US2409219A - Tube expanding - Google Patents

Description

0st, 15, 1946. c. A. MAXWELL 2,409,219 TUBE EXPANDING Original Filed May 15, 1941 5 Shets-Sheet l f IN1/Emmi l Y l I y Car/AMaxwe/ A ITORNE Y 0L15,1946. c, MAXWELL. Y 2,409,219

TUBE EXPANDING Original Filed May 15, 1941 5 Sheets-Sheet 2 `INVENTOR.

Caf/A Maxwe/z A ITORNEY fr 15, S46. c. A. MAXWELL A 2,409,219

TUBE EXPANDING original Filed may 15, 1941 5 sheets-sheet s IN VEN TOR.

Y Carl Maxwell BY A ITORNEY v @et 15, E946. c. A. MAXWELL TUBE EXPANDING Original Filed May 15, 1941 Q A INVENToR.

ATORNEY 5 Sheets-Sheet 4 Patented Oct. 15, 1946 TUBE EXPANDING Carl A. Maxwell, Akron, Ohio, assignor to The Babcock & Wilcox Company, Rockleigh, N. J., a corporation of New Jersey Original application May 15, 1941, Serial No. 393,505, now Patent No. 2,375,235, dated May 8, 1945. Divided and this application January 25, 1944, Serial No. 519,591

2 Claims.

The subject matter of this invention is the expanding of tubular members and, in a more specic sense, the expanding of metallic tubes against the walls of tube seats in which the tubes are tted.

In the manufacture of fluid heat exchange apparatus such as steam generators, metallic tubes are xed in headers, drums, or tube sheets by iirst positioning the tubes within closely fitting openings and then expanding the tubes tightly against the Walls of those openings, and, with the advent of increasing pressures (an increase from 200 pounds per square inch to 2,500 pounds per square inch within a period of thirty years) and the use of furnaces operating at higher and higher temperatures an increasing number of problems have been encountered in such expanding operations. For example, with pressures increasing toward and beyond 2,000 pounds per square inch, the walls of headers and drums have correspondingly increased in thickness, and the same is true of the walls of the tubes.

Steels of improved quality and increased strength have also come into use and, when tubes are to be expanded into tube seats in a ve inch wail of a drum of such improved steel, excessive resistance to the expanding operation has been encountered and greatly increased expanding forces have been necessary.

The expanders of the prior art have operated to expand the tube over the entire length of the tube seat, and as the tube seats have increased in length it has been necessary, with such prior art expanders to take excessively long periods of time to expand even a single tube within a tube seat. There are instances where it has taken a plurality oi expander operators more than an hour to expand a single tube, under such conditions, and furthermore, this expanding, in such instances has involved large expanding forces and increased power.

Furthermore, as tube seats have increased in length and as tube Wall thicknesses have increased, there has been excessive tube metal extrusion consequent upon the expanding operations. Such excessive extrusion has been particularly damaging in the expanding of tubes in steam generators involving a bank of tubes directly connecting and fixed to the same drums or headers. For example, let us consider the expanding of the tubes of a water tube steam boiler in an upper drum and the lower drum at the opposite ends of a large number of tubes which are to be subjected to a pressure of 1,000 pounds per square inch and to furnace gas tempera- (Cl. IZ9-457.5)

2 tures ranging from 1,000 F.3,000 F. Necessarily, the tubes to stand such pressures must be of increased thickness and the manner of securement of the tubes to the drums must be such as to enable the connections to withstand not only high pressure but also the stresses set up by the variations in gas temperatures to which the tubes and Ythe connections are subjected. Let us assume that the upper and lower headers are set in position and that the tubes are fitted in the drum tube seats by sliding them therein. The next step in the procedure is to expand the tubes to form pressure tight connections between the tubes and drums. The prior practice has been to proceed with the expanding operation from an end of a tube toward its mid portion. Now, if this practice is followed and a pressure tight connection is made by such an expanding operation some of the tube metal will be caused to 110W toward the other drum, this action resulting in an increase of the length of the tube. As to the lengthening of the tube, this metal flow is not particularly damaging on the rst tube because that tube can slide in the tube seat of the other drum, but when an attempt is made to use this prior art procedure to expand the other end of the same tube in the other drum, there cannot be the same relatively free movement of the tube totake care of the metal flow. However, the position of the drum may be modied to take care of such action. After this is done, however, the positions of the two drums are fixed. Thereafter, when the same procedure is attempted in the expanding of the successive tubes into the drums, a drum cannot be moved to take care of such metal flow and tube lengthening because the securement of the rst tube has set the drum spacing, and consequently the remaining tube metal will be put under objectionable stresses. These may even be so great as to result in bending of the tubes.

Attempts have been made to eliminate these objectionable results of prior procedures by counter-boring the drum tube seats. This has the effect of decreasing the length of the tube seats and correspondingly decreasing the metal ilows resulting from the tube expanding operation. However, this practice of counter-boring tube seats is objectionable because it reduces the strength of the drums in two ways. First of all, by the removal of metal in the immediate vicinity of the tube, and, secondly, by a consequent decrease in ligament strength.

Among the objects of this invention is the elimination of such difliculties as those above mentioned, the reduction of power and time required to expand tubes within tube seats, and the formation of improved tube seat connections.

The present invention eliminates many of the above indicated difficulties by a procedure which involves, as its initial step, the expanding of that portion of a tube remote from the end oi the tube and against that part of the tube seat metal which is adjacent to the wall of the drum or tube sheet remote from the end of the tube. This initial expanding step is accomplished in such a way that an optimum of tube metal flow is attained with a minimum of power consumption, and in a greatly decreased period of time. This is accomplished by having the roller expander element which does the preponderance of the expanding, of a small length relative to the length of the tube seats, other rollers of the expander acting mainly to guide the expander apparatus and to stabilize it within the tube. After this initial expanding operation, the active expander element is moved to a new and successive circular zone location toward the end of the tube from the rst location and the expanding is continued. In this Way, the flow of metal caused by the expanding operation is toward the end of the tube, and consequently there can be no tendency to put the tubes of a bank of tubes under excessive compressive stresses.

In general, when tubes are expanded in a tube sheet or into the walls of drums or headers, and are subjected to high fluid pressures, the tube and wall connections must be such as to resist great forces tending to move a tube longitudinally with reference to the tube seat and to disrupt the connections. Additionally, there are forces exerted longitudinally of the tubes and through them to the tube seats, resulting from strains induced by temperature changes. There are also torsional forces which may tend to disrupt the tube seat connection. These may result from various internal conditions such as temperature changes, or they may result from loading. These torsional stresses may be considered as exerted tangentially with reference to a tube so that they have a tendency to rotate the tube in the tube seat and thereby destroy the fluid tight connection.

The length of a tube seat measured axially of a tube, is a major factor in the determining of the frictional resistance between a tube wall and a tube seat wall, and, this resistance, in a coinpleted joint should nullify forces tending to longitudinally displace the tube with reference to the tube seat. The longer the tube seat, the greater the resistance, provided, of course, that the tube is expanded throughout the entire length of the tube seat. Additionally, it has been proposed that this pull-out resistance of a tube in a tube seat be increased by the milling of grooves in the seat, the tube metal being displaced into these grooves by the expanding operation. With this practice, some of the tube metal would be subjected to shearing stresses in resisting the forces which during the operation of the apparatus, tend to pull the tube out of the tube seat.

The torsional resistance to forces tending to pull a tube out of a tube seat is also a function of the circumferential area of contact between the tube and the seat and this type of resistance is greater in a long tube seat than it is in a short one. Long tube seats therefore have the advantage of a greater resistance to pull-out forQeS a5 4 well as the advantage of increased torsional resistance.

The suggested practice oi grooving tube seats would not have the desired effect of increasing the resistance to torsional forces tending to disrupt the tube seat. Furthermore, the machining the grooves of tube seats would involve considerable expense.

In expanding a tube within a tube seat, there is a reduction in the thickness of the wall of the tube, this reduction of thickness resulting from metal ow tending to elongate the tube. The longer the tube seat the greater such metal flow and the greater the tendency to elongate the tube. Consequently, when a plurality of tubes are to be expanded between fixed headers or drums, the expanding operations may set up objectionable compression stresses in the tubes and the drums. Among other things, this invention is intended to eliminate this undesirable tendency, while still presenting the advantages of the longer tube seats.

High pressure drums are expensive because of the thickness of the metal utilized in their fabrication, and because of the weight of the drums, and therefore, it is important, that, in the use of such drums, there be eiective utilization of the maximum permissible ligament strength, to reduce drum wall thickness and thereby reduce drum cost.

In distinction to some of the prior art practices, such asV those involving the utilization of counterbored tube seats for high pressure boilers, the tube seats of the present invention, of the outside diameter of the tube, are carried completely throughout the drum metal and are more effective in the providing of adequate ligaments. In some grooved tube seats the length of the tube seat is but a fraction of the total drum thickness and the seat is provided with a counter-bored opening extending initially from the tube seat and of a length suflicient to permit axial movement of the tube. Attempts to roller expand tubes into such tube seats have resulted in flow of metal into the portions of the tubes externally of the tube seats. It has been thought that such metal flow would not be objectionable on account of the limited length of the tube seat, but'l the pull-out strength of such tube seat connections and their resistance to forces tending to develop torsional displacements have been proven to be inadequate. This may have been due to deficiencles in the effect of prior art expanders or their method of employment. The use of prior art roller expanders in attempts to form expanded tube seat connections with grooved tube seats has not been satisfactory because the action of the expanders has caused such flow of metal that the expanded metal in a previously filled groove would be subject to excessive shearing action when other grooves are filled. A first groove might be partially lled with tube metal, but the action of the expander in an attempt to fill a successive groove has resulted in a shearing of a metal within the first filled groove. Such shearing action is eliminated by the use of the expander of this invention, and by its use longer tube seats with a plurality of grooves may be successfully employed. The use of the illustrative expander in such tube sheets results in a, lling of all of the grooves with iiowed tube metal which remains integral with the metal of the expanded tube.

The present invention also provides such tube seats that there may be maximum ligament strengths. The illustrative tube seats .can also 'be machined at much lower cost, but these advantages, along with the advantages of increased pull-out and torsional resistance can be utilized only when the method of expanding is such .that the tube metal ilow resulting from the expanding will not induce excessive stresses in the tube and drum assembly. Such objectionable stresses are avoided by a practice in which the flow of metal during the expanding operation is toward the end of the tube rather than toward the middle of the tube.

This application is a division of my co-pending application Serial No. 393,505, led May 15, 1941 (now Patent No. 2,375,235), and the expanding method claimed herein is 'adapted for expanding tubes of great wall thickness such as those required for installations operating at high pressures where the tube wall thickness may be in excess of 5/16", and the length of the tube seats greater than three inches. Tube seats of such characteristics result in expanding operations which involve forces of high magnitude to cause the necessary metal ilow.

In accomplishing the albove indicated results the present invention includes within its pur- View the expanding method effected by an expander apparatus in which stabilizing rolls are so arranged with respect to the remainder of the expander apparatus that they automatically cause the active portions of the expander rolls to continuously move through the tube and toward the end of the tube.

In general, the present invention may be considered as a method of expanding a heavy wall tube into a tube seat, and more particularly, into tube seats which are of lengths greater than the diameter of the tubes to be inserted therewith, by slower expanding, and working of the metal from the tube seat and remote from the tube end, toward the end of the tube, the illustrated apparatus being such that it is self-advancing.

The various features of novelty which characterize my invention, in compliance with the Federal Statutes relating thereto, are pointed out with particularity in the claims annexed to and forming a part of this specification, but, for a better understanding of the invention and the advantages possessed by it, reference should !be had to the accompanying drawings and descriptive matter in which I have illustrated or described preferred embodiments of my invention. Other objects of the invention will also appear as the following description proceeds.

In the drawings:

Fig. 1 is a transverse section through a tube and tube seat assembly, and the illustrative roller expander for developing a pressure tight joint between the tube and the wall in which the tube seat is formed;

Fig. 2 is a transverse section of the Fig. 1 expander, on the line 2 2 of Fig. 1;

Fig. 3 is an assembly View showing mechanism for operating the illustrative roller expander which is shown in elevation;

Fig. 4 is a combined longitudinal section and side elevation illustrating the last step in the expanding method in which the Fig. 1 expander may be employed;

Fig. 5 is a longitudinal section illustrating the structure and mode of operation of another eX- pander which may be employed to eiect the illustrative method;

Fig. .6 is a transverse section onthe line B--S of Fig. 5.

Fig. 7 is an assembly view showing an operating mechanism connected to the expander as the latter is inserted in the tube to be expanded;

Fig. 8 is mainly a sectional view of the Fig. 5 expander indicating the last step in the expanding of the tube into the tube seat;

Fig. 9 is an enlarged longitudinal section of the Fig. 5 expander showing the relationship of the elements .in detail;

Fig. 10 is a partial plan of the expander cage, illustrating the angular relationship of the center lines of the expander rollers and the centerline of the mandrel;

Fig. l1 is a sectional view of the barrel or vcage `of the Fig. 9 expander showing the conformation and relationships of the expander roll retention sockets in the cage;

Fig. 12 is an end elevation of the expander barrel or cage shown in Fig. 11;

Fig. 13 is a partial longitudinal section of the roller cage of the Fig. 1 expander, illustrating the relationships of the roller retention sockets. This view is taken on the section line |3-Y-I3 `of Fig. 14;

Fig. 14 is an end elevation illustrated in Fig. 13;

Fig. 15 is a partial elevation of the Fig. 13 expander cage particularly indicating the oil"- set angular relationship of the axis of the cage and the axis of one of the stabilizing rolls. The position from which this elevation is taken may of the expander-cage be considered as indicated by the arrow ld;

ing the initial stages of the Fig. 16 is a partial longitudinal section of the Fig. 13 expander cage taken on the section line IS-IB of Fig. 14; and

Fig. 17 is a longitudinal section showing the operation of the Fig. 5 expander during an early stage of the expanding operation.

The expander illustrated in Figs. 1-4, inclusive, and 5-8, inclusive, of the drawings maybe considered as a retractive roller expander in which the expander rolls and the mandrel are eccentric to the roller cage and to the tube to be expanded. The expander barrel or cage ll! is a steel body formed somewhat as a cylinder with such an external diameter that it will be readily received within a tube to be expanded into a tube seat in the wall I4. The cage is formed 'with an eccentric bore to receive a mandrel l5.

Ihe mandrel is formed with a tapered section I8, the surface of which causes the expanding roll 2D and the positioning and feeding rolls 22 and 24 to move outwardly of the expander cage when the mandrel is moved to the right (Fig. l) mith reference to the cage and the tube seat wall The advancement of the mandrel to tube expanding position, after the expander is inserted within the tube as indicated in Fig. 1, is caused by rotation to the mandrel. In practice, the mandrel is rotated by a motor 26 which is readily detachably connected to the squared end 28 of the mandrel. During this Iortation and durtube expanding operation, longitudinal advance of of the mandrel is elected by reason of the inter-engagement of the screw threaded part of the mandrel with an internally screw threaded sleeve 30 formed Iwith a coupling extension 32, the latter being initially held stationary by a wrench .cr Spanner.

The sleeve 3D is formed with a radial flange 34, one face of which contacts the thrust bearing .36 disposed at the bottom of a recess in the end of the cage I0, the sleeve 3U being confined between the bearing 38 and the locking ring 38 screw threaded into the cage I0, as shown.

The distance to which the Fig. 1 expander extends into the tube l2 is determined by the adjustment of a stop sleeve 40 along the cage l0. This sleeve is locked in a predetermined position by the set screw 42.

When the sleeve 30 is thus held stationary the rotation of the mandrel causes it to move to the right so as to force the expanding roll 2B and the stabilizing rolls 22 and 24 against the internal surface of the tube l2.

When the frictional resistance resulting from the contact of the tube and roller surfaces reaches a certain degree, the rolls 20, 22 and 24 begin to rotate on their own axes as planet gears and, consequently, the cage I0, operating somewhat in the nature of an orbit gear, is also rotated, but at a different rate. As this operation continues the expanding roller 20, guided and stabilized within the tube by the rolls 22 and 24 exerts increasing pressure radially outwardly on the inner wall of the tube l2 and causes the tube metal to flow axially of the tube, and toward the right hand end of the tube (Fig. 1). At the same time, due to the differential taper of the rollers and the mandrel, and due to the 2 degree angular relationship (lead angle) of the mandrel center line to the center lines of the positioning and feeding rollers 22 and 24 (see Fig. 15) the rollers begin to advance the entire expander toward the right of the position in which it is indicated in Fig. l. These relationships are such that the tendency of their combined action to advance the expander overcomes the tendency of the expanding roll to mount the tapered portion of the mandrel.

After the bite of the expanding roller 20 into the tube metal reaches the desired degree, the Spanner is removed from the coupling 32, and the above indicated relationship of forces thereafter produces an automatic advance of the expander out of the tube.

The angularity of the center lines of the positioning and feeding rolls 22 and 24 with respect to the center line AB of the mandrel (Figs. 14 and 15 of the drawings) illustrates one of the factors producing the automatic advance, or selffeeding action of the expander out of the tube. The line CD may be considered as representing the center line of the roller 22 mounted in the retention socket 50 of the cage I0. As indicated, the lines CD and AB are disposed at an angle of 2 degrees.

The retention socket 50 for the roller 22, as well as the sockets 52 and 54 for the rollers 24 and 2G, respectively, may be described as formed with walls which are re-entrant at positions such as 55-(59, inclusive, adjacent the periphery of the cage l0. This construction prevents the rolls from falling out of their operative positions around the mandrel I6.

The sockets are otherwise shaped within the annular portion of the cage IIJ so as to permit the rolls to move freely radially with respect to the cage.

After the rolls 20, 22 and 24 are inserted in the sockets 50, 52 and 54 they are retained therein by a closure ring 62 corresponding in external contour to the left hand end (Figs. 1 and 2) of the cage. This ring is held in its operative position by a stud screw 64 fitting within an internally screw threaded bore 66 in the end wall of the cage.

A comparison of the 4extent, of the surface of the expander roller 20 in contact with the metal of the tube l2 during the actual expanding operation to the sum of surfaces of the positioning and feeding rollers 22 and 24 in similar contact will indicate the ratio of roller surface which is actually expanding the tube. All of the actual expanding is done there is a very great reduction of momentary flow of tube metal, in comparison with other expanders which use a plurality of rolls each of which accomplishes the same degree of expanding.

In the present instance, the larger rolls, 22 and 24, serve to stabilize the expanding action and cause the automatic advance of the expander out of the tube.

Now referring to the expander indicated in Figs. 5-12, inclusive, there is a cylindrical cage 'l0 formed at one end with three retention sockets Il- 13 for the similarly formed expander rollers 'I4-16. These sockets are formed with side walls which are converging, or re-entrant at positions Biladjacent the periphery of the cage.

The retention sockets 'l l-13 are also so angled with respect to the center line EF (Fig. 10) of the cage and the mandrel that their center lines present the 2 degree angle GKE to the mandrel center line. The expander rollers 14-16 have their center lines in uniform angular relationship to the cage center line EF so that, the roller expanding operation will involve a factor having a tendency to automatically feed or advance the expander from the initial expanding position in which it is shown in Fig. 5, to the right outwardly of the tube and its tube seat in the wall 92. The mandrel 94 is formed with an active expanding section 9B tapered ag" to the inch, a taper so selected that the mandrel surface active in engagement with the expanding rollers will be presented to the rollers at an angle slightly greater than that which will permit the self-feeding action of the rollers 14-16 to surmount the mandrel. In other words, the taper of the mandrel constitutes an angle slightly greater than one which the self-feed action of the rolls will surmount. Thus the thrust of the mandrel, in the main part of the expanding operation will be always toward the front of the mandrel (or its left hand end as indicated in the drawings) This thrust is taken by the bearing 98 from the coupling collar |00 which has an annular flange |02 confined between the bearing 98 and a lock collar H14. All of these elements are disposed within a recess in the right hand end of the cage as shown.

Each of the rollers 'I4-76 has a central portion ll which is tapered, the taper of this portion being slightly less than one-half the taper of the mandrel. Beyond this tapered portion HU each roller has a portion H2, the taper of which is slightly greater than one-half the taper of the mandrel. Thus the stabilizing portion of H0 of each of the rollers 'I4- 16 rests against the mandrel and does the initial part of the expanding and the portion H2 of the roller (the surface of which is parallel to the axis EF of the tube) does the final or heavier part of the expanding.

In the operation of the expander shown in Figs. 5-12 the collar |20 is adjusted along the cage 10 and xed thereon to determine the extent of the expander within the tube. Then the expander is placed in the tube in the position in which it is shown in Fig. 5 with the collar |20 contacting the end of the tube 90. Then the coupling collar by the roller 20, and thus is held stationary with a wrench or spanner and an air motor 130 is employed to rotate the mandrel through easily detachable engagement with the polygonal coupling end 132 until the rollers 'id- 16 are moved radially outwardly of the cage 'i9 suiciently to expand the tube. Then the coupling or nut mi! is released and the turning of the mandrel operates to maintain the expanding pressure and automatically advance the expander toward the adjacent end of the tube.

Considering the expander of Figs. -l2 to be employed in securing the ends of the tubes of a bank connecting two drums, the purpose of the expander is to roll the tube from the outside of the drum wall toward the inside, thus bringing all axial flow movement of the tube metal, due to the expanding operation, toward the inside of the drum. With this manner of expanding-no stresses are set up upon the intermediate portions of the tubes between the drums. Also, the expander rolls the tube with the major part of the tube metal flow limited to a reduced portion of the tube seat at any one time. This tends to produce maximum holding power of the tube with a minimum stress on the tube seat. Also, with the illustrative apparatus employed in the illustrative method much less power is required for operating the expander.

With further reference to Fig. 9 of the drawings, it will be seen that the center line TW of the roll 'i4 forms an angle of 31/2 with the center line EF of the mandrel or the tube. This relationship of parts, together with the relative degrees of taper of the mandrel and roller surfaces indicates one factor in construction of the illustrative mechanism which tends to cause the action described.

Fig. 17 illustrates an early stage of the expanding operations, the straight line RS when compared to the curved line RUS indicating the extent of deformation of the tube in the expanding operation. The straight line RS is intended to indicate the interior surface of the tube before expansion, and the curved line RUS, the surface of the tube after expansion. An inspection of this figure will show that the portion H2 of the roller 'M has its active surface at a greater distance from the line RS than the stabilizing portion lli), or the remainder of the roller.

The specic apparatus involved in the embodiment shown in Figs. 1, 2, 3, 4, 13, 14, 15, and 16 of 10 the drawings is not claimed in this application but is claimed in a co-pending application, Serial No. 519,141, filed on January 21, 1944.

What is claimed is:

1. A method of retractively expanding tubes into tube seats in a wall of a pressure part; said method including an initial tube expanding operation limited to and continuously advancing over a narrow circumferential zone the width of which is but a fraction of the length of' the tube seat, said initial tube expanding operation being efected at a position adjacent the end of the tube seat remote from the nearest tube end, stabilizing and advancing the expanding operation by guiding reactions against internal surfaces of the tube over an area and a circular zone of an axial extent much greater than the narrow zone of the initial expanding; subsequently repeating said expanding in a continuing expanding operation in contiguous Zones successively nearer the adjacent end oi the tube; said initial expanding operation involving the maximum tube expanding force of the method; maintaining said maximum force beyond the initial expanding operation; and constantly limiting the application of the expanding force to a minor circumferential segment.

2. The method of retractively expanding the end portion of a metal tube into a tube seat formed in a metal wall, the method comprising initially expanding and drawing the tube metal by a rolling action advancing circumferentially of the tube, exerting the maximum expanding force of the initial action in a narrow zone limited to a position adjacent the wall surface at the greater distance from the adjacent tube end to lock the tube to the wall at that position, then continuing a like expanding and drawing operation by a rolling action advancing helically of the tube toward the opposite surface of said wall and away from said locked position toward the adjacent end of the tube, constantly limiting the application of the maximum force of the expanding and drawing eiect of said rolling action at all stages of the continued expanding to a circumferential zone the width of which is but afraction of the length of the tube seat, and maintaining an expanding force of the order of the maximum of that of the initial action for a substantial part of the expanding method beyond the zone of the initial action.

CARL A. MAXWELL.

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