US1888607A - Method of making seamless tubes - Google Patents

Description

iiov. 1932. J w -r 1,888,607

METHOD OF MAKING SEAMLESS TUBES Filed April 6, 1929 A x T 0 1&4.

l4 l5 l6 Jig! Jafi/v M OFFUTT) 6 pal object Patented Nov. 22, 1932 UNITED STATES PATENT OFFICE JOHN W. OFFUTT, OF ELLWOOD CITY, PENNSYLVANIA, ASSIGNOR TO NATIONAL TUBE COMPANY, A CORPORATION OF NEW JERSEY METHOD OF MAKING SEAM'LESS TUBES Application filed April 6, 1929. Serial No. 353,175.

This invention relates to the manufacture of seamless butt and/or lap weld tubes and also electrically welded pipes and tubes and, while not limited thereto, has for its princithe provision of a novel method whereby tubes of small diameter (i. e., materially less than three inches diameter) having the thin wall thickness or gage suitable for commercial use are made in a rapid,

l economical and eflicieut manner.

Heretofore small diameter tubes such as from one-eighth to one inch pipe sizes, when not made by the butt-weld process, have been cold drawn from larger sizes of hot rolled seamlem tubes.

In the manufacture of seamless tubing it v has heretofore not been found practicable to produce hot rolled tubes of thin enough gage to be of commercial diameter. In piercing a solid round or billet of circular cross-section by the universally used rotary piercing mill, it is found that a round billet or blank of about three inches diameter is about the smallest size that can be commercially worked. This limitation in diameter is fixed by the size of the piercing mandrel which must have a diameter large enough to resist the end thrust imposed upon it in the piercing operation. A similar limitation is also set on the minimum size of the pierced billet that can be successfully rolled in the plug mill and then reeled in two operations subsequent to the piercing operation.

It is well established that all seamless tub s of a finished size of less than three inches di ameter must be passed through a sinking mill after the plug rolling and reeling operations to reduce the reeled tubes to the desired diameter.

As is well known, a sinking mill isa continuous universal mill having grooved rolls. with the grooves in each successive stand of rolls smaller than those in the preceding stand. The grooves in the first stand are slightly less in diamcterthan the reeled tube and the grooves in the last stand are of the diameter of the completed tube The roll stands, of which from eight to twenty-four may be used, are arranged in tandem and wall thickness and y 23 of less than one and OIl-Q-llfllf to two inches are usuallyspaced as closely together as their construction will permit. The spacing will vary from thirty inches to as much as five feet, center to center.

The'tube, while being passed through the sinking mill, does not havea supporting man- 'drel on its interior so that the reduction in its diameter is accompanied by thickening of the tube wall; In order to prevent, as far as possible, this'increase in wall thickness the relative roll speeds of the successive roll stands are adjusted to create a pull on the tube between the rolls, which results in stretching the tube. Most-of the reduction'due to the stretching operations is in wall thickness and there is very little, if any, reduction in diameter; the result is, that the amount the wall of the tube is thickened in the sinking mill is lessened. i

It is found, however, that when reduced in diameter in a sinking mill and with the roll speeds adjusted for stretching, the tubes are material heavier in gage on their ends than in the middle. This thickening, which is of marked degree, extends for a distance from each end about equal to twice the distance between roll stands. This is because no pull can be exerted on a given section of its length unless the tube is gripped simultaneously between two or nore pairs of rolls, a condition that does not exist when the tube is entering or leaving the roll train forming the sinking mill.

That is to say, there can be no stretching until after'the front end of the tube has entered the second stand of the rolls and there will be none after the rear end emerges from next to the last stand.

In practice up to the present, the increment in roll speeds on successive stands as heretofore arranged has been proportioned rather closelv to the. reduction of area. due to the reduction in diameter less the natural thickening of the tube walls. in order for the tubcs to be of uniform gage from end to end. This also means that the gage of the tube as rolled prior to the sinking operation must be considerably lighter than the desired gage or wall thickness of the finished tube. Since there is a practical limit to the lightness of gage of the tube which can be rolled and reeled prior to the sinking operation, the minimum gage of the finished tube after sinking is regulated or controlled by the minimum gage which can be rolled on the plug mill prior to the sinking operation.

I have demonstrated by actual trials that by increasing the difference in the speeds of the successive stands of rolls enough stretching can be accomplished to cause a material reduction in the diameter of the tubes and that at the same time the wall of the tubes not only can be held against thickening but, when desired, can even be reduced in thickness. In obtaining these results the rolls of the mill are made small in diameter and the roll stands are spaced very closely, center to center of stands, this close spacing being for the purpose of lessening to a minimum the length of the end portions of thetubes that have the thickened gage at the completion of the sinking operation. It always is necessary to crop and discard these thickened ends as scrap, hence the importance of keeping them as short as possible.

Referring now to the drawing forming part of this specification, Figure 1 is a diagrammatic plan of a standard sinking mill as used in sinking the rolled and reeled tubes.

Figure 2 is a section through a length of tube which has been stopped in the sinking mill of Figure 1, and shows the several reduc-.

tions as made at dilferent points in the length of the tube in passing through the sinking mill of Figure 1.

Figure 3 is a view similar to Figure 1, showing the modified sinking mill used in carrying out the final rolling steps of this novel method.

Figure 4 is a View similar to Figure 2, showing a length of tube which'has been stopped in the mill of Figure 3 to illustrate the reductions made simultaneously at different points in the length of the tube in its passage through the second sinking mill.

Figure 5 is a sectional plan of a tube illustrating the length of the crop ends relative to the length of finished tubes made in accordance with my improved method.

In making tubes by my improved method, a tubular blank designated by the letter A, which has been produced by piercing a round billet or by casting or in any other approved manner after being heated, is first rolled in a plug mill and is then reeled in the usual way. tubular blank A is greatly elongated and ,is correspondingly reduced in wall thickness and outer diameter. Owing toits being rolled over a plug, the inner diameter of the hollow blank is not materially changed in the plug rolling operation.

After being rolled in the plug mill, the billet or blank is then passed through the In the plug rolling operation, the

things, upon the amount of increasei'n the diameter of the tube that results from the reeling operation.

However, the reeling step as ordinarily performed is comparable to an ironing operation whereby scratches and scores and other irregularities on the inner and outer surfaces of the tube are lessened and removed, and variations in wall thickness at different points in the length of a tube, that result from the piercing and later plug rolling operations, are equalized in the reeling operation. In some cases, the reeling step may be omitted and the plug rolled tubes passed directly. to the sinking mill.

In the manufacture of seamless tubes of the small sizes and thin walls that are made possible by using my improved method, two sinking mills, or, what is the same thing, a sinking mill comprising two separate and distinct units B and C will be employed. In the first unit B, which comprises a sinklng mill of existant and well known type, the reeled tube is increased in length and is reduced in diameter and to a gage or wall thickness which, while uniform throughout its length, is thicker than that of the tube at the completion of the reeling operation. The tube becomes thickened in gage or wall thickness because a mandrel or other support for the inside of the tube is not employed in the sinking operation.

The tube 'then passes from the first unit B of the sinking mill into the second unit C. In this operation it is further rolled and also is stretched to a considerable extent while being rolled, its outer diameter being reduced in this operation so as to lessen the gage or wall thickness of the tube to that or somewhat less than that of the tube after completion of the reeling operation prior to its entering the series of sets of rolls forming the first unit B of the sinking mill.

The tube, when rolled in the second sinking mill, isstretched to a very considerable extent because of the pulling action of each set in the successive sets of rolls forming the second unit C of the sinking mill. It will be obvious that because of the close spacing between the roll stands that, in comparison with the total length of the tube, only a small portion of its length, at each of its ing small seamless ends, will not be stretched, with the result that the small unstretched portion at each end of the tube will be of the same or somewhat greater wall thickness than the intermediate stretched portion, and that the unstretched end portions will be of such small proportion of the total length of the tube as to permit of cropping the thickened end portions and discarding them as scrap Without a prohibitive scrap loss.

As tubes made by my improved method will be from fifty to one hundred or more feet in length instead of a maximum of from thirty to forty feet, and as the leng h nec essary to cut off the ends of the tubes to remove the thickened portions is comparatively short, say five per cent, I am enabled to make seamless tubes of small diameter and thin wall with a scrap loss so small as to make the method practicable on a commercial scale.

While I have shown one arrangement of apparatus and have described a certain specific order of steps for carrying out my novel method, it will be understood that I do not wish to be limited thereto since various mcd'fications may be made without departing from the scope thereof, as defined in the appended claims. While this invention is particularly well adapted for use in maktubes, it also is intended for use in'the manufacture of pipes or tubes of any diameter or size.

I claim- 1. The method of making seamless tubes which consists in forming a seamless tube blank by rolling and reeling to a diameter ma terially larger than a wall thickness approximating that of the finished tube, then subjecting the tube to a sinking operation to reduce its diameter and increase its wall thickness and form a tube having a substantially uniform wall thickness, and then subjecting the tube to a second combined sinking and stretching operation in which the tube walls are stretched by an amount sufficient to reduce the thickness of the walls to a greater extent than they are thickened by the first sinking operation, whereby a finished tube is formed of a materially less diameter and a thinner wall than the blank when entering the combined sinking and stretching operation.

2. The method of making hot rolled small diameter seamless tubes which consists in forming a seamless tube blank by rolling and reeling to a diameter materially larger than that of the finished tube and a relatively thin wall, then subjecting said tube to a combined sinking and stretching operation so as to reduce its diameter and increase its wall thickness, forming a tube having a substantially uniform wall thickness, and then subjecting said tube to a second combined sinking and stretching operation in which the tube walls are stretched a sufficient amount to reing it in duce the thickness of said walls a greater amount than they are thickened by the last sinking operation whereby a finished tube is formed having a materially less diameter than the blank and a thinner wall than that entering said last combined sinking and stretching operation.

3. The method of making hot rolled small diameter seamles tubes which consists in forming a seamless tube blank by the usual rolling and reeling steps having a diameter materially larger than the finished tube and a wall thickness approximating that of the finished tube then subjecting said tube to a combined si ing and stretching operation so as to reduce its diameter and increase its wall thickness, forming a tube having a substantially uniform wall thickness, and then subjecting said tube to a second combined sinking and stretching operation in which the tube walls are stretched a sufiicient amount to reduce the thickness of said walls an amount equal at least to the increased thickness formed by both sinking operations, whereby a finished tube is formed having a materially less diameter than the tube when entering said last combined sinking and stretching operation and a wall thickness at least as thin as the original rolled and reeled blank.

4. In the manufacture of seamless tubes,

the steps including increasing the wall thickness and length of a tubular blank while decreasing its inner and outer diameters by rolla sinking mill, and then lessening theouter materially increasing the length of the blank in said rolling operation by rolling it in a second sinking mill, and stretching the blank in rolling it in the second sinking mill.

5. In the manufacture of seamless tubes, the steps includin increasing the wall thickness and length 0% creasing its inner and outer diameters by rolling it in a sinking mill, and then lessening the outer diameter and Wall thickness of the blank Without increasing its inner materially increasing itslen th by rolling it in another sinking mill an stretching the blank in rolling it in the second sinking mill.

6. In themanufacture of seamless tubes, the steps including materially changing the wall thickness and length of a tubular blank while decreasing its inner and outer diameters by rolling it in a sinking mill, and then lessening the outer diameter and wall thickness of the blank without materially changing its inner diameter and materially increasing its length by rolling it in another sinking mill and stretching the blank in rolling it in the second sinking mill.

7. The method of making hot rolled tubes which consists in forming a tubular blank having a diameter and a wall thickness materially greater than the diameter and wall thickness of the finished tube, then subjecting diameter and wall thickness and diameter and ins a tubular blank while dethe heated blank to a combined sinking and stretching operation so as to reduce its diameter without increasing its wall thickness and form a tube having a substantially uniform wall thickness, and then subjecting the tube to a second combined sinking and stretching operation in which the stretching forces predominate over the sinking forces and the tube Walls are reduced in thickness an amount suflicient to provide a finished tube having a materially less diameter than the tube when entering the last combined sinking and stretching operation and a Wall thickness niaterially less than the originally rolled tube.

8. In the manufacture of tubes, the steps including increasing the wall thickness and length of a tubular blank while decreasing its inner and outer diameters by rolling it in a sinking mill, and then lesSening-tIie-JOuter diameter and wall thickness and materially increasing the length of the blank in said rolling operation by rolling it in a second sinking mill, and stretching the blank in rolling it in the second sinking mill.

9.'In the manufacture of tubes, the steps including increasing the wall thickness and 'length'of a tubular blank while decreasing its inner and outer diameters by rolling it in a sinking'mill, and then lessening the outer j diameter and Wall thickness of the blank without increasing its inner diameter and materially increasing itslength byrolling it in another sinking mill and s'tret'ching the blank in rolling it in the second sinking mill.

10. In the manufacture of tubes, the steps including materially changing the; wall thickness and length of a tubular blank while 1 decreasing its inner and outer diameters by rolling it in a sinkingniill, and then lessening the outer diameter and Wall thickness of; the blank without materially changing its inner diameter and materially increasing its length by rolling it in another sinking mill and stretching the blank in rolling it in the I second sinking mill. y

11. The method of making tubes which ineludes the step of subjecting a heated tubularblank to a combined sinking and stretching operation in which the stretching forces predominate over the sinking forces an amount suflicient to more than counteract-the tendency of said sinking forces to thicken the tube walls, whereby the diameter of the blank is reduced and its length increased and its wall thickness is reduced to less than the wall thickness of the original tubular blank.

In testimony whereof, I have hereunto set my hand.

' JOHN IV. OFF UTT.

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