A focus on the extrusion of light alloys and on innovative aspects of the production process of extrusions, especially on the HEH billet induction preheating system with permanent rotating magnets
by Giuseppe Giordano
A cold day and the driving rain did not keep a hundred participants from reaching the Villa Evelina Congress Centre in Capriolo (near Brescia) for the “Aluminium Extrusions” congress, an event which GMS and Alluminio e Leghe magazine organized on April 4th to provide trade operators in the aluminium extrusion industry with an occasion of knowledge and in-depth study on the industry’s current themes. At the start of the works of the Congress, moderated by Alberto Pomari, GMS, the initiative’s sponsoring company, was briefly introduced by General Director Giorgio Rozzi, who recalled that GMS, a company within the ENGITEC group, has its technological origins in Calamari SpA, a historical name in the fusion plant industry, founded in 1944 and specializing in the design and construction of induction furnaces for ferrous and non-ferrous metals as well as in the manufacture of continuous casting plants for the production of non-ferrous billets, pipes, coils and wires and in vertical, horizontal, continuous and semi-continuous casting technologies. Having picked up Calamari’s know-how, GMS was concretely founded by the merger of two companies, ATECO Impianti (semi-continuous vertical casting plants) and PROMES (induction furnace design and construction) and now designs and manufactures internally both independent machines and complete turnkey plants for the production of ferrous and non-ferrous semis. On the occasion of the congress, Giorgio Rozzi then presented the latest industrial initiative by GMS, the foundation of a new business unit dedicated to wire rod and ingots, based on the professional figures of Carmelo Brocato and Flavio Reggiani.
Extrusions in Europe and in Italy
The works went on, focusing on the aluminium alloy extrusion process; in this respect a complete picture of the global market being examined was presented by the editor-in chief of A&L magazine, Mario Conserva, with reference to the very recent data processed by Rome’s LUISS University regarding the aluminium industrial system (an in-depth study regarding the downstream segment is present on this issue of A&L). In order to provide an idea of the quality of market data being presented, we are reporting in tables 1 and 2 the general data of aluminium semis production in Europe, split among different countries.
Subsequently, the Italian aluminium market was presented, with a specific analysis of the extrusion segment, carried out by Orazio Zoccolan and Tatiana Pavia of Assomet’s Centroal; the updated figures regarding Italian extrusion are shown in figure 1.
Extrusion, as the first presentations highlighted in several instances, is a flexible technology, open to innovation as regards materials, machines and processes. The competitiveness of plants depends on intense improvement processes driven by the requests of users, increasingly found in very demanding sectors, in terms of performances and quality. Building up a response to the market of course also implies a greater cost control and a better rate of recycling with a reduction of scrap and an improved reuse. Many of these aspects are present in the HEH billet preheating system which GMS illustrated in detail. HEH (High Efficiency Heater) is the outcome of the MAGNheat project for the development of a billet pre-heating sysem within the extrusion process. The pre-heating system being considered stems from the invention by Inovalab, a spin-off of Padua’s University, of a billet pre-heating system based on the use of rotating permanent magnets. The renderings in figures 2 and 3 provide a good idea of the design: the billet is at rest while the permanent magnets rotate. The magnets are independent and may therefore move even with different speeds, until the inside of the billet matches the optimal thermal profile for that type of semi in a given aluminium alloy. Fabrizo Dughiero, University of Padua, and Marcello Zerbetto, Inovalab, presented this innovative system with two reports, the firs focused on the technological requisites of the rotating magnet heater, the second focused on competitive opportunities in production and quality terms provided by the new billet heating system.
Induction heating is a fast an clean way of heating electrically conductive materials, such as, metals. A traditional induction heating system involves a radio frequency generator, which converts the current from the mains system to high frequency alternate current and a workhead which can generate a strong electromagnetic field within the inducer.
The object which must be heated is placed within or near the inducer, where it absorbs the induced electric current which turns into heat by means of the Joule effect, without any contact with the inducer. Induction heating is applied to processes which envisage temperatures form 10°C to 3000°C. Induction heating is increasingly used in domestic and professional kitchens but also in many industrial heat treatment such as the pre-heating of extrusion billets. Large scale induction furnaces are common in extrusion plants, where they also play the role of homogenization furnaces.
The purpose of the MAGNheat project was mainly that of creating an application on an industrial scale of a new continuous current induction heater, based on the rotation of permanent magnets, and the chosen application was the pre-heating of the billets in an extrusion plant.
The project used the knowledge and innovations available for the inventors of the process at
Inovalab and GMS’s engineering capabilities.
Particularly the GMS HEH system claims:
• Higher efficiency conversion;
• Superior technical performance with competitive costs with respect to traditional induction heaters;
• Greater flexibility and better temperature control;
• Benefits for the environment in terms of reduction of energy consumption: a series of permanent magnets are made to rotate around a static aluminium billet and the heater is made up of different independent rotors, depending on the heating profile requested by the extrusion process.
The evolution of extrusion alloys
The last report of the congress (presented by the author of this article) intended to highlight that with the ongoing evolution of extrusion there are many more products which are tailor made to satisfy fully the requests of such high technology segments as aeronautics or automotive. The first step to reach this aim is the development of new allloys. The most appropriate alloy for a specific use may be defined by changing the alloying agents and the relationship between their percentage presences.
The optimization of the chemical composition is an effective method to obtain specific performances, but it is not the only one. It is, for instance, very interesting to improve the hardening precipitation processes optimizing their effects. At the same time heat and mechanical treatments lead to control of the structure, both in order to obtain, for instance, excellent tensile properties and to prevent negative behaviour such as a reduced corrosion or fatigue resistance. The topics dealt with in this speech will be taken up again in depth in an article which will be published in a forthcoming edition of Alluminio & Leghe; besides, he slides of the different presentations are available online for registered participants.