Exploring The Distinctions Between Physical Tempering And Chemical Strengthening Of Glass

Exploring the Distinctions Between Physical Tempering and Chemical Strengthening of Glass

Introduction:

Glass has become an integral part of our lives, finding applications in various domains such as electronics, furniture, construction, and transportation. As glass undergoes deep processing to produce products like AG glass, AR glass, and decorative glass, the demand for increased strength and safety arises. This is where tempered glass, particularly AG glass, comes into play, offering enhanced protection when integrated into finished devices.

Let's delve into the differences between physical tempering (referred to as "PT") and chemical strengthening (referred to as "CS") of AG glass to gain a better understanding:

Physical Tempering: Strength through Controlled Cooling

PT involves altering the physical properties and behavior of glass without changing its elemental composition. By rapidly cooling the glass from high temperatures, the surface undergoes rapid contraction, creating compressive stress. Meanwhile, the core cools at a slower rate, resulting in tensile stress. This combination produces higher overall strength in the glass. The cooling intensity directly impacts the glass's strength, with higher cooling rates resulting in greater strength.

Chemical Strengthening: Modifying Composition for Resilience

CS, on the other hand, alters the elemental composition of the glass. It utilizes a low-temperature ion-exchange process, where smaller ions in the glass surface are replaced by larger ions from a solution. For instance, lithium ions in the glass can be exchanged with potassium or sodium ions from the solution. This ion exchange creates compressive stress on the glass surface, proportional to the number of ions exchanged and the depth of the surface layer. CS is particularly effective for enhancing the strength of thin glass, including curved or shaped glass.

Processing Parameters:

Physical Tempering:

Processing Temperature: Typically conducted at temperatures between 600°C and 700°C (close to the glass softening point).

Processing Principle: Rapid cooling leading to compressive stress in the glass interior.

Chemical Strengthening:

Processing Temperature: Carried out at temperatures ranging from 400°C to 450°C.

Processing Principle: Ion exchange of smaller ions in the glass surface with larger ions from a solution, followed by cooling to induce compressive stress.

Processing Thickness:

Physical Tempering: Suitable for glass thicknesses ranging from 3mm to 35mm. Domestic equipment often focuses on tempering glass with thicknesses around 3mm and above.

Chemical Strengthening: Effective for glass thicknesses ranging from 0.15mm to 50mm, making it especially suitable for strengthening glass with a thickness of 5mm or less. It proves to be a valuable method for strengthening irregularly shaped thin glass, particularly those below 3mm.

Advantages:

Physical Tempering Cost-Effective: PT is a more cost-effective method, making it suitable for large-scale production.

High Mechanical Strength: PT results in glass with excellent mechanical strength, thermal shock resistance (able to withstand temperatures up to 287.78°C), and high thermal gradient resistance (can endure changes up to 204.44°C).

Safety Enhancement: Wind-cooled tempered glass not only reinforces mechanical strength but also shatters into small fragments upon breakage, reducing the risk of injury.

Chemical Strengthening:

High Strength and Uniform Stress Distribution: CS produces glass with significantly higher strength than regular glass (5-10 times stronger), increased flexural strength (3-5 times stronger), and improved impact resistance (5-10 times more resilient). CS provides enhanced strength and safety compared to PT for glass of the same thickness.

Superior Stability and Formability: CS ensures uniform stress distribution, stability, and dimensional integrity. It retains its shape without deformation or distortion and does not induce optical distortions. It can be applied to glass products of various complex shapes, including curved, cylindrical, boxed, and flat designs.

Resistance to Thermal Stress: CS-treated glass exhibits 2-3 times greater resistance to rapid temperature changes, withstanding temperature differentials of over 150°C without shattering or self-explosion.

Suitable for Thin Glass: CS is highly effective for strengthening glass with thicknesses ranging from 0.2mm to 5.0mm. It produces excellent results without causing bending or warping.

Disadvantages:

Physical Tempering:

Self-Explosion Risk: PT-treated glass may experience self-explosion during processing, storage, transportation, installation, or usage. The time of self-explosion is unpredictable, occurring anywhere from 1 to 5 years after treatment. Visible defects in the glass, such as stones, particles, bubbles, impurities, notches, scratches, or edge defects, as well as sulfur-nickel (NIS) impurities and heterogeneous particle inclusions, may trigger self-explosion.

Chemical Strengthening:

Higher Cost: CS is more expensive than PT, with costs several times higher.

Applications:

Physical Tempering:

Widely used in applications that demand high mechanical strength and safety, such as curtain walls, facade windows, interior partitions, furniture, household appliances, and partitions located near intense heat sources or subjected to rapid temperature changes.

Chemical Strengthening:

Primarily applied in electronic display products like monitors, televisions, tablets, and smartphones as protective screen panels. It offers excellent resistance to damage and impact.

Conclusion:

Both physical tempering and chemical strengthening techniques play significant roles in enhancing the strength and safety of AG glass. Physical tempering provides cost-effective options with broad applications, while chemical strengthening offers superior strength, uniform stress distribution, and excellent formability, making it an ideal choice for thin glass and electronic displays. Understanding the distinctions between these two methods allows for informed decisions in selecting the most suitable approach based on specific requirements and product characteristics.