APPARATUS FOR FEEDING A LIQUID MATERIAL TO AN EVAPORATOR DEVICE

Abstract

An apparatus for feeding liquid metal to an evaporator device in a vacuum chamber, wherein the apparatus includes a container adapted to contain a liquid metal, a feed tube from the closed container to the evaporator device and an electromagnetic pump provided in the feed tube, and wherein the electromagnetic pump is placed in a vacuum enclosure.

Claims

1. An apparatus for feeding liquid metal to an evaporator device in a vacuum chamber, the apparatus further comprising a container adapted to contain a liquid metal, a feed tube from the container to the evaporator device and an electromagnetic pump provided in the feed tube, wherein a vacuum enclosure is provided which encloses the electromagnetic pump.

2. The apparatus according to claim 1, wherein the vacuum enclosure encloses at least part of the feed tube.

3. The apparatus according to claim 1, wherein the vacuum enclosure connects to the vacuum chamber and/or the container.

4. The apparatus according to claim 1, wherein the vacuum enclosure is connected to the vacuum chamber and/or the container adapted to contain a liquid metal by means of a flexible connecting member.

5. The apparatus according to any of claim 1, wherein the electromagnetic pump is at least partially made of an electric conductive material.

6. The apparatus according to claim 5, wherein the electromagnetic pump is at least partially made of graphite.

7. The apparatus according to claim 5, wherein electrodes of the electromagnetic pump are provided against the pump.

8. The apparatus according to claim 1, wherein control means are provided to control a force on the liquid metal in the container adapted to contain a liquid metal.

9. The apparatus according to claim 8, wherein the container adapted to contain a liquid metal is a closed container and wherein the control means control the pressure of a gas in the closed container.

10. The apparatus according to claim 1, wherein control means are provided to control the magnetic field for the electromagnetic pump.

11. The apparatus according to claim 10, wherein the control means control the distance of the magnet poles with respect of the electromagnetic pump and/or where the magnetic field is provided by means of a direct or alternating current electromagnet, control the current through the coil of the electromagnet.

12. Apparatus The apparatus according to claim 1, wherein the magnet is provided outside the vacuum enclosure.

13. Apparatus The apparatus according to claim 1, wherein the magnet to apply a magnetic field for the electromagnetic pump comprises a permanent magnet.

14. Apparatus The apparatus according to claim 1, wherein a valve is provided in the feed tube between the electromagnetic pump and the evaporator device.

15. Apparatus The apparatus according to claim 1, wherein a return tube and an electromagnetic pump in the return tube is provided, wherein the return tube runs from the evaporator device to the container.

16. The apparatus according to claim 15, wherein the electromagnetic pump in the feed tube and the electromagnetic pump in the return tube are positioned adjacent to each other and wherein the magnetic field for both electromagnetic pumps is supplied by the same magnet.

17. The apparatus according to claim 15, wherein the electromagnetic pump in the feed tube and the electromagnetic pump in the return tube are positioned adjacent to each other and wherein the current for both electromagnetic pumps is supplied by the same power supply.

18. The apparatus according to claim 2, wherein the vacuum enclosure is connected to the vacuum chamber and/or the container adapted to contain a liquid metal by means of a flexible connecting member.

19. The apparatus according to claim 18, wherein the electromagnetic pump is at least partially made of an electric conductive graphite, wherein electrodes of the electromagnetic pump are provided against the pump.

20. The apparatus according to claim 19, wherein a return tube and an electromagnetic pump in the return tube is provided, wherein the return tube runs from the evaporator device to the container, wherein the electromagnetic pump in the feed tube and the electromagnetic pump in the return tube are positioned adjacent to each other and wherein the magnetic field for both electromagnetic pumps is supplied by the same magnet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention will be further explained by the example shown in the drawing, in which:

[0038] FIG. 1 shows a schematic view of an apparatus with a container for a liquid metal, an electromagnetic pump in a vacuum enclosure and a vacuum chamber,

[0039] FIG. 2A,2B,2C shows a schematic view of respectively an electromagnetic pump for a feed tube and an electromagnetic pump for a feed tube and return tube,

[0040] FIG. 3A,3B shows schematically two configurations to control the distance of the magnetic poles to the electromagnetic pump, and

[0041] FIG. 4 shows schematically a detail of the feed tube with heating means.

DETAILED DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows a schematic view of an apparatus with a vacuum chamber 1, on both sides provided with vacuum locks 2,3, through which a strip 4 is guided. An evaporator device 5 is positioned inside the vacuum chamber 1 and connected to a vapour distributor 6. The means to supply sufficient energy to the evaporator device, such as an induction coil, are also placed inside the vacuum chamber. For the sake of clarity these means are not shown in the drawing. The vacuum chamber is further provided with vacuum pump 7 and manometer 8.

[0043] At the bottom of fig.1 a closed container 9 is provided with inside the container a vessel 10 to hold a liquid metal. The closed container 9 is further provided with a pump 11, manometer 12 and overpressure relay 13. The vessel is provided with heating means (not shown) to heat and melt the metal and/or to keep the liquid metal at a certain temperature. A gas supply 31 with a valve 32 is connected to closed container 9 to replace the air initially present in container 9 with a non-oxidising gas, for instance N2. Lifting means 14 are provided to lift and lower vessel 10 to be able to immerse the end of feed tube 15 into the liquid metal or lift it out of the liquid metal. The lifting means 14 can also be used in the control of the flow rate of the liquid metal to the evaporator device 5, since with the lifting and lowering the distance between the liquid level in the vessel and that in the evaporation device changes.

[0044] The vessel 10 is placed on weighing devices 35 which allows to continuously weigh the content of vessel 10 which provides additional information on the flow rate of the liquid metal and the evaporation rate.

[0045] The pump 11 is used to lower the pressure in the closed container. In order to prevent oxidation of the liquid metal in the vessel the air in the closed container can be removed and replaced completely or partially with an inert gas. With this operation the air is first partially removed therewith lowering the pressure before being replaced by an inert gas after which the pressure in the closed container is adjusted and controlled in order to control the flow rate of the liquid metal to the evaporator device.

[0046] The feed tube 15 runs from the vessel 10 inside the closed container 9 in upward direction to the evaporator device 5 and in the feed tube an electromagnetic pump 16 and a valve 17 are provided. The electromagnetic pump 16 and valve 17 are placed inside a vacuum enclosure 18. The vacuum enclosure 18 is kept at a low vacuum during operation which prevent heat losses through convection from the electromagnetic pump 16 as well as from the feed tube 15 to a great degree. To that end the vacuum enclosure 18 is provided with a vacuum pump 34 and a manometer 35 or a collocation of these.

[0047] The vacuum enclosure 18 connects to the closed container 9 and the vacuum chamber 1 by means of bellows 19, 20. The connection by means of the bellows 19, 20 is to the outside of the closed container 9 and the vacuum chamber 1 and does not connect the internal spaces of container 9 and vacuum chamber 1. However, the unavoidable vacuum leak at the feed through of the feed tube 15 into the vacuum chamber 1 is much less because of the low vacuum in the vacuum enclosure 18.

[0048] The electromagnetic pump 16 pump is provided with a permanent magnet 21 to generate a magnetic field and a power supply to pass a current through the liquid metal in the electromagnetic pump. The Lorentz force resulting from the magnetic field and the current will exert a force on the liquid metal which is used in the control of the flow rate of the liquid metal. The Lorentz force only works as long as the liquid metal is in contact with the electrodes 22 of the electromagnetic pump and within the magnetic field of permanent magnet 21. As a result when the liquid metal is forced downwards the liquid metal level can not be lower than a level at about the height of the electrodes.

[0049] It is important that the magnet 21 is not overheated because this will result in a decrease of the strength of the magnetic field. For that reason the magnet 21 is placed outside the vacuum enclosure 18, which at least at the location of the magnet and its magnetic field is made of a non-ferromagnetic material.

[0050] The upward force on the liquid metal is given by the pressure difference and the column height:

P3P1(XY)*density liquid, wherein [0051] P3=the pressure in the closed container, [0052] P1=the pressure in the vacuum chamber, [0053] X=height top level of the liquid metal, which can be in the evaporator device or somewhere in the feed tube, and [0054] Y=height level of the liquid metal in the vessel in the closed container.

[0055] Once the evaporation of the liquid metal in the evaporator device has started the driving force for the liquid metal is:

P3P4(XY)*density liquid, wherein [0056] P4 is the pressure in the vapour distributor 6 which will be higher than the pressure in the vacuum chamber. [0057] When the electromagnetic pump is exerting a force against the upward flow of the liquid metal the force is given by:

P3P1(XY)*density liquidB*I*C, wherein: [0058] B is magnetic field, I the current through the liquid metal and C a constant. Once the evaporation has started the equation changes to:

P3P4(XY)*density liquidB*I*C

[0059] If the heating of the electromagnetic pump has to be increased, P3 is increased which will require a larger Lorentz force against the upward flow in order to keep the upward flow constant. The larger Lorentz force is realized to increase the current through the electromagnetic pump and the liquid metal, which will provide the extra resistance heating. FIG. 2A shows a schematic view of an electromagnetic pump 16 for a feed tube 15 with the electrodes 22 on opposite sides against the body of the electromagnetic pump 16. The electrodes 22 are connected to a power supply 23, in this case a variable DC power supply.

[0060] Perpendicular to the electrodes 22 are the poles of magnet 21, which in this configuration are two permanent magnets connected by means of a yoke (not shown). Instead of permanent magnets it is also possible to use an electromagnet, for instance an electromagnet with a DC coil. By varying the current through the coil the magnetic field could be varied.

[0061] Instead of a variable DC power supply and a DC coil it is as well possible to use a variable AC power supply and an AC coil for the electromagnet.

[0062] FIG. 2B shows a configuration with a feed tube 15 and a return tube 24 next to each other with electromagnetic pumps 18, 25 for respectively the feed tube 15 and return tube 24. The magnetic field for both the feed tube 15 and the return tube 24 is provided with the same permanent magnets 21. Separate variable DC power supplies 23, 26 are provided for respectively the feed tube 15 and the return tube 24 which are reversely connected to the electrodes since the Lorentz forces should be in opposite direction. The feed tube 15 and the return tube 24 are in thermal contact with each other but electrically isolated from each other. The flow rate in the return tube will differ by the evaporation rate from the flow rate in the feed tube and for that reason the current through the return tube 24 will be larger than through the feed tube 15.

[0063] FIG. 2C shows a configuration wherein the electrodes 22 of feed tube 15 and feed tube 24 are connected in series which only requires one power supply 23 and wherein the same current passes through both feed tubes. In order to control the flow rate in each tube the magnetic field of the magnet 21, 36 in each tube 15, 24 is controlled separately.

[0064] FIG. 3A,3B shows schematically two configurations to control the strength of the magnetic field of permanent magnets by shorting the flux or by changing the distance of the magnetic poles to the electromagnetic pump. In the configuration according to FIG. 3A the flux between the poles of magnet 21 can be changed by shortening the magnetic flux via a second leg 38. The flux is variable by changing the distance between the poles of this second leg. To this end leg 38 of the yoke is designed to allow such linear displacement.

[0065] In the configuration according to FIG. 3B the magnetic strength is varied by varying the distance between the poles of magnet 21. This can be varied by a rotation or linear displacement. A rotational displacement is depicted in FIG. 3B where yoke 37 is provided with a pivoting point 39 and a spindle device 40 for a controlled rotation and therewith a controlled change of the distance between the poles of the magnet 21.

[0066] FIG. 4 shows schematically a segment of a feed tube 15 with a channel 27 and two different heating embodiments. A first heating method is heating the feed tube by resistance heating with a power source 28 wherein the material of the feed tube serves as the resistance. The second heating method is with a sheath heater 29 with a power source 30, wherein the heater is provided in a hole or a recess in the feed tube 15. The power sources 28, 30 could be DC or AC power sources. This is in fact also resistance heating wherein the resistance is enclosed in a sheath and electrically isolated from the feed tube. All the tubing must be heated to a temperature above the melting point of the liquid metal for which a temperature of 40 C. above the melting temperature will in general be sufficient.