US3021128A - Method and means for continuously annealing metal strips, wire and the like - Google Patents

Description

Feb. 13, 1962 K. e. JONASON 3,021,128

METHOD AND MEANS FOR CONTINUOUSLY ANNEALING METAL STRIPS, WIRE AND THE LIKE Filed Dec. 4, 1956 2 Sheets-Sheet 1 INVENTOR K'ARL GUNNAR JONAS ON Feb. 13, 1962 K. G. JONASON 3,021,128

METHOD AND MEANS FOR CONTINUOUSLY ANNEALING METAL STRIPS, WIRE AND THE LIKE Filed Dec. 4, 1956 2 Sheets-Sheet 2 59 @111 ///l /////l 1111/! I r 4g 1 [ll/rr/ rrr [III/I11 I l 1 Fig.3 MENTOR KARL GUNNAR JONASON BY v f ATTORNEY The present invention relates to a method and means for continuously annealing metal strips, wire and the like by contact with one or more heat supplying rollers and while exchanging heat between the part of the strip or wire entering said rollers and the part of the strip or wire leaving said rollers.

The invention is particularly applicable to the treating of ferrous metal and non-ferrous metals, for instance iron, steel, copper, aluminium etc.

Previously such material was commonly annealed in batches, in which process coil of strips or wire rings of the material were introduced in a furnace and retained therein until attaining a desired temperature. In connection with an increased demand for a uniform quality and in order to reduce t e production costs, however, one has been forced to provide a continuous treatment. By this the disadvantage is avoided which is characteristic for the treatment of coils of strip in batches, viz. the sticking or welding together of the various coils of strip. In addition thereto a better quality is obtained for the finished prod uct due to the fact that the heat treating will be more uniform. Different ways have been suggested for carrying out the continuous annealing of strips. According to one 'of such suggestions the strip is carried through an elongated, horizontal furnace without being sustained during its passage through the furnace proper, guide rollers being disposed at both ends of said furnace. By this the formation of scratches and other indentations upon the strip have been avoided. Although this method may be preferred from many points of view it is not suited for annealing thick or very thin material, since in the first case it will be too stiff and heavy to be handled in the described manner, whereas too thin a material will not provide a sufficiently high production per furnace unit.

In parallel with this method it was suggested to use a vertical furnace which frequently is closed on top. In such an apparatus the strip is entered into and removed from the bottom of the furnace, a guide roller being disposed in the furnace over which the strip is passed. The heating of the strip takes place through convection and radiation, usually from electric radiators.

In this connection it was also suggested to heat the strip by supplying heat directly from a heated guide roller, the strip being conveyed in close engagement with said heated roller.

Experiences from this latter method have proved, however, that it is impossible to overcome the problem which arises in view of the elongation of the strip due to thermal expansion. In such case the strip thus will slide over the heat supplying roller so that scratches in it cannot be avoided.

The primary object of the invention, including methods and apparatus, is to solve the problem that lies in the thermal expansion of the strip or wire material without subjecting the strip to damage. A further object resides in increasing the efiiciency of the method embodying the invention by effecting a regenerative return of heat, otherwise going to waste, to the process, as will hereinafter more fully appear.

tits l ar In accordance with the invention exchange of heat is effected by means of heat transmitting rotating rollers which absorb heat by conduction from heated material reviously heated by heat from an outside source to effect the annealing or other heat treating step and transmit the absorbed heat by conduction to material to be annealed or otherwise heat treated prior to its being heated for that purpose by heat derived from said outside source. I

The invention will be more fully explained in the following with reference to a diagrammatic embodiment of the same shown in the accompanying drawing and in con nection therewith further characteristic features of the invention will be set forth.

FIGURE 1 is a vertical elevation, partially in section, of a heating furnace constructed in accordance with the invention, showing the arrangement of the rollers involved in the invention with feeding means for the strip or wire material in relation to said furnace.

FEGURE 2 is a plan view of FIGURE 1.

FIGURE 3 is a section on line IIIIII of FIGURE 1 With reference to FlGURE 1 reference numeral 10 designates a vertical stationary frame or stand for supporting one or more heat supplying rollers 11 and a plurality of heat conductive rollers 12. As will be evident from this figure the heat supplying roller 11 has no central shaft of rotation, but is supported for rotation, in

this case, by two supporting rollers 13. The rollers 12, however, are conventionally mounted by means of gudgcons in preferably cooled journals 14. As will also be evident from the figure all rollers are disposed at a suitable distance apart, guide rollers designated by lS being provided in the space between adjacent rollers for a purpose which will be described later on.

The rollers may be housed in a compartment or chamber, designated by 16, which is constituted by two displaceable housing halves 17 and 18 having thick walls, roof and bottom and for the major part including a suitable insnlating material applied in furnaces. Both halves l7 and 18 are provided, in theernbodirnent shown, with wheels 19 running on rails or the like 253 and each may be moved to one side of the frame ill. Mounted in the insulation in the lower part of one 1'7 of the halves are a number of guide rollers 21 andmounted in the corresponding part of the right half 18 are guide rollers 22. Furthermore outer guide rollers 23 and 24, respectively, are mounted for rotation at the halves '17 and 18. The guide rollers 21 and 22 are suitably hollow and mutually connected so as to form a circulating system, which may include a heating medium, e.g. water, which is positively circulated through said rollers. Located on the side of the half 17 are'two stationary frames or supports 25 and 26 and located on the side of the half 18 are two similar frames or supports 27 and 28 On the last-mentioned side is also a frame 29. The frames 25 and 26 each support a reel 30 and 31, respectively. Likewise the frames 27 and 28 carry each one reel 32 and 33, respee tively. The reels 30 and 31 may be braked by means of an especial brake means, which in the embodiment shown comprises brake shoes or the like (not shown) and are loaded by means of weights 34 and 35, respectively, hanging from wires 36 and 37, respectively.

With reference to FIGURES 1 and the frame 29 supports an electric driving motor 38, which via a gearing, generally designated by 39, operates a shaft 40, having arranged thereon on one hand a driving roller 41 and on the other hand two driving wheels 42 and 43, respectively, both said last-mentioned wheels being 'of equal diameter. Pivotally mounted above are driving roller 41 are two guide rollers 44 and 45. The driving wheel 43 is pivotaily connected, by means of a chain,

strap or the like 46, with the shaft of the reel 32, and in a similar way the driving wheel 42 is connected, by way of a chain, strap or the like 47, with the reel 33. On the side of the half housing 17 is a brake means generally designated by 48, which may be constituted of two compressible felt bodies 49' and d, at least one of said felt bodies being hydraulically, pneumatically or mechanically actuated upon. Instead of felt material obviously other soft materials may be employed which do not give rise to scratches in a strip passing between said bodies. By means of the hydraulic or pneumatic frictional means 48 an adequate braking surface pressure may be adjusted as desired for a purpose which will be explained later on.

The arrangement according to the invention operates in the following way:

Assuming that a coil of metal strip 51 adapted to be heat treated is placed upon the reel 31, an entering part 52 is led from the coil 51 over the guide roller 23 and between the felt bodies of the brake means 4-3. Thereafter the leading end of the strip is entered through an entrance 53 in the half housing 17 and passed over the guide rollers 21 onto the left guide roller 15. From here the said end of the strip bends upwardly and is allowed to pass over the lowermost heat conductive roller 12 through a certain arc of its periphery and then passes upwardly onto the next roller 12 against which the strip will be pressed by means of a further guide or pinch roller 15. In a similar way the strip continues along the superposed heat conductive rollers 12, against which it is pressed by the pinch rollers 15. After the leading end of the strip has left the topmost heat conductive roller 12 it is allowed to pass over the heat supplying roller 11, being arranged in a particular way, against the periphery of which it is caused to rest through a considerablearc, the entering part of the strip thus changing its direction of movement and actuated by further pinch rollers 15 being caused to pass in a close contact with the opposite side of the heat conductive rollers. The return part, after having passed the lowermost roller 12, is carried over a guide roller 15 and the guide rollers 22. out of the housing 17, 18 over the guide roller24. From this latter guide roller the said return part further travels via a guide roller 44 over the driving roller 40 and after having travelled along its periphery over the guide roller 45 to be coiled on the reel 32. In order to provide for a substantially continuous operation, in the embodiment shown, a double equipment of the reels is arranged on either side of the housing so as to obtain an auxiliary reel 30 on the entering side and an auxiliary reel 33 on the outgoing or discharge side. Preferably provisions are made for the arrangement between the reels and the furnace on either side thereof, of stored strip quantities or, principally considered, coils of the strip adapted to be treated being adjustable to its length, so that the length of the strip in the coils maybe suited to the time that will be consumed for connecting together and separating respectively two successive strips in the process. Thus, it is possible to work alternately with both said reels while the annealing process is taking place in the furnace in order to gain time for joining, in one way or the other, the ends of the strips of different coils in order to avoid the opening of the furnace again. In this connection it should be mentioned that, in order to avoid the trouble residing in the necessity of carrying out the above loading procedure at each start after a stop in the annealing operation, a length of strip is entered into the furnace at such stops and allowed to remain in the furnace.

As an alternative the furnace may be provided with one or more endless chains which will be passed along the path of travel of the strip, preferably at the ends of the rollers.

In accordance with FIGURE 3 the heat supplying roller 11 is provided at each side with a flange 54 and 55, respectively, which, however, are not indispensable.

Furthermore it should be noted that the heat supplying roller 11 is hollow and provided with a plurality of surface extending members taking the form of pins or points 56 of metal. Furthermore the roller has entirely open ends 57 in front of which stationary burners 58 are placed, to which will be supplied, from any suitable outer source, fuel gas mixtures, which 'are caused to burn inside said roller 11. The resulting combustion gases escape into the furnace compartment 16 through the openings 57 in the roller 11 and may form a protecting gas for the strip in course of heating. In a preferred plant the gases may be exhausted continuously, by means of a fan or the like, through one of the openings in the lower parts of the furnace walls. By this the protective gas may be distributed in a suitable way throughout the furnace compartment 16. Also other sources of heat than burners are obviously applicable within the scope of the invention but it has proved that the most concentrated supply of heat is obtained by means of such burners.

In view among other things of the difiiculties em countered in construction in connection with the mount ing of such a roller having centrally entered burners, in accordance with the invention the conventional mounting by means of gudgeons or by means of a shaft has been abandoned and in lieu thereof the entire roller 11 sup ported for rotation upon supporting rollers 13, one of which is shown in a sectional view in FIGURE 3. This supporting roller is formed at both ends with shoulders or flanges so that the roller 11 obtains a careful guiding and support. It cannot be avoided that the roller 13 will be subject to certain stresses due to heat, which may affect their bearings and for this purpose the supporting rollers in accordance with FIGURE 3 are assumed. to be supported in especial cooled bearings, generally designated by 59 and 69, respectively.

After the plant has been operated up to running con dition as far as the distribution of heat is concerned, the entering part, as previously described, continuously travels over the rollers 12 and finally over the upper heat supplying roller 11 in close contact with it while the strip is being subject to the annealing process. The return part then in a heated condition again passes over the heat conductive rollers 12 on the opposite side, however, and during this passage said rollers will absorb a major part of the heat accumulated in the return part, which is thereby successively cooled down to a suitable final temperature upon leaving the lowermost heat conductive roller. However, at the same time the entering part travels along the opposite sides of the rollers 12, this part then being preheated by the heat transferred by the rollers 12 due to the mechanical heat transfer occurring by means of the rollers when they rotate from. the return side towards the entering side. It has proved that this method offers a very promotive distribution of heat and preheating of the entering part respectively, before it attains the heat supplying roller 11, where the true annealing process is brought about; This distribution of heat new contributes to the removal of the previous difficuities due to thermal expansion met with in such annealing plants. Due to the fact that the temperature'of the entering part is successively increased to a considerable amount, the diir'erence in length, which is due to the thermal expansion, will be compensated for in an effective way so that the part of the strip, which passes over the heat supplying roller 11, will be in close contact with it, and not, as in previous plants, removed from its surface due to the thermal expansion, which would result in an impaired heat treatment. By keeping the difference in temperature between the part being passed to the roller 11 and the corresponding return part at a minimum, only a small heat expansion is en countered and therewith a small slipping movement and also a reduction of the formation of scratches will be the result.

In order further to compensate possibly still remaining critical difierences due to changes in length of the strip the brake means 36, 34, 37, 35 and the felt brake 48 have been arranged on the entrance side of the strip 52, the felt brake pressing against the strip while braking it. Obviously it is not necessary to employ both said brake means since only one of them would sufiice, but both of them have been shown for the purpose of illustration. However, both said devices may be preferred when joining successive strips. Said braking devices exert a restraining pull or tension on the entering part of the strip, which tension will be present at all rollers in such a way that the strip will be brought into a close contact with their peripheries, thereby obtaining an even heat transfer 'all over the surface.

As will be apparent from the foregoing the invention provides a process or cycle of operation that is highly eficient from a thermal standpoint in that it effects regenerative heat exchange operative to recover heat previously imparted to the strip material, which would otherwise go to waste, as the treated strip material cools to normal temperature and to return the recovered heat to the strip material to preheat the same prior to the final heating to desired temperature by the addition of heat from an outside source requiring the combustion of fuel to produce. In effecting this regenerative heat exchange for the purpose of preheating the strip material by means of heat which would otherwise go to waste, the heat conductive rollers 12 provide a series of what may be termed heat transfer stations that are sucessively passed by the strip material as it is fed to and removed from the heating roller which supplies heat to the material from an outside source and which latter roller may be said to provide a heat treating station. Further, each of said heat transfer stations may be said to include a heat absorbing station at which heat is absorbed by conduction from the heated strip by a heat conductive roller and a preheating station to which heat is transferred by conduction from the conductive roller to strip material being fed to the heat treating station for final heating to desired heat treating temperature. It is further to be noted that the process also provides what is in effect coun-tercurrent heating flow in the regenerative preheating of the strip, in that when a plurality of heat conductive rollers are employed such rollers are passed successively in inverse order by portions of the strip being fed to the heat treating station and being withdrawn therefrom. With such an arrangement the strip is initially preheated by heat transfer at a relatively low temperature level, is further preheated at the succeeding heat transfer station at a higher temperature level, and so on until at the final heat transfer station heat transfer is effected at the highest temperature level. This provides for the most efficient and economical recovering of all of what would otherwise be waste heat.

In order to further improve the heat economy, as has been indicated above, a heat absorbing fluid may be caused to pass for instance through connecting lines 63 and 64 shown in FIGURE 2 between the guide rollers 21 and 22 in a direction from the latter towards the former ones so that the strip will be subject to a certain heat supply while being entered.

The strip is driven by the motor 38 over the roller 41 and is thereafter positively coiled either on the reel 32 or on the reel 33, which, as described above, are driven from the driving shaft 40 over chains 46 and 47.

In view of the differences in the speed of rotation of the reels 32 and 33 with increasing diameter, which prevails while the strip is being coiled, frictional coupling members of a kind known per se generally designated by 61 and 62, respectively, are provided, which adjust the speed of rotation of the reels according to said increase in diameter of the coil of strip being wound.

An important feature of the invention resides in the fact that the rollers are mounted in a stationary frame or stand and that a chamber or compartment around them 6 is formed by movable walls or half housings. This will permit, upon the first loading of the plant or at repair, the separation of both halves so as to provide access to the various rollersfor passing the leading end or the strip over them. Thereafter both said halves may be pushed together forming the said chamber again.

With this plant a continuous operation can be carried out, the plant discharging a uniformly heat-treated strip or wire material, which is characterized by a uniform quality. The invention thus solves the problem encountered in producing an optimally scratchless product at the same time as the operation may be substantially continuous and considerably more rapid than was the case hitherto. As will be apparent from the foregoing description, the invention .is equally applicable to various kinds of long lengths of materials such as wire, sheet metal strips, and other forms of metallic material that may be produced in long lengths and which require annealing.

It is consequently to be understood that in the ensuing claims, which define the invention, the term strip or strip material is intended to be generic to all such forms of material whether it be in the form of wire, sheet metal strip, grid material, or any equivalent thereof, since the specific nature of the material treated In accordance with the principles of the invention is not critical thereto. Consequently, the term strip or strip material is to be interpreted as broadly covering any continuous length of material that may be treated in accordance with the principles of the method and apparatus of the invention.

The invention is not limited to the embodiment shown and described but may be varied in various respects within the scope of the basic inventive idea.

Having now described the invention, what- I claim as new and desire to secure by Letters Patent, is:

1. In a heat treating process of the kind in which metallic strip is continuously fed to a heat treating station at which it is heated with heat derived from an outside source, that improvement which comprises regeneratively preheating the strip by feeding the strip serially past a series of heat transferring stations on its way to said heat treating station, feeding the strip serially past said heat transferring stations in reverse order after it has left said heat treating station, absorbing heat by conduction from the heated strip at each of said heat transferring stations and transmitting by conduction at each of said heat transferring stations the heat absorbed at that station to the strip being fed to said heat treating station.

2. In a method for continuously heat treating metal strip by causing the strip to traverse in heat absorbing contact a heat treating roller deriving heat from an outside source, that improvement which consists in causing the strip to traverse an arc of the periphery of a heat transferring roller in heat exchanging contact with the surface thereof prior to traversing said heat treating roller to be heated thereby and causing the strip after leaving said heat treating roller to traverse a second and differently located arc of the periphery of the same heat transferring roller in heat transmitting contact with the surface thereof, whereby said heat transferring roller absorbs heat by conduction fro-m heated strip that has left the heat source at said heat treating station to raise the temperature of the strip to desired heat treating temperature, re-

moving heat from the heated strip by conduction at successively lower temperature levels at each of said plurality of heat transfer stations as the strip passes said stations after leaving said heat treating station and transmitting the heat thus abstracted from the strip at successively higher temperature levels by conduction to the strip as it passes said heat transfer stations before reaching said heat treating station, whereby to progressively preheat the strip prior to the heat treatment thereof with heat recovered from the strip following its heat treatment. 10 2,

UNITED STATES PATENTS Morgan Dec. 18, 1917 Whitehead et a1 Sept. 28, 1926 Schon Feb. 13, 1940 Webster May 21, 1940 Erby Dec. 17, 1940 Shepard June 9, 1942 Lorig Mar. 4, 1952

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