EP0393301A2 - Method and apparatus for continuous straightening of strips, in particular sheet metal strips - Google Patents

Abstract

The invention relates to a method for the continuous stretching of metal strips, according to which the respective strip runs through a set of braking rollers and a set of tension rollers and, in the course of its stretching in the plastic range, is subjected between the two sets of rollers to a stretching tension which corresponds to the yield strength of the strip material. In a pair of tension-stretching rollers inserted between the set of braking rollers and the set of tension rollers, the strip is subjected only to the stretching tension required for stretching it in the plastic range. The transverse strain in the course of the plastic stretching is thereby minimised, with the result that central troughs or, in the case of longitudinal strip division, lateral edges of unequal length no longer occur. <IMAGE>

Description

The invention relates to a method for the continuous tensile stretching of thin strips, in particular of metallic strips made of steel, aluminum or the like. Metals with a strip thickness between 0.05 mm and 0.5 mm, according to which the respective strip passes through a brake roller set and a pull roller set and between the two sets of rollers in the course of its stretching in the plastic region, a stretching tension is applied which corresponds to the yield strength or yield strength of the strip material or slightly exceeds this yield strength.

Train stretching systems with a brake roller set and a pull roller set are used to level thin metallic strips. Both roller sets have two or more rollers which are acted upon by staggered torques and consequently draws, so that the draw between the brake roller set and the pulling roller set required for the desired stretching is finally achieved. In the course of the stretching process, the plastic elongation of the strip in question is obtained from the reduction in the strip thickness and strip width. While the reduction in strip thickness is not hindered, the reduction in strip width in the transverse direction is hampered by the friction between the strip and the rollers in question so that transverse stresses build up from the strip edge to the center of the strip and consequently larger plastic deformations occur in the central strip area than in the edge area. In fact, the reduction in bandwidth in the transverse direction is hindered in particular because one uses as little as possible Wants to build up high stretching rollers and consequently uses rollers whose roller jackets are provided with a friction lining made of rubber, plastic or the like. Here, the last role of the brake roller set and the first role of the pull roller set have to transfer the maximum stretch on the belt according to a staggering of the coefficient of friction e ^µα . In any case, the stretching stretches generated are set such that the respective stretching limit or yield point of the band in question is reached between the last braking roller and the first tensioning roller and any lengthening of the band which can be set as desired. The longitudinal stresses that occur here cause the aforementioned transverse stresses, which are dependent on the strip material. The ratio of ε _cross to ε _{longitudinal ',} the so-called Poisson's coefficient µ, is between 0.25 - 0.3 for metals. If a longitudinal tension is applied to a band, the band is constricted both in the elastic and in the plastic area. Since the tape is prevented from sliding across the rollers, the transverse tension builds up from the edge to the center. In conjunction with the longitudinal tensions, this results in major changes in longitudinal shape in the middle of the belt. This applies to both the elastic and the plastic deformation, so that in the course of the stretching process more or less strong center bowls occur, which are particularly unsuitable for tapes for lithographic purposes. In addition, stretching in the plastic region occurs in the longitudinal direction, which is distributed unevenly over the bandwidth. If you cut such a tape in longitudinal strips for different print formats, the inner edges have slightly longer sides than the outer edges, which also disturbs. This effect is further enhanced by the fact that the band can press into the elastic coating of the roll shells, so that the band edges press into the roll shells more strongly in the edge region than in the middle band region.

The invention has for its object to provide a method and an apparatus for the continuous tensile stretching of thin strips, in particular of metallic strips, of the type described at the outset, according to which the strip transverse changes occurring during plastic stretching are reduced to a minimum and consequently the formation of central dishes and of over the bandwidth of unevenly distributed residual voltages can be almost eliminated.

This object is achieved by the invention in a generic method in that the strip is only subjected to the drawing stretch required for stretching it in the plastic area in an intermediate drawing stretching roller pair between the braking roller set and the pulling roller set. In this context, the invention teaches with independent importance that with the pair of tension stretching rollers about 5% - 25% of the maximum stretch for the plastic stretching and with the brake roller set and tension roller set 75% - 95% of the maximum stretching for the elastic stretching of the belt. - Within the scope of the invention, that is now generated by the brake roller set and the pull roller set, that stretching train which is required for the elastic deformation of the continuous belt. The rollers of the brake roller set and the pulling roller set therefore has a relatively high stretching component. This is not a problem, however, because the belt does not experience any permanent transverse changes in the course of its elastic deformation. In contrast, the plastic deformation of the strip in the course of the stretching process takes place only in the area of the pair of drawing stretching rollers, which has the remaining and comparatively low stretching component. The stretching required for the desired stretching of the belt is thus divided between the brake roller set and the pulling roller set for the elastic stretching on the one hand and the pair of tension stretching rollers for the plastic stretching of the relevant strip on the other hand. In this connection, the invention is based on the knowledge that only a low stress component is required for the stretching in the plastic region, that is to say in order to reach and, if necessary, to slightly exceed the yield or flow limit of the strip material. With a modulus of elasticity predetermined by the band material, this results in a correspondingly low transverse elongation. This in turn results in a relatively even distribution of tension over the bandwidth, so that the center dishes practically no longer occur and band lengths of different lengths are no longer to be feared after band length division. As a result, a flawless product is available even for lithographic purposes.

The invention also relates to a train stretching system which is particularly suitable for carrying out the claimed method and has a brake roller set and a train roller set in its basic structure. This train terran location is characterized in that a pair of draw rollers is arranged between the brake roller set and the pull roller set. The tensioning of the brake roller set, pair of draw rollers and pull roller set can take place in a known manner. In order to minimize belt cross changes in the course of plastic stretching and consequently in the area of the pair of drawing stretching rollers by means of a suitable roll design, the invention provides that the drawing stretching rolls have metallic roll shells, the surface of which is hardened or hard-coated and finely machined. As a result, the friction between the belt in question and the pair of tensioning rollers is minimized in such a way that transverse stresses no longer build up due to frictional influences from the belt edge to the belt center, but rather an essentially uniform tension distribution over the belt width is achieved. In this context, the invention provides that the roller shells of the pull rollers made of a metal alloy with a low coefficient of friction such. B. of austenitic cast iron with lamellar or spheroidal graphite, bronze alloys. Like. Consist. This also allows sliding without tendency to seize. The sliding effect can be further optimized in that the tension stretching rollers are preferably coated with a lubricant, e.g. B. an oil emulsion can be applied, which also prevents the caking of loose particles. - The diameter of the drawing stretch rollers is expediently 1,500 times greater than the maximum strip thickness, so that the bend on the drawing stretch rollers which is still involved in the plastic drawing stretch has only a slight influence on the longitudinal curvature or flatness.

• Fig. 1 eine erfindungsgemäße Zugreckanlage in schematischer Aufsicht mit einer hydraulischen Verspannung,
• Fig. 2 den Gegenstand nach Fig. 1 in Seitenansicht ohne die Verspannung,
• Fig. 3 einen Querschnitt durch ein Metallband auf einer Rolle mit elastischem Rollenmantel und daraus resultierendem Spannungsaufbau im Zuge des Reckvorganges,
• Fig. 4 einen Querschnitt durch ein Metallband auf einer er­findungsgemäßen Zugreckrolle mit gleitfreundlichem Rollenmantel und erfindungsgemäßem Spannungsaufbau im Zuge des Reckvorganges und
• Fig. 5 eine abgewandelte Ausführungsform des Gegenstandes nach Fig. 1.

In the following the invention is explained in more detail with reference to a drawing showing only one embodiment; show it

• 1 shows a train stretching system according to the invention in a schematic top view with hydraulic bracing,
• 2 the object of FIG. 1 in side view without the bracing,
• 3 shows a cross section through a metal strip on a roll with an elastic roll casing and the resulting build-up of tension in the course of the stretching process,
• Fig. 4 shows a cross section through a metal strip on a tension stretching roller according to the invention with sliding-friendly roller jacket and tension build-up according to the invention in the course of the stretching process and
• 5 shows a modified embodiment of the object according to FIG. 1.

In the figures, a tension stretching system for the continuous tension stretching of thin metal strips M made in particular of steel, aluminum or the like is shown with a strip thickness between 0.05 mm and 0.5 mm. In its basic construction, this pull stretching system has a brake roller set A with brake rollers 1, 2, 3, 4 and a pull roller set B with pull rollers 7, 8, 9, 10. Between the brake roller set A and the pull roller set B, a pair of draw rollers C with draw rollers 5, 6 is arranged. At least the tension stretching rollers 5, 6 have metallic roller jackets 11, the surface of which is hardened or hard-coated and finely machined. In particular, it can be a metal alloy with a low coefficient of friction such as. B. austenitic cast iron with lamellar or spheroidal graphite, bronze alloys or the like. act. The draw rollers 5, 6 can be acted upon with a lubricant. The diameter of the draw rollers 5, 6 is 1500 times larger than the maximum strip thickness. - In the context of the invention, the brake roller set A and the pull roller set B can basically have two or more brake or pull rollers. The bracing can be done in a known manner.

Example:

It is assumed that the stretching required for the desired stretching is 16 t. Furthermore, the yield point or yield point of the strip material is reached at a yield point of 16 t, that is
16 t ≃ 100% σs
Let σs = 20 kp / mm² and the elastic modulus E = 6900 kp / mm² for, for example, Al as a strip material. The stretch drawing distribution in a conventional draw stretching system, i.e. without the interposition of a pair of draw stretch rolls C, is as follows: role Sz Δ _Sz 1 - 2 t 1 t 2nd - 4 t 2 t 3rd - 8 t 4 t 4th - 16 t 8 t 5 + 16 t 8 t 6 + 8 t 4 t 7 + 4 t 2 t 8th + 2 t 1 t

Querdehnung ε_q = 0,000435
bei µ = 0,3
Längenänderung/1000 mm ΔL = 1,45
Breitenänderung/1000 mm ΔB = 0,435 mmIn this case, the following longitudinal and transverse strains result:
Roll 4/5 ΔS _z = 8 t ≃ 50% σS = 10 kp / mm²

Transverse elongation ε _q = 0.000435
at µ = 0.3
Change in length / 1000 mm ΔL = 1.45
Width change / 1000 mm ΔB = 0.435 mm

Querdehnung ε_q = 0,0000435
bei µ = 0,3
Längenänderung/1000 mm ΔL = 0,145 mm
Breitenänderung/1000 mm ΔB = 0,0435 mmAccording to the invention with a pair of intermediate stretching roller C: role S _z ΔS _z 1 2 t 1 t 2nd 4 t 2 t 3rd 8 t 4 t 4th 15.2 t 7.2 t 5 16.0 t 0.8 t 6 16.0 t 0.8 t 7 15.2 t 7.2 t 8th 8 t 4 t 9 4 t 2 t 10th 2 t 1 t Roll 5/6 ΔS _z = 0.8 t = 5% σ _s = 1 kp / mm²

Transverse elongation ε _q = 0.0000435
at µ = 0.3
Change in length / 1000 mm ΔL = 0.145 mm
Width change / 1000 mm ΔB = 0.0435 mm

redu­ziert, weil das Band in dem zwischen dem Bremsrollensatz A und dem Zugrollensatz B zwischengeschalteten Zugreckrollen­paar C lediglich dem zu seiner Reckung im plastischen Bereich erforderlichen Streckzug unterworfen wird, nämlich etwa 5 % - 25 % des maximalen Streckzuges für die plastische Reckung, während mit dem Bremsrollensatz und Zugrollensatz 75 % - 95 % des maximalen Streckzuges jedoch lediglich für die elastische Reckung des Bandes erzeugt werden.This example makes it immediately clear that the transverse elongation per 1000 mm bandwidth is greater by a factor of 10 in the conventional train stretching system than in the embodiment according to the invention. In fact, in the embodiment according to the invention, the transverse expansion is a factor $\frac{\text{1}}{\text{10th}}$

reduced because the band in the intermediate stretching roller pair C between the brake roller set A and the tension roller set B is only subjected to the stretching stretch required for its stretching in the plastic region, namely about 5% - 25% of the maximum stretching stretch for the plastic stretching, while with the brake roller set and tension roller set 75% - 95% of the maximum stretch, however, are only generated for the elastic stretching of the belt.

FIG. 5 shows a train stretching system which has independent inventive significance. In this tension stretching system, tension-controlled brake drives 12 operate on the brake rollers 1, 2, 3, 4 and tension-controlled tension drives 13 on the tension rollers 7, 8, 9, 10 and a speed-controlled stretching drive 14 on the tension stretching rollers 5, 6, with the interposition of a superposition gear 15 On one of the traction rollers 7, a speed-controlled main motor 16 operates as a speed master for the traction roller set B. In this traction system, the brake roller set A and the traction roller set B are traction-controlled, while the traction roller pair C is connected via a differential gear and the stretching drive 14 as the tensioning motor the desired one Degree of stretching generated by speed control. When the stretching drive 14 operates, plastic stretching takes place. In accordance with the roller diameter and the gear ratios, the stretching drive 14 is set with the percentage of the rotational speed of the main motor 16, so that the stretching drive 14 effects a uniform stretching over the entire speed range. The superposition gear 15 consists essentially of a planetary gear and a bevel gear connecting shaft, via which the draw rollers 5, 6 are supported.

Claims (9)

1. A process for the continuous stretching of thin strips, in particular of metallic strips made of steel, aluminum or the like. Metals with a strip thickness between 0.05 mm and 0.5 mm, after which the respective strip passes through a brake roller set and a pull roller set and between the two Roller sets in the course of its stretching in the plastic region are subjected to a stretching stretch which corresponds to the stretching limit of the strip material or slightly exceeds this stretching limit, characterized in that the strip in a pair of stretching stretching rollers interposed between the brake roller set and the pulling roller set has the stretching stretch required for stretching it in the plastic region is subjected. 2. The method according to claim 1, characterized in that about 5% - 25% of the stretching for the plastic stretching and with the brake roller set and pulling roller set 75% - 95% of the stretching for the elastic stretching of the tape are generated with the pair of tension stretching rollers. 3. tensile stretching system for carrying out the method according to claim 1 or 2, with a brake roller set and a tension roller set, characterized in that a tension stretching roller pair (C) is arranged between the brake roller set (A) and the tension roller set (B). 4. tensile stretching system according to claim 3, characterized in that the tensile stretching rollers (5, 6) have metallic roller shells, the surface of which is hardened or hard-coated and precision-machined. 5. tensile stretching system according to claim 3 or 4, characterized in that the roller shells of the tensile stretching rollers (5, 6) made of a metal alloy with a low coefficient of friction such. B. of austenitic cast iron with lamellar or spheroidal graphite, bronze alloys. Like. Consist. 6. tensile stretching system according to one of claims 3 to 5, characterized in that the tensile stretching rollers (5, 6) with a lubricant, for. B. an oil emulsion, can be acted upon. 7. tensile stretching system according to one of claims 3 to 6, characterized in that the diameter of the tensile stretching rollers (5, 6) is 1500 times greater than the maximum strip thickness. 8. tensile stretching system according to one of claims 3 to 7 and independently thereof, characterized in that on the brake rollers (1, 2, 3, 4) tension-controlled brake drives (12) and on the tension rollers (7, 8, 9, 10) tension-controlled tension drives (13) and on the stretching rollers (5, 6) a speed-controlled stretching drive (14) with the interposition of a superposition gear (15). 9. tensile stretching system according to claim 8, characterized in that on one of the pulling rollers (7) a speed-controlled main motor (16) works as a speed master for the pulling roller set (B).

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