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Modern Strip Production Technologies - CSP and ISP

In July 1989, the first compact strip production (CSP) plant, built by then SMS Schloemann-Siemag AG, started up at Nucor Steel, Crawfordsville, Indiana. Almost at the same time, the In-line Strip Production (ISP) was under intensive development by then Mannesmann Demag AG and Arvedi Group. Now, the both technologies have since long achieved worldwide recognition.

Though there are slight differences in the layouts of the two strip production technologies, they both cast the steel into a thin gage, reheat it, and roll it into finish gage in a limited number of passes, thus great reduce the production stages and lower the energy consumption. Continuous casting and rolling steel strip was a revolution in steel industry at the end of the last century. Some thin gauges that conventionally have to be produced by cold rolling, can be obtained now from hot rolling with the new CSP or ISP process, which can roll 1.2 mm now and maybe 0.7-0.8 mm in the future.

Compact Strip Production (CSP) Technology

General features. The general features are listed as follows:

  • Continuous casting of slab with thickness around 50 mm (40-70mm), coupled with continuous strip rolling with 5-7 stands (mostly 6 stand), thus reduce the production stages and energy consumption
  • Temperature equalisation in the roller hearth furnace (1 per strand) after the casting and before the rolling to achieve a uniform slab temperature
  • Cooling on the run out roller table to obtain the desired metallurgical properties
  • Coiling process on the coiler to ensure a readily transportable product

In most plants, production capacity is about 1 million tons per year (ranging from 0.9-1.5 million tons/year). Slab dimensions range from 40-70 mm in thickness and 900-1600 mm in width in most installations. Minimum finish size of strip from 1.2 mm to 2 mm in most cases; newer mills usually have thinner finish size. Heat size usually is 120-180 ton, ranging from less than 100 tons to over 200 tons.

Temperature. The production process and temperature evolution are illustrated in Fig. 1.

Fig. 1: Production process (above) and temperature evolution (below)

The holding time of the thin slab in the soaking furnace is 15-20 minutes, so that a uniform temperature, about 1100ºC for the grade St45, for example, over the width, thickness, and length. This is the only reheating required to perform the subsequent rolling and cooling; there is no need for any corrective measures such as strip edge heating, or interstand cooling. The product consequently has a microstructure of very high homogeneity. The geometrical precision with respect to thickness and profile is also much better than strips rolled in conventional hot strip mills.

Mold and Nozzle. A specifically developed mold, which contributes most to the success that the CSP, is showed in Fig. 2. Its main characteristic is the funnel shaped expanded opening of the mold in the upper part to provide sufficient space for the installation of a large diameter submerged nozzle.

Fig. 2: CSP mold

The CSP molds are made from a copper-silver alloy and feature a long service life. The mold surface is not plated. The funnel shape of the mold is proportional to the shrink of the strand shell whereby stresses in the strand shell in the horizontal direction are avoided or minimised. Moreover, the distance between submerged nozzle and copper wall is sufficiently long to reliably avert the formation of bridges and to have a sufficient amount of heat available in the bath for casting powder melting.

The shape of the mold, the dimensions and flux conditions in the submerged nozzle are constantly under optimization. Today, the large outlet opening is commonly used in the nozzle to permit a sufficient steel flux in the case of cloggings, and so the bath level area in the submerged nozzle zone is large enough for melting a sufficient amount of casting powder and avoiding the formation of bridges. A magnetic field is produced in the upper part of the mold to slow down the steel flow and produce better uniformly distributed downflow. Another approach to steady the liquid steel inside the mold is to increase the outgoing thickness, for example, from 50 to 70 mm. In addition, it’s also possible to introduce a hydraulic mold oscillator to improve the area of contact between strand skin and mold wall.

Rolling Mill. Most CSP plants have 6 stands, with small portion of them which use 5-stand or 7-stand layouts. CSP plants come with profile and flatness control systems adopting the well known CVC technology for adjustment. The systems enable defined profile heights to be set for the finished strip irrespective of the distribution of pass reductions in the mill. Elastic deformation and thermal crown and roll wear are assessed by the profile and flatness control system and compensated when presetting the roll gaps. Compensation for roll gap presetting for the undesired profile and flatness resulting from:

  • Changes in the elastic deformation of the set of rolls
  • Changes in the thermal crown
  • Changes in the roll crown caused by wear

For recent installations, a newer technology called PFC-CFC is available, based on the combination of the contour and flatness control with the so-called contour and flatness control systems. The the contour and flatness control systems is designed for the purpose of eliminating any profile anomalies resulted rom roll wear and thermal crown. Such roll wear and thermal crown are likely to occur when rolling is done either with constant width or with changing widths over extended periods of time.

A high pressure descaling ahead of the rolling mill, with 400 bar variable pressure pumps for recent installations, or 250 bar high pressure pumps for older ones. If requested, for example for rolling some sensitive grades, a roller side guide (edger) is available to be installed in front of F1 for improved guidance and edge quality, etc.

In-line Strip Production (ISP) Technology

Development of ISP started in 1988 based on an Arvedi-Mannesmann patent. In 1992, the prototype ISP plant was built by Arvedi at its Cremona works, with most development carried with the plant. In 1994-95 the prototype plant completed the first phase of its development and turned profitable in production.

The layout of the ISP process is illustrated in Fig. 3. The major difference between the ISP and CSP is that, in ISP, right after the slab is casted, it is rolling with three stands of rolling mill, as illustrated in the Fig. 3. The slab entering the rolling mill with a liquid core, therefore the so-called cast-rolling is actually carried out. This will further reduce the energy consumption. The slab is then under cutting, temperature equlization and finishing rolling, etc. In most cases there are totally seven rolling stands in the production line. A Cremona box (Cremona furnace) was also used behind the regular reheating furnace (note the "Cremona" is the name of the pilot plant).

Fig. 3: ISP Process schematic layout

The plant's main technical features are:

ISP Integrates the thin slab casting phase with the rolling stage, thus results in the short production cycle and reduced energy cost. In addition, it has following features specific to the process:

  • Cast-rolling to reduce liquid core thickness with low roll separating force (soft reduction), and immediate solid core rolling giving a thin slab of 15-25 mm in thickness.
  • Temperature control from the entry to the exit of the finish rolling passes, through a high efficiency and rapid response induction furnace.
  • In-line rolling through the finishing train at constant speed and temperature via the 'Cremona Box' buffer.

Great features of the ISP is the short production circle (compared with the traditional processes) and the cast-rolling capability (compared with other new processes). The overall ISP plant is only 180 meter long from liquid steel to finished coil, with a production cycle of only 15 minutes. Production capacity is in the range of 0.7-0.9 million tons for one casting line, and up to 2 million tons for two casting lines. Addint a second continuous casting line is only at an additional investment cost of 30%.

Several key features of ISP is summerized in the Table 1.

Table 1: key features of ISP process




0.8-2 M t/y

3.5-4 M t/y

Energy consumption (CC+Rolling)


100% cold charging

80% hot charging

Liquid to coil yield



Thin gauges produced without additional costs

1.2 mm

possible 0.7-0.8 mm

1.7-3 mm

Investment intensity



Conversion cost


100% cold charging

75% hot charging



[32] Ranieri and J. Aylen (ed.): The Steel Industry in the New Millennium. Vol. 1: Technology and Market. 1998. IOM Communications Ltd. ISBN 1-86125-019-3



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