US2618845A - Method of making tubes - Google Patents

Description

2 SHEETS-SHEET 1 Nov. 25, 1952 B. L. QUARNsTRoM METHOD OF MAKING TUBES Filed April l5, 1946 Nov. 25, 1952 B. 1 QUARNSTROM METHOD oF MAKING TUBES 2 SHEETS-SHEET 2 Filed April 15, 1946 I N V EN TOR. 25e/Z @Harina-fram.

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/Vrrfr/vE/" Patented Nov. 25, 1952 UNITED STATES PATENT OFFICE METHOD F MAKING TUBES Bert L. Quarnstrom, Grosse Pointe Park, Mich.

Application April 15, 1946, Serial No. 662,224

(Cl. lZ9-156) 2 Claims. 1

This invention relates to tubes and tubing made from strip metal, and to a method of making tubes by the practices of which either a pair or integrally joined tubes may be formed, or a single tube may be formed, in a new and novel manner.

An important object of the present invention is to provide a method of making tubing from sheet metal.

Another object of the invention is to provide a method of the above-mentioned character wherein the sheet metal is formed to produce a tube having a continuous wall of uniform thickness.

Still another object of the invention is to provide a method of the above-mentioned character wherein the tubing produced as the iinal product has smooth, continuous, inner and outer surfaces.

Yet another object of the invention is to provide a method of the above-mentioned character wherein the tube formed as a iinal product has a longitudinal seam which is at least as strong as the metal from which the tube is formed, so that the tube can be treated mechanically substantially in the same manner as conventional seamless tubing.

Still further objects of the invention include the provision of a method of making tubes which consists in operating upon a strip of metal to cause the opposite side portions thereof to be bent upon themselves about lines parallel to the side edges thereof to form a pair of parallel tubes which tubes are integrally connected together by an intervening bridge or web, and then separating the two tubes thus formed; the provision of a method of making tubes as above described in which the joint formed in each tube as a result of the bending operation is closed and sealed prior to the separation of the two tubes thus formed; the provision of a method as above described in which in the forming of the two tubes a bridge or web is provided integrally connecting the two tubes, which, after the joints in the tubes have been closed and sealed, is separated from both of such tubes; and the provision of a method of making tubes wherein a pair of separate, parallel tubes is simultaneously formed from a single strip of metal and said tubes are thereafter separated from one another.

The above being among the objects of the present invention, the same consists in a certain f new and novel article of manufacture and certain new and novel combinations of steps oi operation by means of which such article may be formed, all of which is hereinafter shown and described with reference to the accompanying drawings, and then claimed, having the above and other objects in View.

In the accompanying drawings which illustrate suitable embodiments of tubing formed in accordance with the present invention and suitable apparatus by means of which the various steps of operation of the present invention may be carried out, and in which like numerals refer to like parts throughout the several different views:

Fig. 1 is a more or less diagrammatic side elevational view of the front end portion of an apparatus suitable for use in producing tubing in accordance with the present invention;

Fig. 2 is a more or less diagrammatic side elevational view showing the rear end portion of the apparatus, the front end of which is shown in Fig. 1;

Fig. 3 is an enlarged, fragmentary, vertical sectional view taken axially to the iirst set of forming rolls as on the line 3-3 of Fig. 1, illustrating the yconformation of the faces thereof and the effect thereof on a strip of metal fed therebetween;

Figs. 4-11, inclusive, are views similar to Fig. 3, that is, they are fragmentary, vertical sectional Views taken axially through sets of successive forming and/or other rolls as on the lines 4--4, 5 5, 6 6, 'l-T, 8 8, 9 9, lil-I0, and l|--|I, respectively, illustrating the shape of the cooperating faces thereof and the corresponding shaping of the metal strip during its travel through such rolls;

Fig. 12 is an enlarged, fragmentary partially sectioned View, taken on the line l2-l2 of Fig. l, illustrating the roll and die structure employed for effecting a weld of the joint in the tubing formed by the preceding sets of rolls in acting upon the metal strip;

Fig. 13 is an enlarged, fragmentary vertical sectional View taken on the line |3-l3 of Fig. 1, and illustrating the construction of the slitting rolls employed for removing the bridge or web between the two tubes formed in the preceding step;

Fig. 14 is an enlarged transverse sectional View illustrating the shape and construction of the tubing formed by the apparatus shown in the preceding views;

Figs. 15, 16, 17 and 18 are views similar to Fig. 14 but illustrating modied forms of tubes capable of being produced by the method of the present invention; and

Figs. 19 and 19a are greatly enlarged, fragmentary sectional views taken transversely of the iinal Siamese tubing Where the joints are of the brazed, and combination brazed and welded types, respectively.

The cooperating faces of the various sets of forming rolls shown in the Idrawings will be understood to be that required to form a tube of the section illustrated in Fig. 14, `and it will be readily understood by those skilled in the art that where tubes of the sections shown in Figs. 15-18, inclusive, lare desired instead of that of the section shown in Fig. 14, the cooperating faces of the various sets of forming rolls will be modified accordingly. It will lalso be understood that the forming and cooperating guide rolls are so constructed Aas to allow the strip blank to be rapidly entered between them and that they are self-threading. As noted in Fig. 14, the tubing 3 there shown in section includes a pair of tubes 20 joined by a central bridge or web 22. Each tube 20 is provided with a joint 2li, which joint will be understood to extend in parallel relation with -respect to the aXis of the corresponding tube. Such joint in the case shown is of the socalled scarfed type and appears at the upper edge of the bridge or web 22, the plane of each joint 24 extending laterally outwardly and downwardly with respect to a vertical plane extending midway between the two tubes 20. The dual tube shown vin Fig. 14 may be employed in the form shown or, and as will hereinafter be more fully explained in connection with the description of Fig. 13, the web 22 may be. removed so as to provideV two separate 'and independent tubes 20.

Inasmuch as the present invention deals with a -continuous method of making tubing from Ia flat metal strip, a coil of such strip of thev cor-rect widt'h and gauge is illustrated in Fig. 1 at 30, land as being conventionallyV mounted upon a reel 32 of conventional construction and from which it may be -continuously withdrawn. The strip 34 is withdrawn'from the coil 3d and is passed with its plane of thickness Ihorizontal through suitable and conventional guide rolls such as 3G', and then between a pair of forming rolls 38, di?. As brought out in Fig. 3, the face of the rolll 3B is 'straight and flat, but the cooperating face of the roll 40 is provided with a iat bottomed depression 42 therein of the same depth as the thickness of the strip 34 and of substantially the same width except that the ends of the depression 42 are bevel-ed as at 44 so as to cause the opposite side edges of the strip 34 to be correspondingly beveled during its passage through these rolls. It will be appreciated that the bevel 44 is that required for forming the corresponding side of the scarfed joints 24 in the final product, as `explained in connection with Fig. 13.4

It will, of course, be `understood that the` nurnber of cooperating forming rolls and the relative shapes of the cooperating faces thereof required to bring the strip 3'4 in the ilat form in which it exists in the coil 3@ to the nal form shown in Fig. 13 may vary considerably in accordance with the ideas of the particular designer and/or manufacturer, the number of lcooperating forming rolls and the shapes of the faces thereof hereinafter shown and described being for the most part indicative of one form which has been found to be satisfactory for forming the tube shown in Fig. 14.

. After the strip 34 has passed between the forming rolls 38, d it preferably travels through one or more pairs of guide rolls such as 45, and then passes between a second pair of forming rolls B8, S. The contour of the cooperating faces of the rolls 48, 5!) is shown in Fig. 4 from which it will be noted these rolls are so shaped as to impart to each side of the strip 3d, on either side of the longitudinal center thereof, a slight upwardly facing concavity, but a relatively narrow central portion is maintained ilat.

As previously mentioned, it is desirable, although not essential, that the upper face of the bridge or web 22 be knurled, serrated, or otherwise roughenedso as to aid in reducing the surface tension of the molten soldering or braZ-ing material and thereby increase its ability to run into the joint being closed, a-s well as to better retain the brazing, soldering or welding iux wherejt-he latter is employed. This knurling, serrating, or other type of roughening may, of

course, be accomplished by passing the strip through a pairof rolls, one of which has a complementary roughened'surface adapted to be impressed into the upper surface of the strip. However, inasmuch as the central portions of the sets of rolls shown and 'described are substantially flat where they contact the -strip 34 over those portionsV thereof which will eventually form the web 22, the central portion of anypair of rolls, prior to those in which the soldering or brazing material, o-r nux, is applied, may 4be formed to serve this function. In the drawings, the roll 48 is selected for this purpose and, accordingly, it will Vbe noted in Fig. 4 that it is centrally provided with a peripherally knurled area- 52, in line with that portion of the strip 34 which will form i the bridge 22, so that as the strip 34 passes through the rolls 48, 5! the upper face of lthis portion of the'strip 34 will be complementarily knurled.

After passing through the rolls 43, 5l). the. strip 3A passes through suitable guide rolls 511 and then ,between cooperating rolls 5t, 5B where, asY illu-.Ss

trated in Fig. 5, thedept-h of the concavity in each side of the strip 34 and particularly the -curvature of the outer and central portions thereof is increased over that shown in Fig.A 4 but the side edges of the strip-are still maintained; at substantially the same level as the central portion thereof.

After pas-sing through the rolls 55, 58, the, strip 3s passes through suitable guide rolls 60 and then between the pair of rolls 62, e4 where, as brought out in Fig. 6, the concavity of the two. ysides 0f the strip 34 is still further deepened and curva-f ture is imparted to the bottom portion of each concave side as shown, the outer edges of the strip still being maintained at substantially the saine level as the centra-l portion thereoi It may be noted, however, that in passing through this last pair of rolls, the web or bridge 22V is definitely produced, that the strip for a short distance on each side of the 4bridge 22 is brought to substantially the curvature desired `in the nal product, and the extreme outer edge portions of the -strip 34 are also brought to, substantially the curvature which they will assume in the final product, only the portions connecting. the corresponding of these last two portions being substantially greater than the curvature in the nal product.

After leaving the rolls 62, 6d', the strip 34. passes between suitable guide rolls 56, and then between cooperating rolls 68 and 1Q, which, as is. brought out in Fig. 7, act to bend the outer portions of each half of the strip upwardly to above the plane of the central Ibridge. portion 22 and to impart a further curvature to each portion of the strip on either side. of the central bridge portion 22 tending to bring it further toward its final curved conformation.

After passing through the rolls B8, 'I0 the strip 34 then passes between further guide rolls 72 and then between a pair of forming rolls 14, 'I which, as brought out in Fig. 8, turn the outer side edge portions of the strip further upwardly and inwardly toward their final conformation.

It will be appreciated, of course, that in order to provide the scarfed type of joint illustrated in the tube shown in Fig, lll, not only must the free edges of the strip 3d be beveled as brought out in Fig. 3, but the strip when bent into. final form must have a complementaiily beveled surface for each beveled free edge of the strip to abut. In the particular tube which is considered to be formed by the apparatus shown and the section of which is brought out in Fig. 14, these beveled faces for complementary reception of the beveled outer free edges of the strip are disposed at each side of the bridge 22, and they are preferably formed by rolls or dies. This beveling of the opposite sides of the bridge or web 122 may, of course, be accomplished simultaneously With any of the above described operations beginning with the operation shown in Fig. 6 where the bridge 22 andthe immediately adjacent portions of the strip vare brought to substantially nal curvature. However, as a matter of convenience, the rolls 14 and 16 are selected as satisfactory for effecting this beveling of the opposite sides of the bridge 22 and, accordingly, the roll 14 over that portion thereof which contacts the bridge 22 is provided with a peripheral groove 18, the opposite sides of which are beveled outwardly as brought out in Fig. 8 so as to effect the complementary beveling of the opposite sides of the bridge 22.

After passing through the rolls 14 and 16, the strip 34 then, as shown in Fig. 9, passes between suitable guide rolls 80 and then through a pair f of forming rolls 82 and 84, where the free edge portions of the strip are further moved inwardly toward each other and now downwardly so as to bring each side portion of the strip into substantially complete circular conformation.

After passing through the rolls 82 and 84, the strip then passes between suitable guide rolls S5 and then through a pair of cooperating forming rolls 88 and 90, where, as brought out in Fig. l0, each side portion of the strip is brought into completely circular conformation with the respective beveled free edge portions of the strip in contact withfthe beveled side portions of the bridge 22, and in which condition the cross-sectional conformation of the strip is identical to that in the final product as shown in Fig. 14. It may be said, however, and assumed, that in passing through the rolls 88 and 90, the strip is so acted upon by the rolls that the walls of the tubes 20 are thereaftervtensioned in a direction to constantly press the free edge portions of the strip into contact with the corresponding beveled sides of the bridge 22, and such free edges are pressed thereagainst with sufcient force to provide a relatively tight joint 24.

In the broader aspects of the invention, the strip thus brought to the form shown in Fig. 10

and thus far described may be sufficiently complete to constitute a final product capable of many uses, this particularly so where it is intended to convey solid particles or the like under relatively light pressures. On the other hand, the bridge 22 may be removed at this point to form two separate tubes which may be employed for the same; or similar purposes. On the other hand, thetube as thus described in the condition it assumes in Fig. 10 may |be subjected to a suitable soldering or brazing operation to solder or braze the joints 24 and/or coat the tubing thus formed, and in such case it will be appreciated that the tubing will then be capable of conveying liquid under pressure and, further, that in such case the two tubes 20 thus formed may be separated from one another by removal of the bridge 22 so as to form two separate and independent tubes, each capable of conveying liquid under pressure.

Where the strip 34 from Which the tubes are formed is of non-ferrous material, such as copper, brass, Monel metal or the like, or at least from a metal not readily lending itself to a resistance welding operation, then, of course, the soldering or brazing of the joints in question will perhaps be the most practical way of closing and sealing the joints and securing the edges of the tube stock at the joints together. Where such brazing or soldering only is employed, then, of course, any suitable means may be provided for carrying out the soldering or brazing operation. The same may be carried out as a part of the continuous operation shown by feeding suitable brazing or soldering material and a suitable ux, where necessary or desirable, to the upper surface cf the bridge 22 between the tubes 20 once they reach the condition illustrated in Fig. 10, and thereafter passing the tube in the position illustrated in Fig. 10 through a suitable heating zone, as, for instance, an electrical or gas fired furnace and preferably in a controlled atmosphere to bring the tube and the soldering or brazing material up to the required temperature to effect the soldering or brazing operation.

Although the soldering or brazing material may be fed to bridge 22 in the form of powder,4

strip, wire or the like, in Fig. 1, for the purposes of illustration, it is assumed that the brazing or soldering material is supplied in wire or strip form and coiled, as indicated at 92. The wire or strip 9d from the coil 92 is fed down through a guiding tube such as 95. The roll following the point of contact of strip 94 with the strip 34 may be relied upon to pull the soldering or brazing strip S4 along with the tube as the tube continues through the machine or apparatus, or separate driving rolls such as 98 may be provided, if desired, for feeding the strip 9d at the same rate that such formed tubing is passed through the apparatus. A container |00 lled with the desired ux may be connected in with the guide tube 96, as illustrated in Fig. 1, so as to simultaneously feed the desired amount of the flux through the guide tube 96 onto the upper surface of the bridge 22 as the soldering or brazing material is fed through the guide tube. As above explained, the knurling, seri-ating or other roughening of the upper surface of the bridge 22 will aid in reducing the surface tension of the molten soldering or brazing material to enhance its wetting and flow characteristics as well as to hold the soldering or brazing material and the flux in proper position of the upper surface of the bridge 22 until the soldering or brazing operation has been completed.

In connection with the above, it is desired to call attention to the following facts in connection with brazing of ferrous metals, and particularly as applied to the above described method. If two parts formed from a ferrous metal are to be bonded by brazing, or, as in the present case, the metal on opposite sides of a joint formed from a single strip is to be brazed to close the joint, an actual alloying or commingling of the grain boundaries of the brazed or ferrous metal may occur without actually raising the ferrous metal to its melting temperature if the temperature is maintained at a sufficiently high value for a sufficient time, as assumed in the present case. In such case, an actual alloying of the brazing metal and the ferrous metal occurs at the junction of the two metals. The bond thus formed is materially stronger than the brazing metal, itself, so that it is evident that if a solid body of brazing material does not actually space the ferrous parts or portions to be bonded, the stronger the joint will be as in such case the actual joint is composed of a commingling of the grain boundaries of the two metals. If, in fact, the two ferrous metal parts or portions on opposite sides of the .joint can be maintained in contact with each other, and preferably at surface contact with a minimum of voids to be occupied by the brazing material, a resulting joint will be obtained which will not only be of much greater strength than the brazing metal, itself, but may be of as great strength as the ferrous material, itself. Because of the inability to consistently provide such a joint in a single wall tubing formed from strip stock in accordance with the heretofore suggested practices, it has been the practice to form such strips into multiple wall thickness tubes, the opposed or intended contacting surfaces of which are bonded together by copper or other suitable brazingmaterial. Such material has been conventionally applied either as a coating on the initial strip or by passing the formed and uncoated tubing through a molten bath of copper or other brazng material. In the former case, after the tube is formed it is heated to cause the copper to melt and flow between the opposed surfaces and join and seal them together, and in the latter case the heat of the bath brings the tube up to a sufficient temperature to cause the material of the bath to flow into the joints and be bonded to the metal of the tube. En either case, because of the inability to get good surface contact between the two parts of the'joint, it is principally the strength of the bracing material, and not an alloying of the two metals, that gives strength to the joint.

In the practice of the present invention, and because of the fact that the strip in passing through the forming rolls 08 and 00 is acted upon so that the free edge portions of the strip are tensioned in contact with the cooperating portions of the bridge 22, actual surface contact of the ferrous metal on both sides of the joint resuits and a minimum of space remains for reception of the brazing material. As a result the bulk of the brazing material in the joint has its grain boundaries intermingled with the grain boundaries of the ferrous material so that an actual alloy of the parent metal and the brazing metal is provided to join the two sides of the joint together, therefore resulting in a joint of maximum strength. The above is brought out in Fig. 19 wherein the ferrous metal of the tubes and bridge is indicated as in actual contact and the crosses, which indicate the copper or other brazing material, are interspersed through the joints and are disconnected to indicate an intermingling of the grain boundaries thereof with those of the ferrous metal and therefor alloyed therewith.

Another reason why joints of the character shown, that is in single wall tubes, have been impractical in accordance with the heretofore suggested practices is that no means has been provided for confining its molten brazing metal substantially to the joint only. In other words, according to previously suggested practices, there has been no way to prevent the molten brazing material from spreading away from the joint and over parts of the tube where its presence is not necessary and may even be objectionable. yThis is where the importance of the bridge 22 becomes appa-rent in accordance with the present invention, inasmuch as the bridge and the cooperating walls of the tube portions 20 corinne the molten brazing material substantially only to the joints to be brazed and substantially prevent owing of the brazing material beyond the area desired. The-bridge 22 is therefore of prime imi8 portance in the practical application of constructing single wall brazed tubing-made fromf strip material.

Perhaps the widest field of use for .tubular structures formed in accordance with the present invention is in connection with such tubes formed from ferrous material and this for two reasons, the first of which is that tubes made from a ferrous material in accordance with the present invention may be made at less costthan any equivalent tube made at the present time and, second, because the joints in the tubes may be readily welded and copper brazed to form: a more rugged tube of single wall thickness when so welded and copper braced, than. any equivalent single wall thickness tube formed from strip, now on the market, and one which is capable of withstanding higher pressures without rupture. Although welding of such joints is preferably combined with a, brazing operation toy produce a joint of maximum strength, uniformity' and density, welding alone may be solely relied upon in many instances. Theapparatus shown -includes means whereby such welding -maybe efffected and this portion of the apparatus will now be described.

On the downstream side of the rolls 88, in the direction of movement of the material through the apparatus is located a welding roll, indicated generally at |02. The roll |02'rotates about a horizontal axis extending transversely of the direction of movement of the tubingbelow it. As brought out in Fig. 12, the roll |02 is made up of two disk-like portions |04 and |06, each preferably formed from a suitable electrode material such as copper, separated from one another by a disk |03 of suitable electrical insulation material. The insulation disk |08 is positioned centrally of a vertical plane passing midwayvbetween the two tube portions 20,-and the peripheries of the portions |04 and |00 are grooved-for complementary reception of the upper surfaces of the corresponding tubes 20, as brought out in Fig. 12. The two sides |04 and |06 of the roll |02 are connected to the opposite sides of a suitable electric welding circuit indicated diagram,- matically in Fig. 12 at ||0. To support the tubing thus formed in nrm contact with the roll |02, a pair of rolls ||2 are rotatably mounted on shafts H below the roll |02. The axes of" the shafts l| I4 are vertical and disposed equallyon opposite Vsides of the roll |02, and the upper por'- tion of each roll ||2 is provided with a curved peripheral seat portion ||6 complementary in section to approximately the lower outer quarter of the corresponding tube 20 and complementarily receiving the corresponding tube 20 thereagainst. Thus, with the construction described, assuming that the tubing is formed from a ferrous or other material lending itself to resist# ance welding practices, and after having reached the condition illustrated, it is passed between the rolls |02 and H2 and subjected to the effects of a welding circuit flowing between the halves |04 and |06 of the roll |02 and through the joints 24, which effects a fusion of the metal at such joints and therefore a welding of the joints. It will be observed that by the arrangement shown and de scribed, al1 of the welding circuit passes through the .bridge 22, and principally through the free edge portions of the strip forming the tubes, thus concentrating the heat at the joints. This tends to produce a better weld with a minimum con# sumption of electrical energy.

Where welding is employed to 'close the joints 24, then, in accordance with a further phase of the present invention, a special arrangement is preferably employed to facilitate such welding so as to permit a good weld to be obtained at a much higher rate than would otherwise be possible. This is accomplished by the use of a pair of rolls |20 and |22 between the pair of rolls 88, 90 and the welding roll |02. As brought out in Fig. l1, the roll |22 is substantially the same as the roll 90, but the depressions in the roll |20 for receiving the upper portion of each tube are such as to cause the free end portions of the strip to be sprung outwardly away from the beveled edges at each side of the bridge 22, or each inwardly toward the axis of its own tube, so as to cause the two faces of the corresponding 'joint to be slightly separated from one another. The amount of separation thus shown in Fig. l1 is greatly exaggerated for the purpose of illustration, it being understood that the amount which the free edges of the tube are thus sprung does not stretch the material of the tube beyond its elastic limit and therefore no permanent deformation results.

By the use of the rolls |20, |22, the opposite sides of the joints in the tubes 20 are sprung away from each other in advance of the roll |02, where the actual welding occurs, a sufficient amount to prevent the ow of electrical energy from the welding circuit across such joints. However, it will be appreciated that the amount which the joints are sprung apart by the rolls |20 and |22 will be a maximum at the rolls |20 and |22 and this clearance will become less and less as the roll |02 is approached, and some time before the roll |02 is reached the spacing of the joint will disappear because of the inherent resiliency of the material from which the tubing is formed. As a result, the length of the joint across which the welding circuit fiows is materially reduced, resulting in increased heating of the metal at the joint and permitting increased speed of welding with the use of a minimum amount of electrical energy. Thus, by the time each increment of length of the tubing reaches the roll |02, the metal on each side of the joint will have become molten, the metal on opposite sides of the joint will tend to commingle, and the coaction between the rolls |02 and ||2, and the tensioning of the metal to close the joint as imparted by the rolls 88, 90 as previously described, will press the two sides of the joint together so as to enhance a commingling of the molten metal, so as to form a homogeneous bond weld, and consequently a closing and sealing of the joint by the metal of the tube itself. A welding flux may be applied during the operation as, for instance, from the container through the guide tube 95, in the same manner as the soldering or brazing flux previously described.

In any welding operation such as that above described, it is, of course, desirable to protect the metal against oxidization when raised `to the welding temperature, as well as prior thereto, in order to enhance the quality of the weld. While broadly this may be accomplished by surrounding and preferably filling the tubes with a controlled atmosphere in any suitable manner and by any suitable means, in accordance with the further phase of the present invention this may be accomplished, in part at least, by introducing a. non-oxidizing or reducing gas, or an otherwise controlled atmosphere, into the interiors of the tubes 20 at a suitable distance in advance of the welding roll |02 and preferably continuing to a point therebeyond. This may be accomplished by introducing a tube such as E211 into each side of the strip 34 as it is being formed and continuing such tube lengthwise of the strip as it is being progressively formed preferably to a point slightly beyond the roll |02. As brought out in Fig. l, in order to introduce the tubes |24 without interference, it is necessary to introduce them into the tube being formed at a time when the side edges of the strip 3d are still positioned laterally outwardly of the center of the final tube. They are, therefore, introduced between the pair of rolls 58, l0 and the pair of rolls M, i5, and preferably substantially coaxial with a corresponding tube being formed, as brought out in Figs. 8-12 inclusive. The free end portions of the tubes |24 are preferably perforated so as to permit the non-oxidizing or reducing gas, or other controlled atmosphere, fed through them to escape outwardly to within the tube being formed. Preferably, these perforations begin shortly after the tubing being formed has passed through the rolls |20, |22 and continue to the free end of the tube. The opposite ends of the tubes |24, shown broken off in Fig. l, may, of course, be extended to any suitable source of supply of the non-oxidizing gas, reducing gas, or other controlled atmosphere employed in the operation. Preferably, a, housing, indicated fragmentarily at |25 in Fig. l, is provided in surrounding relation to the tubes being formed over that portion of its length thereof at which they are subjected to the welding temperature, so as to externally conne the non-oxidizing or reducing gas or the like to the exterior thereof at this point.

Preferably, in accordance with a further phase of the present invention, but not necessary in the broad concept of the invention, where the tubing formed in accordance with the present invention is formed from a ferrous metal and welded as above described, the welding joint is additionally subjected to a soldering or brazing, or copper brazing, operation so that the soldering or brazing metal will alloy itself with the parent metal of the tubes and thereby produce an alloy zone and bond strengthening the joint and resulting in a more perfect product. This is intended to be brought out in Fig. 19a, wherein the overlapping of the section lines at the joints is intended to indicate the commingling of the parent metal on opposite sides of the joint and the non-connected crosses are intended to indicate the brazing material interspersed through the joint and alloyed with the parent metal thereof. Moreover, should any voids be left in the joint by the welding operation, the brazing material will ll such voids.

The above may be accomplished by feeding a brazing or soldering material, with or without a suitable iiux, to the upper surface of the bridge or web 22 at a point shortly before or approximately at the point where the welding of the joint occurs. Although, such material may be fed to the bridge 22 in any suitable form and by any suitable means, the apparatus shown in Fig. 1 and already described for feeding a brazing material and a iiux to the joint may be employed for this operation. In other words, a strip 94 of soldering or brazing material is withdrawn from the coil 92 and fed to the bridge 22 in the manner described, a suitable ux or powder in the container |00 being simultaneously fed thereto where necessary or desirable.

Under such circumstances, the heat generated by the welding operation will automatically melt the soldering or brazing material and cause it to flow over and into the welded joint, forming an alloy bond and filling any voids that may be present therein, without the rnecessity of providing any separate heating means for this operation.

Where the tubing is formed in accordance with the present invention from a ferrous material and the joints welded as above described, it is, of course, desirable that the tubing be subjected to a normalizing operation after the Welding operation so as to remove any stresses that may have been set up in the material because of the welding operation, and to produce a softer and tougher product. While any suitable means may be provided for subjecting the tubing to a normalizing treatment, as, for instance, an oil or gas fired heater, in the case shown and vas brought out in Fig. 2, the tubing thus formed and finally welded between the rolls |02 and |2 is passed through a tubular furnace structure illustrated generally at |30 in Fig. 2, provided with two pair of spaced rolls |32, |34 at spaced points in the length thereof. .The rolls |32 are electrodes connected to the opposite sides of an electric circuit indicated generally at |30 so that as the tubing passes through the pairs of rolls |32, |34 electric current in the circuit |35 is caused to now between that length thereof between such-pair of rolls and, due to the resistance to such now, to raise it to a temperature sufficient to normalize the tubing, or heat it to any desired temperature.

After annealing, the tubing is preferably subjected to a continuous treatment to bring it to its nal completion. The first step of this treatment is a primary cooling step applied as the tubing emerges from the annealing apparatus. This is accomplished by passing the tubing through a housing such as |31 where its temperature is lowered. Inasmuch as the tubing is relatively hot on emerging from the annealing apparatus, the cooling-in the housing |37 is preferably accomplished bythe use of a suitably controlled atmosphere such as non-oxidizing or a reducing gas, which may be refrigerated if necessary or desirable. After the tubing has been cooled as above described, its outer surface is preferably tinned, and this may be accomplished by passing it through a tin pot or tank such as |38 in which is supported an open-ended tube |40 through which the tubing is passed. The tank |38 contains a body |42 of molten tin in the lower portion thereof. A suitable or conventional type of pump |44, and driven in any suitable or conventional manner, may draw the molten tin from thebottom of the tank through the pipe |46 and discharge it through a pipe such as |48 through an opening such as |50 in the upper part ofthe tube |40, the molten tin flooding the interior of the pipe or tube |40 and discharging from an opposite end thereof and in being discharged into the tube IL-coating the tubing passing therethrough. A wiper |5| at the discharge end of the pot or tank |38 in surrounding relation to the tubing being processed is preferably providedfor removing excess amounts of vtin from the tubing.

The tubing may next be projected through a tube or open-ended chamber such as |52 into which a stream of water may be introduced through a pipe or tube such as |54. This water in flowing through the tube or chamber |52 will serve to quickly cool the tubing. They tubing discharged from the tube or chamber |52 may pass through suitable guide rolls such as |56 into a conventional cutting olf apparatus indicated more or less diagrammatically in Fig. 2 at |58, where it may be cut to suitable lengths.

In event it is desired to produce single tubes in accordance with the present invention instead of Siamese tubes as shown and above described, then all that is .necessary is that the web Aor bridge 22 be removed after the Siamese tubing has reached a point of substantial completion, or at least a point where the joints in the tubing have substantially reached their nal condition. In the particular apparatus disclosed, it will be appreciated that this may be at any point subsequent to the welding roll |02 and, in fact, may

be accomplished after the tubing thus formed has been cut to length in the cut-on" mechanism |58. Preferably, however, the separation of the tubes 20 from the web 22 is accomplished shortly after the tubing leaves the welding roll |02, and, in accordance therewith, such tubing after it leaves the welding roll |52 is shown as passing a pair of shear or slitting rolls |60 and |52, as illustrated in Fig. l and as brought out in greater detail in Fig. 13.

As indicated in Fig. 13, the roll |62 is provided with a pair of partially circular peripheral portions complementary to approximately half of the surface of the tube 20 and is provided centrally therebetween with a groove |64, of a width equal substantially to the width of the bridge 22. The roll |60 is provided with a relatively narrow peripheral portion of a width to be relatively closely received bythe groove |64 into which it projects. Thus, as the Siamese tubing is passed through the rolls |50 and |52, the web 22 is sheared from the tubes 20, thus leaving two separate independent tubes 20 as the resulting product, with the strip formed from the bridge 22 as scrap. The two independent tubes thus formed are then separated for subsequent operations thereon. Under these conditions, where it is desired that'the tubes 20 have a smooth exterior surface, they may be passed through suitable and conventional shaving dies, not shown, which will remove any roughness resulting along the area from which the bridge or web 22 has been sheared. Furthermore, .in passing through one or more shaving and/or drawing dies, the tubes 20 may be brought within closely tolerated limits of size and roundness as will be readily appreciated by those skilled in the art. Thetwo independent tubes may then be passed through the same or equivalent apparatus as that above described for normalizing them, effecting a primary cooling, tinning, wiping, cooling and finally being cut to length.l

As previously stated, the method of the present invention is adapted to the formation of `Siamese tubes having a variety of types of joints between the free edges of the initial strip and the central body portion thereof and this simply by suitably changing the contours of the various forming rolls employed Vin the forming'operation to suit the particular type of joint desired. As illustrative of the different type of joints that may thus beprovided, reference may be had to Figs.

15-17, inclusive.

In Fig. 15, the construction is identical to that above described except forthe joint itself. In this case, the free ends of the tubular portions, here indicated at 20a, are beveled in exactly the same manner as in the first describedV construction except in a reverse direction. In this case, the material at the opposite sides of the bridge, here illustrated at 22a, is beveled in the opposite direction from the iirst described construction and with the inner' edge of the bevel downward- 1y offset a slight amount from the upper face of the bridge 22a so as to provide a longitudinally extending groove at each side of the bridge 22a into which the free edge portions of the initial strip are complementarily received, asY shown.

Fig. 16 illustrates a particularly desirable type of joint. In this case, the central portion of the initial strip which is to form the bridge 22h and those portions of the tube immediately adjacent thereto are acted upon by the forming rolls to reduce their thickness, preferably by 50% as shown, with preferably a square shoulder 23 at their junction with the full thickness portion of the strip. The marginal edge portions of this thinned central portion are bent by the forming rolls so as to be included in the walls of the tubes 20h, as shown. The free marginal edges of the initial strip are acted upon by the forming rolls to cause them to be stepped, each into a shape which will be complementary to that of the corresponding marginal edge portion of the tubes 20h at each side of the bridge 2219 as above described, so that when such free marginal edges are nally brought around into engagement with those portions of the strip along the corresponding margin of the bridge 22h, a stepped joint will be provided as shown. This provides a greater area of contact between the two portions of the tubes 2Gb on opposite sides of the joints thus formed, thereby resulting in a more secure and tight joint when closed by brazing, or a combination of brazing and welding, than in the scarred type of joint shown in Fig. 14.

On the other hand, and as illustrated in Fig. 17, the free edges of the initial strip may be first beveled in opposite direction and the extreme edge portions thereof bent to substantially rightangular conformation with respect to the adjacent part of the strip so that in the nnal product these offset edge portions will be arranged with the beveled portions thereof overlapping each other and superimposed upon the bridge or Web 22C.

It is, of course, not necessary that both of the tubes thus formed in accordance with the present invention and integrally joined together be of the same size, as it will be readily appreciated that the various forming rolls described, or their equivalents, may be modified so that one of the Siamese tubes is of a diierent size, or for that matter a different shape, than the other. By way of ilustration in Fig. 18, the two tubes here illustrated at 20d and 20e, respectively, are of different diameters, one being substantially twice as large as the other, but they are integrally joined together by the web or bridge 221, corresponding to web 22 first described, in the same manner as in the first described construction and the joints here shown are of the same type as in the first described construction.

Various other types of joints, sizes, and shapes of tubes Will, of course, be recognized by those skilled in the art as being capable of being formed in accordance with the present invention, and it will therefore be understood that formal changes may be made in the specifically described features, herein disclosed, Without departing from the spirit or substance of the broad invention, the scope of which is commensurate with the appended claims.

It is, of course, appreciated that brazing and soldering are equivalent operations distinguished primarily only by the character of the material employed therefor. With this in mind, it will be understood that in the following claims the terms brazing and soldering are used synonymously.

I claim:

1. In the manufacture ci tubing, the steps of continuously passing a strip of sheet metal through a plurality of forming rolls to form marginal, longitudinal, tubular portions joined by an integral bridge portion; forming longitudinal seats at the juncture of the tubular portions and said bridge portion and shaping the longitudinal edges of the strip to complement said seats; tensioning said tubuiar portions to press the longitudinal edges against said seats; then springing the tubular portions to separate the longitudinal edges from the seats; and pass ing a welding current through said tubular portions while simultaneously permitting said 1ongitudinal edges to gradually approach and finally re-engage said seats.

2. In the manufacture of tubing, the steps of continuously passing a strip of sheet metal through a plurality of forming rolls to form marginal, longitudinal, tubular portions joined by an integral bridge portion; forming longitudinal seats at the juncture of the tubular portions and said bridge portion and shaping the longitudinal edges of the strip to complement said seats; tensioning said tubular portions to press the longitudinal edges against said seats; then springing the tubular portions to separate the longitudinal edges from the seats; and passing a welding current through said tubular portion while simultaneously permitting said longitudinal edges to gradually approach and finally re-engage said seats and at the same time maintaining a reducing atmosphere around at least the sprung portion of the strip.

BERT L. QUARNSTROM.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,104,714 Sonnier July 21, 1914 1,124,766 Lloyd Jan. 12, 1915 1,359,001 Stresau Nov. 16, 1920 1,534,133 Murray Apr. 21, 1925 1,537,405 Bundy May 12, 1925 1,541,051 Murray June 9, 1925 1,889,414 Lutz Nov. 29, 1932 1,892,607 Bundy Dec. 27, 1932 1,952,955 Trageser Mar. 27, 1934 1,978,235 Summers Oct. 23, 1934 2,084,268 Quarnstrom June 15, 1937 2,095,807 Gier Oct. 12, 1937 2,099,806 Gora Nov. 23, 1937 2,224,953 Dunkelberger Dec. 17, 1940 2,375,661 Karmazin May 8, 1945 2,444,778 Kopec July 6, 1948 FOREIGN PATENTS Number Country Date 552,126 Great Britain of 1943

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