Eurothem has always been very present and successful in power glass applications such as:
Flat glass: roof heating, annealing
Bottle manufacturing: boosting, feeder heating
Glass wire manufacturing: boosting, feeder heating, bushing
Windscreen forming
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, the soft glass will take accurately the form banding by gravity.
The first part of the furnace is the pre-heating zone, temperature controlled. 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 air heating and infra-red emission.
The quality and precision of the windscreen banding is given by the accuracy of the pre-heating zone temperature control and the accuracy of forming zone power control.
For such 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. Total power of such furnaces ranges from several hundred kW to several MW.
The architecture of the installation in terms of electrical control 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 thyristor power units, TU Series for both pre-heating and forming 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 TU parameters are available (read and write) on the supervisory system: power setpoint, load output power, status word/alarms.
On the furnace forming part, during process time each windscreen stays in a heating zone; its next working setpoint, for the next heating zone it will move into, is loaded in each TU channel. When all the windscreens reach their next heating zone, a single command through the communication link will transfer all pre-loaded setpoints for each zone as an active setpoint, this being done in a few milliseconds.
Thyristor firing mode: single cycle. Perfectly adapted for this application.
Power control mode for a better process control.
Multichannel unit TU reduces installation cost: floor space saving and smaller panels, lower cost per channel.
Very good accuracy of TU power control U x I : absolutely necessary to get a better process control and windscreen banding accuracy.
Communication
Reduces cost of installation (wiring etc).
Improves process control efficiency and quality.