EP3097218B1 - Method and system for hot-dip coating hot-rolled steel strips - Google Patents

Description

The invention relates to a process for hot-dip coating of hot-rolled steel strip in a continuous strip plant in which the hot strip is subjected to a pretreatment for descaling, is galvanized, is reduced by cold working in its thickness and undergoes a post-treatment. Furthermore, the invention relates to a plant for producing hot-dip coated, hot rolled steel strip.

The liberation of the hot strip from the scale (pretreatment) as a prerequisite for cold forming and galvanizing is preferably carried out by pickling, rinsing and drying. For example, a straightening and / or a chemical treatment can be provided for the aftertreatment.

By the WO2006 / 097237 A1 ( EP 1 861 517 B1 ) for hot dip steel strip hot dip coating, a process and equipment having thickness reduction controlled thickness reduction performed after galvanizing has become known. For this purpose, a rolling stand is provided in the process line, wherein by reaching at least one thickness gauge in the outlet of the rolling mill, the achievement of the finished thickness is controlled and the deviations from this up or down as a control signal to the employment of the rolling stand are returned to increase the thickness reduction or to reduce. This takes place in a continuous process line, in which the steel strip first by descaling, z. B. by means of a scale breaker, and pickling and rinsing is pretreated, then the steel strip passes through a galvanizing, which connects the rolling stand with the thickness gauge in the outlet for controlled thickness reduction, before the steel strip the final Aftertreatment is experienced, such as straightening and chemical treatment. The finished product thus prepared is in a z. B. a tape storage and a trimming scissors having outlet part to tape coils wound with a desired diameter.

In this known method, there are technological disadvantages that can affect individually or together for the production of high-quality, galvanized strip surfaces unfavorable. The disadvantages are the fact that for galvanizing the tape roughness must be accepted, which brings the band through the preliminary processes with it. This can lead to surface problems with very rough strip surfaces and particularly thin layer supports. Furthermore, the soft zinc layer on the much harder steel strip in the controlled thickness reduction by the necessary high pressures in the nip to achieve the desired decreases in the range of 2 to 30%, preferably 4 to 10%, heavily loaded, resulting in increased abrasion of zinc particles which can deposit as contamination on the belt surface and degrade tape cleanliness for downstream processes. Finally, there is the danger that the zinc layer, which must undergo the reduction in the surface area of the strip by elongation due to the reduction in the thickness of the steel base material, damages, eg. As cracks, which destroy the corrosion protection effect of the zinc layer.

Out DE 10 2007 032 874 A1 A method of hot dip coating a hot rolled steel strip is known in which the steel strip is subjected to further surface treatment, eg by temper rolling, subsequent to the hot dip coating in order to achieve certain center roughness values for the finished produced steel strip.

Out EP 0 613 736 A1 and EP 2 816 132 B1 For example, methods for hot-dip coating a hot-rolled metal strip are known, wherein the hot-rolled strip is subjected to a thickness reduction before the coating process.

EP 1 681 363 A1 shows a generic method according to the preamble of claim 1, and a corresponding plant according to the preamble of claim 3.

The invention is therefore an object of the invention to provide a method and a system of the type mentioned, with which can reach high quality, galvanized bands and strip surfaces without the disadvantages mentioned.

This object is achieved by a method according to claim 1, in which the freed from the scale hot strip in a galvanizing preceding process step with reduction of its strip thickness by 0.5 to 10%, cold formed, while the metal strip at the same time a surface structure with a predetermined Center roughness is impressed. Here, in both cold forming, i. both before and after the process step of galvanizing, the strip in each case by a cold rolling process in a cold rolling stand using work rolls having a surface texture with a mean roughness Ra of 0.2 - 3 microns imprinted a surface structure.

In connection with the implementation of the method is to be considered that the size of the cold forming and thus the reduction of the strip thickness both directly from the percentage ratio of the strip thickness, as well as indirectly. B. from the measured and converted ratios of the belt speeds before and after the cold forming, known in practice known as a temper. For all of the following thickness reduction data, this means that less than 30% reduction in thickness corresponds to less than 43% skin pass and the preferred range of 0.5 to 10% reduction is equivalent to 0.5 to 11.1% skin pass.

If, according to a further proposal of the invention, the thickness of the cold-formed strip is measured before galvanizing and a deviation from a nominal thickness as a controlled variable for the reduction in thickness of the cold forming is attributed, a controlled reduction in thickness can be achieved.

According to another proposal of the invention it is provided that before the galvanizing the size of the cold forming, preferably the reduction in thickness, is controlled and regulated to a desired value. By controlling the size of the cold forming, which also includes a determined from the difference in belt speeds in the inlet and delivery of the cold rolling mill, a controlled thickness control is unnecessary when using hot strip with correspondingly narrow hot strip thickness tolerances. In this variant, resulting from the over the band length then constant cold working improved constant material properties, eg. As yield strength, tensile strength and elongation at break, which can not be achieved with controlled thickness decrease so.

This also applies to a variant of the method according to the invention, according to which the strip surface surface of the finished product is applied to the strip surface in a cold rolling mill by means of surface-structured work roll dressing at a degree of 0.5 to 2% tempering.

According to another proposal according to the invention with a galvanizing subsequent, further cold forming the strip thickness is reduced by 4 to 10% by cold rolling, wherein at least after this further strip forming the strip thickness measured and deviations are fed from a target strip thickness as a controlled variable of the cold forming. Optionally, a control can be provided for a constant reduction in thickness.

According to another proposal of the invention, the size of the cold forming after galvanizing to reduce the strip thickness can be controlled and controlled to a desired value, which makes the use of hot strip with correspondingly narrow hot strip thickness tolerances a controlled thickness control superfluous.

During cold forming after galvanizing, work rolls with a mean roughness value of 0.2 to 3.0 μm are used and thereby impress the strip surface on the surface structure of the finished product. The inventive method thus provides the prerequisites for adjusting the strip roughness to a required value before galvanizing by cold forming and / or reducing the thickness tolerance before galvanizing by cold rolling and / or reducing the strip thickness to a desired level by cold rolling prior to galvanizing, with individual ones the aforementioned parameters tape roughness, tape thickness tolerance and tape thickness in coordination with the upstream cold forming can be adjusted or supplemented by a further cold forming after galvanizing. The hot strip galvanizing can be carried out with at least one controlled thickness control either before or after galvanizing or without controlled reduction in thickness by controlling the size of the cold forming or the degree of temper rolling.

It is within the scope of not belonging to the invention process variations, advantageously to provide a semi-continuous process flow in which individual, the galvanizing previous process steps such as strip pretreatment and / or cold forming are performed in a galvanizing line separate, outsourced treatment lines, wherein in the galvanizing line next the application of the zinc layer can also be cold-formed after galvanizing and after-treatment of the strip. Thus, for example, the descaling process may be carried out in a severed pickling line or the cold rolling process may be performed in a severed cold rolling mill before the strip then reaches the galvanizing line with subsequent subsequent treatments such as straightening, passivating, and the like.

The inventive plant for carrying out the above-described method of producing hot dip coated hot rolled steel strip is defined in claim 3. This is characterized in that the hot strip passes through a strip pre-treatment device for removing the scale, then by cold forming the strip thickness is reduced by 0.5 to 10%, and then this passes through the strip galvanizing, in which the band passes through a molten bath , The strip galvanizing device is followed by another thickness reduction device. In the thickness reduction devices, work rolls each come in cold forming for impressing the strip surface structure of the finished product used, which have a surface texture with a mean roughness Ra of 0.2 to 3 microns.

According to a preferred embodiment of the invention, the thickness reduction device is designed as a cold rolling stand, which is associated with at least one measuring device in the outlet with feedback of thickness control signals to the cold rolling stand.

Further advantageous embodiments of the invention provide that the cold forming is performed to reduce the thickness with a cold rolling mill, in which in a turn preferred embodiment, at least one meter is arranged in the outlet of the cold rolling mill and either deviations from a desired thickness as a control signal to the thickness control of the cold rolling mill are returned or which is regulated by a control to a constant amount of thickness reduction.

To expand the concept and to vary the mode of operation of hot galvanizing, it is proposed according to the invention that the strip galvanizing device be followed by a further thickness reduction device designed as a cold rolling stand, in which the strip thickness is reduced by less than 0.5 to 10%, at least this further cold rolling stand being at least a measuring device in the outlet with feedback of measurement signals for thickness control is assigned.

At this point, it should be noted separately that according to the present invention, a cold working is a "cold rolling", and that the thickness reducing means are designed as "cold rolling stands".

Fig. 1

eine Prinzipskizze einer kontinuierlichen Prozesslinie zur Warmbandverzinkung mit Kaltverformung vor dem Verzinken; und

Fig. 2

eine Prinzipskizze einer semikontinuierlichen Prozesslinie zur Warmbandverzinkung mit Kaltverformung vor dem Verzinken.

Further features and details of the invention will become apparent from the claims and the following description of illustrated in the drawings embodiments of the invention. Show it:

Fig. 1

a schematic diagram of a continuous process line for hot strip galvanizing with cold deformation before galvanizing; and

Fig. 2

a schematic diagram of a semi-continuous process line for hot strip galvanizing with cold deformation before galvanizing.

At an in FIG. 1 exemplified, working in continuous operation hot-dip coating equipment 1 is a treated, hot-rolled steel strip 2 from a z. B. with not shown straightening units and a tape storage equipped inlet part ET initially supplied to a belt pretreatment device 3, which has a scale breaker 4 or the like and a pickling 5 and a sink 6 for removing the scale from the steel strip or band 2. The band pretreatment device 3 is followed by the dashed bordered or highlighted core of the hot dip coating installation 1, namely a strip galvanizing device 7 upstream thickness reduction device 8, designed as a cold rolling KWW as a preferred form of cold forming before the steel or hot strip 2 in the Strip galvanizing 7 for applying the coating passes through a molten bath 9.

In the outlet of the cold rolling mill KWW, at least one thickness measuring device 10 with feedback of the measuring signals to the cold rolling mill is arranged by way of example for deviations measured from a nominal thickness. Optionally, a measuring method can be used at the KWW that does not measure the thickness but the size of the cold forming or a skin pass rate and outputs it as a control signal. In cold working in the thickness reducer 8, cold working is performed by reducing the sheet thickness by 0.5 to 10%. In the case of cold forming by cold rolling or temper rolling, a surface structure is impressed on the strip, for which purpose the work rolls having a surface structure with a mean roughness Ra of 0.2 to 3 μm are formed.

The FIG. 1 shows further that the strip galvanizing 7 optionally a further thickness reduction device 11, in a preferred embodiment also as a cold rolling mill KWW, can be followed. The work rolls of this further thickness reduction device 11 can then be designed so that they imprint the surface texture of the finished product with a mean roughness Ra of 0.2 to 3 μm, during cold forming of the strip. In the case of a mode of operation with A thickness reduction device 8 before galvanizing and a thickness reduction device 11 after galvanizing, at least with a measuring device 12 arranged in the outlet of the further thickness reduction device 11, returns the deviation from a nominal strip thickness as a controlled variable of the cold forming of the thickness reduction device 11.

The thickness reduction device 11 for cold forming in the preferred form of a cold rolling mill (KWW) can also carry out the process of temper rolling with 0.5 to 2%, temper rolling degree behind the strip galvanizing device 7 instead of a controlled thickness control. Furthermore, the KWW can perform the cold forming with less than 30%, preferably 0.5 to 10%, even with a constant setpoint of the cold forming.

The hot strip 2 cold-formed in this way with a surface structure then passes through a strip aftertreatment device 13 which, in the plant example, has a draft straightener STR and a chemical treatment part ChBT, eg. As passivation may include, from which the hot strip 2 as a finished product in the example, with a trimming shear and a tape storage (not shown) equipped outlet part AT arrives.

In the FIG. 2 shown, working in semi-continuous operation hot dip coating plant 100, which does not belong to the present invention, differs from the previously described, continuously operating hot dip coating unit 1 only by the fact that pre-galvanizing process steps are outsourced, namely in the embodiment of the process line I for strip pretreatment and the Cold forming process line II, separate from process line III for strip galvanizing.

For the in FIG. 2 matching with FIG. 1 Registered reference numbers apply without restriction to the previously explained functions and effects. Also in FIG. 2 the core of the hot-dip coating plant, namely the cold forming carried out before the galvanizing, is highlighted in dashed lines. The separation of the process lines entails that each line has an inlet part ET and an outlet part AT is assigned, wherein the galvanizing line III in addition to the strip galvanizing 7 includes a belt cleaning 14 upstream of this and integrally includes the following strip thickness reduction device 11 following strip aftertreatment device 13.

LIST OF REFERENCE NUMBERS

1; 100

Hot-dip coating plant

2

Steel strip / hot strip

3

Band pretreatment equipment

4

scale breaker

5

stain

6

kitchen sink

7

Band galvanizing

8th

thinning device

9

melting bath

10

Measuring device / thickness gauge

11

thinning device

12

Measuring device / thickness gauge

13

Band-treatment device

14

belt cleaning

I

Process line strip pretreatment

II

Process line strip cold forming

III

Process line strip galvanizing

ET

inlet part

AT

outlet part

For example,

scale breaker

KWW

Cold rolling mill or stand (as a preferred form of cold forming)

STR

stretch leveler

CHBT

chemical treatment part

Claims (7)

1. Method of hot-dip coating of hot-rolled metal strip in a continuous strip plant, in which the hot strip

   - is subjected to pretreatment for descaling,

   - is reduced in its thickness by cold-deforming in a process step preceding galvanising and

   - is galvanised

   - is reduced in its thickness by cold-deforming in a process step subsequent to the galvanising and

   - runs through a post-treatment,

   characterised in that
   the hot strip freed of scale is cold-deformed in the process step preceding the galvanising by reducing its strip thickness by 0.5 to 10% and
   in both cold deformations, i.e. not only before, but also after the process step of galvanising, a surface structure is imposed on the strip in each instance by a cold-rolling process in a cold-rolling stand with use of work rolls with a surface structure with a mean roughness value Ra of 0.2 to 3 microns.
2. Method according to claim 1, characterised in that in the further cold-deformation subsequent to the galvanising the strip thickness is reduced by 4 to 10% by cold rolling, wherein the strip thickness is measured at least after this further cold-deforming and departures from a target strip thickness are fed as a regulating variable to the cold-deforming.
3. Plant (1; 100) for producing hot-dip coated, hot-rolled steel strip (2) in a continuous process line, comprising a strip pretreatment device (3) including the descaling, a strip galvanising device (7), at least one thickness reducing device (8; 11) by cold-rolling of the strip and a strip post-treatment device (13), for performing the method according to claim 1 or 2,
   wherein connected with the strip pretreatment device (3) for the hot strip freed of scale are initially the thickness reducing device (8) and then following this the strip galvanising device (7), in which the hot strip runs through a molten bath (9), and
   wherein connected with the strip galvanising device (7) is a further thickness reducing device (11) constructed as a cold-rolling stand (KWW),
   characterised in that
   the strip thickness is reducible by 0.5 to 10% by the thickness reducing device (8) arranged upstream of the strip galvanising device (7),
   the strip thickness is reducible by 0.5 to 10% by the thickness reducing device (11) arranged downstream of the strip galvanising device (7) and constructed in the form of a cold-rolling stand (KWW) and
   the thickness reducing devices (8; 11) each comprise, for the cold deformations, work rolls having a surface structure with a mean roughness value Ra of 0.2 to 3 microns for imposing the strip surface structure of the finished product.
4. Plant according to claim 3, characterised in that the thickness reducing device (8) arranged upstream of the strip galvanising device (7) is constructed as a cold-rolling stand (KWW) with which measuring apparatus (10) for the feedback of measurement signals for thickness regulation of the cold-rolling stand (KWW) is associated at least at the outlet of the cold-rolling stand (KWW).
5. Plant according to claim 3, characterised in that the thickness reducing device (8) arranged upstream of the strip galvanising device (7) is constructed as a cold-rolling stand (KWW) configured with regulation to a constant amount of the thickness reduction.
6. Plant according to any one of claims 3 to 5, characterised in that in the case of the thickness reducing device (11) in the form of the cold-rolling stand (KWW) arranged downstream of the strip galvanising device (7) at least one measuring apparatus (12) for feedback of measurement signals for thickness regulation of the cold-rolling stand (KWW) is arranged in the outlet with feedback of thickness regulation signals to the cold-rolling stand (KWW)
7. Plant according to any one of claims 3 to 6, characterised in that the thickness reducing device (11) in the form of the cold-rolling stand (KWW) arranged downstream of the strip galvanising device (7) is configured with regulation to a constant amount of the thickness reduction.

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