EP1761346B1 - Method for increasing the process stability, particularly the absolute thickness precision and the installation safety during the hot rolling of steel or nonferrous materials - Google Patents

Abstract

The invention relates to a method for increasing the process stability, particularly the absolute thickness precision and the installation safety during the hot rolling of steel of nonferrous materials, with small degrees of deformation (f) or no reductions while taking the high-temperature limit of elasticity (R<SUB>e</SUB>) into account when calculating the set rolling force (F<SUB>w</SUB>) and the respective setting position (s). The process stability can be increased with regard to the precision of the yield stress (k<SUB>f,R</SUB>) and the set rolling force (F<SUB>w</SUB>) at small degrees of deformation (f) or small reductions, during which the high temperature limit of elasticity (R<SUB>e</SUB>) is determined according to the deformation temperature (T) and/or the deformation speed (phip) and is integrated into the function of the yield stress (k<SUB>f</SUB>) for determining the set rolling force (F<SUB>w</SUB>) via the relation (2) R<SUB>e</SUB>=a+e<SUP>b1+b2.T</SUP>.phip<SUP>c</SUP>, in which: R<SUB>e </SUB>represents the high temperature; phip represents the deformation speed, and; a, b, c represent coefficients.

Description

The invention relates to a method for increasing the process stability, in particular the absolute thickness accuracy and plant safety, during hot rolling of steel or non-ferrous materials with small degrees of deformation or small decreases taking into account the hot yielding strength in the calculation of the nominal rolling force and the respective employment position.

worin bedeuten:

k_f :

Fließspannung

k_f0 :

Grundwert der Fließspannung

T :

Umformtemperatur

ϕ :

Umformgrad

phip :

Umform-Geschwindigkeit

A;, m_i :

thermodynamische Koeffizienten.

In a pre-publication " Power and Labor Needs of Forming Methods "by A. Hensel and T. Spittel, Leipzig 1978 , and in another pre-publication " Rational Use of Energy in Forming Processes "by T. Spittel and A. Hensel, Leipzig 1981 , various methods for determining the target rolling force during hot rolling as a product of Umformwiderstand and depressed area are described. The forming resistance itself is determined as the product of the yield stress and a factor for taking account of the roll gap geometry and / or friction conditions. The most frequently used method for determining the yield stress is their determination via an approach with influencing factors for taking account of forming temperature, degree of deformation and deformation rate, which are multiplicatively connected to one another, for example in the following form: $${\mathit{k}}_{\mathit{f}}\mathit{=}{\mathit{k}}_{\mathit{f}\mathit{0}}\mathit{•}{\mathit{A}}_{\mathit{1}}\mathit{•}{\mathit{e}}^{\mathit{m}\mathit{1}\mathit{•}\mathit{T}}\mathit{•}{\mathit{A}}_{\mathit{2}}\mathit{•}{\mathit{phi}}^{\mathit{m}\mathit{2}}\mathit{•}{\mathit{A}}_{\mathit{3}}\mathit{•}{\mathit{PhIP}}^{\mathit{m}\mathit{3}}$$

in which mean:

k _f :

yield stress

k _f0 :

Basic value of yield stress

T :

forming temperature

φ:

deformation

phip :

Forming speed

A ;, m _i :

thermodynamic coefficients.

For different material groups, the thermodynamic coefficients were determined; the differentiation of the materials within a group takes place via the respective k _f0 basic values.

In the further article " Modeling the influence of chemical composition and forming conditions on yield stress of steels during hot forming "by M. Spittel and T. Spittel, Freiberg 1996 In addition, it is proposed to determine the basic value of the yield stress of a material as a function of its chemical analysis and to use the other parameters to take into account the temperature, the degree of deformation and the deformation rate according to the material group. Basically, however, the multiplicative character of the approach according to equation (1) remains.

The disadvantage of the multiplicative approach to determining the yield stress is that the function tends to shrink with a degree of deformation φ <0.04 or decreases against a yield stress of zero MPa, i. the function has a zero crossing (shown in the prior art in Fig. 1). However, this theory contradicts the actual conditions. As a result, too small yield stress values and thus too low nominal rolling forces are determined for small decreases. The settlement of the nominal roll gap by the thickness control is roller force dependent and thus faulty. The hot rolled products have a greater actual thickness compared to the desired target thickness.

The error-prone Sollwalzkraft calculation at small Umformgraden or decreases represents a permanent plant hazard during rolling with high rolling forces and / or rolling torques near the maximum allowable plant parameters as they occur, for example, when rolling with lowered temperatures or even at high temperatures and Walzgutbreiten close to the plant technology maximum possible width.

The error-prone Sollwalzkraft calculation also affects the overall process stability negative because downstream automation models and - regulations such as. Profile and planarity models or regulations determine their setpoints using the Sollwalzkraft.

From the WO 93/11886 A1 For example, there is known a rolling plan calculation method for setting the target rolling force and the target rolling gap of a rolling mill which uses stand-specific and / or material-specific rolling force adjustment members. Disadvantageous are framework-specific adjustments in the nominal rolling force calculation for the transferability to other plants.

From the WO 99/02 282 A1 a known method for controlling or presetting of the roll stand depending on at least one of rolling force, rolling moment and overfeed, in which the modeling of the influences by means of an information based on neural networks information processing or by means of an inverted rolling model on the back of the material hardness in the lurch with help a regression model. Such errors, which arise in the Sollwalzkraft calculation according to the multiplicative approach in the range of small degrees of deformation or decreases can be avoided. The disadvantage, however, is that to train a neural network or for an inverted rolling model only Walzergebnisse must be present. An application of the proposed method to not yet rolled materials or systems with other parameters is thus not readily guaranteed.

The described prior art has in common that the effect of small degrees of deformation or small decreases in the yield stress during hot rolling of steel and non-ferrous materials in the context of the known method for target driving on not yet rolled materials or on systems with other parameters is thus not readily guaranteed.

The described prior art has in common that the effect of small degrees of deformation or small decreases in the yield stress during hot rolling of steel and non-ferrous materials in the known methods for Sollwalzkraft calculation and thickness control is not taken into account correctly or insufficiently or the transferability other systems are limited and thus there are risks to the process stability, in particular the absolute thickness accuracy and plant safety.

The invention has for its object to provide a method for increasing the process stability, in particular the absolute thickness accuracy and plant safety during hot rolling of steel and non-ferrous materials, in which the accuracy of the yield stress and the Sollwalzkraft be increased with small degrees of deformation or small decreases can.

integriert wird, indem ein multiplikativer Fließkurvenansatz um die Warmstreckgrenze in Abhängigkeit von Umformtemperatur und Umformgeschwindigkeit gemäß der Formel $${\mathit{k}}_{\mathit{f}\mathit{,}\mathit{R}}\mathit{=}\mathit{a}\mathit{+}{\mathit{e}}^{\mathit{b}\mathit{1}\mathit{•}\mathit{b}\mathit{2}\mathit{•}\mathit{T}}\mathit{•}{\mathit{phip}}^{\mathit{c}}\mathit{+}{\mathit{k}}_{\mathit{f}\mathit{0}}\mathit{•}{\mathit{A}}_{\mathit{1}}\mathit{•}{\mathit{e}}^{\mathit{m}\mathit{1}\mathit{•}\mathit{T}}\mathit{•}{\mathit{A}}_{\mathit{2}}\mathit{•}{\mathit{\varphi }}^{\mathit{m}\mathit{2}}\mathit{•}{\mathit{A}}_{\mathit{3}}\mathit{•}{\mathit{phip}}^{\mathit{m}\mathit{3}}$$

bestimmt wird, wobei bedeuten:

R_e :

Warmstreckgrenze

T :

Umform-Temperatur

phip :

Umform-Geschwindigkeit

a; b; c:

Koeffizienten

The stated object is achieved in that the hot yielding determined as a function of forming temperature and / or forming rate and in the function of the yield stress for the determination of the target rolling force on the relationship $${\mathit{R}}_{\mathit{e}}\mathit{=}\mathit{a}\mathit{+}{\mathit{e}}^{\mathit{b}\mathit{1}\mathit{+}\mathit{b}\mathit{2}\mathit{•}\mathit{T}}\mathit{•}{\mathit{PhIP}}^{\mathit{c}}$$

is integrated by a multiplicative flow curve approach around the hot yield point as a function of forming temperature and forming speed according to the formula $${\mathit{k}}_{\mathit{f}\mathit{.}\mathit{R}}\mathit{=}\mathit{a}\mathit{+}{\mathit{e}}^{\mathit{b}\mathit{1}\mathit{•}\mathit{b}\mathit{2}\mathit{•}\mathit{T}}\mathit{•}{\mathit{PhIP}}^{\mathit{c}}\mathit{+}{\mathit{k}}_{\mathit{f}\mathit{0}}\mathit{•}{\mathit{A}}_{\mathit{1}}\mathit{•}{\mathit{e}}^{\mathit{m}\mathit{1}\mathit{•}\mathit{T}}\mathit{•}{\mathit{A}}_{\mathit{2}}\mathit{•}{\mathit{\phi }}^{\mathit{m}\mathit{2}}\mathit{•}{\mathit{A}}_{\mathit{3}}\mathit{•}{\mathit{PhIP}}^{\mathit{m}\mathit{3}}$$

is determined, where:

R _e :

Hot yield strength

T :

Forming temperature

phip :

Forming speed

a ; b; c :

coefficients

Due to the consideration according to the invention of the hot yielding strength as a function of the forming temperature and the forming speed, the method achieves correct values even with the smallest degree of deformation. The starting value is the respective hot yield strength of the material to be rolled depending on the forming temperature and the forming speed

The advantage of using a new approach to calculating yield stress is to determine the hot yielding strengths for the materials to be rolled from measured data of rolling with forming degrees smaller than a material-specific degree of deformation by measuring the yield stresses of the respective passes as a function of forming temperature and forming speed Rolling forces recalculated and equated to a hot yield point, if they are equal to the measured hot tensile yield from hot tensile tests. The found dependence of the hot yielding strength of forming temperature and forming speed represents the starting point of the approximated hot flow curve.

bestimmt wird, wobei bedeuten:

R_w :

Walzenradius

h₀ :

Dicke vor dem Stich

h₁ :

Dicke nach dem Stich

According to the further invention it is proposed that the yield stress in the conventional rolling force equation for determining the nominal rolling force for the thickness control and also for rake models and control methods according to the following equation $${\mathit{F}}_{\mathit{w}}\mathit{=}{\mathit{Q}}_{\mathit{p}}\mathit{•}{\mathit{k}}_{\mathit{f}\mathit{.}\mathit{R}}\mathit{•}\mathit{B}\mathit{•}{\left({\mathit{R}}_{\mathit{w}}\mathit{•}\left({\mathit{H}}_{\mathit{0}}\mathit{-}{\mathit{H}}_{\mathit{1}}\right)\right)}^{\mathit{1}\mathit{/}\mathit{2}}$$

is determined, where:

R _w :

roll radius

h ₀ :

Thickness before the stitch

h ₁ :

Thickness after the stitch

worin bedeuten:

C_M :

Materialmodul

F_w :

Sollwalzkraft

F_m :

gemessene Walzkraft

dh₁ :

Änderung der Auslaufdicke

In an embodiment of the invention, it is further provided that, due to the nominal rolling force, a material modulus, taking into account the hot yielding limit, is calculated as a function of the deformation temperature and deformation rate for degrees of deformation smaller than a material-specific degree of deformation according to the formula $${\mathit{C}}_{\mathit{M}}\mathit{=}\left({\mathit{F}}_{\mathit{W}}\mathit{-}{\mathit{F}}_{\mathit{m}}\right)\mathit{/}\mathit{d}{\mathit{H}}_{\mathit{1}}$$

in which mean:

C _M :

material module

F _w :

Set rolling force

F _m:

measured rolling force

ie ₁ :

Change of outlet thickness

erweitert wird, wobei bedeuten:

ds _AGC :

Änderung der Walzspalteinstellung

C_M :

Materialmodul

C_G :

Walzgerüstmodul

dh₁ :

Änderung der Auslaufdicke

F_w :

Sollwalzkraft

F_m :

gemessene Walzkraft

S :

Anstellung des Walzspaltes

S_soll :

Sollanstellung des Walzspaltes

The invention is then designed such that the conventional Gaugemeter equation into a mold $$\mathit{d}{\mathit{s}}_{\mathit{AGC}}\mathit{=}\left(\mathit{1}\mathit{+}{\mathit{C}}_{\mathit{M}}\mathit{/}{\mathit{C}}_{\mathit{G}}\right)\mathit{d}{\mathit{H}}_{\mathit{1}}\mathit{=}\left(\mathit{1}\mathit{+}{\mathit{C}}_{\mathit{M}}\mathit{/}{\mathit{C}}_{\mathit{G}}\right)\mathit{•}\left(\left({\mathit{F}}_{\mathit{W}}\mathit{-}{\mathit{F}}_{\mathit{m}}\right)\mathit{/}{\mathit{C}}_{\mathit{G}}\mathit{+}\mathit{s}\mathit{-}{\mathit{s}}_{\mathit{should}}\right)$$

is extended, where:

ds _AGC :

Change of roll gap setting

C _M :

material module

C _G :

Mill module

ie ₁ :

Change of outlet thickness

F _w :

Set rolling force

F _m:

measured rolling force

S :

Adjustment of the roll gap

S _should :

Sollanstellung the roll gap

As a result, the material flow behavior is now displayed correctly with small degrees of deformation or decreases.

On the basis of the Gaugemetergleichung and calculated Sollwalzkraft the Anstellposition the electromechanical and / or the hydraulic adjustment to ensure the outlet thickness of the rolling stock is determined.

In the drawing, diagrams are shown for the yield stress as a function of the degree of deformation according to the prior art and according to the invention and are explained in more detail below.

Fig. 1

schematisch den Verlauf der Fließspannung k_f, über dem Umformgrad ϕ beim herkömmlichen multiplikativen Ansatz (Stand der Technik) und

Fig. 2

schematisch den Verlauf der Fließspannung k_f,R über dem Umformgrad ϕ gemäß der Erfindung, wobei unterhalb des Grenzumfanggrades ϕ_G der multiplikative Ansatz um die Warmstreckgrenze additiv erweitert ist.

Show it:

Fig. 1

schematically the profile of the yield stress k _f , on the degree of deformation φ in the conventional multiplicative approach (prior art) and

Fig. 2

schematically the course of the yield stress k _{f, R} on the degree of deformation φ according to the invention, below the boundary circumference degree φ _G, the multiplicative approach is additively extended to the hot yielding limit.

The disadvantage of the multiplicative approach for determining the yield stress (FIG. 1) is that the function strives for small deformation degrees φ <0.04 or small decreases towards a yield stress k _f of zero MPa, ie the function has a zero crossing, such as drawn.

The consideration according to the invention (FIG. 2) of the hot yielding limit R _e as a function of the forming temperature T and the forming speed phip achieves the method according to the invention even with the smallest forming degrees φ of correct values. The starting value is the respective hot yielding strength R _{e of} the material to be rolled as a function of the forming temperature T and the forming speed phip.

LIST OF REFERENCE NUMBERS

A _i

thermodynamic coefficients

a _i b _i , c

coefficients

B

rolling stock width

C _G

stand modulus

C _M

material module

ie ₁

Change of outlet thickness

the _AGC

Change of roll gap setting

F _m

measured rolling force

F _w

Set rolling force

h ₀

Thickness before the stitch

h ₁

Thickness after the stitch

k _f

yield stress

k _f0

Basic value of yield stress

k _{f, R}

Yield stress, taking into account the yield strength

m _i

thermodynamic coefficients

φ

deformation

φ _G

Grenzumformgrad

PhIP

strain

Q _p

Function to take account of roll gap geometry and friction conditions

R _e

Hot yield strength

R _w

roll radius

S

Adjustment of the roll gap

S _should

Sollanstellung the roll gap

T

forming temperature

Claims (4)

1. Method of increasing the process stability, particularly the absolute thickness accuracy and the plant safety, in hot rolling of steel materials or NE materials, with small degrees of reshaping (ϕ) or small reductions with consideration of the high-temperature limit of elasticity (R_e ) in the calculation of the target rolling force (F_w ) and the respective adjustment position (s), characterised in that the high-temperature limit of elasticity (R_e ) is determined in dependence on reshaping temperature (T) and/or reshaping speed (phip) and is integrated in the function of the flow stress (k _f,R ) for the determination of the target rolling force (F_w ) by way of the equation $${\mathit{R}}_{\mathit{e}}\mathit{=}\mathit{a}\mathit{+}{\mathit{e}}^{\mathit{b}\mathit{1}\mathit{+}\mathit{b}\mathit{2}\cdot \mathit{T}}\cdot {\mathit{phip}}^{\mathit{c}}$$

   

   
   in that a multiplicative flow curve formulation about the high-temperature limit of elasticity (R_e ) is determined in dependence on reshaping temperature (T) and reshaping speed (phip) according to the formula $${\mathit{k}}_{\mathit{f}\mathit{;}\mathit{R}}\mathit{=}\mathit{a}\mathit{+}{\mathit{e}}^{\mathit{b}\mathit{1}\mathit{+}\mathit{b}\mathit{2}\mathit{\cdot }\mathit{T}}\mathit{\cdot }{\mathit{phip}}^{\mathit{c}}\mathit{+}{\mathit{k}}_{\mathit{f}\mathit{0}}\mathit{\cdot }{\mathit{A}}_{\mathit{1}}\mathit{\cdot }{\mathit{e}}^{\mathit{m}\mathit{1}\mathit{\cdot }\mathit{T}}\mathit{\cdot }{\mathit{A}}_{\mathit{2}}\mathit{\cdot }{\mathrm{\varphi }}^{\mathit{m}\mathit{2}}\mathit{\cdot }{\mathit{A}}_{\mathit{3}}\mathit{\cdot }{\mathit{phip}}^{\mathit{m}\mathit{3}}$$

   

   
   wherein:

   R _e : high-temperature limit of elasticity

   T : reshaping temperature

   phip : reshaping speed

   a,;b_j;c : coefficients
2. Method according to claim 1, characterised in that the flow stress (k_f,R ) in the conventional rolling force equation for determination of the target rolling force (F_w ) for the thickness regulation and also for computing models and regulating methods is determined according to the following equation $${\mathit{F}}_{\mathit{w}}\mathit{=}{\mathit{Q}}_{\mathit{p}}\mathit{\cdot }{\mathit{k}}_{\mathit{f}\mathit{,}\mathit{R}}\mathit{\cdot }\mathit{B}\mathit{\cdot }{\left({\mathit{R}}_{\mathit{w}}\mathit{\cdot }\left({\mathit{h}}_{\mathit{0}}\mathit{-}{\mathit{h}}_{\mathit{1}}\right)\right)}^{\mathit{1}\mathit{/}\mathit{2}}$$

   

   
   wherein:

   F_w : target rolling force

   Q_p : function for consideration of rolling gap geometry and friction relationships

   k_f,R : flow stress, with consideration of limit of elasticity

   B : rolling stock width

   R_w : roll radius

   h₀ : thickness prior to the pass

   h₁ : thickness after the pass
3. Method according to one of claims 1 and 2, characterised in that on the basis of the target rolling force (F_w) a material modulus (C_M ) is calculated with consideration of the high-temperature limit of elasticity (R_e ) in dependence on the reshaping temperature (T) and reshaping speed (phip) for degrees of reshaping less than a material-specific limit degree of reshaping (ϕG), according to the formula $${\mathit{C}}_{\mathit{M}}\mathit{=}\left({\mathit{F}}_{\mathit{W}}\mathit{-}{\mathit{F}}_{\mathit{m}}\right)\mathit{/}\mathit{d}{\mathit{h}}_{\mathit{1}}\mathit{,}$$

   

   
   wherein:

   C_M : material modulus

   F_w : target rolling force

   F_m : measured rolling force

   dh₁ : change in exit thickness
4. Method according to claim 3, characterised in that the conventional gauge-meter equation is expanded to a form $$\mathit{d}{\mathit{s}}_{\mathit{AGC}}\mathit{=}\left(\mathit{1}\mathit{+}{\mathit{C}}_{\mathit{M}}\mathit{/}{\mathit{C}}_{\mathit{G}}\right)\mathit{d}{\mathit{h}}_{\mathit{1}}\mathit{=}\left(\mathit{1}\mathit{+}{\mathit{C}}_{\mathit{M}}\mathit{/}{\mathit{C}}_{\mathit{G}}\right)\mathit{\cdot }\left(\left({\mathit{F}}_{\mathit{W}}\mathit{-}{\mathit{F}}_{\mathit{m}}\right)\mathit{/}{\mathit{C}}_{\mathit{G}}\mathit{+}\mathit{s}\mathit{-}{\mathit{s}}_{\mathit{soll}}\right)$$

   

   
   wherein:

   dS_AGC : change in rolling gap setting

   C_M : material modulus

   C_G : roll stand modulus

   dh₁ : change in exit thickness

   F_w : target rolling force

   F_m : measured rolling force

   s : adjustment of the rolling gap

   s_soll : target adjustment of the rolling gap

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