US2240099A - Method of bright annealing elongated metal bodies - Google Patents

Description

April 29, 1941. QSCHINCKE KETHOJ 0F BRIGHT AHNEALING ELONGATED METAL BODIES lll/f SWW f /ff/ 1 ,ANN

Earn

o. scHmcKI-z 2,240,099

Filed sept. 14, 195s 2 sheets-sheet 2 April 29, la'rnon oF BRIGHT HEALING ELoNGATEp uETAL BODIES Patented Apr. 29., 1'941A METHOD F BRIGHT ANNEALIN G ELONGATED METAL BODIES Otto Schincke, Vienna, Austria Aapplnmtien septemberI 14, 193s, semina. 100,749 In austria october 1s, 1935 i 4`Claims.

` other metals and alloys such as for example steel.

The invention has for its object to simplify the technique of and to cheapen the annealing process, in which oxidation ofthe metallic material handled must be inhibited, and makes it possible, first and foremost, for rigid metal bodies of any desired length to be subjected te bright annealing in an uninterrupted working operation without any special precautions having to be taken.

A large number of proposals have already become known for the bright annealing of metallic nealing chambers or pots from which, with the material. According toa widely practised method of Working the annealing is carried out in an-` view of avoiding oxidation of the metal treated,

the air has been removed either by displacement bya protective gas or by evacuation. The evacuation is generally effected by the connection of an exhausting air pump to the annealing container.

In addition, there is also to be found in the existing literature on the subject the proposalto produce the desired reduced pressure in annealing pots by mere heating, the admission of air into the vessel being prevented, after the attainment of the maximum temperature, by closing the outlet valve. With all known-methods of this nature the annealing is effected in a chamber which is gas-tightly closed off from the outside atmosphere. Since the dimensions of the chamber or of the receiving container set a limit to the dimensions of the material to be treated only metal bodies of restricted length can be sub.. jected to the annealing' treatment by these known working methods. Moreover, when annealing containers are used the annealing process `can only be carried out intermittently (in batches). Y

Annealing furnaces have already been built `which admit of continuous operation. For this purpose the procedure adopted has been based on the assumption that, to .avoid oxidation of the annealed material, it is not merely necessary to carry out the annealing process in a protective gas atmosphere, but -also to take special precautions to lprevent the admission of 'air to the an` nealing chamber.

Thus for example a furnace design has been recommended in whichl the two ends. of the annealing-retort take the form of downwardly bent tubes which extend, with the inlet and outlet orifices for the metal material, under the surface of a liquid bath; by the liquid seal thus provided at both ends of the retort the admission of air to the annealing zone is prevented, While a protective gas is introduced into this zone. A bright annealing furnace of this natture is indeed suited for annealing flexible materialsuch as wire, strip, and the like, but the treatment of elongated rigid bodies is not possible in a furnace of this description.

According to another known type of furnace design the retort is sealed by means of stuffingboxs the internal clearance of which corresponds to the cross-section of the material to vbe treated, so that during the passage of the material through' the inlet and outlet apertures no air can enter the annealing zone', while at the same time steam or the like is introduced under pressure water which becomes converted in the annealing zone into steam which acts as a protective gas.

Only for the. annealing of fine wire has a proposal become known by which the Work is carried on uninterruptedly without the introduction of a protective gas into the annealing chamber; also in this case the wire is introduced and withdrawn. through a nozzle the bore of which is adapted to t exactly the cross-section of the Wire, so as to prevent the admission of air,'and in addition dusting with talc is done to aid in the formation of a seal against the access of air.

In consequence of the diiculties attendant on all'these methods of working, which difculties are principally concerned with the sealing of the annealing zone from the access of air and become harder to de al with the larger the crossseetion of the material to be treated is; it is still in the main the usual practice, even to-day, toy

anneal metal" tubes or rods of great length in the air and then to remove the oxide skin thereby formed by the diflicult and troublesome process of pickling.

The present invention is based upon the surprising discovery that it is possible (contrary to the hitherto accepted opinion) in connection with the bright annealing of metal material within a tubular conduit (for example a retort) to dispense with special precautions for preventing the access of air from the outside atmosphere, for instance by tightly closing the entry and outlet apertures (whether by fluid seals and the like or by meansof stuffing-boxes and the like) under certain conditions, namely provided the dimensions of the annealing tunnel, as regards length and inside' clearance, be so determined in dependence upon each other that within the heated part there becomes formed a permanently maintained zone of atmosphere of reduced density, as in this case in spite of communication with the outside atmosphere air from the latter does not enter the annealing zone.

The method according to the present invention for the bright annealing of elongated and more particularly rigid metal bodies such as tubes, in which the metal material travels, preferably continuously, through an annealing zone Within a tubular tunneLthus consists essentially in passing the material through a tunnel which is bathed by combustion gases at the annealing zone, and the length and inside clearance of which are so dimensioned in dependence upon each other that in the heated part a permanently maintained zone of atmosphere of reduced density is formed, with the maintenance of an open communication between the tunnel and the outside atmosphere at the entry end or at the entry and discharge ends, whereby an additional introduction of protective gas can be dispensed with.

The retention l of a bright surface on the metal, with this method, in the absence of protective gas is apparently ensured by the fact that the oxygen content of the-atmosphere in thev annealing zone is reduced to such an extent, by the rarefaction of the air due to the heating, which is constantly maintained, that practically speaking oxidation cannot occur. It may also be that neutral or reducing gases, such as hydrogen, contained in the combustion gases penetrate through the tunnel wall into the annealing zone, and aid in the action of the atmospheric rarefaction in the annealing zone, or themselves exert a reducing action. 1f desired, the air may be displaced at the commencement of the annealing process, in a manner known per se, by the introduction of a protective gas.

It will be clear that it is necessary, in connecton with this method, to avoid the setting up of a chimney action (draught) in the annealing zone, which would bring about the feeding in of air. Thus when the annealing tunnel is inclined to the horizontal it is necessary to seal the lower end of the tunnel, in a manner known per se,.by means of a liquid. Even with this form of construction of the annealing plant, however, the entry end of the tunnel remains in open communication with the outside atmosphere; likewisewith this form of construction an additional introduction of protective gas into the annealing zone is -not necessary.

For the annealing of tubes of anoutside diameter of say mm. there may be employed for example a tunnel the inside diameter of which is about mm. and the length of which amounts to some 6 to 10 m., the annealing zone proper attaining a length of about 1 to 2 m., while the remainder of the length of the tunnel is mainly utilized for the cooling of the treated 'mater-ital. If the tunnel is inclined, and sealed at the outlet or discharge end by means of a liquid in which the annealed material is cooled very considerably shorter tunnels of a total length of say 3 to 4 m. will suffice; in this case greater freedom is given for the `selection of the ratio between the inside clearance and the length of the tunnel.

Given constant furnace temperature, the anhealing temperature assumed by the metallic material in theannealing zone may be adjusted in a manner known per se, by regulating the rate of movement of the metal material through the tunnel, according to the nature of the metal or metal alloy and the dimensions of the material to be treated. For example, a pure copper pipe of an internal diameter of approximately 18 mm. and an external diameter of approximately 20 mm., when the temperature of the furnace is about 900 C., may be conducted through the annealing zone at the rate of about l m. a minute, the annealing temperature of the tube material being only about 650 C. If it is desired to anneal at lower temperatures the rate of conveying is suitably increased, and in the converse case the'rate of conveying is reduced so that the material assumes a higher temperature which may be increased in this way up to a maximum temperature which; is but slightly lower than the furnace temperature. If it is desired to increase the rate of movement through the annealing zone at a given annealing temperature this zone is made correspondingly longer.

The present invention provides the possibility of subjecting metal bodies of any length, for

example of a length amounting to 20 m. and more, to the annealing process without interruption, with the retention of a bright surface, and without the necessity of connecting together the individual pieces or lengths ofthe material or of sealing the entry aperture of the annealing tunnel. The further advantage therefore accrues that a plurality of individual pieces placed side by side can also be annealed simultaneously, provided there is room for them in the annealing tunnel.

Apparatus for carrying out the method according to the invention consists for example of a furnace which is traversed from side to side by a tube made from known heat-resistant materials, and more particularly from heatresisting steel. To 4this tube, which comprises the annealing zone proper, further tubes may be permanently or detachably connected at one side or at both sides. Since the extension tubes are not exposed to the direct action of the furnace heat they may also be made from other materials than refractory or heat-resistant material. The tunnel may equally well be formed of a single tube comprising the annealing zone as well as the cooling zone. The tunnel is preferably of circular cross-section, but it is also possible to arrange for it to be of any other cross-sectional configuration.

The heating of the tunnel from the outside is preferably effected by means of gas or crude oil burners, although it is equally possible to fire the furnace with solid fuels such as coal, coke, or the like.

u 'and tnefncuon wn'eels z5 by the driving shaft 2i. The friction gearing v25 enables the control After-the furnace has been' heated`up 'in the required temperature, having regard for the difference between the temperature in the furnace which` a cooling` liquid is caused to flow.

It is also advisable to discharge the annealed material from the tunnel directly into a cooling bath which may consist for example' of water or oil. The plant is preferably so designed that the discharge end of the'tunnel extends just beneath the surface of the cooling bath, so that the annealed material passes directly into this bath.

In this case, when water is usedas the cooling medium,`decomposition of the water vaporized by contact with the hot metal yields hydrogen which exerts a reducing action upon any oxide present.

Other and further objects and features of the invention will be more apparent to those skilled in the art upon consideration of the accompanying drawings and following specification wherein I disclose two exemplary embodiments of an apparatus for carrying out the method according to this invention, with the understanding, however, that such change may be made in the structure as will fall within the scope of the appended claims without departing from the spirit of the l invention.

Fig. l is a side view of a form of construction of apparatus, partly -in vertical section, according to which the annealing tunnel is disposed horizontally; Fig. 2a section through the furnace on the line 'rl- 2, Fig. l; Fig. 3 a vertical section through the coupling between the annealing tunnel and the cooling tubes; Fig. 4a a side view of another form of construction of apparatus, partly in vertical section, according to which the axis of the annealing #tunnel is inclined tothe horilzontal, and Fig. 4b a continuation of Fig. 4a showing the portion of the container 'withthe cooling liquid, which is broken off in Fig. 4G, the dotted lines illustrating the broken off end of Fig. 4a.

Referring to Figs. 1 to 3 of the drawings, I0

- 4denotes the furnace which is built up of brickwork II and heat insulating material I2, and is encased partly by a shell I3 of sheet metal. The furnace is heated for instance by means of gas or crude oilvburners not shown, the llames being injected into the furnace through the nozzles I4.

' The furnaceis traversed by parallel tubes I5 of y heat-resistant steel which pass through the end walls of the furnace and constitute the annealing' zone within the furnace. Inside the -furnace the tubes l5` are supported bythe platefl, and out- -side the furnace uprights I1 xed to the end walls I9 denotes a of the speed of the rollers 22. 'Ihe upper rollers 23 are mounted adjustably in height so that the distancebetween the surfaces of the upper and lower rollers may be regulated according to the thickness of the metal bodies to be treated.

'I'he annealing tubos l5 are connected by the coupling 21 to the tubes 28 which are encased by a cooling jacket 23. Water is supplied to the cooling jacket 29 through the feed Pipe `3|) and withdrawn through the discharge pipe 3l.

As particularly shown in Fig. 3, the coupling 21 consists of two pipe flanges 32 fixed together by the screws 33 which co-act with' two sockets 34 each of which being screwed on the end of the annealing tube I5 and the cooling tube 28 respectively. Betwegn the sockets there is inserted a packing member 35.

The free ends I5, 28n of the annealing tubes and cooling tubes respectively are open and thus in direct communication with the outside atmosphere.

The form of construction shown in Figs. 4a

and 4b is similar to that of Figs. 1 to 3. However. the axes of the annealing tubes I5 and of -the cooling tubes 28 are inclined to the horizontal, the, inclination being about 8:100, and as cooling means there is used a cooling bath provided in the container 36. Furthermore, the annealing tubes I5 are integral with the cooling tubes 28 so that each tube comprises both the annealing and cooling zones., These 'tubes are open at the entry end I5 as in the above'described-form of construction, and terminate atthe discharge end 28a' below the surface of the cooling liquid in the container 36. With this form of apparatus the annealed metal tubes 2| or the like pass directly into the cooling bath, travel through the same and are conveyed'out of it along the bottom of the purpose. At the end the bottom of the container iseven again' so that the Ametal tubes 2| leave to be annealed, for instance metal tubes 2| is effected by means of a conveying device consisting of two pairs of co-acting rollers 22, 23 the lower rollers 22 of which are driven through the gear the cooling bath in straight condition.

What I claim is:

l. A method of bright annealing elongated rigid metal bodies comprising heating externally by combustion gases a long, straight and horizontal annealing tunnel -of heat-resisting steel, to a temperature at which the density of theatmosphere is reduced to a degree at which a non-oxidizing condition is reached in the tunnel, maintaining said condition, cooling a straight tunnel tightly connected to and in alignment with said annealing tunnel, maintaining an open communication with the outside atmosphere at the entry end of the annealing tunnel and the discharge end of the cooling tunnel,.intro ducing the said elongated metal' bodies into the annealing tunnel through'V the entry end thereof, moving said metal bodies through said annealing and cooling tunnels at a rate controlled so that said metal bodies assume the properl annealing temperature, and discharging the metal bodies through the outlet end of said cooling tunnel.

2. A method of bright annealing elongated rigid metal bodies comprising heating along straight annealing tunnel, tightly connected to and in alignment with a straight cooling tlmnel, externally by combustion gases to a temperature at whichthe density of the atmosphere is reduced to such a degree that a non-oxidizing condition is reached in the tunnel, providing an open communication with the outside atmosphere at least at the entry end of the annealing tunnel, maintaining a non-oxidizing condition in the tunnel by the continued application of heat thereto and by the prevention of a longitudinal draft therethrough, introducing the said elangated' metal .bodies into the annealing tunnel through the entry end thereof, moving said metal bodies through said straight annealing and cooling tunnels at a rate controlled so that said metal bodies .become heated to the proper annealing temperature in the annealing tunnel, and discharging the metal bodies through the outlet end of said cooling tunnel.

3. A method of bright annealing elongated rigid metal bodies comprising heating a. long straightl annealing tunnel, tightly connected to and in alignment with a straight cooling tunnel, externally by combustion gases to a temperature at which the density of the atmosphere is reduced to such a degree that a non-oxidizing condition is reached in the tunnel, providing an open communicating with the outside atmosphere at least at the entry end of the annealing tunnel, maintaining a non-oxidizing Vcondition in the heated portion of the tunnel by the continued application of heat thereto and, by disposing the entry and outlet ends of the tunnel at the same elevation or sealing with liquid the outlet opening if lower than the entry opening, preventing the formation of a. draft longitudinally of the tunnel, introducing the said elongated metal bodies into the annealing tunnel through the entry end thereof, moving said metal ing tunnels at a rate controlled so that said vbodies through said straight annealing and cool- -made of heat-resisting steel, the interior of the said tunnel or mullle being at all times in free communication with the outside atmosphere `at 'least as to the heated portion thereof, raising the temperature within said tunnel to a minimum temperature of 900 C. to render the air therein non-oxidizing, maintaining anon-oxidizing condition in the heated portion of the tunnel by the continued application of heat thereto and, by

disposing the entry Aand outlet `ends of the tunnel at the same elevation or sealing with liquid the outlet opening if lower than the entry opening, preventing the formation of a draft longitudinally of th'e tunnel, maintaining cooling tem peraturesin the unheated portion thereof, and passing an article to be bright annealed through the tunnel or muille. the direction and rate of movement being such that the article is first raised to annealing temperatures in the rarefed atmosphere of the heated portion and thereafter allowed to cool in the unheated portion before being discharged into the outside atmosphere. t O'l'lO SCHINCKE.

Images