Patent Application
20050286605
The invention relates to an electrode system for glass melting furnaces with a melting tank and at least one electrode holder located above the melt surface for inserting electrodes through the melt surface and with an appendage as a coaxial electrical and water connection between the electrode holder and the electrode, whereby the electrode holder is fitted with a coolant supply passage that projects into the electrode.
It is known that glass melts in furnaces can be heated by means of electrodes that are introduced into the melt through the bottom or the side walls of the melting tank or from above through the furnace crown, and these can be advanced as necessary to compensate for the unavoidable corrosion. There is no known material that can permanently withstand the glass melt.
As it is necessary to exchange electrodes their installation through the bottom and/or the side walls of the melting tank is complicated in terms of both design and operation, as the openings that are made must be closed off in order to prevent the glass from draining out. Therefore there is now a tendency to install electrodes from above. These are also described as immersion or top electrodes.
Normally the electrodes and their holders—whether cooled or not—are connected to one another by means of electrically conducting threads, which must remain easily releaseable for the exchange or advancing of the electrodes. This poses a number of diametrically opposed problems. With non-cooled electrode connections the threads are normally outside the furnace chamber, which requires a much longer electrode or electrode section.
A further problem is that the materials used are susceptible to corrosion, in particular in the area of very aggressive batch and glass gall, that float on the glass melt as a result of the melting process. Up to the three phase boundary at the glass melt surface there is also the oxidizing effect of the oxygen contained in air, whereby it should be noted that molybdenum or tungsten for instance oxidize rapidly above about 550° C. to 600° C.
European patent no. 0 372 111 B1 (=U.S. Pat. No. 4,965,812) discloses a tubular electrode holder with a coaxial water supply pipe and a female thread at the inner end to receive the male thread of a complete electrode or an electrode segment made of highly heat resistant metals such as molybdenum, platinum, tungsten or their alloys. The electrodes are provided with coaxial bores, into which the end of the water supply pipe projects. When the electrode is unscrewed, a new electrode segment can be inserted to compensate for the wear of the electrode or segment already in operation. However, the electrode segment inserted is not designed as a permanent or long-term adapter for connection to the electrode holder. In particular it does not have a passage for the water supply tube and the supply and return flow of the cooling water. It is also subject to the same level of wear as those electrode segments already in operation.
Patents DE 195 08 433 C1 and EP 0 799 802 B1 disclose a tubular electrode holder to which a complex connection casing is attached at the inner end by means of two flanged connections screwed to its circumference. A coupling piece and a contact ring are clamped between the flanges of the lower flange connection. The coupling consists of a disc-shaped part and two coaxial appendages with male threads, the upper one of which is used for the attachment of flexible water and electricity connections and the lower for attachment of the electrode. The inner surface of the contact ring is conical to provide contact with the electrode, the ring has a system of cooling channels that mate with cooling channels in the coupling piece. In order to exchange the coupling piece and contact ring for a differently shaped electrode end it is necessary to dismantle the complete bottom part of the connection casing. Manufacturing and change procedures are therefore expensive in both material and financial terms.
Earlier types of top electrodes normally had a diameter of 63 mm. Over the years the diameter of the electrodes increased to 88.90 mm for example (=3.5 inches) in order to increase power. This places an immense load on the electrode holder. Even on electrodes with a diameter of 63 mm in normal operation there is sometimes corrosion in the transition between the molybdenum and the copper of the electrode holder at high currents. It was therefore established that it was not possible to reduce the size of an 88.90 mm electrode to 40 mm in the area of the connection to the electrode holder.
However it is very expensive to increase the diameter of an electrode holder, and transport, installation, operation and maintenance become more difficult. With many top electrodes extensive external scaling has also been found at the joint between steel and molybdenum. This means that the electrode holder must be reworked, but this is often not possible.
The object of the invention is therefore to improve the compatibility and flexibility, and to simplify retrofitting and conversion of electrode holders and electrodes, and reduce the costs of the electrode system described above.
The object is accomplished in accordance with the invention described above in that
In this way the object of the invention is completely accomplished, i.e. the compatibility and flexibility of the electrode holders are improved and retrofitting and conversion of the electrode holders to accept electrodes with different threaded connections is simplified, and the costs are reduced when the mechanical loading is high. The price difference between the old and the new electrode system means that it is now easy for the operator to change the connection between the electrode holder and the electrode using any chosen connection. The electrode material can also be freely chosen and is not limited to molybdenum.
The connection device and its threaded connections comprise a core made of a good electrical conductor such as copper or a copper alloy such as brass, encased in a sheath of chemical and heat resistant material such as stainless steel, and this arrangement offers effective protection against the chemical and thermal attack that occur in a furnace atmosphere with high temperatures of 1400° C. and above.
With regard to further embodiments of the invention it is particularly advantageous, if—either individually or in combination:
Further advantageous embodiments according to the invention are given in the patent claims.
An example of the object according to the invention and its function and advantages are explained here in more detail with reference to
The following are shown:
Outside the melting tank 1 there is a vertical support pillar 10 that is mounted on the supporting steelwork 4. This pillar 10 supports a swivel joint 11, around which the swivel lever 12 with a further joint 13 can be turned. The relative angular position and so the immersion depth of the electrode 7 can be adjusted by the jacking mechanism 14. The swivel movement is carried out by an operator 15, who stands on a working platform 16. The swivel radius 17 of the outermost point of an elbow 18 in the electrode holder 9 is indicated by a dotted arc, the height of the melt surface 20 by a straight line.
The outside of the furnace wall 2 with its thermal insulation 2a is covered by a metal casing 21, towards which several cooling nozzles, that are not detailed, are directed. These cooling nozzles are connected to the supply lines 22 and 23. It can be seen that the electrode 7 can be exchanged when the electrode holder 9 has been completely swivelled out.
A connection device 27 with good electrical conductive properties is fitted between the electrode 7 and the electrode holder 9. This connection device 27 is provided with an appendage 28 formed from a single piece with a male thread 28a and a conical surface 29, that seats in the opposite conical surface 9c of the inner tube 9b to provide a tight, electrical current-conducting connection. This creates the first threaded connection 8a. In addition the connection device 27 has a coupling piece 30 with a concentric female thread 31 with a freely selectable diameter. The coupling piece 30, the core of which is made of copper or a copper alloy, is surrounded by a sheath 32 made of material such as stainless steel that is resistant to chemical attack. This sheath 32 is closed at the bottom by a ring 33, welded onto the sheath 32. The opposite, upper end of the sheath 32 is enclosed by a ring welded to the external tube 9a of the electrode holder 9.
The top end of the electrode 7 has a shaped appendage 7a with a male thread 7b, that is screwed into the female thread 31 of the coupling 30. This threaded connection creates the second threaded connection 8b and another good electrical contact. The coolant supply 24 is centred in the electrode holder 9 by a perforated plate 35. The annular gap 26 is sealed off from the connection device 27 by a gasket 36.
The contents of the melting tank 1 shown in
A multi-facetted ring 40 is fitted at the bottom end of the electrode holder 9 for attachment of a tool. In order to produce a counter torque by means of a second tool notches 41 are provided in the top end of the connection device 27.
It can be seen that it is easy to adapt the electrode holder 9 for electrodes 7 of differing diameters by selecting and changing the connection device 27 which has a coupling piece 30 with a female thread 31. The liquid coolant supply passes through all threaded connections 8a and 8b, so that these also remain easy to release even when the electrode 7 has been in operation for a long period.
From the above description, it is apparent that the objects of the present invention have been achieved. While only certain embodiments have been set forth, alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit of the scope of the present invention. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 031 242.7 | Jun 2004 | DE | national |
