Tempered glass is made from ordinary glass through a special heat treatment process. Its strength is 3 to 5 times that of ordinary glass, and when it breaks, it forms fine obtuse particles, making it safer. The following is its detailed manufacturing process:
1. Selection of original sheet glass
First, defect-free float glass (soda-lime silicate glass) should be selected to ensure that the surface is flat, free of bubbles, impurities or scratches.
2. Cutting and processing
Cutting and shaping: Cut the original glass sheet to the required size (at this time, the glass can still undergo mechanical processing such as drilling and edge grinding).
Edge treatment: Grind the edges to reduce stress concentration and prevent cracking during tempering later.
3. Cleaning and inspection
Clean the oil stains and dust on the glass surface (to avoid blemishes during heating).
Check for cracks or defects. Unqualified glass needs to be removed.
4. Heat to the softening point
The glass is sent into the tempering furnace (continuous or intermittent) and heated to approximately 620-650℃ (close to the softening point, with the glass in a red-hot state but not melted).
Temperature control needs to be precise. The heating time varies for glass of different thicknesses (for example, it takes about 2 to 3 minutes for 6mm glass).
5. Rapid cooling (quenching
Key steps: Quickly feed the red-hot glass into the air grid and evenly blow high-pressure cold air (with a wind speed of approximately 50-80m/s) over both sides of the surface.
Principle: The surface rapidly cools and solidifies, while the interior remains at a high temperature. When the interior gradually cools and contracts, tensile stress will be formed inside the glass, and compressive stress (about 100MPa or more) will be formed on the surface. This stress distribution significantly enhances the impact resistance and bending capacity of the glass.
6. Cooling and inspection
Cool naturally to room temperature.
Stress distribution can be detected by polarized light or impact tests (such as steel ball drop tests) can be conducted.
The characteristics of tempered glass
High strength: The flexural strength is 3 to 5 times that of ordinary glass, and the impact resistance is significantly improved.
Safety: When broken, it forms small honeycomb-like particles, reducing the risk of cuts.
Temperature resistance: It can withstand a temperature difference of approximately 250℃ (ordinary glass is only 70-100℃).
Precautions
Non-reprocessable: After tempering, it cannot be cut or drilled; otherwise, it will burst as a whole.
Self-explosion risk: If the glass contains impurities (such as nickel sulfide), it may self-explode due to uneven stress (the probability can be reduced by hot-dip treatment).
