US2306771A - Method of making metallic tubes - Google Patents

Description

FIG. 1.

Dec. 29, 1942. B. ANMSTER 2,306,771

METHOD OF MAKING METALLIC TUBES Filed Aug. 27, 1940 2 Sheets-Sheet l F'IE.5.

FIEL4- Q M [mm 6502? Dec. 29, 1942.

FIEL'Z B. BANNIST METHOD OF MAKING METALLIC TUBES Filed Aug. 27,

1940 2 Sheets-Sheet 2 liweizfmf Patented Dec. 29, 1942 ENT m;

METHOD OF MAKING METALLIC TUBES Bryant Bannister. Mount Lebanon, Pa., assignor to National Tube Company, a corporation of New Jersey Application August 27, 1940, Serial No.

2 Claims.

This invention relates to a method of making metallic tubes, and particularly to that practice which is known in the art as seamless.

The conventional method of manufacturing seamless pipes and tubes includes the casting of rectangular ingots which are rolled in a blooming mill into square blooms and then reduced to solid round bar in abar mill, after which the bars are cut into desired lengths, cooled, and subjected to an operation which removes scale and surface defects. Such removal of scale and'surface defects is known in the art of making metallic tubes as conditioning, and

comprises the removal of the outer surface of the bars to a certain depth in order to remove thesurface imperfections, chiefly very fine cracks or seams. If these are not removed, they are expanded and enlarged in the finished tube. At the present time there are two widely used methods of conditioning; one utilizing oxygen torches and the other mechanical peeling, the first method burning off the surface metal and, the second method machining or cutting it off. These bars, or billets, as they are known in the art, are subsequently reheated, pierced, and rolled into pipes or tubes.

In my patent No. 2,216,718, issued October 8,

1940, and entitled Manufacturing metallic tubular articles, there is disclosed a method of manufacturing metallic tubular articles which comprises casting a commercially-sized ingot of substantially circular cross-section, substantially reducing the over-all diameter of said ingot by a helical rolling operation whereby it'is bloomed, and performing a tube-rolling operation on the bloomed ingot whereby a metallic tubular article of the desired size is obtained. The method of the co-pending application involves stripping the cast ingot while it is very hot, placing it in a conventional soaking pit and, after it has become properly equalized in temperatura charging it into a helical type of blooming mill Whereby it is advanced helically between rolls which reduce itsdiameter to a size suitable for seamless mill operations. One of the advantages accruing from this practice is that there is a of the ingot to advance more rapidly than the exterior section, and this results in the formation of a symmetrical crater at the back or trailing end of the ingot as it advances into the mill. This results in the throwing of good metal surrounding the center section into the forward bloomed section, thereby increasing the amount of usable bloomed ingot. With the helical blooming mill of the co-pending application referred to, the numberof work increments for a given reduction is from two to four times as great as in conventional blooming practice, each increment of reduction being correspondingly smaller. In addition, the forward movement of the metal increases as the reduction is made, which automatically increases the rate of reduction. Thus, such a helical blooming mill automatically provides gentler manipulation of thedmetal during the early stages of reduction, with an increase inrate of displacement as the ingot structure is refined. This is particularly important for the reason that the cast structure of the ingot is coarse-grained, with relatively weak bonds between the grains. It is among the objects of the presentinvention to provide a method of manufacturing metallic tubularv articles of the seamless variety, utilizing the aforesaid rotary blooming mill in the most eflicient combination with, subsequent rolling operations, which will result in a lowered production cost without decrease in quality.

Another object is the provision of a method of the class described, together with a mill layout for practicing the same which may utilize some equipment of existing design.

v The foregoingand other objects will bejapparent after referring to the drawings, in which:

Figure 1 is a longitudinal sectionof a cylindrical ingot of the type utilized in the practice of the invention. of my co-pending application referred to and embodying a short pipecavity;v

Figure 2 is a plan of the helical rolling mill of said I co-pending application, together with means at the outlet end thereof for peeling or removing surface defects from the billetj Figures 3, 4, 5 and 6 are diagrammatic views, respectively, of a hot saw, reheating furnace, cross rolling mill, and a continuous tube mill wherein the numeral 2 designates a cylindrical ingot which is to be worked in accordance with the teachings of the present invention. This cylindrical ingot 2 is of a size and weight comparable to the rectan ular ingots now in common usage and is preferably obtained by top casting. As shown in Figure 1, this cylindrical ingot 2 has adjacent the top thereofa conical pipe 2a which will be referred to more specifically hereinafter. While the ingot 2 is shown as being of the solid type, it will be readily understood by those skilled in the art that it may be provided with a hollow core (not shown). In accordance with the practice set forth in my Patent No. 2,216,718 entitled Method of preparing billets, the cylindrical ingot is preferably of a size such as will produce two or more commercial lengths of pipe, and of a diameter of at least 16". Such an ingot, therefore, requires temperature equalization prior to rolling, and accordingly resort is had to soaking pit practice. After the temperature of the cylindrical ingot has been equalized, it is bloomed by a single pass through a helical type blooming mill, the reduction being from between 25% to 80% in diameter and down to a diameter of preferably 13" or less. The elongation accruing from the reduction is approximately in the same proportion as the square of the diameter of the entering work-piece is to the square of the diameter of the rolled billet neglecting the slight effect of the holethrough the bloomed ingot.

For the purposes of the reduction mentioned immediately hereinbefore, I employ a pair of suitably driven rolls 3 which are cone-shaped. These rolls 3 are carried on shafts which converge onto the line of pass of the cylindrical ingot 2 and provide wide convergent surfaces 4 of rather acute angularity and relatively short surfaces 5 which I are practically parallel with each other and, accordingly, the line of pass defined by the said rolls. While not shown in the drawings, the metal-working rolls 3 preferably have disposed therebetween a piercing point to reduce the work-piece to a tubular article during the blooming operation. From the foregoing, it will betperceived that the cylindrical ingot 2 entering the. metal-working zone of the pass defined by the rolls 3 will be very materially reduced in diameter, subsequently "rounded-up and then directed onto the outlet bed of the mill in materially elongated condition. Immediately after the work-piece or bloom emerges from between the outlet portions of the rolls 3, it comes into contact with a cutting device generally indicated at In.

This cutting device It) comprises a housing in which there is reciprocably mounted, on slideways l2 a motor (not shown) driving a substantially vertical shaft 14 carrying a disk or cutting member l5. The disk l5 which rotates in a generally horizontal plane, has a cutting edge l6 that may be continuous or serrated in the manner of a milling cutter and is positioned by means of an automatic feed device with its cutting edge in engagement with the helically advancing bloomed ingot or billet, so as to obtain the depth of cut desired: for example, about an eighth of an inch. The automatic feed device 20 is connected to the motor (not shown) by means of a piston-rod 2| carrying a piston adapted to reciprocate in a cylinder 22. The piston is reciprocated in the cylinder 22 by means of fluid under pressure delivered thereto from a suitable source of supply.

It will be noted that the cutting disk I5 is yieldingly and not rigidly held against the work-piece, thereby preventing damage to the cutting disk in case the work-piece, as it is delivered from the rolls 3. should happen to be cobbled or warped.

In operation, the disk I5 is rotated by the vertical shaft M at such speed that the duration of contact with the hot metal of any portion of the cutting edge I6 is a small fraction of a second. By so regulating the speed of rotation of the disk 15, the cutting edge I6 is prevented from becoming overheated by its frictional engagement with the metal and because of the high temperature to which the work-piece is heated, which is approximately 2300 degrees Fahrenheit. The diameter of the disk [5 is such that the width of cut is considerably more than the advanc of the work-piece per revolution. Consequently any portion of the cutting edge is in contact with the metal of the work-piece for only a small part of a revolution of the disk I5.

Normally the cutting edge 16 will cool during the time it is not engaging the metal of the work-piece. However, for certain kinds of metal it may be necessary to supply a cooling agent to the cutting edge l6, which can be done in any conventional manner. Two diametrically opposite cutting disks may be employed if desired; also, disks may be arranged in such a manner that the work-piece causes them to rotate, thus making the driving motors unnecessary.

A pair of guide disks 24 may be provided for steadying the work-piece and, in addition, cooperate with the rolls 3 to helically advance it.

The combination of a rotating disk and the relative longitudinal movement of the rotating work-piece with respect to the rotating disk provides the essential elements for the successful conditioning of metal stock. No portion of the cutting edge is in contact with the metal long enough to reach an objectionably high temperature and between heating contacts there is surficient time to cool the cutting edge effectively. Also, the rotation of the disk provides a true cutting or slicing action instead of a substantially plain shearing action that would occur if the disk were stationary. This is a definite advantage, as it is much more satisfactory to slice a plastic material such as steel, and particularly hot steel, than it is to shear it.

After the bloomed ingot or continuous billet or workpiece has passed the guide disks, it is cut into desired billet lengths. For the purpose of cutting, a conventional hot saw is preferably utilized, this being generally designated at 25 in Figure 3. In order to obtain the best results, it is preferable to reheat the cut billets in a reheating furnace 26 which, so far as the purposes of the present invention are concerned, may be entirely conventional in design. After the cut billets, designated hereinafter at X, have acquired the desired temperature, they are withdrawn from the reheating furnace 26 and directed through a second piercing mill, which comprises a pair of rolls 30 which are barrel-shaped, or of the so-called Mannesmann type, providing short convergent surfaces 3! and relatively wide divergent surfaces 32. A mill of this design provides a thinning of the wall of the work-piece with some increase in diameter. The interior of the billet X is supported, while between the surfaces 3! and 32 of the second piercing mill rolls 30, by means of a mandrel or plug 34, which is supported in the desired position by means of a mandrel bar 35. If a product of smaller diameter is desired, rolls having converging faces as shown at I54 ar provided.

After the billets X emerge from the second piercing operation, with an inner chamber approximately the same as that desired in the fin-- ished product accomplished by the cooperative action of the rolls 30, a cylindrical mandrel bar 48 is inserted in the billets X after which they are directed through a continuous tube mill, il-

lustrated in Figure 6 as comprising a series of those indicated at 46) are substantially parallel to the initial pair 40. Each pair of rolls of the continuous tube mill of Figure 6 defines a portion of a circular groove which is capable of effecting one-half of a complete increment of reduction of wall thickness over the entire billet X. It will be observed from an inspection of Figure 6 that a billet X and an interioriy disposed mandrel 48 have been broken away to indicate that the number of rolls between the second pair 42 and the final pair 46 may be increased. The function of the first two pairs of rolls 40 and 42 is, as before stated, to effect a complete increment of reduction of wall thickness over the entire billet X; while the function of the final pair of. rolls 46 is to round-up the work-piece.

Referring to Figure 7 of the drawings, I have illustrated a mill lay-out, the units of which are so arranged that a Wide range of tube sizes may be rolled without requiring the floor space necessary when using separate and distinct mills for the various sizes. This is possible because the rotary blooming mill has sufl'icient capacity to serve two second piercing mills. The schematic view of Figure 7 discloses the rolls 3 of the heli cal blooming millreferred to hereinbefore with the outlet bed thereof extending through transfer devices I 40 and I42, which are designed to transfer tubes to sets of hot saws 25, from which the billets are cut from the initial elongated or continuous billet X. After cutting, the billets are transferred to adjacent cooling tables I and I46. Disposed adjacent the cooling tables I45 and I46 are bloom heating furnaces I48 and I 49, respectively, which are only used when it is necessary to restore the blooms to hot-working temperature. Normally the blooms are directed through one of a pair of parallel tunnel furnaces I50 and I 5I which extend, respectively, alongside the bloom heating furnaces I48 and I49. Thus, it will be seen that whether or not i it is necessary to divert the bloomsinto bloom heating furnaces I48 and I49, they are moved through one of the tunnel furnaces I50 or I5I and subsequently expanded or sunk in accordance with conventional practice. For the purposes of sinking there is disposed at the exit end of the tunnel furnace I50 a rotary type of sinking piercing mill generally designated at I53 and comprising a pair of opposed cone-shaped rolls I 54 having converging opposed faces and a mandrel or plug supported on a mandrel bar. From the rotary sinking piercing mill I53 the blooms are directed across a suitable transfer device I55 from which they are progressed through the continuous tube rolling mill of Figure 6, which is diagrammatically designated at I56 and shown as comprising eight stands, That is to say, the

continuous tube rolling mill generally designated at I56 will comprise not only the pairs of rolls 40, 42 and 46 of Figure 6, but five additional pairs, which will be disposed between the two lastnamed.

Referring again to Figure 7, it will be'observed that disposed in parallelism with the rotary sinking piercing mill generally designated at I53, there is a rotary expanding piercing mill I60 facing in the opposite direction and comprising a pair of cone-shaped rolls I6I having diverging opposed faces and a mandrel or plug supported on a mandrel bar. According to this construction and arrangement, the function of the cone-shaped. rolls I54 of the rotary sinking piercing mill I53 is to reduce the outside diameter of the billets,

whereas the oppositely disposed cone-shaped rolls- I6I of the rotary expanding piercing mill I60 are adapted to expand the outside diameter thereof. Therefore, dependent'upon the desired product, the billets are directed through the proper tunnel furnace. In the manner of the ancillary instrumentalities of the rotary sinking mill I53, the rotary expanding mill I6I employs a transfer device I65 and a continuous tube rolling mill diagrammatically'designated at I66, the latter of which, like the continuous tube rolling mill I56, is shown as comprising eight stands.

According to the foregoing lay-out, provision, is made for rapidly reducing cylindrical cast ingots, with a minimum of time and expense, to a tubular shell which may be finished in accordance with conventional finishing" operations which, as

such, form no part of the present invention and,

accordingly, are neither illustrated nor described.

While I have shown and described certain specific embodiments of the present invention, it will be seen that I do not wish to be limited exactly thereto, since variousmodifications may be made without departing fromthe scope of the invention, as defined by the following claims.

I claim:

1. The method of manufacturing metallic tubular articles which comprises casting a commercial-sized ingot of substantial circular cross-section, substantially reducing the overall diameter of said ingot by a helical rolling operation by which it is bloomed and pierced, conditioning the surface of said bloom as it emergesfrom said helical rolling'operation, cross-rolling said bloom to partially reduce the wall thickness thereof, then inserting a mandrel in said cross-rolled blank, and reducing the wall thickness to that desired in the finished product by rolling it in a continuous tube mill.

2. The method of manufacturing metallic tubular articles which comprises casting a commercial-sized ingot of substantial circular cross-section, substantially reducing the overall diameter of said ingot by a helical rolling operation by which it is bloomed and pierced, conditioning the surface of said bloom as it emerges from said helical rolling operation, cross-rolling said bloom to partially reduce the wall thickness thereof and obtain an inner diameter which is approximately that desired in the finished product, then inserting a mandrel in said cross-rolled blank, and reducing the wall thickness to that desired in the finished product product by rolling it in a continuous tube mill.

BRYANT BANNISTER.

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