Method for controlling liquid level of tundish molten steel in casting process of continuous casting machine and continuous casting machine

Abstract

The invention provides a tundish molten steel liquid level control method in the casting process of a continuous casting machine and the continuous casting machine. A weight detection unit is adopted and used for monitoring the weight of tundish molten steel in real time, and time pulse signals are generated according to the difference value between the weight W of the tundish molten steel and a tundish molten steel weight target value WZ0, the change rate of the weight of the tundish molten steel along with time, the casting flow number N and the casting pulling speed V; through the time pulse signal, the opening degree of a ladle nozzle is controlled, the tundish molten steel inlet flow is adjusted, the purpose of dynamically controlling the tundish molten steel liquid level is achieved, the tundish molten steel liquid level can be kept stable, and therefore the continuous casting production stability and the casting blank quality are facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking continuous casting process in metallurgical industry, and specifically relates to a method for controlling the liquid level of molten steel in a tundish of a continuous casting machine during the casting process and a continuous casting machine. Background Art

[0002] During the continuous casting process, the large ladle is located above the medium ladle, and the crystallizer is located below the medium ladle. The molten steel flows into the medium ladle through the large ladle water inlet, and then flows into the crystallizer through the medium ladle water inlet for billet casting. The molten steel flow in the large ladle can be controlled by controlling the opening of the large ladle water inlet. The medium ladle, as a transition container for molten steel from the ladle to the crystallizer, affects the stability of the entire continuous casting process and the quality of the billet. A stable liquid level in the medium ladle can maintain a stable flow of molten steel flowing into the crystallizer, which is conducive to stable casting speed; if the liquid level in the medium ladle is too low, a flow interruption accident may occur, forming a cold shut, which will affect the quality of the billet; if the liquid level in the medium ladle is too high, a steel overflow accident may occur, causing harm to equipment and personnel. Therefore, the liquid level control of the medium ladle is a key process in the continuous casting process, which is of great significance to the quality of the billet, production safety and cost reduction.

[0003] When the weight of the molten steel in the large ladle is constant, the main factors affecting the molten steel level in the middle ladle include the opening of the large ladle water inlet, the size of the middle ladle equipment, the casting flow number N, and the casting speed V. 拉速 At present, the control of the molten steel level in the middle package often requires manual intervention. The operator visually inspects the molten steel level in the middle package based on his own experience, and then controls the sliding nozzle. This operating experience is not easy to describe accurately, and the various signal quantities and evaluation indicators cannot be quantitatively expressed. Summary of the invention

[0004] In view of the above technical status, the present invention provides a method for controlling the molten steel level in the middle ladle of a continuous casting machine during the casting process. The method can dynamically control the molten steel level in the middle ladle and maintain the molten steel level stable, thereby facilitating the stable continuous casting production and the quality of the cast billet.

[0005] The technical solution of the present invention is: a method for controlling the liquid level of molten steel in a middle ladle of a continuous casting machine during the casting process, wherein the molten steel flows into the middle ladle through the large ladle water inlet, and flows into the crystallizer casting billet through the middle ladle water inlet;

[0006] A middle bag weight detection unit is set up to monitor the weight of the molten steel in the middle bag in real time through the middle bag weight detection unit to obtain the middle bag molten steel weight W and the middle bag molten steel weight target value W Z0 The difference between , and the rate of change of the weight of the molten steel in the tundish over time (i.e., the rate of change of the weight of the molten steel in the tundish);

[0007] According to the weight of molten steel in the tundish W and the target value of molten steel in the tundish W Z0 The difference between the weight change rate of the molten steel in the tundish, the casting flow number N and the casting speed V拉速 Generate a time pulse signal, the positive and negative of which is determined by the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 The positive and negative difference between them is controlled, and the duty cycle of the time pulse signal is determined by the casting flow number N, the casting speed V 拉速 And the weight change rate control of molten steel in the tundish;

[0008] The opening of the ladle water outlet is controlled by the time pulse signal.

[0009] As a preferred implementation method, the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 When the difference between the two is negative, the time pulse signal is a positive pulse signal, and the time pulse signal is used to control the opening of the large ladle water outlet to increase, that is, the large ladle water outlet is opened to increase the opening of the large ladle water outlet; the weight of the molten steel in the middle ladle W is different from the target value of the weight of the molten steel in the middle ladle W Z0 When the difference between them is a positive value, the time pulse signal is a negative pulse signal, and the time pulse signal is used to control the reduction of the opening of the large bag water outlet, that is, the large bag water outlet contracts to reduce the opening of the large bag water outlet.

[0010] Preferably, the size of the opening of the large ladle water outlet is controlled by the pulse width of the time pulse signal.

[0011] Preferably, the period of the time pulse is determined by the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W. Z0 As a further preferred embodiment, the weight change rate of the molten steel in the middle package is less than the weight change rate threshold value V 变化率阈值 When the duty cycle of the time pulse is zero, that is, the opening of the large ladle water outlet does not change, and the V 变化率阈值 Adjustable.

[0012] As a preferred implementation method, an execution unit is provided for adjusting the opening of the large ladle water inlet; the weight W of the molten steel in the middle ladle detected by the middle ladle weight detection unit is transmitted to the control unit, and the weight W of the molten steel in the middle ladle and the target value W of the molten steel in the middle ladle are obtained in the control unit. Z0 The difference between the two and the rate of change of the weight of the molten steel in the middle ladle over time are calculated to generate a time pulse signal; the time pulse signal is used as the control signal of the execution unit to control the opening of the water inlet of the large ladle to adjust the water inlet flow of the molten steel in the middle ladle, so as to achieve the purpose of dynamically controlling the liquid level of the molten steel in the middle ladle.

[0013] As a preferred implementation method, fuzzy control theory is used to generate a time pulse signal, that is, the basic theory of fuzzy mathematics is used to compare the weight of the molten steel in the middle package W with the target value of the weight of the molten steel in the middle package W. Z0 The difference between the weight change rate of the molten steel in the tundish, the casting flow number N and the casting speed V 拉速The fuzzy data is expressed as a fuzzy set and stored in a PLC (Programmable Logic Controller) program. The fuzzy rules are then used to process the data and output the time pulse signal, thereby achieving dynamic control of the opening of the large ladle water outlet.

[0014] The casting strand number N refers to the number of ingots that can be cast simultaneously on a continuous casting machine, and N is a positive integer.

[0015] The pulse duty cycle is determined by the casting flow number N, the casting speed V 拉速 And the weight change rate of molten steel in the tundish is controlled. The larger the casting flow number N is, the larger the duty cycle is. The casting speed V 拉速 The larger the duty ratio, the greater the weight change rate of the molten steel in the tundish. On the contrary, the smaller the casting flow number N, the smaller the duty ratio, and the casting speed V 拉速 The smaller the duty cycle, the smaller the weight change rate of molten steel in the tundish, and the smaller the duty cycle.

[0016] Preferably, the large water outlet is slidable, and further preferably, the sliding speed of the large water outlet is constant, and the pulse width of the pulse is used as the sliding time of the sliding water outlet. As an implementation method, a hydraulic cylinder is set at the large water outlet, and the large water outlet is driven to slide by the hydraulic cylinder.

[0017] As a preferred implementation method, according to the weight of the molten steel in the middle package W and the target weight of the molten steel in the middle package W Z0 The weight of molten steel in the tundish can be divided into four areas: dead area, micro-control area, medium control area, and fast control area.

[0018] In the dead zone, the weight of the molten steel in the middle package W is different from the target weight of the molten steel in the middle package W Z0 The deviation is within the range of a, that is, W Z0 -a≤W≤W Z0 +a, a>0;

[0019] In the micro-control area, the deviation between the weight W of the molten steel in the middle package and the upper and lower limit weights of the dead zone is within the range of ba, that is, W Z0 -b≤W≤W Z0 -a, W Z0 +a≤W≤W Z0 +b, b>a, when the weight of the molten steel in the middle ladle is in this zone, the opening of the water inlet of the large ladle is controlled by the time pulse, so that the molten steel level in the middle ladle changes to the dead zone;

[0020] The deviation of the weight W of the molten steel in the middle control zone and the upper and lower limit weights in the micro control zone is within the range of cb, that is, W Z0 -c≤W≤W Z0 -b, W Z0 +b≤W≤W Z0+c, c>b; when the weight of the molten steel in the middle ladle is in this zone, the opening of the water inlet of the large ladle is controlled by the time pulse, so that the molten steel level in the middle ladle changes to the dead zone;

[0021] In the fast control zone, the deviation between the weight W of the molten steel in the middle package and the upper and lower limit weights of the middle control zone is outside the range c, that is, W≤W Z0 -c, W Z0 +c≤W, when the weight of the molten steel in the middle ladle is in this zone, the opening of the water inlet of the large ladle is controlled by the time pulse to make the molten steel level in the middle ladle change to the dead zone.

[0022] When the weight of the molten steel in the middle package is in the dead zone, preferably, if the weight change rate of the molten steel in the middle package is less than or equal to the weight change rate threshold value V 变化率阈值 When , no time pulse signal is generated, or the period of the generated time pulse signal can be regarded as 0, the opening of the large ladle water outlet does not move, that is, the opening is constant, and the molten steel level in the middle ladle is the ideal level; if the weight change rate of the molten steel in the ladle is greater than V 变化率阈值 When the time pulse is used to control the opening of the water inlet of the large ladle, the molten steel level in the middle ladle changes to the ideal liquid level shown.

[0023] When the weight of the molten steel in the middle ladle is in the fast control zone shown, in order to avoid overflow or interruption of flow caused by low liquid level control rate, it is preferred to control the opening of the sliding gate of the large ladle to make the molten steel level in the middle ladle change quickly to restore the ideal liquid level. At this time, the casting flow number N, casting speed V 拉速 And the weight change rate of the molten steel in the middle package is controlled, so as to control the duty cycle of the time pulse. At the same time, the period of the time pulse is controlled according to the weight change rate of the molten steel in the middle package. The combined effect of the two can make the adjustment process proceed smoothly.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention adopts a weight detection unit and a control unit. The weight detection unit monitors the weight W of the molten steel in the middle package in real time. The control unit monitors the weight W of the molten steel in the middle package according to the weight W of the molten steel in the middle package and the target value W of the molten steel in the middle package. Z0 The difference between the two, the change rate of the weight of the molten steel in the tundish over time, the casting flow number N and the casting speed V 拉速 Generate a time pulse signal, through which the opening of the large ladle water inlet is controlled, and the water inlet flow of the middle ladle is adjusted to achieve the purpose of dynamically controlling the molten steel level in the middle ladle, which can maintain the stability of the middle ladle liquid level, thereby facilitating the stability of continuous casting production and the quality of the ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a curve showing the change of the molten steel weight of the middle ladle and the water inlet control signal of the large ladle over time in the embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention. Some non-essential improvements and adjustments made to the present invention by technicians in this field based on the contents of the present invention above still fall within the scope of protection of the present invention.

[0028] Embodiment 1:

[0029] During the casting process of the casting machine, molten steel flows into the middle ladle through the large ladle water inlet, and then flows into the crystallizer through the middle ladle water inlet to cast the billet.

[0030] In this embodiment, a middle bag weight detection unit and a control unit are provided. The middle bag weight detection unit monitors the weight of the molten steel in the middle bag in real time, obtains the weight W of the molten steel in the middle bag and transmits it to the control unit. The control unit processes the weight W of the molten steel in the middle bag and the target value W of the molten steel in the middle bag. Z0 The difference between the weight of the molten steel in the middle package and the change rate of the molten steel weight over time are calculated based on the molten steel weight W and the target value W of the molten steel weight in the middle package. Z0 The difference between the two, the change rate of the weight of the molten steel in the tundish over time, the casting flow number N and the casting speed V 拉速 Generate a time pulse signal, the positive and negative of which is determined by the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 The positive and negative difference between them is controlled, and the duty cycle of the time pulse signal is determined by the casting flow number N, the casting speed V 拉速 And the weight change rate control of the middle bag.

[0031] In this embodiment, the large water outlet is slidable, and an execution unit is provided at the large water outlet to drive the large water outlet to slide. In this embodiment, the execution unit is a hydraulic cylinder, and the sliding speed of the large water outlet driven by the hydraulic cylinder is constant. In other embodiments, the execution unit may also be in other ways.

[0032] In this embodiment, the control unit uses fuzzy control theory to generate a time pulse signal, that is, using the basic theory of fuzzy mathematics, the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 The difference between the weight change rate of the molten steel in the tundish, the casting flow number N and the casting speed V 拉速 The data is fuzzified, represented by fuzzy sets, stored in the PLC program, and then processed according to fuzzy rules to output a time pulse signal.

[0033] In this embodiment, the control unit generates a time pulse signal to form a control signal under different working conditions. The control signal is isolated through a signal isolator and output to the execution unit for control, so as to control the opening of the large ladle water inlet and adjust the molten steel inlet flow rate of the middle ladle, so as to achieve the purpose of dynamically controlling the molten steel level in the middle ladle and maintain the liquid level in the middle ladle stable, which is beneficial to the stability of continuous casting production and the quality of the ingot.

[0034] In this embodiment, the weight of the molten steel in the tundish is divided into four zones: dead zone, micro-control zone, medium control zone, and fast control zone.

[0035] In the dead zone, the weight of molten steel in the middle ladle W is different from the target weight of molten steel in the middle ladle W Z0 The deviation is within the range of a, that is, W Z0 -a≤W≤W Z0 +a. In the dead zone, if the weight change rate of the molten steel in the tundish is less than or equal to V 变化率阈值 It is the ideal liquid level state, at this time, the large ladle water outlet does not move, and the opening is constant; if the weight change rate of the ladle steel is greater than V 变化率阈值 When the PLC uses fuzzy control theory to compare the weight of the molten steel in the middle package W with the target value of the weight of the molten steel in the middle package W Z0 The difference between the weight change rate of the molten steel in the tundish, the casting flow number N and the casting speed V 拉速 Processing is performed to generate a time pulse signal, which controls the sliding time of the hydraulic cylinder driving the large ladle water outlet to slide, thereby controlling the opening of the large ladle water outlet and changing the molten steel level in the middle ladle to the ideal liquid level state within the dead zone.

[0036] In the micro-control area, the deviation between the weight of molten steel in the tundish W and the upper and lower limit weights in the dead zone is within the range of ba, that is, W Z0 -b≤W≤W Z0 -a, W Z0 +a≤W≤W Z0 +b. In the micro-control area, PLC uses fuzzy control theory to compare the weight of molten steel in the middle package W with the target value of molten steel in the middle package W. Z0 The difference between the weight change rate of the molten steel in the tundish, the casting flow number N and the casting speed V 拉速 Processing is performed to generate a time pulse signal, which controls the sliding time of the hydraulic cylinder driving the large ladle water outlet to slide, thereby controlling the opening of the large ladle water outlet and causing the molten steel level in the middle ladle to change to the dead zone.

[0037] In the middle control area, the deviation between the weight of molten steel in the middle package W and the upper and lower limit weights in the micro control area is within the range of cb, that is, W Z0 -c≤W≤W Z0 -b, W Z0 +b≤W≤W Z0 +c. In the central control area, PLC uses fuzzy control theory to compare the weight of molten steel in the middle package W with the target value of molten steel in the middle package W. Z0 The difference between the weight change rate of the molten steel in the tundish, the casting flow number N and the casting speed V 拉速 Processing is performed to generate a time pulse signal, which controls the sliding time of the hydraulic cylinder driving the large ladle water outlet to slide, thereby controlling the opening of the large ladle water outlet and causing the molten steel level in the middle ladle to change to the dead zone.

[0038] In the fast control area, the deviation between the weight of the molten steel in the tundish W and the upper and lower limit weights in the middle control area is outside the range c, that is, W ≤ W Z0 -c, W Z0 +c≤W. In the fast control area, the system controls the opening of the sliding nozzle of the large ladle to make the molten steel level in the middle ladle change quickly to restore the ideal liquid level. Under this large inertia condition, the absolute value of the weight change rate of the molten steel in the middle ladle increases, that is, the difference in the flow rate of the molten steel in and out of the middle ladle per unit time increases. At this time, the casting flow number, casting speed V 拉速 The duty cycle of the time pulse is adjusted according to the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W. Z0 The difference between them controls the period of the time pulse. The two work together to produce a certain pulse width to make the adjustment process proceed smoothly, avoiding problems such as overflow or flow interruption caused by low liquid level control rate.

[0039] A specific control process such as Figure 1 As shown, the details are as follows:

[0040] (1) In the initial stage, i.e., during the period from 0 to t0, the control system is not started, the sliding nozzle of the ladle is fully open, and the weight of the molten steel in the tundish increases;

[0041] (2) At time t0, the control system starts and switches to the automatic control mode; during the period from t0 to t3, the weight change of the molten steel in the middle package, the weight change rate of the molten steel in the middle package, the casting flow number and the casting speed parameters are fuzzy processed to obtain a time pulse, and this pulse is used as the sliding time of the hydraulic cylinder to drive the sliding nozzle with a constant sliding speed, that is, the pulse width is used to control the opening of the sliding nozzle;

[0042] During the period from t0 to t3, the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 The difference between them is a positive value, and the pulse signal is a negative pulse signal. The negative pulse signal is used to control the opening of the large bag water outlet to be reduced, that is, the large bag water outlet is contracted to reduce the opening of the large bag water outlet;

[0043] It is in the fast control area during the period t0-t1, in the medium control area during the period t1-t2, and in the fine control area during the period t2-t3;

[0044] Moreover, during the period t0 to t3, the pulse width gradually decreases, that is, the contraction stroke gradually decreases;

[0045] (3) During the period of t3-t4, the liquid level is in the ideal dead zone, and the opening of the large ladle water outlet does not move;

[0046] (4) At time t4, due to the increase in casting speed, the weight of the molten steel in the middle ladle fluctuates, and the opening of the large ladle water outlet needs to be increased, that is, a positive pulse signal is sent, and the opening of the large ladle water outlet is controlled by the positive pulse signal, that is, the large ladle water outlet is opened, so that the opening of the large ladle water outlet is increased.

[0047] During the period of t4-t5, it is in the micro-control area, and the large bag sliding gate is opened;

[0048] (5) At t5-t6, the liquid level is in the ideal dead zone, and the large water outlet does not move;

[0049] At time t6, due to the closure of a casting strand, the weight of the molten steel in the middle ladle increases, and the water outlet of the large ladle needs to be contracted, that is, a negative pulse signal is sent.

[0050] Finally, it should be noted that the specific embodiments described herein are merely examples of the spirit of the present invention, and are not intended to limit the implementation methods of the present invention. Those skilled in the art of the present invention may make various modifications or supplements to the specific embodiments described, or replace them in a similar manner. It is not necessary and impossible to provide all examples of all implementation methods. These obvious changes or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention, and interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A method for controlling the level of molten steel in a middle ladle of a continuous casting machine during casting, wherein the molten steel flows into the middle ladle through a large ladle water inlet, and then flows into a crystallizer casting billet through a middle ladle water inlet; the method is characterized by: A middle bag weight detection unit is set up to monitor the weight of the molten steel in the middle bag in real time through the middle bag weight detection unit to obtain the middle bag molten steel weight W and the middle bag molten steel weight target value W Z0 The difference between the weight of the molten steel in the tundish and the rate of change of the weight of the molten steel in the tundish over time; According to the weight of molten steel in the tundish W and the target value of molten steel in the tundish W Z0 The difference between the weight change rate of the molten steel in the tundish, the casting flow number N and the casting speed V 拉速 Generate a time pulse signal, the positive and negative of which is determined by the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 The positive and negative difference between them is controlled, and the duty cycle of the time pulse signal is determined by the casting flow number N, the casting speed V 拉速 And the weight change rate control of molten steel in the tundish; The opening of the ladle water outlet is controlled by the time pulse signal.

2. The control method according to claim 1: the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 When the difference between the two is a negative value, the time pulse signal is a positive pulse signal, and the opening of the ladle water outlet is increased by controlling the time pulse signal; The weight of molten steel in the middle package W and the target value of the weight of molten steel in the middle package W Z0 When the difference between them is a positive value, the time pulse signal is a negative pulse signal, and the time pulse signal is used to control the reduction of the opening of the large ladle water outlet.

3. The control method as described in claim 1: controlling the size of the large ladle water outlet opening by the pulse width of the time pulse signal.

4. The control method according to claim 1: the period of the time pulse is determined by the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 The difference between the two is controlled.

5. The control method according to claim 1: providing an execution unit for adjusting the opening of the large ladle water outlet; The weight signal of the molten steel in the middle package detected by the middle package weight detection unit is transmitted to the control unit, and the weight W of the molten steel in the middle package and the target value W of the molten steel in the middle package are obtained in the control unit. Z0 The difference between the two and the weight change rate of the molten steel in the tundish are measured, and a time pulse signal is generated; The time pulse signal is used as a control signal of the execution unit to control the opening of the large ladle water outlet.

6. The control method as claimed in claim 1: using fuzzy control theory to generate the time pulse signal.

7. The control method according to claim 6: the large ladle nozzle is slidable; Preferably, the sliding speed of the large ladle nozzle is constant, and the pulse width of the time pulse is used as the sliding time of the sliding nozzle; Preferably, the execution unit comprises a hydraulic cylinder, which drives the large water outlet to slide.

8. The control method according to claim 1: according to the weight W of the molten steel in the middle package and the target weight W of the molten steel in the middle package Z0 The weight of molten steel in the tundish can be divided into four areas: dead area, micro-control area, medium control area, and fast control area. In the dead zone, the weight of the molten steel in the middle package W is different from the target weight of the molten steel in the middle package W Z0 The deviation is within the range of a, that is, W Z0 -a≤W≤W Z0 +a; In the micro-control area, the deviation between the weight W of the molten steel in the middle package and the upper and lower limit weights of the dead zone is within the range of ba, that is, W Z0 -b≤W≤W Z0 -a, W Z0 +a≤W≤W Z0 +b; The deviation of the weight W of the molten steel in the middle control zone and the upper and lower limit weights in the micro control zone is within the range of cb, that is, W Z0 -c≤W≤W Z0 -b, W Z0 +b≤W≤W Z0 +c; In the fast control zone, the deviation between the weight W of the molten steel in the middle package and the upper and lower limit weights of the middle control zone is outside the range c, that is, W≤W Z0 -c, W Z0 +c≤W; The opening of the water inlet of the large ladle is controlled by the time pulse, so that the molten steel level in the middle ladle changes to the dead zone.

9. The control method according to claim 1: In the dead zone, if the weight change rate of the molten steel in the middle package is less than or equal to the weight change rate threshold value V of the molten steel in the middle package, 变化率阈值 When the time pulse signal is not generated, the opening of the large ladle water outlet does not move, and the molten steel level in the middle ladle is the ideal level; if the weight change rate of the molten steel in the ladle is greater than V 变化率阈值 When the time pulse is used to control the opening of the water inlet of the large ladle, the molten steel level in the middle ladle changes to the ideal level.

10. The control method according to claim 1: The weight of the molten steel in the tundish is located in the fast control zone, according to the casting flow number, casting speed V 拉速 The change of the weight change rate of the molten steel in the middle package generates the duty cycle of the control time pulse. At the same time, according to the weight of the molten steel in the middle package W and the target value of the weight of the molten steel in the middle package W Z0 The size of the difference between them controls the period of the control time pulse.

11. A continuous casting machine, comprising a large ladle, a medium ladle and a crystallizer, characterized in that: During the casting process, the method for controlling the molten steel level in the tundish adopts the method described in any one of claims 1 to 10.

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