With the rapidly changing glass panels industry for cars, the complexity of shape and integration of sensors has been critical. As more demands for more stringent tolerances and the introduction of more complex forms and shapes, the automobile production process for glass panels has become extremely complex.

For example in a Tunnel Furnace where hundreds of sub zones, requiring precise and complex temperature control, running multiple recipes to allow maximum production, flexibility is a necessity. Resistive elements as well as medium wave infrared heaters have to be controlled to very tight parameters while maximizing energy efficiency.
Around the world, Eurotherm temperature control, power control and supervisory systems for windscreen forming are in operation. They provide:

  • Accurate open or closed loop power control
  • Accurate multi-zone temperature control
  • Power control set point transfer and monitoring by digital communication, reducing the I/O requirements of the control system
  • Feed through control
  • Advanced single cycling for infra-red elements, eliminating DC components
  • Track and Trace capability

In power glass applications, Eurotherm has always been present and successful:

  • Bottle manufacturing: boosting, feeder heating
  • Windscreen forming
  • Flat glass: roof heating, annealing
  • Glass wire manufacturing: boosting, feeder heating, bushing

The principle of windscreen forming is that the flat windscreen is going through a tunnel furnace on a very precise form. There is one type of form per type of windscreen. When at the right temperature, assisted by gravity the soft glass will take accurately to the form.

The pre-heating zone is the first part of the furnace where the temperature accurately controlled. The second part is the forming zone with a precise electrical power control. Heating elements are metallic resistors, medium wave infra-red, with a low temperature coefficient. Heat transfer to the windscreen is a combination of infra-red emission and air heating.

The quality and precision of the windscreen banding is given by the accuracy of forming zone power control and the accuracy of the pre-heating zone temperature controls.

On these furnaces, the number of zones can be very high, 100 to 300 zones. Present tendency is to increase the number of zones to improve precision of banding and to manufacture more complicated and various windscreen shapes. The total power of such furnaces can be several hundred kW to several MW.

Architecture of the installation

  • The electrical control architecture of the installation is as follows:
  • A PLC supervisory system is controlling the furnace: temperature in pre-heating, zone, power informing zone.
  • Heating elements power control is made with multi-channel communicating power units, EPower Series for both forming and pre-heating zones.
  • Firing mode: single cycle.
  • Control mode: precise power U x I, very important for banding accuracy.
  • Through communication link (Modbus or Profibus depending on type of PLC), all EPower parameters are available (read and write) on the supervisory system: load output, power set point, status word/alarms.

Millisecond set point transfer
On the furnace forming part, during process time each windscreen stays in a heating zone; its next working set point, for the next heating zone it will move into, is loaded in each EPower channel. When all the windscreens reach their next heating zone, a single command through the communication link will transfer in a few milliseconds all pre-loaded set points for each zone as an active set point.

Use this Eurotherm solution to your advantage

  • Perfectly adapted for this application is the Thyristor firing mode: single cycle.
  • Power control mode for a better process control
  • Avoids peak power demands with Predictive Load Management (PLM).
  • Reduce installation cost with multichannel EPower: floor space saving and smaller panels, lower cost per channel.
  • Very good accuracy of EPower power control U x I: absolutely necessary to Communication
  • Installation costs are reduced (wiring, cabinetry, etc.).
  • Process control efficiency and quality are improved.

Checkout all our power controls at http://eurothermonline.com/power-controls.htmlhttp://eurothermonline.com/power-controls.html