MANUFACTURING TECHNOLOGY
The complete stud bolt set for the rotor blade connection
ends, a hexagon head nut, a barrel nut and two washers.
Randack, however, did not have to look around in India to find highly efficient anti-corrosion protection for these fasteners. Just 10 kilometres north of the company’s headquarters in Westphalia, Germany, they found the ideal partner in Dörken MKS-Systeme GmbH & Co. KG of Herdecke. Dörken has been developing and producing micro-layer anti-corrosion protection systems here for 30 years and in addition to numerous applications in the automotive industry these are now also widely used in the renewable energy field. Dörken has been active in the Indian market for quite some time, looking after customers from a local office. The company has also already found its first few coating partners in the Indian market.
In-house coating In 2009, Randack decided that it would also do the anti-corrosion
coating with protective zinc flake systems in-house, thus keeping the entire manufacturing process – from cutting the raw material to size to coating and final quality control – all under its own roof. In early 2010, a further 3,000 square metres of production space were therefore added, including the company’s own coating plant, which went into operation this year and is supplied with DELTA-MKS®
chrome (VI) free coatings Delta®
systems from Herdecke. The products used are the -Tone and Delta®
-Seal, which
have already been used successfully in wind turbines for over 15 years. All threaded connections fitted in a wind turbine are to some
extent exposed to extreme climatic and thus corrosive conditions, as well as dynamic strains from wind loading and the turbine’s own operation. The fasteners used are therefore generally highly rigid. However, if the wrong form of surface protection is chosen, these have a degree of susceptibility to brittle fractures. Such brittle fracture failure is often the consequence of hydrogen penetration during the surface treatment process. This is something that needs to be taken into account when selecting the form of anti-corrosion protection to be used. The protective coating also has to have specific friction coefficients in order to enable connections to be easily screwed together on-site even when often working against the clock and under difficult conditions. Not least, however, the coating must provide highly effective and long-lasting anti-corrosion protection. This, of course, applies especially in the case of offshore locations.
For extreme exposure Zinc flake systems are in effect able to fulfil these requirements as a package. The Delta®
all standard methods of application. Which method to choose depends on the size and shape of the parts. Large format steel components, as used in wind turbines, are, for example, coated at Randack by spraying, while smaller elements are given their surface protection by the dip-spin method. As no hydrogen is introduced in the coating process, it is possible to rule out any danger of the rigid components suffering hydrogen embrittlement caused by the coating procedure. After application, the protective coat is annealed for approximately 30 minutes at an object temperature of on average 240°C. The low annealing temperatures prevent the rigid steel components from getting damaged in the process by unduly high heat exposure and thus have a decisive advantage over rival systems. The subsequent application of an organic topcoat using -Seal significantly increases the anti-corrosion protection
Delta®
still further. In contrast to the basecoat, this topcoat is not electrically conductive. The additional protection from corrosion is provided here by insulating the basecoat against corrosive attack. Depending on the choice of topcoat, further requirements can also be fulfilled, such as colouring, chemical, UV-ray and extreme temperature resistance and defined friction values.
“ All threaded connections fitted in a wind turbine are to some extent exposed to extreme climatic and thus corrosive conditions, as well as dynamic strains from wind loading and the turbine’s own operation.”
Favourable conditions Setting up an Indian subsidiary for producing solid steel bolts
-Tone basecoat provides
active cathodic protection and, with a layer thickness of just 10µm (depending upon geometry, system set-up and application process) achieves corrosion endurance times as per DIN EN ISO 9227 of over 1,000 hours. The coating can be applied using
108 Fastener + Fixing Magazine • Issue 75 May 2012
and fasteners not only opened up the possibility for Randack to manufacture cost efficiently in the locality and to supply the leading companies in an expanding market on a just in time basis, but also, where required, to provide on-site technical advice as well. The other general conditions were also extremely attractive. The situation with regards to the supply of raw materials in western India is very good and the Indian labour market also offers great potential in terms of qualified engineers and well trained specialists for operating production plants. This, along with the imported, highly specialised manufacturing equipment from Hagen and innovative zinc flake coating technology from Herdecke, gave the new company the necessary ‘following wind’. Now, 30% of its production is exported to Europe and to parts of the USA. Quality from Westphalia – made in India!
www.doerken-mks.com
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