The safety hammer mainly uses its conical tip. Due to the small contact area of the tip, when using the hammer to hit glass, the pressure at that contact point on the glass (not pressure, but pressure per unit area) is quite high. This is similar to the principle of a thumbtack, where the film is easily punctured and causes the car glass to undergo slight cracking due to a large external force at that point. For tempered glass, A small amount of cracking means that the stress distribution inside the entire glass is disrupted, resulting in countless spider web cracks in an instant. At this point, with just a few more strokes of a hammer, the glass fragments can be removed.
In addition, the middle part of tempered glass is the strongest, while the corners and edges are the weakest. The best way is to use a safety hammer to strike the edges and corners of the glass, especially the middle part of the upper edge of the glass. Once the glass has cracks, it is easy to break the entire piece of glass.
quality
Tempered glass is obtained by cutting ordinary annealed glass into the required size, heating it to a near softening point, and then rapidly and evenly cooling it. After tempering, uniform compressive stress is formed on the surface of the glass, while tensile stress is formed inside, greatly improving the performance of the glass. The tensile strength is more than three times that of the latter, and the impact resistance is more than five times that of the latter.
It is precisely this characteristic that stress characteristics become an important indicator for distinguishing true and false tempered glass. Tempered glass can see colored stripes at the edges of the glass through a polarizing light plate, while on the surface layer of the glass, black and white spots can be seen. Polarizing lenses can be found in camera lenses or glasses. When observing, pay attention to adjusting the light source for easier observation.
Each tempered glass has a 3c quality and safety certification mark..
Self exploding defect
The automatic cracking of tempered glass without direct mechanical external force is called self explosion of tempered glass. According to industry experience, the self explosion rate of ordinary tempered glass is around 1-3 ‰. Self explosion is one of the inherent characteristics of tempered glass.
There are many reasons for self explosion caused by expansion, which can be summarized as follows:
① The impact of glass quality defects
A. Stones, impurities, and bubbles in glass: Impurities in glass are weak points and stress concentrations in tempered glass. Especially if the stone is located in the tensile stress zone of tempered glass, it is an important factor leading to cracking.
Stones exist in glass and have a different coefficient of expansion from the vitreous body. After glass tempering, the stress concentration in the crack area around the stone increases exponentially. When the coefficient of expansion of the stone is less than that of glass, the tangential stress around the stone is in a tensile state. Crack propagation accompanying stones is highly prone to occur.
B. Glass contains nickel sulfide crystals
Nickel sulfide inclusions generally exist as small crystalline spheres with a diameter of 0. 1-2 mm. The appearance is metallic, and these impurities are NI3S2, NI7S6, and NI-XS, with X=0-0. 07. Only NI1-XS phase is the main reason for the spontaneous fragmentation of tempered glass.
The theoretical NIS is known to be at 379. At C, there is a phase transition process, from the high-temperature a-NIS hexagonal crystal system to the low-temperature B-NI triangular crystal system, accompanied by the appearance of 2. 38%
