0st, 15, 1946. c. A. MAXWELL ' - 2,409,219 TUBE EXPANDING " Original Filed May 15, 1941 5 Sheèts-Sheet l -2010 . l Y ~ l _ I V ` f IN1/Emmi y Car/AMaxwe/Í A ITORNE Y -0¢L15,1946. ' c, ÁMAXWELL. Y 2,409,219- TUBE EXPANDING Original Filed May 15, 1941 94 n À L 5 Sheets-Sheet 2 o 7 132 120 `INVENTOR. Caf/A_Maxwe/z A ITORNEY fr 15, ÈS46. c. A. MAXWELL TUBE EXPANDING A ` 2,409,219 - ` ' original Filed may 15, 1941 5 sheets-sheet s INVEN TOR. Y ` Carl Á. Maxwell BY _ »_ - A ITORNEY v @et 15, E946. c. A. MAXWELL 2,409,219 TUBE EXPANDING Original Filed May 15, 1941 5 Sheets-Sheet 4 Q A INVENToR. ATÃ’ORNEY . ' Patented Oct. 15, 1946 2,499,219 UNITED STATES PATENT OFFICE 2,409,219 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. l The subject matter of this invention is the ex panding of tubular members and, in a more spe ciñc sense, the expanding of metallic tubes against (Cl. I‘Z9-457.5) 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 secure ment of the tubes to the drums must be such the walls of tube seats in which the tubes are ñtted. Ul as to enable the connections to withstand not only In the manufacture of fluid heat exchange high pressure but also the stresses set up by the apparatus such as steam generators, metallic variations in gas temperatures to which the tubes tubes are ñxed in headers, drums, or tube sheets and Ythe connections are subjected. Let us as by iirst positioning the tubes within closely fitting sume that the upper and lower headers are set openings and then expanding the tubes tightly il) in position and that the tubes are fitted in the against the Walls of those openings, and, with drum tube seats by sliding them therein. The the advent of increasing pressures (an increase next step in the procedure is to expand the tubes from 200 pounds per square inch to 2,500 pounds to form pressure tight connections between the per square inch within a period of thirty years) tubes and drums. The prior practice has been and the use of furnaces operating at higher and to proceed with the expanding operation from higher temperatures an increasing number of an end of a tube toward its mid portion. Now, if problems have been encountered in such expand this practice is followed and a pressure tight con ing operations. For example, with pressures in creasing 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 ñve inch nection 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 ñrst tube be cause 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 resistance to the expanding operation has been end of the same tube in the other drum, there encountered and greatly increased expanding cannot be the same relatively free movement of forces have been necessary. the tube to- take care of the metal flow. How The expanders of the prior art have operated 30 ever, the position of the drum may be modiñed to expand the tube over the entire length of to take care of such action. After this is done, the tube seat, and as the tube seats have in however, the positions of the two drums are fixed. creased in length it has been necessary, with Thereafter, when the same procedure is attempted such prior art expanders to take excessively long in the expanding of the successive tubes into periods of time to expand even a single tube with ' the drums, a drum cannot be moved to take care in a tube seat. There are instances where it of such metal flow and tube lengthening because has taken a plurality oi expander operators more the securement of the ñrst tube has set the drum than an hour to expand a single tube, under spacing, and consequently the remaining tube such conditions, and furthermore, this expanding, metal will be put under objectionable stresses. in such instances has involved large expanding These may even be so great as to result in bend forces and increased power. ing of the tubes. Furthermore, as tube seats have increased in Attempts have been made to eliminate these length and as tube Wall thicknesses have in objectionable results of prior procedures by coun creased, there has been excessive tube metal ex ter-boring the drum tube seats. This has the trusion consequent upon the expanding opera ' effect of decreasing the length of the tube seats tions. Such excessive extrusion has been par and correspondingly decreasing the metal ilows ticularly damaging in the expanding of tubes in resulting from the tube expanding operation. steam generators involving a bank of tubes di However, this practice of counter-boring tube rectly connecting and fixed to the same drums seats is objectionable because it reduces the or headers. For example, let us consider the 50 strength of the drums in two ways. First of expanding of the tubes of a water tube steam all, by the removal of metal in the immediate boiler in an upper drum and the lower drum at the vicinity of the tube, and, secondly, by a conse opposite ends of a large number of tubes which quent decrease in ligament strength. are to be subjected to a pressure of 1,000 pounds Among the objects of this invention is the per square inch and to furnace gas tempera 55 elimination of such difliculties as those above wail of a drum of such improved steel, excessive 2,409,219 3 mentioned, the reduction of power and time re quired to expand tubes within tube seats, and the formation of improved tube seat connec 4 well as the advantage of increased torsional re sistance. The suggested practice oi grooving tube seats would not have the desired effect of increasing tions. the resistance to torsional forces tending to dis The present invention eliminates many of the rupt the tube seat. Furthermore, the machining above indicated difficulties by a procedure which the grooves of tube seats would involve consid involves, as its initial step, the expanding of that erable expense. portion of a tube remote from the end oi the tube In expanding a tube within a tube seat, there and against that part of the tube seat metal is a reduction in the thickness of the wall of the which is adjacent to the wall of the drum or tube tube, this reduction of thickness resulting from sheet remote from the end of the tube. This metal ñow tending to elongate the tube. The initial expanding step is accomplished in such a longer the tube seat the greater such metal flow way that an optimum of tube metal flow is at and the greater the tendency to elongate the tained with a minimum of power consumption, tube. Consequently, when a plurality of tubes 15 and in a greatly decreased period of time. This are to be expanded between fixed headers or is accomplished by having the roller expander drums, the expanding operations may set up ob element which does the preponderance of the ex jectionable compression stresses in the tubes and panding, of a small length relative to the length the drums. Among other things, this invention of the tube seats, other rollers of the expander is intended to eliminate this undesirable tend acting mainly to guide the expander apparatus 20 ency, while still presenting the advantages of the and to stabilize it within the tube. After this longer tube seats. initial expanding operation, the active expander High pressure drums are expensive because of element is moved to a new and successive circu the thickness of the metal utilized in their fabri lar zone location toward the end of the tube from cation, and because of the weight of the drums, the ñrst location and the expanding is continued. and therefore, it is important, that, in the use In this Way, the flow of metal caused by the ex of such drums, there be eiîective utilization of panding operation is toward the end of the tube, the maximum permissible ligament strength, to and consequently there can be no tendency to reduce drum wall thickness and thereby reduce put the tubes of a bank of tubes under excessive 30 drum cost. compressive stresses. In distinction to some of the prior art practices, In general, when tubes are expanded in a tube such asV those involving the utilization of counter sheet or into the walls of drums or headers, and bored tube seats for high pressure boilers, the tube are subjected to high fluid pressures, the tube seats of the present invention, of the outside and wall connections must be such as to resist diameter of the tube, are carried completely great forces tending to move a tube longitudi throughout the drum metal and are more effec nally with reference to the tube seat and to dis tive in the providing of adequate ligaments. In rupt the - connections. Additionally, there are some grooved tube seats the length of the tube forces exerted longitudinally of the tubes and seat is but a fraction of the total drum thickness through them to the tube seats, resulting from 40 and the seat is provided with a counter-bored strains induced by temperature changes. There opening extending initially from the tube seat are also torsional forces which may tend to dis and of a length suflicient to permit axial move rupt the tube seat connection. These may result ment of the tube. Attempts to roller expand from various internal conditions such as temper tubes into such tube seats have resulted in flow ature changes, or >they may result from loading. of metal into the portions of the tubes externally These torsional stresses may be considered as of the tube seats. It has been thought that such exerted tangentially with reference to a tube so metal flow would not be objectionable on account that they have a tendency to rotate the tube in of the limited length of the tube seat, but'l the the tube seat and thereby destroy the fluid tight pull-out strength of such tube seat connections connection. 50 and their resistance to forces tending to develop The length of a tube seat measured axially of torsional displacements have been proven to be a tube, is a major factor in the determining of inadequate. This may have been due to deficien the frictional resistance between a tube wall and cles in the effect of prior art expanders or their a tube seat wall, and, this resistance, in a coin method of employment. The use of prior art pleted joint should nullify forces tending to longi 55 roller expanders in attempts to form expanded tudinally displace the tube with reference to the tube seat connections with grooved tube seats tube seat. The longer the tube seat, the greater has not been satisfactory because the action of the resistance, provided, of course, that the tube the expanders has caused such flow of metal that is expanded throughout the entire length of the the expanded metal in a previously filled groove tube seat. Additionally, it has been proposed that 60 would be subject to excessive shearing action this pull-out resistance of a tube in a tube seat when other grooves are filled. A first groove be increased by the milling of grooves in the seat, might be partially ñlled with tube metal, but the the tube metal being displaced into these grooves action of the expander in an attempt to fill a by the expanding operation. With this practice, successive groove has resulted in a shearing of a metal within the first filled groove. Such shear some of the tube metal would be subjected to ing action is eliminated by the use of the ex shearing stresses in resisting the forces which pander of this invention, and by its use longer during the operation of the apparatus, tend to tube seats with a plurality of grooves may be pull the tube out of the tube seat. successfully employed. The use of the illustra The torsional resistance to forces tending to pull a tube out of a tube seat is also a function 70 tive expander in such tube sheets results in a, ñlling of all of the grooves with iiowed tube metal of the circumferential area of contact between which remains integral with the metal of the the tube and the seat and this type of resistance expanded tube. is greater in a long tube seat than it is in a short The present invention also provides such tube one. Long tube seats therefore have the advan tage of a greater resistance to pull-out forQeS a5 ‘ seats that there may be maximum ligament 5 2,409,219 strengths. The illustrative tube seats .can also 'be machined at much lower cost, but these ad vantages, 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-pend ing application Serial No. 393,505, ñled >May 15, 1941 (now Patent No. 2,375,235), and the expand ing method claimed herein is 'adapted for ex panding tubes of great wall thickness such as those required for installations operating at high 6 Fig. .6 is a transverse section on’the line B--S of Fig. 5. Fig. 7 is an assembly view showing an oper ating 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 expand ing 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 pressures where the tube wall thickness may be sockets in the cage; in excess of 5/16", and the length of the tube seats 20 Fig. 12 is an end elevation of the expander bar greater than three inches. Tube seats of such rel or cage shown in Fig. 11; characteristics result in expanding operations Fig. 13 is a partial longitudinal section of the which involve forces of high magnitude to cause roller cage of the Fig. 1 expander, illustrating the the necessary metal ilow. relationships of the roller retention sockets. In accomplishing the albove indicated results This view is taken on the section line |3-Y-I3 `of the present invention includes within its pur Fig. 14; View the expanding method effected by an ex Fig. 14 is an end elevation of the expander-cage pander apparatus in which stabilizing rolls are illustrated in Fig. 13; so arranged with respect to the remainder of the Fig. 15 is a partial elevation of the Fig. 13 expander apparatus that they automatically 30 expander cage particularly indicating the oil" 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 con sidered 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, 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 _ be considered as indicated by the arrow läd; 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 by slower expanding, and working of the metal operation of the Fig. 5 expander during an early from the tube seat and remote from the tube end, 40 stage of the expanding operation. toward the end of the tube, the illustrated appa The expander illustrated in Figs. 1-4, inclu ratus being such that it is self-advancing. sive, and 5-8, inclusive, of the drawings maybe The various features of novelty which charac considered as a retractive roller expander in terize my invention, in compliance with the Fed 45 which the expander rolls and the mandrel are eral Statutes relating thereto, are pointed out eccentric to the roller cage and to the tube to be with particularity in the claims annexed to and expanded. The expander barrel or cage ll! is a forming a part of this specification, but, for a steel body formed somewhat as a cylinder with better understanding of the invention and the such an external diameter that it will be readily advantages possessed by it, reference should !be Ul C received within a tube to be expanded into a had to the accompanying drawings and descrip tube seat in the wall I4. The cage is formed 'with tive matter in which I have illustrated or de an eccentric bore to receive a mandrel l5. ’I’he mandrel is formed with a tapered section scribed preferred embodiments of my invention. I8, the surface of which causes the expanding Other objects of the invention will also appear as the following description proceeds. 55 roll 2D and the positioning and feeding rolls 22 In the drawings: and 24 to move outwardly of the expander cage when the mandrel is moved to the right (Fig. l) Fig. 1 is a transverse section through a tube mith reference to the cage and the tube seat wall and tube seat assembly, and the illustrative roller expander for developing a pressure tight joint The advancement of the mandrel to tube ex between the tube and the wall in which the tube 60 panding position, after the expander is inserted seat is formed; within the tube as indicated in Fig. 1, is caused Fig. 2 is a transverse section of the Fig. 1 ex by rotation to the mandrel. In practice, the pander, on the line 2_2 of Fig. 1; mandrel is rotated by a motor 26 which is read Fig. 3 is an assembly View showing mechanism ily detachably connected to the squared end 28 for operating the illustrative roller expander of the mandrel. During this Iortation and dur which is shown in elevation; ‘ ing the initial stages of the tube expanding op Fig. 4 is a combined longitudinal section and eration, longitudinal advance of of the mandrel is elïected by reason of the inter-engagement of side elevation illustrating the last step in the ex panding method in which the Fig. 1 expander 70 the screw threaded part of the mandrel with an may be employed; internally screw threaded sleeve 30 formed Iwith a coupling extension 32, the latter being initially Fig. 5 is a longitudinal section illustrating the structure and mode of operation of another eX pander which may be employed to eiîect the il lustrative method; 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 2,409,219 7 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 ex tends into the tube l2 is determined by the ad justment of a stop sleeve 40 along the cage l0. This sleeve is locked in a predetermined posi tion 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 8 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 op eration to the sum of surfaces of the position begin to rotate on their own axes as planet gears ing and feeding rollers 22 and 24 in similar con tact will indicate the ratio of roller surface which is actually expanding the tube. All of the ac tual expanding is done by the roller 20, and thus ‘ there is a very great reduction of momentary flow of tube metal, in comparison with other ex panders which use a plurality of rolls each of which accomplishes the same degree of expand ing. ' 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 and, consequently, the cage I0, operating some Figs. 5-12, inclusive, there is a cylindrical cage what in the nature of an orbit gear, is also ro- ‘ 'l0 formed at one end with three retention sockets tated, but at a different rate. As this operation 20 ‘Il-_13 for the similarly formed expander rollers continues the expanding roller 20, guided and 'I4-16. These sockets are formed with side walls stabilized within the tube by the rolls 22 and 24 which are converging, or re-entrant at positions exerts increasing pressure radially outwardly on Bil-85 adjacent the periphery of the cage. the inner wall of the tube l2 and causes the tube metal to flow axially of the tube, and toward the 25 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 angu lar relationship (lead angle) of the mandrel cen ter line to the center lines of the positioning and 30 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 35 the expander overcomes the tendency of the ex panding roll to mount the tapered portion of the 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 pre sent 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 ex panding 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 90 and its tube seat in the wall 92. The mandrel 94 is formed with an active expand ing section 9B tapered ïag" to the inch, a taper so mandrel. selected that the mandrel surface active in en After the bite of the expanding roller 20 into gagement with the expanding rollers will be pre 40 the tube metal reaches the desired degree, the sented to the rollers at an angle slightly greater Spanner is removed from the coupling 32, and than that which will permit the self-feeding the above indicated relationship of forces there action of the rollers 14-16 to surmount the man after produces an automatic advance of the ex drel. In other words, the taper of the mandrel pander out of the tube. constitutes an angle slightly greater than one The angularity of the center lines of the posi- ~' which the self-feed action of the rolls will sur tioning and feeding rolls 22 and 24 with respect mount. Thus the thrust of the mandrel, in the to the center line AB of the mandrel (Figs. 14 main part of the expanding operation will be and 15 of the drawings) illustrates one of the always toward the front of the mandrel (or its factors producing the automatic advance, or self left hand end as indicated in the drawings) . This :30 feeding action of the expander out of the tube. thrust is taken by the bearing 98 from the cou The line CD may be considered as representing pling collar |00 which has an annular flange |02 the center line of the roller 22 mounted in the confined between the bearing 98 and a lock collar retention socket 50 of the cage I0. As indicat H14. All of these elements are disposed within ed, 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 posi tion by a stud screw 64 fitting within an inter nally screw threaded bore 66 in the end wall of the cage. a recess in the right hand end of the cage as shown. Each of the rollers 'I4-76 has a central portion llû 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 man drel 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 ñxed 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 9 2,409,219 |00 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 suñ‘iciently to expand the tube. Then the coupling or nut mi! is released and the turn ing of the mandrel operates to maintain the ex panding pressure and automatically advance the expander toward the adjacent end of the tube. 10 Considering the expander of Figs. 5-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 15 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 ex 20 pander 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 pro duce maximum holding power of the tube with a 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 oper ation 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 ef “ected at a position adjacent the end of the tube seat remote from the nearest tube end, stabilizing and advancing the expanding operation by guid ing 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 expand- ' ing in a continuing expanding operation in con tiguous 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 con minimum stress on the tube seat. Also, with the 25 stantly limiting the application of the expanding force to a minor circumferential segment. tive method much less power is required for oper 2. The method of retractively expanding the ating the expander. end portion of a metal tube into a tube seat With further reference to Fig. 9 of the draw ings, it will be seen that the center line TW of the 30 formed in a metal wall, the method comprising initially expanding and drawing the tube metal roll 'i4 forms an angle of 31/2° with the center line by a rolling action advancing circumferentially EF of the mandrel or the tube. This relationship of the tube, exerting the maximum expanding of parts, together with the relative degrees of force of the initial action in a narrow zone limited taper of the mandrel and roller surfaces indicates to a position adjacent the wall surface at the one factor in construction of the illustrative illustrative apparatus employed in the illustra greater distance from the adjacent tube end to mechanism which tends to cause the action de lock the tube to the wall at that position, then scribed. continuing a like expanding and drawing opera Fig. 17 illustrates an early stage of the expand tion by a rolling action advancing helically of the ing operations, the straight line RS when com pared to the curved line RUS indicating the ex 40 tube toward the opposite surface of said wall and away from said locked position toward the adja tent of deformation of the tube in the expanding cent end of the tube, constantly limiting the ap operation. The straight line RS is intended to plication of the maximum force of the expanding indicate the interior surface of the tube before and drawing eiîect of said rolling action at all expansion, and the curved line RUS, the surface of the tube after expansion. An inspection of 45 stages of the continued expanding to a circum ferential zone the width of which is but afraction this figure will show that the portion H2 of the of the length of the tube seat, and maintaining roller 'M has its active surface at a greater dis an expanding force of the order of the maximum tance from the line RS than the stabilizing por of that of the initial action for a substantial part tion lli), or the remainder of the roller. of the expanding method beyond the zone of the The speciñc apparatus involved in the embodi 50 initial action. ment shown in Figs. 1, 2, 3, 4, 13, 14, 15, and 16 of CARL A. MAXWELL.