The Principles And Advantage And Disadvantage Of Physical Tempering

Physical Tempering is a process used to increase the strength and thermal stability of glass. It involves heating the glass to near its softening temperature and then rapidly cooling it using either gas or liquid mediums. There are two common methods of chemical tempering: gas medium tempering and liquid medium tempering.

 

1. Gas Medium Tempering:

Gas medium tempering, also known as air cooling tempering, includes methods such as horizontal air cushion tempering, horizontal roller tempering, and vertical tempering. In this process, the glass is heated to a temperature close to its softening point (around 650-700°C) and then subjected to a rapid airflow from both sides to cool it quickly. This method increases the mechanical strength and thermal stability of the glass. The essential requirement for the cooling process is fast and uniform cooling to obtain evenly distributed stress within the glass. To achieve uniform cooling, the cooling device needs to effectively dissipate heat, facilitate the removal of occasional glass fragments, and minimize noise.

 

Advantages And Disadvantages:

Gas medium tempering has several advantages. It is cost-effective and allows for high production volumes. The tempered glass produced through this method exhibits high mechanical strength, resistance to thermal shocks (maximum safe working temperature can reach 287.78°C), and high resistance to thermal gradients (it can withstand up to 204.44°C). Additionally, gas medium tempered glass, when shattered, breaks into small pieces, reducing the risk of injury. However, this method has certain requirements for glass thickness and shape (typically a minimum thickness of around 3mm for domestically produced equipment). It also has slower cooling rates, higher energy consumption, and is not suitable for applications requiring highly precise optical quality, especially for thin glass.

 

Applications:

Air cooling tempering is widely used in the automotive, marine, and construction industries.

 

2. Liquid Medium Tempering:

Liquid medium tempering, also known as liquid cooling, involves heating the glass to its softening point and then rapidly immersing it in a cooling medium. The cooling medium can be a mixture of saltwater, such as potassium nitrate, sodium nitrate, or their combination. Mineral oil can also be used as a cooling medium, and additives like toluene or carbon tetrachloride can be added to the mineral oil. Specialized quenching oils or silicone oils can also be utilized. In liquid medium tempering, stress unevenness and resulting cracks can occur due to the glass edges entering the cooling tank first. To address this issue, a pre-cooling process using air cooling or liquid spraying can be employed before immersing the glass in the liquid medium. Another method involves placing the glass in a tank containing water and an organic solution, where the organic solution floats on top of the water. When the heated glass is placed in the tank, the organic solution pre-cools the glass by absorbing some of the heat before it rapidly cools in the water.

 

Advantages And Disadvantages:

Liquid medium tempering offers several advantages. Due to the high specific heat and high heat of vaporization of water, the amount required for cooling is significantly reduced, leading to reduced energy consumption and costs. This method provides fast cooling, high safety performance, and minimal deformation. However, since the glass is inserted into the liquid medium after being heated, there can be uneven heating for large glass sheets, which can affect the quality and yield.

 

Applications:

Liquid medium tempering is primarily suitable for tempering thin glasses with small surface areas, such as eyeglasses, glass for LCD screens, and glass used in optical instruments and devices.

 

In conclusion, Physical Tempering methods, whether using gas or liquid mediums, play a crucial role in increasing the strength and thermal stability of glass. Each method has its advantages and limitations, making them suitable for specific applications. Gas medium tempering, also known as air cooling tempering, is cost-effective and widely used in industries such as automotive, marine, and construction. It provides high mechanical strength and resistance to thermal shocks, while also producing small and safer glass fragments upon breakage. However, it has limitations in terms of glass thickness and shape, slower cooling rates, higher energy consumption, and is not ideal for applications requiring high optical quality.

 

On the other hand, liquid medium tempering, or liquid cooling, offers advantages such as reduced energy consumption, fast cooling, high safety performance, and minimal deformation. It is particularly suitable for tempering thin glasses with small surface areas, such as eyeglasses, LCD screen glass, and glass used in optical instruments. By carefully selecting the cooling medium and employing pre-cooling techniques, uneven heating and potential cracks can be minimized. However, the process may require specific expertise and process control to establish an effective tempering system.

 

Overall, Physical Tempering methods provide enhanced strength and thermal stability to glass, making it suitable for various industrial applications. The choice between gas medium tempering and liquid medium tempering depends on factors such as the desired properties of the tempered glass, the size and shape of the glass, and the specific requirements of the application. These methods continue to evolve and improve, contributing to the development of stronger and safer glass products in numerous fields.

 

And KS Glass committed to produce high quality glass products with the best tempering solution, if you are still in design and uncertain which tempering method is suitable for your products, please feel free to contact us, we will provide the best solution with our rich experience.