Häko Product configurator HÄKO Logo print
Our durable oscillation cylinders:
  • Maintenance cycle of 6 years
  • Small amplitudes of 3-4 mm
  • 200 million load cycles without inspection
  • Wear-free sealing system
Image 1 | 3 Red-hot slab: “End product” of the continuous-casting machine
Image 2 Hydraulic cylinder on the continuous-casting machine: Oscillation at three Hertz prevents the steel strand from sticking to the inner wall of the mould.
Requirement
  • Oscillation of a 25 t mould
  • 3 Hz with any oscillation profile
  • Fail-safe hydraulic cylinders
  • Long maintenance cycles
Oscillation cylinder from Hänchen
  • Hydraulic cylinder of the series 320
  • Force of 400 kN
  • Servofloat® quality for a wear-free sealing system
  • 80 oscillations per minute with a stroke of ± 3-4 mm
  • Maintenance cycle is 6 years / 200 million load cycles
Even with the high production figures typical for steel production, the steel produced in Germany is a precision product. Today, only top-quality products have a chance in the global trade of steel products. Surface, internal quality and mechanical properties determine success on the market and thus profit and loss. One area in which the quality of the end product is determined is the so-called mould, in which the liquid steel first solidifies on its surface through the water-cooled copper plates. The mould receives the steel, which is supplied by the oxygen steel mill in 400 t ladles, introduced via the ladle turret and the tundish, and is over 1,500°C hot. In continuous casting, the metallurgical challenge is to prevent the strand from sticking to the mould wall and at the same time cool it in such a way that the steel strand has already formed a solid, several mm thick “strand shell” when it enters the first segment. Even minimal adhesion leads to irregularities in the steel because the material flow is not continuous. If the strand adheres too strongly, the already solid strand shell can tear. In the event of such a breakout, tonnes of molten steel pour into the plant; this is the worst case in continuous casting.

In order to avoid such a breakthrough in continuous casting, the steel industry developed mould oscillation in the early 1950s. The oscillating movement of the mould ensures that a flux, the casting powder, is introduced between the mould wall and the strand shell for lubrication purposes.

After many development stages, in which SMS Demag played a significant role in shaping and advancing, the current state of the art is hydraulically driven resonance oscillation. At ThyssenKrupp Steel AG in Duisburg-Bruckhausen, a hydraulically operated short-lever oscillation from SMS Demag AG is in use. In the mould, the rectangular strand, which is liquid inside and solidified on its surface, is formed from the molten steel flow. The subsequent strand guide supports the strand. The strand is completely solidified under spray water cooling. This strand guide consists of 13 groups of rollers, the so-called segments, which fulfil several tasks: They prevent the bulging of the steel strand to a dimension greater than a defined thickness of 215 mm with a width of 1,800 to 2,600 mm. And they align the strand from the vertical to the horizontal – with a radius of 9.3 m. In addition, they enable the cooling of the strand by water so that the steel flow is completely solidified when it is cut into slabs at the end of the casting machine.

The hydraulic mould oscillation developed by SMS Demag AG ensures that the mould always has a relative movement in relation to the steel strand through the use of the hydraulic cylinder. It oscillates continuously in a vertical direction, whereby the movement simultaneously serves to introduce the casting powder as a lubricant between the strand and the mould wall. Each of the two lifting tables in use is moved by two Hänchen hydraulic cylinders of the 320 series in Servofloat quality with the patented floating gap seal.

In normal production, they oscillate at 80 oscillations per minute with a stroke of ± 3-4 mm. The curve shape - like amplitude and frequency - can be freely modified during operation in order to keep the relative movement of each individual oscillation between the mould and strand exactly constant. Since the strand has its own movement due to the casting speed, the downward movement of the mould must be significantly faster than the strand's own movement. Hänchen has therefore designed the hydraulic cylinder to be highly dynamic and practically low-friction. The movement is recorded via a magnetostrictive position transducer and controlled with an industrial PC, which in turn ensures the connection to the host computer.
"The replacement cycle for general overhaul was initially increased to two, then to four and now to six years. Even after this time, we did not have to completely replace the Hänchen hydraulic cylinders."
Marc Ramacher, ThyssenKrupp Steel AG

The patented floating gap seal of the Servofloat design is used in the controlled servo hydraulic actuators, which apply a force of 400 kN. A steel bushing follows the radial deflection of the piston rod with a sealing gap of a few 1/100 mm, which is practically constant over the entire pressure range. However, this process only works with a production accuracy in the range of a few μm, as otherwise the leakage leads to high hydraulic losses.

Hydraulic cylinders in Servofloat® quality offer the highest positioning and repeat accuracy due to their negligible friction, are stick-slip-free and are suitable for extremely slow and fast movements. Due to the practically friction-free design, such a hydraulic cylinder does not wear out even in extreme long-term use. This corresponds to the requirement profile in which the highest availability has top priority. In particular, high demands are placed on the cleanliness of the fluid: The filters are replaced as required, and the two pumps for the working pressure of 260 bar are replaced every 35,000 hours. A particle count and the replacement of the servo valves take place once a year. Three-dimensional measurements on the lifting table with an accuracy of 10 μm, which record and display any changes in the oscillation movement, also serve to ensure quality. Originally, we planned to maintain or replace the hydraulic cylinders annually,” reports Dipl.-Ing. Marc Ramacher, the specialist coordinator responsible for maintenance at ThyssenKrupp Steel AG. “However, the replacement cycle for general overhaul was initially increased to two, then to four and now to six years. Even after this time, we did not have to completely replace the Hänchen hydraulic cylinders. It was enough to send them to Hänchen for inspection and general overhaul.

Low-friction hydraulic cylinderPlay video: Please activate the YouTube cookie.

Video about the Servofloat® design

The machine head from SMS Demag AG, together with the hydraulic cylinders from Hänchen, helps ThyssenKrupp Steel AG to produce good steel quality during continuous casting with maximum availability, which is used worldwide. ThyssenKrupp Steel AG produces five different quality types in Duisburg:
  • White strip steel, for example for beverage cans, which poses a particular challenge with its very thin sheet thickness.
  • Steel for dynamos and transformers.
  • Thin sheet metal - for example for the aperture grilles of televisions.
  • IF steel for the automotive industry.
  • Other special steels that differ in hardness, brittleness and composition.

At the end of the casting machine, the strand is cut into slabs transversely and longitudinally with fully automated cutting torches. Transport rollers and cranes bring the slabs to the warehouse. On the way from the mould to there, they go through the entire color spectrum from white heat to all shades of red heat to the steel gray that also have the blanks of the hydraulic cylinders that move the tons of moulds to produce new quality steel.
Jörg Beyer, mediaword
© Hänchen 2006
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