Stoves and furnaces – Stoves – Heating
Patent
1983-11-23
1985-06-04
Dority, Jr., Carroll B.
Stoves and furnaces
Stoves
Heating
432209, F24C 300
Patent
active
045207895
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to improved supports intended, in particular, for the heating bodies for annealing furnaces.
The heating bodies are used especially in furnaces for the continuous annealing of steel strips.
In such furnaces, a reel of steel strip is unwound and the steel strip passes through a degreasing device. It is dried by hot air before entering the furnace, which is divided into a heating section and a holding section. An inert atmosphere and a pressure greater than atmospheric pressure prevail therein in order to prevent any risk of contamination. The strip is guided, along its path through the furnace, between the walls consisting of heating bodies arranged in a staggered formation. On leaving the furnace this annealed strip is wound onto a reel.
From the article in "Gaz d'aujourd'hui", Volume 98, No. 9, September 1974, Paris (France), entitled "Une utilisation rationnelle de l'energie: le tube radiant a gaz" ("A rational use of energy: the gas-fired radiant tube") by Messrs. DOUSPIS, pages 395 to 400, several types of radiant tubes (heating bodies) are known, namely straight tubes, single-hairpin tubes and recirculation tubes.
Other documents, such as U.S. Pat. No. 2,822,798, describe ways of fixing straight radiant tubes, and British patent application No. 487,764 and French patent application No. 861,541 show particular heating bodies or heating bodies of a particular shape.
British patent application No. 1,396,796 relates to a means of supporting U-shaped radiant tubes, consisting of a roller which is fixed to the wall of the furnace and over which the tube can slide without friction during thermal expansion.
This means has the disadvantage that it is bulky and that it cannot be used in furnaces for the continuous annealing of steel strips, for example.
U.S. Pat. No. 2,652,037 relates to supports for heating bodies (radiant tubes) in the form of a double hairpin bend, supported by a single rest fixed in a tube perpendicular to the radiant tube. In this application, the expansion of the radiant tube results in sliding over the rests, which is a cause of wear, microwelds and the like. Moreover, the tubes in which the rests are fixed are bulky and prevent the continuous passage of a steel strip which winds around the radiant tubes arranged in a staggered formation.
U.S. Pat. No. 2,204,144 relates to double-hairpin heating bodies supported or suspended and spaced apart by members permitting the expansion of the unit and acting as sliding points, which thus permit a relative movement of one element of the heating body relative to the other.
However, although the manufacturer indicates a limiting temperature of about 840.degree. C. for the tube, an ambient temperature in the furnace of the order of 930.degree. C., or even exceptionally of 1,040.degree. C., is regularly recorded.
This excessive trend can result from an excessive speed of unwinding of the strip, from a product quality for which the heating rates were not intended, or from an irregularity in the servicing intervals, which leaves the furnace deprived of part of its heating capacity.
Under these conditions, the following disadvantages are observed: consist of spacing members also acting as sliding points, which thus permit a relative movement of one tube element relative to the other, no longer fulfil their role. Seizure, in particular, is observed at the sliding point supporting the upper hairpin bend, and this is due to microwelds generated in particular by an excessively high temperature. Swelling of the upper tube of the hairpin heating body then takes place, which causes off-centring of the burner flame.
As a result of an excessively high temperature, the rest firmly fixed to the outer wall of the furnace becomes deformed and introduces a torque, which causes the heating body to buckle.
A similar torque can also be generated by secondary tensions created during the production of the welds between the tubular elements and the bends, which tensions would be released the first time the heating body was ignited and/or after
REFERENCES:
patent: 2200731 (1940-05-01), Woodson
patent: 2204144 (1940-06-01), Moore et al.
patent: 2652037 (1953-09-01), Lewis et al.
patent: 2822798 (1958-02-01), Ipsen
patent: 3079910 (1963-03-01), Bloom et al.
patent: 3920383 (1975-11-01), Kerr
Gaz d'aujourd'hui, vol. 98, No. 9, Sep. 1974, Paris (FR), M. Douspis: "Une utilisation rationnelle de l'energie: le tube radiant a gaz", pp. 395-400.
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