Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method and device for pickling of a
metal, in particular, steel strip fed to a regulated pickling process.
DE 197 43 022 A1 discloses a method of pickling a metal strip based
on a measurement in the displacement direction after the pickling plant and
in which according to defect categories, which are determined by a
measuring unit, pickling parameters such as, e.g., temperature of the pickling
liquid, displacement speed of the metal strip, acid content in the pickling
liquid, metal content, in particular, iron content, strip parameters such as,
e.g., material and geometrical dimension, are adjusted. In this respect, the
defects can only be subsequently determined as well as a conclusion made as
to favorable pickling. The control system deals only with the pickling plant
itself.
According to another known method (EP-0 482 785 Al), turbulent
streams, which are generated in a pickling container with nozzles, are used.
Thereby, an optimal pickling result with a minimal consumption of a
pickling medium can be achieved. This result should be achieved by
controlling the turbulence of the stream in the pickling medium dependent
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on the displacement speed of the to-be-pickled strip. A far-reaching effect is
not to be expected.
A further method of pickling a rolled strip in a pickling plant is
disclosed in EP-0 602 437 B1. The method is based on a particular
operating mode according to which several pickling vats adjoin each other
one after the other. In the pickling vats, an acid-containing pickling medium
is sprayed by spraying nozzles arranged on a vat partially sidewise of, above
and below the strip displacement plane, with the nozzles being variably
controlled and with the pickling medium being introduced in an arbitrary
preselected amount. At that, the acid concentration, and/or medium
temperature, and/or the outlet speed of the pickling medium from nozzles are
preselected.
An object of the invention is to carry out the pickling process not only
on the basis of conventional pickling parameters but rather taking into
consideration additional parameters outside of the pickling vat.
According to the invention, this object is achieved by regulating the
pickling process, in addition to the pickling medium parameters, by
parameters of a coil and/or metal strip determined and/or measured before
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the metal strip enters the pickling section. The advantage consists in that
the
pickling parameters are so adjusted in advance that under- or over-pickling is
prevented, in that the acid concentration and the acid supply are correctly
adjusted, whereby the pickling medium is economically used, and in that the
correct temperature can be calculated in advance, together with other
adjustable pickling parameters. At that, the scale, which is removed after
casting, shaping, and annealing, and other coatings are already taken into
consideration. The invention also takes into consideration the preliminary
breaking of the scale (by a stretching-bending-straightening leveller),
whereby fissures and pores are formed in the scale layer, which increases the
surface on which the acid acts. In cases when the scale is removed by an
abrasive or hydromechanical treatment, the scale quantity, which is
dissolved in the pickling process, is reduced. Thereby, the preliminary
descaling permits to reduce pickling time. In case, the temperature of the
metal strip increases before the strip enters in the pickling section, the
contact time of the strip surface with the pickling medium increases at an
optimal pickling temperatures.
The heating path of the metal strip is shortened and the pickling time
falls. The pickling time also falls when the scale is removed by laser-optical
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means before the strip enters the pickling section, and the quantity of the to-
be-dissolved scale is reduced.
The method includes preadjustment of the pickling process in
accordance with measured values of a coil effected on a basis of a set-up
computation model, and regulating the process on a basis of a regulating
computation model that takes into consideration at least measured values for
the scale, strip temperature, pickling medium temperature, and/or acid
concentration. The quantity of the scale, e.g., needs not to be assessed, as
was the case previously. An integration of the additional scale calculation
model takes place. A target variable of such optimization can be: minimum
energy use, variable coil output, acceleration reaction dependent on the
surface contamination, minimizing the consumption of the pickling medium
and losses of the pickling medium, minimizing overpickling, and minimizing
underpickling. With regulated descaling units, measurement units for
determining scaling can determine thickness of the scale layer, shape,
distribution and color. To this end, precise calculation models are used.
According to an embodiment of the invention, the servo components
of the pickling section are regulated or readjusted based on a measured value
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for the scale deposit before the pickling section. This makes possible
regulation of the pickling section with a least possible transit time.
Advantageously, additional measured values for scale deposits or
coating are determined in a region in a displacement direction in front of the
pickling section, and are used for readjustment of the servo components of
the pickling section and/or dependent on measured and/or calculated values.
Other parameters outside of the pickling section are taken into
consideration by controlling the pickling times based on strip entrance data
of the coil and on the system adjustment.
In accordance with another method step, the measured values for the
coating or the scale are used for regulation of a pretreatment unit arranged
upstream of the pickling section.
It is advantageous that the pretreatment unit and the servo components
of the pickling section are readjusted in accordance with the measured and
calculated values.
In device for pickling a metal, in particular, steel strip fed in a
displacement direction from a coil of a pickling plant, for which a regulation
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by a plurality of parameters is contemplated, the object of the invention is
achieved by communicating measured values from coil measured value or
data transducers via a set-up computation model and a regulating
computation model to adjustment units of a pickling section. Thereby, the
pickling section can be operated with precise regulation which results in the
above-discussed advantages.
In one embodiment of the device, it is provided that measured value
from coil measured value transducers are input into the regulating
computation model. The set-up computation model uses general entrance
data for the metal strip. The scale deposits can be calculated by using a
trial
computation model for effecting preliminary adjustment of the slow and
rapid servo components of the pickling section or readjustment in
accordance with comparison.
In another case, the measured values of a measured value transducer
for coating or scale are used for readjustment of the servo components of the
pickling section.
According to other features, a pretreatment unit, the measured values
of which are input into the regulating computation model, is arranged
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upstream of the pickling section. Upon recognition of the exigency and by
suitable evaluation of the coil data and the instant system set-up, the
pretreatment unit can influence the pickling time. As a pretreatment unit, a
heating unit, a mechanical, abrasive, hydromechanical, laser-optical, or
oscillating descaler can be used.
Further improvement is achieved by providing an induction heating
unit between the pretreatment unit and the pickling section. The inductive
preheating of the metal strip takes place before the pickling section and is
used for rapid regulation of the metal strip temperature and for adjustment of
the metal strip pickling temperature.
The embodiments of the invention are schematically shown in the
drawings and will be explained in detail below.
The drawings show:
Fig. 1 a block-diagram of a basic design of a coil and pickling
plant with regulation,
Fig. 2 a first variant of the same block-diagram with a measured
value transducer,
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Fig. 3 a second variant of the block-diagram with a pretreatment
unit,
Fig. 4 a third variant of the block-diagram with a measured
value transducer and a pretreatment unit, and
Fig. 5 a fourth variant of the block-diagram with a measured
value transducer, a pretreatment unit, and induction
heating.
According tot he basic design shown in Fig. 1, a metal strip is fed
from a coil 2 into a pickling section 3. At that, coil data 4 from a data
transducer 4a and a data transducer 4b are introduced into a set-up
computation model 6 and/or into a regulation computation model 8 and are
processed in accordance with the program. In the set-up computation model
6 further measured values 7 can be taken into consideration. Thereby, the
pickling process is regulated, in addition to the pickling medium parameters,
before the metal strip 1 is fed into the pickling section 3, by parameters of
the coil 2 and/or the metal strip 1 which were determined, in the system 5,
with servo components and/or measured.
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In accordance with a first variant according to Fig. 2, in addition to the
presetting of the pickling medium parameters, additionally acquires
measured values, which characterized the coating or scale and which are
determined by a measured value transducer M in a scale registration unit 10,
are processed in the regulating computation model 8. The pickling process
is regulated, respectively (Figs. 1-5), on the basis of the set-up computation
model 6 with preset measured values of the coil 2 and on the basis of the
regulating computation model 8 which takes into account at least the
measured values for the scale, bath temperature, the temperature of the
pickling medium and/or acid concentration. The additional measured values
for scale deposits before the pickling section 3 are used for regulating or
readjusting the servo elements in the system 5.
In accordance with a second variant represented in Fig. 3 and a
suitable evaluation of the coil information 4, a pretreatment unit H, which
influences the pickling time, is used. In addition, the slow and rapid servo
components of the pickling section 3 are readjusted in accordance with
measured and/or calculated values output by the regulating computation
model 8, in particular, taking into consideration the changed pickling times.
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According to a third variant, represented in Fig. 4, additional
measured value of the scale deposits and coatings is determined by the
measured value transducer M of the scale registration unit 10 located in front
of the pickling section 3 in the displacement direction 9, and is used for
readjusting of the servo components of the pickling section 3 and/or in
accordance with measured and calculated values. Besides, the pickling times
are regulated on the basis of the strip inlet information of the coiler 2 and
the
system set-up. The acquired measured values with respect to coating and
scale are used for regulating a pretreatment unit H located upstream of the
pickling section 3.
On the basis of the fourth variant according to Fig. 5, in addition to the
scale registration unit 10 and the pretreatment unit H, an induction heating
unit W is provided between the pickling section 3 and the pretreatment unit
H. The pickling time is defined as a contact time of a to-be-cleaned surface
with the pickling medium necessary for a reliable removal of the
contamination from the strip 1. The pretreatment unit H can include a
preheating unit in form of the induction heating unit W.
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The pretreatment unit H basically includes a mechanical, abrasive,
hydromechanical, laser-optical, or oscillating descaler. The induction
preheating of the metal strip by the induction heating unit W is effected
before the pickling section and serves for a rapid regulation of the metal
strip
and pickling medium temperatures.
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List of Reference Numerals
1. Metal Strip
2. Coil
3. Pickling Section
4. Coil-data
4a. Data Transducer
4b. Data Transducer
5. System With Servo Components
6. Set-up Computation Model
7. Measured Values
8. Regulating Computation Model
9. Displacement Direction
10. Scale Registration Unit
M Measured Value Transducer
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H Pretreatment Unit
W Induction Heating Unit
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