eccc112thssen廠不銹鋼的技術(shù)發(fā)展水平

1、New and updated plants – combi, bloom and billet casters Session 13 1Düsseldorf, 27 June – 1 July 2011The “state of the art” slab caster for stainless steel in ThyssenKrupp Acciai Speciali Terni (TKAST), Italy Auth

2、ors Gabriele Paulon, Danieli > Supply and installation of Level 1 and Level 2 systems; > Supply and installation of dedicated water treatment plant, compressed air plant, and iron powder exhaust system for

3、torch cutting machine to serve caster production. Technical solution: design concept To meet the strict quality requirements for slab quality at ThyssenKrupp Stainless, Danieli Davy Distington considered the followin

4、g criteria in its design: Optimized roller geometry As the product mix covers a wide range of stainless grades, such as 300 and 400 series (austenitic, ferritic New and updated plants – combi, bloom and billet casters

5、Session 13 3Düsseldorf, 27 June – 1 July 2011and martensitic grades), and the slab is 215 mm thick, the newly built Danieli caster is a vertical curved type machine with an 8.5 m radius and over 2.8 m vertical le

6、ngth, followed by multi-point bending and straightening. This design allows sufficient inclusion flotation as well as appropriate bending / straightening stress. The typical Epsilon graph is shown in Figure 1. Figure

7、1: Bulging and epsilon of Ferritic stainless grades at Vc=1.4 m/min. The 27.3 m machine length allows the maximum casting speed of 1.45 m/min for austenitic grades and 1.4 m/min for ferritic and martensitic grades. A

8、s we know, the b.c.c. structured ferrite leads to deformation and creep in stainless steel. So the best support for the slabs has to be taken into account when calculating the roll diagram. Especially in the upper par

9、t of the caster, sufficient support is crucial. The selected roll geometry has to overcome the dynamic bulging near the meniscus, particularly at high casting speed. To keep a balance between the stringent dimensiona

10、l requirements and the deformation tendency due to small roller diameter, multiple split rollers are adopted. Three split rolls are used for the bending and straightening zones and two split rolls for other areas. A

11、s far as secondary cooling and closed machine cooling are concerned, special care is taken to secure the best slab quality under all casting conditions. Surface quality is the most critical issue for stainless steel

12、production and the accurate control of the temperature between the slab and the roller surface plays a key role in preventing scale formation. For this reason, peripherally drilled rolls (PDR) are adopted in the segm

13、ents as long as the roller diameter can stand load, i.e., starting at segment 4 and continuing downstream. Figure 2: Roll geometry of the caster The roll geometry shown in Figure 2 guarantees even load distribution on

14、the rolls and can effectively counteract thermal distortion under variable heat fluxes, which is of great importance during casting speed transition. Cooling control during slab solidification Apart from the optimize

15、d roll diagram, another paramount issue for getting the best slab quality is to properly control the slab temperature during cooling. In Figure 3, the correlation between the specific flow rate of secondary cooling w

16、ater and the casting speed for austenitic and ferritic steel grades is shown. Due to the wide range of steel grades to be produced, different solidification characteristics have to be taken into consideration during

17、the design of the secondary cooling system. As a result, water cooling and air-mist cooling are employed. Figure 3: Specific secondarycooling flow rate as a function of Vc for stainless steel grades. In the top zone,

18、water nozzles are installed for hard cooling at high flow rates for ferritic grades. In the bending area and in the following segments, air-mist cooling is applied for fine tuning. All secondary cooling is controlled

19、 by means of a dynamic model that continuously adapts the cooling fluid flow rate and pressure in order to guarantee the proper slab temperature profile, predicted with virtual sensor mathematical modelling that take

20、s into account the “l(fā)ive” status of all the parameters of the casting process that affect slab temperature (superheat, casting speeds, flows, roll cooling, etc.), as well as specific steel grade solidification behavi

21、or and metallurgical needs. Fig. 4: Control loops for secondary cooling. In order to cope with the different slab widths to be cast (from 800 to 1600 mm), and to avoid overcooling of narrow slabs, the lateral zoning i

22、n the secondary cooling area is considered separate from the bending zone. As illustrated in Figure 4, a total of 19 independent control loops are shown. In addition to the secondary cooling nozzles, a dedicated set

23、 of tangential water nozzles are placed along the caster in order to promote scale detachment from the roll surface (hence reducing the risk of scale “printing” on the slab surface). Layout From a layout viewpoint, t

24、he caster design had to take into account the need to reuse the existing casting platform and civil works, with a casting floor at 14.7 meters from ground level (level dictated by the vertical design of the old CSP c

25、aster). As a consequence, the new passline of the caster is located at a height of about 3.3 meters from ground level. Hence, the caster body as well as the slab torch cutting and bottom dummy bar parking area have b

26、een installed on an elevated supporting structure. Specific structural simulations have been carried out on this supporting structure in order to ensure caster rigidity even under severe mechanical and thermal load,

27、preventing vibrations and unwanted deformations. From the end of the caster to the charging area of the mill, (an area previously occupied by a thin slab, roller- type tunnel furnace) an inclined roller table has been

28、 installed (230 meters in length) to gradually transfer the slab from the 3.3-meter elevated platform level to the 800-mm mill entry level. Mechanical solution Mold and its oscillating, width adjustment devices Stric

29、t control of oscillating parameters, as well as limitation of lateral movements on the mold, and oscillation marks are particularly important in casting stainless steels. This INMO (INtegrated MOtion) mold and oscill

30、ating system has been developed by Danieli to provide very precise guidance of the oscillating mold with respect to the strand passline, as well as wide flexibility of operation in terms of the applied stroke, freque

31、ncy and waveform. This now makes it possible to provide the best oscillation condition for both good mold lubrication and the best conditions for good surface quality for the wide range of casting speeds and/or steel

32、 grades. The “Spring free” guiding system with eight rolling elements and two servo-controlled hydraulic cylinders constitutes the precise oscillating system (Figure 5). Fig. 5: Danieli INMO mould and oscillator and r

33、olling element This system also uses so called “inverse oscillation,“ where frequency decreases and stroke increases as casting speed increases. For the new Terni caster, the maximum frequency is 300 opm and the maxi

34、mum stroke setting is + / - 6mm. The copper mold plates are designed to provide uniform cooling around the slab surface, especially in the critical meniscus area. The mold is capable of being adjusted remotely to any

35、 width in the design range, both during and outside the casting operation. The mold’s wide face tapers are fixed; the narrow face tapers are automatically changed during width changes to suit the slab width and stee