Continuous pickling line and cold rolling mill

Transcription

1 Metals Technologies Continuous pickling line and cold rolling mill voestalpine Stahl GmbH, Linz, Austria

2 Extention and modernization offering substantial savings and improvements The challenge: In February 1995 VAI (now Siemens VAI) received a major rolling mill order from voestalpine Stahl GmbH. The scope of this project includes the extension and modernization of the existing four-stand tandem mill into a five-stand cold rolling mill, the modernization of the existing pickling line and the combination of these two lines into a continuous production line. voestalpine Stahl GmbH, Linz is a well-known producer of high quality strip for the automotive and household industry. Pickling and cold rolling are of great importance for these products since quality parameters such as thickness, width, flatness, strip surface cleanness and structure and the final material properties are dominantly influenced by these processes. Our solution: Based on the current experience, the new linked facility has proved to be a highly flexible solution, covering production requirements of highest product quality standards even for a wide range of strip thicknesses and widths as well as for soft to high strength steel grades. The project has been realized within a very short time frame in two phases. Phase 1: Modernization of the pickling line and cold rolling mill in addition to the installation of the coupling section. This phase has been completed within 17 months of contract signature. Phase 2: Installation of the fifth mill stand 9 months after completion of Phase 1 at which time the mill has been running at its final capacity of 1.9 million tons per year. The coupled pickling and cold rolling mill was thus the first major step by voestalpine Stahl Linz to concentrate all of their cold rolling mill activities at one location. Achieved results: Operating cost savings through compact plant layout and fewer operators, reduction in energy consumption and less threading in and tailing out operations Capacity increase from 1.1 to 1.9 million tons per year Thinner gauges strip thickness reduction from min. 0.5 mm to 0.3 mm Quality improvements through constant process conditions, better flatness and surface quality, and higher coiling accuracy Reduction of size and costs of coil storage area through continuous operation and elimination of coil storage after pickling section 2

3 The customer: Name: voestalpine Stahl GmbH Location: Linz, Austria Services: voestalpine Stahl GmbH, the steel center of competence within the voestalpine corporate group, is an important supplier to the European automotive, household appliance, and construction industries. voestalpine Stahl GmbH manufactures high-quality flat steel products for the following industries: Automotive and utility vehicle industry Automotive supply industry Household appliance industry Electrical industry Tubes/sections/cold rollers Construction and building supply industry Mechanical engineering industry The most modern production plants enable the production of high-quality cold rolled steel strip with narrow thickness and flatness tolerances and the highest surface quality. 3

4 The main benefits... Coupled pickling and cold rolling mill + 40% + 45% + 2% - 40% -50% -20% 100% representing seperate units for pickling and cold rolling -90% Improvements Savings Production Yield Quality Roll consumption Personnel costs Production costs Production time Tandem mill entry Benefits from the linked scheme Coupling of the pickling and cold rolling steps results in a number of producer benefits related to productivity, strip quality, yield and production costs. The elimination of strip threading and tailing out means a dramatic increase in the throughput capacity, longer work-roll lifetime and fewer work-roll changes. Continuous operation reduces strip head and tail ends to an absolute minimum and therefore the frequency of off-gauge strip. These features lead to a significant reduction in required maintenance and manpower. The main benefits of the linked facility can be reached in terms of yield, roll consumption, personnel cost, production time, production cost and quality improvements. Except for the geometrical tolerances, which can also be achieved in mills in unlinked facilities, these figures are related to the assumption of separated production units. The following figures are representative of the voestalpine Stahl GmbH, Linz line. Reduced material loss can be attributed to the following: Thick ends eliminated by continuous operation Coil handling damage reduced due to less handling Minimized off gauge lengths as a result of constant process conditions Yield increased by % Improved product quality is attained due to the following criteria: Constant process conditions result in higher quality and more consistent products Reduced strip-edge damage due to less coil handling Higher proportion of coil with stable operating conditions Surface finish flexibility Flatness tolerance: below 15 I-Units (thickness- and width-dependent) Gauge tolerance: standard tolerance (DIN standard) Surface quality: roughness, cleanness improvements Reduced operating cost is reached due to: Continuous, compact plant requires fewer operators 40% longer roll service life because of less damage due to reduced threading and tailing out Reduction in energy consumption of 10% by an optimized process due to fewer acceleration and deceleration operations Reduced roll oil consumption by 32 40% Reduced maintenance costs due to constant operating conditions and less threading and tailing-out operations 4

5 Tandem cold mill Increase of productivity Improvement of strip quality Cost savings Before modernization After modernization Entry section Coil preparation Flash butt welding machine Reconstruction of entry looper by integration of existing exit looper Level machine and scale breaker Pickling section Flat tank pickling section Exit looper Turret-type side trimmer Exit section for pickled hot coils Coupling section Two helical turning devices Steering device Cold rolling tandem mill Entry looper Entry bridle Strip steering device Modernization of stand no. 1-4 New stand no. 5 with SmartCrown Rotary shear Tension reel Inspection station The main benefits for the respective mill sections Capacity mio t/a Pickling line Cold rolling tandem mill Strip / coil data Strip thickness entry [mm] (7.0) Strip thickness exit [mm] Strip width [mm] 600-1,620 Max. coil weight [t] 30 Average specific coil weight [kg/mm] 17.5 Maximum specific coil weight [kg/mm] 25 Coil outside diameter [mm] Entry 2,000 2,150 Exit 2,000 2,100 Mill speeds [m/min] Pickling line entry Pickling section Coupling section 360 Cold rolling tandem mill entry Cold rolling tandem mill exit 640 1,200 Cold rolling tandem mill Number of mill stands 4 5 Power [kw] 10,800 22,100 Tension reel, maximum tension [kn] Plant data before and after modernization 5

6 ... of a linked facility Coupled pickling and cold rolling mill Cold rolling t andem mill Shear Coupling looper Helical turning device Welding machine Rotary shear Shear Tension reels Tension reel In-line inspection station Scale breaker Pickling section Side trimmer Oiler Flattener Crop shear Flash butt welder Intermediate looper Entry looper Steering rolls Pay-off reels Bridle and deflector rolls Layout of continuous pickling and cold rolling mill Scope of project The linked line was assembled by existing, partly renewed and supplementary new equipment including the following: Entry section including pay-off reel(s), flattener, shear and flash butt welder Six-strand horizontal entry looper to pickling section Pickling section including scale breaker Four-strand horizontal exit looper after pickling section Exit section of pickling line, comprising turret-type side trimmer, shear, oiler and tension reel (shear, oiler and tension reel are only used during intermediate production of pickled and oiled products, usually performed in special campaigns during maintenance shutdowns of the mill) Coupling section including an auxiliary welder and two 90 helical turning devices Four-strand coupling looper to the tandem mill entry Entry section of tandem mill, including bridle unit, steering units, auxiliary shear and strip clamping Five-stand cold-rolling tandem mill Exit section to tandem mill comprising bridle unit, rotary shear and two tension reels In-line inspection station. Capacity of coupled pickling and cold rolling mill Two of the main targets of the project were to maximize the capacity of the cold rolling and pickling sections and to utilize as much of the existing mill equipment as possible. It was also essential that the different speeds of the strip are regulated and balanced through the installation of accumulators in the pickling and cold rolling sections. For the calculation of the required looper buffer capacities under a wide range of layout and operating conditions Siemens VAI applies a specially developed computer simulation program. For this particular project the required looper lengths were determined on the basis of the following calculation steps: 1. Determination of coil-to-coil times for the following sections: Entry section Pickling line Side trimmer Tandem mill 2. Determination of maximum coil-to-coil times and bottlenecks 3. Determination of required looper length at reduced strip speeds in each section while assuring max. coil-tocoil time 4. Determination of plant capacity 6

7 Pickling section Coupling section The existing pickling line and the cold rolling tandem mill were located in different bays with a distance center line to center line of approximately 80 m. Since the new facility had to be placed in the same locations as the existing lines, coupling had to be established by use of special helical turning devices both diverting the strip by 90 in a planar view perpendicular to the strip plane. During diversion the strip is also rotated by 180 around its longitudinal axis, meaning that in the coupling section the original bottom surface appears on top and vice versa. Since two turning devices are used, the original surface location is retained. The strip tracking turned out to be highly reliable as no strip misleading appears. Helical turning device 7

8 Modernization of the cold rolling mill Tandem cold mill upgrade Millstand no Tension reel Upgrade Existing mill Gear ratio Power Millstand no Gear ratio i=1.54 2,600 kw 1 i=2.34 i=2.0 i=1.72 i=1.36 3,000 kw 3,000 kw 2,200 kw i=1.54 i=1.19 i=0.9 5 i=0.64 i=1.03 1,600 kw Tension reels no 1 i= i=1.03 Power 3,500 kw 5,200 kw 5,200 kw 5,200 kw 3,000 kw 2,000 kw 2,000 kw Mill power and gear ratios of cold rolling tandem mill Extensive assessment of the exisiting four-stand tandem mill showed that the following new installations and modernization activities were necessary in order to meet the project targets: Reconstruction and replacement of gear boxes and main drives for optimization of speed cone Improvement of hydraulic automatic gauge control systems (AGC) through the installation of new sealings, servo-valves, roll gap transducers and a hydraulic pressure system operational up to 280 bar (220 bar), and through the reconditioning of existing roll load cylinders to assure the fast response necessary especially for the narrow gauge tolerances New mill stand no. 5 with flatness control, including the shifting-system for productivity increase, rolling gauges down to 0.3 mm and excellent strip surface quality Key-less back-up roll bearings for less bearing eccentricity and thus improved strip thickness tolerances New measuring systems for strip speed and tension to control material flow and to ensure minimum thickness deviations Automatic roll change equipment for maximum mill availability Automatic adjustment of passline by hydraulically actuated wedges for constant passline Rotary shear for strip cutting after rolling Tension reel with Siemens VAI patented filler ledgetype mandrel for excellent strip quality, even for the initial coil windings In-line inspection station for strip sampling at programable intervals and for any strip position over the entire strip length Mill power Since mill speed had to be increased to meet the capacity targets, a power upgrade of the existing mill drives from 10,800 kw to 22,100 kw was necessary. The optimization of the speed cone required an adaptation of the gear ratios and hence new gears. Mill stands The 5th stand uses smaller work-rolls than stand no. 1 4 which is required to obtain the aimed maximum reduction of approximately 6% in particular for rolling of strong hardening, high strength materials down to the minimum thickness of 0.3 mm. Since the maximum total reduction from hot gauge to cold gauge can reach 84%, the material hardening is significantly high. The required reductions on the last stand could therefore not be performed with conventional work-roll diameters. To compensate for the decrease in flexural stiffness of the work-/back-up roll assembly due to the smaller work-roll diameters, the diameter of the back-up rolls was increased accordingly. 8

9 Pickling section Mill exit section Stand no Mill type 4-high 4-high 4-high 4-high 4-high with SmartCrown Main drive Current AC AC AC DC DC Main drive Power [kw] 3,500 5,200 5,200 5,200 3,000 Main drive rpm 215/ / / / /600 Work-roll diameter [mm] 595/ / / / /420 Work-roll barrel length [mm] 1,700 1,700 1,700 1,700 1,950 Back-up roll diameter [mm] 1,550/1,400 1,550/1,400 1,550/1,400 1,550/1,400 1,470/1,400 Back-up roll barrel length [mm] 1,700 1,700 1,700 1,700 1,700 Roll gap adjustment AGC AGC AGC AGC AGC Roll seperating force [kn] 30,000 30,000 30,000 30,000 30,000 Bending force [kn] ± 440 ± 440 ± 440 ± , Work-roll shifting stroke [mm] ± 100 Back-up roll key-less bearings Automatic flatness control Thickness gauge u, d u, d Laser speed measurement u, d Tension measurement u, d d d d d Flatness measurement d d u = upstream of mill stand; d = downstream of mill stand Technical data of cold rolling tandem mill 9

10 Mill stand no.5 Installation and technical features Roll bending Effect of roll bending Roll shifting (SmartCrown roll contour) Effect of roll shift Max. strip width 4 th order shape defects Narrow strip Multi-zone cooling Roll swivelling via hydraulic screwdown Preassembled mill stand no. 5 with shifting device Working principle of actuator systems for flatness control Technical features of the new 5 th mill stand The installation of an additional fifth mill stand ensures the improvement of rolling performance, as follows: Reduction of minimum strip thickness from 0.5 mm down to 0.3 mm Maximized control range for strip flatness One of the key elements in the modernization and expansion of the tandem line was to expand the range of attainable output thickness. In this particular case, the minimum thickness was decreased from the original 0.5 mm down to 0.3 mm, which increased the range of total reduction up to approximately 84%. Rolling of medium to high-strength grades with these reductions on a four-stand mill approaches the physical limits of the process. This new mill stand was designed by Siemens VAI in 4-high technology using an approximately 20% smaller work-roll diameter than on the existing stands. Taking full advantage of the latest cold rolling technology, the stand is equipped with the full range of actuator systems for flatness control as follows: SmartCrown technology Positive and negative work-roll bending Multi-zone cooling A high speed AGC system was installed for accurate thickness and swiveling control. Special features have been additionally included to simplify and automate the operation of the stand to the utmost: Automatic passline adjustment by a hydraulically actuated wedge below the bottom roll assembly Automatic work-roll change with cassette-type work-roll chocks Bayonet-type joint for the flat-neck-type connection from work-rolls to drive spindles Highly efficient emulsion blow-off systems for the strip and the interface between work-roll and back-up roll. Additional nozzle check for easy maintenance by using water In particular, the attainable work-roll change time of five minutes, demonstrates the efficiency of this equipment. Flatness control The flatness control model calculates the set point values for the four flatness actuator types: Roll swivelling via hydraulic screwdown for the linear part of the tensile stress distribution Shifting for symmetrical deviations Work-roll bending also for symmetrical deviations (takes effect immediately) Multi-zone cooling for the residual deviations of higher orders 10

11 Tandem cold rolling mill Tandem mill entry looper The deviation between the target and measured flatness distribution is approximated using special polynomials. The relevant flatness measurement data is condensed and filtered in order to determine the respective portions of the flatness distribution curve. In order to minimize the difference between target and measured flatness distribution, new set point values are calculated which take into consideration the degree of flatness sensitivity to the flatness actuators. Strip width, thickness and steel grade are decisive factors affecting flatness sensitivity. A further reduction of residual deviations can be achieved by multi-zone cooling. Emulsion system To ensure the required high degree of surface cleanness on the finished strip, the existing mill was already equipped with a two-circuit emulsion system. The last stand was supplied by an independent emulsion system with significantly lower oil concentration (approx. 20% of the emulsion in the preceding stands). This philosophy was fully retained on the up-graded mill, where stand no. 5 in place of stand no. 4 is supplied with this system. In addition to the emulsion systems in the stands, a direct emulsion application in front of stand no. 1 was installed on the new mill. In-line inspection The continuous operation of cold rolling mills requires the possibility of in-line inspection of strip surface for an effective quality assurance during the rolling process. Both top and bottom strip sides need to be inspected. These requirements are fulfilled by the new inspection station, which is located directly downstream of the tension reels. The samples are cut by the rotary shear and transported by magnetic conveyors to the inspection table where the strip top side is carefully examined. The strip is then turned over magnetically for a bottom side inspection. After completion of inspection the sample is transported to the scrap shear. The samples can be selected at any strip position by the operator. This checking procedure allows for fast response e.g. in order to determine when roll changes are required due to work-roll damage. The strip surface is inspected visually and detection of surface defects can be facilitated using an automatically driven grindstone, which enhances the visibility of defects and thus assists the operator in localizing defect sources. Technical data: Sample length: 10 m Exit speed during sample cutting: max. 150 m/min 11

12 Headquarters: Siemens VAI Metals Technologies GmbH P.O. Box 4, Turmstrasse Linz, Austria Phone: Fax: Order No. E10001-M4-A122-V Dispo No.: K-No.: Printed in Austria SPS SVAI RF , Siemens AG The information provided in this brochure contains merely general descriptions or characteristics of performance which in actual case of use do not always apply as described or which may change as a result of further development of the products. An obligation to provide the respective characteristics shall only exist if expressly agreed in the terms of contract. All rights reserved. Subject to change without prior notice. SIROLL is a trademark of Siemens AG.