AU2000279370A1

AU2000279370A1 - Apparatus for rolling workpieces, particularly metal foils

Info

Publication number: AU2000279370A1
Application number: AU2000279370A
Authority: AU
Inventors: Antal Pelcz
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-03-21
Filing date: 2000-10-13
Publication date: 2001-10-03
Also published as: HUP0001196A2; BR0017177A; KR20020087421A; HK1052666A1; NO20024533D0; CA2401912A1; CZ20023173A3; RU2002124861A; BG107129A; CN1452524A; EP1274522A2; PL363225A1; WO2001070423A3; WO2001070423A2; YU70302A; NO20024533L; HU0001196D0; JP2003527968A

Description

APPARATUS FOR ROLLING WORKPIECES. PARTICULARLY METAL

FOILS

Technical Field

The invention is related to an apparatus for rolling workpieces, such as metal sheets and rods, particularly metal foils.

Background Art

As it is known, in the course of rolling, the raw material is driven through roll stands and workpieces are rolled by the rolls to the desired thickness or profile in one or more steps. In the course of rolling, due to plastic shaping, the hardness of the material is increased as the material structure is aggregated, but its tensibility decreases. It is known that cold-rolled workpieces are of particularly high dimensional accuracy and with good surface properties.

Foils, such as aluminium foils, are rolled at present between 'closed' working roils by stressing while being coiled up and down. As a result of the working rolls being closed, the roll stand acts as a pre-stressed stand, and the 'roll gap' is actually provided when the foil is inserted. The shape of the strain area, due to a considerable flattening of the working rolls, is varied or distorted as com- pared to sheet rolling, which is taken into consideration when calculating the rolling force. The working rolls, the bearings, and the elastic deformation of the stand halves, as well as the low strength of thin foils limit the thickness of foils to be rolled in one piece, which is about 12 micrometers.

As regards roll stands used today, one or more working roll pairs collaborating with each other are embedded, at their two ends, in a rotary manner in bearings arranged in the roll stands, and all working rolls are connected to rotary drives. Furthermore, the working rolls are associated with a generally mechanical or hydraulic roll adjustment device positioned transversally to the rolling direction, together with which the working rolls are displaceable at their two respective ends in order to adjust rolling pressure and the rolling gap. The apparatus further comprises devices for leading the workpiece in and out.

A common characteristic of the known rolling equipments is that working rolls suffer deformations due to bending as a result of relatively high rolling pressures. These are partly eliminated at present by arranging free-turning back-up or supporting rolls behind the working rolls, parallel with said working rolls. The role of said supporting is to support the working rolls by preventing working roll deformations. The supporting rolls are arranged at the external side of working rolls in one or more pairs.

US-4,611 ,479 describes such an apparatus for rolling metal foils, where a pair of working rolls is supported by a respective back-up rolls. Here foil thickness differences are desired to be eliminated by arranging pressure units to be regulated externally within the skirt of the outside back-up roll, the pressure force of which are controlled by signals of pressure sensors arranged on the foil to be pressed. This solution disregards the embedding of working rolls, intending to improve only the back-up rolls. A similar solution is disclosed in US- 4,480,452, wherein the two working rolls are also supported by external back-up rolls, and hydraulic power cylinders are applied as pressure units in one of the back-up rolls in order to achieve a more even pressure force, and to decrease foil thickness dispersion.

However, practical experience shows that the enforced rolling of back-up rolls applied for various rolling procedures entails considerable friction and roll deformation. On the other hand, significant roll abrasion is to be taken into ac- count. Friction losses, of course, increase the demand for drive force, which greatly increases the operational costs of the apparatus. Deformation and friction due to back-up rolls result in a relatively low lifetime and frequent replacement of working rolls, which entail enforced machinery outages, lapses of working time as well as considerable costs. Disclosure of the Invention

The objective of the present invention is to eliminate the deficiencies mentioned above, that is, to provide an improved apparatus for rolling workpieces, particularly foils, which can be constructed much more simply, and which can reduce ^' the deformation of the working rolls. A further object is to provide an apparatus which can be operated for a longer lifetime and more economically than the above mentioned traditional equipments.

According to the present invention an apparatus has been provided for rolling workpieces, such as sheets or rods, particularly metal foils, comprising: • at least one roll stand;

• at least two driven working rolls rotatably embedded in said roll stand, cooperating with each other in rolling said workpiece to a required shape and/or size, located orthogonally to a rolling direction;

• at least one of said working rolls is displaceable within said roll stand, or- thogonally to the direction of rolling, and is associated with a pressure unit which is capable to exert rolling pressure to said working roll;

• at least one of said working rolls is without any back-up rolls, and is embedded in a rotary manner into a bearing bracket located opposite to the rolling area, supporting at least a part of an external surface of said working roll as a trough;

• means for providing a lubricant film between the external surface of said working rolls and the bearing bracket, preferably at least one inlet channel or groove-like fluid chamber being provided in the part of said bearing bracket embedding said working roll; • said means is connected to a fluid source;

• said working roll is connected via said bearing bracket to said pressure unit for transferring rolling pressure;

« said pressure unit is provided as a means for transferring rolling pressure evenly along the length of said bearing bracket, preferably as one or more hy- draulic power cylinders. According to a further feature of the invention said bearing bracket is provided with a central fluid chamber located in the longitudinal middle plane of the apparatus, arranged transversally to the rolling direction and/or at least one lateral fluid chamber arranged laterally from said longitudinal middle plane, said fluid chamber/s is/are advantageously connected to an individually controllable fluid source.

Preferably, said pressure unit is arranged along about the whole length of the bearing bracket and comprises a series of hydraulic power cylinders, which are preferably connected to a common pressure fluid source.

According to the present invention, said central and/or lateral fluid chamber, connected to fluid sources with controllable pressure, and are formed as hydro- dynamic bearings for said working surfaces of the working rolls. So, in the arrangement according to the invention, the traditional embedding system at the two ends of the rolling working rolls has been departed from and embedding is actually solved by'bearing brackets embedding the working rolls on their external sides as a trough along the majority of their operational surface. The means for providing a lubricant film between the external surface of said working rolls and the bearing bracket may contain a nest-like or groove-like fluid chamber provided in the part of the bearing bracket embedding the working roll, and it is connected with a lubricant fluid source, thereby creating a hydrodynamic bearing support on the surface of the working roll also participating in rolling, in a unique manner.

The bearing bracket is a rigid unit in itself, affected by the rolling pressure of the pressure unit, evenly distributed along the entire operational length of the working roll. Therefore, in this arrangement, the rolling pressure can be guaranteed to be transferred evenly via the bearing bracket to the working roll, so back-up rolls, as applied forcibly in traditional art, become unnecessary, the application of which entails the harmful consequences as described above.

Due to the measures above, therefore, a surprisingly simple and well sizeable solution is provided by the present invention, which results in surprising additional effects for operators with highly favourable operational and economical consequences, such as longer working roll life, lower abrasion, lower drive energy demand, etc.

Brief Description of the Drawings

The invention is described in more detail in the drawings enclosed, showing an embodiment of the apparatus according to the invention. The drawings show the following:

• Figures 1A and 1B illustrate a perspective view of an embodiment of the apparatus according to the invention, with structural parts partly removed;

• Figure 2 illustrates a side view of the solution according to Figure 1 A; • Figure 3 illustrates a section of Figure 2 along line Ill-Ill;

• Figure 4 illustrates a front view of the solution according to Figure 2;

• Figure 5 illustrates a cross-section of Figure 4 along line V-V;

• Figure 6 shows more details of the solution according to Figure 5, together with accessories; • Figure 7 shows more details of Figure 6.

Description of an Embodiment of the Invention

The possible embodiment of the apparatus according to the invention as illustrated on the drawings serves for rolling metal foils. It comprises a roll stand 1 , which, in the present case, is provided with one pair of working rolls 2 and 3 for rolling metal foils. These are, according to the invention, especially embedded to be able to roll, to be described below. The working rolls 2 and 3 are arranged transversally to a rolling direction (moving direction of a foil) indicated by arrow 4, as illustrated in Figure 6.

The working rolls 2 and 3 are provided with an 'axle stub 5 and 6, respectively, protruding sideways from roll stand 1 and connected to a rotary drive, not included in the drawing, such as a change-speed electric motor. In Figure 2, arrows 7 and 8 indicate the direction of rotation of the working rolls 2 and 3, respectively, illustrating that they rotate in opposite directions. A working length of co-operating outer cylindrical surfaces 9 and 10 of the working rolls 2 and 3, respectively, to roll workpieces, particularly aluminium foil in the present case, is designated by L, which actually participate in rolling the foil (Fig. 3).

According to the invention, the working rolls 2 and 3 are embedded in a rotary manner in the roll stand 1 not at their respective ends; furthermore, no back-up or supporting rolls are applied as it is customary in traditional solutions. In sharp contrast, in the arrangement according to the invention, the working rolls 2 and 3 are embedded in a rotary manner into bearer brackets 11 and 12, respec- tively, supporting and embedding at least a part of the external cylindrical surfaces 9 and 10 of the working rolls 2 and 3 co-operating in the rolling of foils.

In the present case, the bearer brackets 11 and 12 are arranged as mirror images of each other, as reflected to the rolling direction indicated by the arrow 4. Each of them is provided with means for providing a lubricant film between the external surface 9, 10 of said working rolls 2, 3 and the bearing bracket 11 , 12. In the present case, said means are formed as groove-like lubricant chambers 29 and 30, respectively, in the parts of the bearing brackets 11, 12 embedding the working rolls 2 and 3, which are connected to a lubricant fluid source of controllable pressure, discussed bellow. It is to be noted that such means can also be formed as an inlet channel for lubricant, being in communication with the surfaces of said rolls 2, 3 and/or of said bearing brackets 11, 12 (not illustrated).

The bearer brackets 11 and 12 are substantially rigid, and in the present case, embedding the surfaces 9 and 10 of the working rolls 2 and 3 along their entire length, their dimensions being such that they can provide equal support for working rolls 2 and 3 when rolling pressure is applied, therefore ensuring the required constant foil thickness for greater foil widths as well, thus higher product quality.

According to the invention, at least one working roll in the pair of working rolls is associated with a pressure unit, capable to exert a rolling force - designated by arrow N - to the working roll transversally to the direction indicated by arrow 4 (Fig. 6). In the illustrated embodiment of the invention, each of working rolls 2 and 3 are provided with a pressure unit 13 and 14, respectively. But, they transfer the rolling pressures to the working rolls 2 and 3 by the interposition of the bearer brackets 11 and 12, respectively, as shown in Figures 5 to 7.

The pressure units 13 and 14, as a series of hydraulic power cylinders H, are arranged in the present case (see Figures 1A and 3) serially beside each other, being connected to a common fluid source 41 providing controllable oil pressure and oil quantity (Figure 7). Therefore, the pressure units 13 and 14 are arranged, according to the invention, so that they can transfer even rolling pres- sure along the entire length of bearer brackets 11 and 12, respectively.

It is to be noted that in the arrangement illustrated in Figure 3, the roll stand 1 is provided with the hydraulic power cylinders H, as the pressure units 13 and 14, wherein their cylinders 38 are arranged adjacent to each other. However, it is also possible to arrange these cylinders 38 with a gap between each other. In Figure 3, the cylinders of the eight hydraulic power cylinders H are fixed into roll stand 1 at both side edges by locking collars 15.

It can be seen in Figure 4 and 5, that the roll stand 1 is provided with cover plates 16 and 17 on both sides, respectively, which comprise an inlet opening 18 to enter and an outlet opening 19 to exit a workpiece to be shaped, respec- tively. The length of inlet and outlet openings 18, 19 can be adjusted according to the width of the foil to be produced (not illustrated).

It can be seen in Figure 6 that the apparatus for rolling foils according to the invention is provided with known devices for leading in and out the workpiece to be rolled, including a storage drum 20 for storing the foil material to be worked in a roll, and a foil drum 21 for rolling up and pulling down the ready-made foil, which are shown only schematically. Arrows 22 and 23 show the rotation directions of the storage drum 20 and the foil drum 21, respectively. In Figure 6, the foil to be worked is referred to by the reference number 24 and indicated by a thicker line, whereas the ready foil following rolling is referred to by the refer- ence number 25 and indicated by a thinner line. Furthermore, in Figure 6, arrows indicate the rolling pressures exerted by the pressure units 13 and 14. As it has been mentioned in the introductory part of the description, the outer working surfaces 9 and 10 of working rolls 2 and 3 are in abutment with each other when the foil is being roiled, therefore there is practically no measurable "rolling gap" in the basic position of the apparatus between the co-operating rolls 2 and 3. That is why, in the present case, the working rolls 2 and 3 are only required to be supported axially, which is provided by covers 26 and 27 at the both sides, shown only schematically on the roll stand 1, which are fixed in a detachable manner to the locking collars 15 (Figure 3).

\t has been mentioned earlier that the bearer brackets 11 and 12 are provided with means for providing a lubricant film between the external surface 9, 10 of said working rolls 2, 3 and the bearing bracket 11 , 12, preferably at least one groove-like fluid chamber in their part embedding the working rolls 2 and 3, respectively, connected to a lubricant fluid supply unit, advantageously providing controllable pressure, which is, in the present case, a lubricant supply unit. Un- der the term "lubricant" all materials and fluids having lubricant characteristics are to be understood, such as oils, water, or emulsions thereof, etc.

In the arrangement illustrated in Figure 7, each of the bearer brackets 11 and 12 are provided with a central fluid chambers 29 and 30, respectively, formed as longitudinal grooves located in a longitudinal middle plane 28 of the appara- tus, which lies transversally to the direction indicated by the arrow 4. Both central fluid chambers 29 and 30 are extended along the entire length l_ of the operating surfaces 9 and 10 of the working rolls 2 and 3, respectively, as shown in Figure 3 (it is to be noted that the size of the grooves is highly exaggerated for the sake of better illustration).

The fluid chambers 29 and 30 are connected to a common fluid source 31 via lines or pipes, which are indicated in the present case by thin dash-and-dot lines only, which fluid source 31 is capable to provide a lubricant, e.g. oil of controlled quantity and pressure. On both sides of the longitudinal middle plane 28 of the apparatus, as in the illustrated embodiment of the apparatus according to the invention (Fig. 7), the bearer brackets 11 and 12 are also provided with two lateral fluid chambers 32, 33, and 34, 35, respectively. These are also formed as longitudinal grooves in the bearer brackets 11 and 12, extending to the ends of the bearer brackets.

In the arrangement shown in Figure 7, the fluid chambers 33 and 35, and 32 and 34 are connected to each other, respectively (connecting lines and pipes ^" are indicated schematically by thin dash-and-dot lines), which are attached to a fluid source 36 and 37, respectively, which are fluid supply units with controllable pressure. The opposite fluid chambers 32 and 33, and 34 and 35 may also be connected to each other in order to adjust or equalise the operational oil pressures on both sides.

Figure 7 illustrates a more detailed sectional view of a hydraulic power cylinder H of each of the pressure units 13 and 14, respectively. The cylinders 38 of the hydraulic power cylinders lj_are fixed into the roll stand 1 in the present case as illustrated; front surfaces of their pistons 39 are axially displaceable in the corresponding cylinders 38, and are supported against outer surfaces of the bearer brackets 11 and 12, respectively. Internal oil chambers 40 of the hydraulic working cylinders H are connected to a fluid source 41 via pipes indicated by thin dash-and-dot lines. These can provide the apparatus with an operating fluid, in the present case with hydraulic oil, at a pressure required for rolling. It is to be noted that although connections are not illustrated separately, said fluid sources 31 , 36, 37, and 41 are connected to a central control device 42, which may comprise a known computer (not illustrated) suitable for rolling process control.

In Figure 7, the lateral fluid chambers 32, 33, 34 and 35 are also mirror- symmetric to the plane of the direction indicated by the arrow 4, as well as to the longitudinal middle plane 28 on the two sides thereof, such that an angle α is formed between their longitudinal middle plane 28 and the roiling direction indicated by the arrow 4. In the present case, this angle is 30°.

It is to be noted that such embodiment is also possible, where one or both of the lateral fluid space/s is/are abandoned or more than two of them are applied. Their basic role thereof is to provide embedding support for the working rolls 2 and 3. Such lateral loads affect the working rolls 2 and 3 as loads arising from the pull-off force of the workpiece to be processed, on the one hand, and there are also presented lateral bending forces arising from the rotary drive of the working rolls^' 2 and 3, depending on the drive type and arrangement, on the other hand, which can be simply taken up by this way.

^' Therefore, in^' the shown embodiment, a pressure force is exerted to working . rolls 2 and 3 transversally to the rolling direction indicated by the arrow 4 by the pressurised lubricant driven into the fluid chambers 29 and 30, and this pressure value is to be selected such that fluid bearing embedding can be achieved. A precondition for this is that there always should be a continuous lubricant oil film on the embedded surfaces 9 and 10 of the working rolls 2 and 3 in the course of operation. The lubricant oil entered into the two respective lateral fluid chambers 32, 33, and 34, 35 at the required pressure also assist in providing hydrodynamic bearing; however, as it has been mentioned above, support is thereby provided against the lateral loads as well.

Possible embodiments include ones in which hydrodynamic support is provided for working rolls 2 and 3 only on one side, for which only one of the iateral fluid chambers is applied. In other applications, however, the central fluid chambers 29 and 30 can also be abandoned and substituted by one or more lateral fluid chambers.

In the apparatus described above, the central control device 42 can regulate the current rolling pressure N such that the pressures in the central fluid chambers 29 and 30 and in the oil chambers 40 are advantageously harmonised with the pressure value required for providing. hydrodynamic bearing. That is, a continuous oil film is provided all the time besides the. required rolling pressure N, by way of the oil pressure in the central fluid chambers 29 and 30. Consequently, the fluid sources 31 and 41 are required to be controlled in correlation in this sense. The details thereof, however, are obvious to an expert generally skilled in the art on the basis of our description.

The operation of the embodiment of the apparatus as illustrated is to be de- scribed in relation with Figures 6 and 7. In operation, the raw foil 24 to be rolled is aluminium foil with a width of 1000 millimetres and a thickness of 300 micrometers) which is fed from the storage drum 20 through the inlet opening 18 to the feeding area of the working rolls 2 and 3. During the rolling operation our objective is to receive the ready foil 25 of 150-micrometer thickness after being lead through between the working rolls 2 and 3. The finished foil 25 as product has been produced this way and being rolled onto the drum 21.

The diameter of the working rolls 2 and 3 were selected as 100 mm for our experiments. The value of rolling pressure (arrow N) was adjusted experimentally according to the desired 150-mm thickness of the finished foil 25 as product (e.g. 50 bars) by duly controlling the fluid sources 31 and 41 , respectively. This can be simply performed by an expert skilled in the art, since the basic data for this controlling step are provided by the measurable thickness of the ready foil 25 as finished product.

In the present case, hydraulic pressure is adjusted for the lateral fluid chambers 32 to 35, according to the lateral loads of the working rolls 2 and 3, by the fluid sources 36 and 37. The oil pressure in the central fluid chambers 29 and 30 as well as in the lateral 32 to 35 fluid chambers was defined so that there was a continuous lubricant film on the embedded surfaces 9 and 10 of the working rolls 2 and 3 during rolling, that is, hydrodynamic bearing is provided all throughout the rolling process. The oil as working fluid also serves for cooling the working rolls 2 and 3 as well as the bearing brackets 11 and 12.

In the illustrated apparatus according to the invention, a roll adjustment device is provided by the pressure units 13 and 14, formed in the present case as hy- draulic power cylinders H; however, they can be replaced by any other mechanic, electro-mechanic or pneumatic devices 'being capable to exert the rolling pressure.

So, before the foil 24 to be worked is introduced in between the working rolls 2 and 3, the working rolls 2 and 3 are closed, that is, adjacent to each other. Therefore, actually, the 'rolling gap' is formed when the foil 24 is started to be formed, that is, introduced. The shape of the forming area is actually produced by the deformation of the working rolls 2 and 3, which should be taken into consideration when calculating the rolling pressure N.

The working rolls 2 and 3 are made of forged chromium steel; the surfaces are shaped by surface chilling to achieve a hardness of 95 to 100° Shore. The de- ^' gree of shaping (decrease of thickness) within one introduction of the foil 24 can be adjusted by controlling the rolling pressure N. Of course, the apparatus according to the invention may also have several pairs of working rolls, and more roll stands arranged along the foil path, which may decrease the thickness of the workpiece to be shaped in a series of introductions in the course of several operational phases until the desired thickness of the finished product is achieved. The foil 25 after the first rolling can be re-introduced into the same pair of the working rolls 2 and 3 for a further rolling step.

The main benefit of the invention is that it provides a considerably simpler and more economical solution by eliminating the back-up rolls and by providing a new embedding system for the working rolls, thus eliminating abrasion and energy losses which are inevitable in the case of the know solutions. So the basic idea of the invention lies in that the pair of working rolls 2 and 3 is supported by the bearing brackets 11 and 12 embedding the operating surfaces 9 and 10, where hydrodynamic bearing conditions are provided during the whole opera- tion. The pressure units 13 and 14 transfer the rolling pressure N via the bearing brackets 11 and 12 to the working rolls 2 and 3. The bearing bracket 11 and 12 can be made rigid enough to prevent the rolling pressure N from deforming the working rolls 2 and 3 to an extent that the quality of the finished product would be affected.

The same is the purpose of the arrangement of more pressure units 13 and 14 along the length of the bearing brackets 11 and 12, therefore the rolling pressure N can be transferred much more evenly, which provides a further guarantee that the harmful deformations of the working rolls 2 and 3 can be avoided.

With a view to the fact that back-up rolls applied in traditional solutions, which are burdened with abrasion losses, have been completely eliminated, the drive energy demand of the apparatus according to the invention is relatively low. Consequently, operational costs are also decreased. Another important advantage is that by eliminating back-up rolls, the technical obstacle to the production of foils or other rolled products practically in any width has completely been eliminated. There has been a consumer demand for producing wider foils, since their printing and further processing is much more economical.

It is to be mentioned that although the embodiment presented is suitable for rolling foils, theoretically an embodiment of the apparatus according to the invention may be similarly provided for rolling metal sheets or other rod-like profiled products. As regards such embodiments, however, the ends of working rolls should be embedded, for example in the ends of the bearing brackets, too, in order to adjust the rolling gap.

The material of the bearing brackets 11 and 12 can be any material presently applied in bearing technology as bushing material. Of course, not the entire bearing bracket needs to be made of such materials: it is sufficient if only the embedding part is made of such bushing material, and the other parts of the bearing brackets can be made of other materials of adequate rigidity, such as steel, for example.

Finally, we note that many amendments, combinations or variations of the above embodiments of the invention are possible within the scope of the claims, but these do not require any additional teaching for a person having ordinary skill in the art, in view of the above disclosure.

Claims

1. An apparatus for rolling workpieces, such as sheets or rods, particularly metal foils, comprising:

• at least one roll stand (1);

• at least two driven working rolls (2, 3) rotatably embedded in said roll stand (1), co-operating with each other in rolling said workpiece to a required shape and/or size, located orthogonally to a rolling direction (4); • at least one of said working rolls (2, 3) is displaceable within said roll stand (1), orthogonally to the direction of rolling (4), and is associated with a pressure unit (13, 14) which is capable to exert rolling pressure (N) to said working roll;

• at least one of said working rolls (3, 4) is free of any back-up rolls, and is embedded in a rotary manner into a bearing bracket (11, 12) located opposite to the rolling area, supporting at least a part of an external surface (9, 10) of said working roll (2, 3) as a trough;

• means for providing a lubricant film between the external surface (9, 10) of said working rolls (2, 3) and the bearing bracket (11, 12);

« said means for providing the lubricant film is provided with a lubricant fluid source;

• said working roll (2, 3) is connected via said bearing bracket (11, 12) to said pressure unit (13, 14) for transferring rolling pressure;

• the pressure unit (13, 14) is provided as a means for transferring rolling pressure (N) evenly along the length of said bearing bracket (11, 12), preferably as one or more hydraulic power cylinders (H).

2. An apparatus according to claim 1, characterised in that said bearing bracket (11 , 12) is provided with a central fluid chamber (29, 30) located in the longitudinal middle plane (28) of the apparatus, arranged transversally to the rolling di- rection (4) and/or at least one lateral fluid chamber (32, 33, 34 and 35) arranged laterally from said longitudinal middle plane (28), said fluid chamber/s is/are advantageously connected to an individually controllable fluid source (31, 36, 37).

3. An apparatus according to claim 1 or 2, characterised in that said pressure unit (13, 14) is arranged along the length of said bearing bracket (11, 12) and comprises a series of hydraulic power cylinders (H), which are preferably connected to a common pressure fluid source of controllable pressure.

4. An apparatus according to claim 1 or 2, characterised in that said central and/or lateral fluid chamber/s (29, 30, 32-35) connected to fluid sources (31, 36, 37) of controllable pressure, are formed as hydrodynamic bearings for said working surfaces (9, 10) of the working rolls (2, 3).

5. An apparatus according to any of claims 1 to 4, characterised in that said means for providing the lubricant film is at least one inlet channel, or at least one groove-like fluid chamber (29, 30; 32 to 35) being provided in the part of said bearing bracket ( 1, 12) embedding said working roll (2, 3).