What are the common quality defects of tempered glass?

The process of physically tempering glass involves thermal processing, which can be challenging to control accurately due to the large thermal inertia of thermal equipment. As a result, defects can arise during the tempering process, affecting the quality and yield of tempered glass. These issues can include glass breakage, deformation, insufficient tempering, and other quality problems that may arise during or after the tempering process. In this article, we will explore some of the common quality defects that can occur during the physical tempering of glass.

The number of glass fragments is not qualified

Tempered glass is designed to shatter into tiny, blunt pieces to minimize the risk of injury. Unlike ordinary glass, which breaks into large, sharp shards, tempered glass should break into tiny, harmless components, and the number of fragments of tempered glass meets a certain standard, such as 4-12mm flat tempered glass fragments number shouldn’t be less than 40 pieces. Failure to meet this requirement can pose a significant threat to people and property in the event of accidental breakage.

glass fragments

Low impact strength

The low impact strength of tempered glass can be attributed to several factors. Firstly, the temperature difference or uneven cooling during the heating and cooling process may result in inconsistent stress on the upper and lower surfaces of the glass, leading to reduced strength or even bending of the glass panel. Secondly, scratches on the surface of the glass, especially those incurred after tempering, can release surface stress and weaken the strength.  To ensure the high impact strength of tempered glass, it is crucial to control the heating and cooling process carefully, avoid surface scratches, and provide proper edge treatment. Any defects or damages should be addressed before tempering to prevent further strength deterioration.

tempered glass surface stress

Thermal cracking

Thermal cracking is a common issue in tempered glass caused by excessive temperature differences between the surface and interior of the glass. This phenomenon can occur at various stages of the glass tempering process, including heating, quenching, cooling, or even after tempering is complete. The causes of thermal cracks may vary depending on the process stage.


Tempered glass spontaneous breakage refers to the automatic explosion without external force. This is one of the inherent characteristics of tempered glass and can happen during processing, storage, transportation, installation, and use. The reasons for the self-explosion of tempered glass can generally be divided into three categories. First, glass quality defects are one of the leading causes of self-explosion, including stones, impurities, surface defects, etc. Second, uneven or offset stress distribution can cause the glass to self-explode. Finally, uneven tempering may also be one of the reasons for glass self-explosion.

It should be noted that even if production is by standards, it is impossible to avoid tempered glass spontaneous breakage altogether. There is a high probability of nickel sulfide and heterogeneous impurities in hundreds of tons of glass used in large buildings. Therefore, unexpected breakage is somewhat inevitable. In addition, the sources of uncontrollable spontaneous breakage in tempered glass are not only the traditional understanding of nickel sulfide particles but also many other foreign substances. Designing large plate sizes, missing positioning pads and rubber strips during installation, and uneven heating can all increase the risk of spontaneous glass breakage. In conclusion, tempered glass spontaneous breakage is a complex problem, and many factors can cause this phenomenon.


In conclusion, understanding the potential quality defects of tempered glass and taking appropriate measures to prevent them is essential to ensure the safety and reliability of the glass in various applications. It is vital to prioritize quality control and address any issues promptly to avoid compromising the performance of tempered glass.