Abstract
Digital fluid systems are controlled solely by on-off valves, in contrast to analogue fluid systems which use continuously adjustable valves. Many digital fluid systems have been in practical use for some decades. The steel industry relies on several fluid technologies. Apart from the handling of the liquid steel, several other fluid processes exist to fulfill indispensable functions; examples include cooling, motion control, torch cutting, descaling, and lubricating. Many of these processes need better control concerning precision, dynamics, resource demand, reliability, and environmental impact or must offer additional functionalities for use in factories of the future. In several cases digital fluid systems are the better solutions. In this paper this is demonstrated by four examples, ranging from proven simple solutions and concepts going currently into industrial application to promising concepts for the future.
Highlights
Zusammenfassung: Digitale Fluidtechniken verwenden Schaltventile zur Steuerung bzw
A proportional control of the volume flow for each nozzle has three major drawbacks: (i) It requires air mist cooling systems if the cooling rate range is to go beyond 1:3; they cause high investment and energy costs; (ii) the small orifices in the corresponding flow control valves endanger the robustness against contaminated cooling water; (iii) the environmental continuous casting (CC) conditions require the proportional valve to be located in a protected area and the complexity of piping would dramatically increase for these several hundred of valve and nozzle pairs
A project of the Linz Center of Mechatronics has shown that the required dynamical performance can be achieved with digital hydraulic control principles
Summary
Fluid systems play a strong role in steel production, for cooling, torch cutting, descaling, lubricating, and for motion generation. The duty cycle, i.e. the relative on time of the valve, is the control input into the system, a high gap between switching frequency and process bandwidth lowers the effects of the on-off switching [2]. In case of fast processes, control methods must be used which consider the effects of all individual switching operations [4]. Parallel valve technologies are a method to replace analogue valves by several on-off valves They discretize the effects of the analogue valves with several advantages, like higher robustness to oil contamination, fault tolerance, or lower number of valve sizes required ([1, 5,6,7,8]). An example is a sizing press drive, which is a mixture of an analogue primary pump control and a parallel cylinder system [10]
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