US1801498A - Flexible tubular corrugated wall - Google Patents

Description

April 21, 1931. w. M. FULTON ET AL Y FLEXIBLE TUBULAR CORRUGATED WALL Original Filed Dec.

4 Sheets-Sheet l i VIII April 21, 1931.

w. M. FULTON, ET AL 1,801,498

FLEXIBLE TUBULAR CORRUGATED WALL Original Filed Dec. 6, 1924 4 Sheets-Sheet 2 67 l/'ig 57 5556 52 6/ 64 f Il i 2.9: i e' Z8; 5

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FLEXIBLE TUBULAR CORRUGATED WALL Original Filed Dec. 6, 1924 4 Sheets-Sheet 3 Hl 5 I @6 62 ITWUUIII ,u 62

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" FLEXIBLE TUBULAR CORRUGATED WALL i Original Filed Deo. 6, 1924 4 Sheets-Sheet 4 Va Z7 26 72 46 ,47 7@ 4i ,46 6'? f 3 K gi v1 r 4Z 54/ 54 t N'Z 5i w55 1 44 a [i I $190 y 56 I ywentoz vPatented Apr. 21, 1931 UNITI-:D- STATES PATENT OFFICE 'WESTON M. FULTON AND JEAN V. GIESLER, OF IKNOXVILLE, TENNESSEE, ASSIGNORS TO THE FULTON SYLPHON COMPANY, OF KNOXVILLE, TENNESSEE, A CORPOBATIONOF DELAWARE, l FLEXIBLE 'rUBULAn 'Original application led December 6, 1924,'Seria1 No.

1927. Serial This invention relates to relatively-thin, iiexible, tubular corrugated Walls, this application being a division of our application Y Serial No. 754,444, filed December 6, 1924, for

exible tubular corrugated walls and method and apparatus for making the same.

Corrugated Walls have heretofore been manufactured by various mechanical meththe use of expanding dies, etc.

tain thickness and tozdevelop Weak spots in the material of the Wall. Itv has also been suggested to corrugate Walls by forcing the Wall by hydrostatic pressure into a corrugated die or form. If the Wall has been held Y against longitudinal displacement during the pressing operation, the formation ofthe tcorrugations has been attended by an undue stretching and thinning of the material as' much or more than in the mechanical methods heretofore discussed.- n Similarly, if the Wall has been subjected to hydrostatic pressure throughout its extent at the surface to be corrugated,a similar result has been obtained because the application of equal force on each side of the respective ridges in the die'has displaced the material of the Wall transversely Without permitting a corresponding longitudinal movement thereof.

It has also been suggested in the manufacture of tubular corrugated Walls to position the Wall in operative relation to a corrugated tubular die and progressively ex pose successive portions of the Wall to the hydrostatic pressure. This method has been ,e productive of corrugated Walls wherein the material has been stretched and thinned to a less extent but has not entirely overcome the undesirable stretching and thinning of the material because of ",frictional opposition to axial movement of the Wall. It has also been suggestedl to icorrugate tubular walls by subjecting the Wall to end pressure While the connUGA'rn'D WALL 754,444'. Divided and this application filed April 20, No. 185,312.

tube is filled with liquid. This method has effected the corrugationsby subjecting the material of the Wall to a crushing or buckling pressure, the contained liquid constituting a variable counter-die that prevents collapse of the Wall other than into the corru-V gations of the forming die. But this method of procedure is defective when applied to relatively thin walls because of the tendency of the Wall tov buckle at its weaker portion and the consequentformation of body Wrinkles.

It is an object of this invention to provide a relatively-thin, highly-'flexible tubular corrugated Wall which has not been unduly stretched or thinned and which is also free of body Wrinkles. o

Another object of this invention is to provide a relatively-thin, highly-iexible tubular corrugated Wall with a superficial area or mean thickness, or both, not substantially less than the superficial area or thickness of the tube from which said Wall is formed.

Another object of this invention is to provide a relatively-thin, highly-iiexible tubular corrugated Wall Whose longitudinal elements are shorter than the longitudinal elements of the tube from which said Wall is formed, or Whose superficial area is less or Whose mean thickness is greater, or both, than the superficial area or thickness of the. tube from which the corrugated wall is formed.

Another object of this invention is to provide a relatively-thin, highly-flexible tubular corrugated Wall of the character set out in any of the foregoing objects which isof substantiallyuniform thickness; or which has corrugations the `bends of which have been rendered predeterminately resilient.

One -suitable method and apparatus by which a relatively-thin, liighly-iiexible tubular corrugated Wall as characterized in the foregoing objects may be produced -is illustrated on the accompanying drawings and described in det-ail, but it is to be expressly understood that such method and apparatus have been selected for purposes of illustration only and are not to be taken as restricting the inventionbeyond that deiined in the claims, as other suitable methods and a pal ratus for producing such awall as de ned will readily suggest themselves to those skilled in the art.

Referring in detail to the drawings wherein the same characters of reference are employed to designate corresponding parts in the several figures,

Fig. 1 is a more 'or less diagrammatic view of suitable apparatus for producing walls in conformity with the present invention;

Fig. 2 is a more or less diagrammatic view of a second apparatus for producing walls in conformity with the present invention;

Fig. 3 is an enlarged fragmentary view corresponding to Fig. 2 but illustrating the position of the parts after one corrugation has been formed in the tubularwall;

Fig. 4 is a corresponding view illustrating the position of the parts when a second' corrugation is about to be formed in the 'tubular wall;

Fig. 5 is a perspective view of the elements which are moved into position to protect the formed corrugations and constitute a die element in the formation of a succeeding cor- L rugation;

Fig. 6 is a. detail view illustrating means for clamping a tube in one of the die elements when a predetermined stretching of the material is desired; and

Figs. 7 and 8 respectively illustrate diagrammatically a blank tube and a tube that has been corrugated in conformity with the present invention.

The wall to be corrugated, which may bev is suitably clamped ixedly in the die, as by a threaded tapered plug 4 which has threaded engagement with both the die 2 andthe frame work 5. Said plug is shown as provided with ay passage 6 with which communicates suitable piping 7 leading from any suitable apparatus for developing pressure, such as the pump diagrammatically illustrated at 8 for developing hydrostatic pressure, this term beling used as generic to the application of pressure by the use of oil, water, or any other suitable Huid. It is to be expressly understood, however, that the apparatus shown for developing pressure is to be taken as typical of any suitable means for supplying pressure to effect the corrugating of the wall.

Mounted Within the tubular wall 1 in the form shown, is a piston or plunger 9 provided with a suitable packing 10 to prevent th'e leakage of fluid between said plunger and the wall of the tube. The rod or stem 11 of said plunger is shown as provided with a plurality of apertures 12 which are spaced by distances equal to the spacing of the ridges of the form or die 2. A pin 13 is adapted to be inserted in the respective apertures 12 and to coact with the base 14 of the frame to predetermine the position of `the plunger 9 and prevent the pressure Within the confined space 15 from forcing the plunger beyond its predetermined position. The illustration of the pin 13 insertible in the apertures 12 for cooperation with frame 14 is to be taken, however, as merely typical of any suitable device for indexing or predetermining the extent of movement of the plunger 9 each time a fresh portion of the wall is to be eX- posed to the hydrostatic pressure.

Cooperating with the free end of the tube 1 is any suitable means employing weight, spring, hydraulic, pneumatic or other pressure for exerting a longitudinal force on said wall to overcome frictional opposition to longitudinal movement thereof and insure that thewall shall move longitudinally and flow freely into the corrugations of the die under the transverse pressure exerted thereon. In the form shown, a collar 16 is mounted freely on the -rod or stein l1 of the plunger 9 so as to engage the lower end of the tubular wall 1, and means of any suitable construction are provided to exert a predetermined axial pressure on said collar 16 and wall 1. The apparatus illustrated comprises a lever 17 pivoted at 18 on a bracket 19 projecting from the frame and formed at its inner end as shown at 2O to engage a flange 21 on the collar 16. The other end of the lever carries a weight 22 which may be varied predeterminedly. yIt is to be understood, however, that the weight is only shown as typical of any suitable means for exerting a force of compression on the wall 1.

To corrugate a tubular wall in the apparatus so far outlined, the wall is clamped in the die or form 2 by the plug 4 and the plunger 9 is inserted into said wall until only that portion of the wall overlying the uppermost corrugation of the die is exposed within the confined space between the plug 4 and the plunger 9. The plunger is retained in this position by insertion of the pin 13 in the aperture l2 which is iush with the surface of the base 14, the frame being adjusted if necessary to properly position the aperture with respect to the frame. Collar 16 being engaged with the free end of the tube 1 and weight 22 applied, hydrostatic pressure is admitted to the confined space between plug 4 and plunger 9, the pump illustrated providing means for gradually applying and increasing this pressure, and the wall is forced into the corrugation or inter-ridge space of the die by the combined action of the hydrostatic pressure acting radially and the pressure of the Weight acting axially or longitudinally of the tube, the uncorrugated portion of the wall slipping over the plunger and die to supply the material which forms the corrugation. The pin 13 is then withdrawn from its aperture and introduced into the next adjacent aperture.v Hydrostatic pressure is then again admitted to the confined space between the plug and plunger and its first operation is to` move the plunger until the plunger is displaced by the predetermined amount which is represented by the spacing of the aperture 12 and which conforms with the spacing of the ridges or'I corrugations of the die. When the pin 13 engages the base 14 the plunger can be displaced no further and the hydrostatic pressure is increased to force the wall into the next corrugation of the die under the combined action of the bending and compression forces. This procedure is repeated, alternately predetermining the extent of displacement of the plunger and forming the corrugations by the combined action of the radially and axially acting forces until the entire wall has been progressively corrugated by intermittent application of pressure.

- During the formation of these corrugations the longitudinal force exertedon the wall l tends to compress said wall intoy the corrugations of the die and aids the transverse pressure or bending force in forming the corrugations. The 'quantity of force exerted longitudinally of the wall can be varied coni-4 siderably in accordance with the nature of the wall being operated upon. It should beV less than the strength of the material of the wall to resist crushing -or buckling so as to insure against any tendency. to buckling or the formation of body wrinkles, while on the other hand, it should be at least as great as the frictional opposition to movement of the'wall longitudinally ofthe die so as to insure that the wall shall flow freely underr the transverse bending pressure and prevent y any undesirable stretching and thinning of By selecting a` the mater-iall of the wall. longitudinal force between these extremes the lformation of f the corrugations under the transverse bending pressure is greatly facili-l tated and this longitudinal force may be selected of such a valut as to i enable the f formation of the corrugations by hydrostatic pressure much less than would be necessary if the longitudinal forces were not employed. has been found from experience that, particularly in the manufacture of relatively thick corrugated tubes of small diameter, the hydrostatic pressure may be reduced as much as seventy-five per cent (7 5%) or more when applying longitudinal force to the wall, and at the same time a wall of .more uniform thickness be obtained than when*` using the higher hydrostatic pressure in the, absence of longitudinal force.

55 The method heretofore described of corrugating walls may be employed to form the inal or relatively-deep, narrow corrugations in the wall in the first instance, or it may be employed for the formation of initial corrugations in the wall as illustrated, andthe ycorrugations are thereafter deepened by\ Patent No. 971,838, granted Oct. 4, 1910, so

as to work resilience to the desired extent into the bends of the corrugations. This rolling method may also be employed to complete corrugated walls which are formed by hydrostatic pressure alone whether with or without the application of a longitudinal force.

In the apparatus shown in Figs. 2 to 5 inclusive, the tube 1, which may be of any suitable length, size, shape, etc., is suitably clamped at its end 25 in a die element 26 by means of a tail-piece 27 which is tapered to clamp the tube end 25 against a correspondingly tapered surface in the die'element 26, said tail-piece 27 being retained in clamping position by means of an annular nut 28 which surrounds the stem4 29 of the tail-piece and engages interior threads .on the die element 26r Aj .passage 30 extends through said tailpiece 27 and communicates throughv a pipe 31 i liquid or gas under pressure may be admitted through the pipe 31 and passage 30 to the interior of the tube 1. A valve v32 is interposed in the pipe 31 at a suitable point in order to control the time and extent of application of the pressure as hereinafter explained.

p Die element 26 with its tail-piece 27 is supported` in any suitable ,way, being shown-as attached to a yoke member 33 provided with a centrally arranged aperture `34 through which the pipe 31 communicates with the l passage 30 in said tail-piece. Pipe 31 is pro-l. vided in any suitable'way, in the construction illustrated, with a collar 35 against the die element 26 and partscarried thereby y iixedly in position. By tightening the screws 37 the strap 36 can be yforced against the collar 35 so as to hold the die element 26 firmly and tightly in unitary relation with the lyoke member 33.

l Coo erating with the die element 26 is a secon die element 40 which is mounted on an upstanding tubular support (41 provided pose to be explained, and at its lower end said tubular support is threaded into a supporting member 44. Axially arranged within said tubular support 4l is a piston 45 provided with one or more suitable packing rings 46 and a cup leather 47 suitably attached thereto as by a screw 48. Piston is supported by a rod 49 which extends axially ot the tube 4l and is suitably supportedA in the supporting member 44, as by an annular block 50 which ts the interior ol the tubular support 4l and the exterior of the end of the piston rod 49. Said piston with its packing ring and cup leather, however, is to be taken as typical of any suitable means for providing a. Huid-tight joint with the interior of the tube in radial alignment with the die element 40. The piston 45 is thereby fixed in position with respect to the die element 40 with the tube l proj ecting within the tubular support 4l between said piston 45 and the die element 40, said piston forming a fluidtight oint with said tube.

The lower end of the tube l is received in a thrust element 5l which is provided with a peripheral upstanding collar 52 to guide the end of the tube. Thrust element 5l fits slidably within the tubular support 4l and has a central aperture 53 through which the piston rod 49 extendsn Said thrust element 5l also has one or more radially projecting lugs 54, corresponding in number with the slots 43, which project through said slots and coopera-te therewith to prevent rotation between said thrust element and tubular support while permitting relative axial movement thereof. Mounted below said thrust 'element 5l on the tubular support 4l is an annular nut 55, threaded on the threads 42 of' said tubular support and adapted to be brought into contact with thelug or lugs 54 of the thrust element 5l to constitute an abutment therefor during the. formation of the corrugations as will be explained hereinafter. The Supporting member 44 is mounted in any suitable way on a plate 56, the samebeing shown as removably retained in position, as by a set screw 57, in an aperture in a. strap piece 58 which is clamped to the face of said plate 56 in any suitable way, as by means of bolts 59 and spacing pieces 60.

The yoke member 33 and plate 56 are so yarranged that one may be moved with respect to the other in the direction ot the axis of the tube l so that an axial thrust may be exerted on said tube to apply a force of compression longitudinally of the same. In the form shown, the yoke member 33 is the movable member, and is mounted on a pair of screw threaded rods 61, being suitably retained thereon as by nuts 62. Said screw` threaded rods pass through apertures in the plate 56 and on the opposite side of said plate cooperate with nuts 63 which are suitably provided, preferably integrally therewith, with surrounding gears 64 of equal size. The two gears 64 mesh with an intermediate gear 65 mounted on a stub-shaft 66 which is suitably journaled in the frame ot' the machine and carries a beveled gear 67 that meshes with a second beveled gear 68 on an operating shaft 69. In the form shown said shaft 69 is provided with an operating` crank 7 0 terminating in a'handle 7l whereby the axial pressure or thrust to be exertedon the tube l may be applied by hand, and the time and extent of application of such forces thereby left to the skill of the operator. lt is to be understood, however, that the shaft 69 may be operated in any other suitable way and the crank 70 is therefore to be `taken as typical of any suitable apparatus for controlling the application of axial force to the tube so that the said torce may be gradually applied to the tube in the manner hereinafter described. When the crank 70 is rotated, the gears 68, 67, 65 and`64 cause simultaneous and equal rotation of the nuts 68, and the two threaded rods 6l are thereby caused to move simultaneously and equalliv to move the yoke member 33 toward or away from the plate 56, the former movement exerting a force of compression axially ot' the tube l which is abutted on the thrust piece 5l and clamped at its opposite end between the die element 26 and the tail-piece 27.

The die element 26 and the die element 40 are suitably formed, as shown at 72 and 7 3 respectively, to constitute a die for a corrugation of the character to be formed, so that when said die elements are brought into contact with each other, the two surfaces 72 and 73 together form a recess conforming with the shape of the corrugation to be made, as shown in Fig. 8. This corrugation is preferably made of final depth and width at one operation, i. e. it is made as a relatively-deep, narrow corrugation having lateral sides which are at substantially right angles to the axis of the tube, as illustrated in Fig. 3.

Also mounted on the machine in any suitable way, preferably so that they ca'n be moved rectilinearly into and out ot operative position, are a plurality of pairs ot plates 74 and 75 which are shaped at their adjacent ends, as shown in Fig. 5, so that when brought into endwise engagement the abutting ends form a circular opening into which projects a circular rib 76 which exactly corto form a second corrugation. As many pairs of die elements 74 and 75 are provided as there are corrugation tobe formed in a tube 1 andafter each corrugation is formed a pair of these die elements is moved into operative position as shown in Fig. 4, where they become in effect a part of the die element 26 'and not only protect the corrugation or corrugations which are already formed from being deformed by subsequent Aoperations, but also cooperate with the die element liuid-ti'ght joint between said die element and the end of said tube. Die element 40 and die element 26 are so spaced that the length ofthe tube 1 between the formed surfaces 72 and 73 exactly corresponds with the amount of metal which is to go into the first corrugation, this amount being determined in the manner to be explained, and

the lower end of the tube 1 is engaged with the thrust element 51 with the nut 55 in abutting engagement therewith by rotating said nut on the tubular support 41.

Pressure is nowv admitted to the confined space within the' tube 1 between the piston and the tail-piece 27 by manipulation of the valve 32, the amount of pressure thus admitted to said conflned space preferably be-l ing such asl to place the metal of the wall 1 under a slight tension but without imposing any set or stretch therein such as would be produced if the pressure were sufficient to cause the tube 1 to bulge to any considerable extent. The pressure in said confined space is then gradually increased, as by manipulation of the valve32, at the same time actuating the operating shaft 69 to exert an axial thrust on said tube through the yoke member 33 and die element 26. It is preferable to increase both of thesepressures gradually and; simultaneously, as experience has demonstrated that an application of the axial pressure without increase of the radial pressure exerted by the fluid tends to produce a buckling or wrinkling of the section of the tube between the die elementsl 26 and 40, while an increase of the radial pressure without application of the axial pressure tends to produce an undesirable'stretching of the section of tube between said die elements. Experience has also demonstrated that the radial pressure should rise rather rapidly but gra'du; ally vfor approximately the first third of the time that the die element`26 is being moved toward the die element 40, after whichthe radial pressure may be and preferably is maintained substantially-constant, and to this end a by-pass 81 is provided in communication with the inlet pipe 31 and includes an adjustable relief valve 82 of any suitable character so as to maintain a substantially constant predetermined pressure on the iuid in the confined'space between the piston 45 and the tail-piecev 27 during the remainder of the l operation. The axial pressure lon said tube should also increase rather rapidly but gradually for approximately the first seventh of the time that the die element 26 is being moved toward the die, element 40, and then should continue to increase more slowly for approximately the next three-sevenths of this period, after which the'axial pressure should rem'ain substantially lconstant or even be vslightly -diminished during the remainder of thel operation. As the metal of the tubular wall bends into corrugated shape its effective area at an angle to the axis of the tubeJ isincreasing, and this results in a gradual increase in the resistance to the movement toward each other of the lateral elements of the corrugation being formed, because yof the increasing effective area upon which fluid pressure may act; hence there should be a gradual increase ofthe pressure longitudinally of the metal in order to cause it to flow into the space between the die elem- ents 26 and 40 without an undesirable lstretching of the metal; If the radial pressure is also increasing therevis a consequent increase in the resistance of. the

.movableelements toward eachother which must also betaken intoconsideration.

The combined radial and axialpressures are applied until the die elements 26 and 40 come into contact with each other, at which time the formed surfaces 72 and 7 3 constitute a completed die -for the corrugation, and during the approach of said die elements the metal of the tube between the same has under the combined action of the radial and -axial forces-been bent and compressed so surfaces 72 and 7 3,1.'

The first corrugation having thus been formed, the yoke member 33 with its die element 26 is backed 0E, pulling the tube 1 between the piston 45 and the die element 40 until a fresh section of the tube, equal in length to that formerly acted upon, is exposed between said die elements 26 and 40. Any suitable means, asa pawl and ratchet mechanism (not shown), may. be provided for limiting the-extent of the backward movement ofthe yoke member 33 or its actuating mechanism, so as to index the advancement y of the tube and exactly positionthe die element 26 with respect to the die'element 40 so that a predetermined length of tube is ex' posed between the same. A pair of die plates 4 and 75 are now moved into position to embrace the first corrugation between the formed surfaces 72 and 78 as illustrated in Fig. 4, and to present a pair of die surfaces 79 and 73 for the formation of the next corrugation. The advancement of the tube 1 by the backward .movement of the yoke member 33 has withdrawn the end of tube 1 fromv the thrust piece 51 or, if the latter ts snugly on the end of said tube, has withdrawn the thrust element 51 from contact with the nut 55. In either event the nut 55 is advanced by rotation on the tubular support 41 until the thrust element 51 and nut55 constitute an abutment for the end of the tube 1 during the next application of axial pressure. Radial pressure is again admitted to the confined s )ace between the piston 45 and the tail-piece 217 and this pressure holds the first corrugation in contact with the formed surfaces 72 and 78 sothat the subsequent application of axial pressure does not cause a collapse or deformation of the corrugation already formed. As previously pointed out, this pressure should not be such as to cause any substantial stretching of the `metal in the portion of the tube about to be corrugated. The second corrugation is now formed in the manner heretofore described by the gradual application of increasing axial and radial pressures until the die elements are again brought into contact, after which the movable die element is again backed off to the predetermined amount, a fresh pair of die plates 74, 7 5 are moved into position, and'these operations repeated until the entire tube or the desired portion thereof has been corrugated.

It is sometimes desirable to positively prevent lslippage betweenV the piston 45 and the tube 1, particularly when a predetermined amount of stretching is to be given the tube during the formation of the corrugations. In the embodiment shown in Fig. 6 provision is made for thus positively clamping the tube 1 between the piston 45and the die element 40.

As here shown, the piston rod 49 is provided A with an extension 85 which has a plurality of cam surfaces 86, the piston being shown as secured to the rod 49 by means of a screw and washer 87. The piston 45 carries one or more clamping rings 88, and between said rings 88 and the 'cam surfaces 86 are a corresponding number of pins or lugs 89 which when actuated by the cam surfaces 86 exert a thrust on the clamping rings 88 and force thg latter into clamping engagement with the tu e 1.

The opposite end of the piston rod 49 is provided with a thrust collar 90 and is extended beyond the supporting member 44, where it carries a pinion 91 secured thereon by spline or equivalent means. Pinion 91 is in mesh with a pinion 92 on a stub-shaft 93 which carries a crank 94 provided with a handle 95. By oscillating'Y the crank 94 the piston rod 49 is rotated through the pinions 91 and 92 so as to actuate the cam surfaces 86 and either relieve or exert thrust on the pins 89 to respectively release the clamping rings or cause them to be forced into clamping engagement with the tube 1.

The axial pressure exerted on the tube during the formation of the corrugations may be so selected with respect to the radial pressure that the superficial area of the resulting corrugations is substantially the same as that of the superficial area of the tube in which the corrugations are formed, or the mean thickness of the resulting corrugations is substantially the same as that of the thickness of the tube in which the corrugations are formed, or the axial pressure may be so selected as to actually reduce the superficial area, or decrease the length of the longitudinal elements of the wall, or thicken the metal of the wall. Not

only is this true in the operation of the ap- .f

paratus of Fig. 1, but the same conditions may also be obtained by use of the apparatus shown in Figs. 2 to 6 inclusive by predeterminately spacing the relatively movable die elements between which the respective corrugations are formed. Taking L as the distance between the points where the two formed surfaces 72 and 7 3 engage the tube 1 at the initial setting of the die elements 26 and 40, said dimension may be readily determined by equating the superficial area of an outwardly directed corrugation, between parallel radially extending planes which pass through the centers of curvature of two successive inwardly directed bends, with the superficial area of a cylinder of L length, and solving for L-in the case where the final superficial area is to be the same as or have a predetermined relation to the original superficial area; or by equating the Volumes of metal using the predetermined thicknesses and solving for L-in the cases where equality or a predetermined increase in the mean thickness of the metal is desired, etc. i

From the dimension L, the predetermined spacing of the die elements 26 and 40 for the various cases can be readily determined,

taking into consideration the depth in an axial direction of the forming surfaces which constitute the die; for example, where the sides of the corrugations are to be at substantially right angles to the axis of the tube and the radius of curvature is to be the same for the outer and the inner bends of the corrugations, the predetermined spacing of the die elements26 and 40 is equal to L minus 4R, where R is the radius of curvature of said bends. Where the superficial area of the resulting corrugations is to be no greater than the superficial area of the original tube, or the mean thickness of the corrugations is to be no greater than the mean thickness of the original tube, care must be exercised in applying the radial pressure so that it shall not be suicient to unduly stretch the metal circumferentially while thel axial pressure is being applied.

Tn these cases the radial pressure should be little more, if any, than is sufficient to prevent the formation of body Wrinkles7 the axial thrust doing the major portion of the Work in forming the corrugations; but as the extent of the pressure Which is necessary to prevent the formation of body Wrinkles will vary with the thickness of the tube and the length of the tube section exposed to the fluid pressure, the limit of the radial pressure to be used cannot be definitely stated. The extent to which the axial pressure is increased Will also vary with the amount of radial pressure used, the thickness of the tube, etc., but must be such as to cause the metal to fiow into the shape of the die.

Whether the corrugated tube is made in the apparatus of Fig. l or of Figs. 2 to 6 inclusive, the corrugations maybe, and preferably are, treated so as to obtain the desired distribution or amount of resiliency in the Walls of the corrugations. This treatment may be of any suitable character and carried out in any suitable Way, as by rolling or ot-h'- erwise cold Working the bends of the corrugations. During these rolling or cold Working operations, the corrugations may be deepened and narrowed to a further extent if desired, or the shape and size of the corrugations may be left unchanged and the Working of the metal effected by relative slippage of the rolls or otherwise. If desired, the process may be carried out with the Wall raised above normal atmospheric temperature so as to reduce the amount of resilience that is imparted to the metal by the cold working operations.

It will therefore be perceivedthat a relatively-thin, highly-fiexible tubular corrugated Wall has been provided wherein the superlicial area of the Wall may be made no greater than, or less than, the superficial area of the tube from which the corrugated Wall is formed, or the mean thickness of the Wall may be made vno less than, or greater than,

,- the thickness of the tube from which the corrugated wall is formed, or the longitudinal elements of the corrugated Wall may be made less than those of the tube from which the corrugated Wall is formed. Thereby a What is claimed is: 1. A fiexible corrugated tubular Wall having a superficial area not substantiallygreater than that of the tube from Which it is formed.

2. A flexible corrugated tubular Wall having a mean thickness not substantially less than that of the tube from which it is formed.

3. A flexible corrugated tubular wall having its longitudinal elements shorter than those of the tube from which it is formed.

4. A flexible corrugated tubular Wall having its Wall of greater mean thickness than that of the tube from which it is formed.

5. A flexible corrugated tubular'wall having avv superficial area which is less than that of the tube from Which it is formed.

G. A flexible corrugated tubular Wall having a superficial area not substantially greater than that of the tube from which it f is formed, and having bends rendered predeterminately resilient.,

7. A flexible corrugated tubular Wall having a mean thickness not substantially less than that of the tube from Which it is formed, and having bends rendered predeterminately resilient.

8. A flexible corrugated tubular Wall having its longitudinal elements shorter than those of the tube from Which it is formed, and having bends rendered predeterminately resilient.

9. A flexible corrugated tubular Wall having its Wall of greater mean thickness than that of the tube from which is is formed, and having bends rendered predeterminately resilient.

10. A flexible corrugated tubular Wall having a superficial area which is less than that of the tube from which it is formed, and having bends rendered predeterminately resilient.

In testimony whereof We have signed this specification.

WESTON `M. FULTON.

JEAN V. GIESLER.

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