Glass

Glass melting and fining is a delicate balance between energy efficiency, glass quality and maximum throughput keeping emissions within legislative boundaries.

To enhance the glass melting process, increase throughput, and improve glass quality and to reduce CO2 emissions electrical furnace boosting is often used.

Changing composition raw materials into a molten glass that meets the needs of production is one of the most complex processes in the industry.

Extreme dead times and sometimes frequent pull rate fluctuation of the glass furnace makes the control of the furnace process complex. As the furnace is one of the most expensive resources for a glass manufacturing plant, stable and smooth control is a must, capable of keeping all parameters inside their narrow boundaries, as this will have a positive effect on the furnace lifetime.

The 3500 is a fully programmable controller suitable for stoichiometric combustion control in glass applications.
It is capable of being used solely to control the Lambda potential of the furnace, or as an integrated controller where this variable is controlled in conjunction with temperature.

Additional features provide maths and combined logic functions.

At the heart of the controller is a specially designed function block capable of accepting most zirconia probes. Standard features include an automatic probe cleaning routine diagnostics indicating that the probe is about to fail and should be replaced.

Fossil fuel burners are often used as the principle medium for delivering energy to industrial furnaces and ovens.
Increasing focus on reducing energy costs has led manufacturers to concentrate on new burner design techniques and important advances in efficiency gains have been made over the years. Burner management and control systems must be equally adaptive.

Eurotherm® provide efficient, well implemented control techniques capable of reducing operating costs whilst providing resources for greater flexibility in plant management and control.

Over the last decade the use of glass panels in cars has increased rapidly along with the complexity of shape and integration of sensors.
With the automotive industry demanding more and more stringent tolerances and introducing more complex forms and shapes, the production process of automotive glass panels has become extremely complex.

Resulting, for example in a Tunnel furnace, having hundreds of sub zones, requiring precise and complex temperature control running multiple recipes to allow maximum production flexibility. Resistive elements as well as medium wave infra red heaters have to be controlled to very tight parameters whilst maximizing energy efficiency.

Many modern glass applications require additional production or processing such as coating technologies and coating materials for advanced building or solar applications.

Most common today are self cleaning, anti reflective, infra-red reflective and low-emission coatings for automotive, architectural and PV solar panel applications. The application of these coatings happens via complex on-line chemical vapor deposition and off-line cathodic sputtering technologies. These processes requiring precise control of chemical flows as well as highly accurate temperature control as part of the integrated production process.

Bushing Control
The Eurotherm bushing temperature control application has been specifically designed to control temperature cycling in glass fibre manufacture and has been shown to bring you:

- Increased efficiency
- Improved recovery time
- Increased availability and productivity
- Set point depression and ramping
Allowing control of the temperature profile during a production cycle.
- ‘Cold bushing’ protection
Preventing thermal shock to the bushings in the event of operational or mechanical failure.
- Better than 1°C resolution.
- Operation with one or two thermocouples
Efficient implementation in complex control systems requiring programmed start-up of a heat sensitive process from stand-by condition.

Modern regenerative side or end port furnaces
Modern regenerative side or end port furnaces as well as recuperative furnaces profit from a stable, controlled combustion process. Such a stable and precisely controlled process will result in improved furnace lifetime as well as optimum, efficient fuel consumption. Energy saving up to 2% can be achieved which will result in a fast return on investment. The glass melting process will also profit from a stable furnace combustion space environment.

The extremely high temperatures and challenging atmospheric conditions involved in glass melting, fining and conditioning processes require the application of special thermocouple technology.
These thermocouples need to be capable of accurate measurement whilst demonstrating the minimum in temperature drift over time.

Bath Roof Heating
The multiple zones of a tin bath roof require a huge electrical heating system that takes care of hundreds of silicon-carbide (SiC) heating elements. In order to guarantee the lifetime of those electrodes combined with the highest energy efficiency they have to be controlled in a special way.

Annealing Lehr Heating Control
Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The process is carried out in a temperature-controlled Lehr. Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change or mechanical shock. Annealing glass is critical to its durability. If glass is not annealed, it will retain many of the thermal stresses caused by quenching and significantly decrease the overall strength of the glass.

The 3500 is a fully programmable controller suitable for stoichiometric combustion control in glass applications.
It is capable of being used solely to control the Lambda potential of the furnace, or as an integrated controller where this variable is controlled in conjunction with temperature.

Additional features provide maths and combined logic functions.

At the heart of the controller is a specially designed function block capable of accepting most zirconia probes. Standard features include an automatic probe cleaning routine diagnostics indicating that the probe is about to fail and should be replaced.

Think about the future
When choosing a boosting solution for your glass furnace, you need to look ahead 15 to 20 years to get the best return on investment (ROI) in terms of capital expenditure (CAPEX) and operating expenditure (OPEX). Think about the changes you might need to make if your business grows. Will you need to increase your output, what will the most efficient methods be in future, and which new energy regulations might affect your costs and carbon footprint?

Eurotherm by Schneider Electric have over 50 years knowledge in the glass industry, and our boosting solution is designed with the future in mind. Giving you the flexibility you need to “buy what you need now”, “expand later” and “re-use elsewhere”.

Float Glass and Rolled Glass
Float Glass
The float process, invented by Sir Alastair Pilkington in 1952, makes flat glass. This process allows the manufacture of clear, tinted and coated glass for buildings, and clear and tinted glass for vehicles.

There are around 260 float plants worldwide with a combined output of about 800,000 tonnes of glass a week. A float plant, which operates non-stop for between 11-15 years, makes around 6000 kilometres of glass a year in thicknesses of 0.4mm to 25mm and in widths up to 3 metres.

A float line can be nearly half a kilometre long. Raw materials enter at one end and from the other plates of glass emerge, cut precisely to specification, at rates as high as 6,000 tonnes a week. In between lie six highly integrated stages.

Characteristics of silicon carbide heating elements:

Construction

Silicon carbide is a ceramic material with relatively high electrical conductivity when compared to other ceramics. Elements are produced by pressing or extruding and then sintering.

Electrical characteristics

The resistance of these elements varies with both temperature and time. The nature of these variations depends on the particular grade of material and manufacturer.

Gob temperature measurements
The availability of modern ultra fast in-situ gob temperature measurements proved that there is lot going on in between the nine-grid and the orifice. Since it is of outmost importance for the forming process to obtain equal gob temperatures in seems to be obvious to look after different ways of controlling the glass running into the spout and the way it is transported in the spout to the orifice. Plungers and tube control proved to have a big influence on the temperature distribution over the gobs hence they are still not actively controlled by any systems other then gob weight control.

Managing equal gob temperatures in a double gob forming process can be done without major issue. However, the gob temperature stability is not guaranteed by the nine-grid stability.

“Controlling equal gob temperature in triple gob or quad-gob processes becomes exponentially more difficult”.