News and press releases

10/10/2007 From the steel billet to the piano string CERATIZIT responds to new developments in hot rolling technology with a new family of grades

It’s a Friday morning in May, it’s slightly drizzling, the scent of spring is in the air, but for René Mauer it is going to be a very hot day. René Mauer is the segment manager for hot rolls in the business segment wear parts for general industrial wear parts at CERATIZIT in Luxembourg. He has been working in the roll industry for 35 years and knows his business perfectly. Today he is going to STFS in Schifflange. The company has a hot rolling line which is equipped with carbide from CERATIZIT.
Mr Mauer parks his car in front of the huge red brick factory building with high dark windows. This is where Emmanuel Rossi, responsible for the rolling mill, and his assistant Eric François are already expecting him. Wearing a helmet and work clothes the three men enter the semi-dark factory hall. It smells like steel and oil, the gigantic fully automatic conveyor belt is in continuous operation.

From rolling stock to wire
In this hall STFS produces wire with diameters ranging from 5.5 to 16 millimetres. The wire is then sent as semi-finished material to companies in the most varied industrial sectors who process the wire to produce cables and wire for bridges, lifts and cable cars, shopping carts, piano strings, nails and Steelcord for tyres.
The entire process starting from the rolling stock and resulting in the wire does not take longer than about two minutes. Per year STFS produces around 700,000 tons of wire in 3-shift operation; with a diameter of 5.5 millimetres this corresponds to a length of around 3 million kilometres, or in other words, 75 times around the earth.
STFS’s main sales market is France (50%), followed by Italy and Luxembourg.

The hot rolling procedure
Rolling is a forming procedure, either for the production of flat products like strips, foils or sheet metal, or for long products like profiled sections, rails, tubes, wire or rods. Contrary to cold rolling, in the hot rolling process the base material is heated to 1,250°C in special furnaces (walking beam furnace).
After heating the slabs (first form of the steel resulting after the production process in a liquid condition), their size and shape are formed repeatedly and converted into electrically driven rolls. During the rolling process the red hot material has a temperature between 720 and 980° Celsius, depending on the quality and diameter of the steel.
Hot rolling is a procedure consisting of various forming processes, the so called roll passes. Every roll pass increases the length and simultaneously reduces the thickness of the rolling stock and leads to the ‘destruction’ of the original structure. The fact that the rolling stock is heated causes its crystallographic condition to change.
When processing steel the structure is changed from the hard ferritic to the soft austenitic form. In this condition the plastic deformation takes place, deformation grades of up to 250:1 are possible. This is why a slab may have a thickness of 240 mm before hot rolling and afterwards of only 0.8 mm. In cold rolling the maximum deformation grade is 10:1. In addition, when hot rolling the required deformation can also be reached more easily


The steps in the rolling process
1. The slabs or steel billets come from the steel plant and are transported to the special furnace.
2. The slabs are heated to 1,250° Celsius.
3. The rolls form the red hot steel until, at the end of the line (length of almost 500 metres) the wire exits.
4. The wire is coiled, stored or transported to the customers


Rolling carbide: forming process and guides
CERATIZIT produces two different types of products for hot rolling lines: firstly, the work rolls, i.e. the parts of the line which form the material under rolling pressure, and secondly the guide rollers which transport the red hot material over the very long line from one machine part to the next. Also in this procedure the advantages of the carbide can be seen very clearly: the hot rolling process is carried out at high temperatures and high speed, i.e. up to 14,700 RPM for the work rolls and 50,930 RPM for the guide rollers. Machine parts which are subject to such conditions show a very high degree of wear.
CERATIZIT offers 9,000 products for rolls and guides for a variety of hot rolling lines. The team of Philippe Lanners at the CERATIZIT site in Mamer/Luxembourg is responsible for the production of the carbide components for over 100 customers in the hot rolling sector.

The latest developments in the field of hot rolling
In the past years rolling technology has witnessed numerous changes:
1. Controlled cooling or low temperature rolls for the improvement of the rolling stock’s properties.
2. Higher roll speed.
3. Application of a ’Reducing-Sizing’ mini-block for small tolerances while rolling.
4. Computer Aided Management (CAM) for rolling programmes to produce precisely consistent tonnages per week
CERATIZIT has adapted all its carbide grades to these conditions and has developed the new ‘E’-family. The objective is to provide better resistance to mechanical shock and crack propagation without decreasing the performance of the rolling mill.

The properties of the new 'E’-family from CERATIZIT
> Slightly larger grain size as the smallest grain size has been eliminated from the micro-structure.
> Regular grain size distribution, so chains of the smallest particles in the micro-structure are avoided.
> Thanks to these improvements the internal tension is reduced.
> Higher toughness, therefore lower hardness of around 40-50 HV (Vickers).