WO2002095790A2

WO2002095790A2 - Electromagnetic radiation lamp

Info

Publication number: WO2002095790A2
Application number: PCT/FR2002/001664
Authority: WO
Inventors: Christian Lumpp
Original assignee: Lumpp & Consultants
Priority date: 2001-05-23
Filing date: 2002-05-17
Publication date: 2002-11-28
Also published as: WO2002095790A3; AU2002313066A1; FR2825190B1; FR2825190A1

Abstract

The invention concerns a lamp, for instance a mercury UV lamp, comprising, at each of its ends, an electrode chamber (6), whereof the internal diameter is larger than that of a longitudinal transmitter tube (1) with which it communicates. The output zone of the electrode chamber is spherical, it centre of curvature (C) being arranged on a front zone, covered by a filament (3b), a support rod (4) of an electrode (2) housed in the electrode chamber. The infrared rays (Ri) transmitted by one exposed front end of the support rod are reflected (Rr) towards the rear of the electrode by a reflecting material (7) covering the chamber. Additionally, the flow rate of the air cooling the tube (1) is modulated proportionally to the electric voltage at the lamp terminals. In case of temporary pause of the installation, this ensures uniform and longitudinal condensation of mercury in the tube (1), without formation of mercury droplets in the electrode chambers.

Description

Electromagnetic radiation lamp

Technical field of the invention

The invention relates to an electromagnetic radiation lamp comprising an electrode disposed at each of the two ends of a longitudinal emitter tube, filled with gas, each electrode consisting of at least one filament wound around a support rod having a front end. uncovered and fixed at a rear end to a connection end of the lamp connected to an electrode chamber in which the electrode is housed, the electrode chamber being covered with a reflective material and having an internal diameter greater than the internal diameter of the emitter tube with which it communicates, at its front part, through an outlet orifice of an outlet area

State of the art

Electromagnetic radiation lamps, in the ultraviolet, visible and / or infrared, are commonly used, in particular in the field of graphic arts, for applications such as the drying of inks, varnishes or adhesives, radical or cationic type, on supports such as paper, cardboard, plastic or textile.

WO-A-9801700, for example, describes an ultraviolet emitter in the form of a mercury lamp with electrodes disposed at both ends of a longitudinal emitting tube, said to be discharge, filled with gas and provided with side reflectors. A plasma arc is formed between the two electrodes by mercury or any other metallic iodide. In this document, each electrode can be placed in an electrode chamber, wider than the emitter tube and covered with a reflection material. The plasma beam of UV radiation may have a very small radiating section, for example of the order of 10 mm ² .

When a flat substrate, constituted for example by paper or by a thermosensitive plastic film, is irradiated by a lamp with ultraviolet radiation comprising reflectors, in particular elliptical reflectors, for example in a drying device, the interruption, even momentary , movement of the substrate tends to cause a burn line thereon. This is linked to the fact that the lamp emits radiation not only in the ultraviolet but also in the infrared, the calorific power of the infrared radiation being close to 50% of the total power of the lamp. The extinction of the lamp does not eliminate this problem, the thermal inertia of the tube causing an emission of infrared radiation for a certain time after its extinction. To avoid the risk of fire, known devices include either reflectors which close on themselves by hiding the lamp, or a mechanical element or cover ("shutter") interposed between the lamp and the irradiated substrate. Such devices are cumbersome and thermodynamically delicate. They also cause excessive expansion of the irradiating enclosure, which simultaneously makes it necessary to reduce the power of the ultraviolet lamp by approximately half of its value. It should be noted that a greater reduction in the power of the lamp would extinguish the plasma arc. In all cases, the lamp is subjected to a cooling cycle of several minutes and restarting the lamp at its operational level requires several minutes, resulting in a significant loss of productivity.

Subject of the invention

The object of the invention is to provide an electromagnetic radiation lamp which does not have the drawbacks of known devices and which has improved performance, in particular during the temporary or total shutdown of an installation comprising such lamps.

According to the invention, this object is achieved by the fact that the outlet zone of the electrode chamber has a substantially spherical shape, with a predetermined radius of curvature and a center of curvature disposed substantially on a front region of the rod. support, in the part on which the filament is wound, so that the infrared radiation emitted by the exposed front end of the support rod and reflected by the reflection material covering the exit area of the electrode chamber are directed towards the rear of the electrode.

According to a development of the invention, the lamp comprising cooling means, the lamp is associated with means for modulating the flow rate of a cooling fluid circulating along the emitter tube in proportion to the electric voltage applied across the electrodes of the lamp. Brief description of the drawings

Other advantages and characteristics will emerge more clearly from the description which follows of particular embodiments of the invention given by way of nonlimiting examples, and represented in the appended drawings, in which:

FIG. 1 illustrates, in schematic form, an electromagnetic radiation lamp according to the prior art.

FIG. 2 represents in more detail, one end of a lamp according to the prior art comprising an electrode chamber.

Figure 3 shows one end of a lamp according to the invention.

FIG. 4 illustrates, in more detail, the reflection of the radiation in an electrode chamber of a lamp according to FIG. 3.

FIG. 5 represents, in cross section, a particular embodiment of an electromagnetic radiation device of known type, in which the invention can be implemented.

FIG. 6 illustrates a circuit for controlling the ventilation of a lamp according to the invention. Description of particular embodiments.

As shown in FIG. 1, an electromagnetic radiation lamp, and more particularly an ultraviolet radiation lamp, conventionally comprises a longitudinal emitter tube 1_ with an electrode 2 at each of its ends. The tube is generally a transparent quartz tube, with a diameter of 18 to 25mm, with a length which can range from a few centimeters to several meters, filled with an ionizing gas under a pressure of the order of a few bars. The gas may, for example, be a mixture of argon or xenon and mercury, mercury iodide or any other metallic iodide. When a sufficient alternating electric voltage, conventionally of the order of 12V / cm, is applied between the electrodes, a luminous plasma arc, of substantially cylindrical shape, forms in the tube, between the electrodes and generates the desired ultraviolet radiation.

Each electrode 2 is conventionally constituted by at least one filament 3, for example made of tungsten, wound around a support rod 4 emitting electrons. In FIG. 1, each electrode has two filaments in superimposed windings. The front end of the support rod 4, oriented towards the central part of the tube, is uncovered while its rear end is fixed to a connection end 5 of the lamp. The tungsten electrodes are so-called hot electrodes which, in operation, are brought to a high temperature, for example 2000 ° C.

The lamp end shown in FIG. 2, described in the document WO-A-

9801700, has an electrode chamber 6 in which is housed the electrode 2. The electrode chamber 6 has an internal diameter greater than internal diameter of the transmitter tube with which it communicates. For example, a tube 1 of 8mm in diameter is connected to an electrode chamber 6 of 13mm in diameter. The length of the electrode chamber 6 corresponds to the length of the milky zone which becomes opaque during operation around the electrode, that is to say approximately 20mm. It is thus possible to obtain an intense plasma arc of smaller section (3 mm in diameter, for example), that is to say having better energy efficiency. It is then possible to increase the line voltage between the electrodes, for example up to values of the order of 30V / cm, which promotes better concentration of the ultraviolet plasma arc while maintaining a low current , of the order of 5A.

To maintain a certain temperature at the level of the electrode, the electrode chamber 6 is, like the end of the tube surrounding the electrode 2 in FIG. 1, covered with a reflection material 7.

The electrode chamber 6 according to the invention, shown in FIG. 3, differs from the known electrode chamber, according to FIG. 2, by its geometric shape. It has a reduced length, while having a radius of curvature for connection to the tube 1. In fact, the outlet zone of the chamber 6, which communicates through an outlet orifice 8 with the interior of the tube 1, has a substantially spherical shape. Its radius of curvature r and its center of curvature C are such that the infrared radiation emitted by the uncovered front end of the support rod and reflected by the reflection material 7 are directed towards the rear of the electrode. The center of curvature C is disposed substantially on a front zone of the support rod 4, in the part on which the filament is wound. This preferably comprises, as in FIG. 2, two filaments. A first filament 3a is wound over almost the entire length of the rod 4 located inside the electrode chamber and only a small part of the rod 4, exposed, protrudes forward, out of the filament 3a. A second filament 3b is superimposed on about the front half of the first filament. The center of curvature C is located on the front part of the support rod on which the second filament 3b is wound, preferably about 1mm from the front end of the filament 3b.

In the embodiment of FIG. 3, the radius of curvature r of the outlet zone of the electrode chamber 6 is greater than or equal to approximately 6mm, for an internal diameter of the tube of the order of 6mm and a thickness of the wall of the chamber on the order of a millimeter. For example, the support rod projects forward about 2mm beyond the winding 3b and the center of curvature C is located about 3mm from the free end of the rod 4, c ' that is to say 1 mm from the front end of the filament 3b.

The electrode 2, brought to high temperature, essentially emits infrared radiation in the electrode chamber. In the electrode chamber of FIG. 2, the temperature of the front end of the electrode, that is to say of the exposed front part of the rod 4 is significantly higher, for example of the order 2000 ° C, that the temperature of the spiral rear part of the electrode, for example of the order of 500 ° C, near the first filament 3a. The quartz constituting the wall of the electrode chamber being naturally opaque to infrared radiation emitted at low temperature, only the infrared radiation emitted by the uncovered front part of the rod passes through it and is reflected by the reflection material 7. The reflection material is a material resistant to a temperature of approximately 900 ° C., while adhering to quartz. The reflection coefficient of this material is of the order of 90% for the wavelengths of infrared radiation to be reflected towards the rear of the electrode. For example, the materials that can be used are gold, platinum, zirconium oxide, etc.

The geometric shape of the electrode chamber 6 in FIG. 3 therefore makes it possible to reflect towards the rear of the electrode 2 the infrared radiation emitted by the front part of the electrode. The uncovered front end of the support rod constitutes a radiating cylinder emitting at 2000 ° C. the entire outer surface of which is radiant. This uncovered front end emits infrared rays at all points on its surface, which are directed onto the reflective spherical concave front surface of the electrode chamber.

As shown in FIGS. 3 and 4, an incident ray Ri crosses the wall of the chamber 6, then is reflected by the reflection material 7. The reflected ray Rr, after having crossed the wall of the chamber in the opposite direction, is directed towards the back of the electrode 2. The rays Ri and Rr make respectively angles ai and ar, equal, with an axis of symmetry S passing through the center of curvature C. The difference in refractive index of the two crossed media, gas in the electrode and quartz chamber of the wall, is such that the return to the rear of the infrared radiation is accentuated.

Thanks to the location of the center of curvature C in the part of the support rod on which the filament is wound, any ray emitted by a point any of the exposed front end of the support rod, towards the internal surface of the electrode chamber, is returned towards the rear of the electrode, i.e. on the surface of the filament 3 in the embodiment of FIG. 3. Only the rays emitted in the direction of the orifice 8 are not reflected.

The geometric shape of the electrode chamber according to the invention makes it possible to improve the performance of the lamp, in particular during the temporary or total shutdown of an installation comprising such a lamp. In fact, in the case of a mercury lamp, the return towards the rear of the electrode of infrared radiation emitted by the uncovered front end of the support rod makes it possible to ensure the evaporation of the mercury around and at the back of the electrode even when the lamp power is reduced in the event of a temporary shutdown of the installation.

It will be recalled that, conventionally, in a UV lamp whose tube is filled with a mixture of argon and mercury, mercury whose melting point is close to 350 ° C., or any other doping metal iodide intended for ensure the conductivity of the gas, is in a liquid or solid state before using the lamp. Argon (melting point of the order of -30 ° C) firstly has a priming function for the plasma arc.

The various operating phases of such a lamp are as follows: - a warm-up phase, - a stand-by phase during which the installation is ready to operate, but where the power is reduced, - a nominal operating phase, during which the plasma arc formed between the electrodes generates the desired ultraviolet radiation,

- a momentary stop phase, corresponding to the waiting phase,

- a total stop phase.

In a lamp comprising an electrode chamber according to FIG. 2, it can be noted, in certain cases, the formation of mercury droplets in the region of the electrode, in particular during the waiting, momentary stopping and d '' total stop. In known lamps, the temperature at the rear of the electrode is generally not sufficient to ensure the vaporization of these mercury droplets. The accumulation of mercury droplets in the region of electrode 2, and more particularly behind it, thus gradually leads to an increasing deficit in the quantity of mercury present in the emitter tube 1 and increasing inertia during the transition to nominal phase. The intensity of the current in the lamp being, for a given voltage, a function of the mercury charge in the plasma arc, this also leads to a progressive reduction in the power, and therefore in the efficiency, of the lamp.

The geometry of the electrode chamber according to the invention makes it possible to recover the heat energy, hitherto unused, contained in the infrared radiation emitted by the front part of the electrode to heat the rear part of the electrode and prevent the formation of mercury droplets in this zone during the standby phases, that is to say during the standby and momentary stop phases, by ensuring the evaporation of residual mercury droplets which would have deposited, during a total stop of the installation, on the spiral filament of the electrode whose surface temperature would be lower than the melting temperature of mercury.

According to a development of the invention, a further improvement in the performance of the lamp, which is more particularly linked to its operation during the standby phases, can be obtained by appropriate regulation of the lamp cooling device and, more particularly, ventilation of the emitter tube, while eliminating any mechanical sealing of the lamp.

A device for cooling a lamp is, for example, described in the document WO-A-0118447 which places more mainly the emphasis on the means for cooling an electromagnetic radiation lamp comprising parabolic static reflectors, more particularly elliptical . Figure 5 shows, in cross section at the emitter tube 1, a particular embodiment of a lamp according to this document, in which the invention can be implemented.

The lamp described in the aforementioned document is mounted in a support structure 9 in which an intermediate wall 10 delimits on the one hand a longitudinal pipe 1 1, intended for the circulation of a cooling fluid, more particularly for the circulation of air , and secondly a housing 12, open on one side, for the lamp. The intermediate wall 10 has orifices 13 ensuring the circulation of the cooling fluid between the longitudinal pipe 11 and the housing 12. Two lateral reflectors 14, static, are arranged on either side of the longitudinal tube 1 in the housing 12. As shown in FIG. 5, the cooling fluid coming from the longitudinal pipe 11 circulates both in a corridor of cooling 15, located between the reflectors 14 and the external walls of the housing 12, and, homogeneously, around and along the tube 1, by means of a longitudinal slot 16 separating the side reflectors 14 and parallel to the tube axis 1.

According to the invention, to allow the removal of any mechanical sealing, the flow rate of the cooling fluid is regulated so as to be proportional to the electrical voltage applied between the electrodes 2.

An electrical circuit for controlling the ventilation of a lamp in which the coolant is air, is illustrated in FIG. 6. In the embodiment shown, an alternating electrical voltage, of the order of 400V, is applied, via a contactor 17 to the terminals of a primary winding of a power transformer 18. The electrodes 2 of the lamp are connected to the terminals of a secondary winding of the transformer 18. A fan 19, intended to determine the flow rate of the air flow circulating in the lamp cooling circuit, is controlled by a motor 20.

The motor 20 is itself controlled by a variator 21 supplied by the alternating electrical network. The primary of a step-down transformer 22 is connected in parallel to the secondary of the power transformer 18, while the secondary of the transformer 22 is connected to a drive control input 21. The drive control input 21 thus receives, via the transformer 22, a quantity representative of the voltage applied between the electrodes 2. The variator 22, which is preferably a frequency variator, thus regulates the flow of cooling air of the lamp so that it is proportional to the voltage applied between the electrodes 2 of the lamp. By way of example, the maximum output voltage of the transformer 22 can be of the order of 10V.

An inductor 23 is conventionally connected in series with the primary winding of the power transformer 18, while a contactor 24, of the relay type, is connected in parallel with the inductor 23.

When the installation is switched on, the contactor 17 is closed, the contactor 24 being initially closed. Upon ignition, the voltage across the lamp is zero and the dimmer 21 imposes a minimum air flow. The lamp temperature then increases rapidly. The plasma evolves and the tension gradually increases. Simultaneously the air flow increases, until the lamp reaches, in 2 or 3s, its nominal power.

In nominal operating phase of the installation comprising the lamp, the contactors 17 and 24 are closed. A voltage of the order of 400V is then applied to the primary of the power transformer 18, which then applies, for example, a nominal voltage of the order of 2500V between the electrodes 2 of the lamp, with an arc length about 90cm, for a nominal current of the order of 6A. The variator 21 then controls the fan to impose on the cooling air a sufficient flow rate to maintain the walls of the tube 1 at a temperature admissible by the latter, 700 ° C. for example. In the momentary shutdown phase, the contactor 24 is open, introducing the inductor 23 in series with the transformer primary. The voltage applied between the electrodes 2 is not modified, but the intensity of the current is greatly reduced, for example up to 1 A, reducing the power of the lamp in an equivalent manner. The reduction in the power of the lamp results in a reduction in the amount of infrared radiation emitted by the emitter tube 1. Simultaneously, the voltage between the electrodes not being reduced, the variator 21 continues to impose a maximum flow rate on the cooling air.

The thermal imbalance thus generated causes the lamp to cool in a few seconds, causing, along the longitudinal slit 16, a uniform and longitudinal condensation of the mercury inside the emitter tube 1. The voltage then decreases to the point of equilibrium of argon plasma. The air flow follows the evolution of this voltage while maintaining the plasma state of argon, whose energy level is very low compared to that of mercury. The plasma temperature is then too low for there to be a significant emission of ultraviolet radiation. Furthermore, the argon plasma then occupies the entire inner part of the tube 1. The radiation then produced by the tube is a diffuse radiation and of low energy level, so that the temperature of the insulated substrate is close to the ambient temperature. Thus, any risk of burns or fire is eliminated, despite the elimination of any mechanical sealing. We can consider that the cold argon plasma then plays the role of a static seal.

When the installation comes to a complete stop, with the opening of contactors 17 and 24, a cooling air flow greater than that is automatically triggered corresponding to the nominal power of the lamp, thus bringing the lamp to room temperature in a minimum of time.

The regulation of the flow rate of the coolant is combined with the geometry of the electrode chambers to ensure uniform and longitudinal condensation of the mercury inside the emitter tube 1, without condensation of the mercury in the electrode chambers, more particularly at the back of the electrodes. ^' The condensation of mercury inside the emitter tube 1 is characterized by a shiny strip, longitudinal and continuous, with a geometric surface substantially identical to the cooling air slot and directly above it. This makes it possible to significantly reduce the inertia of the lamp after any stop, total or even momentary.

The invention is not limited to the particular embodiments described above. It applies in particular to all electromagnetic radiation lamps in which one of the elements constituting the plasma arc is likely to form droplets during a shutdown of the installation. It also applies to any type of cooling fluid and cooling circuit. It is also not limited to the use of argon to form cold plasma, but extends to any neutral gas allowing the same result to be obtained.

Claims

claims

1. Electromagnetic radiation lamp comprising an electrode (2) disposed at each of the two ends of a longitudinal emitter tube (1), filled with gas, each electrode consisting of at least one filament (3, 3a, 3b) wound around a support rod (4) having an uncovered front end and fixed, at a rear end, to a connection end (5) of the lamp connected to an electrode chamber (6) in which the electrode is housed , the electrode chamber (6) being covered with a reflection material (7) and having an internal diameter greater than the internal diameter of the emitter tube (1) with which it communicates, at its front part, by an outlet orifice (8) of an exit zone, lamp characterized in that the exit zone of the electrode chamber has a substantially spherical shape, with a predetermined radius of curvature (r) and a center of curvature (C) disposed substantially on an area before the a support rod (4), in the part on which the filament (3) is wound, so that the infrared radiation (Ri) emitted by the uncovered front end of the support rod (4) and reflected ( Rr) through the reflection material (7) covering the exit area of the electrode chamber are directed towards the rear of the electrode (2).

2. Lamp according to claim 1, characterized in that, the electrode (2) comprising a first filament (3a) and a second filament (3b), superimposed on about the front half of the first filament, the center of curvature (C ) of the exit zone of the electrode chamber (6) is located on the front part of the support rod on which the second filament (3b) is wound.

3. Lamp according to claim 2, characterized in that the center of curvature (C) of the exit area of the electrode chamber (6) is located about 1mm from the front end of the filament (3).

4. Lamp according to any one of claims 1 to 3, characterized in that the radius of curvature (r) of the exit area of the electrode chamber (6) is greater than or equal to approximately 6 mm.

5. Lamp according to any one of claims 1 to 4, characterized in that, the lamp comprising cooling means, the lamp is associated with means (21) for modulating the flow rate of a cooling fluid circulating along of the emitter tube (1) in proportion to the electric voltage applied to the terminals of the electrodes (2) of the lamp.

6. Lamp according to claim 5, characterized in that the longitudinal emitter tube (1) is provided with lateral reflectors (14) static, separated by a slot (16) through which the coolant passes.