The modern long products mini mill

Transcription

1 11:21 am Page 152 The modern long products mini mill Two Danieli-supplied plants at Deacero SA in Mexico epitomise the modern long products mini mill, encompassing electric steelmaking, fast billet casting directly linked to reheat furnaces and fast, flexible rod/bar mills providing high quality, low cost products. Current and expanded facilities are described. AUTHORS: David Gutiérrez and Giovanni Nigris Deacero SA and Danieli Morgårdshammar T he Deacero Group was founded in 1952, making wire products in a small shop in Monterrey, Mexico. Today it is the largest wire supplier in Mexico and one of the biggest in the world, with eight wire factories having a capacity of 1Mt. There are two steel plants supplied by Danieli at Celaya and Saltillo comprising two EAF melt shops and three rolling mills with an overall capacity of more than 2Mt. In December 2004 Deacero SA de CV awarded a further contract to Danieli for new steel making and hot rolling facilities which will double the capacity of its Celaya mini mill to 2Mt/yr, strengthen its r Fig.1 Panoramic view of the Celaya mini mill leading position as a wire rod and bar producer in Mexico and boost the Group s total capacity to approximately 3Mt/yr. THE SALTILLO MINI MILL The Deacero Saltillo plant has been developed in stages since 1979 when Danieli installed a semi-continuous wire rod mill with a 150,000t/yr capacity and a finishing speed of up to 70m/s. The melt shop, supplied in 1985, underwent several upgrades over the years to increase productivity. The present configuration includes a 56t EAF, LF and a 4-strand billet caster suitable for billet hot charging. The unit performs at world class level with an average 42 heats/day achieved during The rolling mill was also upgraded over the years to a fully continuous arrangement with a speed of 90m/s, resulting in a capacity of approximately 450,000t/yr in 2003, before the last upgrading stage. This involved the supply of a new 110m/s high-speed wire rod line featuring the latest generation Danieli DWB finishing block and the BF (Bearing Free) Laying Head, which makes use of magnetic fields to support the rotor instead of roller bearings as in traditional units. Mill capacity in 2004 was over 700,000t with a product mix mainly of 5.5 and 7mm diameter wire rod (90%). Another significant upgrade was made in early 2005 with the start up of the new Endless Welding Rolling (EWR ) billet welding line. This has made possible, for the first time in North and South America, uninterrupted production of endlessly rolled wire rod in variable customised-weight coils in any size up to 3t, starting from 160mm, 6.5m long (1.2t) standard billets. THE CELAYA MINI MILL Symbol not found table 2028in Symbol found not table 2028in Configurazione CadMEC 152 r Fig.2 The 2Mt/yr plant expansion layout Built on a greenfield site, the Celaya plant location was strategically selected in order to serve the central regions of Mexico, as well as the Mexico City area, taking advantage of good rail and road connections. The mini mill, initially designed for a production capacity of 600,000t/yr, started commercial production in September A second phase was completed in 2000 and the plant now includes a melting shop with one 110t Danarc AC EAF, LF, 6-strand caster and two fully independent super flexible rolling mills, with an overall

2 11:24 am Page 153 FORMING PROCESSES r Fig.3 EAF in operation at Celaya production capacity of over 1Mt/yr of bars and wire rod. It is now one of the most modern, lowest cost mini mills in the world. At the end of 2004 the decision was taken to expand further and the order for the new steelmaking and rolling facilities was awarded. The plant expansion includes a new steelmaking plant of 1.1Mt/yr capacity and a third rolling mill of 110t/hr capacity. This phase will be completed in summer The plant (see Figures 1 & 2) has a mini mill T-type layout to optimise material flow and allow hot charging of billets. The melt shop is fed with scrap mainly from the company s scrap yards in Mexico City. Raw materials are stored in a scrap yard arranged on two bays. The scrap is charged by six 20t cranes and is conveyed to the melt shop bay by remote controlled cars with weighing facilities connected to an automation system. The melt shop bay contains the EAF, LF and all auxiliary equipment. Furnace slag handling is carried out by tapping the slag from the EAF onto the floor and collecting it by means of a front-end loader. The ladle and tundish slag is dumped in the same way and stored in dedicated areas. After steel refining at the LF, the ladle is transferred to the Fast Cast continuous casting machine. This high-speed caster is directly connected to the two rolling mills for hot charging, and associated auxiliaries are located in the rolling mill bays where temporary billet storage areas are also provided. Cast billets are cut-to-length and sent at approximately 750 C to the re-heating furnace. r Fig.4 CCM in operation at Celaya Capacity (tapped steel), t Shell type Shell diameter, mm Transformer power, MVA Charge mix Electrode diameter, mm Pitch circle diameter, mm O2/C injection Existing furnace 110 EBT 6, % scrap 610 1,150 Supersonic side-wall O2/C lance, O2 wall tuyeres New furnace 112/120 EBT 6, % 100% scrap 610 1,250 4 x 2800Nm3/hr (O2) HiJET units Table 1 EAF main features The two rolling mill facilities, product finishing services and relevant finished product storage yards are installed in three parallel bays, while general services are strategically located beside the melt shop and rolling mill bays. This layout rationalises the casting and rolling areas and is particularly dedicated to automated black-box a THE PRESENT CELAYA PLANT CONFIGURATION AND PROCESS ROUTE 153

3 combustion and oxygen/carbon injection are essential for foaming slag control and steel decarburisation. Burners, supersonic side-wall O 2 /C lance and O 2 wall tuyeres are also installed. The EAF is completely sealed. Foaming slag control is automatic and arc coverage is guaranteed with great advantages for the life of refractories and the watercooled panels. Slag formers and ferroalloys are stored in a bunker system arranged beside the furnace bay and are automatically added to the ladle at tapping according to the steel grade requirement. A spare shell for the EAF is used to eliminate shut-down for refractory preparation. r Fig.5 Hot charging operation Existing LF New LF Nominal heat size, t Transformer power, MVA % Electrode diameter, mm Pitch circle diameter, mm Heating rate C/min Table 2 Ladle furnace features Machine type Existing caster, New caster, Fast Cast Fast Cast BLC 906 BLC 1006 Number of strands 6 6 Bending radius, m 9m 10m, multiple bending Castable sections, mm Actual outfit, mm 160 x x 170 Mould type 1,000mm multi-tapered 1,000mm multi-tapered copper tube copper tube Billet cutting Oxy-gas torches Oxy-gas torches Max. productivity, t/hr Steel grades Table 3 Main caster features Low, medium and high carbon steels alloy steels, resulphurised steel, boron steel technology. Lower investment costs were made possible by optimising the steel building arrangements, EOT cranes, civil works, piping and wiring. The same concepts are adopted in the design of the present 2Mt/yr plant expansion. EXISTING STEELMAKING FACILITIES The Danarc EAF (Figure 3). The main features of the EAF are shown in Table 1. To meet the challenging performances the EAF was provided with a set of technological packages: Efficient CO post Ladle furnace After tapping the ladle, mounted on a car with a weighing system, is transferred to the LF which has a ladle turret to move the ladle in the refining position thereby reducing the power-off time and maximising the steel refining time. The main features are shown in Table 2. Fast Cast continuous casting machine The caster is designed to produce commercial and quality steels. The main technical features are shown in Table 3. High-speed casting technology is characterised by: ` Open stream casting equipment, including Flying Nozzle Technology (FNT) allowing a casting sequence up to 50 heats with the same tundish ` Submerged casting equipment, including mould electromagnetic stirrers and a quality control tracking system to maintain casting parameters constant for reliable and good internal billet quality ` Primary and secondary cooling system to control the billet cooling/reheating to ensure good surface and internal quality ` 1,000mm long copper mould of Danieli multi-taper design which provides excellent surface quality and an improved distributed solidification ` Delta shape tundish design to minimise the temperature differential between strands ` Retractable mould oscillator to allow mould change on the fly to reduce off-times and increase productivity. Billet hot charging facilities The caster is directly connected to the re-heating furnaces of rolling mills 1 and 2 for hot charging of billets. At the caster exit (see Figure 4) the billets are delivered directly to the re-heating furnaces at approximately 750 C for reheating to the desired rolling temperature (see Figure 5). EXISTING ROLLING MILL FACILITIES At present there are two rolling mills: No.1 bar mill and No.2 high-speed wire-rod mill. Mill No.1 started production in September 1998, rolling 3 and 4-strand-slit 154

4 11:42 am Page 155 FORMING PROCESSES small size rebars onto a cooling bed. Between 1999 and 2000 No.2 mill was commissioned, including welding of the first billets by EWR. The production range of the two mills includes low, medium and high carbon steel bars and wire rods for a nominal capacity of 1.2Mt/yr in the following sizes: ` mm diameter bars and rebars from mill No.1 ` mm diameter wire rod in 2.5t coils from mill No.2 The starting material for both mills is continuously cast billets coming directly from the CCM in hot charging mode or from the billet yard. No.1 bar mill The 18 stand bar mill is made up of six ESS compact cantilever roughing units and 12 SHS housingless intermediate/finishing stands arranged continuously and with quick changing facilities. Mill supply also included a 10-pass DWB high-speed finishing block and the associated wire rod production line that is now fed directly by mill No.2. Mill No.1 can also feed the wire rod block if so required. The mill is served by a 100t/hr Danieli Centro Combustion reheating furnace, directly connected to the CCM for direct casting and rolling. The EWR line provides uninterrupted production cycles through continuous billet welding before entering the first roughing stand. Smaller product sizes are produced using multi-strand slit rolling technology to fully exploit the re-heating furnace capacity. In particular, 4-strand slit rolling is used to produce 9.5mm diameter rebars at a speed of 14m/s, corresponding to an output of over 100t/hr. The finishing services comprise a 78m long cooling bed, cold cutting-to-length facilities and automatic finishing services with bar counting, sub-bundling and master bundling station. The finishing facilities are particularly designed to produce very small sub-bundles at very high output rates, enabling Deacero to supply the market with 100kg high quality sub-bundles at a rate of 100t/hr. No.2 wire rod mill The 18-stand mill has a similar configuration to No.1 and independently feeds the 10pass block and the wire rod line originally supplied with the No.1 mill. It is fed by an identical re-heating furnace to that in No.1 mill. Direct connection to the caster for a r Fig.6 EWR billet welding line in operation at Celaya 155

5 11:43 am Page 156 direct casting/rolling is also provided. Provision for future addition of an EWR line is made. The high speed wire rod line produces low, medium and high carbon steel wire rod finished at the Delta block at a production speed of up to 110m/s and processed at the DSC controlled cooling line. At the end of the roller conveyor the 2.5 t coils are regularly formed and vertically conveyed in their as-formed condition to the coil compacting and tying station by a vertical trestle line. The system provides excellent quality in terms of regular coil formation, shape and compactness, as well as a safe and reliable flat-knot type bundling system. MAIN HIGHLIGHTS OF THE ROLLING MILL FACILITIES EWR The on-line automatic head-to-tail flash welding of billets at the delivery side of the reheating furnace enables uninterrupted production of wire rod and straight bars with significant benefits in plant productivity, efficiency, material yield and production costs (see Figure 6). The billet welding process is particularly beneficial in wire rod mills as it enables production of customised weight coils. Extra-heavy coils can be produced, even starting from relatively low billet weights. Deacero was the first plant in the Americas with EWR and this resulted in significant benefits in material yield and productivity (+2% and +4.5% respectively, in straight bar production). Including Saltillo, a total of 16 units have now been supplied worldwide. r Fig.7 High speed multi-strand slit-rolling operation 156 r Fig.8 Controlled cooling conveyor High-speed production of multi-strand slit-rolled small-size bars Mill No.1 is at present the fastest multi-strand slit rolling production line world-wide (see Figure 7). 4-strand slit 9.5mm diameter rebars are delivered onto the cooling bed at a finishing speed of 14m/s, leading to the full achievement of the 100t/hr reheating furnace capacity. The latest generation Danieli Morgårdshammar 4strand slitting guide gives a considerable contribution in precise and safe multistrand slitting operation granting absolute quality of the finished product. Small size bar sub-bundles One of the mail highlights of Celaya mill No.1 finishing facilities is the very high production output (100t/hr) of extrasmall sub-bundles (weighing 100kg only) made up of precisely counted bars. Absolute counting accuracy,

6 11:44 am Page 157 FORMING r Fig.9 RM1 main pulpit High-speed production of quality wire rod coils High-speed stable production of low, medium and high carbon steel quality wire rod is made possible by the advanced characteristics of the latest-generation Delta-type finishing block and the associated precise guiding system. The final technological and mechanical wire rod properties are achieved thanks to the DSC in-line treatment and controlled-cooling process (see Figure 8). Superior finished coil quality The combined RRT (Rotary Reforming Tube) and Easy-Down systems at roller conveyor s end enable eccentric wire rod loops to deposit in the pit which, coupled with gradual coil lowering during formation, vertical type coil handling, compacting, tying and transportation system to the collecting station, results in superior coil final quality. ELECTRICALS AND AUTOMATION SYSTEM All automation systems and electrical equipment for the mini mill are from Danieli Automation. The automation system contributes to achieving the following goals: Reduced manpower thanks to: ` Powerful operator interfaces ` Ergonomic control desks ` Minimum number of control pulpits ` Computerised support maintenance. Consistent operation and minimal human errors thanks to computer guided operation. Reduced consumption and increased material yield thanks to: ` Optimised process control ` Process models ` Metallurgical calculation models ` Advanced alloy calculations Reduced equipment failures and material losses thanks to fully automatic operation. The modern control room in RM1 is shown in Figure 9. The automation systems have been developed in two hierarchical levels with the automation units integrated through a Local Area Network (LAN): ` Level 2 (process control), ALFA-Vms with ORACLE RdBMS-based, dedicated to support the process technology ` Level 1 (equipment control), PLC-based, to control the mechanical equipment a granted by the Danieli Morgårdshammar precise bar counting system. 157

7 FORMING The computer architecture is based on the client-server concept, allowing flexible and reliable configurations. The operator-machine interface is based on redundant PC stations running SCADA packages, allowing an efficient, user-friendly operation of the mini-mill. The main functions developed by the Level 2 System are: ` Management of technological databases including steel tables, process routes manufacturing practices for melting, casting and rolling ` Management of production schedules ` Production and heat tracking ` Processing mathematical models ` Operator guidance ` Report generation ` Data logging The basic functions required for running sequences, controls, operator interfaces, alarms and monitoring functions are implemented in the level 1 system. THE 2MT/YR PLANT EXPANSION The new melt shop comprises a 120t EAF, a 120t LF, a sixstrand Fast Cast high-speed caster and associated equipment and auxiliary plant. The new LF, part of the melt shop auxiliary equipment and the caster ladle turret and tundish platform area are installed in a 50m extension of the existing EAF bay. A new melt shop bay, located at 90 to the existing one, contains the new EAF. A set of buckets mounted on remote controlled cars supply scrap from the new scrap yard consisting of two bays measuring 30 x 258m each. Two other auxiliary bays house the new refractory maintenance shop and future cast billet storage. The main equipment of rolling mill No.3 is housed in a new bay parallel to the existing rolling mill buildings. The new high-speed wire rod line is located in a 204m extension of mill No.2 bay, while the new mill s finished products are stored in a 204m bay located beside mill No.3 main building. The expansion project also includes new auxiliary facilities and plants such as electrical substation, fume treatment plant and water treatment plant to serve the new melt shop and rolling mill. The consolidated technology already in operation at the existing steelmaking and casting plant will be duly updated with all technical innovations and improvements available currently by Danieli. ` Full platform compact design with minimised foundation volume ` Cantilever roof supporting structure for easy maintenance of roof refractory Continuous caster The main features are shown in Table 3. Casting is open-stream but provision is made for submerged casting in the future. The oscillating bench is a hydraulic, retractable type and there is a 4-zone water spray secondary cooling system. At discharge there is liftable side-transfer of billets and a walking beam cooling bed. No. 3 rolling mill The No.3 rod mill hot rolling area is an exact copy of mill No.1, while the wire rod line is identical to that installed at mill No.2. The 110t/hr mill has 18 stands plus a 10-pass high-speed block, wire rod controlled cooling line and coil finishing facilities which are also connected to those already serving mill No.2, for higher operation flexibility. Space is left available for the future installation of an EWR line. The mill is designed to produce mm diameter wire rod in up to 3t coils, from 170mm billets. All equipment is standardised with those supplied at previous stages for optimising spare parts, consumables and maintenance. Electricals and automation system System expansion was fully proven with its extension to wire rod mill No.2. It will be further expanded to serve the new melt shop and rolling mill No.3. The automation system will be fully integrated with the existing automation system. The advanced automation system strongly contributes to minimising manpower, reducing consumption, equipment failures, and human errors, while enabling consistent operation and improved material handling and plant efficiency. CONCLUSIONS Proven equipment technology coupled with high quality management and highly experienced operative staff are the key elements that made the Deacero Celaya mini mill one of the most successful long product production units, worldwide. The additional Celaya plant capacity, added to that of the Saltillo mini mill, further strengthens the company s leading position as a wire rod producer in Mexico and in the Americas. MS 120 t EAF The main features are shown in Table 1. ` EAF Danarc design for high secondary voltages and longer arc ` High impedance technology for arc optimisation ` HiReg digital electrode regulation David Gutiérrez is Group Plant Director at Deacero SA, Deacero, Mexico and Giovanni Nigris is Vice President, Danieli Morgårdshammar, Buttrio, Italy. CONTACT: info@danieli.com 158