A variable descaling control method between stands of hot rolling finishing mill

Abstract

The present invention discloses a variable descaling control method for inter-stands of a hot-rolling finishing mill, comprising the following steps: a. in a process machine control system, setting function codes for corresponding inter-stand water use as descaling water or cooling water based on the steel grade and specification information of different products; b. receiving and identifying the function codes issued by the process control system by a basic automation control system; c. based on the identification, opening and closing of the corresponding inter-stand water set for descaling water is controlled according to a descaling water control sequence; simultaneously, opening and closing of the corresponding inter-stand water set for cooling water is controlled according to a cooling water function sequence. The present invention can flexibly change the amount of available descaling water and available cooling water based on different steel grades and specifications, thus remedying the problems of limited descaling water and insufficient descaling capacity in the original system.

Description

Technical Field

[0001] The invention relates to a hot rolling control technology, in particular to a variable descaling control method between stands of a hot rolling finishing mill. Background Art

[0002] The final rolling temperature of hot-rolled strip is closely related to product quality and is one of the key factors affecting the microstructure and performance of hot-rolled strip. Therefore, the final rolling temperature needs to be stably controlled within the specification. At the same time, the surface quality of hot-rolled strip is also a key control point. Due to the particularity of the chemical composition and process system of certain products, surface iron oxide defects are very likely to occur during the hot rolling process, which ultimately leads to unqualified product surface quality. Both final rolling temperature control and surface quality control rely on "water". Conventional hot rolling finishing areas are equipped with inlet descaling boxes, inter-stand descaling water, and inter-stand cooling water. As the name suggests, the main function of descaling water is to "remove scale" to ensure the surface quality of the strip; the main function of inter-stand cooling water is to "cool" to control the final rolling temperature of the strip.

[0003] Problems that exist in actual production operations:

[0004] 1. The functions of inter-stand cooling water and descaling water are clearly defined and cannot overlap. Descaling water is used to descale the entire length of the strip solely to control surface quality, without considering its impact on the finishing mill exit temperature. When the hot strip (hot slab after roughing) reaches the descaling box at the finishing mill entrance, the corresponding descaling water header opens. When the tail of the strip leaves the descaling box, the corresponding descaling water header closes.

[0005] The inter-stand cooling water set between every two stands of the finishing mill is only controlled by flow and opening and closing from the perspective of temperature control without considering the surface quality. Its control logic is: first, the process control machine calculates the number N of inter-stand cooling water that needs to be opened based on the strip temperature measured by the thermometer at the entrance of the finishing mill, the inlet and outlet thickness of each finishing stand (according to the strip thickness H at the entrance of the finishing mill, the target thickness h at the outlet of the finishing mill, and the inlet and outlet thickness of each stand obtained by the load distribution of the finishing mill group), the set rolling speed of each finishing stand, and the target temperature at the outlet of the finishing mill. When the strip reaches the first rolling mill F1 at the entrance of the finishing mill (the rolling force of F1 is large), the inter-stand cooling water is turned on. A steel bite signal is generated after a certain threshold value, indicating that the strip has arrived at this stand. All N groups of inter-stand cooling water are turned on. After the strip passes through each stand of the finishing mill, the thermometer at the outlet of the finishing mill measures the actual final rolling temperature, triggering the start of the temperature feedback control function. This adjusts the amount of inter-stand cooling water turned on based on the deviation between the actual finishing mill outlet temperature and the target temperature. When the actual temperature is higher than the target temperature by a certain threshold value ΔT1, the amount of inter-stand cooling water turned on is increased until the temperature deviation is lower than ΔT1. When the actual temperature is lower than the target temperature by a certain threshold value ΔT2, the amount of inter-stand cooling water turned on is reduced until the temperature deviation is higher than ΔT2. The inter-stand cooling water adjustment amount is dynamically calculated based on the temperature deviation periodically, and the inter-stand cooling water is dynamically adjusted (original model function). When the tail of the strip leaves stand Fi (the rolling force of stand Fi is less than a certain threshold value, which is considered steel throwing, according to the original control logic), the inter-stand cooling water between stands Fi and Fi+1 is adjusted to the closed state.

[0006] 2. The descaling capacity at the finishing rolling entrance is insufficient, and the iron oxide scale produced by the hot strip between the finishing rolling stands cannot be removed.

[0007] Hot rolling mills typically have one or two high-pressure descaling water systems at the finishing mill entrance, primarily used to remove the surface scale formed on hot strips. Different hot-rolled products have varying properties, and some are prone to developing surface scale during the hot finishing mill rolling process. The high-pressure descaling water at the finishing mill entrance cannot fully guarantee surface quality, and scale defects may still remain on the surface of the strip exiting the finishing mill. Strengthened inter-stand descaling is needed to promptly remove the scale formed between stands during the finishing mill rolling process. Furthermore, existing stand water systems only provide dynamic temperature control and do not control inter-stand descaling. Summary of the Invention

[0008] In order to solve the above-mentioned problems of the prior art, the present invention provides a variable descaling control method between stands of a hot rolling finishing mill. According to the production process characteristics of the hot-rolled products, the main control function of the cooling water between stands can be flexibly adjusted. It can be used as "descaling water" to control the surface quality, and can also be used as "inter-stand cooling water" to control the final rolling temperature of the strip.

[0009] A variable descaling control method between stands of a hot rolling finishing mill of the present invention comprises the following steps:

[0010] a. In the process machine control system, set the function code for using the water between racks as descaling water and cooling water according to the steel grade and specification information of different products;

[0011] b. The basic automation control system receives and identifies the function code issued by the process control system;

[0012] c. According to the identification, the corresponding rack water used for descaling water will be set to be opened and controlled according to the descaling water control sequence; at the same time, the corresponding rack water used for cooling water will be set to be opened and closed according to the cooling water function;

[0013] The opening control according to the descaling water control sequence is specifically as follows:

[0014] When the head of the hot strip reaches the F1 stand at the finishing rolling entrance, all the water supplies between the stands set for descaling water will be turned on and kept on until the steel is thrown in the rear stand among the stands set for descaling water. Then the water supply between the stand and the previous stand will be turned off, and the rest will remain unchanged until all the water supplies between the stands set for descaling water are turned off (such as when steel is thrown in F2, the descaling water in F12 will be turned off).

[0015] In step c, the on-off timing control according to the cooling water function is specifically as follows:

[0016] The process machine control system calculates the amount of cooling water that needs to be turned on based on the finishing rolling inlet temperature, final rolling target temperature, rolling speed, thickness, reduction rate of each stand and the original iterative control model to determine whether the water supply between the corresponding stands needs to be turned on. If it needs to be turned on, when the previous stand in the stand set for cooling water use has steel bite, the water supply between the stand and the next stand will be turned on.

[0017] In step b, after identifying the function code, the actual temperature at the finishing outlet is controlled by precalculating the adjustment of water consumption between stands and making it within the tolerance range allowed by the target final rolling temperature, specifically:

[0018] The process machine control system calculates the total temperature drop caused by opening the water between all stands set for descaling water according to the finishing rolling inlet temperature, intermediate billet thickness, rolling speed, and load distribution coefficient of each finishing rolling stand;

[0019] When the total temperature drop falls between the maximum and minimum temperature drop required to achieve the target temperature tolerance range at the finishing rolling exit, no adjustment is made, and the feedforward setting of the finishing rolling exit temperature is completed;

[0020] When the total temperature drop is less than the minimum temperature drop required to reach the target temperature tolerance range at the finishing rolling exit, the inter-stand water used for cooling water is selected from the front to the back, and the number of additional inter-stand cooling water groups to be opened is determined based on the temperature drop calculation results; when the number of inter-stand cooling water groups to be opened is greater than the total amount of available inter-stand water, an iterative adjustment is made to reduce the finishing rolling speed; if the finishing rolling exit temperature calculated by the model after the iterative reduction of the rolling speed is still higher than the convergence interval to the finishing rolling exit target temperature, an alarm message is output;

[0021] When the total temperature drop is greater than the maximum temperature drop required to reach the tolerance limit of the finishing rolling outlet target temperature, an iterative adjustment is made to increase the finishing rolling speed; if the finishing rolling outlet temperature calculated by the model after the iterative increase of the rolling speed is still lower than the convergence range of the finishing rolling outlet target temperature, an alarm message is output.

[0022] The iterative step length for reducing the finishing rolling speed is n% of the original set speed V; the iterative step length for increasing the finishing rolling speed is m% of the original set speed V. Both n% and m% are empirical values, and the value range is 1% to 10%.

[0023] The process also includes step d: when the strip head passes the temperature measuring point at the finishing rolling exit, starting the final rolling temperature feedback control, and performing feedback adjustment of water use between stands according to the deviation between the target temperature and the actual temperature:

[0024] When the deviation is greater than the upper limit of the feedback control temperature, the cooling water is increased; when the deviation is less than the lower limit of the feedback control temperature, the rack cooling water is reduced; the corresponding inter-rack water use set for cooling water use is increased or decreased, and the same calculation method as the pre-calculation is used to determine the amount of inter-rack cooling water to be increased or decreased.

[0025] The corresponding inter-rack water used for descaling water always remains in a normally open state after the feedback control is started.

[0026] The upper and lower limit values of the feedback control temperature are both empirical values, and the value ranges are +20℃~+40℃ and -20℃~-40℃ respectively.

[0027] The following beneficial effects are achieved by using the variable descaling control method between stands of a hot rolling finishing mill group according to the present invention:

[0028] 1. The amount of available descaling water and available cooling water can be flexibly changed according to different steel grades and specifications, making up for the problem of limited amount of original descaling water and insufficient descaling capacity.

[0029] 2. The descaling capacity between stands of the finishing mill has been increased, which can effectively control the iron oxide scale produced during the finishing rolling process and enhance the descaling control capability of steel grades that are sensitive to surface iron oxide scale.

[0030] 3. The descaling function between racks can be flexibly set. It can be between two racks or between several racks. It is usually set in the front rack (before the F4 rack) for better descaling effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flowchart of a variable descaling control method between stands of a hot rolling finishing mill. DETAILED DESCRIPTION

[0032] The following further describes a variable descaling control method between stands of a hot rolling finishing mill group according to the present invention in conjunction with the accompanying drawings and embodiments.

[0033] like Figure 1 As shown, a variable descaling control method between stands of a hot rolling finishing mill of the present invention specifically comprises the following steps:

[0034] a. In the process machine control system (L2), the function code for the use of inter-rack water as descaling water or cooling water is set according to the steel grade and specification information of different products (set according to production experience): if it needs to be used as descaling water, the function flag of the corresponding inter-rack water is designated as "1", and if it needs to be used as cooling water, the function flag of the corresponding inter-rack water is designated as "0", for example:

[0035] Steel Type thickness width temperature Function code setting for water use between corresponding racks 1001 2.52mm 1200mm 880℃ F12, F23, and F34 are 1; F45, F56, and F67 are 0

[0036] b. The basic automation control system (L1) receives and identifies the function code issued by the process control system;

[0037] c. According to the identification, the corresponding rack water used for descaling water will be set to be opened and controlled according to the descaling water control sequence; at the same time, the corresponding rack water used for cooling water will be set to be opened and closed according to the cooling water function;

[0038] The above-mentioned opening control according to the descaling water control sequence is specifically as follows:

[0039] When the head of the hot strip reaches the F1 stand at the finishing rolling entrance (that is, when the rolling force of F1 is greater than a certain threshold value, it is considered that the strip has reached this position), all the water supply between stands set for descaling water is turned on (for example, the water supply between F12, F23, and F34 is fully turned on), and the open state is maintained throughout the entire length until the water supply between stands set for descaling water occurs when the latter stand (for example, F2) throws steel, the water supply between the stand (F2) and the previous stand (F1) is turned off (F12), and the rest remain unchanged. Then, when F3 throws steel, the water supply between F23 is turned off, and so on until all the water supply between stands set for descaling water is turned off.

[0040] The above-mentioned opening and closing timing control according to the cooling water function is specifically as follows:

[0041] The process machine control system calculates the amount of cooling water that needs to be turned on based on parameters such as the finishing rolling inlet temperature, final rolling target temperature, rolling speed, thickness, reduction rate of each stand, and the original iterative control model to determine whether the water supply between the corresponding stands needs to be turned on. If it needs to be turned on, when the previous stand in the stand set for cooling water use has steel bite (when the rolling force of the stand is greater than a certain threshold value, such as 3500KN, it is considered that the stand has steel bite, such as F4 has steel bite), the water supply between the stand (F4) and the next stand (F5) is turned on (F45), otherwise it will not be turned on; then when F5 has steel bite, the water supply between F56 is turned on, until the water supply between the corresponding stands set for cooling water use required by the model calculation is turned on.

[0042] The hot rolling finishing process also requires the regulation of inter-stand cooling water to control the actual temperature at the finishing outlet, ensuring that the actual temperature at the finishing outlet is within the tolerance range of the target final rolling temperature. Therefore, in step b, after identifying the function code, the finishing outlet temperature needs to be pre-calculated as follows:

[0043] The process machine control system calculates the total temperature drop caused by opening the water between all stands set for descaling water according to the finishing rolling inlet temperature, intermediate billet thickness, rolling speed, and load distribution coefficient of each finishing rolling stand;

[0044] When the total temperature drop falls between the maximum and minimum temperature drop required to achieve the target temperature tolerance range at the finishing rolling exit, no adjustment is made, and the feedforward setting of the finishing rolling exit temperature is completed;

[0045] When the total temperature drop is less than the minimum temperature drop required to reach the target temperature tolerance range at the finishing rolling exit, the inter-stand water used for cooling water is selected to be opened in the forward and backward direction (i.e., from F1 to F7), and the number of additional water systems to be opened is determined according to the temperature drop calculation result; when the number of inter-stand cooling water groups to be opened is greater than the total number of available inter-stand water systems, an iterative adjustment is made to reduce the finishing rolling speed, and the iterative step size is n% of the original set speed V, i.e., the new speed Vnew=V(1-n%); if the finishing rolling exit temperature calculated by the model after the rolling speed is iteratively reduced is still higher than the convergence interval to the finishing rolling exit target temperature, an alarm message is output, prompting "the rolling speed system is inappropriate and the final rolling temperature cannot reach the target value";

[0046] When the total temperature drop is greater than the maximum temperature drop required to reach the tolerance limit of the target temperature at the finishing rolling outlet, an iterative adjustment is made to increase the finishing rolling speed, and the iterative step size is m% of the original set speed V, that is, the new rolling speed Vnew = V(1+m%); if the finishing rolling outlet temperature calculated by the model after the iterative increase of the rolling speed is still lower than the convergence range of the finishing rolling outlet target temperature, an alarm message is output, prompting "the rolling speed system is inappropriate and the final rolling temperature cannot reach the target value"; the iterative step sizes n% and m% of the speed increase and speed decrease are empirical values, and the values are generally between 1% and 10%.

[0047] The present invention further includes step d: after the strip head passes through the finishing exit temperature measuring point, starting the finishing temperature feedback control, that is, performing feedback adjustment of the water use between the stands according to the deviation between the target temperature and the actual temperature (i.e., the deviation Δtemp between the actual finishing temperature and the target value, Δtemp = actual temperature Tact - target temperature Taim):

[0048] When the deviation Δtemp is greater than the feedback control temperature upper limit Tupper, the water consumption between the corresponding racks set for cooling water use is increased; when the deviation Δtemp is less than the feedback control temperature lower limit Tlower, the water consumption between the corresponding racks set for cooling water use is reduced, and the same calculation method as the pre-calculation is used to determine the amount of cooling water between racks to be increased or decreased.

[0049] The upper and lower limit values of feedback control, Tupper and Tlower, are empirical values. The value of Tupper is generally between +20℃ and +40℃, and the value of Tlower is generally between -20℃ and -40℃.

[0050] Example

[0051] When a certain hot rolling mill produces a certain brand of product, because scale is easily formed during the finishing rolling process, the water supply between the F12 and F23 stands of the finishing mill is set to descaling water, with the function code flag set to "1." When the hot strip arrives at the finishing stand F1 and an On signal is generated (the rolling force of the F1 stand is greater than 3500kN), the water supply between the F12 and F23 stands is turned on simultaneously and remains on throughout the rolling process until the F2 stand is de-rolled (the rolling force of the F2 stand is less than 3500kN). At this time, the water supply between the F12 and F3 stands is turned off (the rolling force of the F3 stand is less than 3500kN), and the water supply between the F23 stands is turned off.

[0052] When the model pre-sets the target temperature for the finishing exit, with both water systems F12 and F23 turned on and an initial rolling speed of V0 = 10 m / s, the model calculates that the finishing exit temperature is 20°C lower than the target. The temperature deviation during model iteration convergence is 10°C, indicating that the finishing exit temperature does not meet the target under the current stand water status and rolling speed. Because the function flag for the inter-stand water use for F12 and F23 is "1," these two water systems are not included in the water shut-off iteration. Therefore, iterative rolling speed adjustment is initiated, and the post-iteration rolling speed Vnew = V0 * (1 + 5%) = 10.5 m / s.

[0053] After the head of the strip leaves the final stand of the finishing mill, the actual temperature is measured by the thermometer at the finishing mill outlet. During the speed-up rolling process of the finishing mill, when the actual temperature is 20 degrees higher than the target value, water supply between the stands is increased. First, water supply is turned on between the F34 stands. If the temperature is still too high after 500ms, water supply is turned on between the F45 stands. The system is checked and judged periodically in turn until the deviation between the actual temperature and the target temperature is controlled within 20 degrees.

[0054] (Under traditional methods, the water used between the F12 and F23 stands is used as cooling water for temperature control. Its on / off status is determined by the temperature model calculation results. The model calculation gives priority to the on / off status of the stand water. If the stand water cannot be adjusted, the rolling speed is adjusted. Under traditional methods, the model calculation results in this example should indicate that F23 is in the off state.)

[0055] In summary, the present invention assigns different function codes to the inter-stand cooling water of the finishing mill, allowing for specific control functions to be assigned based on different product characteristics and production process control requirements. Once the control function is determined, the L1 control system adjusts the relevant control function logic, and the mechanical system controls the opening and closing of the water valve to achieve the final control function.

[0056] However, those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A variable descaling control method between stands of a hot rolling finishing mill, characterized by: The following steps are involved: a. In the process machine control system, set the function code for using inter-rack water as descaling water and cooling water according to the steel grade and specification information of different products; b. The basic automation control system receives and identifies the function code issued by the process control system; c. Based on the identification, the corresponding inter-rack water used for descaling water will be controlled according to the descaling water control sequence; at the same time, the corresponding inter-rack water used for cooling water will be controlled according to the cooling water function on and off sequence; The opening control according to the descaling water control sequence is specifically as follows: When the head of the hot strip arrives at the F1 stand at the finishing rolling entrance, all water supply between the stands set for descaling water will be turned on and kept on until the next stand in the stand set for descaling water has steel throwing, then the water supply between the stand and the previous stand will be turned off, and the rest will remain unchanged until all water supply between the stands set for descaling water are turned off; In step b, after identifying the function code, the actual temperature at the finishing outlet is controlled by precalculating the adjustment of water consumption between stands and making it within the tolerance range allowed by the target final rolling temperature, specifically: The process machine control system calculates the total temperature drop caused by opening the water between all stands set for descaling water according to the finishing rolling inlet temperature, intermediate billet thickness, rolling speed, and load distribution coefficient of each finishing rolling stand; When the total temperature drop falls between the maximum and minimum temperature drop required to achieve the target temperature tolerance range at the finishing rolling exit, no adjustment is made, and the feedforward setting of the finishing rolling exit temperature is completed; When the total temperature drop is less than the minimum temperature drop required to reach the target temperature tolerance range at the finishing rolling exit, the inter-stand water used for cooling water is selected from the front to the back, and the number of additional inter-stand cooling water groups to be opened is determined based on the temperature drop calculation results; when the number of inter-stand cooling water groups to be opened is greater than the total amount of available inter-stand water, an iterative adjustment is made to reduce the finishing rolling speed; if the finishing rolling exit temperature calculated by the model after the iterative reduction of the rolling speed is still higher than the convergence interval to the finishing rolling exit target temperature, an alarm message is output; When the total temperature drop is greater than the maximum temperature drop required to reach the tolerance limit of the finishing rolling outlet target temperature, an iterative adjustment is made to increase the finishing rolling speed; if the finishing rolling outlet temperature calculated by the model after the iterative increase of the rolling speed is still lower than the convergence range of the finishing rolling outlet target temperature, an alarm message is output.

2. The variable descaling control method between stands of a hot rolling finishing mill according to claim 1, characterized in that: In step c, the on-off timing control according to the cooling water function is specifically as follows: The process machine control system calculates the amount of cooling water that needs to be turned on based on the finishing rolling inlet temperature, final rolling target temperature, rolling speed, thickness, reduction rate of each stand and the original iterative control model to determine whether the water supply between the corresponding stands needs to be turned on. If it needs to be turned on, when the previous stand in the stand set for cooling water use has steel bite, the water supply between the stand and the next stand will be turned on.

3. The variable descaling control method between stands of a hot rolling finishing mill according to claim 1, characterized in that: The iterative step length for reducing the finishing rolling speed is n% of the original set speed V; the iterative step length for increasing the finishing rolling speed is m% of the original set speed V. Both n% and m% are empirical values, and the value range is 1% to 10%.

4. The variable descaling control method between stands of a hot rolling finishing mill according to claim 1, characterized in that: The process also includes step d: when the strip head passes the temperature measuring point at the finishing rolling exit, starting the final rolling temperature feedback control, and performing feedback adjustment of water use between stands according to the deviation between the target temperature and the actual temperature: When the deviation is greater than the upper limit of the feedback control temperature, the water consumption between the corresponding racks set for cooling water is increased; when the deviation is less than the lower limit of the feedback control temperature, the water consumption between the corresponding racks set for cooling water is reduced, and the water consumption between the corresponding racks set for descaling water is always kept in the normally open state after the feedback control is started.

5. The variable descaling control method between stands of a hot rolling finishing mill according to claim 4, characterized in that: The upper and lower limits of the feedback control temperature are both empirical values, with the ranges of +20°C to +40°C and -20°C to -40°C respectively.

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