The accidents caused by the quality problems of tin bath bottom refractory bricks in actual production are mainly the following aspects.
(1) The tin bath bottom refractory bricks bubble up, and the bubbles float up and impact the unhardened glass strip, forming pits on the lower surface of the glass (open bubbles under the plate).
(2) The Na2O released by the glass penetrates into the bottom brick structure, reacts to form nepheline minerals, and is accompanied by a volume expansion of about 20%, and the reaction layer curls and peels off and floats up.
(3) The brick body breaks horizontally, and the upper half floats up, commonly known as the "7-inch effect" (1 inch = 0.0254m).
(4) The bottom brick arches.
(5) The sealing material is delaminated and floats up, causing scratches on the lower surface of the glass.
(6) The bolts that fix the bottom bricks are corroded and melted by the tin liquid, and the bottom bricks float up.
(7) Tin leaks from the bottom of the tank.
The causes of the above accidents may be one or a combination of the following factors.
(1) The water content of the tin bath bottom refractory bricks is high, and it is not completely drained during the heating and baking. When the temperature in the bath fluctuates during production, a large amount of bubbles will be generated. The bubbles float up and impact and damage the soft glass belt, forming a quality defect of open bubbles under the board. In addition, after the water in the bottom of the bath is baked and sublimated, many through pores are left, and the tin bath protective gas can easily penetrate and cause bubbles.
(2) Clay quality The tin bath bottom brick absorbs Na2O from the glass. On the contact surface with the tin liquid, the glass phase of the clay brick reacts with Na2O to form nepheline minerals, accompanied by volume expansion (20%). When the thermal expansion shear force exceeds the strength of the brick, the new nepheline peels off and floats up, causing glass defects and shortening the service life of the tin bath. This situation usually occurs one year after the production is put into operation, which is one of the main problems that plague the service life of the tin bath bottom brick. The main reason is that the tin bath bottom brick has a large air permeability and poor anti-penetration ability.
(3) In the 1970s, there were many "7-inch fracture and floating" accidents of bottom bricks abroad. In my country, there were arching accidents of bottom bricks in some manufacturers. The main reason was that the strain rate of the tin bath bottom refractory bricks used was low, generally less than 0.5%, and the expansion joints between bricks were also small. The brick body was subjected to great stress, resulting in horizontal fracture along the cone of the fixing bolt hole. The upper part of the brick body floated up, and the bottom brick expanded due to heat to produce high extrusion stress. In order to release the stress, the brick body deformed and caused the bottom brick arching accident.
(4) There are two main reasons for the occurrence of the sealing material delamination and floating accident. One is that the sealing material material does not meet the design requirements and does not match the performance of the bottom brick material. The other is improper construction. Layered tamping causes the sealing material to not combine well with the bottom brick inverted cone hole.
(5) The bolts that fix the bottom bricks are corroded and melted by the tin liquid, and the bottom brick floats. There are two main reasons:
One is that the material of the fixing bolts, graphite, sealing material, etc. does not meet the design requirements; the other is improper construction. The main reasons are: the sealing material of the inverted cone hole of the bottom brick is not sealed tightly; the straight hole of the tin bath bottom refractory bricks is not sealed tightly, causing the tin liquid to enter the straight hole when the temperature of the bottom plate fluctuates. Under normal circumstances, due to the cooling air at the bottom of the tank, the temperature of the bottom plate is generally below 150°C (lower than the melting point of tin). Even if the tin liquid flows from the brick joints to the bottom plate, it will solidify and will not enter the straight hole. However, under abnormal conditions such as power outages and wind outages, the bottom plate is not cooled enough, and the tin liquid enters the straight hole. Since the temperature of the bolt neck is higher than the melting point of tin, the tin is in a molten state, which continues to corrode the bolt. The tin tank bottom plate is not flat, resulting in a large gap between the bottom plate and the bottom brick. Graphite powder easily penetrates into the gap during construction, making it difficult to tamp the graphite powder in the straight hole, and the construction effect is difficult to guarantee.
(6) Under the premise of stable production, there are two reasons for the leakage of tin from the bottom of the tank. One is the poor welding quality of the copper shell at the bottom of the tank; the other is that the side sealing material is not rammed tightly, causing the tin liquid to directly contact and corrode the steel shell at the bottom of the tank.
