Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – By means introducing treating material
Patent
1980-10-01
1983-01-11
Sheehan, John P.
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
By means introducing treating material
266270, C21C 532
Patent
active
043678688
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a refractory sheath for a metal pipe or tube, preferably a steel pipe, which is to be protected from high temperature and from the attack of molten metals and slags. The sheath in accordance with the invention is preferably intended for use with so-called lances in metallurgical processes, e.g. lances for injecting a gas into a molten metal. To advantage, the sheath can also be used for protecting metal pipes and tubes in general, e.g. burner lances for cement furnaces and cooling tubes in pusher-type furnace.
BACKGROUND ART
Lances intended for metallurgical processes consist in principle of a steel tube provided with a nozzle at one end and a lance holder at the order, the tube being surrounded by a refractory casing or sheath. This refractory sheath was originally made up from annularly shaped refractory bricks, joined to each other with refractory mortar. In this case, however, as with most metallurgical sheaths, there is a tendency to go over to a so-called monolithic sheath, which is generally more resistant and more simple to produce.
Monolithic sheaths have the disadvantage of not being self-supporting to the same extent as those made from prefabricated bricks. They have not been able to be made with an insulating air gap between the sheath and the lance pipe, as with the sheaths made from annularly shaped bricks, since attempts to do so have much too often led to cracks in the sheath, with the risk of molten metal penetrating through the cracks to the lance pipe and melting it. The monolithic sheaths have so far usually been made by moulding a refractory composition in a mould in which the lance pipe forms the inner wall. Anchoring pieces have usually been welded onto the lance pipe to ensure retention of the sheath. However, such a construction also leads to the formation of cracks in the sheath due to thermal stresses caused by the great temperature difference between the sheath which is in contact with the molten metal having a temperature of say 1600.degree. C., and the lance pipe, which can have a temperature below 100.degree. C. due to the heavy air blast through it.
DISCLOSURE OF INVENTION
The invention relates to a sheath for a metal tube or pipe which enables the avoidance or reduction of said disadvantages. The inventive sheath is characterized in that it comprises two coaxially placed cylindrical walls, between which there is moulded a refractory ceramic composition, the inner cylindrical wall consisting of a metal tube which can slide on the metal pipe to enable thermal movements between the metal pipe and the sheath.
The metal tube is made to slide on the metal pipe. Therefore, a clearance will necessarily be provided between the metal pipe and the metal tube, and this clearance reduces the heat transfer between the sheath and the metal pipe.
The sheath can be made so that the ceramic composition forms a monolithic unit. Alternatively, it can be made in several parts which are joined together during assembly with the help of a refractory cement.
The inner cylindrical wall of the sheath is thus to consist of a thin metal tube.
It is preferred that the metal tube is made from sheet metal, this being an inexpensive way of producing metal tubes. A preferred method of manufacturing a sheet metal tube is to wind a sheet metal strip into the form of a pipe. The strip is preferably provided with longitudinal ridges and grooves, resulting in a helical corrugation of the sheet metal tube, which will consequently be able to absorb thermal movements more easily. The thin sheet metal tube can also be provided with welded-on anchoring pieces in a conventional mode for improved retention of the monolithic sheath. Steel fibres can also be mixed into the sheath composition, to reinforce it in a manner known per se.
The outer cylindrical wall can consist of e.g. a cardboard tube. However, we prefer to let this wall also consist of a sheet metal tube, preferably manufactured by winding a sheet metal strip into tubular shape. The Spiro tube, which is on the
REFERENCES:
patent: 1793849 (1931-02-01), Groninger
patent: 2023025 (1935-12-01), McKee
patent: 3031178 (1962-04-01), White
patent: 3779534 (1973-12-01), Leroy et al.
patent: 3971548 (1976-07-01), Folgero et al.
patent: 3976286 (1976-08-01), Thompson et al.
patent: 4123042 (1978-10-01), Pearce et al.
The American Heritage Dictionary of the English Language, Houghton Mifflin Co., Boston, 1969, p. 760.
Blom Ingvar G. A.
Vuokivi Reima J.
Hoganas AB
Sheehan John P.
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