9th ECCC European Continuous Casting Conference – ECCC 2017

General Information Slab Milling According to today's state of the art, the continuous casting process is almost entirely used for the production of flat steel material. In the manufacturing process for high-quality rolled products, the requirement especially on the surface quality and homogeneity of slabs has increased significantly in recent years due to the quality and price pressure. A few years ago it was still common to generously recirculate the end pieces of rolled products into the material cycle but by reasons of economic this is no longer possible. Due to quality and costs, imperfections in the slab now have to be detected at the beginning and have to be removed before further processing in the rolling mill. If this is not done, imperfections show up subsequently in quality problems in the final product. This results in high requirements on the slab manufacturing process and the material quality regarding crack-, kerf- and inclusion-free surface quality. Based on the final product, the energy balance is reflected in the production costs and therefore also in the final product. Because of the discontinuous procedure and the consequence of cooling and heating cycles an increased energy expenditure results. The steel industry is constantly on the lookout for potential energy savings and quality improvement measures in order to represent the overall process and the final product competitive. Each potential savings with the same or even better material quality represents a major competitive advantage in the global world market. Current status of technology in slab finishing before rolling: • The requirement for the surface quality of the slab rises highly since defects in the end product cause far higher costs these days. • Slabs are parked after the continuous casting and therefore cool down (energy loss). It can happen that the slabs tear during cooling. • The required processing of the surfaces can only take place at max. 600 ° C (technology milling and scarfing). The grinding method can be carried out at 600 ° C but it is more and more undesirable in this sector due to the high dust levels. • After treatment, the slab needs to be heated again which means considerable energy expenditure. • The surface treatment for the elimination of defects is performed nowadays in practice with o Scarfing and grinding: approx. 80%, Tendency decreasing o Milling: approx. 10%, Tendency increasing o Without treatment: approx. 10% Development beginning of the milling solution at 600 ° C The company's internal development group of MASCHINENFABRIK LIEZEN focused in 2014 on the new development of a powerful milling machine for slabs with the following objectives: 1. Continuous milling of steel, SS and aluminum slabs at up to 600 ° C with high milling performance 2. Topographic surface recording in order to allow milling adjusted to the slab contour 3. Automatic defect detection on the surface 4. Software for the combined processing of point 2 and 3 to minimize the material removal through modulated milling in one pass at simultaneous fault clearance 5. Reduction of operating personnel 6. High level of safety due to a self-sufficient, fully automated system 7. High performance / flow rate Details of the development work 1. According to the current state of the art, the slabs have to be cooled to a temperature of around 300 ° C after the casting process, to allow subsequent processing. The aim of the hot working process is that after the casting process the slab (with a temperature of about 600 - 700 ° C) is directly transported to the milling treatment, to process the slab immediately while hot in order to avoid the cooling of the slab. Since the slab doesn’t cool down and has not to be heated again to about 600 ° C for further processing in the rolling mills, it results in enormous potential energy savings around several gigajoules per slab based on the large thermal capacity of solid metal blocks (up to 50 tons). It follows a major cost saving potential because the heating in an oven is no longer necessary. In addition, structural advantages in the manufacturing process arise, thus there is a further significant step forward in quality. The hot processing of slabs therefore represents a unique feature in innovation. Concerning the milling tools, new replaceable inserts with new geometry have been developed which dissipate the heat faster and are adapted to the altered fracture characteristics of the chips. 2. Topographic surface recording Before milling, the surface of the slab is measured by means of a specially designed laser measuring system to subsequently keep the chip removal as low as possible during milling. This causes a considerable cost saving especially for high-grade steels. 3. Automatic surface defect detection The development of the crack detection respectively the slab surface detection and assessment in hot condition is an innovative step which has a positive effect in process safety and hence on the quality and also on the costs. Currently the detection of defects takes place by visual inspection of employees. Nondestructive-working online devices are not available at continuous casting facilities. The used crack detection is on the one hand intended to declare the points to be processed and on the other hand to remove defects of the slab automatically partially after processing of the slab. 4. Reduction of operating personnel Another apparent desire of the steel industry is the personnel reduction directly on the machine base with respect to possible threats. By increasing the level of automation of this new machine and the fully automated tool changing system, the heads of the worn inserts are automatically exchanged. All this is monitored in the control room. Consequently this milling machine works with only 2 employees (1x control room, 1x crane) 5. High performance / flow rate The machine is equipped with 2 milling heads with each of 250 Kw that secure a material removal of max.12 mm respectively 600.000 year-tonnes. Description of a typical milling work process Sequence o Complete topographic laser examination (contour), afterwards: o Modulated milling followed by thermographic surface defect detection o During milling:  Permanent tool breakage monitoring  100% Chip recycling o Finishing: Local milling of detected defects