AN EXPLOSION-PROOF LIGHTING FITTING OF A HIGH SAFETY CLASS

Abstract: The present invention relates to an explosion-proof lighting fitting comprising a branch box (7), a mounting element (13), a light-transmitting screen (1) and a housing (14, 15) which accommodates the lamp (2) and the required electronic components (12), which explosion-proof lighting fitting is characterized in that the lamp (2) is placed on a baseplate (3) within the housing (14, 15), which baseplate (3) functions to dissipate the heat generated by the lamp, and that a heating element (17) is provided in the space enclosed by the housing.

Description: An explosion-proof lighting fitting of a high safety class. The present invention relates to an explosion-proof lighting fitting comprising a branch box, a mounting element, a light- transmitting screen and a housing which accommodates the lamp and the required electronic components. Such an explosion-proof lighting fitting is preferably used in areas where there is a risk of explosion and in areas where the environment presents large problems, for example a corrosive, acidic or salty or other aggressive environment. A lighting fitting of the above type can be used indoors as well as outdoors at various locations, such as petroleum refineries, chemical and petrochemical plants, oil drilling platforms and other process industry facilities where there are similar risks. A construction as described above makes it possible to use these lighting fittings in areas which constitute a danger, due to the presence of inflammable vapours, gases or highly inflammable dust flows. French patent publ ication 2246812 relates to a warning lamp for use in harzardous atmosphere comprising a holow base member, a plate member within the hollow base member and a transparant light- focussing dome mounted on said plate member and surrounding a gas discharge lamp. Although electrical control means are encapsulated in a potting compound within said hollow housing there is still a risk of the generation of condensation water within said housing. U.S. patent 5,528,474 relates to a LED array vehicle lamp wherein the LEDs and circuit boards are fully embedded in a resin material cured with thermally conductive particles suspended therein for conducting excess heat to the outer aluminum housing and the outer environment. As such, the temperature of the LEDS may be kept sufficiently cool to prevent degradation of the brightness of the lamp. However, the luminescence of such a vehicle lamp is too low, due to the presence of the LEDs, and said vehicle lamp can not be used in areas where there is a risk of explosion because a generation of condensation inside the aluminum housing is observed under severe conditions. German Offenlegungsschrift 4017654 relates to a hand held lamp wherein the heat generated by the lamp is dissipated via cooling fins located on the outside of the housing. A lighting fitting of the above kind is for example known from European patent application Nr. 0823589. The lighting fitting disclosed therein is only suitable for one or more light-emitting diodes (LED) which are fitted in a construction provided with a light-transmitting screen, through which the status of the LED can be observed. When such a construction is used with an incandescent lamp, however, the heat generated by the incandescent lamp will not be dissipated to a sufficient degree, as a result of which stresses will be induced in the material. As a result of such stresses, the explosion safety requirements are no longer met. European patent application Nr. 0 695 909 relates to an explosion-proof lighting fitting as referred to in the introduction. The drawback of such a lighting fitting is the fact that the heat generated by the lamp is not dissipated to a sufficient degree, so that the life of such a construction is adversely affected. European patent application Nr. 0 598 724 relates to an explosion-proof lighting fitting for use in explosive atmospheres. Such a 1 ighting fitting comprises a housing provided with a cover plate, wherein the problem of the heat generated by the lamp is solved by providing fins or ribs. The object of the present invention is to provide an explosion-proof lighting fitting, which eliminates the above-descri ed drawbacks of the cited prior art documents. Another object of the present invention is to provide an explosion-proof lighting fitting, which is also suitable for use in humid conditions. Another object of the present invention is to provide a lighting fitting which can be used within wide temperature limits, namely from -50 °C to +52 °C. Another object of the present invention is to provide an explosion-proof lighting fitting of robust construction, which is resistant to external magnetic force fields, which is resistant to vibrations and shocks and which enables a maintenance-free period of at least 100,000 hours. The above objectives and further advantages are accomplished by an explosion-proof lighting fitting as referred to in the introduction, which explosion-proof lighting fitting is according to the present invention characterized in that the lamp is placed on a baseplate within the housing, which baseplate functions to dissipate the heat generated by the lamp and that a heating element is provided in the space enclosed by the housing. In order to make the explosion-proof lighting fitting suitable for use especially in cold conditions, it is necessary to provide a heating element in the space enclosed by the housing. It is preferred to use a self-regulating tape heating element for that purpose. In a preferred embodiment, the heat conducting baseplate is made of a metal , which metal is preferably coated with a slightly light- reflecting material on at least one side thereof, in particular the upper side. Such a baseplate ensures that the heat generated by the lamp is dissipated, so that no accumulation of heat will take place within the lighting fitting. The advantageous dissipation of the generated heat considerably prolongs the life of the lamp, whereby it should also be mentioned that the occurrence of stresses in the housing is prevented. The use of the baseplate according to the present invention does not have an adverse effect on the light output of the lamp, due to the use of a light-reflecting material. In a preferred embodiment of the explosion-proof 1 ighting fitting according to the present invention, the baseplate consists of nickel-plated copper. Copper is a material which has a high heat conducting coefficient and the nickel which is plated thereon ensures that the light output of the lamp is not adversely affected by the presence of such a baseplate, due to the fact that the light is reflected by the nickel layer In a special embodiment it is furthermore preferred for the baseplate to extend radially up to the edge of the housing. The heat generated by the lamp is thus evenly distributed over the baseplate, so that no stresses will be induced in the material. Moreover, in this manner the heat dissipating properties of the metal being used are util ized optimally. In order to prevent condensation within the housing, it is preferred to encapsulate the electronic components that are present in a moulding resin. Another special function of the moulding resin is that is also functions as a heat dissipating medium. In certain embodiments it is furthermore preferred to increase the heat conducting capacity of the moulding resin by adding a heat conducting material, in particular metal particles, to the moulding resin. If iron is used as the heat conducting material, the amount of iron is preferably at least 10 g/kg of moulding resin. If the amount of iron is less than 10 g/kg of moulding resin, the intended effect, in particular the increasing of the thermal capacity of the moulding resin, will be insufficient. Besides the heat regulation, the use of the moulding resin also ensures the explosion safety. Thus, the generation of heat in the explosion-proof lighting fitting according to the present invention will be regulated advantageously both by the heat conducting baseplate and by the moulding resin, to which a heat conducting material has been added in a special embodiment. In order to prevent the electronic components from coming into contact with the moulding resin, to which a heat conducting material, in particular iron particles, has preferably been added, it is advisable in certain embodiments to envelop the electronic components in a latex layer first, after which the electronic components are encapsulated in a moulding resin. Such a latex layer also performs a function as regards the prevention of condensation. In a special embodiment of the explosion- proof lighting fitting according to the present invention, the problem of the generation of heat is thus solved by the special combination of the above-described measures, namely the baseplate, the latex-like sealing of the electronic components and the encapsulation of the electronic components in a moulding resin to which a heat conducting material may have been added. The present invention is not limited to the simultaneous use of the above measures, however. According to the present invention, the light- transmitting screen is seal ingly connected with the housing, using a spacer and a sealing material. In a special embodiment, the light-transmitting screen is made of a shock-resistant glass, and in order to increase the sealing action, a spacer is placed between the contact surface of the housing and the light-transmitting screen. Since the baseplate extends radially up to the edge of the housing in a special embodiment, the spacer is positioned on said radially extending baseplate. A suitable sealing material is for example a sealing material with a base of silicone. For special uses it is desirable to use a coloured light-transmitting screen. In order to increase the light output of the present explosion-proof lighting fitting, it is preferred to place a reflector in the space enclosed by the baseplate and the light-transmitting screen, between the lamp and the baseplate. The reflector preferably extends radially up to the light-transmitting screen with a view to increasing the light reflection output. The reflector is slightly concave at its end, which concave shape functions to ensure that the light emitted by the lamp is reflected in the desired direction. Suitable materials for the reflector are for example polished stainless steel or anodised aluminium. It is also possible, of course, to use such a reflector in a lighting fitting which does not need to satisfy any explosion safety requirements. In order to obtain a maintenance-free construction, it is preferred in a special embodiment to use a branch box separate from the housing, wherein the branch box is preferably connected to the housing via the mounting element. Thus, the explosion-proof lighting fitting will be readily accessible upon repair and/or replacement of special parts. In other words, an authorized person, for example an electrician, can make the desired electrical connection only in the separate branch box. Since it is not possible to access the lighting fitting, in particular the housing, the electrician is efficiently prevented from influencing the specific characteristics of the lighting fitting, as a result of which it would no longer meet the requirements of explosion safety and water tightness. Furthermore, a simple and robust construction is obtained in this manner. The explosion-proof lighting fitting according to the present invention is suitable for use in the offshore industry, refineries, the chemical industry and at locations which are difficult to reach, for example airfields or helicopter landing sites. The lighting fitting according to the present invention is in particular suitable for a type QL lamp which is marketed by Philips. By using such a lamp and the explosion-proof lighting fitting according to the present invention, a lighting level corresponding to a 2x 36 Watt EEX strip lighting fitting can be obtained. Such a capacity makes the explosion-proof lighting fitting according to the present invention suitable in particular for use at a height of 3 - 6 metres. Moreover, the construction according to the present invention is so robust that the industrial explosion-proof 1 ighting fitting according to the present invention does not require any maintenance for more than 100,000 hours in very demanding conditions. The present invention will now be described in more detail with reference to a number of drawings, wherein it should be noted, however, that the present invention is by no means limited to the special embodiments as shown in said drawings. Figure 1 is a perspective front view of a special embodiment of an explosion-proof lighting fitting according to the present invention. Figure 2 is a schematic, cross-sectional view of the explosion-proof lighting fitting which is shown in Figure 1. Figure 3 is a schematic plan view of the explosion-proof lighting fitting according to the present invention. The reference numerals used in Figures 1 - 3 indicate the following: 1 = light-transmitting screen 2 = lamp 3 = baseplate 4 = sealing material 5 = seal ing material 6 = spacer 7 = branch box 8 = union 9 = lead passage 10 = moulding resin 11 = bottom plate 12 = electronic components holder 13 = mounting element 14 = housing (base part) 15 = housing (cover part) 16 = reflector 17 = tope heating element 18 = protective material 19 = terminals Figure 1 is a perspective front view of the explosion- proof lighting fitting according to the present invention. Housing 14 is connected on its bottom side to two mounting elements 13, with branch box 7 being secured to one of said mounting elements 13. Branch box 7 is provided with a union 8. Housing 14 (base part) is connected to housing 15 (cover part), in which cover part the light-transmitting screen 1 is sealingly provided. The connection between light-transmitting screen 1 and housing 15 (cover part) is shown in more detail in Figure 2. The explosion-proof 1 ighting fitting as shown in Figure 1 furthermore comprises a reflector 16, which reflector 16 is positioned between lamp 2 and baseplate 3. The explosion-proof lighting fitting 1 according to the present invention is by no means limited to the use of such a reflector 16, however. Figure 2 schematically shows a cross-section of the explosion-proof 1 ighting fitting of Figure 1. Electronic components holder 12 is disposed within the housing (base part) 14 (refer in particular to Figure 3) and comprises an explosion-proof bottom plate 11, in particular also called explosion-proof cover, with electronic components holder 12 being enveloped in a latex layer (not shown). Electronic components holder 12 is furthermore encapsulated in a moulding resin 10, to which moulding resin 10 a heat conducting material has been added in a special embodiment. Light-transmitting screen 1 is placed on baseplate 3, using spacer 6. By placing light-transmitting screen 1 on spacer 6 and subsequently forming a hermetic seal, using sealing material 4, 5, a condensation-free and moisture-free lighting fitting is formed. Light-transmitting screen 1 is sealingly connected to housing 15 (cover part), wherein likewise a reflector 16 is used with a view to increasing the light output of lamp 2. Figure 3 schematically shows a plan view of the explosion-proof lighting fitting of Figures 1 - 2. Figure 3 clearly shows the tape heating element 17, which tape heating element 17 is preferably present on the circumference of housing 14. In order to increase the heat absorbing capacity, moulding resin 10 is provided with a heat conducting material (not shown). The electronic components holder 12 is enveloped in a layer of protective material 18, in particular a latex layer. Branch box 7 is provided with terminals 19, which branch box 7 is secured to mounting element 13, which mounting element 13 is connected to housing 14 (base part). With a view to enabling precise positioning of the explosion-proof lighting fitting according to the present invention, two mounting elements 13 are preferably connected to bottom plate 11. The use of the explosion-proof lighting fitting as described in Figures 1 - 3 makes it possible to achieve a lighting fitting efficiency of 90%. The special construction of the tape heating element, the moulding resin, the latex-1 ike seal and the baseplate makes it possible to use the explosion-proof lighting fitting according to the present invention within a temperature range of -50 °C to +52 °C. The present lighting fitting is by no means limited to the special combination of the above-described measures, however. Moreover, the present embodiment prolongs the 1 ife of the 1 ighting fitting. The electrical connections which are provided in a separate branch box facilitate the making of the electronic connections. The explosion-proof lighting fitting according to the present invention is in particular suitable for use in the offshore industry, refineries, the chemical industry and as a lighting device to be used at helicopter landing sites and all locations which are difficult to reach, such as access doors to storage spaces and the like. The explosion-proof lighting fitting according to the present invention is furthermore suitable for use as obstruction light.

Claims: CLAIMS 1. An explosion-proof 1 ighting fitting comprising a branch box, a mounting element, a light-transmitting screen and a housing which accommodates the lamp and the required electronic components, characterized in that the lamp is placed on a baseplate within the housing, which baseplate functions to dissipate the heat generated by the lamp, and that a heating element is provided in the space enclosed by the housing. 2. An explosion-proof lighting fitting according to claim 1, characterized in that said baseplate is made of a metal and in that said baseplate is coated with a light-reflecting material on the upper side. 3. An explosion-proof lighting fitting according to claim 2, characterized in that nickel-plated copper is used as a baseplate. 4. An explosion-proof lighting fitting according to claims 1 - 3, characterized in that the baseplate extends radially up to the edge of the housing. 5. An explosion-proof lighting fitting according to claim 1 - 4, characterized in that the electronic components that are present are encapsulated in a moulding resin. 6. An explosion-proof lighting fitting according to claim 5, characterized in that a heat-conducting material is added to the moulding resin. 7. An explosion-proof lighting fitting according to claim 6, characterized in that metal is added as said heat-conducting material. 8. An explosion-proof 1 ighting fitting according to claims 6 - 7, characterized in that the amount of iron is at least 10 g/kg of moulding resin. 9. An explosion-proof lighting fitting according to claim 1, characterized in that a self-regulating tape heating element is used as the heating element. 10. An explosion-proof lighting fitting according to claims 1 - 9, characterized in that said heating element is encapsulated in said moulding resin and that it is provided on the circumference of the housing. 11. An explosion-proof 1 ighting fitting according to claims 1 - 10, characterized in that the electronic components are enveloped in a latex layer. 12. An explosion-proof lighting fitting according to claims 1 - 11, characterized in that said light-transmitting screen is sealingly connected to the housing, using a spacer provided with a seal ing material . 13. An explosion-proof lighting fitting according to claim 12, characterized in that said spacer is positioned on the radially extending baseplate. 14. An explosion-proof lighting fitting according to claims 12 - 13, characterized in that a sealing material with a base of silicone is used. 15. An explosion-proof lighting fitting according to claims 1 - 14, characterized in that a reflector is disposed between said lamp and said baseplate. 16. An explosion-proof lighting fitting according to claim 15. characterized in that said reflector extends radially up to said light- transmitting screen. 17. An explosion-proof lighting fitting according to claims 15 - 16, characterized in that said reflector is slightly concave at its end. 18. An explosion-proof 1 ighting fitting according to claims 1 - 17, characterized in that said branch box is mounted separate from the housing. 19. An explosion-proof lighting fitting according to claim 18, characterized in that said branch box is connected to said housing via said mounting element. 20. An explosion-proof lighting fitting according to claims 1 - 19, characterized in that a QL type lamp is used.

Inventors: GELUK JAN MARINUS, GELUK, JAN, MARINUS
Applicants: GELUK JAN MARINUS, IND MANUFACTURING AND TRADING, GELUK, JAN, MARINUS, INDUSTRIAL MANUFACTURING AND TRADING B.V.
Application year: 1999
Main classification: F21V25
IPC codes: F21V15, F21V23, F21V25, F21V29