EP0037752B1 - Device for guiding webs and its applications - Google Patents

Description

The present invention relates to devices for guiding a strip material, of the type comprising at least two series of rollers situated in different horizontal planes, and in which the strip passes alternately from a roll of a series to a roll of 'another series.

Such devices are used in particular in vertical accumulators of the type described in patent FR-A-1248731 the accumulators are interposed in continuous strip processing lines, so as to constitute a reserve of strip making it possible to slow down or stop the line upstream of the accumulator while maintaining the downstream operating speed, or vice versa, slowing down or stopping the line downstream of the accumulator while maintaining the normal upstream running speed. In such an accumulator, there is provided a series of fixed lower (or upper) rollers and a series of upper (or lower) rollers carried by a frame which can be moved vertically depending on the length of material present at a given time in the accumulator.

A similar arrangement is also used in continuous treatment ovens and in particular in annealing ovens in which to obtain a sufficient treatment time, the strip follows a winding path alternately passing from a roll of a series to a roller from another series. However, in this application the distance between lower and upper rollers is constant.

In order to obtain self-centering of the strip on each of the rollers, a biconical or domed shape is chosen for the latter, of generally parabolic section, the maximum diameter of which is situated in the median plane of the roller. With such an arrangement, any accidental offset of the strip unbalances the reactions on contact between the strip and the roller by favoring the off-center side which, due to the offset, has a larger contact surface than the other side, resulting in a Almost automatic re-centering of the strip, However, given this convex shape, the length of the generators of the strip varies depending on whether one is in a middle section of the rollers or in an edge section, so that to obtain contact satisfactory between the rollers and the strip, and consequently, correct guiding, it is necessary to exert high tensile forces in particular for sheets of thickness greater than 2 mm. This is a serious drawback.

In fact, in the application to vertical accumulators, the total force exerted on the structure of the tower supporting the series of rollers, and which is constituted by the sum of the tensile forces exerted on each strand, becomes very large. so that one is led to carry out heavy and expensive constructions.

Furthermore, in the second application envisaged above, in the hot chambers of continuous annealing ovens (heating and holding chambers) the strip brought to relatively high temperatures can only withstand very low tensile forces. In the heating zone, the rolls are brought to a high temperature and the strip is significantly cooler than the roll. It follows that the expansion of the roller, stronger outside the strip than in the zone cooled by contact with this strip, produces an unfavorable thermal profile for the holding of the strip. Taking into account the temperature of the strip and the curved shape of the rollers, as well as the tensile force necessary to apply the strip against the rollers, it is possible to generate permanent deformation in the latter, in particular for very thin and wide strips. .

Finally, according to US Pat. No. 3,401,866, a device is known for guiding a material in dandelion in which the inclination of one or more rolls of vertical axes is varied relative to the direction of scrolling the strip to maintain the strip at an approximately constant level. However, this patent concerns a completely different technical sector (manufacture of masks for color television tubes), the problem targeted is different and the nature and dimensions of the bands are very far from those targeted by the invention. Furthermore, there are no two series of rollers located in different horizontal planes in this prior arrangement. This document is therefore not relevant to the subject of the invention.

The problem to be solved therefore consists in perfecting a guiding device of the type defined above, in order to allow satisfactory guiding and self-centering of the strip for traction levels lower than those which are necessary in known devices.

To this end, the subject of the invention is a device for guiding a strip material, characterized in that at least the rollers of each serue, which are arranged between the inlet and outlet rollers, have their parallel axes between them, and that seen in projection on a horizontal plane, the axes of the rollers of one series form with the axes of the rollers of the other series, an acute angle whose bisector is perpendicular to the mean direction of travel of the strip .

• -la Fig. 1 est une vue schématique en perspective montrant la position des rouleaux de guidage dans un accumulateur vertical selon l'invention;
• - la Fig. 2 est une vue en plan du dispositif de la Fig. 1;
• - la Fig. 3 est une vue de détail montrant les zones de contact entre la bande et le rouleau dans une condition de fonctionnement particulière;
• - la Fig. 4 est une vue, également schématique, d'un dispositif suivant l'invention appliqué dans un four de traitement thermique en continu.

The invention will be described in more detail below with reference to the attached drawing given by way of example and in which:

• -Fig. 1 is a schematic perspective view showing the position of the rollers guiding in a vertical accumulator according to the invention;
• - Fig. 2 is a plan view of the device of FIG. 1;
• - Fig. 3 is a detailed view showing the contact areas between the strip and the roller in a particular operating condition;
• - Fig. 4 is a view, also schematic, of a device according to the invention applied in a continuous heat treatment oven.

We see in Fig. 1 a device for guiding a strip material B which can, for example, be used in a vertical accumulator inserted in a continuous processing line. Such an accumulator comprises a tower, a fixed lower frame in which the rollers of a first series are journalled, and an upper frame movable vertically and on which the rollers of a second series are journalled. However, these various components and devices being perfectly known and conventional have not been shown in the drawing, a simple diagram sufficient to highlight the characteristics of the invention.

The device comprises an input roller 1 an output roller 2 of the accumulator, these two rollers with axes perpendicular to the direction XX of travel of the strip being situated at the same level as a series of lower rollers 3. The guide device is completed by a series of upper rollers 4. As can be seen more particularly in FIG. 2, seen in projection on a horizontal plane, the axes U-U and V-V of the lower and upper rollers form acute angles between them, the bisector Y-Y of which is perpendicular to the direction X-X of travel of the strip. In other words, the axes of the lower rollers and the axes of the upper rollers form, with respect to the normal to this direction, acute angles equal to and opposite, preferably less than 45 °.

qui correspond à une compensation parfaite.Although this does not appear on the drawing, given its small scale, the rollers have a convex shape and according to the invention, a relationship is established between the angle a and the value of this convex which can be characterized by the difference between the maximum diameter and the minimum diameter of the roller. Preferably, the roll has a parabolic profile. The relationship between the angle a and the convex value is intended to obtain compensation for the variation in length of the generatrices of the strip, between two consecutive rollers, which results from the convex shape of these rollers. If we call b the difference between the maximum and minimum values of the diameter of the roll, / the length of this roll and d the distance between the horizontal planes containing the axes of the upper and lower rolls, we preferably choose the angle a In a way that:

which is perfect compensation.

However, in the application considered, since the distance d is variable during the operation of the accumulator, it is impossible in practice to perfectly compensate for the differences in lengths along the path of the strip. If the angle a is greater than the value calculated according to the formula indicated above, the tension is higher at the edge and the edges of the strip are strongly applied while the contact may become worse in the center. Under these conditions, the guidance remains satisfactory because as the variation in cross section of the roller becomes greater as one moves away from its axis, it is the edge contact which is essential for the guidance. Conversely, if the angle a is less than the calculated value, the tension becomes higher in the central part of the strip and the latter is applied less tightly to the edges of the rollers. However, it can be seen as shown in FIG. 3 that the contact surface S between the strip B and the roller R in such a situation is such that this contact is maintained on the side where the twist of the strip tends to bring it closer to the roller so that the guidance remains satisfactory. We therefore choose a so that the above relationship is verified for an average distance between the two series of rollers.

According to a characteristic of the invention, the upper rollers and the lower rollers may not have the same convex characteristics, the upper rollers having a more marked profile than their lower counterparts. Indeed, under the effect of its own powders, the strip is applied more effectively on the upper rolls which can therefore have a greater variation in section than the lower rollers. This results in good contact of the strip with the rollers and perfect guidance for the entire useful travel of the accumulator.

By way of example, a roller accumulator is produced, the series of lower and upper rollers of which are inclined more or less 20 ° respectively from the normal to the line of displacement. The input and output rollers located as in the drawing roughly at the level of the fixed rollers are perpendicular to this line of travel The angle of twist of the input and output strands being smaller than in the normal part current of the accumulator, we adopt for these input and output rollers a significantly lower convex value. Thus, for an angle a of 20 ° and a maximum distance d of 80 meters between lower and upper rollers, the convexity of the input and output rollers is b = 1 mm for 1 = 2 m while the curved rollers of the clean accumulator ment said is between 2 and 10 mm and may preferably be of the order of 6 mm for the same length of 2 m.

As indicated above, it is advantageous to be able to provide a higher convex value for the upper rollers for which the tension of the strip is higher. Thus, for a strip of 3 mm thick and 1500 mm wide, and a roll diameter of 1000 mm, the minimum input tension is 3000 newtons and for an accumulator 80 m high, having a useful stroke of 60 m, the maximum tension at the level of the upper rollers is approximately 32,000 newtons. We can then choose a curved 9 mm for the upper rolls and 3 mm for the lower rolls. The minimum voltage at the output of such an 8-strand accumulator is approximately 15,000 newtons.

Thanks to the arrangement according to the invention and to the orientation of the axes of the upper and lower rollers, it is obtained that the lengths of all the generators of the strip between two consecutive rollers are approximately equal so that satisfactory contact strip with the roller can be obtained with a lower pull, just sufficient to bend the strip in contact with the roller. The different characteristics chosen for the input rollers, the lower rollers and the upper rollers make it possible to further improve this result.

Of course, the invention can be implemented under similar conditions in the case of a pit accumulator whose upper rollers are fixed and whose lower rollers are carried by a frame which can be moved vertically. In this case, the input and output rollers are located in the vicinity of the fixed upper rollers.

In another application (FIG. 4), a device according to the invention is used in a heat treatment oven 10 and in particular in an oven for continuous annealing of a strip material. In this application, the inlet 11 and outlet 12 rollers, the axes of which are normal to the line of travel of the sheet are located approximately halfway up the furnace and the guide device.

As in the previous example, the rollers 13 of the lower series are inclined at an angle + a relative to the normal to the line of travel, while the rollers 14 of the upper series are inclined at an angle -a compared to this same normal. This arrangement is particularly well suited to this application, since the distance between the upper and lower rollers is invariable, so that the relationship between the angle a and the convex value of the lower and upper rollers can be chosen so as to obtain a approximately constant generator length over the entire width of the strip in its path in the guide device.

Furthermore, in this case it is not sought to compensate for all the bulging given to the rollers but only the residual bulging after thermal deformation. By way of example, the following values can be given: the rollers having a diameter of 700 mm and a length of 1600 mm are spaced 18 m apart. The angles a are 15 °, which makes it possible to compensate for a bulge representing a difference in diameter of 3 mm. Taking into account the thermal deformations of the rollers, the convex machining at room temperature is between 4 and 8 mm for the rollers of the furnace heating zone and can be 2 to 4 mm for the rollers of the holding zone and cooling zones. The inlet and outlet rollers of each chamber are, as in the example shown, placed halfway up in the oven and are normal to the line of travel. The curved value of these input and output rolls is between 1 and 2 mm.

Of course, the heating devices which are incorporated in the oven and which in general extend from the side walls of the latter must be arranged taking account of the helical path of the strips inside the oven. The position and orientation of these heating elements is determined by the shape of the intervals delimited between two adjacent strands of the strip.

It follows from the foregoing description that the arrangement according to the invention makes it possible to provide a particularly effective and elegant solution to an important problem. The reduction in the tensile forces necessary to cause the correct driving and guiding of the strip in the device constitutes in fact significant progress in the various applications considered in particular when the strip is brought to a relatively high temperature and therefore risks undergo permanent deformation.

Claims (9)

1. A device for guiding a band of material, comprising at least two series of rollers (1, 2, 3, 4, 11, 12, 13, 14) contained in different horizontal planes, in which the band passes alternately from a roller of one series to a roller of the other series, characterized in that at least the rollers (3, 4, 13, 14) of each series, which are located between the input and output rollers (1, 11; 2, 12), have their axes mutually parallel and that when viewed in projection on a horizontal plane, the axes of the rollers of one series make with the axes of the other series an acute angle (a) whose bisector (Y-Y) is perpendicular to the mean direction (X-X) of travel of the band.

2. A device according to claim 1, characterized in that the axes of a series of rollers make with the perpendicular to the direction of travel of the band an angle a which is less than 45°.

3. A device according to claim 1 or 2, characterized in that the input and output rollers (1, 11; 2, 12) are perpendicular to the direction (X-X) of travel of the band.

4. A device according to claim 1, 2 or 3, comprising crowned rollers, characterized in that the values of said angle a and of the crown of the rollers are so chosen that the following relation is substantially satisfied:

in which b is the difference between the maximum and minimum diameters of a roller,

/ is the length of a roller,

d is the distance between the horizontal planes containing the axes of the upper and lower rollers.

5. A device according to claim 4, wherein the distance between the two series of rollers (3,4) is variable, characterized in that the values of said angle a and of the crown of the rollers are so chosen that said relation is substantially satisfied for a mean distance between the two series of rollers.

6. A device according to any one of the claims 1 to 5, characterized in that the upper rollers (4) are more crowned than the lower rollers.

7. A device according to claim 6, characterized in that the input and output rollers <1,2) are less crowned than the lower and upper rollers (3, 4).

8. A device according to any one of the claims 4 to 7, characterized in that the device operates at a given temperature and said angle a is so chosen as to compensate for the differences of length of the generatrices corresponding to the residual crown resulting from thermal deformation of the roller.

9. An installation for treating bands comprising a device according to any one of the claims 1 to 8, and heating means, characterized in that said heating means are disposed and oriented in such manner as to extend in gaps between adjacent portions or reaches of the band.

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