Tempered glass blew can be expressed as the phenomenon of automatic cracking of tempered glass in the absence of external direct effects. In the steel processing, storage, transportation, installation, use, etc. can occur during the process of glass blew. Blew, according to the different causes can be divided into two kinds: one: from the visible defects in the glass caused by blew, such as stones, sand, bubbles, inclusions, gaps, scratches, burst, etc .; two: (NiS) impurity expansion caused by blew. This is two different types of blew, should be clearly classified, different treatment, using different methods to deal with and deal with. The former is generally visible, detection is relatively easy, so the production control. The latter is mainly caused by the volume expansion of tiny nickel sulfide particles in the glass, which can not be visually inspected and therefore uncontrollable.
In the actual operation and treatment, the former can generally be removed before installation, which can not be tested and continue to exist, become the use of tempered glass bleaching the main factors. Nickel sulfide blew after the replacement is difficult, high processing costs, while accompanied by greater quality complaints and economic losses, resulting in the owners of the dissatisfaction even more serious other consequences. Therefore, the explosion caused by nickel sulfide is the focus of our discussion.
The expansion of nickel sulfide inside the tempered glass is the main cause of the toughening of tempered glass. After the glass has been tempered, the surface layer forms compressive stress. The inner core layer has tensile stress, compressive stress and tensile stress together constitute a balance body.
The glass itself is a brittle material, resistant to pressure but not pull, so most of the broken glass is caused by tensile stress. During the phase transition of the nickel sulfide crystal in the tempered glass, the volume expansion of the nickel nitride crystal in the tempered glass causes a greater tensile stress in the tempered glass. When the tensile stress exceeds the limit that the glass itself can bear, It will lead to tempered glass blew.
Glass main material quartz sand or sandstone into the nickel, fuel and accessories into the sulfur, 1400 ℃ ~ 1500 ℃ high temperature melting furnace melting and melting to form nickel sulfide.
When the temperature exceeds 1000 ° C, the nickel sulfide is randomly distributed in the molten glass liquid in the form of droplets. When the temperature dropped to 797 ℃, these small droplets crystallized and the nickel sulfide was in the high temperature α-NiS crystal phase (hexagonal crystal). When the temperature continues to drop to 379 ° C, the crystal phase transition becomes a low temperature state of β-NiS (tetragonal), accompanied by a 2.38% volume expansion. The speed of this transition process depends both on the percentage of the different compositions (including Ni7S6, NiS, NiS1.01) in the nickel sulfide particles and on the ambient temperature.
If the conversion of nickel sulfide is not complete, the process will continue even at the temperature of natural storage and normal use, but at a very low speed.
When the glass is heated, the inner core temperature of the glass is about 620 ° C, and all the nickel sulfide is in the high temperature α-NiS phase. Subsequently, the glass enters the wind gate and quenches, and the nickel sulfide in the glass undergoes a phase change at 379 ° C. Unlike the float annealed kiln, the quenching time is very short, too late to change to low temperature β-NiS and high temperature sulfur nickel α phase is "frozen" in the glass. Rapid quenching to the glass to be tempered, the formation of external pressure inside the stress balance of the body.
In the steel has been tempered in the nickel sulfide phase transition at low speed continued, the volume of expansion and expansion, the surrounding glass of the force increases. Tempered glass plate core itself is the tensile stress layer, located in the Zhang stress layer of nickel sulfide phase change occurs when the volume expansion also forms tensile stress, the two sheets of stress superimposed together enough to cause the rupture of tempered glass blew.