AU593375B2 - Process of operating a bell-type convection annealing furnace - Google Patents

Description

I

-I 4 a COMMQONWEALTH OF AUSTRALIA Patent Act 1952 ETE SPECIFIC

(ORIGINAL)

93375 A T I 0 N COM P L Class Int, Class Application Number Lodged Complete Specification Lodged Accepted Published Priority; Related Art Name of Applicant EBNER INDUSTRIEOFENBAU GESELLSCHAFT m.b.H.

Address of Applicant Ruflinger Strasse 1211, A-4060 Leonding, Austria Actual Inventor Peter Ebner Address for Service F.B. RICE CO., Patent Attor4xys, 28A Montague Street, BALMAIN. 204;.

Complete Specification for the invention entitledt PRocEss oF oSRATING A BELL-TYPE CONVElCTION ANNEALING FURNAC The followAng statement is a full deepription of this invention including the best method of performing it known to us:la The present invention relates to a process of operating a bell-type convection annealing furnace, in particular for processing coils of steel wire and steel strip, in which annealing and a subsequent cooling are performed under a combustible protective gas.

In the operation of such bell-type annealing furnaces which are provided with a fan, the protecting bell is placed over and aLound the stack of coils, then the heating bell is placed over and around the protective bell and air is purged from the protective bell by means of an incombustible protective gas. Before or during the annealing treatment, the incombustible protective gas is purged by means of hydrogen or another combustible protective gas. When the annealing has been completed, 15 the heating bell is pulled off and is replaced by a .4 cooling bell. Shortly before the cooling is terminated, the hydrogen or the other combustible protective gas is f t 0 ("iisplaced from the protecting bell hv an incombustible protective gas and both bells are rem'ved.

In that operation of a bell-type anne;aling furnace with a combustible protective gas, parti~larly hydrogen, risks will obviously arise if leaks ar cacks have formed in or at the prote-tive bell and the uedestal on which St, said bell is supportd. In the previous practice virtually no steps have beeni taken to avoid such risks.

Wherear it is known to subject furnaces fcr annealija brass to vacuum tests, such furnaces must have a much more v ti t massive structure, whirh in bell-type furnaces for Sannealing coils of wire steel or ateel strip would reduce 30 the efficiency because larger masses would have to be heated, The present i vention seeks to provide a process by which a be 1 -type convection annealing furnace can be operated with' a combustible protective gas witI a negligibly low safety risk.

f 2 In accordance with the present invention, the gas pressure under the protective bell is increased above the operating pressure before the beginning of the annealing treatment and/or before the beginning of the cooling treatment, the gas pressure under the protecting bell is subsequently intentionally decreased to a testing pressure, which also exceeds the operating pressure, and the pressure drop taking place during a predetermined period of time is monitored.

The amount of the pressure drop taking place during the predetermined time will indicate whether or not leaks are pres.ent. A perfect seal is virtually impossible.

Substantial leaks, which involve a certain ct .1 r: 0 csa A at

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I 1 o I I* I^ f' 4 y ~A~AA -3risk and may consist, of cracks in the protective bell or of leaks at the seal between the bell and the pedestal, can easily be detected cy the higher pressure drop occurring within the predetermined period of time if such leaks tave a total c-oss-aectional 2 area in excess 'of I mm In' that case the supply of incombustible rather than combustible protective gas can be continued if the test has been conducted before the beginning of the annealing treatment. The preceding increase of the gas pressure under the protective bell and the subsequent intentional decrease of said :pressure will ensure that the pressure is the same at the beginning of each measurement. But a test for .the pressure drop during the predetermined period of 15 time. will make sense not only before the annealing S.treatment. Cooling will cause the protective gas to *".000contract under the protecting bell and unless a sufficient amount of make-up protective gas is supplied that contraction will result in a vacuum under the

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20 protective bell so that air can be sucked into the protecting bell through any leak, For this purpose the test for a pressure drop is suitably effected 0 before the annealing treatment as well as during the last part of the annealing treatment or between tIa annealing and cooling treatments. It will be understood that the gas pressure under the protecting bell is maintained by a supjiy o. c'ombustible protective gas for the last-mentioned "est.

In practice, the coils to be annealod are often in a hot state as they are placed under the protecting bell. In that case a circulation of air and/or gas may result in a temperature rise of the 4 atmosphere and in a certain pressure rise, which would prevent an exact pressure test to be conducted. For this reason it will be desirable to conduct the test of the pressure drop during the predetermined period of time before the annealing treatment while the fan is inoperative and to operate the fan during such test conducted befLre the cooling treatment so that the stability of the fan wheel will not be adversely affected.

The present invention will now be further described with reference to the accompanying drawing, wherein the drawing shows a diagrammatic representation of a bell-type annealing furnace which can be operated by the process in accordance with a preferred embodiment of the present invention.

*t 15 A protective bell 2 is placed on a pedestal 1 with a seal interposed. A shaft of a fan 3 extends through the pedestal 1. A stack 4 of coils of steel wire or steel strip is disposed under the protecting bell. A heating bell or a cooling bell 5 has been placed over and around the protecting bell 2.

From the motor room of the fan 3, incombustible prot.ctive gas from line 6 can be supplied through the solenoid valve 7 to the interior of the protecting bell 2 or combustible protective gas can be supplied to the interior of the protecting bell 2 from a line 8 through a solenoid valve 9. An outlet line 10 leads from the interior of the protecting bell 2 into ft

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'6 7 A^ if l 110* the open air through a solenoid valve 11. A line 12 leading to a pressure monitor 15 branches from the outlet line 11 before the solenoid valve 11. Two time limit relays 14, 15 are associated with the pressure monitor 15. The intentional increase and decrease of the gas pressure under the protecting hood 2 are controlled by means of the solenoid valves 7 and 9 under the control of the time limit relay 14 and the pressure monitor 13. The actual pressure drop during the predetermined period of time is monitored by the pressure monitor 13 under the control of the 4. .time-limit relay

EXAMPLE

Steel strip coils having a total weight 15 of about 80,000 kg were to be annealed at a temperature of 7000C in a bell-type convection annealing furnace. The protecting bell contained a remaining volume of 8.5 m that was to be filled with protective gas.

When the furnace had been charged and the protecting bell had been positioned, incombustible protective gas containing up to 5/a by volume hydrogen was supplied into the protecting bell until a pressure of 22 millibars above the ambient pressure had been obtained in 4.

the annealing space. The gas pressure under the pro- 25 tecting bell was then reduced to a testing pressure of S^ 20 millibars, which exceed the operating pressure of 12 millibars, and the pressure drop taking place during a period of time amounting to 15 minutes was detected r while the fan of the furnace was inoperative. Because the pressure dropped only by 5 millibars during thattime, it was permissible to place'the heating bell over the protecting bell and to purge the incombustible protective gas by the protective gas proper, which con-

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-6sisted of 100 hydrogen, and the annealing could then be initiated. When the annealing had been te.minated, the heating bell was replaced by the cooling bell. Before this was effected, a similar test for tightness was performed while the fan was operated.

In that tightness test the pressure of the protective gas was increased to 22 millibars and was subsequently reduced to 20 millibars and the pressure drop within a period of time of 15 minutes was then detected.

Because that test resulted also in a pressure drop of millibars, the charge was cooled. Otherwise the protective gas would have to be supplied at a higher rate for the cooling step.

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Claims (1)

1. 7- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A process of operating a bell-type convection annealing furnace wherein annealing and a subsequent cooling are performed under a combustible protective gas, comprising, increasing the pressure of said protective gas under a protective bell of said furnace above an operating pressure of said protective bell, before the beginning of the annealing treatment and/or before the beginning of the cooling treatment, said increased protective gas pressure under said protective bell being subsequently intentionally decreased to a testing pressure, which also exceeds said operating pressure, and the pressure drop taking place during a predetermined period of time is monitored. 2. A process as claimed in claim 1, wherein, the test Sfor the pressure drop during the predetermined period of a ftime before the beginning of the annealing treatment being S. conducted whilst a fan of said annealing furnace is inoperative and the test for the pressure drop during the predetermined period of time before the beginning of the a ,coollng treatment being conducted whilst said fan is operated. 3. A process for operating a bell-type convection annealing furnace substantially as hereinbefore described 4 with reference to the accompanying figure and example. DATED this 20 day of November 1989 EBNER INDUSTRIEOFENBAU a GESELLSCHAFT m.b.H. u fPatent Attorneys for tle ;r AI pplicant: F.B. RICE CO. U 3. Afae 0i ai ea ee uyX *y 1JL DAE hs20dyo4oeme 99s a _6