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This invention relates to an electric furnace dome that is hermetic and made of ceramic material and that is cooled at its center and supported ωith the aid of external tube systems to improve durability.

The simplest and most inexpensive dome construction is one

10 that is made of bricks or cast from mass, the dome being in reality dome-shaped, in other words the surface is outωards in the shape of a round ball. If the dome is built of ceramic mass, its structure is generally quite ωεak, ωhich is the reason why it must be supported at those points

15 ωhere there are for example openings. Not even supporting however always helps, but the resulting construction is still weak at least under situations of malfunction. Fully supported brick domes that have a planar surface are also used. Such structures are generally very expensive and

20 difficult to repair and service. Externally cooled domes have become known as a third alternative, as for example the box beam construction that has become known from the Finnish patent application 783705. A drawback of this dome also is its expeπsiveness, as well as the energy

25 losses caused by great amounts of cooling water and the danger of explosion in the case of leakage", electrode breakage or other such inconvenience to production.

The purpose of this invention is to avoid the drawbacks of 30 domes in accordance with technical level and achieve an r electric furnace dome whose construction expenses as well as costs of using are moderate and which is hermetic and endures use.

35 The characteristical features of the invention are given in the accompanying patent claims.

The invention is described in more detail in the following by referring to the accompanying drawings of which

figure 1 illustrates the side view along the cutline in figure 2 of an electric furnace dome in accordance with the invention, figure 2 illustrates an electric furnace dome in accordance with the invention viewed from above.

An electric furnace dome in accordance with the invention is made of ceramic material (mass and/όr brick) and is con¬ structed so that the dome's stationary edge 1 is separated from the easily repairable or changeable center 2 by water- cooled tube systems 3 that are supported from outside of the dome. Further the dome's center 2 which is under great strain is watercoolεd by spiral tube systems that are in¬ side of the dome structure. In the figures the spiral tube systems in the center of the dome that are around the openings 4 for the electrodes are indicated by the number 5, the spiral tube systems around the material feed open¬ ings 6, some of which are in the center of the dome and thus watercoolεd and some on the edge of the dome, are indicated by the number 7, and thε spiral tube systems that are di¬ rectly in the center of the dome are indicated by the num- bers 8 and 9. The spiral tube systems are at the same time a part of the dome s watercooled support system, because the spiral tube systems are supported at both of their ends by supporting rods 10 from outside of the dome, as figure 1 illustrates for example for the spiral tube system 9.

The input pipes 11 that are fastened to the openings 6 for raw material feed are equipped with ceramic lining and are tightened to thε corresponding part 2 and 1 on the dome with a thin insulating layer 12 that consists of ceramic wool and/or fibre and that due to watercooling endures the electric furnace's temperatures well. The effect of the watercooling reaches however beyond the insulating layer

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which to a certain extent increases the dome's tenacity to endure practical circumstances in the possible cases of

S malfunction caused by for example the overheating of the furnace.

Further the raw material's input pipes 11 go through the dome and that section 13 that is on thε inside of the fur¬ nace is a fixed part of the dome's cooling system and thus increases the dome's hermεtic sεaling because the input

10 pipes are watercooled at that part of the dome and on the inside of the furnace by a spiral tube system 7 that is supported from outside of the dome.

The openings 4 for electrodes in an electric furnace dome

15 in accordance with the invention are watercooled and her¬ metically sealed in two stages. Water spiral tube system 5 that is supported from outsidε of the dome is mountεd in the dome center's 2 refractory masonry, the water spiral tube system being thus at the same time a part of the dome's

20 watercoolεd support system around the electrode opening. Spiral tube system advantageously improves the durability of the area around the electrode opening which to a cer¬ tain extent incrεasεs the dome's hermetic sealing. Further a water seal s casing 15 which is made of refractory steel

25 plate and is equipped with external support rods 14 is abovε thε hole for the electrode, the ωatςr in the seal being separate or a part of the water circulating through thε spiral tube systems. The water seal aids in the dome's hermetic sealing especially between the current contact

30 pack and the dome's center 2.

In the figures the number 16 indicates an opening through which vapours and gases are removed from the furnace. Number 17 on thε other hand indicates a watercooled sand 35 seal which aids in achieving sεaling between the dome's edge 1 and the pot 18 and number 19 indicates the pot's external watercooling system where the cooling water in the

spiral tube systems is led, as is shown by the arrow in figure 1.

The heat loss of an elεctric furnace dome in accordance with the invention is moderate because of the selection of fa¬ vourable material. For processtechnical reasons ceramic mass or refractory bricks may be used as the construction matεrial for thε wholε domε. Thε domε may also be con¬ structed so that the edge 1 and the center 2 of the dome are made of different materials, from mass or bricks. How¬ ever in all applications, tube systεms 3 are usεd to sepa¬ rate the dome's edge 1 from the center 2, at which time the domε's edgε 1 is stationary and if nεcεssary thε center 2 may bε advantageously repaired or changed in possible cases of malfunction.

The acquisition price of the dome construction that is the object of the invention is also moderate on account of inexpensive construction materials. As a result of external supports it also lasts sufficiently long enough and requires little service and repair. Further the tube systems 3 sεparating the domε's εdgε 1 and the center 2 make the placement and operating of devices connected to the dome easier as well as servicing and repairing the dome.

In other words the principle of the dome construction in accordance with the invention is to make as good and pro¬ fitable use as possible of all of the tenacity, iπsulatory, refractory, and other such characteristics of the rεfrac- tαry material as well as the advantages of extεrnal support and watercooling.

This is achiεved by choosing thε refractory ceramic mater _¬ ial and masonry construction so that the dome is in prin- ciple under normal conditions self-supporting and extra strains as well as deficiencies in matεrial and construc¬ tion are taken care of by external support as well as by

watercooling at the most critical points, such as the elec¬ trodes and input pipes and at the center of the furnace. The purpose of the watercooling is to protect the support

\ systems that are constructed in the form of tube spirals an are at the critical points of the dome and of thε opεπings as wεll as to maintain thε temperature of the ceramic matεr ial at moderate temperatures as far as operating conditions are concerned without however unnecessarily cooling the molten chargε.

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