EP0041025B1 - Process and device for the rolling of metal without tension - Google Patents

Description

The present invention relates to the unconstrained rolling of metals and, more specifically, a method and a device for such rolling applicable to a continuous rolling train including at least two non-reversible cages whose respective drive motors are controlled by means of '' a circuit connected to a cruise control.

Methods are known for detecting and correcting any tension or compression of the metal between two successive cages, methods according to which the value of the forward or backward sliding of the metal in each cage is regulated as an essential characteristic of any stress on the metal . For example, French patent 2,395,086 describes such a process.

On the one hand, the speed sensors which must be used are generally either imprecise, such as the tachogenerators, or expensive, such as the electronic correlators, and are practically unusable for certain measurements, because of the ambient conditions of temperature. On the other hand, this process does not take into account variations in the parasites of the rolling focus and in particular the volume flow rate of the rolled product. This results in a certain imprecision in the calculation of the slip value which is, therefore, maintained at a value such that each cage exerts a traction on the metal, it being understood that a very slight traction on the metal is entirely preferable to compression of the metal, or even at the sole risk of possible compression.

A process which is the subject of French patent 2354154 has been developed to overcome these well known drawbacks. According to this method, just before the introduction of the metal into the second stand, the value of the rolling torque of the first stand is determined and recorded, then, as soon as the metal is introduced into the second stand, the value of the rolling torque of the first stand is kept constant by acting on the speed reference of the speed regulator of the first stand, until the speed of this first stand stabilizes, and immediately after and until the end of rolling, the speed ratio of the two cages is kept constant by action on the main reference of the torque regulator of the first cage. However, this latter method does not take account of any variations in the cross-section of the metal, from which considerable traction or compression forces may result.

The object of the present invention is to obviate all of the aforementioned drawbacks.

The invention relates to a method for the unconstrained rolling of metals applicable to at least two successive non-reversible stands of a continuous rolling train comprising, for each stand, a torque regulator and a speed regulator acting respectively on a control circuit for the motor driving said cages, and comprising a first step, just before the introduction of the metal into the order cage (n + 1) during which the value of the rolling torque of the cage order (n) is determined and recorded, then a second step, starting from the introduction of the metal into the order cage (n + 1), during which the value of the rolling torque of the cage order (n) is kept constant by acting on the speed regulator of the order cage (n).

According to the invention, the second step continues until the moment preceding the introduction of the metal into the order cage (n + 2) and is followed by a third step continuing until the end of the operation. rolling of the order cage (n), during which the metal volume flow is kept constant at the right of each cage, despite possible variations in the section of the metal, by applying a variable multiplying coefficient to the signal representative of the speed ratio of the order cages (n) and (n + 1).

The invention will be better understood and other objects and advantages will appear more clearly on reading the following description of an embodiment given without limitation, description to which two drawing sheets are appended.

FIG. 1 represents the block diagram of operation of two successive non-reversible stands of a continuous rolling train for long products, in accordance with the invention, and FIG. 2 represents more precisely the detail of one of the control units represented figure 1.

Referring now to Figure 1, the metal 1 is introduced between the cylinders of the order 2 rolling cage (n) before being introduced into the order 3 cage (n + 1). The non-reversible continuous rolling trains generally comprise several successive stands designated here symbolically by their date, for example (n), (n + 1) in which n is an integer at least equal to 1.

Each cage is provided with a drive motor, respectively 4 and 5, coupled to a pulse generator 6, 7, the frequency of which is proportional to the speed of rotation of a motor to which it is coupled.

In front of each cage, an electric photo cell 8, 9 for example makes it possible to detect the immediate introduction of the metal into the cage, while a strain gauge 10, 11, placed in the cage, makes it possible to generate a signal representative of the rolling effort of the corresponding cage.

The drive motors 4, 5 are supplied from the mains line 12 by means of converters 13, 14, in particular with thyristors.

These converters are controlled respectively by a control unit 15, 16 of which the diagram will be studied in more detail by means of Figure 2.

Each control unit for example 15 associated with the order cage (n), receives at its input terminal 20 the information relating to the control unit 16 associated with the immediately higher order cage (n + 1) , and, at its input terminals 21, 22, 23, 24 and 25, the signals respectively from the photoelectric cell 9 disposed at the input of the order cage (n + 1), of the gauge constraint 10 placed in the cage 2 of order (n), of the sensor 17 of the intensity of the current flowing in the converter 13 which it controls, of the pulse generators 6, 7 coupled to the order cages (n) and (n + 1). In addition, a general speed reference signal 18 of all the cages is applied to the input terminal 26 of all the control units so as to uniformly vary the rolling speed of the entire train under consideration.

Finally, each control unit 15 has at least two output terminals 27 and 28, one connected to the downstream control unit and the other to the converter 13 which it controls.

The control unit 15 of the order cage (n) is shown in more detail in FIG. 2 with the same references.

This control unit 15 essentially comprises, in addition to the logic 30, a speed regulator 31 the output of which is connected to a current regulator 32 itself connected to the input terminal 23 of the unit, a terminal which is connected to the sensor 17. The regulator 32 is connected to the output terminal 28 of the unit 15, itself connected to the converter 13. The signal from the pulse generator 6 is applied, via the input terminal 24 of the unit 15, to a converter 33 at the output of which is generated a digital signal representative of the frequency of the pulses. This output is connected, on the one hand, to the speed regulator 31, on the other hand, to a circuit for determining the rolling torque 34 which is also connected to the output of the speed regulator 31, and finally, to a circuit divider 35 which reports the speeds of the order cages (n) and (n + 1), and to the other input of which is applied the digital signal from a converter 36 identical to the converter 33 but connected to the terminal input 25 of the unit 15 itself connected to the pulse generator 7 coupled to the motor 5 of the cage 3 of order (n + 1).

One of the outputs of the circuit 34 for determining the rolling torque is connected to one of the inputs of the speed regulator 31 by means of a loop for regulating the rolling torque of the order cage (n) . This loop includes, in known manner, a first memory 37, a comparator 38 and a regulation circuit 39, operating during the first step of the method according to the invention, and a second memory 40 used during the second step of the method. This torque determination circuit 34 also has an output connected to an input of a circuit 41 for developing a multiplier coefficient, another input of which is connected to the input terminal 22 of the unit 15, which even connected to the strain gauge 10 disposed in the order cage (n).

This processing circuit 41 is connected to a multiplier circuit 42, to the other input from which the signal from the divider circuit 35 is applied.

The output of the multiplier circuit 42 is connected to one of the inputs of the speed regulator 31 by means of a loop for regulating the flow of the rolled metal operating during the third step of the process. This last loop includes a memory 43, a comparator 44 and a regulator 45.

Finally, the speed regulator 31 has an input terminal connected to the input terminal 26 of the unit 15 to which the general speed reference signal 18 is applied.

The logic input terminals 30 are respectively connected to the input terminals 24, 22, 21 and 20 of the unit 15 and to an output terminal of the circuit 34 for determining the rolling torque, while its terminals outputs are connected on the one hand to the output terminal 26 of the unit 15 connected to the control cage control unit (n - 1), and respectively to the control terminals of the memories 37 and 40 and of the circuit 39 of the torque regulation loop, as well as to the memory control terminals 43 and of regulator 45 of the flow regulation loop.

The operation of the device is as follows: the taking over of the cage 2 of order (n) is detected by the appearance of a rolling torque in the motor 4, or by means of the strain gauge 10.

Just before the introduction of the metal 1 into the cage 3 of order (n + 1), the value of the rolling torque, which is then carried out without constraint, is determined by the circuit 34 and is recorded in the memory 37. The precise moment can be determined for example, either by means of a photoelectric cell 9 disposed at the input of the cage 3 as shown in FIG. 1, or by means of a counter connected to the output of the pulse generator 6 it being understood that the distance separating the two successive cages is well known.

When the metal 1 is introduced into the cage 3 of order (n + 1) detected by means of the strain gauge 11 or the appearance of a rolling torque in the motor 5, the value of the torque rolling in the cage 2 of order (n) is kept constant by means of the regulation loop connected to the speed regulator 31 controlled in a known manner by the logic 30. Just before the introduction of the metal into the cage not shown order (n + 2), the correction signal from comparator 38 is stored in memory 40, and remains permanently applied until the end of rolling or cruise control 31. The logic 30 which has already controlled the succession of above operations, then orders the commissioning of the flow control loop until the end of the rolling carried out by the order cage (n). This flow regulation is obtained by applying a corrective term to the gear ratio. This corrective term is a multiplying coefficient which has the form of the expression 1 + k in which k is a function, inter alia, of the force of separation of the cylinders of the cage considered, of the coefficient of yielding of this same cage, of radius of the cylinders and also the thickness of the slot between the cylinders, in particular at the neutral point. This corrective term is developed by the circuit 41 and is applied to the ratio of the speeds of the cages of order (n) and (n + 1) by means of the multiplier circuit 42. The signal from this latter circuit 42 is then processed in a loop identical to a speed control loop for cages.

Such a process is favorably implemented for the rolling of long products such as rails, profiles, beams, it being understood that the product is simultaneously during rolling, engaged in several successive non-reversible cages. In this case, the pulls or the compression of the product between two successive cages causes deformations in the desired profile of the finished product and the method according to the invention makes it possible to avoid such drawbacks.

Claims (3)

1. Process for the stress-free rolling of metals, applicable to at least two non-reversible successive stands of a continuous rolling mill comprising, for each stand, a torque regulator and a speed regulator acting respectively on a control circuit of the driving motor of the said stands, and comprising a first stage just before the introduction of metal into the stand which is (n + 1) in order, during which the value of the rolling torque of the stand which is (n) in order is determined and recorded, then a second stage, beginning from introduction of metal into the stand which is (n + 1) in order, during which the value of the rolling torque of the stand which is (n) in order is kept constant, with action on the speed regulator of the stand which is (n) in order, characterised in that the said second stage continues until the instant prior to introduction of the said metal into the stand which is (n + 2) in order, and is followed by a third stage continuing until the end of the rolling operation of the stand which is (n) in order, during which the volume flow of the said metal is kept constant level with each stand, despite possible variations in the section of the said metal, by application of a variable multiplier coefficient to the signal respresenting the ratio of the speeds of the stands which are (n) and (n + 1) in order.

2. Device for carrying out the process according to claim 1, characterised in that the control unit (15) of the supply converter (15) of the driving motor (4) for the rolls of the stand (2) which is (n) in order comprises especially a circuit (34) for determining the value of the rolling torque of the stand which is (n) in order, a divider circuit (35) generating a signal representing the ratio of the speeds of the stands which are (n) and (n + 1) in order, and a speed regulator (31) for the motor of the stand which is (n) in order, the said circuit (34) for determining the rolling torque having one of its output terminals connected to the said speed regulator (31) by way of a torque regulation loop, and another output terminal connected to a circuit (41) for producing the said multiplier coefficient whereof another input terminal is connected to a strain gauge (10) situated in the said stand which is (n) in order, the said divider circuit (35) being connected to a multiplier circuit (42) to which there is also fed the signal emitted by the said circuit (41) for producing the said multiplier coefficient and whose output is connected to the said speed regulator (31) by means of a regulation loop acting then on a signal representative of the volume flow of the metal in the said stand which is (n) in order.

3. Device according to claim 2, characterised in that two pulse generators (6, 7) respectively coupled to the driving motors (4, 5) of the said stands which are (n) and (n + 1) in order are connected to the said input terminals of the said divider circuit (35) determining the ratio of the speeds of the said stands by means of two converters (33, 36) at the output of which there is produced a numeric signal representative of the frequency of the pulses produced by the said generators (6, 7).

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