US2749963A - Manufacture of flexible corrugated seamless metal tubing - Google Patents

Description

E. T. CANDEE June 12, 1956 MANUFACTURE OF FLEXIBLE CORRUGATED SEAMLESS METAL TUBING 3 Sheets-Sheet 1 Original Filed April 12, 1946 EQJE 51.40

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ATTORNE Y5 June 12, 1956 E. T. CANDEE 2,749,963

MANUFACTURE OF FLEXIBLE CORRUGATED SEAMLESS METAL TUBING Original Filed April 12, 1946 3 Sheets-Sheet 2 INVENTOR. 17/3200? 7. Carla?! ATTORNEYS June 12, 1956 E. T. CANDEE r 2,749,963

MANUFACTURE OF FLEXIBLE CORRUGATED SEAMLESS METAL TUBING Original Filed April 12, 1946 3 Sheets-Sheet 3 TIE-l7 1 15.15 7 71 7d 72 III INVENTOR BY m 50%.; M u.

ATTORNEYS United States Patent MANUFACTURE OF FLEXIBLE CORRUGATED SEAMLESS METAL TUBING Ellsworth T. Candee, Watertown, Conn., assignor to Technicraft Laboratories, Inc., a corporation of Connecticut vided and this application November 16, 1950, Serial No. 196,049

12 Claims. (Cl. 153-73) This invention relates to the manufacture of flexible corrugated seamless metal tubing. The invention provides a new and improved method, and new and improved apparatus, for making such tubing in rectangular or other polygonal cross-sectional shape. This application is a division of my copending application Serial No. 661,903, filed April 12, 1946, now Patent No. 2,563,578, granted August 7, 1951, in which I have described and claimed rectangular or other polygonal flexible corrugated seamless metal tubing as a new article of commerce, and in which I have described and claimed a flexible wave guide in which such tubing forms the fundamental flexible element.

Flexible corrugated seamless metal tubing of circular cross section, both with annular corrugations and with helical corrugations, has been available for many years. Heretofore, however, it has not been possible to produce polygonal tubing of this character. For those uses requiring flexible metal tubing of rectangular or other polygonal cross section, it has been necessary to employ tubing of the strip wound, mechanically interlocked type, or other type of flexible metal tubing formed with seams.

The rectangular or other polygonal flexible corrugated seamless metal tubing provided by this invention is characterized by having a plurality of deep narrow corrugations spaced apart a distance approximating their depth. (In referring to the corrugations as being spaced apart a distance approximating their depth, both throughout the specification and in the claims, I mean that the ratio of spacing to depth of the corrugations is small enough to render the tubing quite flexible, but do not mean that it is necessarily 1:1 it may vary, for example, from 1:3 to 3:1, or over an even somewhat wider range, depending upon such factors as size of the tubing, actual depth of the corrugations, wall thickness, etc.) The outer surface of the corrugations at the corners of the tubing is generally formed with a substantial radius of curvature in a plane normal to the axis of the tubing. These corrugations render the tubing extremely flexible, and permit it to be bent readily through a short radius.

Seamless corrugated flexible metal tubing of polygonal cross section is made in accordance with the invention by forming an outward peripheral bulge on a seamless polygonal metal tube, and subsequently squeezing the bulge at its base to narrow and deepen it into a corrugation. The initial bulging of the tube advantageously is effected under conditions such that somewhat greater bulging pressure is applied at the corners of the tube than at the sides, thus assuring adequate bulging of the tube wall at the corners to form, in the subsequent squeezing operation, full-depth, unwrinkled and unruptured corrugations even at these points of maximum metal deformation. The initial outward peripheral bulging of the tube may be effected by applying pressure to a deformable plug located within the tube, while the tube is positioned within an opening in a die plate configured to limit bulging of the metal and to prevent improper deforming of the tube.

2,749,963 Patented June 12, 1956 The apparatus provided by the invention for making seamless corrugated flexible metal tubing of rectangular or other polygonal cross section comprises a pair of separable die plates defining between them a polygonal die opening. At least one peripheral groove is formed in the die plate walls of said opening. Means advantageo'usly in the form of a deformable but substantially incompressible plug positioned within a tube to be corrugated is provided for bulging the walls of the tube outwardly into the grooves. The apparatus also includes means for closing a bulge thus formed in the tube to form therefrom a corrugation. These means advanta geously comprise a pair of closure plates mounted one over each die plate and defining between them a tubereceiving opening of the same size and shape as the die opening, and axially aligned therewith. The closure plates are mounted so as to be movable toward and away from the die plates, thereby to permit closing into a corrugation a bulge in a. tube gripped between the closure plates and the die plates.

To facilitate operation of the apparatus, a pair of locating plates may be mounted one over each closure plate and spaced therefrom a distance corresponding to the thickness of a corrugation. The locating plates engage between the corrugations of the previously corrugated portion of the tube being corrugated and assist in locating the corrugation-closure plates in the proper position preliminary to closing a bulge into a corrugation.

Spacers between the closure plates and the die plates advantageously are provided to limit movement of the closure plate toward the die plate to prevent excessive flattening of a corrugation as it is being formed by such movement from a previously formed bulge.

An advantageous embodiment of the invention is described in greater detail below with reference to the manufacture of flexible seamless corrugated metal tub.- ing of rectangular cross section. It is understood, however, that the following description is also applicable to tubing of other polygonal cross sections. The description is presented in connection with the accompanying drawings, in which:

. Fig. 1 is a longitudinal section through apparatus for producing corrugated rectangular seamless tubing in accordance with the invention;

Fig. 2 is another longitudinal section through the apparatus, taken at right angles to the section shown in Fig. 1;

Fig. 3 is a view of the tube-corrugating apparatus taken along the line 3-3 of Fig. 1;

Fig. 4 shows a column for transmitting force from a press ram to the corrugation-closure assembly;

Fig. 5 is a cross section taken substantially alongthe line 5e5 of Fig. 4;

Fig. 6 is a plan of a deformable plug used in initially bulging the wall of a rectangular tube to be corrugated in the apparatus shown in Figs. 1 to 3;

Fig. 7 is an elevation of the plug shown in Fig. 6;

Fig. 8 is an end view of the plug shown in Figs. 6 and 7;

Figs. 9 to 12 are sections on an enlarged scale through the die plates and closure plates in the region of the die opening, showing successive stages in the tube corrugation operations;

Fig. 13 is a horizontal section taken substantially along the line 13-13 of Fig. 10;

Fig. 14 is a cross section taken substantially along the line 1414 of Fig. 11;

Fig. 15 is a fragmentary plan of one half of'the closure plate assembly;

Fig. 16 is a plan of a rectangular tube as it appears while being corrugated in accordance with the invention,

showing the bulges formed preliminary to forming the corrugations;

Fig. 17 is an elevation of rectangular corrugated seamless tubing according to the invention;

Fig. 18 is a cross section through the tubing shown in Fig. 17;

Fig. 19 is an elevation of a flexible wave guide made from rectangular flexible corrugated tubing according to the invention.

Fig. 20 is an end view of the wave guide shown in Fig. 19;

Fig. 21 is a section through a modified form of apparatus for producing corrugated tubing in accordance with the invention; and

Fig. 22 is an elevation of tubing as it appears in the course of manufacture by means of apparatus as shown in Fig. 21.

Referring to Figs. 1 to 3, the tubing-corrugating apparatus comprises a pair of separable die plates 25 formed with horizontal flanges 26. The die plates are supported on a base plate 27 which in turn is supported on a press platform or other supporting structure 28. Guides 29 formed integrally with the base plate 27, or fastened thereto, define a channel in which the die plates 25 may move toward or away from each other. Retaining plates 30 bolted to the guides 29 and overlying the top surface of the die plate flanges 26 confine the die plates to movement toward and away from each other in this channel.

Holes 31 are drilled in the die plate flanges 26 to receive compression springs 32 which urge the die plates apart. Cam locks 33 may be rotated by handles 34 to move the die plates together against the force of the compression springs 32 and to lock the die plates in this closed position.

Each of the die plates is formed with a channel in that edge which bears against the adjacent edge of the other die plate, and when the two die plates are brought together by the cam locks 33, these channels are in registry so as to form the rectangular die opening in which a rectangular tube 35 to be corrugated is received. The tube 35, of course, fits quite snugly in the die opening, which is of the particular size and shape required to insure such fit of the tube to be corrugated. Oversize openings in the base plate 27 and in the press platform 28, directly beneath the die opening between the die plates 25, permit the tube 35 to enter the die opening from beneath the press platform.

The die plate walls defining this tube opening are formed with upper and lower peripheral grooves 36 and 37 into which the walls of the tube 35 may be bulged upon application of an expansive force within the tube.

The means for applying the expansive bulging force within the tube 35 comprises a lower mandrel 3S bearing at its lower end against a platform 39 and terminating at its upper end just below the lower edge of the lower peripheral groove 37. This mandrel extends up through the tube 35 to be corrugated, and its cross-sectional dimensions are such that it fits fairly snugly within the tube 35. The lower end 40 of this lower mandrel may be of reduced size to fit within a socket 41 in the platform 39, to prevent it from being accidentally displaced from proper alignment with the die opening between the die plates 25.

An upper mandrel 42, similar in cross-sectional size and shape to the lower mandrel 38, extends into the upper portion of the tube 35. The upper end 43 of this mandrel is of reduced size to fit within a socket 44 formed in a press ram 45, and to provide a shoulder 46 against which the press ram may bear to apply force to the mandrel 42. As with the similar arrangement of the lower mandrel, the reduced end 43 of the upper mandrel 42 is held in the press ram socket 44 to prevent the upper mandrel from being accidentally dislodged from proper alignment with the die opening.

Located within the tube 35 between the mandrels 38 and 42 are a pair of deformable but substantially incompressible plugs 47 and 48. When the press ram 45 is forced downwardly and exerts pressure against the shoulder 46 of the upper mandrel 42, these plugs are squeezed between the two mandrels and deform, transmitting a bulging force to the walls of the tube 35 and causing it to be bulged outwardly into the grooves 36 and 37.

The deformable plugs 47 and 48 advantageously are of rubber and are configured as shown in Figs. 6 to 8. As shown, each plug comprises a substantially rectangular body or base portion 49 surmounted by a pyramidal roof portion 50. The base portion of the plug is of a length and breadth such that it fits fairly snugly within the tube 35 to be corrugated, and is of a height approximately equal to the height of the bulge formed by its deformation. The pyramidal roof portion 50 of the plug provides the excess of rubber necessary to expand the tube into the grooves 36 and 37 in the die plates, and advantageously this pyramidal roof section is truncated as shown in the drawings, so that the base of the upper plug 47 will have a good bearing surface against the roof of the lower plug 48 when the two plugs are positioned within the tube during corrugating operations.

It is generally preferable to apply somewhat greater bulging force to the corners of the tube being corrugated than to its sides, and for this purpose the sides 51 of the plug base portion 49 advantageously are slightly concave, as indicated especially in Fig. 6. However, especially when the tube to be corrugated is of fairly heavy wall-thickness, it is not essential that the sides of the plug be concave.

The provision of two peripheral grooves 36 and 37, and two corresponding plugs 47 and 48, leads to final formation of the bulge in two steps and is advantageous to insure formation of a full-depth bulge which is uniform about the periphery of the tube 35. After initial bulging of the tube into the lower groove 37, the tube is raised a distance such that the bulge formed in this groove is brought into alignment with the upper groove 36, and in this position the bulging operation is repeated. The bulge preliminarily formed in the lower groove 37 thus is completely formed in the upper groove 36 in the next subsequent bulging operation. If desired, the lower groove 37 may be slightly shallower than the upper groove 36, but this is not essential.

An important advantage of the use of two deformable plugs is that the upper plug and groove prevent deformation of the bulge positioned in that groove when the next bulge is formed in the lower groove by the deformation of the lower plug. When a bulge is formed in the lower groove, metal is drawn up from below the lower groove, and would also be drawn down from the bulge in the upper groove except for the fact that the upper plug holds the bulge firmly in the upper groove. If any substantial amount of metal is drawn down from the bulge in the upper groove, the resulting deformation of the upper bulge, especially at the corners, leads to creasing and cracking of the metal when the bulge is subsequently closed into a corrugation. This effect is particularly pronounced with thin gauge metal. Thus bulging in two steps, even when the two grooves are of the same depth, insures that the tube will be adequately and uniformly bulged completely about its periphery and particularly at the corners, so that subsequent closure of a bulge into a corrugation will not cause creasing or rupturing of the corrugation at the corners, where the metal is most severely worked and subjected to maximum stresses, and so that the corrugations will be of uniform size and inside diameter.

After bulging the tube 35 outwardly and peripherally, the next step is to close the bulge thus formed into a corrugation. For this purpose the apparatus is provided with a corrugation-closure plate assembly 52. This assembly comprises a pair of closure plates 53 each mounted above one of the die plates 25, and each recessed at that edge which meets with the corresponding edge of the other closure plate, so as to form between the plates a tube-receiving opening of substantially the same size and shape as the die opening between the die plates, and axially aligned therewith. A pair of locating plates 54, which are shown in the drawings as being of the same size and configuration as the closure plates 53, are fastened one to each closure plate with a spacer 55 between them. These spacers separate the locating plates from the closure plates by a distance'corresponding to the thickness of a finished corrugation. A second pair of spacers 56, also of a thickness equal to the thickness of a corrugation and arranged below the closure plates 53, and a pair of cover plates 57, complete the closure plate assemblies. Each assembly is held together by screws 58 passing through the several plates and spacers and threaded into the bottom spacers 56.

Press fitted into each closure plate assembly is a pair of dowel-pins 59 which enter dowel-pin holes 60 drilled or bored in the die plates. The dowel-pin locate the closure plate assemblies on the die plates and prevent lateral movement of these parts relative to each other, but permit movement of the closure plate assemblies toward and away from the corresponding die plates.

After a bulge has been formed in the wall of the tube 35 being corrugated, it is raised (as stated above) by an amount such that the bulge formed in the lower peripheral groove 37 is aligned with the upper peripheral groove 36. When so raised, the bulge that had been finally formed in the upper peripheral groove 36 now is located with the base of its lowerside bearing against the die plates at the edge of the die opening. In this position, the closure plate assemblies must be raised from the die plate sufficiently to permit the closure plates 53 to embrace the bulged tube and to bear against the upperside of the bulge at its base. Then, when a force is applied to the closure plate assembly to force it down against the die plate, the bulge gripped between the closure plates and the die plates is narrowed and deepened into a corrugation. The spacers 56 at the bottom of the closure plate assemblies limit movement of these assemblies toward the die plates, so that when the bulge'is narrowed into a corrugation it is not excessively flattened. The locating plates 54, which engage the corrugated tube over the corrugation just above that being formed, facilitate locating the closure plate assemblies at the proper distance above the die plates each time the tube is raised to perform the operations resulting in formation of a further corrugation.

In order to apply pressure to the closure plate assembly, a column 61 (Figs. 4 and 5) is provided. This column advantageously is made of fairly heavy-walled tubing having .a longitudinal segment cut from it, so that it is essentiallyin the form of a channel. The ends of the channel column may be reinforced by flanges 62. The length of the column is somewhat greater than the effective length of the upper mandrel 42 from the top surface of the closure plate assembly to the shoulder 46. The column 61 therefore may be placed in position substantially surrounding the upper mandrel 42, with its lower end bearing against the top surfaces of the closure plate assemblies and with its upper end somewhat above the mandrel shoulder 46' With the column thus in position, downward movement of the ram 45 brings the ram into contact with the upper end of the column and results in the force of the ram being transmitted through the column to the closure plate, without any force being eXertedon the mandrel 42. Thus, when a bulge in the tube wall is gripped between the closure plates 53 and the die plates 25, and when the column 61 is in position substantially surrounding the mandrel and bearing against the closure plate assembly, the same ram 45' used for applying force to the mandrel 42 to form the bulge now may serve to apply force to the closure plate assemblies for the purpose :of narrowing and deepening the bulge into a corrugation. The channel shape of the column facilitates placing it in position about the mandrel and removing it from such position, as required in the sequence, of operations performed in first bulging the tubing and then closing the bulge to form a corrugation.

The sequence of operations involved in using the abovedescribed apparatus to corrugate rectangular seamless metal tubing is illustrated in Figs. 9 to 12, which incidentally show the abutting portions of the die plate and closure plate assemblies on an enlarged scale. Fig. 9 shows the tube 35 being corrugated in a position that may be termed the starting position in the sequence of operations involved in forming each corrugation. As shown in this figure, the tube has just been raised so that the initially formed bulge 63 is in position to be finally formed in the upper peripheral groove in the die plates 25, while that portion 64 of the tubing which is in position adjacent the lower groove 37 has not yet been bulged. The bulge 65 which was finally formed in the preceding sequence of operations is gripped between the upper surface of the die plates 25 and the closure plates 53. The closure plates have been located in the proper position with the aid of the locating plates 54-, which engage the tubing just above the last-formed corrugation 66. Above the locating plate 54 is the corrugated portion 67 of the tubing which was formed during preceding corrugationforming operations. The lower mandrel 38 is in position in the tube 35, with the undeformed plugs 47 and 48 immediately over it and approximately opposite the periph eral grooves in the die plates. The upper mandrel 42 extends through the corrugated upper portion of the tubing into position for applying force to the plugs.

In the next step, as shown in Fig. 10, force is applied to the upper mandrel 42, thereby deforming the plugs 47 and 48. The deformed lower plug 48 bulges the wall of the tube 35 out into the lower peripheral groove, initially forming a new lower bulge 68. At the same time the bulge 63 is finally formed, by deformation of the upper plug 47, into a full-depth bulge which is substantially uniform about the periphery of the tube 35. During this operation the closure plate assemblies 52 remain in the same position as before In the first step of the bulging operation, illustrated in Fig. 11, the force on the upper mandrel 42 is released and the column 61 is placed in position substantially surrounding this mandrel, with its lower end bearing against the top surface of the closure plate assemblies 52. Force then is applied to the column 61, forcing the closure plate assemblies down toward the die plates 25. The applied force results in squeezing the bulge (65 in Figs. 9 and 10) which was gripped between the closure plates 53 and the top surfaces of the die plates into the narrowed and deepened form of a new corrugation 69 (Fig. 11). The spacers 56 at the bottom of the die plate assemblies prevent fiattening the corrugation 69 beyond the desired limit.

The final step (illustrated in Fig. 12) is to raise the tube 35 into position for repeating the above-described sequence of operations. To do so, the cam lock holding the right-hand die plate 25 in position is released, and this die plate is thereupon pushed away from the lefthand die plate by the action of the compression springs 32,. This results in disengaging the right-hand die plate and the right-hand closure plate assemblies 52 from the corrugated and bulged tubing. It is now possible to tilt the tube 35 and the mandrels 38 and 42 sufficiently to the right to disengage the bulged tubing from the grooves 36 and 37 in the left-hand die plate, and the corrugations from the left-hand closure plate 53 and locating plate 54. The tube then may be moved up manually along the mandrels sufficiently to bring the last-formed bulge 68 opposite the upper groove 36. The tube 35 then is tilted back to the left so that the lowest bulge 68 enters the upper groove 36 in the left-hand die plate; and at the same time the left-hand closure plate assembly is lifted up from the die plate and manipulatedso that the closure plate 53 engages with the tubing over the now finally formed bulge 63 and just below the last-formed corrugation 69, and the locating plate 54 engages the tubing just above this corrugation. With the tube thus repositioned in the left-hand die plate and left-hand closure plate assemblies, the right-hand die plate and closure plate assemblies may now be brought back by operation of the right-hand cam lock, into closed position with the corresponding left-hand members. At the completion of this operation, the apparatus is again in the position illustrated in Fig. 9, and the above-described sequence of operations may be repeated to form another corrugation.

In the hands of a practiced operator, manipulation of the apparatus as above-described may be carried out rapidly and without damage to the tubing, even though it may be very thin-walled.

It is not essential to tilt the tubing, as described above in connection with Fig. 12, in advancing it upwardly. If desired, both rightand left-hand cam locks 33 may be released, and the tubing may be moved up while still perfectly straight. In general, however, tilting the tube as described permits of more rapid and convenient operation of the apparatus.

The apparatus has been described with particular reference to hand-operation, but it is understood that it may be operated automatically. It may be fully automatic in operation, so that opening and closing of the die plates, upward advance of the tubing, and operation of the ram all are eflected automatically; or if desired the apparatus may be designed so that some of these operations are automatic while others are hand-performed or hand controlled.

Tubing as it appears in the course of being corrugated is shown in Fig. 16. Immediately above the uncorrugated seamless tubing blank 35 are the bulged sections 63 and 65, and above this is the finished corrugated section 67.

Figs. 17 and 18 illustrate a completed length of corrugated tubing 70. In this tubing, all bulges have been narrowed and deepened into corrugations 71. The corrugations are relatively deep and narrow, and are spaced apart a distance approximating their depth. As best shown in Fig. 18, the tubing is substantially rectangular in cross section. At the corners of the tubing, however, the outer surfaces 72 of the corrugations are formed with a substantial radius of curvature. The depth of the corrugations is substantially, if not quite, as great at the corners as in the middle of the side or edge wall of the tube. In consequence of these relatively deep, narrow and closely spaced corrugations, the tubing is extremely flexible and may be bent through a short radius, either sidewise or edgewise.

The new tubing is admirably suited for use in making flexible wave guides, of which one form is shown in Figs. 19 and 20. The wave guide shown comprises a length of corrugated seamless metal tubing 73 of rectangular cross section. The dimensions of the tubing are, of course, preselected according to the wave length of the radiation to be transmitted through the guide. End fittings 74 are brazed or otherwise secured to the ends of the length of tubing 73. The end fittings are formed with a substantially central opening 75 accurately matched to the minimum inside diameter of the tubing, and is provided with holes 76 for mounting purposes.

Flexible wave guides of this character are excellently suited for connecting rigid wave guides to each other, or to other equipment, at points where some flexure is necessary or desirable. Rectangular tubing ordinarily is necessary for efficient wave guides, and flexible corrugated seamless rectangular metal tubing may be made in acaccordance with the invention with proper spacing of the corrugations, and with the necessary uniformity in size and shape of corrugations, to insure minimum power losses due to reflection or other causes when the tubing is employed in the manufacture of flexible wave guides.

While tubing produced in acordance with the invention is extremely flexible to bending forces applied parallel to a side or edge, it is resistant to torsion forces. Also, when a bending force is applied to the tubing, the closely spaced corrugations each accommodate substantially equal increments of the total bending force, so that even when the tubing is bent, uniformity in spacing of the corrugations is preserved. These characteristics make the new tubing very useful for wave guide purposes, and for other uses as well.

The invention has been particularly described above in connection with the manufacture of flexible corrugated seamless metal tubing in apparatus comprising die plates formed with two peripheral grooves in the walls of the die opening, but in some instances a single peripheral groove is sufiicient. Particular mention also has been made above of a closure plate assembly including a locating plate, but if desired this plate may be omitted. Apparatus embodying these modifications is shown in Fig. 21. In this modification, separable die plates 77 form between them a die opening in which a rectangular metal tube 78 is positioned; and but a single peripheral groove 79, into which the tube 78 is to be bulged, is formed in the die plate walls defining the die opening. Otherwise the die plates 77 may be made and mounted similarly to the die plates 25 described above.

As shown in Fig. 21, only a single deformable plug 80 is positioned between the ends of a lower mandrel 81 and an upper mandrel 82. Closure plate assemblies 83 each having only a closure plate 84, a cover plate 85, and a spacer 86, are provided to narrow and deepen the bulges formed in the tubing stock into corrugations.

Fig. 21 shows the modified apparatus with the tubing in the position corresponding to that shown in Fig. 9, described above. The sequence of operations involved in using this apparatus, including (1) applying force to the mandrel 82 to bulge the tube outwardly into the groove 7 8, (2) subsequently applying pressure to the closure plate assembly 83 (the closure plate 84 of which engages the upper side of a previously formed bulge 87) to deepen and narrow the bulge into a corrugation, and (3) thereafter raising the tubing 78 into position for repeating this sequence of operations, may be as described above with reference to Figs. 9 to 12.

Fig. 22 is a side view of the rectangular corrugated metal tubing as it appears during manufacture with the use of apparatus as shown in Fig. 21. Above the lower uncorrugated portion of the rectangular tube stock 78 is the single bulge 87, and above this is the corrugated portion 88 previously formed in the manufacturing process.

While the apparatus and method of the invention have been described specifically with reference to the manufacture of rectangular corrugated seamless metal tubing, they are equally applicable to the manufacture of corrugated seamless metal tubing of other polygonal cross sections, such as corrugated seamless metal tubing of pentagonal, hexagonal or octagonal cross section. The only major change required in the apparatus described above to make corrugated seamless metal tubing of these other polygonal cross sections is to make the die opening of the shape and size desired, and to make the upper and lower mandrels and the deformable plugs of the corresponding cross-sectional shape and size. The method of making corrugated seamless metal tubing of these other cross-sectional shapes is essentially the same as herein described for making the rectangular tubing.

As with the rectangular tubing, flexible corrugated seamless metal tubing of these other polygonal cross sections is characterized by having a plurality of deep and narrow annular corrugations, spaced apart a distance approximating their depth, and with the outer surfaces of the corrugations being formed with a substantial radius of curvature at the corners of the tubing.

It is evident that other modifications than those specifically described herein may be made within the scope of the invention.

I claim:

1. Apparatus for manufacturing seamless corrugated flexible metal tubing of rectangular or other polygonal cross section comprising a pair of die plates each formed with a tube-receiving channel in an edge thereof, the walls defining said channel being peripherally grooved, means for bringing said die plates into closed engagement with the channels in registry so as to form a polygonal die opening for receiving a rectangular or other polygonal seamless tube and with the peripheral grooves therein also in registry, a lower mandrel for insertion into a rectangular or other polygonal tube positioned in said die opening and having its upper end adjacent the lowermost internal groove, a deformable but substantially incompressible plug for insertion into said tube directly above said lower mandrel, an upper mandrel for insertion into said tube with its upper end overlying said plug, means for moving one mandrel toward the other to deform the plug and expand the tube into the peripheral groove, thereby forming a fulldepth outward bulge of substantially uniform wall thickness completely about the periphery of the rectangular tube, corrugation-forming means cooperating with said die plates for engaging the bulged tube on both sides of the bulge adjacent the base thereof, and means for applying pressure to said corrugation-forming means in such manner as to narrow and deepen the bulge into a corrugation of substantially uniform wall thickness.

2. Apparatus for manufacturing seamless corrugated flexible metal tubing of rectangular or other polygonal cross section comprising a pair of die plates each formed with a tube-receiving channel in an edge thereof, the walls defining said channels being peripherally grooved, means for bringing said die plates into closed engagement with the channels in registry so as to form a polygonal die opening for receiving a rectangular or other polygonal seamless tube and with the peripheral grooves also in registry, a deformable but substantially incompressible plug for insertion into a rectangular or other polygonal tube positioned within said die opening, upper and lower mandrels for insertion into said tube above and below said plug and confining the plug to the region adjacent the peripheral grooves in the die plate, means acting on at least one mandrel for squeezing the plug between the mandrels and expanding the walls of the tube into the peripheral grooves, thereby forming outward bulges completely about the periphery of the tube, a corrugation closure plate mounted above each die plate and each formed with a tube-receiving aperture, means for bringing said closure plates together with the apertures therein in registry, said closure plates being adapted to embrace a bulged tube with the edges of the apertures therein engaging one side of the bulge adjacent the base thereof while the other side of the bulge is engaged at the base thereof by the die plate at the edge of the die opening, and means for pressing the closure plates against the die plates to pinch the bulge in the tube therebetween, thereby narrowing and deepening the bulge into a corrugation.

3. In apparatus of the character described, a pair of die plates each formed with a tube-receiving channel in an edge thereof, the walls defining said channel in each die plate being formed with a pair of spaced peripheral grooves, means for bringing and locking the die plates together with the channels therein in registry to form a polygonal die opening and with the grooves also in registry to form a pair of spaced peripheral grooves into which the walls of a polygonal metal tube can be bulged, means for bulging the walls of a tube positioned in said die opening outwardly into said grooves, and separable corrugating means for closing a bulge thus formed in said tube to form therefrom a corrugation, said corrugating means being constructed with an opening to receive the work and being disposed adjacent the die opening formed in said pair of die plates and being adapted to move toward and away from said die plates, said corrugating means also being constructed to engage with the side of a bulge 10 formed in the tube, and in movement of the corrugating means toward the die plates to compress a bulge between it and the die plates, when the work has been advanced out of the die opening to position a bulge between the die plates and the corrugating means.

4. In apparatus of the character described, a pair of die plates each formed with a substantially rectangular tube-receiving channel in an edge thereof, the walls defining said channel in each die plate being formed with. a pair of spaced peripheral grooves, spring means urging the die plates apart, means for bringing and locking the die plates together against the force of the springs with the channels therein in registry to form a die opening and with the grooves also in registry to form a pair of spaced peripheral grooves into which the walls of a rectangular metal tube can be bulged, means for bulging the walls of a tube positioned in said die opening outwardly into said grooves, and separable corrugating means for closing a bulge thus formed in said tube to form therefrom a corrugation, said corrugating means being constructed with an opening to receive the work and being disposed adjacent the die opening formed in said pair of die plates and being adapted to move toward and away from said die plates, said corrugating means also being constructed to engage with the side of a bulge formed in the tube, and in movement of the corrugating means toward the die plates to compress a bulge between it and the die plates, when the work has been advanced out of the die opening to position a bulge between the die plates and the corrugating means.

5. In apparatus of the character described, a pair of separable die plates defining between them a polygonal die opening having on its inner surface a pair of spaced polygonal grooves into which the walls of a polygonal metal tube can be bulged, and a pair of separable corrugation closure plates mounted one over each die plate and defining between them a tube-receiving opening of substantially the same size and shape as the die opening and axially aligned therewith, said closure plates being movable toward and away from the die plates so as to permit closing a bulge in a tube gripped between the closure plates and the die plates into a corrugation.

6. In apparatus of the character described, a pair of separable die plates defining between them a polygonal die opening, a pair of closure plates mounted one over each die plate and defining between them a tube-receiving opening of substantially the same size and shape as the die opening and axially aligned therewith, and a pair of locating plates mounted one over each closure plate and spaced therefrom a distance corresponding to the thickness of a corrugation in a tube being corrugated, the assembly of closure plates and locating plates being movable toward and away from the die plates so as to permit closing into a corrugation a bulge in a tube gripped between the closure plates and the die plates.

7. In apparatus of the character described, a pair of separable die plates defining between them a polygonal die opening, a pair of closure plates mounted one over each die plate and defining between them a tube-receiving opening of substantially the same size and shape as the die opening and axially aligned therewith, a pair of locating plates mounted one over each closure plate and spaced therefrom a distance corresponding to the thickness of a corrugation in a tube being corrugated, the assembly of closure plates and locating plates being movable toward and away from the die plates so as to permit closing into a corrugation a bulge in a tube gripped between the closure plates and the die plates, and spacers between the closure plates and the die plates to limit movement of the closure plates toward the die plates to prevent excessive flattening of a corrugation as it is being formed by such movement.

8. In apparatus of the character described, a plug for forming an outward peripheral bulge on a polygonal tube to be corrugated comprising a polygonal body portion of deformable substantially incompressible material, surmounted by a pyramidal roof portion of such material.

9. In apparatus of the character described, a plug for forming an outward peripheral bulge on a polygonal tube to be corrugated, said plug being composed of deformable substantially incompressible material and comprising a polygonal body portion integrally united with a roof portion in the form of a truncated pyramid, at least some sides of said body portion being slightly concave.

10. In apparatus of the character described comprising a mandrel adapted to be moved axially to deform a plug and so produce an outward bulge on a tube to be corrugated, a closure plate assembly adapted to be moved to close such bulge into a corrugation, and a ram for applying force both to the mandrel and to the closure plate assembly, means for transmitting force from the ram to the closure plate without actuating the mandrel comprising a column substantially channel-shaped in cross section, the open side of the channel-column being of sulficient width to permit the column to be placed in position substantially surrounding the mandrel and bearing against the upper surface of the closure plate assembly, and the effective length of said column being greater than the effective length of the mandrel between the ram and the upper surface of the closure plate assembly.

11. The method of making seamless corrugated flexible metal tubing of polygonal cross section which comprises forming an outward peripheral bulge completely around a 12 polygonal seamless metal tube by applying a somewhat greater bulging pressure at the corners of the tube than at the sides thereof while confining within a polygonal die the portions of the tube adjacent the portion thereof being bulged, and subsequently narrowing and deepening the bulge into a corrugation.

12. The method of making seamless corrugated flexible metal tubing of polygonal cross section which comprises bulging a polygonal seamless metal tube outwardly and peripherally by applying pressure to a deformable plug within the tube and transmitting through said plug somewhat greater bulging pressure at the corners of the tube than at the sides thereof while confining within a polygonal die the portions of the tube adjacent the portion thereof being bulged, and subsequently narrowing and deepening the bulge into a corrugation.

References Cited in the file of this patent UNITED STATES PATENTS 1,605,194 Kopf Nov. 2, 1926 1,754,922 Weldon Apr. 15, 1930 1,879,663 Dreyer Sept. 27, 1932 2,306,018 Frentress Dec. 22, 1942 FOREIGN PATENTS 23,828 Great Britain of 1896

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