Proceedings of the Tomsk Technological Institute of Emperor Nicholas II.

Vol. XXI, 1911, No. 1.

Rolling, Its Heterogeneities, Varieties, and Types.

S. K. Konyukhov.

(With 4 figures.)

The first question arising in the study of the phenomena of rolling naturally consists in determining what kind of shaping of metal, or of any other material, should be considered rolling; that is, in other words, in clarifying what is called rolling. However, simple though this question may be in itself, to answer it logically proves rather difficult. This difficulty arises because, in both generic and specific senses, the concepts of rolling have not yet taken on strictly defined forms, in most cases not quite successfully embracing the extraordinary abundance of features and varieties inherent in individual cases of rolling. Whether we roll material cold or hot; whether we operate upon a simple cross-section, from a geometrical point of view, or a complex one; whether we curve the axis of the object or not; whether the direction of elongation coincides with the direction of the tangent to the rolls at their nearest points, if the rolls are smooth (Fig. 1, points \(A_1\) and \(A_2\)); whether we are dealing with a pair or with a larger number of rolls; whether the rolls or the bodies being rolled all rotate or only some of them; whether the form of the bodies being rolled is the same or not—all this introduces its own specific features into the process of rolling, and all this is reflected in the character of rolling. Hence it is clear that to define, to clarify the concept of “rolling” simply and logically, proceeding from the very nature of rolling or mill-rolling,

Fig. 1

not so easy as it seems at first glance. There are many more or less uniform attempts, both by Russian and by foreign authors, aimed at clarifying the concept of “rolling,” but all these attempts represent only a rough approximation, skirting the boundaries of the concept that interests us, in a direction more centrifugal than centripetal in character.

In what follows I shall cite a number of excerpts, both from the works of Russian and foreign authors, and shall show that complaining of the incompleteness and inaccuracy of the definition of “rolling” is not unfounded.

Professor Codron, in his magnificent work “Procédés de forgeage dans l’industrie,” defines rolling as follows: “D’une façon générale, on entend par laminage l’opération, qui consiste a étirer, allonger en bande, transformer les dimensions d’une masse métallique au moyen des rouleaux animés d’un mouvement de rotation continu ou alternatif et qui constituent les outils de la machine appelée laminoir,” i.e., by rolling is understood such an operation in which a metal, drawn out into a strip, is given a definite form by means of the constant or alternating rotation of rolls that are parts of a rolling mill.

I do not translate this passage literally, but merely convey the sense of the definition, which, I think, will not be held against me.

Let us analyze this definition of rolling and show wherein lies its weak point, from the standpoint of the inaccuracy and lack of clarity of the characterization of rolling.

First of all, why restrict the concept of “rolling” to operations only on metal? Can other materials not be rolled, such as clay, glass, paper, asphalt? We know, for example, that nowadays plate glass, linoleum, caoutchouc, rubber, celluloid, etc., are rolled. Secondly, a definite form can be imparted to the object being rolled by rotating and non-rotating bodies (drawing); a strip or other body can be obtained under a hammer, a press, or by casting, or by forcing it through an opening of any form under additional pressure or under the influence of gravity, or of atmospheric pressure if there is a vacuum on the outlet side. Thus, the definition of rolling given by Professor Codron suffers from inaccuracy and cannot be recognized as logically correct.

In the work of L. Geuze, “Traité théoritique et pratique du laminage du fer et de l’acier,” we encounter the following definition of rolling:

“Le laminage est l’opération qui consiste à transformer en barre de section déterminée une masse de fer ou de l’acier brut de section supérieure à celle demandée. Il y a donc toujours diminution de section et allonger de la masse par passage de celle-ci d’une cannelure dans une autre,” i.e., rolling is the kind of operation in which an iron or steel mass is transformed into strips of the required cross-section by passing from a section of larger dimensions to a section of a previously designated profile. The constant reduction of the section, with simultaneous elongation of the metallic mass, is the result of passing from one pass to another.

V. G. Dreiman, in an article on the rolling of iron and steel, says: “Rolling is one of the metal-working processes based on malleability, and takes place when metal is passed through rolls that rotate in opposite directions. In general, rolling is expressed in the reduction and drawing-out of the metal.”

This definition is closer to the truth, but it too is inaccurate, because it limits rolling solely to operation upon metal, and also because it makes rotation of the rolls a condition of rolling.

Professor Gavrilenko says: “Rolling is the process by means of which a metal billet or ingot, passing between two rolls, being compressed in its transverse section (direction) and drawn out lengthwise, is transformed into sheets or long strips with a transverse section constant over the entire length.”

Among Russian technicians the name of Professor Gavrilenko enjoys great popularity; his writings receive prizes (as, for example, Boilers), and therefore we shall treat his words with due attention and circumspection. It nevertheless seems to us that Professor Gavrilenko is profoundly wrong in his definition; his words smack of triteness and cliché. In fact: why limit rolling to operation only upon metal, passed only between two rolls, when there may be several rolls; why characterize rolling by the emergence of a product of constant transverse section over its entire length, when this section may be of the most whimsical character at different places of the transverse section, as, for example, ornamental iron, where there is a periodic repetition of the profile; why speak of compression in the transverse direction, when only one dimension, as for example in sheet and strip iro—

iron decreases, while another increases. All these questions remain unanswered by the definition itself.

Other, more cautious authors avoid, or wish to avoid, the difficulty in defining the concept of “rolling” and give a definition of the nature of the working process in rolling. Thus, for example, Professor von Hauer, in the well-known course Die Hüttenwesens Maschinen, expresses himself as follows: “Der Arbeitsprozess besteht darin, dass das glühende Eisenstück zwischen zwei durch eine Kraftmaschine entgegengesetzt gedrehten Walzen mehrmals durchgehen und dabei sein Querschnitt so lange geändert und verkleinert, bis die gewünschte Form erzielt ist,” i.e., the working process in rolling consists in the fact that a heated piece of iron is passed several times between two rolls, rotating in opposite directions by means of an engine, whereby the cross-section of the piece of iron is changed, decreasing until it assumes the desired shape.

Professor Desmuth, in his work on the mechanical technology of metals, defines rolling in the following manner: “Unter Walzen versteht man das Hindurchführen eines Werkstückes zwischen sich drehenden, walzenförmigen Rotationskörpern, wobei der Querschnitt des Werkstückes eine Veränderung erleidet; gewöhnlich wird der Querschnitt ähnlich wie bei Ziehen nach und nach verkleinert”... i.e., by rolling is meant the passage of a metallic piece between rotating, roll-shaped bodies (of rotation), when the cross-section of the piece undergoes a change; usually this section, as in drawing, is gradually reduced.

Professor Ledebur approaches the definition of the rolling process thus: “Man nennt Walzwerk eine Vorrichtung, bei welcher das Arbeitsstück zwischen zwei parallelen, sich in entgegengesetzter Richtung drehenden Walzen hindurchgeführt wird, dabei eine Querschnittsänderung erleidend”... i.e., a rolling mill is the name given to a device in which the workpiece being treated is passed between two parallel rolls rotating in opposite directions, whereby a change in the cross-section of the piece being passed through takes place.

The inaccuracy of this definition is clear on the basis of the preceding considerations, and therefore comment is superfluous.

T. Beckert, in the book Leitfaden zur Eisenhüttenkunde, writes: “Walzwerke sind formgebende Vorrichtungen, welche ähnlich der Schmiedepressen mit ununterbrochenem Druck über die ganze Länge des Arbeitsstückes wirken”... i.e., rolling mills are form-...

changing devices which, like forging presses, act along the entire length of the piece being worked with continuous pressure.

The likening of rolling to forging is, in our opinion, an entirely correct idea, but only not under presses, rather under hammers, since when the rolls seize the billet what is manifested is not a static action, but a dynamic one.

In the work of Professor Brovot on the pass design of rolls we find the following passage: “Hier doch tritt an Stelle der ebenen Fläche, auf welcher die Bearbeitung stattfand, eine zweite Walze ûnd zum Unterschiede von der ihren Ort verändernden Strassen—oder Teigwalzen wirken die beiden Blechwalzen derart, dass sie sich ûm die ihre festliegenden Mittelachsen und zwar in einander entgegengesetztem Sinne drehen und dass ihnen zûr Bearbeitung übergebene Eisen zwischen sich hindurchziehen,” i.e., here, instead of the surface to which the working was imparted, there is another roll; and, unlike the rolls for leveling streets and for rolling dough, which, as is known, are moved about, both rolls have fixed axes, rotate in opposite directions, and the iron being worked is passed between them. Here again I render the passage in translation not literally, but only preserving its meaning.

It seems to me that T. Beckert, who worked under the direction of Professor Brovot, penetrated more deeply into the essence of rolling than did his honored teacher.

Like Brovot, Dr. H. Wedding also gives a somewhat lengthy explanation of the operation of a rolling mill. Here it is: “Ein Walzwerk besteht aus zwei in entgegengesetzter Richtung durch einen Motor ûmdreheten Cylindern zwischen welchen das dûrch die Reibung an den Walzenmänteln mitgenommene Eisen hindûrchgeht, dabei seinen Querschnitt in der Richtung des Drückes d. h. also seine Höhe verkleinert und seine Länge entsprechend vermehrt”... Here we already encounter the now familiar repetition of the story of two rotating rolls, which by the force of friction at their periphery draw between them a piece of iron being passed through, whose length increases while its height decreases.

In the same way rolling is characterized also by Professor E. von Goyer.

The series of definitions of rolling could be extended indefinitely, but there is hardly any need for this. Already from the numerous definitions cited—though essentially uniform—the incompleteness of the characterization of rolling is evident. More than other authors, those who liken rolling to forging provide it. Among Russian authors, as I recall, R. Tonkov holds the same view in his dissertation on rolling.

We also adhere to the same view.

If by forging, according to Professor Gavrilenko’s definition, one understands such a method of working in which metal (or, better, material) is deformed under the action of strong pressure applied at various points of the object being worked, then the definition of rolling is considerably simplified.

By rolling we understand the process of the mechanical integration of differential forging, or simply integral forging. Rolling mills, in such a case, are a modification of elementary lever hammers acting over the entire periphery, or only over part of the periphery, of the section of the billet.

Hence it is clear that the process of rolling may be considered on the basis of the theory of lever hammers.

Like forging, rolling may be both cold and hot. This is its first division into heterogeneous kinds (generic concepts). Then each of these heterogeneous kinds has its own varieties. Thus Professor Codron, in the work already cited by me, divides rolling into three kinds: 1) longitudinal, 2) transverse, and 3) helicoidal.

Each of these varieties has its own types. Thus, in longitudinal rolling the same Professor Codron distinguishes the following types: a) horizontal and vertical rolling, b) profile rolling, c) die rolling, d) periodic rolling, e) continuous rolling, f) endless rolling.

Transverse and helicoidal rolling must have types of the same kind as well.

Professor Codron does not have this division of transverse and helicoidal rolling, but, of course, one cannot assert positively that since such types do not yet exist in technology, they never will. It is all only a matter of time and circumstances. Today they are not yet there, and tomorrow, behold, they have appeared. Human inventiveness is inexhaustible, and the laws of nature are all-powerful. The sciences—these codices of the laws of nature—can always assist an inquisitive person in need. Let Comte say: “each time we perform any strong action, this

Rolling, Its Heterogeneities, Varieties, and Types.

is achieved only because our knowledge of the laws of nature allows us to introduce, among the definite circumstances under whose influence the phenomenon takes place, several new elements which, in known cases, prove, despite their insignificance, sufficiently strong to change to our advantage the final result of the action of all the causes taken together. In a word, prediction is founded upon science, and action upon prediction.”

Let us return, however, to rolling.

1) By longitudinal rolling in general, Professor Codron understands such rolling when a metallic billet, in a more or less worked state, is placed between two rolls whose axes are parallel or inclined and which rotate in opposite directions.

This definition is not only unclear, but also inaccurate. Here one speaks of the arrangement of the rolls and their motion, but by no means of rolling, which is characterized by the elongation of the fibers in a definite direction. The pure form of longitudinal rolling will be that in which the elongation of the fibers coincides in direction with the direction of the final tangent to the gripping arc of the rolls, and thus, with horizontal cylindrical rolls whose axes are parallel and form a vertical plane, the direction of exit of the object being worked will be horizontal and rectilinear. Longitudinal rolling is also called parallel rolling. But this definition, too, is not entirely correct. In purely longitudinal rolling, the fibers of the material will also be parallel and of equal length.

Let us briefly examine the individual types of longitudinal rolling.

a) Horizontal and vertical rolling is characterized by the fact that the transverse widening, in a direction perpendicular to the elongation, of an ideally thin layer in one case spreads in the horizontal direction, and in the other in the vertical. In universal mills the transverse widening goes alternately now in one direction, now in the other. It has been observed that these transverse widenings are directly proportional to the difference in the thicknesses of the billet before and after passage through the rolls and inversely proportional to the tangent of the half-sum of the central angles, in degrees, of the gripping arcs. Or,

\[ B = 2\left[(D - d)\cdot 0{,}01 \operatorname{cotg}\left(\frac{\alpha+\beta}{2}\right)\right]. \]

An example of horizontal and vertical rolling may be strip iron, square iron, beam iron, angle iron.

c) Shape rolling, according to Codron, has the property that the length of the billet does not change, while only the shape of the cross-section is subject to change. For example, corrugated iron, hoops with ribs. Thus, here there is no longitudinal elongation proper, but only a rearrangement of particles in the cross-section.

d) Die rolling, or rather forging of an all-around character, is used to obtain articles of small dimensions in finished form. In this case, closed recesses in the rolls, both in the upper and the lower one, form, with coordinated motion of the rolls, a closed shape fully corresponding to the external outline of the article. The process fully deserves the name “circular die-stamping.” The upper roll with the corresponding recess plays the role of the punch, and the lower one—that of the die. In this way one may obtain, for example, knife blades, nails, crutches, files, etc. The number of rolls, of course, may also be greater than two.

e) Continuous rolling is used to obtain thin strips, wire, and bar iron. Here the billet passes continuously between rows of rolls and, upon leaving the last of them, assumes its final shape.

f) Endless rolling is used to obtain, for example, rings, the webs of circular and endless saws, and disks.

g) Finally, in periodic rolling the billet being worked, before acquiring its final form, passes periodically several times between the rolls.

2) Transverse rolling, rolling, roulage, which according to Codron represents the second variety, is distinguished by the fact that elongation of the fibers occurs in a direction perpendicular to the plane of the cross-section of the rolls, or parallel to the axes of the rolls. A clear example of this kind of rolling is the rolling-out of dough. In this case the rolling bodies are sometimes given the form of planes, or more precisely, a body with a flat face, moving backward and forward; the flat faces may be arranged horizontally, vertically, or obliquely. Preference should be given to the last arrangement of the rolling planes, because inclined forces facilitate the passage of the billet. As an example one may cite the method, patented in 1861, for rolling wagon axles by the Fren-

ingot of E. Martin. By transverse rolling one obtains bolts, screws, and projectile capsules with ovally conical ends. In the technical literature there are often indications that the rolling of boiler links and tubes, practiced at present on a large scale at the Reisholz works in Düsseldorf, and also at some English works, chiefly of the naval department, is likewise carried out according to the principle of transverse rolling. But this is unquestionably incorrect. It is precisely in hollow bodies that the principle of transverse rolling loses the ground beneath its feet.

3) As for helicoidal, screw, or inclined rolling, according to Codron it occupies an intermediate place between longitudinal and transverse rolling. By helicoidal rolling one obtains tubes by the Mannesmann method, Galloway tubes, corrugated tubes of Field, Fox, etc.

For the present it may be said that only longitudinal rolling occupies a dominant position in technology, while the other varieties have to play a secondary role; but, of course, this phenomenon is temporary. War gives birth to heroes, and life is a continuous war, only of a more meaningful character. Already with the appearance of such men as Mannesmann and Ehrhardt, the attitude of engineers toward transverse and helicoidal rolling changed fundamentally. It became clear to everyone that, from the realm of assumptions, conjectures, and generalizations of a projective character, the matter had passed into the crucible of vital tests and had at once taken a deserved and honorable place.

Codron’s classification of rolling is not widely disseminated among engineers. Usually they adhere to the division of rolling into heavy-section and light-section rolling. How characteristic such a division of rolling is for the very nature of the process, I leave to the reader to judge; personally, this classification satisfies me least of all. Having set forth in the most general outlines the essence of the varieties of rolling and its types, I have left room for a personal view of questions of rolling. These views I intend later to share with the circle of engineers.

I do not share Professor Codron’s views on rolling entirely, but I find much in these views deserving of attention. Least of all am I satisfied by the division of rolling into longitudinal, transverse, and helicoidal. In Professor Codron’s views little space is allotted to clarifying the question of changes of form in the material being worked itself. And yet he has much data for drawing the picture in full

a finished form. This is indicated indirectly by the fact that he included rolling in the domain of forging, which fully corresponds both to its historical origin and to the very nature of the phenomena in rolling. However, he gives no positive answer, no logical conclusion from entirely correct premises. This uncertainty can only harm the matter and introduce confusion into the concepts of rolling and rolling mills.

Personally, it seems to me that, in questions of rolling, it is simpler and more expedient to proceed from the foundations of so well-developed a science (of course, only relatively) as the strength of materials, and, on the basis of these foundations, to treat questions of rolling. I hasten, however, to make the reservation that by the definition “well-developed” I refer chiefly to the cold strength of materials, but by no means to the strength of materials heated at least to a bright-red heat. The strength of heated materials is still a field little touched upon, and if in certain parts there do exist deviations from this general proposition, then these very conclusions have not yet managed to enter into everyday practice. To the ordinary engineer who is not a specialist, these conclusions are in most cases unknown. In my opinion, metallography, that wondrous flower of modern technology, will have to play a prominent role here. If it becomes possible to obtain polished sections of heated materials and to observe, depending on changes in temperature, the regularity of changes in the structure of materials, such as, for example, the transformation of austenite into sorbite, decomposition into pearlite, and so on, then the entire doctrine of the resistance of heated materials will be placed on a purely scientific basis. But this, of course, is a matter for the future.

As the nearest position of ours, let us choose the treatment of the question of cold rolling from the point of view of the strength of materials.

Let us take the simplest case of longitudinal rolling, when, between two cylindrical rolls, for example, strip or square iron is being rolled. For the time being let us turn our attention to the transverse section of the billet (Fig. 2). Under the influence of the dynamic pressure of the rolls upon the billet, the outer fibers tend to draw closer together. But since the pressures from above and below are opposite to one another, the fibers must seek an outlet along the line of least resistance. There will obviously be three such lines, or directions of least resistance, for the movement of the fibers. Two of these directions go along

by the sides, and the third in the direction perpendicular to the plane of the drawing. This third direction is the most convenient for the exit of the rolled strip, since in this direction there also acts the resultant force of friction on the periphery of the rolls. As for the two lateral symmetrical directions, for the fibers to move sideways they must bend to the sides, as is shown approximately in Fig. 3. Thus, widening of the billet occurs as it passes through the rolls. One may imagine that along the line \(M M\) a separating plane is formed. We shall conventionally call this plane neutral. The projection of this plane onto the profile plane is represented by a straight line. This consideration will serve as a characteristic for rolling of the first kind.

Fig. 3

Rolling of the second kind will be that in which a true neutral layer is formed in the bar being rolled. Let us imagine that we are rolling a boiler shell course, a ring, a tire, and so forth. It is obvious that the outer layers will be stretched, while the inner ones will be compressed, and that somewhere between these extreme layers there will lie a layer of unchanged length, the neutral layer. In a circular body (a hollow cylinder, a pipe) bent along a circular cylinder, in each transverse section this neutral layer will be a circle of planar character, if widening is neglected. If the diameter of the circular cylinder is infinitely large, and widening is also neglected, then rolling of the first kind is obtained.

The second kind of rolling of an ideal character, therefore, exactly resembles the phenomenon of bending.

If the first kind of rolling is characterized as “stretching,” then the second kind of rolling should justly be given the name “bending.”

Finally, to the third kind of rolling we shall assign those phenomena in which the neutral layer, or better, the axis of each fiber, will be not of planar character, but of curvilinear-surface character.

Formulating briefly the subdivision of rolling into heterogeneities, one may say that rolling of the first kind has a neutral layer in the fiber—a line of the first order; the second kind of rolling has a neutral layer—a line of the second order; and the third kind has a neutral layer—a line of the third and higher orders.

In fact, in all kinds of rolling, the phenomena of change of form of the material fibers will be very complex. Thus, for example, in tensile rolling there will be not only tension and bending, but also shear. This occurs because, in such rolling, three periods are observed: 1) when the outer layer of the billet is sheared and the middle layer is pushed back (in this period the velocity at the periphery of the billet is greater than the velocity of the neutral layer); 2) when there is no shear (the velocity at the periphery and in the neutral layer is one and the same); 3) when the shear is in the direction opposite to the first (the neutral layer runs ahead of the motion of the particles at the periphery). These phenomena, first established by Hollenberg’s experiments, partly explain the widening of the billet at the beginning and at the end of the arc of contact at the rolls. In a somewhat distorted representation the picture appears as follows (Fig. 4).

Fig. 4.

With regard to bending rolling with the formation of a neutral layer, the following may be said: here, of course, we are not dealing with pure bending. Here there are also tension, and compression, and bending, and shear; that is, a deformation phenomenon of great complexity—

ness. To take these phenomena into account in all their fullness in the language of mathematical analysis appears to be an extraordinarily difficult task—indeed, perhaps a rather unproductive one. The point is that, as the starting point, one would have to take the operation on a material of ideal structure, i.e., to repeat, to a certain degree, Klebs’ error. It is far simpler to introduce the concept of predominant deformations and, neglecting secondary ones, to solve the problem with a certain approximation. Rolling of the second kind may, for example, be considered as a combination of the phenomena of bending and stretching. As for phenomena that are deliberately not taken into account, practice has long since worked out a means of bypassing the incompleteness of theoretical investigations by introducing proportionality coefficients.

And, finally, still more complex are the phenomena of deformation in rolling of the third kind. Undoubtedly, here we have the manifestation of all the simplest deformations: stretching, compression, bending, torsion, and shear. One of these deformations will be assigned the dominant position in the process, while another will occupy a more modest place.

Depending on the character of the form of the product obtained, it is possible, with a degree of accuracy sufficient for practice, to distribute the roles among the agents of deformation and, consequently, to take the phenomenon into account in the language of analysis.