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Edge Stress Analysis and Control of Automobile Tempered Glass (2)
Source : www.landglass.co    Release time:2014-02-21

Relation between edge tensile stress and spontaneous breaking 

Glass is a fragile material at normal temperature. Its theoretical strength is very high. However, its practical strength is much lower in production and use because of a number of micro cracks on its surface and edges. Under compressive stress, micro cracks on glass surface and edges tend to shrink, and the glass strength is very high; under tensile stress, they tend to extend, and the glass strength is greatly reduced. Therefore, glass strength depends on the balancing and values of compressive and tensile stresses. Over high edge tensile stress may lead to split and finally glass will break.     
Reasons of edge tensile stress of automobile tempered glass 
1. Too many low-conductivity cover layers are used on cold ring, and air from lower chiller is somewhat blocked;   
2. Strips are used on cold ring to repair low-conductivity cover layers, and air from lower chiller is somewhat blocked; 
3. The low-conductivity cover layers on cold ring have poor thermal and mechanical properties; 
4. The design of cold ring structure is unreasonable or the contact area of glass on cold ring is too large; 
5. The effective height of glass on cold ring is unreasonable; 
6. Relative slip degree of glass on cold ring is too high; 
7. Upper air pressure is too high above the lower air pressure during tempering quenching. 
8. The female ring of press mould is overloaded during glass pressing and forming. 

Control of edge tensile stress of automobile tempered glass in production 
1. The low-conductivity cover layers on cold ring should have uniform thickness, good ventilation, joints sewing without overlapping; low-conductivity cover layers should be checked at fixed intervals so as to ensure their integrity. Timely repair or replace it if any one is damaged. The repair method should ensure the smooth air from lower chiller. 
2. Ensure symmetric positions of cold rings in the chiller during mould assembly. 
3. Choose the low-conductivity cover layers with satisfactory thermal and mechanical properties for the cold ring. 
4. Reasonably design the cold ring structure and reduce the glass contact area as much as possible; 
5. Ensure the effective height of glass on cold ring; 
6. Reduce the relative slip degree of glass on cold ring as much as possible; 
7. Reasonably set the upper and lower air pressures during tempering quenching. 
8. Reasonably arrange the closing clearance between female and male moulds of press mould.  



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