Question: What is the stress standard after glass chemical strengthening?
Answer:
Chemical strengthening (also known as ion exchange strengthening) is a core process to improve the mechanical strength of glass, which is widely used in high-strength display glass, mobile phone cover glass, automotive glass and other fields. The stress index is the most critical quantitative standard to evaluate the quality and performance of chemically strengthened glass. A complete set of scientific and standardized stress standards includes surface compressive stress (CS) and stress layer depth (DOL), and different application scenarios have different grade requirements.
1. Core Concept: Surface Compressive Stress (CS)
Surface compressive stress refers to the compressive stress formed on the glass surface after ion exchange, which is the core force to resist external impact and bending. The unit is MPa (Megapascal). The higher the surface compressive stress, the stronger the ability of the glass to resist external damage such as sharp object impact and bending deformation.
- Basic Qualified Standard: For general consumer electronics glass (such as entry-level mobile phone cover glass), the surface compressive stress of qualified products must be ≥ 600MPa. This is the minimum threshold to ensure that the glass can withstand daily drop and collision.
- Mid-to-High End Standard: For mid-range smart devices and industrial control glass, the standard is 700MPa ≤ CS < 900MPa. This level of glass has better impact resistance, and can pass higher drop height tests.
- Premium Standard: For high-end mobile phones, automotive display glass and high-strength application scenarios, the surface compressive stress is required to be ≥ 900MPa. This ultra-high stress glass has extremely strong anti-drop and anti-impact capabilities, and is the highest grade in the current market.
2. Core Concept: Stress Layer Depth (DOL)
Stress layer depth refers to the depth of the compressive stress layer formed on the glass surface by ion exchange, and the unit is μm (micrometer). It directly determines the scratch resistance and long-term strength of the glass. If the stress layer is too shallow, even if the surface stress is high, the glass is easy to be scratched and the strength will drop sharply.
- Basic Qualified Standard: For conventional glass thickness (0.5mm-1.1mm), the stress layer depth of qualified products must be ≥ 10μm. This ensures basic scratch resistance.
- Mid-to-High End Standard: For products with high scratch resistance requirements, the standard is 15μm ≤ DOL < 30μm. This depth can effectively prevent surface scratches during use.
- Premium Standard: For ultra-thin glass (thickness <0.5mm) and high-strength automotive glass, the stress layer depth is required to be ≥ 30μm, and some special products even reach 40μm. This deep stress layer can ensure that the glass still maintains high strength after long-term use.
3. Industry-Unified Qualification Standards
Combined with the international optical glass industry standards (such as ISO 12799, ASTM C1036), the complete stress standards for different types of chemically strengthened glass are summarized as follows:
Glass Type Surface Compressive Stress (CS) Stress Layer Depth (DOL) Application Scenario
Soda-Lime Glass (Entry Grade) 500-700MPa 8-15μm Low-end home appliances, ordinary display panels
Aluminosilicate Glass (Mid-Grade) 700-900MPa 12-25μm Mainstream mobile phones, tablets, automotive displays
High-Strength Aluminosilicate (Premium Grade) ≥ 900MPa 20-40μm Flagship mobile phones, curved glass, automotive control panels
Ultra-Thin Strengthened Glass 600-800MPa 15-30μm Foldable devices, ultra-thin touch screens
4. Testing Principles and Unqualified Judgment
The stress of chemically strengthened glass is usually tested by a stress meter (photoelastic stress meter) based on the principle of photoelasticity:
1. Place the glass sample on the stress meter, and use polarized light to irradiate the glass.
2. The stress distribution inside the glass will change the polarization state of light, and the instrument will calculate the surface stress and stress layer depth through the obtained interference fringes.
Unqualified Judgment Criteria:
- If the surface compressive stress is lower than 500MPa, it is a serious unqualified product, and the risk of breakage during use is extremely high.
- If the stress layer depth is lower than 8μm, it is unqualified, and the glass is prone to strength degradation after being scratched.
- If the stress distribution is uneven (the difference between multiple test points exceeds 100MPa), the product is unqualified, which may cause local breakage.
5. Our Product Advantages and Process Control
As a professional optical glass manufacturer, our chemically strengthened glass strictly follows the highest industry standards, and has the following core advantages:
- Precise Process Control: The fully automated ion exchange production line strictly controls parameters such as temperature, time and salt bath concentration, ensuring that the stress index of each batch of products is within the target range, with a tolerance of ±50MPa.
- Multi-Grade Customization: We can provide stress standards of different grades according to customer needs, from entry-level 550MPa to premium 1000MPa, to meet the application requirements of different products.
- Strict Quality Inspection: Each piece of glass is equipped with a stress test report, and the pass rate of 100% sampling inspection ensures product stability.
- High Compatibility: Our stress layer depth design is perfectly matched with different glass thicknesses, which can effectively avoid the problem of glass warping or delamination caused by excessive stress.
In summary, the stress standard after glass chemical strengthening is not a single value, but a combination of surface compressive stress and stress layer depth. Only when both indicators meet the standard can the glass have reliable mechanical strength and service life.
