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APPLICATION OF DUCTILE IRON GJS 400-18U-LT IN HEAVY CASTINGS FOR WIND POWER PLANTS"
Jozef Turzynski, Head of Ferrous Alloys Department, Foundry Research Institute, Tadeusz Bogacz, General Menager, S.A. Metalodlew, Cracow, Poland
Summary. The article presents one of the most advantageous trends of the development in the world power industry, it means the wind power stations. One third of the weight of the installations in the wind power stations consists of castings. Till the year 2006 the increase in the demand for such castings and what is connected with it, the increase in the chances of the European and Polish foundries is foreseen. The Enterprise METALODLEW S.A. (Joint Stock Company) in Krakow as the main element of its development strategy assumed an increase in the production of large-sized, technologically advanced castings made in high quality foundry materials and designed chiefly for export. Among this group of castings are castings of parts for the wind power stations. A challenge for METALODLEW and the scientific circles in Krakow, with whom this enterprise cooperates, was an order for a casting of a platform for the wind power station of the type N-60 according to the strictly determined acceptance requirements, quality inspection and anticorrosion protection. The authors of the article presented the characteristics of the above-mentioned casting of the platform and the preparatory work connected with the realisation of this order for the wind power station of the type N-60. Finally, the obtained mechanical properties of this casting which allow its application under extreme static and dynamic loads and low temperature were given.
Key words: wind power plants, ductile cast iron.
Introduction
In experts' opinion, the use of recoverable energy is in many aspects the most desired trend in development of the world power engineering strategy [1]. This is quite true in the case of wind power plants. Using wind power plants, the EU member states intend to gain by 2010 about 12% of the overall produced energy. In its "Strategy for recoverable energy development in Poland", the Ministry of Environment expects that by this time the energy from recoverable sources will make 7.5% of the overall electric energy produced in Poland. The ten major producers of wind power plants - listed in Table 1 - covering 97% of the world market, supplied in 2001 installations estimated at a total power of 6627 MW. The chief users are Germany, USA and Spain - see: Table 2. The world consortia and industrial groups in Europe are planning to use on a wide-scale the potential hidden in wind power plants located in mainland and in sea, estimating that in the sole German inshore sea areas there are conditions which enable generation of up to 4000 MW [1]. Poland
also has favourable geographical conditions for development of wind power plants.
Table 1 Ten major producers of wind power plants
Supplier Sales [MW] Market share [%]
Vestas [DK] 1648 24,1
Enercon [D] 1036 15,2
NEG Micon [DK] 874 12,8
Enron [USA] 865 12,7
Gamesa [ES] 648 9,5
Bonus [DK] 593 8,7
Nordex [D] 461 6,7
Made [ES] 191 2,8
Mitsubishi [J] 178 2,6
REpower [D] 122 1,9
Total 6627 97,0
According to the statistical data, in terms of weight, 30% of the whole wind power plant are castings, and therefore in 2002 the demand for castings from the ten major producers was 235 th. tons. At the same time, by the year 2006, the total amount of castings
operating in wind power plants is expected to grow further up to 425 th. tons. These are very optimistic forecasts for the foundry market in Europe, and also a good opportunity for the domestic foundries trying to fight the recession.
Table 2 Ten major users of wind power plants
Country New installations Total installed
in 2001 [MW] capacity [MW]
Germany 2627 8734
USA 1635 4245
Spain 1050 3550
Italy 276 700
India 236 1456
Japan 217 357
Denmark 115 2456
England 107 525
Greece 84 358
China 75 406
All World 6824 24927
The leading producers offer installations always larger and larger. To give just an example, NORDEX produced the biggest in the world N-80 power plant of 2,5 MW capacity, and the next goal they have in mind is designing a sea wind power plant of total capacity going up to 5 MW, where a turbine with a propeller of 110 m diameter will be placed on a top of 86-metre tower [1]. The dynamically increasing size of the constructed wind power plants intensified the demand for large castings weighing up to 30 tons. These are mainly elements like : platforms, frames, rings, casings, mountings for propellers, and blocks. Because of extra high-duty conditions to which parts of this type are exposed on running, specially preferred are ferritic grades of ductile iron assigned for operation at low temperature, like EN-GJS 400-18U-LT
(-20 °C) and EN-GJS 350-20U-LT (-40 °C) [4, 5]
MANUFACTURE OF CASTINGS FOR POWER INDUSTRY - THE CHIEF ELEMENT OF METALODLEW S.A. ENTERPRISE STRATEGY
All past decade, Metalodlew SA has been persistent in its attempts at making the enterprise more modern, both as regards the technology and management system. A very important element in this part of activity was obtaining PCBC and IQ NET certificate in the scope of Integrated Quality, Environmental and Occupational Health Management System according to PN-EN ISO 9001:2001, PN-EN ISO 14001:1998, PN-N-18001:1999, and Certificate of Conformity for products made for power industry (SIMPTEST) [2, 3].
Along with raising technical level, the structure of sales has also changed. In 1993, 97% of castings were made for the in-plant needs of T. Sendzimir Steelworks (HTS), power industry using only 3% of
production. In 2002, HTS SA was consuming 8% of production, while 16% was for power industry [2, 3]. In the development strategy adopted by Chief Executive Officers (CEOs) of Metalodlew SA Enterprise, special emphasis was put on increasing the share of production of large and advanced castings poured from high-quality cast materials, assigned mainly for export. The sector of castings for power engineering industry - specially as regards wind power plants - fits in an excellent way the adopted strategy of development. The already possessed certificates of Det Norske Veritas, Germanischer Lloyd, Lloyd's Register and Bureau Veritas enable active search for customers abroad and being effectively competitive in international market of castings [2, 3].
The CEOs activity regarding modernising of the technical and technological conditions of the Enterprise as well as active cooperation with research and development centres enabled undertaking even more ambitious tasks. As an example may serve implementation to production of cast base frames (grundrahmen) for N-60 type wind power plant made by NORDEX. So far, only few foundries in Europe have been able to produce castings of this type.
Characteristic of cast base frame for n-60 type wind power plant made by nordex
The cast base frame has a complex design with numerous ribs and great variations in wall cross-section; it has well developed flat surfaces. The overall dimensions are 4,139 x 2,710 x 1,370 mm. The weight of a raw casting is 12 700 kg; average wall thickness-about 100 mm, with minimum of 60 mm and maximum of 160 mm. So, in terms of the art of founding, this is a highly intricate shaped casting with high requirements as regards surface quality, cast material homogeneity and mechanical properties. The cast material was in this case ductile iron, grade EN-GJS 400-18U-LT according to PN-EN 1563.
Table 3 Material Characteristics
Parameter Designation according to PN-EN 1563
EN-GJS 400- EN-GJS 350-
18U-LT 20U-LT
Tensile strength Rm, N/mm2 370 320
Proof stress 0,2%, 220 200
Rp0.2 N/mm2
Elongation A5, % 12 15
Impact resistance KCV, J 10 (-20 °C) 10 (-40 °C)
The table gives the, required for the above mentioned ductile iron grades, minimum mechanical properties, measured on cast-on test pieces for castings of the wall
thickness comprised in a range of 60 < t < 200 mm.
Technical acceptance require- ments (tar)
The Customer specified all details concerning the required test methods, quality control, properties, and anti-corrosive protection. The following conformity certificates and reports were needed:
- testing of mechanical properties according to PN-EN 1563, measured on cast-on test pieces for castings of the wall thickness comprised in a range of 60<t<200 mm,
- non-destructive magnetic powder and ultrasonic inspection in class S3V3 according to DIN 1690 Part II for selected zones of casting,
- casting measurements,
- anti-corrosive coating.
Development of technological process
The technological process of making cast base frame was developed by a team of process engineers from Metalodlew SA and experts from R&D centres in Krakow - Foundry Research Institute and the University of Mining & Metallurgy. The personal constitution of the team was established by CEOs of the Enterprise. The Chief Coordinating Officer was Dr Eng. J. Turzynski. The short (one-month only) period available for project execution required maximum concentration of means and efforts, and reducing the technological tests to minimum. To reduce the number of tests to a most indispensable minimum only was also dictated by the very high unit cost of making one single casting. Therefore the team adopted as a starting point the rule of "zero defects". The emphasis was put on a careful analysis of problems that might be encountered in a technological process, application of modern methods in foundry technology designing and computer-aided simulation of pouring, solidification and feeding. Additional drawback was the fact that the melting and moulding shops were located in separate bays, distant from each other by over 200 m. Thus, besides strict observance of the work safety conditions during the 20 minutes when 15.000 kgs of metal were transported by car, it was also necessary to counteract the possible drop of metal temperature. The short period available for contract execution also required ready-at-hand solution to a number of problems regarding logistics, i.e. supply of special tooling (boxes, ladles, pattern, core boxes), as well as high-quality moulding and charge materials, which needed active involvement from almost all the departments and services operating at Metalodlew SA, supported by the cooperating units.
Simulation of pouring, feeding and solidification
The simulation of pouring, feeding and solidification was performed on MAGMASOFT program, using
its wide computation potential. Different designs of the gating and feeding system were examined, along with the directional solidification of casting forced by a system of chills. The parameters obtained in the simulation process, time of pouring, directional distribution of metal volume, solidification process, and the adopted porosity index shortened the time of implementation and, more important even, enabled the cost of tests to be reduced to minimum (Figure 1).
Fig. 1. Simulation of solidification
Mechanical properties obtained
Making the first casting of base frame in August 2002 crowned all the efforts taken by Metalodlew SA Work Team and marked the beginning of production of large shaped castings poured in iron of grade EN-GJS 400-18U-LT for wind power plants (Figure 2).
Fig. 2. Raw casting of platform
Preparatory works have also been started on implementing in practice the production of castings even larger and heavier. The obtained mechanical properties were consistent with the requirements of PN-EN 1563 Standard (Table 3). The metallographic examinations, made on cast-on specimens, fully confirmed the presence of ferritic structure in as-cast
condition (over 95 %), with graphite of the type A6 PN-EN ISO 945. The homogeneous and fine-grained structure was obtained applying a multi-step inoculation with complex inoculants. Due to the adopted technological regime, it was possible to obtain in as-cast condition the structure ensuring high toughness of cast iron, satisfying the requirements established for the grade EN-GJS 350-20U-LT. This, in turn, enabled safe application of castings under extra high-duty conditions of static-dynamic loads and low temperature (-40 °C). The obtained properties exceeded even the Customer's expectations put forward in TAR.
Table 4 Mechanical properties of ductile cast iron -N60 base frame
Ba Rm Rp0, A Z KV KCV
se [MP 2 [% [%l - -
fra al [MP l 20°C 20°C
me al [J] [J/cm
no 2l
1 386 234 21 22, 10,6 13,3
6 8
2 384 219 24 24, 19,4 23,1
6 7
3 416 241 23 20, 10,4 13,1
3
4 448 258 17 16, 10,6 13,2
9 4
5 409 252 25 0 24, i 12,6 15,7
6 403 246 24 i 25, 9 14,3 18,0
7 393 246 23 24, 16,3 20,2
i 8
Summary
The statistical data indicate a dynamic growth of the wind-propelled power industry, with increasing rated power of turbines and growing size of power plants. Raising demand for castings made in high-quality ductile iron creates various opportunities also for Polish foundry industry. For the CEOs at Metalodlew S.A. the opportunity of starting up the production of large castings for wind power plants is a very important element in the adopted strategy of development. And more important even, manufacturing successfully the cast base frames for N-60 wind power plant made by NORDEX in a time so short has been:
- a confirmation that the basic guidelines adopted in the strategy of development are correct,
- an obvious success of the research and technical team,
- a next step made by Metalodlew SA towards raising the quality of products and the technical and technological level of the Enterprise,
- a good example of cooperation between several research and development centres operating in Krakow.
References
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Рецензент: С.С. Дьяченко, профессор, д.т.н., ХНАДУ
Статья поступила в редакцию 18 июля 2006 г.
