The accidents caused by the quality of the refractory bottom brick in actual production mainly include the following aspects.
(1) The brick at the bottom of the tin bath bubbled, and the bubbles floated up and impacted the unhardened glass ribbon, forming pits (open bubbles under the board) on the lower surface of the glass.
(2) The Na20 released by the glass penetrates into the refractory bottom brick structure and reacts to produce nepheline minerals. With the volume expansion of about 20%, the reaction layer curls and flakes up.
(3) The brick body breaks horizontally, and the upper half rises, commonly known as the "7-inch effect" (1 inch = 0.0254m).
(4) The refractory bottom brick is arched.
(5) The sealing material peeled and floated in layers, causing scratches on the lower surface of the glass.
(6) The bolts fixing the refractory bottom brick are eroded and melted by the tin liquid, and the refractory bottom brick floats.
(7) Leakage at the bottom of the tank.
The cause of the above accident may be a combination of one or more of the following factors.
(1) The bottom of the tin bath has a large water content, which is not exhausted when heated and baked. A large amount of bubbling will occur when the temperature in the tank fluctuates during production. The bubbles float up and impact and damage the soft glass ribbon, forming a defect in the quality of the opening under the board. In addition, after the water in the bottom of the tank is baked and sublimated, many through holes are left, and the protective gas of the tin tank is easy to penetrate and it is also easy to cause bubbling.
(2) The clay quality tin bath refractory bottom brick absorbs Na20 from the glass. At the contact surface with the tin liquid, the glass phase of the clay brick reacts with Na20 to form nepheline minerals, accompanied by volume expansion (20%). When the thermal expansion shear force exceeds the strength of the brick, the new biological nepheline flakes and floats, causing glass defects and shortening the service life of the tin bath. This situation generally occurs one year after it is put into production and is one of the main problems that plague the service life of tin bath refractory bottom bricks. The main reason is that the refractory bottom brick of the tin bath has greater air permeability and poor resistance to penetration.
(3) In the 1970s, there were many "7-inch fracture and floating" accidents of refractory bottom bricks in foreign countries, and the arching accidents of refractory bottom bricks occurred in some manufacturers in China. The main reason is that the strain rate of the tin bath refractory bottom bricks used is generally low. Less than 0.5%, the expansion joint between bricks and bricks is also small, the brick body is subjected to extreme stress, which causes horizontal fracture along the taper of the fixed bolt hole, the upper half of the brick body floats, and the refractory bottom brick is thermally expanded to produce a higher Extrusion stress, in order to release the stress, the deformation of the brick body caused the arching accident of the refractory bottom brick.
(4) There are two main reasons for the accident of delamination and floating of the sealing material. First, the material of the sealing material does not meet the design requirements and does not match the performance of the refractory bottom brick material. The second is improper construction. Layered tamping, resulting in poor combination of the sealing material and the inverted cone hole of the refractory bottom brick.
(5) The bolts used to fix the refractory bottom brick are eroded and melted by the tin liquid, and the refractory bottom brick floats accidents. There are two main reasons: 1.
The material fixing bolt, graphite, sealing material, etc. do not meet the design requirements; the second is caused by improper construction. The main reasons are: the incorrect sealing material of the inverted cone hole of the refractory bottom brick is not tightly sealed; the straight hole of the refractory bottom brick is not tightly sealed, so that in the case of fluctuations in the temperature of the bottom plate, tin liquid enters the straight hole. 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 joint to the bottom plate, it will solidify and will not enter the straight hole in. However, under abnormal conditions such as power outages and wind cuts, 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 has always eroded the bolt. The bottom plate of the tin bath is not flat, resulting in a large gap between the bottom plate and the refractory bottom brick. During the construction, the graphite powder easily penetrates into the gap, making the graphite powder in the straight hole difficult to tamping, and the construction effect is difficult to guarantee.
(6) Under the premise of stable production, there are two reasons for the leakage of tin at the bottom of the groove. The first is the poor welding quality of the steel shell at the bottom of the tank. The second is that the edge sealing material is not rammed tightly, causing the tin liquid to directly contact and erode the steel shell at the bottom of the tank.
