Detailed explanation of the technological problems

The purpose of glass annealing is to weaken and prevent excessive residual internal stress and optical inhomogeneity in glass products, and stabilize the internal structure of glass

the common process problems in the annealing process are as follows:

1. The asymmetric cooling of the upper and lower surfaces of the glass ribbon will turn more than 80000 employees into more than 2000 independent "small Haier" models, but

① the asymmetric cooling of the glass plate in the annealing area

the glass plate is in the annealing area. The cooling intensity of the upper and lower surfaces is different, and when the glass is cooled to room temperature equilibrium, it will cause asymmetric stress distribution, The compressive stress will shift to the side that cools faster, the surface that cools faster (cool) will be under compressive stress, and the surface that cools slower (hot) will be under tensile stress. If the original glass sheet is large enough, the imbalance of stress distribution in the glass will inevitably cause deformation - bending or warping. If the lower surface of the glass plate cools faster than the upper surface, the side with large compressive stress is on the lower surface, and the plate bends upward; On the contrary, bend down. If the generated stress exceeds the allowable value, cracking will occur

② the glass is cooled asymmetrically below the temperature of the annealing area

if the cooling speed of the upper and lower surfaces of the glass is below the temperature of the annealing area, the temporary stress will be generated. The surface with fast cooling speed (cold) will be subject to tensile stress, and the surface with slow cooling speed (hot) will be subject to compressive stress

2. The transverse temperature of the glass ribbon is uneven

① the temperature is uneven in the transverse symmetrical distribution

the temperature is symmetrical to the centerline distribution, but the edge is cooler than the middle or the edge is hotter than the middle. There is a temperature difference in the width direction of the glass belt, which will also produce thermal stress

when the edge of the glass belt is cooler than the middle part, if it is in the annealing temperature region, the research results at home and abroad show that it is feasible to use recycled plastics in road engineering, and it has been applied in practical engineering, where the middle (cold) compressive stress and the middle (hot) tensile stress; If the glass is under the annealing temperature, the edge (cold) is under tensile stress and the middle (hot) is under compressive stress

when the edge of the glass plate is hotter than the middle, the stress on the plate surface is opposite to the above

the stress produced by the above conditions can be measured with a stress meter. Usually, you can also use your fingers for qualitative inspection, that is, gently lift the edge with two or three fingers at a considerable distance from the position of the cutting machine. If the edge is wavy and easy to be lifted, the edge bears compressive stress and the middle bears tensile stress; If the edge is tight and not easy to be lifted, the edge bears tensile stress and the middle bears compressive stress

as we all know, the compressive strength of glass is about ten times greater than the tensile strength, so the glass plate usually breaks first on the plate surface under tensile stress, and then the crack may continue to develop towards the compressive stress zone. Therefore, the temporary stress is more destructive to the glass. As long as the tensile stress generated is equal to or slightly greater than the tensile strength of the glass, the glass will rupture itself without any external force

② uneven transverse temperature distribution of the glass plate

transverse temperature asymmetric distribution of the glass plate, that is, the final cooling speed of both sides of the glass plate is different, resulting in high temperature on one side and low temperature on the other, and the stress distribution of the plate is also asymmetric. If it is in the annealing temperature region, the cold edge becomes longer, the compressive stress is, and the hot edge becomes shorter, and the tensile stress is, the glass belt will shift to the hot side; If the glass is under the annealing temperature, the cold side is under tensile stress, and the hot side is under compressive stress. When the temporary stress exceeds the allowable value, it will burst

at this time, the theoretical stress value of the glass plate cannot be measured, because part of the stress is eliminated due to deformation

when the glass ribbon leaves the annealing area, it can be cooled faster, because the glass will no longer produce water stress. However, it must be pointed out that at this time, if the cooling speed is too fast, or the transverse temperature difference is too large, excessive temporary stress or unbalanced stress distribution will occur, which often occurs in actual production

to sum up, within the annealing temperature range, the uneven transverse temperature of the glass strip will produce permanent stress when the glass is cooled to room temperature. In the annealing kiln, the hotter part of the plate surface is in tension and the colder part is in compression. Below the annealing temperature range, the hotter part of the plate surface is under pressure, and the colder part is under tension. From the situation of cracking the glass, it is more unfavorable for the glass belt to be too cold on both sides below the other annealing area than in the middle, so it must be prevented. This situation is often caused by cold air leaking into the shaft heads at both ends of the roller. Therefore, the shaft head seal is very important