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The secret of glass making was known already by the ancient Egyptians. This has been proved by glass accessories in graves, such as glass beads found in the graves of Egyptian kings dating back as far as 3500 BC. Nowadays, man has access to the latest methods of producing many and varied types of glass for different applications. This also involved the increasing automation of the production process. But glass manufacture is still based on melting silica sand (SiO2), sodium carbonate (Na2CO3) and calcium carbonate (CaCO3), in which other substances are added to achieve special properties or a special colouring. The creation of high quality glass involves, amongst other things, the precisely controlled supply of oxygen, oxy fuel and natural gas to the melting furnace. Depending on the particular composition, the melting temperature ranges between about 1000°C and 1600°C.

The maintenance of the optimal ratio of oxygen and fuel for each individual burner requires precise control. Sliding gate valves from Schubert & Salzer Control Systems offer the ideal prerequisites for this task. The most important prerequisites for very short reaction times for an actuator are short positioning paths, small actuation volumes and low actuation forces resulting from these. All of these properties come together in the sliding gate valve. In this valve, a pair of slotted discs slide against each other transversely to the direction of flow. Thus, the sliding gate valve seals without any metallic seat. The typical stroke between closed and open is a mere 6 to 9 mm. One of the most notable advantages resulting from this operating principle is the low actuation force required for the positional movements. Sliding gate valves therefore control with rapidity and precision, enabling fast adaptation to the quantities flowing through and the power required by the glass crucible. This ensures that the oxygen/fuel mixture is optimised for the firing of the glass crucible. After the melting process, sliding gate valves are used again to control urea or ammonia for the denitration of the gases given off from the crucibles (nitrogen removal process). But it is not just the glass melting process which offers opportunities to use valves from Schubert & Salzer: they are employed also for the fine metering of cooling air in the production of windscreen glass (for aircraft windows, for example).

Sliding gate valves from Schubert & Salzer Control Systems have DVGW approval and are available also in an EX protection version.
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