US2085968A - Tube rolling method - Google Patents

Description

July 6, 1937. J. GASSEN TUBE ROLLING METHOD Filed Feb. 14, 1935 2 Sheets-Sheet 1 INVENTOR- JOJEF 6'4 SSE/V i ATTOR N EY July 6, 1937. J. GASSEN TUBE ROLLING METHOD Filed Feb. 14, 1955 2 Sheets-Sheet 2 INVENTOR fosEF GA sJE/v,

ATTORNEY duced at the same time.

Patented July 6, 1937 UNITED STATES PATENT OFFICE 2,085,968 TUBE ROLLING METHOD many Application February 14, 1935, Serial No. 6,431 In Germany December 2.8, 1933 1 Claim.

Tubes of a diameter of less than 50 millimetres are made by being rolled down in a hot state on a reducing rolling mill until the desired finished diameter of the finished tube is attained, or else by being drawn hot on the drawing benches in one or more operations to as small a diameter as is required, or else by being drawn cold over a plug or a mandrel rod in one or more operations to the desired diameter. In the last instance, the wall thickness of the tubes is usually also re- Quite small tubes, below half an inch in diameter for example, can be further reduced only by cold drawing. The production of the initial tubular body from a solid ingot cannot be effected with smaller diameters than 50 millimetres, not even when tube extrusion presses are used for the production of the hollow bodies, at least not for many non-ferrous A metals. v

Especially in those tubes which consist of nonferrous metals dilficulties arise in tube extruding which render it necessary to produce the tubes with a comparatively large diameter and comparatively great wall thickness in the press. The demand for tubes of non-ferrous metals is however quite considerable in rather small dimensions, so that it becomes necessary to produce 7 these small tubes mostly from comparatively large initial hollow bodies by cold drawing, in which case very numerous reducing operations are employed.

This method of reducing is however very ex-' pensive and suggestions have recently been made to reduce tubes in a cold state by the well-known pilger process, upon either a cylingical or a conical mandrel, depending on whether the internal diameter'of the tube is to remain unaltered or is to be diminished. This process has however a number of very serious disadvantages, particularly when conical mandrels are employed. In these cases the forward feed of the tube at each pilger stroke can only be made exceedingly slight, of the order of magnitude of a few millimetres for example, on account of the conical taper of the pilger pass, and the feed is the smaller the more the pilger pass tapers, that is to say, the greater the reduction that is to be attained in the pass. Therefore upon one stand only a very small number of tubes can be produced in a given time. i

The rate of working of the pilgering rolls is therefore limited, if it is desired to avoid numerous breakages of the elements that have to bear the stresses arising from the inertia of the heavy reciprocating masses in the pilgering mill. Consequently, it becomes necessary to connect a plurality of these cold working pilger stands in parallel in order to obtain a sufiiciently large output. This however increases to an excessive extent the cost of installing and maintaining the-plant. In this connection it is to be taken into consideration that the conical mandrels for example have to be very frequently renewed, because the shaping operation as a whole always occurs at one and the same part of the mandrel surface, and this is just the part of the surface that is exposed to very high pressures in cold working. These stresses may lead to such rapid wear or even distortion of the mandrel that the latter changes its dimensions even during the treatment of a single workpiece.

The object of the process forming the present invention is to obviate the disadvantages above set forth.

The invention is illustrated by way of example in the accompanying drawings, in which Figure 1 is a plan of a plant for carrying out the said process.

'Figures 2 and 3 are diagrammatic side views of two embodiments of reducing mills suitable for carrying out the process according to the present invention.

With my new process tubes are reduced to their finished dimensions in a cold state, after having first been reduced in a hot state by other known processes, on ordinary reducing rolling mills for example, without appreciable change in their wall thickness, so far that their internal diameter is only a little greater than the final dimension. The finishing of the tubes by a cold method proceeds however according to the present invention not upon a pilger tube-rolling mill, but upon a reducing rolling mill consisting of one or more stands.

The reducing of the tubes by the process according to this invention is carried as far as possible in a hot state, with the result that the cold shaping of the tubes can be allowed to take place upon the machines that are best suited to stand the high stresses occurring, without the advantages of the cold working and the advantageous structural formation resulting therefrom, as well of tubes can be made thereon, since the speed at Y which the tubes leave the last housing of the reducing mill amounts to from 1 to 2 metresper second, as compared with the few millimetres ation, the wear of the latter is negligible. Re-.

ciprocating masses such as occur in pilger tuberolling mills are likewise absent in the present instance, so that the stresses caused thereby are obviated.

In the construction of a reducingmill. which is suitable for carrying out the process according to this invention, care must be taken that on the one hand the working rollsbeof the smallest possible diameter, because it is only then that they exert their best stretching action and can force the material away in a direction opposite to the direction of rolling, and that on the other hand the rolls, on account of the great resistance to change of shape of the cold material, are subjected to a very high roll pressure, and are thus very liable to bend. According to this invention, therefore, for the cold rolling of tubes a reducing mill is proposed, I

in which there are associated with the thin working rolls backing rolls for the purpose of taking up the very considerable roll pressure.

In the case of ordinary two-high mills, for example strip mills, it is already known to provide backing rolls for the purpose of taking up the roll pressure .of the thin working rolls.

. mounting of the backing rolls in the roll housing .10 does not give rise to any difi'iculty in those cases,

because there is'ample space available.

In reducing mills such as are required for carrying out the process according to the'present invention, however, the conditions are not so fav- 4-5 ourable, because the number of working rolls, and the corresponding numbenof backing rolls, are usually greater than two, and furthermore special means must be provided to keep the running of the working rolls of one and the same housing synchronous. It has been found to bea particularly advan- ,tageous solution of this problem to arrange the working rolls in an overhung position, and to provide at the end of each driving shaft remote from the working roll a counter-shaft at right angles thereto,-that .is, parallel to the direction of rolling. The counter-shafts of one and the same housing'therefore admit of being kept in synchronism -by simple means, for instance by the aid of a chain passing round all of them.

u I According to Figure 1, the pierced ingots, either after first passing through an intermediate fur-' nace a or directly, come to areducing mill b of ordinary construction, where they are rolled down in a hot state to about their final internal diameter. 5 Between the furnace a andthe. reducing mill b is provided a live roller bed c.

,From the reducing mill b the tubes pass over a live roller bed 11 to a cooling bed e and are provided, at the point of introduction 2, with a mandrel previously coated with a lubricant, this unandrel being taken from a storage grate f and guided along a channel g to the point of introduction.

'I'hetube then passes, with the mandrel, over a grate h to'a live roller bed i, and from the latter to a cold-reducing mill'lc comprising a plurality of stands which may be constructed as illustrated in Figure 2 or in Figure 3. In this cold- 10 reducing mill the tube is reduced to its finished dimensions and more particularly to its final external diameter. The tube is therefore mounted upon the mandrel in consequence of the appropriate construction of the roll pass, only sutfi- 15 ciently firmly so that the mandrel can be withdrawn from the tubewithout difilculty when the latter leaves the last housing. The mandrel then is returned to the storage grate f, by a conveying means not shown, while the tubes are taken up 20 a by trays and conveyed away by the latter.

In the embodiments illustrated in Figures 2 and 3, the reducing mills shown each comprise three working rolls l, which together form a closed round pass. With each of these working 25 rolls is associated a backing roll 2 ofconsiderably larger diameter than the working roll. .The bearing surfaces between the workingv rolls and the backing rolls are-conical inshape, in order to enable lateral pressures to be taken up. 0

While the backing rolls 2 are not positively driven, the working rolls l are set in rotation by 7 means of shafts 3, upon which they are overhung,

by a source of power, e. g.,as a motor 4. To each housing in this embodiment, there pertains 35 one such motor, which sets in rotation a; countershaft 6 by means of a worm drive 5. This countershaft is at right angles to one of the three shafts 3, and is connected with the latter by means of bevel gearing L' The other shafts 3 40 likewise have each a counter-shaft.6 at right angles to them and a bevel gearing 1. A common driving chain 8 passes round-the three counter-shafts 6 thus keeping. them in synchronism. 45.

It is also possible'to' provide only asingle motor v for a plurality of standsin the same reducing mill, and then to'arrange on the individual stands transmission gears which impart to the working rolls the requisite speed of revolution: 50

In the embodiment ilIustrated'in'Figure" 3 the source of power for driving the roll housing, and the arrangement for keeping the rolls in;- syn-. chronism are omitted. As shown the backing rolls 2 rest inbearing arms In, which are pivotally and 55 V resiliently connected with the bearing arms ll ofthe shafts 3. In all other respects. this con,-

. struction is the same as that of Figure 2. V

. I claim as my invention:

, The method of rolling thin-walled tubes of {IO small diameter, comprising gflrstly reducing the tube in a hot state, without appreciable diminution of its wall thickness, to aninner diameter substantially corresponding to-that of the finished product, and then diminishing the wall 05 thickness of the tube in a cold stateby subjecting it to the action of a succession of positively driven backed rolls of small-diameter rolling the tube over a mandrel.

JOSEF GASSEN. 7o-

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