How does glass form compressive stress through heating and rapid cooling during the tempering process?

In the process of tempered glass production, the internal stress state of the glass undergoes a fundamental change through specific process steps of heating and rapid cooling, which gives tempered glass higher strength and better impact resistance than ordinary glass. The specific process is as follows:
Heating stage: First, ordinary glass is heated to a temperature close to its softening point, which is usually around 700°C. At this high temperature, the molecular and atomic structures inside the glass become active and begin to rearrange, and the glass gradually softens, but its overall shape is still maintained. The purpose of this step is to allow the glass material to be heated evenly and prepare for subsequent rapid cooling.
Rapid cooling stage: When the glass reaches the predetermined temperature, it is immediately cooled quickly and evenly. This step is the key to the tempering process. Since the glass surface is in more direct contact with the cooling medium (such as air or water), the surface cools much faster than the inside. This temperature difference between the inside and the outside leads to different thermal shrinkage rates: the surface layer shrinks due to rapid cooling, but the inside still maintains a higher temperature and shrinks relatively slowly.
Stress formation: Due to the difference in cooling speed between the surface and the interior, the glass surface generates compression (compressive stress) during the cooling process, while the interior generates tension (tensile stress) due to slower contraction. This distribution of internal and external stresses is the key to the strength of tempered glass. The surface compressive stress can resist external impact and pressure, while the internal tensile stress enhances the overall structural stability of the glass.
Tempered glass forms compressive stress on its surface and tensile stress inside by heating it to near the softening point and then cooling it rapidly. This unique stress distribution gives tempered glass higher strength, better impact resistance and thermal stability than ordinary glass. These characteristics make tempered glass widely used in doors and windows, curtain walls, glass tabletops, partitions, shower rooms and many other occasions.

What method is used for the cooling process in the tempering process of transparent tempered glass?

The cooling process in the tempering process of transparent tempered glass is a crucial step, which directly determines the performance and quality of the final product. In this process, we use rapid cooling technology, also known as quenching or rapid cooling. The core of this method is to quickly expose the glass that has been heated to a point close to the softening point (about 700°C) to a cooling medium, usually using high-speed airflow or spraying water mist, to achieve rapid cooling of the glass surface.
The purpose of rapid cooling is to form a compressive stress layer on the glass surface through rapid temperature changes. When the glass is heated to a high temperature, its molecular structure becomes relaxed and the internal stress tends to balance. However, during the rapid cooling process, the glass surface cools down rapidly due to direct contact with the cooling medium, and the surface molecules solidify rapidly, forming a dense compressive stress layer. At the same time, due to the hysteresis of heat transfer inside the glass, the cooling rate is relatively slow, resulting in tensile stress in the center layer. This unique stress distribution state, that is, the combination of surface compressive stress and internal tensile stress, gives tempered glass excellent physical properties.
After such treatment, the strength of transparent tempered glass has been significantly improved, and it can withstand greater external forces and impacts without being easily broken. Even in the case of breaking, tempered glass will form countless small fragments rather than sharp fragments, which greatly reduces the risk of injury to the human body and improves the safety of use. In addition, tempered glass also maintains a high light transmittance and excellent heat resistance, making it widely used in doors and windows, curtain walls, glass tabletops, glass partitions, shower screens, shower rooms and other fields.
In the field of construction, transparent tempered glass is often used as the exterior wall and ceiling material of large public buildings, as well as the door and window system of high-end residences due to its excellent safety performance and aesthetics. In bathroom and furniture design, tempered glass is an ideal choice for shower rooms, wash basin countertops and various furniture door panels due to its waterproof, moisture-proof and easy-to-clean characteristics. In the electrical industry, tempered glass is also widely used in the panel production of household appliances such as ovens and microwave ovens, which is both beautiful and durable.
The cooling process of transparent tempered glass during tempering successfully builds a unique stress distribution state inside the glass by using rapid cooling technology, giving it higher strength, better impact resistance, and excellent safety and durability. These characteristics make transparent tempered glass have broad application prospects and market demand in many fields.