The drive technology employed offers great potentials to machine builders and plant operators when operating energy-intensive machines more efficiently. The electro-hydrostatic drive concept developed by SMS group for forming machines such as ring rolling, hydraulic presses and slab shears demonstrates how higher productivity with minimized power consumption and at the same time simplified and cost-effective installation brings competitive advantages.
Apart from the main roller drives, there are up to nine position- or force-controlled axes used in parallel during the ring rolling process. Traditionally, these axes are constructed as cylinder units with control valves and supplied by a central hydraulic system. Together with Moog GmbH, an innovative drive concept was developed based on the electro-hydrostatic pump unit (EPU). This unit consists of a radial piston pump with adjustable displacement volume, featuring a maximum operating pressure of 350 bar and providing a servomotor screwed on by an adapter flange. As module system, the EPU units are scalable to a delivery volume from 85 up to 450 liters per minute. The pump drive unit has been optimized for fourquadrant operation using a variable-speed drive. The selected drive concept is based on a speed-regulated pump drive with a double-acting cylinder.
For a slab shear with a force of 14,000 kilonewton (kN), a similar drive concept has been realized together with Bosch Rexroth. The challenge has been to achieve a particularly high number of cycles of five cuts per minute in a cutting time of six seconds each.
In a conventional system the necessary peak performance, which results thereof, leads to an above-average number of pumps and accumulators in the central pump station which would cause both high investment and operating costs. When employing the direct drive concept, the investment costs continue to be high due to a more expensive drive design on the one hand, but are compensated on the other hand by an optimized drive performance (reduced losses) and through the omission of components such as valves and accumulators. Operating costs are reduced significantly which results in a more cost-effective operation in the long term.
For the slab shear a compact drive unit was provided with six variable-speed pumps (one electric motor with two pumps each) for each cutting cylinder. The unit is equipped with all necessary oil-conditioning units and it is optimally placed immediately next to the cylinder.
For ring blank presses with very large forming strokes very high rapid traverse speeds of up to 500 millimeters per seconds are required. To achieve this, the DvP drive concept (variable-speed pump drives) was extended with the surface changeover principle. The new drive concept CLH (Closed-Loop Hydraulics) is an innovation in hydraulic press construction. The principle is based on variable-speed piston pumps operating in the closed oil circulation system in four-quadrant mode. The speed is controlled precisely and highly dynamically via water- cooled servomotors. By means of additional auxiliary cylinders the pendulum capacity of the differential cylinders is taken up. Therefore, the oil tank can be omitted almost completely. Surface changeover between rapid and working speed enables a ratio of up to 1:10 of the cylinder speed.
Initial experiences with electro-hydrostatic compact drives revealed an excellent controllability (position and force) of the axes. Due to the small number of components, a highly robust system is attained which is not susceptible to disturbances. By reducing the energy demand by about 70 percent and with reduced noise emissions of approx. 30 percent the machine is eco-friendly and thus conforms to the Ecoplants concept of SMS group.