Why is it called a physical tempered mirror?

The meaning of the word "physics" : It refers to its processing technology

"Physical tempering" is a process that alters the internal structure of glass through physical methods (heating and rapid cooling) to enhance its strength. This process is also known as "thermal strengthening".

· Process flow:

1. Heating: Heat the cut and ground glass lenses to a temperature close to their softening point (approximately 600-700 degrees Celsius).

2. Rapid cooling (quenching) : Then, a high-pressure cold air flow is used to rapidly cool the surface of the lens evenly from all directions.

· Physical principles:

The surface cools rapidly and solidifies to contract, while the interior remains in a state of high-temperature expansion.

As the interior gradually cools and contracts, a strong compressive stress is exerted on the already cured surface, while a tensile stress is formed inside to balance it.

This internally distributed stress structure requires the glass to overcome the huge compressive stress on its surface to break, thus significantly enhancing its impact and bending strength, which is usually 4 to 5 times that of ordinary glass.

Because the entire process does not change the chemical composition of the glass but only alters its internal stress through physical thermodynamic processes, it is called "physical tempering".

2. The meaning of the two characters "tempering" : It refers to its final performance

After the above-mentioned physical process treatment, the glass lens becomes as strong as "steel" (of course, it is a metaphor), hence the name "Tempered".

Its main advantages include:

· High strength: More resistant to impact and scratches, and less likely to break.

· Safety: This is the most crucial point. When subjected to a huge impact force and broken, physical tempered glass shatters into tiny, obtuse, granular pieces (similar to car window glass), rather than the large, sharp, knife-shaped fragments produced when ordinary glass breaks. This greatly reduces the risk of harm to the eyes.

Summary and Comparison

· Physical tempered glass: Specifically refers to tempered glass lenses made through a physical process of heating and cooling. This is the most common type of tempered glass in our daily life, widely used in glasses, doors and Windows, mobile phone screens, etc.

· Chemical tempering mirror: There is indeed another "chemical tempering" process, mainly through the chemical method of ion exchange (immersing the glass in molten potassium salt, allowing the sodium ions on the glass surface to exchange with potassium ions, with the potassium ions being larger, thereby forming a compressive stress layer on the surface). This process is more suitable for thin, small and complex-shaped glass, but its fragmentation state is not as safe as that of physical tempered glass, so it is rarely used in the field of spectacle lenses.

Therefore, when optical stores say "physical tempered glasses", what they want to convey is: "This is a kind of safety lens made through a physical thermal strengthening process, which is very strong and will not produce sharp fragments that harm the eyes even if it breaks."

However, it should be noted that the mainstream spectacle lenses nowadays are mostly made of resin, which is lighter and less likely to break than glass, and thus has a naturally high level of safety. To a large extent, it has replaced glass lenses. However, the "physical tempering" process remains very important in glass lenses and many other glass products.