08/10/2008
Building bridges in the world with CERATIZIT
Customer story: carbide specialist CERATIZIT helps with the machining of stainless steel for giant tankers and bridges |
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Stainless steel is a material which is difficult to machine. It is characterized by low thermal conductivity and a relatively high tendency to cold hardening; it is tough and tends to adhesion. The consequence: its machinability is four times worse than the one of machining steel. A big challenge, as shown by the example of the CERATIZIT customer Outokumpu in Degerfors in Sweden.
Stainless steels are very popular thanks to their particular properties. The material has an aesthetic appearance, is resistant to corrosion and can be recycled completely. It is mainly applied in the fields of catering and household (33%), construction of industrial plants (26%) and transport (16%). Stainless steel consists of at least 10.5% to 13 % of chrome. Thanks to this high chrome content, a protective passive layer of chrome oxide is created on the work piece surface. Stainless steel is mainly used in sectors where cleanliness and hygiene are of utmost importance. In fact this steel is resistant to water, vapour, humidity, salt, acids in food and weak organic or inorganic acids.
Know-how for high-tech bridge construction
The Outokumpu group achieves a turnover of six billion euros with 8,000 employees worldwide. The vision of the group is to become the uncontested number 1 in the stainless steel sector.
The Outokumpu plant in Degerfors mainly manufactures stainless steel flat and long products. “We have a very wide product range and countless applications are possible”, says Business Development Manager Anders Finnås. One of our speciality fields is ship and bridge building. The company produces sheet metal for the internal panelling of tankers which transport chemical products. In the field of high-tech bridge construction the company's know-how lies primarily in the production of sheet metal and structural parts made of stainless steel. “Both appearance and corrosion resistance play a very important role. A bridge in stainless steel is not only technically interesting but also has a longer service life, and is also visually appealing thanks to the material,“ says Finnås.
Stonecutters Bridge in the Hong Kong harbour: a prestige project
In Hong Kong at the moment one of the longest cable-stayed bridges in the world is being built: Stonecutters Bridge. From 2009 onwards this highway bridge will relieve the city centre of container trucks and serve as a prominent gateway to the harbour of the city. The bridge’s structural system will have a width of 51 m and will be provided with 4 lanes in every direction plus a break-down lane. The total length of the bridge will amount to 1596 metres with a span of 1018 metres. Due to the saline air and the strong gale-force winds in Hong Kong the upper 120 metres of the 300 metres high bridge pylons were cladded with high-tensile stainless steel (duplex) by Outokumpu. The company produced both the cladding elements made of stainless steel (all in all 2,000 tons) and the anchoring of the main bearer cables. What is so special about it? The duplex stainless steel will need no maintenance work for the entire service life of the bridge.
More than only stainless steel sheets
Outokumpu however does not only supply stainless steel sheets. The company supports customers with regard to material selection, planning and construction during the entire project and optimally prepares the sheet metal with perfect surface treatment, precise form and joints tailored to the welders’ needs.
High demands with regard to the CERATIZIT inserts
The CERATIZIT cutting inserts are used at Outokumpu for the preparation of joints. With the HyperCoat grade CTP2235 Outokumpu mills the most varied joint profiles. Stainless steel is a material which is difficult to machine. For example, its thermal conductivity is only a third of the thermal conductivity of machining steel. For this reason the heat that is produced during machining can only be evacuated insufficiently through the swarf. The tendency towards work hardening is relatively high. This means that after a first machining step the material on the surface becomes harder than before, so the cutting edge needs to perform even better in the second operation. Furthermore, stainless steel is particularly tough, has a relatively high tendency to adhesion and bad chip formation. This is why its machinability is four times worse than the one of machining steel. Especially for Outokumpu CERATIZIT has developed the cutting insert SEAN250161 and offers a tailored solution for the machining of stainless steel. The inserts are used in a strip edge milling cutter by Outokumpu. In this way the ideal tool is created for the machining of difficult materials such as stainless steel. Good clamping, small tool overhang and small corner radius or radius of the cutting edge are decisive to avoid vibration and cutting forces. Sufficient cutting depth should be applied so that the cutting edges in the following operation interact as little as possible with the cold formed layer.
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