The use of high temperature thermocouples in the glass manufacturing industry

One of the industrial applications of Kamet’s high temperature thermocouples is in the extreme temperature processes of the glass and ceramic manufacturing industries. Here we go into detail on glass manufacture and explain which of our thermocouples and special sheath materials are most applicable. However, the ceramic manufacturing process is very comparable, involving high temperature melts to which our specialized thermocouples are well suited. 

The manufacturing process of glass is a complicated process requiring ultra high temperatures. Raw materials include silica sand, calcium oxide, magnesium and soda (reduces energy consumption by lowering the melting point). Recycled glass (cullet) is also added to decrease the use of virgin raw materials. These components are carefully mixed in specific amounts to create what is called the glass batch, the starting point for the rest of the glass-making process. Before a finished product comes out as glass, it undergoes several steps:

In the first step after batching, the mixture is heated to an extremely high temperature of up to 1600°C—hotter than molten lava. At this point, a single molecule of sand embarks on a three-day journey through the factory, gradually transforming into a sheet of glass.

The process is carefully monitored, raking the molten mix to reduce air pockets. Bubbles can be a glassmaker’s nightmare, as they create imperfections that hinder transparency. To achieve perfectly flat and bubble-free window panes, a method involving liquid tin is employed whereby molten glass is poured onto a river of liquid tin. Tin and glass do not mix, so the lighter glass floats on the denser tin, ensuring a flawlessly flat surface.

The liquid glass and tin travel together as a continuous sheet, cooling gradually along the way. Once it reaches a manageable temperature, it moves down the production line. After the lengthy cooling process, the long ribbons of glass are cut into slabs, which are then packaged and shipped to distributors.

Temperature sensors for glass manufacturing

Accurate temperature measurement in molten glass is crucial for ensuring smooth production processes. As an example, ultra high temperature thermocouples located at the bottom of a glass tank are crucial for ensuring efficient operation of the tank and can lead to a significant energy consumption reduction. In the distributor, forehearth, and feeder, a monitoring system is employed to maintain a constant glass temperature. To achieve this, various high temperature thermocouples with precious metal protection tubes (thimbles or Pt10%Rh sheathed MI cables) are utilized, with their measuring tips in constant contact with the liquid glass. This is a so-called high temperature immersion thermocouple.

There are also parts of the production process where the thermocouples are not in direct contact with the liquid glass. In these cases, the main ultra high temperature thermocouples type B with ceramic protection tubes and type C with molybdenum protection tubes are used.

In the parts of the production process where temperatures tend to be lower than 1100°C, more regular type K, type N or type J mineral insulated thermocouples are used in various designs. In these cases, the thermocouples are often covered with a SS310 sheath material which has good resistance to oxidation and sulfidization. This property is crucial because glass manufacturing processes involve high temperatures and exposure to various chemicals and gasses, which can lead to oxidation and sulfidization of materials.

For more extensive technical information about Kamet’s exotic thermocouples, their specific properties and applications please have a look at the following product brochure. Our team of experts are also available to advise you on any of your technical application questions, you can contact them.