System and device to control time intervals between billets in rolling mills

Abstract: The present invention refers to a system and device to control time intervals between billets or blocks in rolling mills and/or similar equipment that allows such control. The system uses a signal which indicates the moment in which a billet has to be introduced in the first stand (1) of the rolling mill, observing a preset time interval and a real time interval indicator between billets. The device is a current comparator/analyser circuit. The invention allows an effective time interval control between billets minimizing this time interval, thus guaranteeing among other advantages, a significant increase in productivity.

Description: The present invention relates to a system and device according to the precharacterising part of claim 1 to control time intervals between billets or blocks in rolling mills and/or similar equipment which allow such control. The system provides a signal which indicates the moment in which a billet has to be introduced into the first stand (1) of the rolling mill (Figure 1) on the basis of a preset time interval and an indicator of the real time interval between billets. For this the system includes a current comparator/analyser circuit. In the present state of technology, the time interval between successive billets occurs without control i.e, it depends on the observation and experience of the operator who withdraws the coke billets and works at the pulpit (14) next to the furnace output (15). As the pulpit operator cannot see the billet tail end coming out from the first stand, for the first stand itself obstructs the operator's vision field, there is a mirror to help him. But it is not an effective aid, since the operator has to determine a random reference point located between the first and second stand. When the tail reaches that point he will have to introduce a new billet in the first stand. However, this point of reference changes according to the speed of rolling mill and from operator to operator. This is because he has neither precise information as to when he has to introduce a new billet nor a feedback of the real time interval. So he is limited by these two factors, and consequently there is a loss in productivity. To minimize these variations and limitations and obtain an increase in productivity, a system and device has now been developed to make control of the time intervals possible. This system was originally devised to work in two strand rolling mills, but it can be applied to a rolling mill of any number of strands. SU-A-876224 describes a control system for a heating furnace and rolling mill of the continuous type, wherein hot billets are extracted from the furnace by an actuator. A drive motor is used to drive billets through part of the rolling mill, and the current in the motor is sensed and its value supplied to a control system which itself supplies a correction signal to the actuator. In accordance with the present invention there is provided a system for enabling the time interval between the feeding of successive billets to rolling mills or like equipment to be controlled, the system comprising means for sensing the entry and/or exit of a billet to and/or from a part of the rolling mill or like equipment in response to a change in current supplied to a drive motor used to drive the billet through said part and means for generating a signal which can be used to indicate when a subsequent billet is to be fed, characterised in that the billets may be fed into one of two channels, the system further comprising means for detecting whether a billet is present in either or both of said channels, said signal generating means comprising a respective timer for each channel enabled by the detection by said detection means of the presence of a billet in its associated channel to generate said signal at a time following a said change in current. The main advantages of the invention in comparison with the present state of technology are the following: increase in productivity, due to the shorter interval between billets; effective gap control between billets to be rolled; flexibility to change the gap observing variables such as difference of mechanical properties of the material to be rolled, and/or other productional problems. There now follows a detailed description of a preferred embodiment of the invention, and reference is made to the accompanying drawings, wherein: Figure 1 shows a chart illustrating the components of the rolling mill having gap control between billets in rolling mill systems, including a billets reheating furnace (15), an operation pulpit (14) for withdrawing the coke billets, a first stand (1), a fourth stand (16), a driving motor (2), an HMD - Hot Metal Detector (21,22,24 and 25), strand 1 and strand 2; Figure 2 shows a block diagram of the system for controlling the time interval between billets in rolling mills; Figure 3 shows a block diagram of the sub-system for determining the real time interval between billets in two-strand rolling mills; Figure 4 shows a block diagram of the Figure 3 sub-system (11); Figure 5 shows a block diagram of a current comparator/analyser circuit. Figures 2 and 3 show, in block diagram form, the interval control system between billets in rolling mills. According to Figure 2, the driving motor (2) requires a current (I₁) from the direct-current converter source (3). The load variation on the motor shaft produces a variation in the d.c. current (I₁) and consequently a variation in the feeding a.c. current (I₂) which is transformed to a lower current (I₃) by means of transformers (4). The current signal (I₃) is rectified by an electronic rectifier and gives rise to a rectified signal (I₄). This signal is amplified by an operational amplifier (6) which generates an amplified signal (I₅). The current comparator/analyser circuit (7) reads the amplified current signal (I₅), memorizes it and afterwards compares it with a new reading. IN this way, when the motor current rises by a given percentage in relation to the memorized one during a given period of time (in seconds) the system understands that a billet has entered the first stand (1) of the rolling mill (Figure 1). So, the cycle will be repeated whenever a current rise above the memorized value occurs. On the other hand, the current comparator/analyser circuit (7) will also sense a decrease in current corresponding to the exit of the billet from one of the strands of the first stand (1). Similarly, after a preset time (in seconds) this circuit will memorize the current value for later comparison. The position of the output contact (52) of this circuit is defined after the comparison. It is opened when there is a given percentage rise in current value, which characterizes the entrance of a billet in the first stand (1) or the actuation of an external reset (51). It is closed when there is a given percentage decrease of the current value, which characterizes the exit of a billet from the first stand (1). The strand selector circuit verifies the exit and begins the time count in the timer circuit (9, 10), corresponding to the respective strand after the exit, and the external habilitation. The strands selector circuit (8) can operate in a manual and/or automatic mode. The timers (9) and (10) are preset according to the desired interval and the feedback given by chronometers (12) and (13) (Figure 3), situated in the pulpit which measure the real interval. When the preset gap of time is over a signalling device is activated which shows the operator that he has to introduce a new billet in the mill. A Programable Logical Controller-PLC (11) (Figures 3 and 4), selects and enables the chronometers (12) and (13), one for each strand, to start the counting of the real gap of time between billets. It receives information (signals 21s, 22s, 24s and 25s) from Hot Metal Detectors-HMD (21, 22, 24 and 25) (Figure 1). Two of these sensors (21 and 22), are located after the first stand (1) and the others (24 and 25), are located after the fourth stand (16). The purpose of the sensors (21 and 22) is to indicate if there is a billet in one of the strands or in both. If there is a billet in just one strand, the PLC (11) will enable one of the two chronometers (12) or (13) to show the real time interval between billets of that strand. If there are billets in both strands, the chronometers (12 and 13) will show individually the real time interval between billets of each strand. The purpose of the sensors (24 and 25) is to set to zero, start and stop the counting of time. When one of the sensors (24) or (25) does not detect a billet, the PLC (11), sends a command to the chronometer (12 and 13) to set to zero and start the counting of time. When one of the sensors (24) or (25) detects the head end of the coming billet, the PLC (11) sends a command to the chronometer (12 or 13) to stop the counting of time. The device to control the time interval between billets in rolling mills, which is a current comparator/analyser circuit (7) or sensor device of motor current, is more fully described below in relation to Figure 5. The device has an input for the amplified current signal (I₅), an input for reset or external inhibition (51), an operational amplifier (circuit) (31) to allow the use of the information coming from the d.c. converter of the first stand (1) of the rolling mill, without causing any interference in the own converter system. There is a filter included in this circuit whose purpose is to flatten the amplified current signal (I₅) to avoid peak values which would "cheat" the system in case of low loads on the motor shaft. These current peaks are normal and exclusively dependent on the direct current converter source (3). An OR gate (32), to which is input several control signals, determines when the memorization of the new load sampling from the first stand (1) must be done i.e., new current value of the motor. Its output enables the memorizing circuit (33), "SAMPLE AND HOLD", to read a current sampling and maintain its output unchanged so that it can be used as a basis of comparison. The moment of sampling is determined by the OR gate output (32). A level and switching detector circuit (34) supervises the output signal generated by the memorizing circuit (33). When this signal becomes less than the reference set in the detector, the circuit (34) ignores the signal and switches internally to maintain its output at a known adjustable value which indicates that there is no load in the motor shaft. When the signal is higher than the set reference, the detector allows the signal to pass straight to the comparator circuit (36). An operational amplifier (35) multiplies the motor current signal by a factor greater than 1 before it is compared with the memorized value. The comparator circuit (36) checks the inputs A and B. If input A is greater than B. it means that there was a given percentage reduction in the motor load. A timer circuit (37) delays the output signal of the comparator (36) so that the system does not sense the disturbances of the motor current caused by the load variation when a billet leaves the first stand (1). It is also used to filter peaks of current that may happen bacause of temperature variation along the billet and therefore load variation on the motor. A pulsator circuit (38), ONE SHOT, defines the sampling time for memorization of a new current value, related to the exit of a billet from the fist stand (1), and inhibits the output of AND gate (40), during this time, in order to have another signalling in the moment of the consecutive exit of billets. A FLIP-FLOP (39) receives a pulse from the pulsator circuit (38) and keeps its output activated until it is reset by a signal from the OR gate (48), guaranteeing in this way, that the output remains active until a new positive alteration of load is perceived by the system. An AND gate (40) with an inverter input inhibits the output for a period of time equivalent to the pulse duration of the pulsator circuit (38). A buffer (41) amplifies the signal from the AND gate (40) output so that a relay (42) can be activated. The relay contact is the interface between the current comparator/analyser circuit (7) and the strand selector system (8). A proportional amplifier circuit (43) of gain less than 1, supplies an output signal to the comparator circuit (45). A switching and level detector circuit (44) supervises the signal memorized in the memorizing circuit (33). When the memorized signal becomes greater than the set reference the circuit maintains in its output the memorized value which corresponds to the load at the moment of sampling and memorization. A comparator circuit (45) compares inputs A and B. If input A is less than B. it means that there was a given percentage rise in the motor load. A timer circuit(46) delays the output information from the comparator circuit (45) so that the system does not feel disturbances of the motor current caused by load variation when a billet enters the first stand (1). It is also used to filter current peaks that may occur because of temperature variation along the billet and therefore load variation on the motor. A pulsator circuit (47), ONE SHOT, defines the sampling time for memorization of the current value at the moment of the entrance of another billet in the first stand (1). An OR gate (48) resets the output automatically when a billet enters the first stand (1) or when an external reset is actuated. An output contact (52) is closed when there is a given percentage decrease of the current value, which characterizes the exit of a billet from the first stand (1). The contact is opened when there is a given percentage increase in the current value, which characterizes the entrance of a billet into the first stand (1) or the actuation of the external reset (51).

Claims: A system for enabling the time interval between the feeding of successive billets to rolling mills or like equipment to be controlled, the system comprising means (4-7) for sensing the entry and/or exit of a billet to and/or from a part (1) of the rolling mill or like equipment in response to a change in current supplied to a drive motor (2) used to drive the billet through said part (1) and means for generating a signal which can be used to indicate when a subsequent billet is to be fed, characterised in that the billets may be fed into one of two channels, the system further comprising means (8) for detecting whether a billet is present in either or both of said channels, said signal generating means comprising a respective timer (9,10) for each channel enabled by the detection by said detection means (8) of the presence of a billet in its associated channel to generate said signal at a time following a said change in current. A system as claimed in claim 1, wherein said sensing means (4-7) comprises means (33) for storing a signal indicative of the level of current supplied to said drive motor (2) and means (36,45) for comparing the signal with a signal indicative of the present level and for providing, in response to a predetermined difference therebetween, a signal for indicating that the billet has reached a predetermined location, and for causing the present current level to be stored in place of the previously-stored level. A system as claimed in claim 1 or claim 2, further comprising, for each channel, means (12,13) for determining the time interval between successive billets at a position downstream of said part (1) and means responsive to the determined time interval for calculating the time at which said signal is to be generated. A system as claimed in claim 3, further comprising first sensors (21,22) and second sensors (24,25), the first sensors (21,22) being disposed upstream of the second sensors (24,25) and a Programmable Logical Controller (11) for selecting and enabling the time interval determining means (12,13) to effect the counting of real time between billets in response to the sensor output signals (21s,22s,24s,25s); the function of the first sensors (21,22) being to indicate if there is a billet in one or both of the channels and, if there is a billet in just one channel, to allow the two time interval determining means (12,13) to indicate the real time interval between billets of said one channel and, if there are billets in both channels to indicate individually the real time interval between billets of each channel, the function of the second sensors (24,25) being to set to zero, start and stop the counting of time, the Programmable Logical Controller (11) being arranged to send, after the passage of a billet past the second sensors (24,25), a command to said time interval determining means (12,13) to set to zero and start the counting of time, and, when a subsequent billet activates one of said second sensors (24,25), to stop the counting of time. A system as claimed in any preceding claim, wherein said sensing means (4-7) is arranged to detect a said change in current by means of a current transformer (4), a rectifier (5) and an operational amplifier (6). A system a claimed in claim 4, wherein said sensing means (4-7) further comprises a current comparator-analyser (7) to which an output (50) of said operational amplifier (6) is fed, and a reset input (51) for permitting external inhibition, said comparator-analyser (7) comprising a first operational amplifier (31) for passing the output of said operational amplifier (6), a logical OR gate (32) for receiving control signals indicating a change in said current, a memory circuit (33) for receiving the output of said OR gate (32) and for maintaining a current sampling value at its output to serve as a basis for comparison, a first level and switching detector (34) for passing the output of said memory circuit (33), a second, proportional operational amplifier (35) for amplifying the output of said first operational amplifier (31) to be compared with a memorized value; a first comparator (36) for comparing the outputs of said level switching detector (34) and said second amplifier (35), a timer (37) for delaying the output of the first comparator (36) by a time sufficient for the motor load to be stabilized completely; a first pulsator (38) for defining the sampling time for the memorization of a new current value, and for inhibiting the output from an AND gate (40) during this time; a FLIP-FLOP (39) arranged to receive a pulse from the pulsator (38) and to maintain the signal at its output until a reset pulse is sent by an OR gate (48), said AND gate (40) having an inverter input which inhibits the output for a period of time equivalent to the duration of pulse of the first pulsator (38), a power amplifier (41) for activating a relay (42) and its associated contact (52); a third, proportional amplifier (43) of gain less than 1 whose output is connected to a first input of a second comparator (45); a second level and switching detector (44) for passing the output of said memory circuit (33), said second comparator (45) being arranged to compare the outputs of said third amplifier (43) and said second level and switching detector (44), a timer (46) for delaying the output of the second comparator (45) by a time sufficient for the motor load to be stabilised completely, a second pulsator (47) for defining the sampling time for the memorization of the new current value and an OR gate (48) for providing at its output said reset pulse in response either to an output from said second pulsator (47) or to an external reset signal.

Inventors: DRUMMOND JOSE AFONSO CENACHI, DRUMMOND, JOSE AFONSO CENACHI
Applicants: MENDES JUNIOR SIDERURGICA, SIDERURGICA MENDES JUNIOR S.A.-SMJ
Application year: 1989
Main classification: B21B37
IPC codes: G04G15, G05B19, B21B37