StewartFloat® Float Bath
The term “float” refers both to a type of glass and to the process by which it is made. Float glass is the basic glass from which almost all flat glass products are derived. It may be clear or colored, and is produced in large sheets (6 x 3 m) that are normally processed into secondary products. The float process involves literally floating the molten glass on a bath of liquid tin, producing a perfectly flat surface on both sides. The raw materials for float glass are 57% sand (silicon dioxide), 17% soda ash (sodium carbonate),15% dolomite, 4% limestone (calcium carbonate), 1% salt cake and 6% others.
The float process produces large volumes of glass with exceptionally good surface and optical qualities. When glass is shaped in a float bath, both sides come out with a brilliant finish that requires no grinding or polishing.
A typical 500 tonne per day float bath will be approximately 60 meters in length and 8 meters in width. The overall size of a float bath varies with its capacity and the products being made.
A typical 500 tonne per day float facility will require approximately 10 hectares including buildings, rail, and plant auxiliary systems.
Basically, your market’s demand determines your float glass facility’s parameters.
A well-constructed float bath, that is properly operated, will have a minimum campaign life of 10 to 12 years. The rebuilding of a float bath normally consists of reconditioning equipment and replacement of some materials. The rebuild costs are normally less than 30% of the new build cost.
The technology employed in the float bath furnace is considered to be proprietary intellectual property by all legitimate float glass technology providers. A “Float License” provides the licensee with the right to use that technology and the ability to provide it to the licensee without infringing on the intellectual property of others.
Yes, float glass has been produced in all standard colors including clear, ultra-clear, green, blue, gray, dark gray, and bronze.
Yes, with oxygen being harmful to the process, the float bath must be pressurized with a barrier gas.
Top Roll Machines are used in the float bath furnace to shape and stabilize the glass ribbon. The machine has a rotating shaft with a knurl head on the end. That knurl head stretches and pulls the glass ribbon through the tin bath.
Cullet is the name given to scrap glass that is stored and used for making new glass.
Refractory is the name given to the fireproof block used in the assembly of the float bath. Refractory comes in many different grades and quality depending on application.
The Tweel is a damming device used to control glass flow into the float bath.
The Batch House is a building where the raw materials are stored and measured. It consists of multiple silos, conveyors, scales, and mixers that are computer controlled for accurate use. After the batch leaves the batch house, it goes into the melting furnace.
The Melting Furnace is the furnace before the float bath where the raw materials are melted and molten glass is formed.
This furnace is called a Float Bath because the glass “floats” in an even layer on the perfectly smooth surface of the molten tin. Heating in the float bath is carefully controlled to melt out any roughness in the glass. Because glass turns solid at a higher temperature than tin, it can be moved from the molten tin for further cooling.
The Annealing Lehr is the furnace after the float bath where the glass is slowly cooled to handling temperature.
The Cutting and Packing Line is the process after the annealing lehr. It consists of multiple conveyors and glass cutting tools. It is where the continuous glass ribbon is cut to the desired length and width.
A Cullet Return System is a series of shoots and conveyors located under the annealing lehr and cutting line extending to an external cullet pile. The scrap cullet is glass that has been cut off in the cutting and packing line due to defects or the standard edge trim that is due to the marks left by the top roll machine.
A Distributed Control System is a process control system that uses disbursed computers throughout the manufacturing line for robust control.
A 500 metric tonne per day facility costs about 120 million United States dollars. (Not including local costs, civil works, and coating equipment.)
Nothing; they are two names used to describe the same furnace.
Yes, it is possible to coat float glass. Using Chemical Vapor Deposition, it is possible to create reflective, Low E, Solar Control, and Photovoltaic coated glass all before the glass leaves the float bath. It is also possible to coat the glass after it has finished the float process.