** ****.

* 25 * "medium wavelengths", "mediumflong wavelengths", or the selector switch may be labelled with the intended uses to which the emitted wavelengths are associated -for example a selling for drying water-based paints or coatings.

These embodiments may be generalised to a situation where there are n filaments (n being an integer that is 2 or greater) in series and in a given operational mode the input voltage is applied across m filaments where in is an integer from I to vi. It is assumed that all filaments are identical. The applied voltage is V1,, and the power emitted by an individual filament is Pmax when V is applied to a single filament. The power Pv emitted by a single filament at a given voltage V where V is less than V1 is Pv = 1(V)Pmax where 1(V) is a factor between 0 and I that decreases as V decreases though not necessarily in a linear fashion. Generally speaking P will decrease faster than V but the particular characteristics of the power/voltage relationship will depend on the characteristics of the filament.

In.an embodiment where there are ri identical filaments and the embodiment is operated in a mode where the input voltage is applied across m filaments the total emitted power PtothI = m x f(Vinim)Pmax. This will still be less than Pmax because the factor f(V) decreases faster than the applied voltage, but this is mitigated by the presence of the factor m, ie although the power output by a single filament is reduced -perhaps substantially -the power is being emitted by multiple emitters.

Thus -at least in preferred embodiments -the present invention provides an infra-red emitter in which by a simple selection of the number of filaments to which the input voltage is applied the spectrum of the emitted radiation may be shifted to longer wavelengths. Applying the input voltage over increasing number of filaments shifts the * * spectrum to longer wavelengths, and while in doing so the power input from each* individual filament may fall sharply this is mitigated by the number of filaments that are being ënergised.

In the above embodiments and examples it is assumed for the ease of explanation that all emitters are identical. They may be identical in the sense that if the input voltage is * applied across multiple filaments then the voltage is divided across them equally -ie the filaments have an equal resistance or inductance -and/or they may be identical in * * * the sense that for a given applied voltage across them they will each produce identical *S**** * 25 emitted infra-red spectra. However, the filaments may be varied in either of these respects (either independently or together) to allow further variations and refinements in theemitted infra-red spectrum. For example, while the filaments may be identically constructed and of the same material, they may have different lengths such that when the input voltage is applied across multiple filaments it is not divided equally and different filaments will emit different infra-red spectra. Additionally or alternatively, different filaments may be made of different materials such that even if the same voltage is applied across them then they will emit different spectra. Such variations allow for the possibility of further control of the infra-red spectrum emitted by the * * emitter. * 35. * .

Claims

CLAIMS: I. An infra-red emitter comprising a plurality of filaments connected in series, wherein an input voltage may be selectively applied across any number of said filaments.
2. An infra-red emitter according to claim I wherein a first filament in said series and a last filament in said series are each provided at one end with means for applying an input voltage, and wherein voltage taps are provided between at least some adjacent filaments, whereby the input voltage may be applied either to the said ends of the first and last filaments, or may be applied to the said end of the first or the said end of the last filament and to * a selected voltage tap.

* 15
3. An infra-red emitter according to claim 2 wherein there are n filaments where n is an integer that is 2 or greater, and there are n -I voltage taps.
4. An infra-red emitter as claimed in any of claims I to 3 wherein said filaments are electrically identical such that if a voltage is applied across a plurality of said filaments the voltage is divided equally between them. S..S S55

*
5. An infra-red emitter as claimed in any of claims I to 3 wherein at least some of said filaments are electrically dissimilar such that if a voltage is applied across a plurality of said filaments the voltage is divided unequally between * 25 them. * S. * S * **5 *

*
6. An infrared emitter as claimed in any of claims Ito 3 wherein said filaments have identical infra-red emission characteristics such that when a given voltage is applied to a plurality of said filaments each filament emits an identical infra-red spectrum.
7. An infra-red emitter as claimed in any of claims I to 3 wherein said filaments have dissimilar infra-red emission characteristics such that when a given * voltage is applied to a plurality of said filaments said filaments emit dissimilar infra-red spectra.
8. An infra-red emitter substantially as hereinbefore described with reference to the accompanying drawings.
9. An infra-red heating apparatus including an infra-red emitter as claimed in any preceding claim.
10. An infra-red heating apparatus as claimed in claim 9 further comprising * control means for controlling operation of said emitter, said control means including selector means for selecting the filaments of the emitter to which the input voltage is to be applied.
11. An infra-red heating apparatus as claimed in claim 9 or 10 further comprising means for supporting the infra-red emitter in a desired position.
12. An infra-red heating apparatus substantially as hereinbefore described with * reference to the accompanying drawings.
13. A method of heating a surface using infra-red radiation, comprising: providing an infra-red heating apparatus including an infra-red emitter comprising a plurality of filaments connected in series, positioning said emitter such that infra-red radiation emitted by said emitter is directed *****.* * towards the surface to be heated, and selectively applying an input voltage * across any number of said filaments to adjust an infra-red emission * spectrum to longer or shorter wavelengths.

****** * 25
14. A method of adjusting the emission spectrum of an infra-red emitter, S.. I comprising providing a plurality of filaments connected in series, and selectively applying an input voltage across any number of said filaments to adjust an infra-red emission spectra to longer or shorter wavelengths.
15. A method of heating a surface using infra-red radiation substantially as * hereinbefore described with reference to the accompanying drawings. 11*
16. A method of. adjusting the emission spectrum of an infra-red emitter substantially as hereinbefore described with reference to the accompanying drawings. . * * ***.S * S5.55.. . * S S. * 5. . * .. . . . * . . **.* S S.. S.S * S.