US 2971871 A
Description (OCR text may contain errors)
Feb. 14, 1961 D. BEGGS ANNEALING FURNACE SEAL Filed Jan. 29, 1958 INVENTOR. DONALD Bases ATTORNEY m 3 N Y 7 B a n Z M M S k .l 2 Ill 3 r I I, l Z B I 1 mm H T 1 M 2 E 7 M 0 2 G 3 F M m F United States Patent ANNEALING FURNACE SEAL Filed Jan. 29, 1958, Ser. No. 711,995
2 'Claims. (Cl. 148-16) This invention relates generally to heat treating furnaces, commonly referred to as bell annealers, and more particularly to an improved method and apparatus for reducing or preventing the contamination of the work charge therein. The apparatus is particularly adapted for use with single stand bell annealers and will be described in that connection.
Bell annealing furnaces generally comprise a base upon which the coils are stacked, a removable inner cover on said base forming therewith a heating chamber and having suitable sealing means therebetween, a fan in the base for circulating atmosphere in the heating chamber and a refractory lined heating cover disposed over the inner cover and adapted to supply heat to theinner cover.
In annealing furnaces, there are several factors which contribute to the. contamination of the work charge. One such factor is the infiltration of outside air which tends to oxidize the work. A seal is usually provided between the inner cover and the base-in order to reduce air infiltration. The ro'lling oil on the work charge vaporizes during an early stage, is entrained and carried by the circulating atmosphere to the sealing medium surface where it condenses. During the later stages of the annealing cycle this condensed oil becomes hot and breaks down chemically or cracks. Such cracking causes the oil to smoke and contaminate not only the inner cover but the Work as well by virtue of the smoke creeping up and into the inner cover.
It is accordingly an object of the present invention to "provide a method and apparatus for purging the inner cover and controlling the flow of at least a portion of the circulating atmosphere from the inner cover in a manner which reduces the contamination of work by the above mentioned factors.
The present invention combats the problem of air and smoke infiltration by providing a positive flow of atmosphere gases outwardly of the inner cover in those areas where infiltration is likely to occur.
Heretofore, most of the furnaces of the type described, particularly in the non-ferrous industry, have utilized oil as the sealing medium between the inner cover and the base. A water seal was objectionable because with prior sealing construction and operation the water would be inspirated or vaporized into the inner cover and wet the atmosphere gases and also contaminate the work.
A disadvantage concomitant with oil seals is cracking and carbonization of the oil which causes smoke in the same manner as described above in connection with the condensed rolling'oil.
The present invention combats this problem of smoking oil in two primary ways: first, the rolling oil that vaporizes and condenses on the surface of the liquid seal is immediately removed; and second, water is employed as the sealing medium.
Application of increased atmosphere circulation to furnaces of the type described has added to the importance of convection .as a process of heat transfer and has concomitantly increased the problem of infiltration ICC of undesirable air and the inspiration of contaminants which have collected on the liquid surface of the inner cover sealing means. In carrying out the object of this invention and minimizing the above cited problems, a positive venting flow of at least a portion of the circulating protective atmosphere from within the inner cover outwardly over the liquid seal is provided to prevent the infiltration of air and other contaminants from the seal area, and means for discharging contaminants which are deposited on the surface of the liquid seal by the protective atmosphere circulated thereto, as they collect, is also provided.
An advantage of the present invention is that it is possible to employ lower dew point atmosphere gases with a water seal than heretofore possible, the dry gases having a dew point as low as 40 P. which is especially useful for annealing ferrous materials. Heretofore, this was not effectively done because of inspiration of water or contamination of Water vapor from the Water seal which would tend to decarburize the work in ferrous practice. In the present invention such inspiration is virtually eliminated. With the use of atmosphere gases having a low dew point better quality and brighter work is attainable.
Another advantage of the present invention is the possibility of reclaiming at least a portion of the atmosphere gases discharged through the sealing means. Heretofore; it was not desirable to reclaim and recirculate the atmosphere gases so discharged because they were constantly being circulated through or adjacent the contaminants deposited on the seal.
It is accordingly another object of this invention to provide a method and apparatus for reclaiming and recirculating the atmosphere discharged from the inner cover.
For a consideration of what is considered to be novel and invention, attention is directed to the following specification and the claims appended thereto.
In the accompanying drawing forming a part of this specification:
Fig. 1 is a cross-sectional elevation view of a single stand bell annealing furnace embodying the present invention; a
Fig. 2 is a fragmentary view of the liquid charging means-of the liquid seal indicating how circulation of the liquid is attained; and
Fig. 3 is an enlarged fragmentary sectional View showing the shim construction of the inner cover. v V
The furnace comprises a base 10 and a bell type heating hood 11 removably seated on the base in a conventional sand seal 8. The base 10 is provided with-a coil supporting grid type stand 13 whereon a stack of coils 12 to be annealed may be supported, the stack being interspersed with separators 9 and covered by a metal inner cover 15 to permit a protective atmosphere to be circulated about the coils during the annealing operation by fan 16 which is driven by motor 17. The stand comprises a series of top plates 18 defining a grid; a series of radial vanes 19 which define gas passages between bearing plates 20 and .21 for the atmosphere circulated by fan 16. The grid structure is separated from the vanes 19 by annular spacer 22. A deflector 23 may be incorporated in the stand 15 to assist in initially directing the atmosphere longitudinally of the inner cover side wall. The atmosphere, which is non-oxidizing, is sup plied to the inner .cover 15 by a supply pipe 14 which eX- tends through the coilstand 13 from below.
A plurality of burners 25 are shown within the circumferential recess 26 in the peripheral wall 27 as the heating means, however, any suitable means may be employed. 1
In the present invention the refractory pedestal 30 is bounded by bands 31 and 32 and annular bottom plate 33 to surround all of said refractory pedestal except the top side 34. The refractory 30 is preferably sulficiently porous to enable gases to flow therethrough. An annular passage 35 is provided within the refractory 30 to serve as a plenum chamber for the gases fiowing through said refractory. A small portion, preferably approximately of the circulating atmosphere is bled through the refractory to said plenum chamber. In accordance with the invention, the amount of gases so bled is controlled by gas flow restricting means, shown as an orifice plate 37 in gas vent pipe 38. Accordingly, by providing a positive bleed-off of gases through the refractory 30 the refractory is initially purged of any residual air and infiltration of extraneous air or gas is prevented through the said refractory to preclude oxidation of the work.
To prevent objectionable leakage of gas out of the inner cover or of air into the inner cover, it is necessary to provide a substantially gas tight seal between said inner cover 15 and the inner base 10a.
A first seal, or flow restricting means, is formed at the juncture of the inner cover support means and the base. The cover 15-is provided with horizontal annular plate 40 which seats on outer band 32 and is supported thereby. -Some leakage or seepage will occur through this flow restricting means and in practice the volume of seepage is preferably controlled by placing intermittent shims 29 on the plate 40 where it rests on hand 32 to insure uniform fiow around the seal periphery. In practice, it is preferred that approximately 90% of the atmosphere discharged from the inner cover be discharged through said restricting means at a preferred minimum velocity of 50 ft./min.
A vertical annular flange 41 extends from the plate 40 into the liquid 42 contained in annular trough 43 to form a second seal. Thetrough 43 is welded to the base 10 and extends beneath the bottom plate 33. The trough 43 in addition to serving as asealing medium containing means also serves as a collecting chamber for any con taminants passing with the gases through the flow restricting means. Y r a While the contaminant collecting chamber has been described as the trough at the juncture of the inner cover and base, a collecting chamber separate from the trough may be placed at any point adjacent to said inner cover together with restricted passage means interconnecting it with the heating chamber-formed by theinner cover and'with a positive flow of atmosphere gases from the heating chamber perform the. same contaminant collecting function as the trough chamber.
The work charge of coils in an inner cover is generally enveloped by a film of rolling oil from previous work treatments. Such oil vaporizes at 400500 F. and circulates with the atmosphere and condenses on the surface of the liquid seal generally provided with such furnaces. After the work charge is brought up to temperature and held at temperature for the desired length of time, the outer cover is removed, to cool the inner cover and concomitantly the work charge within. Upon the removal of the outer cover the inner cover cools rapidly, cooling the atmosphere gas within and reducing the pressure within until the inflow of atmosphere gas makes up for the volume lost by contraction. The eddy currents of gases flowing outwardly from vanes 19, as they turn upwardly past the seal, will cause relatively low and high pressure areas adjacent the seal, and during the period of lowered pressure at the start of the cooling cycle there will often be some local reverse flow of gases through the seal adjacent some of the shims 29 even though the net flow adjacent all the shims is outward from the inner cover. If smoke, oil vapor or water vapor is allowed In accordance with the invention, means is provided to discharge the oil as it condenses on the liquid 42 and thus avoid contamination of the work with oil or other contaminants that fioat on the surface of the liquid seal. Such means comprises a weir 46leading to discharge pipe 47. Such means also comprises a liquid inlet 48 to the liquid seal from which additional liquid sealing medium is discharged in a direction which tends to circulate the .liquid within the trough 43 and thus continually present a new liquid surface to the weir 46 from which the condensed oil may be skimmed off. The inlet 48 may be placed in the bottom plate. 33 as shown in Fig. 2 or it may be incorporated in the side wall tangential to the center line of the trough 43. An outlet 44 is also provided so that the trough 43 periodically may be flushed out.
Since some of the atmosphere gas flowing to the liquid trough will escape with the oil through weir 46, means is provided to control the flow of atmosphere so escaping. Such means comprises a bubbling tower or chamber 50 into which discharge pipe 47 extends. A column of water 51 is maintained in the chamber 50 to a height above the discharge end of pipe 47that corresponds to the desired back pressure, i.e., if it is desired to maintain a back pressure in the gas Within the pipe and sealing trough 43 of two inches water column, the column of water within the chamber 50 will extend two inches above the end of discharge pipe 47. The gas that bubbles through the water column is thenvented through pipe 52. A weir 53 leading to a drain 54 is also provided to maintain the liquid level within the chamber 50 and to serve as a discharge for the contaminants that pass to chamber 50 from trough 43.
For those operations where economics .dictate that it is feasible to reclaim the atmosphere discharged through pipe 47, means is provided to direct such atmosphere to supply pipe 14 for recirculation in the inner cover 15. Such means comprises passage 56 leading to a decontaminator 57, which will ordinarily be a dryer, and may if de-- sirable include a chemical reformer such as a catalytic oxidizer, and passage 58, pump 59 and passage 60 leading to supply pipe 14. During the early part of the work cycle when the rolling oil vaporizes and condenses on the liquid seal, valve 61 in passage 56 may be closed and valve 49 in pipe 47 opened to carry the contaminated gases to the vent 38. During the later stages of the work cycle the inner cover has been purged and most of the oil contaminants have been discharged, thus the only contaminant being discharged with the gases passing through weir 46 is water picked up at trough 43. Valve 61 may then be opened and valve 49 closed to direct the discharged atmosphere to decontaminator 57 where it is dried and pumped I to supply pipe 14. An orifice plate 62 is also provided in passage 56 to control the flow therethrough.
It will be readily apparent that vent pipe 38 may also be interconnected to passage 56 to reclaim and recirculate gases discharged therethrough. Appropriate valves may be provided to accomplish this, preferably after the refractory pedestal 30 has been initially purged of residual contaminants.
The above described recirculation means may be employed during any stage of the working cycle but is particularly efiective in the manner described. Automatic clocking means not shown may also be provided to' automatically close valve 49 and open valve 56 after a predetermined time of the work cycle has expired.
The various features of the invention combine to provide a method and apparatus which produce clean, bn'ght to collect 'in the chamber between the shims 29 and the 1 work uncontaminated by the harmful effects of air filtering through the pedestal, or by oil condensed on the surface of forming part of the liquid seal. The described system also provides recirculating method and apparatus by which a comparatively small size gas generator may. be employed to provide atmosphere gas for several units...;.By .virtue of this recirculation, once an inner cover has been purged the only additional gas required is make-up due to sealing losses. Heretofore, the atmosphere gas passing through the seal was vented and lost.
The foregoing is an extensive disclosure of the principies involved in the present invention which will enable a person skilled in the art to take advantage of this invention in similar or equivalent forms.
1. The method of operating a bell annealer containing an inner cover to heat the work charge therein and prevent contamination of said work charge, which comprises: supplying heat to the inner cover; transferring at least a portion of the heat from said inner cover to said work by circulating atmosphere within said inner cover contiguous to at least a portion of the inner cover side wall, said atmosphere being introduced to the inner cover at a rate sufiicient to produce a positive outward flow of escaping atmosphere at the juncture of said inner cover and the base; collecting such escaping atmosphere together with any entrained contaminants in a liquid containing trough forming part of the sealing means between said base and said inner cover; discharging the excess liquid and contaminants occasioned by such collecting in a manner to maintain a fixed level of liquid in said trough and simultaneously withdrawing a portion of the circulating atmosphere through the refractory portion of the base at a predetermined rate.
2. In an annealing furnace having a base, an inner cover on said base and forming therewith a heating chamher, a flange member depending from said inner cover, means for adding protective atmosphere to the heating chamber defined by said inner cover and said base, a fan in the base for circulating said atmosphere, a refractory lined heating cover disposed over said inner cover on said base, a plurality of shims disposed between said base and said inner cover and forming therewith passage means between said inner cover and said base whereby said atmosphere can escape at a substantial rate, a liquid containing trough in said base whereby a seal is formed by the insertion of said flange member of said inner cover below the liquid level of said liquid containing trough, a first weir in said liquid containing trough by which excess liquid and contaminants floating on the surface of said liquid may be discharged from said liquid containing trough, the combination which comprises: a liquid containing chamber, means for maintaining a predetermined liquid level in said liquid containing chamber, piping means connectin" said liquid containing trough with said liquid containing chamber in liquid communicating relation to permit the passage of liquid from said trough to said chamber, the outlet of said piping means being lower in elevation than the liquid level of said liquid containing chamber; whereby the pressure of the protective atmosphere in said heating chamber can be maintained at a desired positive pressure.
References Cited in the file of this patent UNITED STATES PATENTS 1,869,025 Seastone May 26, 1931 1,976,557 Haskell Oct. 9, 1934 2,146,760 Pearson Feb. 14, 1939 2,175,922 Scott Oct. 10, 1939 2,176,473 Rosecrans Oct. 17, 1939 2,177,031 Tanner Oct. 24, 1939 2,282,226 .Hoop May 5, 1942 2,284,014 Peck May 26, 1942 2,769,630 Keller Nov. 6, 1956 2,843,514 Kunz July 15, 1958 2,854,226 Cone Sept. 30, 1958 FOREIGN PATENTS 5' 15,331 Great Britain Dec. 1, 1939 2,283,982 Germany May 26, 1942