Active vibration damping system of a rolling mill

Abstract

The active vibration damping system of a rolling mill comprises a rolling stand and an adjustment system for the bending of the rolling rolls (1, 1) having hydraulic actuators (2\2, 2, 2iv) acting on the chock (20) of the rolling rolls (1, 1) and hydraulic feeding circuits (7, 9, 11, 12) and injectors (8, 8, 8, 8iv), preferably piezoelectric injectors, directly inserted into the chambers (6\6, 6, 6iv) of the hydraulic actuators (2, 2, 2, 2iv) with the advantage of exploiting the dampening effect resulting from the high- pressure oil injection.

Claims

1. An active vibration damping system for a rolling stand, comprising two or more working rolls with respective chocks, the damping system comprising: a plurality of hydraulic actuators having respective movable pistons, acting on said chocks, and respective bending chambers, a hydraulic circuit for feeding said plurality of hydraulic actuators, one or more injectors within said hydraulic circuit, wherein said one or more injectors are directly arranged within or in proximity of a structure of the respective bending chambers of the hydraulic actuators to actuate an active damping of vibrations of the working rolls, said injectors being adapted to inject pressurized oil into a respective bending chamber of the hydraulic actuators under control of an electronic control unit.

2. An active vibration damping system according to claim 1, wherein said hydraulic circuit comprises an actuating line, adapted to draw oil from a first hydraulic station to feed said hydraulic actuators, and a high-pressurized branch, having an oil pressure greater than an operating pressure along the actuating line, adapted to draw oil from a second hydraulic station, and wherein said injectors are adapted to put in communication the respective bending chambers of the hydraulic actuators with said high-pressurized branch.

3. An active vibration damping system according to claim 1, wherein the one or more injectors are of piezoelectric type.

4. An active vibration damping system according to claim 1, wherein an injection orifice of the injectors is in direct communication with a respective bending chamber.

5. An active vibration damping system according to claim 1, wherein an injection orifice of the injectors is in direct communication with a first side of a connecting sleeve, placed in proximity of a respective bending chamber and connected thereto by means of a conduit extension.

6. An active vibration damping system according to claim 5, wherein the conduit extension connects a second side of the connecting sleeve to the bending chamber, while the actuating line is connected to said conduit extension by means of a third side of the connecting sleeve.

7. A rolling mill comprising at least one rolling stand provided with two or more working rolls with respective chocks, and an active vibration damping system comprising a plurality of hydraulic actuators having respective movable pistons, acting on said chocks, and respective bending chambers, a hydraulic circuit for feeding said plurality of hydraulic actuators, one or more injectors within said hydraulic circuit, wherein said one or more injectors are directly arranged within or in proximity of a structure of the respective bending chambers of the hydraulic actuators to actuate an active damping of vibrations of the working rolls, said injectors being adapted to inject pressurized oil into a respective bending chamber of the hydraulic actuators under control of an electronic control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will become more apparent from the detailed description of preferred, but not exclusive, embodiments of an active damping system for the resonance vibrations of a rolling mill, particularly a cold rolling mill for strips, shown by way of a non-limiting example with the aid of the accompanying drawings, in which:

(2) FIGS. 1a-1e show some examples of rolling stand configurations of the prior art to which an active vibration damping system according to the present invention can be applied;

(3) FIG. 2 shows vibration modes of a rolling stand without an, active damping system;

(4) FIG. 3 shows two graphs depicting a thickness variation of a rolled strip over time and a pattern of a forcing in the same period of time determining said thickness variation, respectively; the vertical dashed line indicating a time instant when the phenomenon takes place and the horizontal dashed line indicating a breakage limit of the strip;

(5) FIG. 4 schematically shows, according to the present invention, examples of three further graphs, depicting, from top to bottom, a thickness variation of a rolled strip over time, a pattern of a forcing in the same period of time determining said thickness variation, and a pattern of a damping action aimed at eliminating the effect of said forcing;

(6) FIG. 5 shows a scheme for implementing the active damping system of the invention to the chocks of a rolling stand of a rolling mill;

(7) FIG. 5a shows a variant of part of the scheme in FIG. 5;

(8) FIG. 6 shows a scheme of a component of the active damping system of the invention in a first variant;

(9) FIG. 7 shows a scheme of a component of the active damping system of the invention in a second alternative variant;

(10) FIG. 8 shows a scheme of a component of the active damping system of the invention in a third alternative variant.

(11) The same reference numerals and letters in the drawings identify the same elements or components.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(12) With reference to a stand of the type in FIG. 2, a simplified dynamic model of a rolling stand for strips is shown. Typical vibration modes of the stand at different frequency values are shown therein: particularly, in that example, the vibration modes are obtained for frequencies of 132, 174, 544, 666 Hz which depend on the dimensional and elastic features of the stand under examination. Therefore, as the bulk, elastic rigidity and damping parameters vary, the natural resonance frequencies change, being known that each rolling stand has its own resonance frequencies.

(13) Due to the active damping of the present invention, irrespective of transient or stationary conditions generating the instability, the forcing Fv is cancelled due to the opposite damping Fs.

(14) FIG. 3 shows an example of the third-octave resonant vibration when the active damping system of the invention is disabled or is not provided. Specifically, in the upper graph in FIG. 3, there is shown a strip thickness tolerance variation which, at the point where the chattering triggersindicated by a vertical dashed linestarts to overstep its optimal conditions indicated by a band which is usually of +/2 m; therefore, the thickness becomes variable since the resonance takes place at a higher frequency than the passband of the control system of the planarity of the rolling mill. In the lower graph in FIG. 3, a pattern of the forcing which induces such tolerance variations is shown. Therefore, in similar instances, the thickness of the rolled strip undergoes variations which may reach and exceed +/50 m, with the risk of breaking the strip itself.

(15) Furthermore, FIG. 2 schematically shows the vibration modes of a rolling stand comprising two working rolls 1, 1 and only two resting rolls 10, 10, when the active damping system of the invention is absent or disabled.

(16) The invention includes the integration of an active vibration damping device, as described in detail below, within the device for controlling the bending of the working rolls 1 and 1, i.e. within the system for controlling the planarity (bending) of the working rolls.

(17) Referring to the schematic configuration of the active damping system in FIG. 5, there is shown the chock 20 of an upper working roll 1 but, for ease of understanding, the chock of the lower working roll 1, which is equal to chock 20 except that it is symmetrically arranged, has not been shown. The ends 20a, 20b of chock 20 are respectively arranged between the pistons 3, 3, 3, 3.sup.iv of the hydraulic actuators 2, 2, 2 and 2.sup.iv , also simply referred to as bending cylinders.

(18) Specifically, the motion of the hydraulic actuators 2, 2, 2 and 2.sup.iv is coordinated so that a lifting of the upper roll 1 corresponds to a lowering of the lower roll 1, and vice versa. To do so, the pairs of actuators 2, 2 and 2, 2.sup.iv work coordinately together in the same direction of mutual approach/spacing, while the pairs (not shown) of hydraulic actuators operating on the chock of the lower roll 1, work coordinately together in the same direction of mutual approach/spacing.

(19) The bending cylinders 2, 2, 2, 2.sup.iv are typically fed by an actuating line 11 drawing oil in a known manner from a suitable hydraulic utility or plant (not shown in FIG. 5).

(20) For each bending cylinder 2, 2, 2, 2.sup.iv , one or more respective injectors 8, 8, 8, 8.sup.iv are further provided, which are controlled by means of mechanical means, as in FIG. 6, or by means of solenoid valves, as in FIG. 8. Preferably, the injectors are of the piezoelectric type, as shown in the scheme in FIG. 7, such a variant allowing for a much better reaction to the control. The injectors put the chambers 6, 6, 6, 6.sup.iv of the bending cylinders 2, 2, 2, 2.sup.iv in communication with a high-pressurized branch 12 of the hydraulic circuit provided in the rolling plant.

(21) Injector 68, shown in the scheme in FIG. 6, which is mechanically controlled by means of a cam which acts with an actuating force directed in the direction of arrow 61, has a valve 62 of the solenoid type for controlling the pressurized oil, which is controlled synchronously with the action of the cam by injecting oil from orifice 65 into the chamber 6, 6, 6, 6.sup.iv , according to a control algorithm which produces the active damping of the vibrations in order to eliminate the chattering phenomenon.

(22) Injector 88, shown in the scheme in FIG. 8 and similar to that in FIG. 6, provides for the oil injection control by means of a hydraulic solenoid valve 82 and injects the oil into the chamber 6, 6, 6, 6.sup.iv through orifice 85.

(23) The injectors of the piezoelectric type, with particular reference to FIG. 7, where the scheme of one of them is shown with reference numeral 78, which may be used in the present solution, also are of the type used for feeding fuel into diesel engines, just like the previous injectors, with high control dynamics and a minimum interval of 200 s between two subsequent injections; such injectors are commercially available. It is understood that all the injectors 8, 8, 8, 8.sup.iv are perfectly equal to one other irrespective of their amount,

(24) Piezoelectric injectors 8, 8, 8, 8.sup.iv are electrically powered and suitably controlled in a coordinated manner by an electronic control unit 5, or control unit CU which, based on the signals received by instruments for detecting the vibrations occurring within the stand, detects the vibration level and controls the piezoelectric valve 72 (FIG. 7) with a convenient active damping law. i.e. by means of a suitable control algorithm of known type, which controls the opening and closing of the valve required to produce the active damping.

(25) The electronic control unit 5, when necessary, activates the piezoelectric valves 72 of the piezoelectric injectors 8, 8, 8, 8.sup.iv through an electric control, so as to instantaneously introduce high-pressure oil into the chambers of the bending cylinders 2, 2, 2, 2.sup.iv through orifice 75 from the high-pressurized branch 12, so as to dampen the undesired vibrations within the rolling stand according to the aforementioned damping law.

(26) The injector control process which allows the active damping to be produced includes the following stages:

(27) 1) detecting the chattering phenomenon by means of the continuous control carried out with said detection instruments, such as vibrations sensors or velocimeters,

(28) 2) processing the acquired data in the electronic control unit 5, and

(29) 3) controlling the injectors 8, 8, 8, 8.sup.iv to make them introduce oil into the bending chambers 6, 6, 6, 6.sup.iv in order to dampen the vertical vibrations of the stand.

(30) The oil operating pressure within the bending chambers 6, 6, 6, 6.sup.iv of the bending cylinders 2, 2, 2, 2.sup.iv and along the actuating line 11 of the bending cylinders reaches about 200 bars. The oil pressure within the high-pressurized line 12 is 700-1800 bars and corresponds to the pressure at which oil is introduced into the bending chambers 6, 6, 6, 6.sup.iv of the bending cylinders 2, 2, 2, 2.sup.iv when the piezoelectric injectors 8, 8, 8, 8.sup.iv open their valve and allow for the oil to flow.

(31) In a first variant, the preferably piezoelectric injectors 8, 8, 8, 8.sup.iv are advantageously placed directly within the structure of the respective bending chambers 6, 6, 6, 6.sup.iv of the bending cylinders 2, 2, 2, 2.sup.iv , with the injection orifice being in direct communication with the respective bending chamber so as to have an immediate and optimal effect, and avoid the spoilage necessarily resulting if the damping effect is applied along the feeding line, at a greater distance from the respective bending chamber.

(32) Depending on the pressures involved in the active damping system of the invention, two or more piezoelectric injectors 8, 8, 8, 8.sup.iv for each of the bending cylinders 2, 2, 2, 2.sup.iv can also be provided, so as to achieve an even wider range of effects and oppose any type of vibrations which are likely to occur within the rolling plant.

(33) A second variant, shown in FIG. 5a, provides injectors 8, 8, 8, 8.sup.iv advantageously placed in direct proximity to the structure of the respective bending chambers 6, 6, 6, 6.sup.iv of the bending cylinders 2, 2, 2, 2.sup.iv . For simplicity, only one injector and only one bending chamber 6 are shown in FIG. 5a.

(34) Preferably, the injection orifice of the single injector is in direct communication with a first side of a connecting sleeve 50, for example T-shaped, placed in the proximity of the respective bending chamber and connected thereto by means of a conduit extension 51, so as to still have an immediate and optimal effect and avoid the spoilage necessarily resulting if the damping effect is applied along the feeding or actuating line 11, at a greater distance from the respective bending chamber. The distance between the connecting sleeve 50 and the structure of the respective bending chamber 6 preferably ranges from 0.5 to 10 m, preferably from 0,5 to 1 m, from 1 to 5 m, from 5 to 10. The conduit extension 51 covers the distance between the connecting sleeve 50 and the structure of the respective bending chamber 6, connecting a second side of the connecting sleeve 50 to the bending chamber 6. The actuating line 11 is connected to said conduit extension 51 by means of a third side of the connecting sleeve 50.

(35) The oil of the active damping line is advantageously, but not necessarily, drawn from the hydraulic station 9 (FIG. 5) of the rolling stand, filtered and inserted into a line or branch or common rail of high pressure distribution 12, which with its volume compensates for the instantaneous pressure difference due to the injectors. Pump 7 can be controlled in torque (brushless) to maintain the pressure in the line constant. Optionally, a small accumulator 4 (FIG. 5) can be also used.

(36) Due to the configuration of the above-described active damping system of the invention, various advantages are achieved: using injectors already widely commercially available for other applications, the manufacture of the active damping system results in a considerable advantage in terms of costs; in the preferred variant which includes the arrangement of injectors in the bending cylinder chamber, or in the proximity thereof, the whole damping effect resulting from the high pressure oil injection is exploited; the active damping system is small in size; the plant simplicity obtainable in the rolling plant design is not of secondary importance, since making a new complex hydraulic plant in addition to the existing one is not required. The elements and features shown in the different preferred embodiments can be combined without departing from the scope of protection of the present invention.