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AJZ & ASSOCIATES CONSULTING

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Float glass offers the quality of plate glass combined with the lower production cost traditionally associated with sheet glass manufacturing.  Float glass is virtually distortion and defect free, making it ideal for various premium glazing applications in buildings and homes or for automotive glass along with hundreds of other glass fabrications.

Float glass manufacturing is not unlike the manufacturing of commodities like steel or plastic. Each of the processes requires raw materials to be weighed, mixed, melted at high temperatures, formed into continuous ribbons, cooled and cut into a size that fits its use.

Float glass is made from a combination of several ingredients such as sand, soda ash, dolomite, limestone, salt cake, and cullet.

The raw materials are received and stocked in the silos or on/in the optional storage areas. If the raw materials are stocked in the optional storage areas they are then moved as needed to the silos. The raw materials are then drawn down from the silos for batch weighing and mixing. Cullet, which is crushed glass from edge trim of the cut lites or from broken cut lites, is blended with the mixed batch to make from up from 15% to 30% of each batch. The mixture is then delivered to the melting furnace by belt conveyor.

The batch house consists of, silos, hoppers, conveyors, chutes, dust collectors, and the necessary controls to properly handle the raw materials and mixed batch. The raw materials storage and handling is designed to suit the types of glass which will be produced along with the availability and cost of the raw materials.

The mixed batch is delivered from the batch house to the furnace storage bin, by a belt conveyor system, where it's stored and then feed into the furnace at a controlled rate by the batch charger. As the batch is feed into the furnace melter area it's heated by the natural gas burners to approximately 2900 degrees F. From the melter the molten glass flows through the refiner then through the waist area, where stirrers homogenize the glass, then into the working end where the glass is allowed to cool slowly to the proper temperature for delivery to the float furnace.

The melting furnace consists of refractory bricks and special shapes, support and binding steel, insulation, a fossil fuel firing system, temperature sensors and a computerized process control system. The design of the furnace is carefully made to meet the plant's specific gross daily glass production tonnage goals.

The insulation, special airflow features, and combustion air heating enable the furnace to operate at maximum fuel efficiency with negligible pollutant emissions. The furnace is sized and designed to provide high quality glass with the smallest amount of energy per ton of glass melted.

From the working end of the melting furnace, the glass flows through the canal area and then into the float furnace (tin bath or float bath) onto molten tin. The float furnace atmosphere is controlled by a mixture of nitrogen and hydrogen gas to prevent the tin from oxidizing.

The molten glass, which by now has dropped to 2000 degrees F, forms a continuous ribbon that floats on the molten tin. The desired width and thickness is obtained through an operator controlled program which sets the speed of the annealing lehr and knurl machines. The ribbon thickness can range from 2 to 12 mm. As the continuous ribbon moves through the float furnace its temperature is gradually reduced allowing the glass to become flat and parallel.

The float furnace consists of support steel, upper and lower welded steel casings, a refractory liner, tin, electric heating elements, an oxygen eliminating atmosphere system, temperature sensors, and a computerized process control system. Each customer's float furnace is specifically designed to respond to heat flow balance, desired ribbon width, glass thickness, glass color and the gross daily production tonnage.

The glass leaves the float furnace at about 1100 degrees F and enters the annealing lehr, which controls the cooling of the glass. The glass ribbon is carried through the lehr by a series of rollers driven by motors and a mechanical drive system. The temperature of the glass is reduced according to a precise time/temperature gradient profile, established for each annealing lehr, to produce glass that meets industry standards. The time/temperature profile, for all of the glass thicknesses and colors produced by the plant, is installed in the computerized annealing lehr process control system.

The components of the annealing lehr include a steel lined inner chamber and a steel outer shell separated by insulation, steel alloy and insulated steel rollers, a mechanical drive system, air circulation fans and ducts, heating elements, and temperature sensors and computerized process control system. The design of the annealing lehr is adapted to meet the critical cool down requirements of each float plant's gross daily production tonnage and glass colors.

The cooled glass ribbon exits the annealing lehr and is conveyed to the cutting area by a system of rollers and drives linked to the lehr drive system. The glass is scored by carbide cutting wheels, parallel and perpendicular to the ribbon travel, into sizes that meet the plant's customer requirements. The scored glass ribbon is then separated into lites for packaging by unloading personnel or automatic equipment for transfer to the wareroom for storage or shipment to the customer.

The cutting system consists of steel support frames, a mechanical roll drive system, "X "and "Y "cutting system, a glass trim and scoring system, manual unloading conveyors and/or semiautomatic or automatic unload systems and a computerized process control system.

Rev. 1 - 2006