DAC 2021_12

38 n SAFETY November/December 2021 www.drivesncontrols.com Burner control benefits are not wafer-thin E very second edible wafer manufactured worldwide is baked using a machine developed and built by an Austrian company which has systems for producing almost any kind of wafer, from ice cream cones and waffles to flat and hollow types, as well as wafer snacks. Company founder Franz Haas invented his first wafer machine in the 1940s. Since 2018, the company has been part of the Swiss Bühler group. Some 700 people work in the wafer operation of the company’s consumer foods division in the town of Leobendorf. Customers from around the world come to the site’s Wafer Innovation Centre to test and optimise production processes for their products. At the heart of every wafer production line is an oven that can be up to 35m long, depending on the product and plant configuration. The heating is usually provided by gas-fired long-tube burners. “The dough is poured onto individual baking plates, which circulate through the oven at up to 0.5 m/s,”explains Wolfgang Grassberger, who is responsible for machinery safety in Buhler’s wafer division.“The typical baking time for a wafer depends on the product, but is around two minutes. The burner controller’s most important task is to monitor the extinguishing of the flame and, if necessary, to interrupt the gas supply safely and immediately. In this way we can prevent the escape of unburned gas and – in the worst-case scenario – an explosion.” This apparently simple process turns out, on closer inspection, to involve a complex control sequence. It starts with the ignition process, consisting of almost 20 individual steps. “Each burner has two redundant, diverse main gas valves, which undergo a tightness test even before the actual ignition process,” says Grassberger. An ionisation current sensor detects the flame and therefore successful ignition – UV flame monitors can be used as an alternative. “The minimum and maximum gas pressure, the suction function, compliance with the permitted maximum temperature and many more are monitored during firing,” he adds. Since the early 2000s, Bühler has been using small SIL 3 / PL e compliant safety controllers to implement functional safety on its machines. The safety tasks include emergency stops, safety gate monitoring and SLS (Safely Limited Speed) functions for set-up. Initially, Bühler used Pilz’s PNOZmulti controlllers, but has now turned to its successor, the PNOZmulti 2, which is available in version specially developed for An Austrian machine-builder that specialises in machinery for making edible wafers is taking advantage of a combined safety and conventional controller that was specifically developed to control and monitor furnaces. To produce an ice cream cone, dough is poured on to individual baking plates, which circulate through an oven. The wafer is then shaped into a pointed cone.