The melting furnace of the float glass furnace is the part for melting and refining. It consists of the melting zone and the refining zone from the front to the rear and the upper flame space and the pool from top to down. The flame space consists of the front wall, the liquid level, the crown and the upper sidewall, which is full of flame. The pool consists of the bottom and the sidewall. The melting zone is where the batch materials are melt into liquid, while the refining zone is where to remove the bubbles in glass liquid.

The flame space is full of hot flame and gases from the heat source. The flame and gases melt the batch materials with its heat and also radiate heat to the molten glass, kiln walls and the crown. The flame space can ensure the complete combustion of fuel and enough heat supply for glass melting, refining and homogenizing. It can also reduce heat dissipation.

 

This part is where the batch materials are melted into liquid, refined and homogenized. It can supply enough transparent glass liquid. To expand the service life of the pool, the pool is generally 250-300mm thick. The thickness of the bottom varies according to the insulation conditions. The bottom without insulation is generally 300mm thick.

 

The front wall is the wall in the front end of the flame space of the melting zone. It spans the upper part of the feeding pool to block the heat radiation and the escapement of hot flame and gases. Since the front wall is burnt by flame and eroded by powders, it is easy to get damaged and deformed when preheating. So, L-shaped suspend wall is widely used in float glass furnaces.

 

Compared to the traditional multi-arch crown, L-shaped wall can expand the service life of the front wall and checker bricks, save more energy, improve the environment of the site, protect the feeding machine, increase the melting rate and reduce fly ash. When designing the front wall, it is important to determine the reasonable distance between the front wall and the center line of the port. A too-short distance between the front wall and the center line of the port #1 will speed up the burning of the front wall and the ports and the clogging of the ports and reduce the preheating effect on the batch materials. A too-long distance will make the temperature of the feeding pool low and the the melting and proceeding of materials difficult. Currently, based on the fuel and tonnage, the distance is generally 3.2-4.3m.

 

The arch front wall is composed of two or three layers of arches. A fire wall should be added to the lower bow shaped mouth to block the flame to save energy and protect the feeding machine.

 

The load bearing of the fire wall is provided by a big water drum spanning the the pool. Knife-shaped refractory bricks are hung on the water drum to prevent the flame from touching the water drum. Then lath bricks are laid on the knife-shaped bricks. Due to security considerations and the limit of the ratio of the crown height and crown span, its span cannot be too long, generally no more than 7m. Even so, since the crown and the fire wall are subjected to the burning of the flame and corrosion by the alkali gases, it is easy to be broken. When the fire wall and water drum are broken, they can be hot repaired and replaced, but if the crown is severely burnt, it can only be cold repaired. So, this structure is gradually out of date in the float glass furnaces but still used in other flat gglass furnaces. To increase the melting area, the feeding pool should be broadened. To solve this problem, L-shaped wall is designed.

 

The L-shaped wall is separately suspended. The distance between it and the liquid level can be adjusted with a mechanical jack. L-shaped wall is composed of heat-resistant steel and refractory materials. Its structural safety is not affected by the width. Its width can be equal to that of the melting pool.

 

L-shaped wall is composed of heat-resistant steel and refractory materials. its structural security is not affected by its width. Its width can be equal to the width of the melting furnace. L-shaped wall coupled with a longer feeding pool can not only reduce dust but also strengthen the pre-melting of the batch materials. L-shaped wall is divided into straight port and an L-shaped part. The straight port is built with high quality silica brick. The nose part is built with sintered mullite bricks and sintered zircon materials. The external wall of the suspended wall is insulated with ceramic fiber blanket. Water drums are set on the nose part for sealing after cooling.

 

Since different parts are subjected to different corrosion conditions and have different hot repair time, to ease separate and independent hot repair of different parts, the breast wall, crown and the pool are separately supported. Finally, the load spreads on the bottom steel. The load of the breast wall spreads from the pallet (cast iron or angle iron) to columns, finally to the bottom steel.

 

The breast wall should have enough strength at high temperature. The tuckstone is the key part. It is set on the bottom of the breast wall to block flame. In the melting zone, the breast wall is built with fused cast AZS 33#. Upper making-up brick is built with low creep anti-chipping sintered zircon bricks. The breast wall in the refining zone is generally built with high quality bricks.

 

The height of the breast wall is up to the fuel, melting rate, heat consumption, the size of the furnace, heat loss and air layer thickness.

 

In theory, as long as the breast wall has enough corrosion resistance, it will not be a weak point of the furnace. But, in the actual use, the interward tilt of the breast wall always shorten the service life of the furnace. In the late campaign of some furnaces, breast wall collapses due to untimely feeding. The main reason is the tilt of the pallet caused by the fastening of lashing strips. Another reason is the deformation of the pallet. To reduce or avoid this phenomenon, making-up bricks are removed, so the foot of the crown can touch he breast wall tightly. The pallet is lowered and the upper of the breast wall is interward tilted intentionally. The crown is built with three layers of zircon bricks. the hook design of the tuckstone brick is removed to avoid the interward tilt of breast wall caused by the fracture of the tuckstone bricks due to the quality of fused cast AZS and silica brick. Besides, in some large furnaces, 50mm thick plain carbon steel pallets are replaced with 60mm thick silicon ductile iron pallets. Good results are achieved.

 

The crown makes up the flame space with the breast wall and the front wall. At the same time, it can work as the medium of radiation heat transfer from flame to the material and glass liquid.

 

Its load spreads from the crown steel springer, to the hand iron, then to the column, finally the bottom steel structure.

 

The height and characteristics of the crown can be reflected by the rise to span ratio. From a thermal point of view, a lower crown is beneficial and can radiate heat to the glass as possible. The height of the crown can be reduced by the reducing the height of the breast wall and the rise of the crown. But, the height of the breast wall is limited by the port and the structural strength. The smaller the rise, the greater the pushing force, the less the heat loss. Reduce the rise can increase the horizontal thrust which makes the crown unstable. In most float glass furnaces, the rise to span ratio is 1:8. Depending on the length of the melting furnace, a crown can be divided into several sections, generally at least more than three. The expansion joints reserved between every section is 100-120㎜. The expansion joints in the front and back gables should be wider.

 

The crown is built with high quality wedge silica bricks by staggered laying. The size of mortar joints is determined depending on the specific requirements of mortar, generally 1-2 mm.

 

The crown springer of float glass furnaces is generally made of steel and should be air cooled. The incline extension line of both sides of springers should pass through the center of a circle of the crown arch. Their included angle is the central angle of the crown.

 

The service life of the crown determines the service life of the furnace. The weak point of the crown is holes(the thermometer hole and pressure hole), head joints, the crown heads and crown edges. During normal operation, the pressure is positive, so holes are easy to be bigger and bigger due to flame. If the crown edges do not touch tightly with steel springers, they will be easy to be eroded and burnt. So, sintered zircon bricks are mostly used in these parts.

 

The pool is composed of the sidewall and the bottom. Both are built with large refractory bricks. The pool is built on the steel beams supported by the furnace columns. The load of the furnace and the glass liquid are borne by the steel structure supported by the columns. The columns are generally built with concrete or steel columns. I-beam and H-beam are erected on the columns along the along the length of the furnace. In general, the float glass furnace has 4 main beams. I-beams are installed on the main beams in the vertical direction.

 

Flat steel is laid on the sub-beams when the bottom is not insulated. Large fire clay bricks are laid on the flat steel. The sub-beams should keep away from the brick joints. Under each brick, there should be 2 flat steels and 2 sub-beams. Nowadays, insulation technology has been widely used in the furnace bottom. Channel steel is laid on the sub-beams in the vertical direction. Pile bricks are laid in the channel steel. Large fire clay bricks are laid on the pile bricks. Before laying, active steel support frames are welded on the channel steel and insulation layer is built on the support frame between the pile bricks. when the depth of the pool is reduced and the bottom is insulated, the temperature and mobility of the bottom glass liquid increases. To reduce the corrosion of glass liquid to the bottom bricks, a protective layer is laid on the large fire clay bricks. The protective layer is composed of a 25mm thick layer of AZS ramming mass or zirconite ramming mass and a 75mm thick layer of fused cast AZS or sintered zircon bricks.

 

The sidewall is built on the bottom fire clay bricks. Since the consumption of fuel and the melting of batch materials are carried out on the surface of the glass liquid, the temperature of the glass liquid is up to 1450℃. The convection of molten glass is also strong. Coupled with the fluctuation of the liquid level, the corrosion of the sidewall is serious, especially near the liquid level. Given investment costs and other factors, the sidewall always adopts a multi-layer structure: fire clay brick->fused mullite brick->fused cast AZS from the bottom to the top. The sidewall with this structure is subjected to uneven corrosion and has a big effect on the glass quality.

 

Currently, large mono-block bricks are used in the float glass furnaces. In general, the material is fused cast AZS block 33#. The bricks are dry built with vertical joints with the knife hand. There is transverse joints. The material has good corrosion resistance, long service life and little pollution to the glass liquid.

 

After 2000, knife-hand sidewall bricks are used in the float glass furnaces. the materials are AZS 33# and AZS 36#. In some cases, AZS 41# is also used. But AZS 41# has bad stabiltiy and is easy to crack when preheating. The sidewall in this structure can greatly prolong the service life of the sidewall (more than 10 years).