MELTING FURNACE FOR THE MELTING OF MINERAL FIBRE RAW MATERIAL

Abstract: The invention concerns a melting furnace for the melting of mineral fibre raw material which furnace comprises a bottom part (1), sidewalls (2) and a cover (3), and supply means for the raw material. The melting furnace is provided with a discharge opening (4) in the sidewall (2) for mineral melt (8) at a distance from the bottom part (2) of the melting furnace, and a discharge opening (6) for emptying the melting furnace, at the level of the bottom part (2). The melting furnace further comprises an additional discharge opening (7) for discharging of iron melt (11) formed during the melting process provided in the sidewall (2) at a level above the discharge opening (6) for emptying the melting furnace, but at a level below the discharge opening (4) for the mineral melt (8).

Description: Melting furnace for the melting of mineral fibre raw material This invention concerns a melting furnace for the melting of mineral fibre raw material, the furnace comprising a bottom part, side walls and a cover, supply means for the raw material, as well as a discharge opening in the side wall for mineral melt arranged at a distance from the bottom part of the melting furnace, and a discharge opening for emptying the melting furnace, at the level of the bottom part. Mineral wool products of glass wool, rock wool and slag wool type are the most well known and used products for both heat and acoustical insulation. These products are made e.g. so that the raw material, such as rock mineral or slag from iron production, are melted in a melting furnace. Mineral melt is withdrawn continuously from the furnace and converted to fibres e.g. in a spinning unit consisting of a plurality of rotating wheels, from which the mineral melt is spun under the formation of fibres. The thus formed fibres are transported with an air current from the spinning unit and collected onto a conveyor in the form of a fibre felt. The fibre felt is then subjected to further processing steps, e.g. impregna¬ tion with a binder, such as a resin, which in a final stage of the manufacturing process is cured, e.g. in a curing oven. During curing the fibres are fixed to each other forming a form stable felt of the desired density and thickness. The cured fibre felt can thereafter e.g. be cut to the desired shape, such as sheet products or roll products, which thereafter are packed or processed further. During the melting process, the iron oxide, or part thereof, contained in the mineral raw material or the slag is reduced to metallic iron and sinks to the bottom of the furnace in the form of an iron melt, which continuously increases in volume. In order to prevent iron melt from accompanying mineral melt into the spinning unit, the iron melt has to be removed at regular intervals from the melting furnace. In the prior known melting furnaces the iron melt is removed through a discharge opening in the bottom of the melting furnace, whereby the iron melt is completely removed at each emptying operation. This method cf proceeding is used e.g. in the melting furnace according the Fl-patent application no 853458. The mineral melt formed during the melting process has a very corrosive effect on the walls of the melting furnace. This results in the fact that the melting furnace on its inside has to be provided with an extremely corrosion resistant lining, which is both expensive and difficult to apply. Tests made have shown that the iron melt which collects at the bottom of the melting furnace has a much gentler effect on the lining than the mineral melt. If it is possible to prevent the iron melt from sinking below a predetermined level, it is possible to use in the bottom part of the melting furnace a much cheaper lining. This is achieved in the melting furnace according to the present invention by providing an additional discharge opening for discharging iron melt formed in the melting process, in the side wall at a level above the discharge opening for emptying the melting furnace, but at a level below the discharge opening for the mineral melt. With this solution the level of the iron melt is prevented from sinking below the level of the additional discharge opening. In order to ensure that the bottom part of the melting furnace as soon as possible after starting up the furnace is covered by a protective layer of iron melt, pig iron is added to the melting furnace prior to starting the introduction of rock raw material. The other characteristics of the invention appear from the appended Claims 1 to 6. In the following the invention will be described in more detail referring to the drawing which shows schematically an example of a melting furnace according to the invention. The melting furnace comprises a bottom part 1, side walls 2 and a cover 3. A number of electrode rods 5, preferably of graphite, extend through the cover by means of which the raw material 9 is melted. This raw material 9 is introduced into the melting furnace by means of supply means (not shown), which are arranged to distribute the rock raw material 9 in a substantially even layer over the mineral melt 8 formed during the melting process. Mineral melt 8 is withdrawn during the melting process in a constant flow from the melting furnace through a discharge opening 4 arranged in the side wall 2 to a spinning device (not shown) for the formation of mineral fibres. The discharge opening 4 is situated at a level at a distance from the bottom part 2 of the melting furnace. For emptying purposes the melting furnace is provided with a discharge opening 6 at the level of the bottom part 2. Above the discharge opening 6, there is arranged in the side wall 2 an addi¬ tional discharge opening 7 for discharging iron melt 11 formed during the melting process. This additional dischar¬ ge opening 7 is situated at a level lower than the dischar¬ ge opening 4 for the mineral melt 8. The two lower discharge openings 6 and 7 are suitably arranged in a common block, which according to a preferred embodiment is a carbon block divided into four parts, where the two outer parts, in which the respective discharge openings 6 and 7 are arranged, are replacable. The inside of the block is preferably covered with a lining mix 10. During the melting process some of the iron oxide in the raw material 9 is reduced to metallic iron which sinks to the bottom of the melting furnace and results in a steady increase of the amount of iron melt 11. The discharge openings 6 and 7 are normally closed and are opened only when necessary. In order to prevent the level of the iron melt from reaching the opening 4 for the mineral melt, excess iron melt has to be removed at regular intervals. Normally excess iron melt 11 is removed from the melting furnace at about 2 to 3 months intervals. The discharge opening 7 is then opened using a drilling machine or by burning with oxygen. When the desired quantity of iron melt 11 has been withdrawn from the furnace, the discharge opening 7 is closed using a mud gun (not shown) which has been precharged with heated sealing mud. The drawing shows the state when all excess iron melt has been removed. The discharge opening 6 is opened only when the whole melting furnace is to be emptied, e.g. for service or for renewing the lining. Opening of the discharge opening 6 takes most conveniently place by burning with oxygen.

Claims: Claims 1. Melting furnace for the melting of mineral fibre raw material which furnace comprises a bottom part (1), side walls (2) and a cover (3), supply means for the raw material, as well as a discharge opening (4) in the side wall (2) for mineral melt (8) at a distance from the bottom part (2) of the melting furnace, and a discharge opening (6) for emptying the melting furnace, at the level of the bottom part (2), characterized in that an additional discharge opening (7) for discharging of iron melt (11) formed during the melting process is provided in the side wall (2) at a level above the discharge opening (6) for emptying the melting furnace, but at a level below the discharge opening (4) for the mineral melt (8). 2. Melting furnace according to the Claim 1, characterized in that the two lower discharge openings (6, 7) are arranged in a common block. 3. Melting furnace according to the Claim 2, characterized in that the two lower discharge openings (6, 7) are normally closed and are opened by drilling and/or burning with oxygen. 4. Melting furnace according to the Claim 3, characterized in that the discharge opening (7) for iron melt (11) is closed with a mud gun. 5. Melting furnace according to the Claim 2, characterized in that the block is a carbon block divided into four parts the two outermost parts being replacable. 6. Melting furnace according to the Claim 5, characterized in that the block on the inside of the furnace is protected with a lining mix (10).

Inventors: HJERPPE PERTTI KALEVI, NYGAARDAS CARL-GUSTAV, SOLIN PETER ARNOLD HENRIK, HJERPPE, PERTTI, KALEVI, NYGAARDAS, CARL-GUSTAV, SOLIN, PETER, ARNOLD, HENRIK
Applicants: PAROC OY AB
Application year: 1991
Main classification: C03B5
IPC codes: C03B5