US2310091A - Machine for and method of bending tubing - Google Patents

Description

Fel 2, 1943; l, F. M. KEPLER v 2,310,091,

I mammina AND Mm'aon vor' BENDING TUBING l Filgd Jan. 9, 1942 3 Sheets-Sheet 1 INVENTOR.

Feb.2,1943. M. man

MACHINE FOR AND METHOD Y0F BENDING TUBING Feb. 2,` 1943. F. M. Kl-:PLER 2,310,091

AND METHOD 0F BENDING TUBING snee Jui. 9, 1942 s shuts-shuts Patented Feb. 2, 1943 M. FOR 0F BENDING *C il fi la cis M.. .Kepler, Upper Darby, Pa.

Application January '9, 19152, Serial No. 426,257

18 Cl (Cl. 153-54) The present invention relates' to a method of and apparatus for bending pipe, tubing, or the like, and it relates more particularlyto a method of and apparatus for forming smooth bends in pipe, tubing or the like, so, that the bent sections tubing. Still another object of the present invention is to provide a method for bending pipe or tubing vwithout disturbing the smooth inner walls thereof by causing the metal of the outside walls to be displaced in accordance with the respective lengths of the inner and outer edges of the curve, Another object of the present invention is to provide a method for bending sections of pipe or tubing and, atthe same time, uniformly increasing or decreasing the inside dimensions of the pipe or tubing.

Another object of the present invention is to provide yapparatus for carrying out4 the abovestated objects;

With the above and other objects and advantages as are apparent from the.y following speciilcation, appended claims and accompanying out disturbing the inside walls of the sections,

and subsequently passing the so-corrugated sections through forming rolls thereby smoothly to bend vvsaid sections and to cause the corrugations upon the inner edge of the bend to become deeperv and the corrugations upon the outer edge of the bend to become shallower.

For the purpose of illustrating theI invention,A

there `are shown in the accompanying drawings forms thereof which are at present preferred,

give satisfactory and reliable results, although v it is to be understood that the various instrumentalities of which the invention consists can be variously arranged and organized and that the invention is not limited to the precise arrangements and organizations of the instrumentalities as herein shown and described.

Referring to the accompanying drawings in which like reference characters indicate like parts,

Figure 1 represents a frontelevational view of one embodiment of the present invention,

Figure Zrepresents a side elevational view of the embodiment shown in Figure 1,

Figure 3 represents a horizontal cross-sectional Y view along the line 3-3 of Figure 2,

Figurev 4 represents a vertical cross-sectional view along the line 4 4 of Figure 1,

Figure 5 represents a fragmentary elevational view of the driving roll shown inFigure 4; illustrating the senil-circular groove formed therein j and the corrugations,

Figure 6 represents a cross-sectional view along the line 6--6 of' Figure 5, Figure 7 represents an elevational view of the gearing shown in Figures '1 and 3,

Figure 8 represents a view similar to that of Figure l11 represents a cross-sectional View ofV a sectionot tubing after it has been bent into a 90 curve in accordance with the present invention,

Figure' l2 represents a perspective view on -a' reduced scale of the bent section shown in Figure 11, showing the appearance of the section along the inner edge of the curve,

Figure 13 represents a perspective yview similar y to that of Figure 12, but showing the appearance of the bent section along the-outer edge of the curve.

Figure 14 represents a fragmentary cross-sectional view showing a bent section constructed in accordance with the present invention as it appears when aillxed to a straight section.

ysince the same have 'been found in practice to .Figure 15 represents a cross-sectional view of'v a pipe section as' it appears during the process of 4 the bending; the appearance of the section during the different steps 'of the process being illusing downwardly.

to that of Figure 12 but showing a section of ltubing which has been bent through approximately 180 of arc in accordance with the present invention.

In one embodiment of the present invention shown in Figures 1 to 1, I may. provide a base 20 to which are attached generally upright side plates 2| and 22. A plurality of spacing bolts 23 connect the side plates 2| and 22.

A drive shaft 24 passes through suitable openjings in the side plates 2| and 22 and is rotatably mounted therein and carries a driving roll 25 intermediate the plates 2| and 22.

A spur gear '26 is mounted upon the end of the shaft 24 outside of and adjacent to the side plate 22 and is adapted to be driven by the worm 21 "carried by the shaft 28 which is turned by the V-belt pulley 29, which in turn may be actuated by any prime-mover. 4

A gear 30 is mounted at the other end of the the rolls (when not in operation) by a spring- Vsupporting plate 4| which rests upon the upper edges of the side plates 2| and 22 and through rwhich the'mandrel stem 40 passes. A coil spring 42 is disposed about the mandrel stem 40 above thespring supporting plate 4|. A washer 43 is disposed about the mandrel stem 40 above the coil spring 42 and a nut 44 is screw-threadedly attached to the uppermost end of the mandrel stem 40. When the nut 44 is tightened, the coil spring 42 is compressed between the washer 43 and the spring-supporting plate 4|, and the mandrel is thus more or less resiliently supported intermediate the rolls when the machine is not in operashaft 24 outside of and adjacent to the side plate i A driving roll 3| is keyed to and carried by the shaft 32 which is rotatably mounted within the side plates 2| and 22. The driving rolls 25 and 3| have semi-circular grooves formed about their outer peripheral edges and are so disposed that the outermost portions ofl their peripheral edges contact each other to dene a generally circular and vertically extending opening 33 therebetween.

A-gear'34 is mounted upon the drive shaft 32 outside of and'adacent to the side plate 2|. The

' gear 34 meshes with the gear 30 on the shaft 24 so that the'drivmg runs 2s and 3| rotate in opposite directions at the same rate of speed; the portions -of lboth rolls defining the opening 33 mov- The grooves of theldriving. rolls and 3| are provided with corrugations 35 extendingl perpendicularly across the grooves; `the corrugations being deepest at the center portion of the grooves y and becoming shallower at the outer axial edges of the grooves.

A plurality (as, for example, 3) of rolls 38 are disposed peripherally about the driving roll 25 upon shafts 31 joumalled within the side plates 2| and 22. Rolls 3B are provided with generally semi-circular grooves formed in their outer peripheries and are adapted to denne generally circular openings with the adjacent portions of the roll 25. Thegrooves in the rolls 35 are, prefer ably, uncorrugated.

Gears 38 may be provided upon the shafts 31 to mesh with the gear on the shaft 24 and to rotate the rolls 36 oppositely vfrom the roll 25. It is possible. and, indeed, it may sometimes be preferred, to omit the gears 38 so that the rolls' 36 are free or idle rolls.`

The rolls 36 are preferably so disposed. that. with the driving roll 3|, they provide 'a plurality of generally circular openings extending more or tion. As will hereinafter be described, parts 4| to 44 inclusive are intended to be leftoff when the machine is in operation; the mandrel lbeing held in`position by the tubing being bent under pressure of the driving and bending rolls so that it may be considered as a free oating" mandrel.

The embodiment shown in Figure l is adapted to bend steel or other metal tubing which may be either seamless or welded tubing or pipe into a smoothly curved elbow. The final curved tubing may extend through any desired arc by varying thelength of tubing inserted relative to the4 circumferential dimension of the main drivingroll 25. Thus, the final bent tubing may extend through more or less approximately 90 of arc as shown in Figures 11, 12 and 13 by employing a length of tubing corresponding more or less approximately to one-quarter of the circumference of the main drivingroll 25. By employing a section of tubing which is equal to or longer vthan half the circumference of the main driving roll 25. the nal bent tubing can extend through 180 of arc.

'Ihe operation of the presentI invention will j now be described. The nut 44, the washer 43, the coil spring 42 and the spring supporting plate 4| are first removed from the mandrel stem 40. A length of steel tubing is then placed over the mandrel stem 40 and upon the uppermost straight portion 46 of the mandrel 39. Parts 4| -to 44 are left off the mandrel stem 40.

Power is then applied to the V-belt pulley 25 and is transmitted through the shaft 23, the worm 21, the spur gear 25 and the drive shaft 24 to the driving roll 25. The power is also transmitted from the drive shaft 24 through the gears 30 and 34 and the shaft 32 to the driving j roll 3|. The driving rolls 25 and 3| thus rotate downwardly at the opening 33 defined therebeless approximately around one-half the circumf ference of the driving roll 25.V

A mandrel 46 having a circularcross-section Y 1 tween. The tubing 45 is caught by the corrugations 35 on the driving rolls 25 and 3| and is forced downwardly upon theV mandrel 39.

Since the mandrel ts snugly within the tubing 45, it is held in position within the tubing 45 under pressure of the rolls 25 and 3| and may be considered as a. floating mandrel.

. While, in Figure 4, there is shown only a single piece of tubing 45 being bent, it is possible and is contemplated to have a continuous supply of sections 45 bent. 'I'hat is, sections 45 are inserted over the mandrel stem 4l! as fast as room.

is available for them so that straight sections are set in and bent sections are removed from the machine in a continual now. These sections may be of the length shown in Figure 4 so that bent sections corresponding to those shown in Figures 11 to 13 are obtained or the sections may be approximately twice the length shown in Figure 4 so that bent sections extending through approximately of arc as shown in Figure 16 are obtained.- Y

'i The tubing is thus forced through the annular clearance existing between the mandrel 39 and thev adjacent portions of the grooved driving rolls 25 and 3l.

'I'his annular clearance is such that the metal of the outer wall of the tubing 45 is displaced by the corrugations 35 in the manner shown in Figure 14;. alternate crests and troughs being formed with the crests extending outwardly beyond the original outer diameter of the tubing aardbei crests and troughsare changed to accommodate d5 and with the troughs extending inwardly of j the original outer diameter of the tubing.

smoo the portion 4s of the mandrel as ntsy more or less snugly Within the'tublng 45, the

inner wall of the tubing remains smooth and generally unaltered in passing through the annular clearance betweenl the driving rolls 25 and 3l..

As the tubing d5 is forced further down upon the curved portion 52 of 'the' mandrel 39 by the driving rolls ,and 3|, it is bent more or less smoothly along its axis into the curvature of the semi-circular portion 52; the benttubing being forced along between the roll 25 and the rolls 36 finally to emerge in the form shown in Figures 11 to 13.

As hereinabove stated, the rolls 36 may be free or idle rolls, in which case the subsequent movement of the bent pipe d5 is `eected by the driving roll 25 alone. On the other hand, the rolls .33 as well as the roll 25 may be power driven as shown in Figures 1, 3 and '7 in which case both 'the portion of the curved `section e5 adjacent the rolls 36 moves'at a somewhat greater rate of speed than that portion of the section d5 adjacent 'the roll 25. Where this difference in speed is pronounced, as for example, where sections of tubingor pipe of large outside diameter are being bent, it should preferably be compensated for by rotating the rolls 3G at a somewhat higher rate of speed than the roll 25.

the change in shape of the tubing. Thus, the crests 41 and troughs 48 become deeper and closer together as shown at 41-a and 48-.a due to the compression which occurs along the inner side of the curve. On the other hand, the crests 49 and the troughs 50 'become shallower and further apart as' shown at 49-a and Ell-a due to the stretching of the material along the outer side of the curve. l

The inner wall ofthe tubing 45 remains smooth due to the close-fitting portion 52 of the mandrel 39.

By modifying-the shape of the mandrel 3-9, and

`the clearances between the roll 25 and the rolls '36, it is possible to change the inside diameter of the tubing during the bending operation.

Thus, if the curved portion of the mandrel is reduced in cross-section slightly beyond the opening 33 as shown in greatly exaggerated view at 52--a in Figure 9, the inside diameter of the tubing is reduced correspondingly under the pressure of the roll 25 Iand the rolls 36. On the other hand, if the curved portion of the mandrel is increased in cross-section slightly beyond the opening 33 -as shown in greatly exaggerated view' at.

52`b in Figure 10, the tubing will be forced upon the increased portion by the driving rolls 25 and maintaining a smooth inner Wall surface and at 3i so that the inside diameter o f the tubing will vbe increased correspondingly with a slight increase in the outside dimension of the tubing as well. 4

Thus, it is possible to bend the tubing d5 while the same time it is possible to maintain the original inside diameter, or to increase the inside diameter or to decrease the inside diameter, as

desired.

Since this entire bending and shaping operation is performed cold, it is apparent that the present invention affords a rapid, inexpensive,

.and highly desirable bending step whichhas many advantages over old-type bending devices.`

In order to rotate the rolls 36 at a higher rate y meshing with the gear 30 to drive the rolls 25 and 3l at the same rate of speed as hereinabove described. A somewhat larger gear is alsokeyad to the outer end of the shaft 24 adjacent the` gear 30. The shafts 3l carrying the rolls 36 are regularities are presented in the path -of fluid `flow so that friction is greatly decreased and provided with somewhat smaller gears 33--0' which mesh with and are driven by the larger gear 5i.` In this way, rolls 36 are driven at a somewhat higher rate of speed than the rolls 25 and 3 i As shown in Figure 15, when the tubing 5 rst passes through the annular clearance between the portion 46 of the mandrel 3S and the driving rolls 25 and 3l, the crests dl and troughs 48 formed by the driving roll- 25 are generally the same size as the -crests 49 and the troughs '50 formed by the driving roll 3|. As the tubing 5 is bent, however. the configurations of the Thus, the present invention provides a smoothly bent pipe or tubing section which has a smooth and uniform inner wall surface so that a minimum of turbulence and resistance is created during the passage of uid therethrough. Furthermore, the present invention makes it possible to bend a piece .of tubing without changing its inside characteristics or dimensions so that it can :be connected` (by welding or other means)y to a straight piece of similar tubing, as shown in Figure 14, toprovide a pipe line which is substantially uniform throughout its entire length regardless of bends. Thus, no constrictions or irpower loss during -nuid transmission is minimized.

While the present invention has been described in connection with the bendingof relatively short pieces of tubing or pipe, it is equally well adapted to bend a continuous relatively long length of tubing or pipe. Where a continuous length of pipe is bent, the bent portion may be cut o to the desired length. Thus, the continuous bent tubing may be cut into 180 lengths or lengths or any other desired lengths.

The expression free-floating mandrel" as 'used inthe following claims designates a mandrel mandrel and the rest of the machine during operation. t

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it isA therefore desired that the present embodiments -be considered in all respects as'illustrative and cross-section of said tubing whereby said tubing is enlarged in inside diameter.

4.- In a method of bending tubing or the like, the step of initially passing said tubing over a smooth snugly-fitting stationary mandre1 and between apair o f juxtaposed driving rolls, each having an annular concave channel formed in its outer periphery, said channels having generally transverse corrugations formed therein, thereby ly-tting mandrel and through the generally v circular opening defined by a pair of juxtaposed driving rolls, each roll having an annular semicircular channel formed in its outer periphery, said channels having generally transverse corrugations formed therein, thereby to form diametrically opposed series of semi-circular corrugations in the outer surface of said tubing while maintaining -a smooth inner surface on said tubing, and subsequently passing the so-corrugated tubing over a curved mandrel between a pair of juxtaposed channeled bending rolls thereby to bend said tubing while deepening the corrugations along the inner edge of the bend and flattening the corrugations along the outer edge of the bend and while maintaining a smooth inner surface on said tubing.

2. A method of bending tubing or the like comprising passing the tubing over a smooth snuglyfitting mandrel and through the generally circular opening defined by a pair of juxtaposed driving rolls, each having an annular semi-circular channel formed in its outer periphery, said channels having generally transverse corrugations formed therein, thereby to form diametrically opposed series of semi-circular corrugations in the outer surface of said tubing while maintain- -to form diametrically-opposed series of generally semi-circular corrugations in the outer surface of said tubing while maintaining a smooth inner -surface on said tubing.

5. A method of bending tubing or the like comprising initially passing the tubing over a smooth snugly-ntting mandre1 and through the generally circular opening defined by afpair of juxtaposed driving rolls, each having an annular semicircular'channel formed in its outer periphery, said channels having generally transverse corrugations formed therein, thereby to form diaing a smooth inner surface on said tubing, and l subsequently passing the so-corrugated tubing over a curved mandrel between a pair of juxtaposed channeled bending rolls thereby to bend said tubing while deepening the corrugations along the inner edge of the bend and attening the corrugations along the outer edge of the bend and while maintaining a smooth inner surface on said tubing, said curved mandrel having a crosssection somewhat smaller than the original inner cross-section of said tubing whereby said tubing is reduced in inside diameter by said pair of juxtaposed channeled bending rolls.

3. A method of bending tubing or the like comprising passing the tubing over a smooth snuglytting mandrel and through the generally circular opening dened by a pair of juxtaposed driving rolls, each having an annular semi-circular channel formed in its outer periphery, said chan,- nels having generally transverse corrugations formed therein, thereby to form diametrically opposed series of semi-circular corrugations in the outer surface of said tubing while maintaining a smooth inner surface on said tubing, and subsequently passing the so-corrugated tubing over a `curved mandrel between a pair of juxtaposed channeled bending rolls thereby to bend said tubing while deepening the corrugations along the inner edge of the bend and flattening the corrugations along the outer edge of the bend and while maintaining a smooth inner surface'on said tubing, said curved mandrel having a crosssection somewhat larger than the original inner metrically opposed series of semi-circular corrugations in the outer surface of said tubing While maintaining a smooth -inner surface on said tubing, and subsequently passing the co-corrugated tubing over a free-oating curved mandrel between a pair of juxtaposed channeled bending rolls thereby to bend said tubing while deepening the corrugations along the inner edge of the bend and attening the corrugations along the outer edge of the bend and while maintaining a smooth inner surface on said tubing, and subsequently passing the so-corrugated tubing over a curved mandrel thereby to bend said tubing while deepening the corrugations along the inner edge of the bend and flattening the corrugations along the outer edge of the bend and while maintaining a smooth inner surface on said tubing.

6. A tube-bending machine comprising a central driving roll having an annular generally semi-circular channel formed in its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll in juxtaposition to said central driving roll and defining a generally circular forming-opening therewith; a channeled bending roll in juxtaposition to said central driving roll and forming a generally circular bending-opening therewith; and a mandrel having a straight portion generally tangent to said central driving roll and passing through said forming-opening and having a curved portion continuing around said central driving roll and passing through said bending-opening.

7. A tube-bending machine comprising a central driving roll having an annular generally semi-circular channel formed in its outer perlph- H ery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll in juxtaposition to said central driving roll and defining a generally circular forming-opening therewith; a

'channeled bending roll in juxtaposition to said ery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll in juxtaposition to said central driving roll and `defining a generally circular forming-opening therewith; a channeled bending roll in juxtaposition to said central driving roll and forming a generally circular bending-opening therewith; and a mandrel having a straight portion generally tangent 4tosaid central driving roll and passing through said forming-opening and having a curved portion continuing around said central driving roll and passing through said bending-opening, said curved portion having a somewhat larger crosssection than said straight portion,

9. A tube-bending machine comprising a central driving roll having an annular generally senil-circular channel formed in its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll in juxtaposition to said vcentral driving roll and defining a generally circular forming-opening therewith; a plurality of channeled bending rolls peripherally disposed in juxtaposition to said central driving roll and forming generally circular bending-openings therewith; and a mandrel having a straight portion generally tangent to said central driving roll andpassing through said forming-opening and having a c urved portion continuing around said central driving roll and passing through said bending-openings.

10. A tube-bending machine comprising a central driving roll having an annular generally senil-circular channel formed in its outer. periphery, satid channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll in juxtaposition to said central driving roll and deining a generally circular forming-opening therewith; -a plurality of channeled bending rolls peripherally disposed in juxtaposition to said central driving roll and forming generally circular bendtral driving roll having an annular generally senil-circular channel formed in its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll Lin juxtaposition to said central drivingl roll and dening a generally circular forming-opening therewith;

a plurality of channeled idle rolls peripherallyI disposed in; juxtaposition to said central driving ,roll and forming generally circular bending-openings therewitli; and a mandrel having a straight portion generally tangent to said central driving roll and passing through said forming-opening and having a curved portion-continuing around said central driving roll and passing lthrough. said bending-openings. y Y

13. A tube-bending machine comprising a.

frame; a central driving roll rotatably mounted in said frame and having an annular generally semi-circular channel formed' in its outer periphery, said Achannel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll rotatably ing-openings therewith; means for driving said' juxtaposed driving roll and said bending rolls from and in conjunction with said central driving roll; and a mandrel havinga straight portion generally tangent to said central driving roll and passing through said formingopening.and

having a curved portion continuing arund said central driving roll and passing' through said bending-openings.

li. A tube-bending machine comprising a central driving roll having an annular generally semicircular channel formed in its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll in juxtaposition to said central driving roll and defining a generally circular forming-opening therewith; a plurality of channeled bending rolls periph'erally disposed in juxtaposition to said central driving mounted in said frame in juxtaposition to said central driving roll'and dening a generally circular forming-opening therewith; a plurality of channeled bendingrolls rotatably mounted in' said iframe and peripherally disposed in juxtaposition to said central driving roll and defining generally circular bending-openings therewith; and a mandrel supported from said frame, said mandrel having a straight portion generally tangent 4to said central driving roll and passing through said forming-opening, said straight portion having a smaller cross-section than said forming-opening and providing an annular clearance therein, said mandrel having a curved portion continuing around said centraldriving roll and passing through said bending-openings and forming annular clearances therein.

' 14.' A tube-bending machine comprising a frame; a central'drivin'g roll rotatably mounted in' said frame and having an annular generally semi-circular channel formedin its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving' roll rotatably mounted in said framein juxtaposition to said central driving roll and defining a generally circular forming-opening therewith; a plurality oi lchanneled bending rolls rotatably mounted in said frame and peripherally disposed in juxtaposition to said central driving roll and dening generally circular bending-openings therewith; and a mandrel resiliently'supported from said frame, said mandrel having a straight portion generally tangent to said central driving roll and passing through said forming-opening. said straight portion having a smaller cross-section than said forming-opening and providing an annular clearance therein, said mandrel having aV curved portion continuing around said central driving roll and passing through said bendingopenings and forming annular clearances therein, said curved `portion having a somewhat smaller cross-section than said straight portion. f

l5. A tube-bending vmachine comprising a fram'e; a central driving roll rotatably mounted lnsaid frame and having an annular generally semi-circular channel formed in its outer periphery, said channelhaving generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll rotatablyl mounted in said frame in juxtaposition to said central driving roll and. defining a generally cirand a free-oating mandrel disposed within said Y frame, said mandrel having a straight portion generally tangent to said central driving roll and passing through said `forming-opening, said straight portion having a smaller cross-section than said forming-opening and providing an annular clearance therein, said mandrel having a curved portion continuing around said central driving roll and passing through said bendingopenings and forming annular clearances therein, said curved portion having a somewhat larger cross-section than said straight portion.

16. A tube-bending machine comprising a frame; a central driving roll rotatably mounted in said frame and having an annular generally semi-circular channel formed in its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll rotatably mounted in said frame in juxtaposition to said central driving roll and defining a generally cir` cular forming-opening therewith; a plurality of channeled bending rolls rotatably mounted in said frame and peripherally disposed in juxtaposition to said central driving `roll and deining generally circular bending-openings therewith; means carried by said frame for rotating 'said mounted in said frame in juxtaposition to said central driving roll and denning a generally circular forming-opening therewith; a plurality ci channeled bending rolls rotatably mounted in said frame and peripherally disposed in juxtaposition to said central driving roll and dening generally circular bending-openings therewith;

` means carried by said frame for rotating said driving rolls and said bending rolls at predetermined speed; and a free-floating mandrel disposed within said frame, said mandrel having a in said frame and having an annular generally i semi-circular channel formed in its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving roll rotatably juxtaposed driving roll at the'same rate of speed as, but in the opposite direction from, the centrai-driving roll; means carried by said frame for rotating said bending rolls at a somewhat higher rate of speed than, and in the opposite direction from, said central driving roll; and a free-oating mandrel disposedwithin said frame, said mandrel having a straight portion generally tangent to said central driving roll and passing through said forming-opening, said straight portion having a smaller cross-section than said forming-opening andv providing an annular clearance therein, said mandrel having a curved portion continuing around said central driving roll and passing through said bending-openings and forming annular clearances therein.

18. A ltube-bending machine comprising a frame; a central driving roll rotatably mounted in said frame and having an annular generally semi-circular channel formed in its outer periphery, said channel having generally transverse corrugations formed therein; a similarly channeled and corrugated driving rcll rotatably mounted in said Iframe in juxtaposition to said central driving roll and defining a generally circular forming-opening therewith; a plurality of vchanneled idle rolls rotatably mounted in said frame and peripherally disposed in juxtaposition to said central driving roll and deilning generally circular bending-openings therewith; means for rotating said driving rolls in opposite direc tions at the same rate of speed; and a free-deating mandrel disposed within said frame, said mandrel having a straight portion generally tangent to said central driving roll and passing through said forming-opening, said straight portion having a smaller cross-section than said forming-opening and providing an annular clear ance therein, said mandrel having a curved por,- tion continuing around said central driving roll and passing through said bending-openings and forming annular clearances therein.

FRANCIS M. KEPLER.

Images