A cold continuous rolling mill strip thickness control method based on performance detector

Abstract

The application discloses a cold continuous rolling mill strip steel thickness control method based on a performance detector, and comprises the following steps: calculating a feedforward roll gap adjustment amount model caused by incoming material thickness deviation and incoming material performance deviation; respectively establishing a speed difference and tension difference relationship model, and calculating front tension change value and rear tension change value of the roll gap adjustment during the i-th strip steel rolling based on the speed difference and tension difference relationship model; establishing a feedforward roll gap adjustment amount model caused by the rolling force fluctuation caused by the tension difference based on a rolling force fluctuation formula; solving the feedforward roll gap adjustment amount model; and calculating the optimal roll gap adjustment amount under the current incoming material thickness deviation and the incoming material performance condition. The application overcomes the strip steel thickness over deviation caused by the strength improvement and performance fluctuation of the ultrahigh-strength steel, and greatly reduces the whole roll thickness difference compared with the traditional cold continuous rolling mill thickness control method.

Description

Technical Field

[0001] This invention belongs to the field of cold rolling technology, and specifically relates to a method for controlling strip thickness in cold rolling mills based on a performance testing instrument. Background Technology

[0002] In recent years, with the continuous development of my country's manufacturing industry, it has gradually moved from low-end to high-end manufacturing. As raw materials for manufacturing industries such as automobiles, home appliances, construction, and instrumentation, sheet and strip steel faces higher requirements regarding shape, surface quality, and thickness variation. The cold rolling process, as the final production step for sheet and strip products, directly affects the finished product quality and the stability of the strip steel during continuous annealing. Sheet shape, as a key flatness indicator for cold-rolled products, has been extensively studied in recent years. Advanced domestic steel companies have achieved sheet shape indices of 2-3I, reaching international leading levels. With the rapid development of the automotive industry, to further reduce energy consumption while ensuring collision safety, high-strength thinning has become a research direction for cold-rolled sheet and strip steel. However, with the expansion of the ultra-high strength steel product outline and the transformation of the traditional hood-cooling + pickling + single-stand rolling mode to the hot-rolled incoming material insulation hood cooling + pickling continuous rolling production scheme, the inconsistent cooling rate of the whole coil during the saddle cooling process of the hot-rolled incoming material caused differences in mechanical properties, which further aggravated the thickness difference defect of the strip steel at the exit of the cold continuous rolling mill.

[0003] To reduce the thickness difference of finished strip steel, a performance testing instrument was installed on the existing AGC feedforward control system of the No. 1 stand of the cold continuous rolling mill to test the mechanical properties of the hot-rolled incoming material. Combined with the thickness testing instrument, the thickness difference of the incoming material was detected. By adjusting the mill roll gap, speed, etc., the rolling pressure and front and back tension during the rolling process were controlled to reduce the thickness difference of the strip steel exit. Summary of the Invention

[0004] To solve the above problems, the technical solution adopted by the present invention is: a method for controlling strip thickness in a cold continuous rolling mill based on a performance testing instrument, comprising the following steps:

[0005] A: Calculate the feedforward roll gap adjustment model ΔS caused by deviations in incoming material thickness and properties. i,n (t)1;

[0006] B: Establish models for the relationship between speed difference and tension difference, and calculate the change in pre-tension ΔT after roll gap adjustment during the rolling of the i-th strip based on these models. 0,i,n Post-tension change value ΔT 1,i,n ;

[0007] C: Based on rolling force fluctuation ΔP ey,i,nThe formula establishes a model for the feedforward roll gap adjustment ΔS caused by the rolling force fluctuation due to the tension difference. i,n (t)2;

[0008] D: Model for feedforward roll gap adjustment ΔS i,n Solve for (t)2;

[0009] E: Calculate the optimal roll gap adjustment ΔS under the current material thickness deviation and material performance conditions. i,n (t), mm.

[0010] Further: Obtain the number m of actual thickness deviation percentages of the i-th volume of incoming strip steel. i ; Bearing structural parameter coefficient k; Roll speed n when the rolling mill rolls the i-th coil of strip at the n-th position. i,n ,r·min -1 The actual value of the rolling force P when the rolling mill rolls the i-th coil of strip at the n-th position. i,n KN; Working roller speed n0, r·min at manual zero position. -1 ; Rolling force P0, kN, determined by the manual zero-position method when the roll gap of the rolling mill is zero under no-load conditions; Plasticity coefficient W of the incoming strip steel in Volume i. i The mill stiffness M of the stand is kN·mm. -1 The percentage deviations of the actual incoming strip performance for the (n+1)th and nth actual incoming strips in Volume i are respectively b i,n+1 b i,n The set value H for the incoming strip thickness of Volume i. i,set mm; The coefficient of variation Q of the yield strength of the incoming strip steel in Volume i with rolling force i The initial yield strength setting value σ for the incoming strip steel in Volume i. s,i,set MPa; Calculate the feedforward roll gap adjustment ΔS caused by the deviation in incoming material thickness and performance based on the following formula. i,n (t)1.

[0011]

[0012] Further: Obtain the change in mill inlet speed ΔV after roll gap adjustment during the rolling of the i-th strip. 0,i,n ΔV, the change in export speed 1,i,n ,m·min -1 The tension adjustment coefficient c during the rolling of the i-th strip. 1,i,n Speed ​​adjustment coefficient c 2,i,n The pre-tension setting value T during the rolling of the i-th strip. 0,i,set Back tension setpoint T 1,i,set ,kN, the calculation of the change in pre-tension ΔT after roll gap adjustment during the rolling of the i-th strip. 0,i,nPost-tension change value ΔT 1,i,n KN uses the following formula.

[0013]

[0014] Furthermore: the amount of rolling force fluctuation ΔP ey,i,n The KN formula establishes a model for the feedforward roll gap adjustment ΔS caused by the rolling force fluctuation due to the tension difference. i,n (t)2 is as follows:

[0015]

[0016] Furthermore: the model for the feedforward roll gap adjustment ΔS i,n The process of solving (t)2 is as follows:

[0017] B3: Obtain the rolling pressure weighting coefficient α, and calculate and establish the control objective function C(X) for the change in rolling force;

[0018] B4: Set the speed adjustment step size d1, d2, inlet speed adjustment coefficient k1, and outlet speed adjustment coefficient k2;

[0019] B5: Let ΔV 0,i,n =ΔV 0,i,n -k1d1, ΔV 1,i,n =ΔV 1,i,n -k2d2;

[0020] B6: Determine if the following conditions are met simultaneously: ΔV 0,i,n ≤ΔV 0,i,nmin , ΔV 1,i,n ≤ΔV 1,i,nmin If the conditions are met, then calculate the control objective function C(X) for the current rolling pressure change, and C i If (X) = C(X), then the rolling force fluctuation ΔP can be calculated using the formulas in steps B1 and B2. ey,i,n Then jump to B5; if the condition is not met, then C(X). opt =min(C i (X)) and output the corresponding roll gap adjustment ΔS caused by fluctuations in front and rear tension and rolling speed. i,n (t)2.

[0021] Furthermore, the formula for establishing the objective function C(X) for controlling the change in rolling force is as follows.

[0022]

[0023] Furthermore: the optimal adjustment amount ΔS of the roll gap i,n The formulas for (t) and mm are as follows:

[0024] ΔS i,n (t)=ΔS i,n (t)1+ΔS i,n (t)2

[0025] This invention provides a method for controlling strip thickness in a cold continuous rolling mill based on a performance testing instrument. First, a model is established to determine the feedforward roll gap adjustment caused by incoming material thickness deviation and performance deviation. Then, a model is established to determine the feedforward roll gap adjustment caused by changes in rolling speed and tension, and the adjustment is optimized based on speed. Finally, the feedforward roll gap adjustment is established by combining the adjustments generated by the two factors mentioned above. The advantages of this invention are: based on a performance testing instrument in a cold continuous rolling mill, it overcomes the strip thickness deviation caused by the strength increase and performance fluctuation of ultra-high strength steel, significantly reducing the overall coil thickness variation compared to traditional cold continuous rolling mill thickness control methods. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 It is based on the feedforward control principle of the cold rolling mill performance testing instrument.

[0028] Figure 2 It is the optimal control principle for the roll gap adjustment of cold continuous rolling mill.

[0029] Figure 3 This is a flowchart for calculating the roll gap adjustment of a cold continuous rolling mill. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0034] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0035] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0036] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0037] A method for controlling strip thickness in a cold continuous rolling mill based on a performance testing instrument includes the following steps:

[0038] A: Calculate the feedforward roll gap adjustment model ΔS caused by deviations in incoming material thickness and properties. i,n (t)1;

[0039] B: Establish models for the relationship between speed difference and tension difference, and calculate the change in pre-tension ΔT after roll gap adjustment during the rolling of the i-th strip based on these models. 0,i,n Post-tension change value ΔT 1,i,n ;

[0040] C: Based on rolling force fluctuation ΔP ey,i,n The formula establishes a model for the feedforward roll gap adjustment ΔS caused by the rolling force fluctuation due to the tension difference. i,n (t)2;

[0041] D: Model for feedforward roll gap adjustment ΔS i,n Solve for (t)2;

[0042] E: Calculate the optimal roll gap adjustment ΔS under the current material thickness deviation and material performance conditions. i,n (t).

[0043] The steps A / B / C / D / E are executed sequentially;

[0044] Further: Obtain the number m of actual thickness deviation percentages of the i-th volume of incoming strip steel. i ; Bearing structural parameter coefficient k; Roll speed n when the rolling mill rolls the i-th coil of strip at the n-th position. i,n ,r·min -1 The actual value of the rolling force P when the rolling mill rolls the i-th coil of strip at the n-th position. i,n KN; Working roller speed n0, r·min at manual zero position. -1 ; Rolling force P0, kN, determined by the manual zero-position method when the roll gap of the rolling mill is zero under no-load conditions; Plasticity coefficient W of the incoming strip steel in Volume i. i The mill stiffness M of the stand is kN·mm. -1 The percentage deviations of the actual incoming strip performance for the (n+1)th and nth actual incoming strips in Volume i are respectively b i,n+1 b i,n The set value H for the incoming strip thickness of Volume i. i,set mm; The coefficient of variation Q of the yield strength of the incoming strip steel in Volume i with rolling force i The initial yield strength setting value σ for the incoming strip steel in Volume i. s,i,set MPa; Calculate the feedforward roll gap adjustment ΔS caused by the deviation in incoming material thickness and performance based on the following formula. i,n (t)1. Its control principle diagram is shown below. Figure 1 ;

[0045]

[0046] Further: Obtain the change in mill inlet speed ΔV after roll gap adjustment during the rolling of the i-th strip. 0,i,n ΔV, the change in export speed 1,i,n ,m·min -1 The tension adjustment coefficient c during the rolling of the i-th strip. 1,i,n Speed ​​adjustment coefficient c 2,i,n The pre-tension setting value T during the rolling of the i-th strip. 0,i,set Back tension setpoint T 1,i,set ,kN, the calculation of the change in pre-tension ΔT after roll gap adjustment during the rolling of the i-th strip. 0,i,n KN, change in back tension ΔT 1,i,n KN is calculated using the following formula.

[0047]

[0048] Furthermore: the amount of rolling force fluctuation ΔP ey,i,n The KN formula establishes a model for the feedforward roll gap adjustment ΔS caused by the rolling force fluctuation due to the tension difference. i,n (t)2 is as follows:

[0049]

[0050] Furthermore: the model for the feedforward roll gap adjustment ΔS i,n The process of solving (t)2 is as follows:

[0051] B3: Obtain the rolling pressure weighting coefficient α, and calculate and establish the control objective function C(X) for the change in rolling force;

[0052] B4: Set the speed adjustment step size d1, d2, inlet speed adjustment coefficient k1, and outlet speed adjustment coefficient k2;

[0053] B5: Let ΔV 0,i,n =ΔV 0,i,n -k1d1, ΔV 1,i,n =ΔV 1,i,n -k2d2;

[0054] B6: Determine if the following conditions are met simultaneously: ΔV 0,i,n ≤ΔV 0,i,nmin , ΔV 1,i,n ≤ΔV 1,i,nmin If the conditions are met, then calculate the control objective function C(X) for the current rolling pressure change, and C i If (X) = C(X), then the rolling force fluctuation ΔP can be calculated using the formulas in steps B1 and B2. ey,i,n Then jump to B5; if the condition is not met, then C(X). opt =min(C i (X)) and output the corresponding roll gap adjustment ΔS caused by fluctuations in front and rear tension and rolling speed. i,n (t)2.

[0055] Furthermore, the formula for establishing the objective function C(X) for controlling the change in rolling force is as follows.

[0056]

[0057] Furthermore: the optimal adjustment amount ΔS of the roll gap i,n The formulas for (t) and mm are as follows: The control principle diagram is shown below. Figure 2 The overall calculation flowchart is shown below. Figure 3 .

[0058] ΔS i,n (t)=ΔS i,n (t)1+ΔS i,n (t)2

[0059] The following example uses a cold rolling mill in a steel plant, combined with... Figure 3The following examples further illustrate the application of the strip thickness control method for cold continuous rolling mills based on performance testing instruments described in this invention.

[0060] Example 1:

[0061] (A): Number of actual thickness deviation percentages of the first roll of strip steel collected: 1; bearing structural parameter coefficient: 0.9; roll speed at the first position when the first roll of strip steel is rolled: 95 r / min. -1 The actual rolling force at the first position of the first coil of strip rolling was 9340 kN; the work roll speed at the manual zero position was 90 r / min. -1 The rolling force when the roll gap is zero under no-load conditions, determined by the manual zero-position method, is 9000 kN; the plasticity coefficient of the incoming strip steel in Volume 1 is 5000 kN·mm. -1 The mill stand stiffness is 10000 kN·mm. -1 The percentage deviations of the second and first actual incoming strip properties of the first roll are 0.2 and 0.1, respectively; the coefficient of yield strength of the first roll of strip with rolling force is 0.9; the initial yield strength setting of the first roll of strip is 980 MPa; the feedforward roll gap adjustment amount of 0.2 mm is calculated due to the deviation of incoming thickness and the deviation of incoming properties.

[0062] (B1): Collected 0.3 m·min values ​​of mill inlet and outlet speed changes after roll gap adjustment during the rolling of the first strip. -1 0.45 m·min -1 The tension adjustment coefficients during the rolling of the first coil of strip are 0.1 and 0.6; the front and rear tension settings during the rolling of the first coil of strip are 320kN and 260kN. Calculate the changes in front tension after roll gap adjustment during the rolling of the first coil of strip: 38kN and 32kN.

[0063] (B2) Calculate the rolling force fluctuation of 785kN; calculate the roll gap adjustment of 0.079mm caused by the fluctuation of front and rear tension and rolling speed.

[0064] (B3) Collect the rolling pressure weighting coefficient of 0.5 and calculate the control objective function of rolling force change of 392.5kN.

[0065] (B4) Set the speed adjustment step size to 0.05 and 0.05 respectively, and the inlet and outlet speed adjustment coefficients to 1 and 1.5 respectively;

[0066] (B5) Let ΔV 0,i,n =ΔV 0,i,n -k1d1, ΔV 1,i,n =ΔV 1,i,n -k2d2.

[0067] (B6) Determine whether ΔV is satisfied simultaneously. 0,i,n ≤0.1, ΔV 1,i,n ≤0.15; if the condition is met, calculate the control objective function C(X) for the current rolling pressure change, and C i If (X) = C(X), then the rolling force fluctuation ΔP can be calculated using the formulas in steps B1 and B2. ey,i,n Then jump to B5; if the condition is not met, then C(X). opt =370.9, and output the corresponding roll gap adjustment amount of 0.064 caused by fluctuations in front and rear tension and rolling speed. Steps B1-B6 are shown in Table 1.

[0068] (C) Therefore, under the current conditions, the optimal adjustment amount of the roll gap is 0.264 mm.

[0069] Table 1 Optimization Process Data Table

[0070]

[0071] Example 2:

[0072] (A): Number of actual thickness deviation percentages of the incoming strip steel from Volume 2 collected: 1; bearing structural parameter coefficient: 0.9; roll speed at the first position when rolling the second roll of strip steel: 105 r·min. -1 The actual rolling force during the rolling of the second coil of strip at the first position was 9340 kN; the work roll speed at the manual zero position was 90 r / min. -1 The rolling force when the roll gap is zero under no-load conditions, determined by the manual zero-position method, is 10400 kN; the plasticity coefficient of the incoming strip steel in Volume 2 is 6000 kN·mm. -1 The mill stand stiffness is 10000 kN·mm. -1 The percentage deviations of the second and first actual incoming strip properties in Volume 2 are 0.25 and 0.15, respectively; the coefficient of yield strength of the incoming strip in Volume 2 with respect to rolling force is 0.9; the initial yield strength setting value of the incoming strip in Volume 2 is 1080MPa; the feedforward roll gap adjustment amount due to the deviation of incoming thickness and the deviation of incoming properties is calculated to be 0.18mm.

[0073] (B1): Collected 0.5 m·min values ​​of the mill inlet and outlet speed changes after roll gap adjustment during the rolling of the second strip. -1 0.75 m·min -1 The tension adjustment coefficients for rolling the second strip are 0.2 and 0.6; the front and rear tension settings for rolling the second strip are 263 kN and 250 kN. Calculate the changes in front tension after roll gap adjustment for the second strip: 36 kN and 39 kN.

[0074] (B2) Calculate the rolling force fluctuation of 875kN; calculate the roll gap adjustment of 0.875mm caused by the fluctuation of front and rear tension and rolling speed.

[0075] (B3) Collect the rolling pressure weighting coefficient of 0.5 and calculate the control objective function of rolling force change of 437.5kN.

[0076] (B4) Set the speed adjustment step size to 0.05 and 0.05 respectively, and the inlet and outlet speed adjustment coefficients to 1 and 1.5 respectively;

[0077] (B5) Let ΔV 0,i,n =ΔV 0,i,n -k1d1, ΔV 1,i,n =ΔV 1,i,n -k2d2.

[0078] (B6) Determine whether ΔV is satisfied simultaneously. 0,i,n ≤0.1, ΔV 1,i,n ≤0.15; if the condition is met, calculate the control objective function C(X) for the current rolling pressure change, and C i If (X) = C(X), then the rolling force fluctuation ΔP can be calculated using the formulas in steps B1 and B2. ey,i,n Then jump to B5; if the condition is not met, then C(X). opt =383.4, and output the corresponding roll gap adjustment amount of 0.058mm caused by fluctuations in front and rear tension and rolling speed. Steps B1-B5 are shown in Table 1.

[0079] (C) Therefore, under the current conditions, the optimal adjustment amount of the roll gap is 0.238 mm.

[0080] Table 2 Optimization Process Data Table

[0081]

[0082]

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling strip thickness in a cold continuous rolling mill based on a performance testing instrument, characterized in that: Includes the following steps: A: Model for calculating feedforward roll gap adjustment due to material thickness and material performance deviations ; Get the Number of coiled strip steel with actual thickness deviation percentage ; The structural parameter coefficient k of the bearing; the rolling mill rolling process Coiled steel No. Roll speed at position ,r·min -1 ; Rolling mill rolling Coiled steel No. Actual rolling force at each position KN; Working roller speed at manual zero position ,r·min -1 ; Rolling force when the no-load roll gap of the rolling mill is zero, determined by the manual zero-position method , kN; No. Plasticity coefficient of coiled strip steel kN·mm; Mill stiffness of the stand kN·mm -1 ;No. The first of the coiled strip steel , The percentage deviation of actual incoming material performance is as follows: , ;No. Incoming thickness setting value for coiled strip steel , mm; No. The coefficient of variation of yield strength of coiled strip steel with rolling force ;No. Initial yield strength setting value of coiled strip steel MPa; Calculate the feedforward roll gap adjustment amount caused by the deviation in incoming material thickness and performance based on the following formula. : ； B: Establish models for the relationship between velocity difference and tension difference, and calculate the first... Change in pretension after roll gap adjustment during strip steel rolling Post-tension change value ; Get the Change in mill inlet speed after roll gap adjustment during strip steel rolling Changes in export speed ,m·min -1 ;No. Tension adjustment coefficient during strip steel rolling Speed ​​adjustment coefficient ;No. Pre-tension setting value during strip steel rolling Back tension set value ,kN, the calculation of the first Change in pretension after roll gap adjustment during strip steel rolling Post-tension change value The kN is calculated using the following formula: C: Based on rolling force fluctuation The formula establishes a model for the feedforward roll gap adjustment caused by the rolling force fluctuation due to the tension difference. ; The amount based on rolling force fluctuation The KN formula establishes a model for the feedforward roll gap adjustment caused by the rolling force fluctuation due to the tension difference. as follows: D: Model for feedforward roll gap adjustment Solve the problem; E: Calculate the optimal roll gap adjustment under the current material thickness deviation and material performance conditions. , mm.

2. The method for controlling strip thickness in a cold continuous rolling mill based on a performance testing instrument according to claim 1, characterized in that: Optimal adjustment of roll gap The formula for mm is as follows: 。

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