In glass manufacturing, temperature is not simply a process variable, it defines how the material behaves.
Molten glass viscosity is highly sensitive to temperature. Even small variations can significantly influence how the glass flows through the furnace and forehearth, ultimately affecting forming performance and product quality.
For plant engineers, this creates a constant challenge. Maintaining stable thermal conditions is essential to avoid issues such as inconsistent gob weight, unstable flow behaviour and defects in the finished product. At the same time, many facilities must also manage the risk of unplanned downtime caused by heating system failures, particularly where legacy switching technologies are still in use.
Continuous production environments, where furnaces operate 24/7, both thermal stability and system reliability are critical to maintaining output, quality and cost control.
Glass behaves very differently from many other materials because its viscosity changes rapidly with temperature.
A variation of just a few degrees can alter how the molten glass flows, stretches and forms. This sensitivity means that even small disturbances in heat input can propagate through the process.
Container glass production can suffer from temperature instability in the forehearth, leading to variations in gob weight and shape that reduce forming consistency. Similarly, flat glass manufacturing may experience thickness control issues and poorer surface quality due to thermal fluctuations. Meanwhile, fibre glass processes can produce inconsistent fibre diameters and diminished mechanical performance when temperature variation occurs.
Because these effects are closely linked to temperature, maintaining stable thermal conditions is essential for protecting product consistency, yield and quality.
Many modern glass furnaces use electric boost heating to supplement combustion systems and improve melt control. By introducing electrical energy directly into the molten glass, boost systems help improve melting efficiency and increase furnace throughput. They also provide a level of control that can be difficult to achieve with combustion alone.
However, these systems operate at very high currents and are sensitive to how electrical power is applied. If power delivery is unstable or uneven, it can introduce localised thermal variations within the melt.
Over time, this may lead to:
inconsistent temperature distribution
reduced melt homogeneity
increased wear on electrodes
For this reason, the method used to control electrical power plays an important role in maintaining stable furnace operation.
After leaving the furnace, molten glass passes through the forehearth where its temperature is conditioned before forming.
Unlike the main furnace, the forehearth has a lower thermal mass and responds more quickly to changes in heat input. This makes it particularly sensitive to fluctuations in heating power.
If heat delivery is unstable, the viscosity of the glass can vary as it flows toward the forming machine. This can result in inconsistent gob formation, which in turn affects the quality and repeatability of the final product.
Because forming processes rely on precise and repeatable material behaviour, maintaining stable forehearth conditions is critical to reducing defects and improving production consistency.
While much attention is given to temperature control, the reliability of heater switching devices is often overlooked.
Many glass plants still use mechanical contactors to control electrical heating systems. In high-power and high-cycle applications, these devices are exposed to repeated electrical and thermal stress.
Each switching event generates electrical arcing, which gradually degrades the contact surfaces. Over time, this can lead to:
contact erosion
welded contacts
unreliable switching behaviour
When contactors fail, the consequences can be significant. Heating systems may become unstable, heaters may remain permanently energised or fail to operate altogether, and protection systems may trip.
In continuous glass production, where processes cannot be easily stopped and restarted, these failures can result in unplanned downtime, product loss and extended recovery periods.
Improving the reliability of heater power control is therefore just as important as improving temperature accuracy.
Temperature controllers regulate the process by determining how much heat is required. However, they do not control how that energy is physically delivered to the heating system.
When power is applied in large on/off steps, as is typical with basic switching devices, it can introduce fluctuations in heat input. In a process as temperature-sensitive as glass manufacturing, even small fluctuations can affect melt stability and flow behaviour.
More precise control of power delivery allows heat to be applied smoothly and continuously. This supports more stable temperature conditions within both the furnace and the forehearth.
SCR (thyristor) power controllers regulate electrical power by modulating the AC waveform rather than switching it fully on and off.
This allows energy to be delivered proportionally, closely matching the thermal demand of the process.
In glass manufacturing applications, this approach provides several advantages:
smoother and more stable heat input
improved melt and forehearth temperature stability
reduced electrical stress on transformers and electrodes
CD Automation’s REVO C and REVO-PC controllers are designed for high-current applications such as electric boost and forehearth heating, providing precise and reliable power control in demanding environments.
Glass manufacturing depends on maintaining consistent process conditions over long periods of continuous operation.
By improving how electrical power is delivered to heating systems, manufacturers can achieve:
more stable melt conditions
improved product consistency
reduced defect rates
lower production waste
improved equipment reliability
Reliability is just as important as control accuracy in continuous processes. A stable heating system not only improves product quality but also reduces the risk of costly production interruptions.
If your glass plant uses electric boost or forehearth heating and you are experiencing instability, product defects or unplanned downtime, CD Automation can help.
Our engineers can review your heating system and recommend the most suitable power control solution for your process.
Contact CD Automation to discuss your glass manufacturing application.
Further application information can be found on our Industry page here.
Or contact our engineering team to assess your current heating control strategy.
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