Process and computer program for controlling a rolling process
View Patent ↗The invention relates to a method for controlling a rolling process, in which a metal strip is rolled flat by use of at least one roller. It is known from the prior art that the relative position of a neutral point represents a measure of the instantaneous stability of a rolling process. However, traditional methods for calculating the position of the neutral point do not accurately represent the actual properties of metal and therefore have only limited usefulness for predicting the stability of a rolling process. In order to allow better control of a rolling process for rolling a metal strip with regard to the actual behavior of the metal strip, the invention proposes a new method for calculating the relative position of the neutral point, in which in particular the flat yield stress k e and the hydrostatic pressure p N H at the neutral point are incorporated.
1. A method of controlling a rolling process in which a metal strip is rolled flat by use of at least one roller, the method comprising the steps of:
detecting the position of a neutral point in a contact arc between the metal strip and the roller;
stabilizing the rolling process such that a position ξ of the neutral point is between a lower threshold value of 0.12 and an upper threshold value of 0.40 by intervening in the rolling process by use of suitable measures;
calculating the value of the flat yield stress k e of the metal strip and the value of the hydrostatic pressure p N H at the neutral point as not directly measurable process parameters based on the calculated values for the flat yield stress k e and the hydrostatic pressure p N H on the basis of a first group of measurable process parameters and on the basis of the flat modulus of elasticity E* of the metal strip and of the compressibility K of the metal strip;
calculating the position ξ of the neutral point according to the following formula:
ξ
=
(
f
slip
+
1
)
(
1
-
σ
A
3
K
-
p
N
+
q
N
2
K
+
k
e
-
σ
A
E
*
)
-
1
h
E
/
h
A
(
1
+
k
e
-
σ
A
E
*
)
-
1
where
f slip : represents the advance;
σ A : represents the strip outlet tension;
K: represents the compressibility of the metal strip;
p N : represents the pressure in the roller gap at the neutral point, perpendicular to the metal strip;
q N : represents the pressure in the roller gap at the neutral point, in the longitudinal direction of the metal strip;
k e : represents the flat yield stress;
E*: represents the flat modulus of elasticity of the metal strip;
h E : represents the strip thickness at the inlet; and
h A : represents the strip thickness at the outlet.
2. The method according to claim 1 wherein the first group of measurable process parameters for calculating the flat yield stress k e , the hydrostatic pressure p N H at the neutral point, or the position of the neutral point comprises the parameters advance f slip , the strip inlet thickness h E , the strip inlet thickness h A , and the strip outlet tension σ A of the metal strip.
3. The method according to claim 1 wherein the second group of measurable process parameters for calculating the flat yield stress k e or the hydrostatic pressure p N H at the neutral point comprises the strip inlet tension σ E , the roller force F, the strip width b, the radius R 0 of the roller, and the flat modulus of elasticity E* R of the roller.
4. A method of controlling a rolling process in which a metal strip is rolled flat by use of at least one roller, the method comprising the steps of:
detecting the position of a neutral point in a contact arc between the metal strip and the roller;
stabilizing the rolling process according to a position ξ of the neutral point by intervening in the rolling process by use of suitable measures by increasing the strip tension at the outlet, decreasing the strip tension at the inlet, or increasing the friction in the roller gap when the position ξ of the neutral point is between zero and a lower threshold value of 0.12;
calculating the value of the flat yield stress k e of the metal strip and the value of the hydrostatic pressure p N H at the neutral point as not directly measurable process parameters by use of a mathematical model for the individual rolling process on the basis of a first and a second group of measurable process parameters;
calculating the position of the neutral point based on the estimated values for the flat yield stress k e and the hydrostatic pressure p N H on the basis of the first group of measurable process parameters and on the basis of the flat modulus of elasticity E* of the metal strip and of the compressibility K of the metal strip; and
calculating the position of the neutral point according to the following formula:
ξ
=
(
f
slip
+
1
)
(
1
-
σ
A
3
K
-
p
N
+
q
N
2
K
+
k
e
-
σ
A
E
*
)
-
1
h
E
/
h
A
(
1
+
k
e
-
σ
A
E
*
)
-
1
where
f slip : represents the advance;
σ A : represents the strip outlet tension;
K represents the compressibility of the metal strip;
p N : represents the pressure in the roller gap at the neutral point, perpendicular to the metal strip;
q N : represents the pressure in the roller gap at the neutral point, in the longitudinal direction of the metal strip;
k e : represents the flat yield stress;
E*: represents the flat modulus of elasticity of the metal strip;
h E : represents the strip thickness at the inlet; and
h A : represents the strip thickness at the outlet.
5. A method of controlling a rolling process in which a metal strip is rolled flat by use of at least one roller, the method comprising the steps of:
detecting the position of a neutral point in a contact arc between the metal strip and the roller;
stabilizing the rolling process according to a position of the neutral point by intervening in the rolling process by use of suitable measures;
calculating the value of the flat yield stress k e of the metal strip and the value of the hydrostatic pressure p N H at the neutral point as not directly measurable process parameters by use of a mathematical model for the individual rolling process on the basis of a first and a second group of measurable process parameters;
calculating the position of the neutral point based on the estimated values for the flat yield stress k e and the hydrostatic pressure p N H on the basis of the first group of measurable process parameters and on the basis of the flat modulus of elasticity E* of the metal strip and of the compressibility K of the metal strip;
decreasing the strip tension at the outlet, increasing the strip tension at the inlet, or reducing the friction when the position ξ of the neutral point is greater than an upper threshold value of 0.4; and
calculating the position ξ of the neutral point according to the following formula:
ξ
=
(
f
slip
+
1
)
(
1
-
σ
A
3
K
-
p
N
+
q
N
2
K
+
k
e
-
σ
A
E
*
)
-
1
h
E
/
h
A
(
1
+
k
e
-
σ
A
E
*
)
-
1
where
f slip : represents the advance;
σ A : represents the strip outlet tension;
K: represents the compressibility of the metal strip;
p N : represents the pressure in the roller gap at the neutral point, perpendicular to the metal strip;
q N : represents the pressure in the roller gap at the neutral point, in the longitudinal direction of the metal strip;
k e : represents the flat yield stress;
E*: represents the flat modulus of elasticity of the metal strip;
h E : represents the strip thickness at the inlet; and
h A : represents the strip thickness at the outlet.
6. The method according to claim 1 wherein the rolling process is stabilized either automatically or by intervention by an operator in the rolling process, according to the calculated position of the neutral point.
7. The method according to claim 1 wherein the calculated position of the neutral point is preferably stored over its elapsed time period, or is displayed for an operator on a display device.