Method for adjusting a flattener under traction and corresponding device

The invention concerns a method for adjusting a flattener under traction and a corresponding device, for providing a metal strip (5) in particular a cold-rolled steel plate, comprising a cage (1), cage posts (8), two stacked cassettes (2, 3) supporting each a plurality of rollers (4) between which the metal strip (5) is fed. The invention is characterized in that it consists in measuring a physical quantity representing the angular position of said cassettes (2, 3) relative to the feeding direction of the said trip (5).

The invention relates to a method and a device for adjusting a multi-roller flattener under traction, which flattener is to flatten a metal strip, in particular cold-rolled sheet steel.

Before it is shaped by drawing, the cold-rolled sheet metal used in the fields of packaging, motor vehicles and electrical household appliances undergoes a specific surface treatment (tinning, galvanisation or zinc electroplating) in order, on the one hand, to protect the steel against corrosion and, on the other hand, to give it particular mechanical characteristics. The invention relates also to cold-rolled sheet stainless steel or cold-rolled sheet iron-nickel alloy of the Invar type.

Cold-rolled sheet metal often has substantial flatness defects, such as undulations at the edges or the centre and curvature over the length or width of the strip. These defects make the sheet metal unsuitable for the remainder of the manufacturing cycle: one possibility for correcting all the flatness defects of the strip is to cause it to pass into a multi-roller flattener under traction.

The sheet metal under traction passes at rates of the order of from 100 m/min to 700 m/min between rollers supported by two cassettes mounted in a frame, one at the bottom and the other at the top. The rollers are held in place by roller bearings and lateral thrust bearings. In order to obtain excellent flatness of the sheet metal, it is necessary from the outset to ensure correct adjustment of the cassettes supporting the rollers, which rollers have to be absolutely perpendicular to the nominal direction of movement of the strip. The positioning of a cassette in the frame is effected by contact of the bearing surfaces of the cassette against the thrust bearings of the uprights of the frame. However, it sometimes happens that this positioning is not entirely satisfactory, and this gives rise to lateral forces which are applied to the rollers and to their thrust bearings.

If these lateral forces against the thrust bearings exceed the intensity that the thrust bearings can withstand, the result will be their fracture through fatigue and the partial or total destruction of the rollers. As soon as a roller breaks, often the roller of a given cassette that is the closest to the flattener inlet, the cassette is unusable and flattening is impossible. This event makes it necessary to stop the production line in order to change the cassette(s), at least one roller of which has just broken, and this leads to a loss in productivity and also substantial financial losses.

The cassettes of a flattener must have an average service life of the order of one month in the context of optimum use of the line, that is to say, if the cassettes are adjusted in such a manner that the rollers supported by the cassettes are absolutely perpendicular to the direction of movement of the strip.

However, an incorrect adjustment or a loss of adjustment of the cassettes may in some cases generate lateral forces such that the lateral thrust bearings and the rollers may be destroyed after a few hours of the sheet metal passing between the rollers.

The object of the invention is therefore to propose a method and a device for adjusting a multi-roller flattener under traction which ensures a service life of the cassettes compatible with production requirements.

The invention relates to a method for checking the adjustment of a flattener under traction which is to flatten a metal strip, in particular cold-rolled sheet steel, of the type comprising a frame, frame uprights and two stacked cassettes each supporting a plurality of rollers between which the metal strip passes, characterised in that a quantity representing the angular position of the cassettes relative to the direction of movement of the strip is measured and, if necessary, the angular position of the cassettes is corrected in order to cause it to comply with a predefined angular position.

According to other preferred features of the invention:the quantity representing the angular position of the cassettes relative to the direction of movement of the strip is constituted by the lateral forces, generated by the rotation of the rollers, on the cassettes;the angular position of the cassettes is corrected by inserting at least one means permitting modification of the angular position of at least one cassette relative to the frame between at least one upright of the frame and at least one cassette as a function of the results of the measurement representing the angular position.

The invention relates also to a device for adjusting a flattener of the type comprising a frame, frame uprights and two stacked cassettes each supporting a plurality of rollers between which a metal strip passes, each of the ends of the rollers provided with a lengthening piece being in contact with a thrust ball bearing connected to a preloading spring, which is itself connected to a bearing piece which slides longitudinally when the roller moves laterally, the device comprising two sensors connected to the bearing pieces, measuring quantities representing the angular position of the cassettes relative to the direction of movement of the strip, and at least one adjusting means permitting modification of the angular position of the cassettes relative to the frame as a function of the measurements provided by the sensors.

According to other features of the invention:the means for modifying the angular position of the cassettes relative to the frame is a shim;the adjusting means for modifying the angular position of the cassettes relative to the frame is constituted by an element of variable thickness;the device comprises automatic means for inserting the adjusting means permitting modification of the angular position of the cassettes relative to the frame as a function of the measurements provided by the sensors.

As will have been appreciated, the invention consists in measuring the lateral forces generated by the rollers on the thrust bearings. If an intensity is detected which reaches a threshold which is determined in advance as a function of the mechanical constraints of the installation and which cannot be exceeded without breaking the rollers, it is thus possible to stop the movement of the strip and to take rapid action to adjust the cassettes, in order to prevent the rollers from being destroyed.

FIG. 1shows diagrammatically a multi-roller flattener under traction, which flattener is constituted by a frame1and two stacked cassettes2,3supporting rollers4which are positioned in an offset manner relative to one another and between which a cold-rolled metal strip5passes. The motorised units for placing the sheet metal under traction are shown at6and7.

FIG. 2shows only the lower cassette3supporting the rollers4over which the cold-rolled strip5passes. The cassette3is held in place in the frame1by the uprights8of the frame1, the orientation of the cassette3being, according to the invention, ensured by at least one means permitting modification of the angular position of the cassettes2,3relative to the frame1, so that the orientations of the rollers4of the cassette3and of the axis of the moving strip5are absolutely perpendicular. In the example shown, this means is constituted by a shim9inserted between one of the uprights8of the frame1and the cassette3.

FIG. 3shows a flattening roller4provided with a lengthening piece4a, the rotation of which is ensured by a rolling element, such as a needle roller bearing10. The end of the lengthening piece4aof the roller4is in contact with a thrust ball bearing11in order to avoid friction of the roller4against the structure of the cassette2,3of the flattener in the lateral direction.

The thrust ball bearing11is connected to a preloading spring12which enables the rolling elements to be kept in contact with the two collars11aof the thrust ball bearing11.

The preloading spring12is connected to a bearing piece13which slides longitudinally when the roller4, during its rotation, moves laterally, in the case where the cassette2,3carrying the rollers4is incorrectly adjusted or loses its adjustment.

A force sensor14in contact with the bearing piece13measures the intensity of the forces generated by any lateral displacement of the roller4and sends a measurement signal which, when it exceeds a critical threshold determined in advance as a function of the mechanical constraints of the installation, brings about an adjustment of the positioning of the cassette2,3. A connection15connected to the force sensor14returns this measurement signal to the means for transmitting data to the operator who is managing the adjustment.

The invention may be used as follows.

When the cassettes2,3have just been changed, these cassettes2,3are first of all adjusted. The metal strip5is caused to pass between the rollers4of the flattener and the force intensity measured by the force sensor(s)14is recorded. If necessary, the orientation of the cassettes2,3is corrected by suitable adjustment of the shims9in such a manner that the orientations of the rollers4, the cassette2,3and the moving sheet metal5are absolutely perpendicular and that, simultaneously, the lateral forces are minimised.

As soon as these adjustments have been made, it is possible to flatten the strip5without risk of breaking the rollers4, the thrust bearings11and the strip5.

Each instrumented roller4of the lower cassette and the upper cassette is connected to two independent force sensors14, one on each side of the roller. Measurements of the intensity of the lateral forces are thus taken, two at the lower cassette and two at the upper cassette.

According to a variant of the invention, the insertion of the shim9between the upright8of the frame1and the cassette3is effected automatically.

In that case, the measurement signal is returned to the means for transmitting data to an installation which manages the adjustment automatically.

It will be appreciated that the device permitting modification of the angular position of the cassettes2,3relative to the frame1is not limited to shims. Other devices, such as an element of variable thickness comprising one or more hydraulic jacks, may be used.