US1983934A - Method and apparatus for making seamless tubes - Google Patents

Description

De'c. 11, 1934.

J. U. DEVINE METHOD AND APPARATUS FOR MAKING SEAMLESS TUBES Filed July 18, 1931 Patented Dec. 11, 1934 UNITED STATES PATENT; OFFICE METHOD AND mm'rvs Fon MAKIN snAMLEss TUBES The present invention relates broadly to metal working as applicable to 4the manufacture of tubular objects, and more particularly to an "improved method end apparatus for the manufacture of so-called seamless tubes. La

In accordance with one method of nufacturing seamless tubes as now practiced, an ingot after being heated to the proper temperature is forged on a. pilger mill, after which both ends are customarily cropped to a greateror lesser extent. In many cases also the pilgered ingot is sawed at intermediate points into two or more sections or lengths, depending upon the number of tubes which it is desired to produce from a given ingot. These lengths are then reheated in a reheating furnace, and after being brought to i the proper temperature are taken to a plug mill effective for decreasing the wall vthickness and smoothing the interior and exterior walls. To this end any desired number of passes is taken through the plug mill. The tubes thus formed are then taken to the reelers and sizing or reduc- Inasmuch as a pilger mill necessarily operates to reduce the wall thickness of the pierced ingot, the 'surface of the ingot which is exposed, is materially greater when the ingot leaves the pilger mill than. it is when the ingot leaves the piercing mill. Due to this greater surface, the reheating operation eifects a very appreciable scaling, the amount of scale being comparatively large as compared to the weight of the metal being reheated. Thus from a standpoint of scale produced, it would be highly desirable to utilize a billet' having thicker walls as it leaves the pilger mill. In accordance with the known manner of producing tubes, however, this would not be feasible, inasmuch as the plug mill would not be eiective for reducing the wall thickness to the required extent.

Present methods of forming ingots also usually contemplate the utilization of an ingot of fairly large diameter as compared to the diameter of the finished tubes produced therefrom. Since the pilger mill usually operates in such manner that it produces an outwardly ared end on one end of the ingot, it is necessary in accordance with known processes of seamless tube manufacture wherein the pilger mill is utilized, to crop o the entire outwardly flared end portion, thus providing alength of substantially uniform outside diameter. The amount of cropping thus ingly reduced, which 'is of decided advantage particularly with respect to the reheating equipment.

Another object of the present invention is to provide a method such that the wall thickness of the intermediate article leaving the pilger mill is greater than that heretofore considered fea-,

sible, thus reducing to a corresponding extent the surface exposed to scaling during the reheating operation.

Still another object of the present invention is to aord a method by means of which scrap losses may be materially reduced.

In the accompanying drawing I have shown byY have illustrated a layout comprising an ingot heating furnace 2 wherein the ingots or billets to be formed into tubes may be brought to the proper temperature. At this temperature the ingots are carried in any well known manner to a first piercing mill 3 wherein they are subjected to a piercing operation suitable for producing a hollow ingot or billet 4 substantially as illustrated in perspective in Figure 2 of the drawing. In this figure the pierced ingot or billet is shown as of substantially constant exterior diameter throughout the main body thereof, the exterior and interior. walls 5 and 6 respectively at the ends extending inl slightly converging relationship. In Figure 2 such a shape, which is characteristic of a piercing mill, is indicated in a much .exaggerated scale.

After leaving the piercing mill the pierced ingots or billets may be delivered in any desired manner, as by a suitable conveyor 7, to a transfer track 8 cooperating at its ends with the rolls 9 of pilger mills driven in any customary or desired manner. Cooperating with the pilger mills are mandrel operating and feeding mechanisms In accordance with the present invention, it is A contemplated that the pilger mills 9 will perform less forging than has heretofore beerr customary. thereby delivering anintermediate article 11, as. illustrated in Figure 3, which will have a rela.- tively thick wall, and thus a less surface available for scaling. This intermediate article has a substantially uniform outside dimension throughout the maior portion of its length, but at the trailing end has an outwardly ared portion 12, characteristic ofthe pilgering process.V In view of the fact that this intermediate article has heretofore been passedy directly to a plug mill, it has been necessary to crop the same-so as to remove, entirely, the outwardlygared portion. To this end cropping has usually been effected along a line such as indicated at a--a in Figure 3. This cropping has been not only for Ythe purpose of squaring up the intermediate article, but for the purpose of removing the portion of the ingot in which the segregation or piping usually appears, the ingot being presented so that such piping is contained within the thickened end portion 12. In accordance with my invention, the crop loss will be materially reduced by delivering the intermediate article from the pilger mills to hot saws 14 effective for sawing the same along a line such as indicated at b-b in Figure 3.

The sawed article with its fairly thick walls. will then be delivered to a conveying trough 15 and out to an inspection table 16. Here the billets may be inspected, and if found satisfactory, may be rolled into a reheating furnace 1'?. If, however, seams, scabs, or other defects show up at this point, the biiiets may either be chipped at the inspection table and made acceptable for further working, or may be conveyed out to a chipping or cross-over table 18 where they can be worked upon or VVconveyed either to a scrap pile or some other desired point, depending upon the disposition to be made thereof'. In the reheating furnace the billets will be brought to the desired temperature for subsequent operations.

Inasmuch as the billet or ingot utilized in the Vflrst instance has arelatively smaller diameter than ingots or billets as heretofore utilized for the production of tubes of the same size, the dimensions of the reheating furnace may be smaller than the dimensions of reheating furnaces customarily provided. Furthermore, since the amount of forging effected by the pilger mill is less than that'customarily resorted to, thus leaving a greater wall thickness, the billets leaving the pilgerYY mill have a smaller overall length, thereby further contributing to the use of smailer reheating furnaces.V This is advantageous not only from the standpoint of the cost of the installation, but also from the standpoint of compactness of the different units. The small amount cf forging 1S desirable in that it not only gives a lighter load on the pilger mill with consequent less likelihood of roll breakage, but for the reason that it leaves a greater wall thickness effective for retaining a greater amount of the initial heat supplied in the furnace 2. This greater heat correspondingly reduces the heating period in the reheating furnace 1'1.

After a billet has been reheated in the reheating furnace 1'?, it is discharged therefrom onto a suitable conveying mechanism 19 by which it is delivered to a second piercing mill 20 which may be similar to the rst piercing mill 3. This second piercing mill will produce an intermediate article 21 as illustrated in Figure 4, having end portions 22 as before described, and as characteristic of a piercing mill, with an intermediate portion of substantially constant diameter and cross section. The operation of the second piercing mill will not only tend to decrease the wall thickness, but to increase the inner and outer diameters of the article and increase the length thereof. It will also be effective for dislodging any scale formed on either the inside or outside of the billet during the reheating operation.

I am aware that it has heretofore been proposed to practice the so-called double piercing of an ingot in which the piercing occurred in successive steps. Such an operation as heretofore practiced, however, has not been satisfactory for the production of a billet for plug mill operation, due to the amount of working performed on the metal at the piercing mills, the amount of working being such that the ingot has been subjected to strains suciently severe to produce tearing thereof. In accordance with my invention, although successive piercing is utilized, the billets Yor ingots are subjected to an intermediate forging operation in the pilger mill, which operation is effective for refining the grain structure and increasing the strength of the metal, thus permitting a second piercing operation to be performed without davger of disruptive straining of the metal.

nThe piercing operation following the reheating is also desirable from the standpoint that it effects substantially complete removal of the scale formed by reheating. Heretofore when Va lbillet has been passed Vdirectly-from a reheating yfurnace to the plug mill, the scale has given considerable trouble. The scale being extremely hard, has a destructive action on such plugs. By the npresent invention, the scale is eliminated, thus reducing the wear on the plugs in the plug mill vand giving the same a materially greater life. l

In generally like manner, the less scale produced in the reheating furnace due both tothe decreased heating time and the less surface area, is advantageously reflected in the second piercing mill. Y

The second piercing operation also enables the outwardly flared portion intermediate the lines a-a and b-b as shown in Figure 3 to be easily brought down to the desired thickness. A piercing mill being of much sturdier construction than a plug mill, and therefore capable of taking greater loads, makes possible the decrease in crop losses, since a piercing mill may readily compensatefor the aring left by the pilgering process.

This resulted in slipping at the plug mill, the slipping being augmented by the large amount of scale present.

'I'he tapered ends characteristic of a piercing mill operation facilitate insertion of the article into the plug mill, and also eliminate any shock or jar on such mill at the time of insertion. The htermediate article may be given any number of passes in the plug mill, and the wall thickness reduced to substantially the finished thickness desired. Such plug mill is effective not only f or removing irregularities produced in the article-by the severe working in both the piercing mills and in the pilger mill and smoothing both the inside and outside surfaces, but also for giving to the articles the desired uniformity in wall thickness from end to end thereof.

By reference to Figure 1, it will be noted that the article upon leaving the second piercing mill 20 goes to a transfer table 23 effective for delivering the same to a plug mill 24 provided with the usual plug mill pusher 25. After the article 'has been subjected to the desired number of passes, it is discharged onto a suitable conveyor 26 from ywhich it may lpass to reelers effective for rounding and increasing the diameter thereof, and thence to -sizing machines constituting no essential part of Vthe present invention.

For purposes of a clearer understanding o! the present invention, and by way of illustration and not by way of limitation, it may be assumed that it is desired to produce a finished pipehaving the outside diameter indicated in the rst table below. In such case I may advantageously utilize an ingot `having a diameter as indicated in the second Size oi .finished diier pipe (O.D.)

Assuming conditions as represented by the above tabulation, the iirst piercer, the pilger mill, the second piercer and the plug mill may then be operated to dimension the article as indicated in the following tables:

The values a: indicated in the abovev table will depend on the wall thickness desired in the linlished pipe, while the values y depend also upon the thickness desired in the wall of the iinished pipe, these being subject to change asrequired to meet specified conditions.

In accordance with the present invention, it will be apparent that I provide -a process characized by double piercing with a refining operation intermediate the same, the refining being eiective for increasing the strength and improving the grain structure of the article. 'Ihis constitutes one of the advantages of the present invention.

A further advantage of the invention arises from the fact that a double piercing operation is utilized, thus decreasing the load on each piercing mill, and making it possible to employ successive piercing operations without danger of rupturing the metal or subjecting the same to objectionable strains.

Still another advantage of the present invention arises from the fact that by reducing the wall thickness in the rst piercing mill, the area of the intermediate article delivered by the pilger mill for reheating purposes may be kept at a minimum, thus conserving heating time and reducing scale formation.

Further advantages.arise from the. use of a relatively smaller diameter ingot for the production of a given sized pipe or tube and from the consequent possibility of reducing the size of the reheating furnace.

Another advantage of the invention is' inherent in the reduction in crop losses made possible by pilgering an article intermediate successive piercing steps, and from the improved operation of a plug mill occasioned by piercing an article after a pilgering step.

Other advantages will foregoing description taken in connection with the accompanying drawing forming a part thereof.

While I have herein illustrated and described a preferred method and apparatus for carrying out the present invention, it will be understood that changes in the steps employed as well as in the apparatus utilized for performing the same, may be made without departing either from the spirit of my invention or the scope of my broader claims.

I claim:

1. In the method of forming seamless tubes, the steps comprising subjecting the product of a pilger mill to a. piercing operation and then rolling the same in a plug-mill.

2.`In the method of forming seamless tubes, the steps comprising piercing an ingot, pilgering the pierced ingot, piercing the product of the 4pilger mill, and thereafter rolling such product in a plug mill.

3. In the method of forming seamless tubes, the steps comprising heating an ingot, piercing and pilgering the same, reheating the product Aof the pilgering process, subjecting the pilgered product to a piercing operation, and then smoothing and sizing the same by subjecting the same successively. to plug mill, reeling and sizing goperations.

4. In the method of forming seamless tubes,

to a plug mill.

5. In the method o! forming seamless tubes, the steps comprising subjecting a pierced ingot to a pilgering process, tapering the end portions of the pilgered article by subjecting the same to a piercing operation, and delivering the same to a plug mill.

6. In the method of forming, seamless tubes, the steps comprising piercing an ingot, pilgering the same, cropping the pilgered article so as to retain a portion of the flared end, and thereafter removing the flared portion by subjecting the same to a piercing operation.

'7. In a tube making system, means for piercing ingots, means for reducing the wall thickbe apparent from the ness of the pierced ingots to produce semiiinished tubes, means for again piercing the seminishedtubes, means for thenheating the tubes and a plug mill for changing the diameter of the tubes received from the second piercing means and heating means.

8. In the method of preparing articles for operation in a plug mill, the steps comprising subjecting the same to a plurality of piercing op- JOHN U. DEVINE.

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