Werner von Siemens discovered the dynamo-electric principle in 1866. Reversing that principle led to the development of the first electric motors, which toward the end of the 19th century began replacing the steam engines commonly used in many commercial and industrial operations, thus helping machine production to achieve a breakthrough. The world’s first reversing rolling mill engine, built by Siemens, became a pioneer in the electrification of the steel industry.
Steam first, then electricity – Electric motors gradually replace conventional steam engines
In iron and steel production especially, the operators of smelting and rolling mills were intrigued with the new drive technology, and gradually transitioned away from their previous steam engines and transmission belts and toward direct drives and electric motors. As a first step, they electrified their rolling mills, where multi-ton, red-hot steel ingots were rolled out into increasingly thin bars or sheets. To keep the metal from cooling, these processes had to be executed as quickly and precisely as possible. But achievable capacities were relatively low. All that changed in 1897, when Elektrizitäts-Aktiengesellschaft vorm. Schuckert & Co. (EAG), of Nuremberg, delivered a 250-horsepower DC motor to Dillinger Hütte as the first electric drive for a rolling mill for fine iron and corrugated sheet. Three-phase motors, though significantly more robust, were not usable yet because their speed was still too hard to control. Electric motors were soon also recruited to run the roller tables to convey the red-hot material, a task formerly handled by small steam engines.
Heavy loads – The new electric motors are adapted step by step
Over the course of the first applications of the new drive technology, it became evident that the sharp jolts that occur in the rolling process posed special requirements for electric motors’ ability to withstand overloads. The first motor with a reinforced configuration – now with a maximum rating of 420 horsepower – was built by EAG for the Peiner Walzwerk mill in 1901. Shortly afterwards, thanks to the introduction of the Ward-Leonard control and an Ilgner converter, the means became available to control and reverse even large motors quickly and largely loss-free.
A pioneering development – Siemens achieves breakthrough with the reversible drive
Over the next few years, engineers at the newly founded Siemens-Schuckertwerke (SSW), headed by Carl Köttgen, laid the groundwork for the power needed for rolling mill drives. On the basis of their discoveries, in 1906/07 Köttgen, now a deputy member of the SSW Managing Board, built the world’s first electric reversible drive for a blooming mill at the Georgsmarienhütte steel mill near Osnabrück, with a maximum capacity of 6,550 kilowatts (kW). Since the rolling mill itself was still under construction when the order was placed and no other electric reversing rolling mills yet existed, Köttgen first had to calculate power needs with experiments on a steam-driven reversing blooming mill at Gutehoffnungshütte.
Subdividing the motor into two units made it possible to significantly reduce the rotor diameter, and thus its flywheel. This design made possible the rapid motor reversals that were necessary for rolling operations, while reducing the amount of energy required. When the rolling mill was not under load, the direction of the rolling motors could be reversed 28 times a minute – at a maximum speed of 60 revolutions per minute. This made electric drives far more controllable than was needed for actual operating requirements.
The steel and rolling mill at Georgsmarienhütte was the first large plant of its kind to do entirely without steam engines. It became a pioneer in the advancing electrification of the steel industry. By the time World War I broke out, Siemens-Schuckertwerke had already delivered 30 heavy-duty reversing mills. The company thus made an important contribution toward the breakthrough of machine production and to speeding up industrial production processes. Today, Siemens supplies drives for virtually every industrial application. A comprehensive portfolio of reliable frequency converters, motors, couplings and gearboxes satisfies the highest performance standards and quality requirements. New interfaces and modules ensure drive components are ready for digitalization.
Dr. Franz Hebestreit