Proportional valves modulate hydraulic parameters according to electronic reference signals. Atos spa, Sesto Calende, Italy, has developed a range of electrohydraulic components in collaboration with plastics machinery manufacturers. These components increase the efficiency of individual process steps. The digital Atos electronics can control position, speed and/or force in any electrohydraulic axis within a closed-loop system.
The components are designed to international standards according to a modular system and produced in high volume. In the injection molding process, a digital servo-proportional valve with a specially shaped piston controls the injection rate and pressure profiles, which is normally the job of 2 or 3-way directional control valves or conventional proportional valves. The built-in p/Q controller is connected for this purpose to an external pressure transducer in order to control the injection phase and the holding pressure and ensure transition phases that are both rapid and even. Digital proportional 2 or 3-way cartridges with high dynamic performance (response time <15ms) in a double closed loop circuit are perfectly suited to applications with controlled volume flow rates of up to 10,000l/min and minimal pressure drop ( dp < 25bar), such as occur in the processing of semi-crystalline plastics. To increase the injection rate and improve damping at the end of the mold closing stroke, servo-proportional valves with a double stroke transducer and differential piston have been developed.
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