Blow Molding Plant with Three Piston Accumulator Systems
Synergy-Effects for Plastic-Products in the US
Roth Industries GmbH & Co. KG, Dautphetal, Germany, leveraged company-wide synergy effects to develop a new large blow moulding plant for plastic products at its production site in the US city of Watertown. The project brings together the manufacturer’s skills in two fields – hydraulics and plastics processing. The design of the hydraulic accumulators permits rapid plant movements, ample power reserves and energy savings.
Roth boasts much experience in blow molding products and incorporates this knowledge into the machinery it develops. Weighing in at some 125 tons and with a clamping force of roughly 300 ton, the blow molding plant is equipped with three extruders. The production plant is also kitted out with three sensor-controlled Roth Hydraulics piston accumulator systems for various hydraulic applications in the production process. This is because hydraulic energy is required to open and close the nozzles, to extrude the plastic tube and for all movements that the blow molding plant undertakes. The hydraulics facilitate movement in the plates, the two-part mold, the blow pin and blow needles for letting in air, the mold closing mechanism during the blow molding process and the control of wall thickness in the plastic.
Both halves of the mold can be moved separately, allowing them to move both in and out of synch and at different speeds. Cylinders fitted with locking devices at the four corners of each mold half regulate the clamping force. Clamping cylinders support the mold as it closes to a precise fit while withstanding blowing pressure of up to 6 bar. The mold itself weighs 15 tons (7.5 tons per half) and can open by up to 3 meters at a speed of 300 millimeters per second. Each piston accumulator system has a working pressure of 180 bar and a maximum pressure of 210 bar. Proportional valves control how the two mold halves close and how the plastic tube feeds into the blow mold.
Customized Piston Accumulator Systems
Roth Hydraulics piston accumulators for machinery and systems come in sizes ranging from 0.1 to 1,500 liters. Standard systems are available with a maximum operating pressure of 350 bar, while customized designs can handle up to 1,200 bar with variable pre-load pressure. These are used where power needs to be drawn in large quantities and with a high level of performance. Depending on their field of use, significant increases in capacity can be achieved by placing gas tanks downstream of the systems.
Even compact, large-scale systems with a total volume of well over 100 cubic metres can be manufactured and supplied ready for connection – by coupling together any number of piston accumulators and downstream gas tanks. The accumulator systems are suitable for use in temperatures ranging from -10 to +80 degrees Celsius, with versions available that can handle larger extremes: as low as -60 °C and as high as +200 °C. Roth designs fluid connections and sealing systems for the piston accumulators to order based on its customers’ requirements. It is not possible for any gas to escape suddenly on the fluid side. Sealing systems that minimize friction guarantee a high degree of efficiency, including in operation. Optional add-ons such as an in-built stroke limiter and a wide range of measuring and monitoring devices give an indication of the system’s operating status and energy level. The piston accumulators can be installed anywhere.
John Pezzi, V.P. Operations at Roth North America, explained: “The piston accumulator systems have allowed us to reduce the electrical load of our hydraulics by around 75%. This covers the load from our pumps, motors and heat exchangers.
Hydraulic accumulators use powerful technology to store energy and draw hydraulic power. This technology involves compressing a hydraulic fluid such as oil in a gas-filled pressure tank. The gas and the hydraulic fluid are separated out using a piston, bladder or diaphragm. The hydraulic fluid compresses the gas, storing hydraulic energy that can then be released mechanically at any time. As the system pressure falls, the gas expands, pushing the fluid out of the accumulator and back into the hydraulic system.
Hydraulic accumulators are used wherever maximum output needs to be generated using little energy, i.e. in plant engineering, in measuring and testing technology and in mobile hydraulics as well as increasingly in systems that use natural resources such as wind and hydropower.