EP0532560B1 - Process for the production of low-residual-stress rolled strip - Google Patents

Abstract

The invention concerns the production of low-residual-stress strip and is applicable to the metal-forming field. The invention proposes that, during rolling, the gap between the finishing rolls is adjusted in n strip elements by adjustment means by an amount ΔSi, although the number n of measurement zones does not necessarily have to be equal to the number of adjustment zones. The adjustment amounts ΔSi for the individual strip elements, including the no-slip point, are continuously determined by determining, before or at the beginning of the roll pass, the mean pass reduction ε^¨B7h,ges and the reduction value ε^¨B7h,k characteristic of the reduction from the no-slip point to the exit side of the roll gap. The quotient of these two parameters, ε^¨B7h,ges/ε^¨B7h,k, gives, following multiplicative combination with the final thickness h1, a constant quantity valid for the particular roll pass. Multiplicative combination of this constant quantity with the instantaneous strip elongation or contraction values Δεl,i, obtained for the particular strip element i from the stress measurement device gives the adjustment amounts ΔSi necessary for control of the fine adjustment of the roll gap contour by the adjustment means.

Description

According to the preamble of claim 1, the invention relates to the production of low-stress tape and is applicable in the field of metal forming.

The aim of rolling strip is to avoid and secure strip curl. that the strip is low in residual stress after rolling in the longitudinal direction across the strip. Recently, different actuators for setting the fine rolling gap have been used specifically. Actuators of this type include, among other things, roll bending devices, intermediate rolls which can be displaced in the axial direction with symmetrically or asymmetrically shaped roll bales, displaceable work rolls, devices for inclining the rolls. furthermore the influencing of the thermal profile of the rolls by means of defined local application of coolant as well as support rolls which change in the profile of the rolls. In the case of 20-roll mills, the support saddles are also the outer ones Support rollers used to adjust the fine roll gap (H. Galla. H. Jung: "Rolling flat products", German Society for Metallurgy, Information Society, Verlag 1986).

In order to be able to use these actuators sensibly for profile control of the fine roll gap with the aim of producing low-tension strip, additional measuring devices are used in modern rolling plants to record the strip longitudinal tension curve over the strip width. These measuring devices record the band tension curve u. a. with special measuring rollers, styli or via electromagnetic force effects.

   + Eigendruckspannungen
   - Eigenzugspannungen
und gemäß dem Hooke'schen Gesetz die Längsdehnungs- oder -stauchungsbeträge $$\text{Δεl, i =}\frac{\text{Δσl,i}}{\text{E}}$$

   + Längsstauchungsbeträge
   - Längsdehnungsbeträge
ermittelt werden (Bild 1).From the measured strip tension curve σli, the longitudinal tension applied from outside (e.g. by reel tension) during rolling can be eliminated σ l the residual stress curve Δσl. i in the strain relief strip $$\text{Δσl, i = σl, i -}\overline{\text{σ}}\text{l}$$

+ Residual compressive stresses
- internal tensile stresses
and, according to Hooke's law, the amounts of elongation or compression $$\text{Δεl, i =}\frac{\text{Δσl, i}}{\text{E}}$$

+ Longitudinal compression amounts
- amounts of longitudinal expansion
can be determined (Figure 1).

The aim is to use the actuators mentioned to set the fine roll gap using the signals continuously generated by the measuring devices in such a way that band ripple is avoided and low-tension band is produced.

For the correct conversion of the strip tension measurement values Δσ _{l, i} or longitudinal expansion and compression measurement values Δεl, i into the setting values ΔS _i required for the correction of the fine roll gap, separate transfer functions are required.

besteht und folglich aus den Δε_l,i -Meßwerten die Dickenanstellwerte abgeleitet werden können.It has heretofore been assumed that in the absence or only slight spreading of the strip during the rolling pass, a proportionality between the Δε _{l, i} values and the deformation values Δεh derived from the thickness profiles of the strip entering and leaving the strip. i
according to $$\text{Δεl, i = Δεh, i}$$

exists and consequently the thickness values can be derived from the Δε _{l, i} measured values.

wobei $$\text{εh,i =}\frac{{\text{h}}_{\text{0,i}}{\text{- h}}_{\text{1,i}}}{{\text{h}}_{\text{0,i}}}$$

und

The picture is 2 $$\text{Δεh, i = εh, i -}\overline{\text{ε}}$$

in which $$\text{εh, i =}\frac{{\text{H}}_{\text{0, i}}{\text{- H}}_{\text{1, i}}}{{\text{H}}_{\text{0, i}}}$$

and

eingeführt wurden (Gl. (7) steht analog zu Gl. (2) mit Gl. (3) in Verbindung).However, rolling practice has shown that the thickness setpoints ΔSi determined for the reduction of the longitudinal stresses from the measured elongation and extension values Δεl, i, including equation (3), do not lead to the desired goal. Special investigations (Bernsmann, GP; Iron and Steel Engineer, 1972/3, pages 67-71). (Becker, H .; Freundel, P .; Scientific Journal of the TU-Magdeburg 19, 1975, Issue 7/8, pages 753-761), (Köpstein, E .; Grigorjan, GG; Zeleznow, Ju. D .; Neue Hütte 1975, 4, pages 226-228), taking into account the incoming and outgoing band profile (see also Figure 2), resulted in very large and strongly scattering deviations. which as the correction factor K _M in the relationship $${\text{Δσl, i = K}}_{\text{M}}\text{. E (εh, i -}\overline{\text{ε}}\text{)}$$

were introduced (Eq. (7) is connected to Eq. (3) analogously to Eq. (2)).

These correction factors include value ranges K _M = 0.05 .... 0.1 ... 0.2. Similarly, it was found that measured with Bandspannungsmeßgeräten longitudinal tension values (Δσl, i) _{in accordance with} are much lower than that calculated from the thickness profiles longitudinal stress changes (Δσ _{h, i) calcd.} This is the difference according to Köpstein $$\frac{{\text{(Δσl, i)}}_{\text{acc}}}{{\text{(Δσh, i)}}_{\text{about}}}\text{≈ 0.07 .... 0.14}$$

A dependency of these strongly fluctuating correction factors on characteristic rolling conditions could not be recognized. Therefore, there are currently very large uncertainties and inaccuracies in the determination of the adjustment values ΔSi required for setting the fine roll gap from the Δσl, i - and Δεl, i measured values obtained from strip tension measuring devices, so that the rolling of low-tension strip causes considerable problems. The resulting quality deficiencies of the rolled strips reduce the value in use and result in economic losses.

The aim of the invention is to use the adjustment options for the fine roll gap in such a way that low-tension strip can be produced, thereby creating prerequisites so that a higher strip quality is achieved during rolling and less technological difficulties arise when processing the strips and sheets.

The invention is based on the technical problem in the production of low-tension strip, where rolling is carried out in the usual way, using actuators for adjusting the fine rolling gap and measuring devices for the course of the strip length tensions over the strip width to perform the strip rolling process in such a way that the Adjustment values ΔSi corresponding to the real rolling conditions for setting the fine rolling gap in the production of low-tension strip are determined and used.

According to the invention the object is achieved by carrying out the method steps of claim 1 in that during the rolling by actuators the fine rolling gap in n strip elements is set by actuating amounts ΔSi, but the number n of measuring sections does not necessarily have to match the number of adjusting sections, whereby the actuating amounts ΔSi for the individual Strip elements, including the flow sheath (Figure 1), are continuously determined in such a way that the mean stitch decrease before or at the start of the stitch ε _h, tot and the partial purchase amount ε _{h, k} , which indicates the decrease from the flow sheath to the roll gap exit. The ouotient formed from both sizes ε _{h, tot} / ε _{h, k} results after multiplicative combination with the final thickness h₁ a fixed amount valid for the respective rolling pass $$\frac{{\overline{\text{ε}}}_{\text{h, sat}}}{{\overline{\text{ε}}}_{\text{h, k}}}\text{· H₁}$$

After multiplicative linking of this fixed amount with the current strip elongation or compression values Δε _l, i obtained from the strip tension measuring device for the respective strip element _i , the actuating amounts ΔS _i required for the fine adjustment of the roll gap contour result as a default value for the fine adjustment of the roll gap contour, which is carried out by means of an actuator.

In cases in which the strip tension measuring device for the respective strip elements i does not display the measured values as current strip elongation or compression values Δε _{l, i} , but rather as strip longitudinal stresses Δσ _{l, i} , these tension values are initially converted into strip elongation or - according to Hooke's law. compression values converted.

h_o,i

örtliche Dicke vor dem Stich im i-ten Bandstreifelement,

h_i,i,

örtliche Dicke nach dem Stich im i-ten Bandstreifelement,

h₀

mittlere Banddicke vor dem Stich,

hi

mittlere Banddicke nach dem Stich,

h_k

mittlere Dicke an der Fließscheide (Bild 1),

l_k

Abstand der Fließscheide vom Walzspaltaustritt,

l_d

gedrückte Länge des Walzspaltes,

R

Radius der Arbeitswalzen.

Bild 1

veranschaulicht den Walzvorgang.

The invention will be explained in more detail in the following example. the following 6 sizes are included (see also Figure 2):

h _{o, i}

local thickness before the stitch in the i-th strip strip element,

h _{i, i} ,

local thickness after the stitch in the i-th strip strip element,

h₀

average tape thickness before the stitch,

Hi

average tape thickness after the stitch,

h _k

average thickness at the flow sheath (picture 1),

l _k

Distance of the flow sheath from the roll gap exit,

l _d

pressed length of the nip,

R

Radius of the work rolls.

Image 1

illustrates the rolling process.

A metal strip made of deep-drawing steel with a width of 300 mm is rolled from an average starting thickness h₀ = 0.47 mm to an average final thickness h _i = 0.34 mm on a 20 roller mill with a work roll radius R = 21 mm. Here, the external longitudinal tension applied by the tension reel to the outgoing belt is σ₁ = -180N / mm². A strip tension measuring device in n = 11 strips elements evenly distributed over the bandwidth in Table 1, column 2 measured longitudinal stress σ _{l, i} , registered. According to Eq. (1) The curve of the longitudinal stress Δσ _{l, i} determined for an instantaneous state is shown in column 3 of Table 1. This gives the amounts of longitudinal expansion or compression Δε _{l, i} according to Eq. (2) in column 4 of Table 1.

mit ε _{h, ges} = 0,2766

• die Fließscheidenhöhe h_k gemäß bekannter Gleichungen (z. B. Knuschner, A.; Freiberger Forschungshefte B 267, VEB Dt. Verlag für Grundstoffindustrie. Leipzig 1989 oder Neue Hütte 1981, 3. Seiten 94-99). $${\text{h}}_{\text{k}}{\text{= h₁ + 2 R [1-cos[arc sin (l}}_{\text{k}}{\text{/l}}_{\text{d}}{\text{· l}}_{\text{d}}\text{/2 R)]]}$$
  
  
  Im vorliegenden Beispiel wird für einen bezogenen Abstand der Fließscheide l_k/l_d = 0,3 die Fließscheide nach Gl. (9) zu
  h_k = 0,3517 ermittelt.
• der die mittlere Abnahme von der Fließscheide bis zum Walzspaltaustritt kennzeichnende Teilabnahmebetrag $$\overline{\text{ε}}\text{h,k =}\frac{{\text{h}}_{\text{k}}\text{- h₁}}{\text{h₀}}$$
  
  
  Im Beispiel beträgt ε _h,k = 0,0249.
• der für diesen Walzstich gültige Festbetrag $$\frac{{\overline{\text{ε}}}_{\text{h, ges}}}{{\overline{\text{ε}}}_{\text{h, k}}}\text{· h₁}$$
  
  nimmt im Beispiel den Wert 3,7773 an.

According to the invention, the following are determined before or at the start of the stitch: $${\overline{\text{ε}}}_{\text{h, sat}}\text{=}\frac{\text{h₀ - h₁}}{\text{h₀}}$$

With ε _h, tot = 0.2766

• the flow sheath height h _k according to known equations (e.g. Knuschner, A .; Freiberger Research Books B 267, VEB Dt. Verlag für Grundstoffindustrie. Leipzig 1989 or Neue Hütte 1981, 3. Pages 94-99). $${\text{H}}_{\text{k}}{\text{= h₁ + 2 R [1-cos [arc sin (l}}_{\text{k}}{\text{/ l}}_{\text{d}}{\text{· L}}_{\text{d}}\text{/ 2 R)]]}$$
  
  
  In the present example, for a related distance between the flow sheath l _k / l _d = 0.3, the flow sheath according to Eq. (9) to
  h _k = 0.3517 determined.
• the partial purchase amount characterizing the average decrease from the flow sheath to the roll gap exit $$\overline{\text{ε}}\text{h, k =}\frac{{\text{H}}_{\text{k}}\text{- h₁}}{\text{h₀}}$$
  
  
  In the example is ε _{h, k} = 0.0249.
• the fixed amount valid for this roll pass $$\frac{{\overline{\text{ε}}}_{\text{h, sat}}}{{\overline{\text{ε}}}_{\text{h, k}}}\text{· H₁}$$
  
  takes the value 3.7773 in the example.

During the roll pass, the respective actuating amounts ΔS _{i are determined} as default values for the fine adjustment of the roll gap contour by continuously multiplying the fixed amount of 3.7773 valid for this roll pass with the current elongation and compression amounts Δε _{l, i} determined by the strip tension measuring device

In this way, the employment amounts ΔS _i are obtained in column 5, table 1.

If the ΔS _i values are negative, the fine roll gap height h1, i in the associated strip elements is narrowed by the specified values ΔS _i using suitable actuators. In contrast, positive ΔS _i values require an increase in the roll gap height h _{1, i} by the specified ΔS _i values. After this correction of the fine roll gap, the strip is free of longitudinal tension. If the measured values Δε _{l, i} change on the belt tensioner _, the ΔS _i values must be determined again in the manner indicated.

Claims (2)

1. A method for producing low-internal-stress strip during rolling, in which rolling is performed in conventional manner and positioning members for setting the fine roll nip and measuring devices for the curve of the longitudinal stress of the strip across the width are used,
   characterised in that during rolling the fine roll nip is set by positioning members into n strip elements each by positioning amounts ΔS_i, but in so doing the number n of the measuring sections does not necessarily have to correspond to the number of the positioning sections, the positioning amounts ΔS_i for the individual strip elements being determined continuously, including the neutral point, such that before or at the beginning of the pass the average reduction per pass ε _{h, ges} and the partial reduction amount ε _h,k which characterises the reduction from the neutral point to the exit from the roll nip are determined, the quotient ε _{h, ges}/ε _h,k formed therefrom is multiplicatively joined with the average end thickness h₁ and this fixed amount ε _{h, ges}/ε _h,k · h₁ which is valid for the respective pass after multiplicatively joining with the current strip elongation or strip upsetting value Δε_l,i obtained by the strip stress-measuring apparatus for the respective strip element i represents the respective positioning amounts ΔS_i for the fine adjustment and is used for setting.
2. A method according to Claim 1, characterised in that in cases in which the strip stress-measuring apparatus for the respective strip elements i indicates the measured values not as current strip elongation or strip upsetting values Δε_R,i, but as longitudinal strip stresses Δσ_l,i, these stress values are first converted into strip elongation or strip upsetting values in accordance with Hooke's Law.

Images