US1990607A - Rolling mill having inclined rolls - Google Patents

Description

ROLLING MILL HAVING INCLINED ROLLS F99 12, 1935., F. KOCKS 1,990,907-

ROLLING MILL HAVING INCLINED 4ROLLS Filed April 2. 1952 5 Sheets-snee? 2 y MM2@ -Jl/,15% w Feb. l2, 1935. F. KocKs ROLLING MILL HAVING INCLINED ROLLS Filed April 2, 1932 5 Sheets-Sheet 5 mr-w k m. Mn 0 D 0 `0 l n m mmm Q Q .4.. O .Rv .0 0 0 u n Q ma i 1 ia.

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Feb. 12, 1935. F KOCKS 1,990,607

ROLLING MILL HAV-ING INCLlNED ROLLS Filed April 2. 1932 5 Sheets-Sheet 4 Patented Feb. 12, 1935 UNITED STATI-:s

PATENT OFFICE Application April 2, 1932, Serial No. 602,805 In Germany April 29, 1931 11 Claims.

My invention relates to a rolling mill having inclined rolls for rolling solid or hollow blanks. It is an object of my invention to provide a mill of the kind described which is superior to the exist- 5 ing mills with inclined rolls in that the most varied operations may be performed on the blanks in the simplest manner and with the fewest means. This applies particularly to the reducing of the diameter of the blank for considerable percentages and also to .the expanding of hollow blanks while varying their length to a considerable extent.

With these objects of my invention in mind I provide the mill with very thin and comparatively long rolls.l In view of this character of the rolls a hitherto unequalled number of rolls may be provided, and the blank may be altogether enclosed between the circle of rolls, it being of the utmost importance that the blank be forged as uniformly as possible and at las many points of its perimeter as possible.

According to the present .invention I provide an abutment for the thin long rolls so that the rolls transmit the rolling pressure exerted on one side of each roll to the abutment arranged on the other side, and are not subjected to bending stresses'. It is important to so arrange the rolls that they form a substantially continuous pass.

The lower limit of the number of rolls is about ten, while in many cases about twenty or even more rolls may be provided.

The particular advantage of providing so many rolls is that the feeding velocity imparted to the mill is higher than has ever been suggested before, because the number of forging operations to which the material is subjected per revolution greatly surpasses that attained in the existing rolling processes. In consequence thereof the rolls may be so inclined with respect to the axis of the blank that the direction of the peripheral velocity at the point of contact between each roll and the blank includes an angle with the direction of the blank axis which isr'75 degrees as a maximum, i. e. the rolls may have an effective feeding inclination of not less than 15 degrees, an amount which would be impracticable in the existing rolling mills with inclined rolls.

The further consequence of this arrangement is that the central point of the system constituted by the rolls and the axis of the blank lies within the housing or the operating surfaces of the rollsv at a feeding inclination of 15 degrees.

The relation of the diameter of the rolls to the 5 diameter of the blank undergoes a change in prinferent velocities.

ciple, the diameter of the blank being far greater than the diameter of the rolls.

Any suitable means may serve as abutments for supporting the rolls. For instance the abutment may be a revolution body and all the rolls may rotate within the same revolutionbody or the same portions of revolution bodies. Alternatively the rolls may be supported on abutting rolls either individually or in pairs.

In a. particular embodiment of my invention the rolls a'nd the abutments are so shaped in conformity with each other, that the rolls rotate, without slipping, on the abutment in the direction of rotation about theaxis of the system, i. e. in the direction which includes an angle of 90 degrees with the axis of the abutment. In this case the rolls and the abutment are revolution hyperboloids.

A characteristic feature of the rolls which are employed according to my invention, is the ratio of their length to their diameter. 'I'his ratio can be made larger than in any one of the tube-rolling mills heretofore designed, because the rolls are relieved by the abutment of all bending stresses and are subjected exclusively to compression. The lower limit of the ratio of 'length to diameter is a length of the rolls, equal to eight to ten times their diameter. By altogether relieving the rolls of bending stresses it is possible to mount them in end bearings without provid. ing any transverse bearing notwithstanding their small diameter.

'I'he rolls have a tendency to shift in the direction of their axes. According to my invention they are equipped with anti-friction thrust bearings which may be ball bearings.

In order to employ the same mill selectively for reducing and for expanding blanks, (which is practicable according to my invention), the rolls have sufficiently long operating surfaces at both sides of their centres. In order to permit the feeding of blanks in opposite directions, with the rolls also rotating in opposite directions, antifriction thrust bearings are arranged at both ends of each roll.

In a mill according to my invention the several members, i. e. the rolls, the mandrel, the abutment and the bearing rings for the rolls, may perform the most varied movements, as desired. Thus for instance the abutment may be fixed and the rolls, the bearing rings, in which the ends of the rolls are supported, and the mandrel may rotate in the same direction but at dif- Alternatively, the mandrel may be held against rotation, while the rolls, the

bearing rings and the abutment rotate about the axis of the mill; or the bearing rings may be held against rotation, so that the abutment rotates in opposite direction to the mandrel.

The same applies to the supply of forging energy to the rolling process. There is no diiiiculty about supplying the total power required only through the mandrel; or only through the rolls; or only through the bearing rings; or only through' the abutment. But the power supply may also be subdivided by supplying the power partly through the mandrel and partly through the rolls; or partly through the mandrel and partly through the bearing rings; or partly through the mandrel and partly through the abutment; or partly through the bearing rings and partly through the abutment, etc.

It is a condition for the satisfactory operation of the mill according to my invention, that the two bearing rings which support the thrust ball bearings on the journals of the rolls, must never undergo relative rotation. This condition may be fulfilled in Various Ways. For instance both bearings rings may be connected directly by screws, in which case the two bearing rings support the abutment within them. In this case the abutment is mounted for rotation with respect to the bearing rings and may be rotated in the bearing rings by gearing. This arrangement is favorable since it assists in the rolling of the rolls on the abutment without slipping.

There is another possibility of preventing relative rotation of the bearing rings which consists in providing the rings with two gear wheels of equal diameter in mesh with two pinions, also of equal diameter, on a single shaft. This arrangement offers the advantage that the abutment may be fixed.

In order to effect positive rolling of the rolls on the abutment skew pinions may be arranged on the journals of the rolls which mesh with skew gears, for instance, on the housing. As the rolls rotate bodily with the bearing rings, the rolls are rotated about their axes by the skew gearing. If the abutment is a revolution hyperboloid, the pitch lines of the gears and pinions should coincide with the extension of this revolution hyperboloid.

The same object, i. e. positive rolling of the rolls on the abutment, may be attained by dcsigning portions of the surface of the rolls and the abutment as skew gearings with very low teeth. Care must obviously be taken that these loW-teethed gearings will not interfere with the 'final rolling sections of the blank. At the points where the blank is drawn into the mill, such lowteethed' gearing may also be provided without risk of overstressing the material and act like the roughening of a roll, such as is usual in other rolling mills.

Another important condition for the favourable performance of the rolling process is that the scalel is removed from the mill as quickly as possible so that sticking of the rolls and the abutment is avoided. According to my invention the abutment is perforated like a sieve and the scale may be removed through the holes by suction. The means for generating suction is preferably operatively connected to the driving means of the rolling mill.

Another possibility of removing scale is to blow air through the perforated abutment counter to the direction in which the blank moves through the mill, the blowing device being preferably also operatively connected to the driving means of the rolling mill.

In order to limit to a minimum the frictional wear of the abutment, the surface of the abutment which cooperates with the rolls, or the entire part involved, is hardened and, if desired, polished. For reasonsof economy the abutment may be divided and be formed of an outer unhardened support and an inner hardened body of wear resistive material.

The rolls may also be hardened and polished, if desired.

The fact that in a rolling mill according to my invention the entire perimeter of the blank is forged practically without interstices and under uniform conditions throughout, provides the possibility of performing the most varied operations. Thus, for instance, hollow blanks may be expanded and solid or hollow blanks reduced, under widely varying conditions.

With a rolling mill according to my invention and with suitably designed rolls it is possible to expand hollow blanks while stretching them longitudinally to a considerable extent, a deformation process which was hitherto impracticable.

On the other hand it is possible to expand hollow blanks while upsetting their walls to a con-- siderable extent, provided that all the rolls are so shaped that the inlet velocity imparted to the blanks by the rolls is higher than the outlet velocity and that the mandrel is shaped in conformity with the desired deformation of the blanks. In the mills of the inclined roll type as hitherto designed this was impracticable also.

The new rolling mill further provides the possibility of reducing the diameter of solid round blanks as well as that of tubular blanks while reducing, maintaining constant or increasing the wall thickness of tubular blanks, provided that the feeding velocity exerted on the blank by the rolls is suitably chosen and the mandrel suitably shaped. All these forging operations are practicable because the blank, as explained, is forged uniformly throughout its perimeter.

Heretofore rolling mills having inclined rolls which permit reducing the diameter of solid or hollow blanks without detrimental action on the material, have never been suggested.

'I'he most important improvement of the present invention as compared lwith all existing mills having inclined rolls is the provision of a mandrel the diameter of which increases in the direction in which the blanks move through the mill and which determines the wall thickness of the reduced tubular blanks.

In the drawings aixed to this specification and forming part thereof several rolling mills embodying my invention for expanding, and a mill for reducing tubular blanks are illustrated diagrammatically by way of example.

In the drawings,

Fig. l is a sectional elevation of a mill for expanding tubular blanks to which power is supplied exclusively through the mandrel,

Fig. 2 is a section on the line II-II in Fig. 1,

Fig. 3 is a diagram showing the arrangement of the rolls with respect to the axis of the mill,

Fig. i is a sectional elevation of a mill in which power is'supplied to both bearing rings from a driving shaft through gearing, the abutment is stationary and the rolls are driven by skew gearing,

Fig. 5 is a sectional elevation, and

Fig. 5 is an end elevation of amill in which I scale, of an 'abutment having skew bevel gearings Fig. 1 for the sake of clearness.

connecting it to the rolls, and

Fig. 9 shows the abutment and accessories arranged for reducing tubular blanks.

Referring now to the drawings, and ilrst toV Figs. 1 to 3, 1 is a housing and 2 and 3 are bearing .rings which are mounted to rotate in the end plates of the housing by means of hollow journals 4 and 5 in plain bearings 6V and 7, respectively. 8 is an antifriction thrust bearing intermediate the bearing 6 and -the bearing ring 2. The two bearing rings are connected at their inner ends by a flange 9 on the inner end face of ring 2 and screws 10 extending through the flange and the body of ring 3.

Mounted to rotate in cavities of the two inner end faces of bearing rings 2 and 3 in bearing bushings 11 and12 is an abutment-13, here shown as a ring, with its grooved ends 14 extending partly into recesses in the corresponding end faces of the bearing rings 2, 3. The outer face of the abutment 13 is shouldered and equipped with an antifriction thrustfbearlng 15 in a shouldered recess of bearing ring 2. 16 is a gear wheel on the outer face of the abutment 13 and 17 is a central pinion on a shaft 18 which meshes with the gear wheel 16 on the abutment. The shaft 18 is mounted to rotate in bearings 19 and 20, respectively, of the bearing rings 2 and 3f 21 and 22 are pinions cn the outer ends of the shaft 18 which mesh with xed gears 23 and 24. 25 are screws by which the xed gears 23 and 24 are connected to the respective end plates of the housing 1. Any number of shafts 18 may be distributed over the bearing rings 2 and 3. Fig. 2 shows three shafts, each with the three pinions 17, 21 and 22.

v26 is the mandrel, v27 is the mandrel rod and 28 is the tubular blank which is expanded on the rod while moving through the mill from the left to the right. 29 is a mandrel-'rod holder, 30 is a spur gear on the holder, 31 is a pinion in mesh with the spur gear and32 is a clutch connecting the pinion to the shaft of an electric motor 33.

Mounted to rotate in thrust bearings 34 and 35 in the bearing rings 2 and 3, respectively, with nuts at the ends of their spindles, are twelve rolls 36- which while forming a circular pass for engaging the blank 28 with Atheir inner sides, Vare supported at their outer sides by the abutment 13. Bearing sleeves 37 and 38 may be provided for each roll 36 in addition to the thrust bearings 34 and 35. Only one of the rolls 36 is shown in Fig. 3 shows the distribution of the bearings 34,35 of the rolls on circles in the bearing rings 2 and 3. Only three ofthe rolls are indicated by heavy black lines. The rolls, Vin addition to being inclined to the axis of the mill related to a vertical plane, also have an inclination to the axis related to a horizontal plane.

The rolls 36, as mentioned, are made as thin as may be, so that a greater number of rolls than has been practicable heretofore, may be provided in order to obtain a practically uniformkneading of the blank 28 at the many points of contact between the blank and the rolls in the circular pass. 'I'he rolls, being supported at their outer sides by the abutment 13, transmit the rolling pressure from the blank directly to the abutment and are not subjected to bending stress at all. or only to a negligible extent, and means such as transverse bearings for supporting the rolls are not required.

By eliminating the bending stress on the rolls 36 it is possible to make them with a diameter which is smaller related to the length of the rolls, than in any existing tube-rolling mill. The lower limit, as'mentioned, is a diameter, which is 1%; to $4; their effective length. The reaction between the blank. 28 and the rolls tends to shift the rolls axially which is counteracted by the thrust ball bearings 34 and 35. Thrust bearings are provided at both ends of the rolls in order to employ the same set for expanding and for reducingblanks, and the rolls are made as long as required for expanding and reducing.

In the example illustrated, twelve rolls 36 have been shown. The uniform action of so many rolls 36, with a corresponding number of bites making up a circular pass, permits to attain a feeding velocity for the blank which has never been attained in the mills as designed heretofore. The consequence is that the axes :zj-' y of the rolls 36 may be arranged at such an angle to the axis of the blank that the direction of thc circumferential velocity v at the point of contact between each roll and-the blank is atan angle to the axis xof the mill the upper limit of which is 75 degrees as shown in Fig. 1, and the inclinationfof the axes y-y of the rolls 36 to the axis :c-:r is not less than l degrees which is not practicable in any one of the mills having inclined rolls as designed heretofore. A further consequence of the aforesaid arrangement of the rolls is' that the centre c of the system which consists of the axes y-y of the rolls 36 and the axis :zt-:r of the mill, may be arranged within the frame or between the eiective faces of the rolls 36.

Preferably theV cooperating faces of the rolls 36 and the supporting ring 13 are so designed that the rolls 36 roll without slipping on the abutment 13 about the axis .1r-1: of the mill in the direction of rotation, i. e., at right angles to the axis of the abutment 13. This condition is fulfilled if the cooperating faces of the rolls 36 and the abutment 13 are shaped as revolution hyperboloids, as shown in Fig. 1.

However, I am not limited to the particular type of annular abutment, illustrated, but any other suitable type of abutment may be provided. Thus. instead of an. annular.v abutment 13, as shown, I may provide abutment rolls (not shown) on which the rolls 36 are supported individually or in pairs.

In order to limit to a minimum the frictional wear of the rolls 36 and the annular abutment 13, or other abutment member, the rolls and the cooperating face of the abutment are hardened. for instance, case-hardened, and preferably ground. In order to save cost the abutment and, if desired, also the rolls, may be built up from a hard- Vened shell of high-class material and an unhardened body of cheaper material.

While in the mill illustrated in Figs. 1 to 3 the power for rotating the abutment 13 and the bearing rings 2 and 3 is supplied exclusively through the mandrel rod 27 and transmitted to the abutment 13 by the mandrel 26 and the blank 28, a

driving shaft 39 operating on the two bearing rings 2 and 3 is provided in Fig. 4, and the abutment 13 is fixed in the housing. The driving shaft 39 is mounted to rotate in suitable bearings 40 in a bracket 4l at the top of the housing 1, and 42 are ribs on the bracket to which anges 43 on the abutment 13 are attached. 44 and 45 are pinions on the driving shaft 39 which mesh with gear Wheels 46 and 47, respectively, on the. bearing rings 2 and 3. 48 and 49 are anti-friction end-thrust bearings intermediate the inner end faces of the lxed abutment 13 and the inner end faces of the rotary bearing rings 2, 3. Rotation is imparted to the rolls 36 by annular skew gears 50, and 51, respectively, which are fixed in suitable recesses of the housing 1 in the space between the gears 46 and 47 and the journals 4 and 5 of the respective bearing rings, and 52 are skew pinions on the ends of the roll spindles which project from their bearings 34 andv35, the pinions meshing respectively with the bevel gears 50, 51. The meshing points of the pitch circles of the skew gearings are in the extension of the hyperboloid inner face of the annular abutment 13.

It will be understood that, as the bearing rings 2 and 3 rotate, the rolls 36 are entrained .and their skew pinions 52 roll on the respective annular skew gear 50, 5l, so that rotation is imparted to the rolls 36.

Obviously relative rotation of the bearing rings 2 and 3 must be prevented as this would exert bending and shearing forces on the rolls 36. Fig. 1 shows a direct connection of the bearing rings 2 and 3 by the screws 10. In the mill illustrated in Fig. 4 the same result is obtained by operatively connecting the gears 46 and 47 of bearing rings 2, 3 by the pinions 44 and 45 on the driving shaft 39. Obviously the ratio of the pinion 44 to its gear wheel 46 must be equal to that of the pinion 45 to its gear wheel 47.

Means may be provided for removing scale from the abutment 13.

As shown in Fig. 4, the abutment has perforations 53 which open into a vacuum chamber 54 in the portion of the bracket 41 which extends between the bearing rings 2 and 3 for holding the abutment 13, as described, and 55 is a suction pipe connected to the vacuum chamber 54.

Instead of removing the scale by suction it may also be removed by pressure, compressed air being supplied to the pipe 55. In a pressure appliance the perforations 53 must obviously be inclined toward the adjacent end faces of thebearing rings 2 and 3 so that the scale will be blown out through the hollow journals 4 and 5. Preferably, the suction pump or compressor (not shown) for the chamber 54 is operatively connected to the drive of the mill. It is understood that the pneumatic scale remover is not limited to a. fixed abutment, such as shown in Fig. 4, but may be adapted to any type of mill.

The mill shown in Figs. 5 and 6 is designed sub1 stantially on the lines of the mill illustrated in Figs. l to 3, i. e., it has a rotary abutment 13 mounted in rotary bearing rings 2 and 3, which are connected by screws 10, and shafts 18 are provided for rotating the abutment in the manner described. In this instance, ho l f the power is supplied from a driving bearing ring 3 from the driving shaft through a pinion 56 on the driving shaft and a gear wheel 57 on the bearing ring 3. The rotation imparted to the bearing ring 3 is transmitted to the abutment 13 through shafts 18, as described with.'

reference to Figs. 1 to 3, but in this instance the power is transmitted to, and not from, the abutment 13.

As will appear from Fig. 6 the housing 1 is preferably divided in the plane of the axes of driving shaft 39 and of the journals 4, 5 of bearing rings 2, 3, so that the upper portion of the housing is readily lifted by any suitable tackle for exposing the members in its lower portion.

In Fig. 7, the only rotary member is the abutment 13 to which rotation is imparted from the driving shaft 39 through the medium of a pinion 56 meshing with the gear wheel 16 on the abut ment. The bearing rings 2 and 3 are fixed in the end plates of the casing with their tubular ends 57 and 58 and held against rotation by keys 59.

In Fig. 4, skew gearings 50, 52 and 51, 52 have been illustrated for effecting positive cooperation of the rolls 36 with the face of the abutment 13. Instead of placing the gearings at the ends of the rolls they may be arranged within the abutment 13 as shown in Fig. 8, where 60, 62 and 64 are annular skew gears on the inner face of the abutment 13, and 61, 63 and 65 are skew pinions on the rolls 36 which mesh with the gears in the abutment 13. 4The teeth of the skew gearings are preferably short in radial direction and obviously the gearings must not extend into the range where the rolls act on the blank. Any other number of skew gearings than three, as shown, may be provided.

Referring now to Fig. 9, the blank 28 is reduced on the mandrel 26 by the rolls 36 and an abutment 13. The blank enters the mill from the right where the mandrel 26 has its largest diameter. The mandrel rod 27 is under tension and the blank moves through the mill in the direction of the arrow.

I wish it to be understood that I do not desire to be limited to the exact de ails of construction shown and described for obtvi\ous\modiiications will voccur to a person skilled in the art.

I claim:-

1. In a rolling mill in combination a housing, a plurality of long rolls extending through said housing, said rolls being arranged in a circle about and all at the same angle to their common axis, a radially immovable abutment mounted in said housing in contact with and arranged to support substantially the entire operating faces of said rolls, a pair of bearing rings arranged to support the ends of said rolls, and gearing connecting said bearing rings for rotation at equal angular velocity.

2. In a rolling mill, the combination of a housing, a plurality of long rolls extending across said housing, said rolls being arranged in a circle around a common axis and all lying across said axis at the same angle, said angle being between the limits of and 75, and an abutment surrounding said rolls and abutting their surfaces for substantially the entire operative length thereof, said abutment being carried in said housing in such a manner as to prevent radial displacement with respect to said axis and being shaped as a hyperboloid to maintain rolling contact with said rolls during their rotation without substantial slipping.

3. In a rolling mill, the combination of a housing, a plurality of long rolls extending across the housing, said rolls being arranged in a circle around and all at the same angle across a common axis, said angle being between the limits of 15 and '15",4 two elements in said housing for journaling opposite ends of said rolls, means .to

prevent rotation of said elements relative to one another and an abutment radially immovable with respect to said axis mounted insaid housing and abutting the surfaces of the rolls for substantially their entire operative length, said abutment being shaped as a hyperboloid to maintain rolling contact with said rolls during their rotation without substantial slipping.

' 4. In a rolling mill, a housing, a plurality of long rolls extending across the housing, said rolls being'arranged in a circleY around and all at the same angle across a common axis, said angle being between the limits of. 15 and 75, two elements in said housing for journaling opposite ends of said rolls and an annular abutment mounted in said housing between said elements and abutting the surfaces of said rolls for substantially their entire operative length, the cooperating faces of said rolls and said abutment being shaped as hyperboloids to maintain rolling contact without slipping between said rolls' and said abutment during rotation of the rolls.

. means to prevent rotation of said elements with respect to one another and an abutment radially immovable with respect to said axis mounted in said housing between said elements and abutting the surfaces ofthe rolls for substantially their entire operating length, said abutment being adapted to rotate relative'to said elements and vbeing shaped as a hyperboloid to maintain rolling contact with said rolls during their rotation without slipping. Y

6. In a rolling mill for swaging tubular blanks, a housing, a plurality of long rolls extending across said housing, said rolls being arranged in a circle around and all at the same angle to a common axis, a radially immovable abutment rotatably mounted in said housing in contact with and arranged to support substantially the entire operating faces of said rolls, a pair of ring elements rotatably mounted in said housing and arranged to journal the ends of the rolls, means for preventing rotation of said ring elements relative to one another, and gearing connecting said ring elements with said abutment in such a manner that rotation of said abutment in said housing in one direction imparts a reverse rotation to said ring elements. e

'1. In a rolling mill, ahousing, a'plurality of long rolls, said rolls being arranged in a circle about and all'lying at the same angle across a common axis, two opposite ring elements rotatably mounted in said housing each journaling one end o f eachJroll, means for preventing relative ment may rotate relative to one another within said housing.

8. In a rolling mill, a housing, a plurality of long rolls, said rolls being arranged in a circle about and all lying at the same angle across acommon axis, two opposite ring elements rotatably mounted in said housing each journaling one end of each roll, means .for preventing relative rotation' between said elements, and an annular abutment fixed against rotation in said housing and mounted between said elements, said abutment being adapted tov maintain rolling contact with and abut the surfaces of said rolls substantially throughout their entire operative length,

whereby said elements and said rolls may rotate relative to said iixed abutment.

9. In a'rolling mill, a housing, a plurality of long rolls, said rolls being arranged in a circle about and all lying at the same angle across a common axis, two opposite ring elements rotatably mounted in said housing each journaling one end of each roll, an annular abutment fixed against rotation in said housing and mounted between said elements to abut the surfaces of said rollsl substantially throughout their entire operative length, said abutmentbeing shaped as a hyperboloid to maintain rolling contact with said rolls Without slipping during -their rotation, a source of power and gearing between said source of power and each of said ring elements adapted to rotate said ring elements at equal angular velocities.

10. In a rolling mill, a housing, a plurality of long rolls, said rolls being arranged in a circle about and all lying at the same angle to a common axis, two opposite ring elements each rotatably mounted in said housing and each journaling one end of each roll, means for preventing relative rotation between said elements, an annular abutment rotatably mounted in said housing between said elements and adapted to rotate relative thereto, said abutment being adapted to maintain rollingy contact with the surfaces of` said rolls through substantially their entire length, means to cause rotation of said elements under power and gearing between said elements, said housing and said abutment -for causing rotation of said elements in one direction to impart a reverse rotation to said abutment.

11. In a rolling mill for swaging tubular blanks, a mandrel, a tubular blankthereon, a housing, a plurality of long rolls extending across said housing, said rolls being arranged in a circle around and all at the same angle across said tubular blank and in contact therewith, a rotatably mounted abutment in said housing surrounding said rolls and in contact withtheir surfaces for substantially their entire length, said roll surfaces and said abutment beingshaped as hyperboloids to maintain rolling contact with each other without slipping, a pair of ring elements rotatably mounted vin said housing and arranged to journal the ends of the rolls, means for preventing rotatiorr'of said ring elements with respect to one another, gearing connecting said ring elements with said abutment in such a manner that rotation of said abutmentl in said housing in one direction imparts a reverse rotation to said ring elements and means to move said blank to impart rotation to said rolls and hence to said abutment and said ring elements.

FRITZ KOCKS.

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