Liberty Speciality Steels Accelerates Production of Ultra-Clean Speciality Steels with New Vacuum Induction Melting Furnace
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Liberty Speciality Steels accelerates production of ultra-clean speciality steels with new vacuum induction melting furnace Reprint from „MPT International“ (2017), issue-no. 4, page 48 – 53. LIBERTY SPECIALITY STEELS Liberty Speciality Steels, Stocksbridge, Sheffield, UK Contact: www.libertyspecialitysteels.com E-mail: [email protected] SMS group, Düsseldorf, Germany Contact: www.sms-group.com E-mail: [email protected] 2 Liberty Speciality Steels accelerates production of ultra-clean speciality steels with new vacuum induction melting furnace At its Stocksbridge, Sheffield site (South Yorkshire, UK), Liberty Speciality Steels – the speciality steel business of newly formed Liberty Speciality Steels is improving its Liberty Steel – has been successfully producing alloy and specialist alloy manufacturing facilities by increasing stainless steel grades for over sixty years for use in de- production levels at the VIM X-eed® vacuum induction manding sectors such as aero space, oil & gas, industrial melting furnace supplied by SMS Mevac. This new met- engineering and in the manufacture of bearings, bright bar, allurgical facility produces high-purity steels and spe- narrow strip and niche engineering applications for custom- ciality alloys for extremely demanding applications like ers around the world. aerospace, motorsports and oil & gas. These facilities are coupled to a unique integrated mill, machined part Their strength in speciality steels lies in the fully integrated and service centre offering, and are supplied globally production capability, which includes electric arc steelmak- as ingot, bar, cut piece or machined part. ing, vacuum induction melting (VIM), mill processing capa- The ingots produced will be refined further by processing through a vacuum arc remelting unit before being rolled or forged into products (Picture by courtesy of Liberty Steel). 3 LIBERTY SPECIALITY STEELS bilities and dedicated service centres. Typical products in- of such materials Liberty Speciality Steels has been oper- clude ingots, blooms, billets, bars, slabs and narrow strip; ating numerous remelting plants, i.e. two electro-slag re- in cast, rolled, drawn, peeled, heat-treated or re-melted melting plants (ESR) and nine vacuum arc remelting (VAR) condition, in exactly the quantities required by customers. plants at the Stocksbridge site, with feedstock mainly pro- vided by the nearby steelmaking operations. However, the The production centres in Sheffield and the West Midlands business previously supplied small quantities of VIM-derived area of the UK are backed by dedicated service centres in steel using ingots sourced from third parties. Bolton, UK, Nagpur, India and Suzhou and Xi’an in China. The service centres enable Liberty Speciality Steels to ser- Because of the enormous potential of the growing market, vice their customers’ supply chains with bespoke combina- in 2013 the company decided to invest in creating its own tions of added-value processing and just-in-time delivery. VIM base. In late 2013 the company announced it would More than 100 component and equipment manufacturers, build together with SMS group a vacuum induction melting end users, third parties and national bodies have validated (VIM) furnace at its Stocksbridge site to enable the steel the quality management systems. producer to tap into new market opportunities and develop on its own innovative new products for the aerospace and oil & gas industries. A challenging project had been launched. VIM plant enables Liberty Speciality Steels The company decided for a brownfield project. The furnace to deliver the highest purity steels location was the site of a former continuous billet casting plant, in order to take advantage of existing buildings, over- Liberty Speciality Steels has gained an excellent reputa- head cranes and plant services. The final layout integrated tion for supplying high-integrity steel to major commercial the main furnace components with the raw materials prepa- and military aerospace programmes around the world, using ration area, the crucible relining and pre-heating area and tailored supply chain solutions. Andrew Douglass, engineer- the mould preparation and ingot stripping area. ing director at Liberty Speciality Steels, underlines: “We are a key supplier to some very significant aerospace players.” He continues: “It is definitely a growth sector in terms of VIM: vacuum induction melting process aerospace production; Boeing forecasts a need for a record 41,000 new aeroplanes over the next twenty years. 38% of The VIM facility produces ultra-clean ingots, i.e. remelt elec- new planes will be for the Asian market, driven by China and trodes, that will be refined further by a remelting process, India.” Some of the most demanding products – delivered usually a vacuum arc remelting (VAR) unit before being rolled as ingot, bar and cut pieces – are used in the production or forged and finally manufactured into products such as en- of engine components, landing gear, controls, aerostruc- gine, transmission and structural components for the aero- ture, helicopter rotor components, etc. For the production space market. Tapping and all other process sequences are remote controlled and monitored from the control room. 4 The VIM production route involves vacuum melting high-pu- After casting: the filled mould exits the casting chamber rity steel and alloys in a crucible furnace, and then vacuum on rail car to the stripping area. casting the purified liquid steel into ingot moulds – all with- After hours: the solidified ingots are stripped out and in a low pressure vacuum chamber (vacuum level approx. placed under insulated hoods to cool slowly. This pre- 0.05 mbar or even less). The VIM technique comprises con- vents cracking of sensitive steel grades. secutive process steps as follows: As the entire melting and casting operation is conducted in The upper furnace and lower crucible are sealed togeth- an oxygen-free atmosphere, the resulting steel is very clean er, evacuated and charged with raw material. and has very low gas content. The technology enables the The raw material is melted by electrical induction heating. achievement of very tight analytical tolerances. Alloying ad- Induced current stirs the liquid metal; exposing it to the ditions, also carried out under vacuum, allow for precise vacuum during hours of refining to remove gasses. control of the steel’s chemical composition. Alloying elements can be added under vacuum. Moulds are prepared and set. The moulds travel on rail Melting in an oxygen-free atmosphere prevents the forma- car into the casting chamber. tion of oxides and also the loss of elements with an affinity Launder/tundish are prepared and set. Launder/tundish for oxygen. Unwanted accompanying elements which have travel on rail to the casting chamber. a high vapour pressure can be removed. The ingots pro- Casting chamber is sealed and evacuated and connect- duced will be refined further by processing through a vac- ed to the melting chamber. uum arc remelting (VAR) unit before being rolled, or forged After setting the exact composition of the alloys and the into products such as engine, transmission and structural casting temperature, the liquid metal is tapped under vac- components for the aerospace market. uum. The furnace tilts forward to pour liquid metal via the launder/tundish into the mould during casting. Production of speciality alloys at the Stocksbridge works, using the new VIM X-eed® unit supplied by SMS group. 5 LIBERTY SPECIALITY STEELS Launder/tundish prepared and set for tapping under vacuum. Technological concept and machine design All core components supplied by SMS Mevac have been de- signed to allow Liberty Speciality Steels to increase the melt The concept of the VIM unit is based on a three-chamber size to 18 t at a later date. system, in which casting, melting and exchange chambers are arranged adjacent to each other. The independent de- The mechanical vacuum pump system consists of three sign of the three chambers allows for individual evacua- skids that can be connected in parallel or alternately at tion of those. three exhaust points (melting chamber, casting chamber and exchange chamber/charger). To protect the vacuum The heart of the VIM X-eed® unit comprises an 8 t vacu- pumps against dust and metal particles, SMS group has um induction melting crucible and the associated vacuum developed special dry-type filters for this application. Sep- pumping, material charging and process control equipment. arate filter systems have been installed for each chamber. 6 Also ancillary equipment for crucible preheating and lining and electro-slag remelting (ESR). These facilities are cou- maintenance was included in the supply scope. The plant in- pled to an integrated rolling mill and service centres, which corporates vacuum pouring equipment for both top poured allow the company to deliver its products around the world and bottom poured ingots, in single or multiple ingot con- as ingot, bar, cut piece or machined part. Their highly qual- figurations. All process sequences are remote controlled ified technical teams provide advice and help with day-to- and monitored from the control room. The main process day problem solving, and are available to assist with lon- parameters and status indications as well as all important ger-term developments. system functions are displayed on the HMI monitor and are additionally recorded to permanent files for full quality as- Andrew Douglass, engineering