How to ensure the "vacuum life" of vacuum glass

As an important innovative material in the field of building energy conservation, vacuum glass has its core performance index "vacuum life" that directly determines the actual use effect and value of the product. Based on the authoritative book "Vacuum Glass" by Professor Tang Jianzheng, the inventor of vacuum glass, combined with the latest industry data and technological development, this paper systematically expounds the key elements to ensure the vacuum life of vacuum glass, and provides practical reference for practitioners and designers in the door, window and curtain wall industry.

First, the basic concept and importance of vacuum life

The life of vacuum glass can be divided into mechanical life and vacuum lifeTwo major types. The mechanical life refers to the life of the glass without cracking under the action of self-weight, wind load and temperature difference. Vacuum life, on the other hand, refers to the life of maintaining the internal vacuum level without failing. For architectural applications, vacuum life is particularly critical, as once the vacuum level is reduced to more than 10 Pa (one ten-thousandth of an atmosphere), the thermal insulation benefits are lost.

In his research, Professor Tang Jianzheng clearly pointed out that vacuum glass is based on the principle of a thermos flask, which seals two pieces of glass around to form a vacuum layer of 0.15mm, and achieves excellent thermal insulation performance by eliminating gas heat transfer. China's patented technology has successfully solved the problem of oxidation failure of getter in traditional vacuum glass, so that the service life of the product can reach 50 years. The national standard GB/T 38586-2020 stipulates that the vacuum degree of qualified vacuum glass shall not be less than 1Pa, and the average thermal conductivity of the center part shall not be greater than 0.005W/(m²K).

Second, the four key factors affecting the life of the vacuum

1. Material penetration and leakage

• Edge banding material: The vacuum glass is melt sealed with low melting point glass powder commonly used in electric vacuum devices, and the leakage rate of the sealing material is ≤10⁻¹²Pa·m³/s, which has been verified by more than half a century of practice。

2. Degassing of the inner surface of the glass

The glass surface and body contain a large number of gases (more than 90% of which are H₂O, the rest are CO₂, O₂, etc.), which are desorbed into the vacuum layer under the action of temperature and light. Studies have shown that there are two distinct peaks of outgassing during the baking and exhausting of glass: 100-200°C and 300-400°C.

3. Production process control

• High-temperature baking and degassing: The vacuum glass needs to be baked and exhausted at about 350°C for more than 1 hour, and sealed when the vacuum degree is better than 1.0×10⁻⁴Pa。
• Support arrangement: Metal or ceramic supports with a diameter of 0.3-0.5mm need to evenly disperse the atmospheric pressure of about 10 tons/㎡ to avoid local stress concentration。

4. Environmental stress effects

• Temperature difference fluctuation: The metal edge banding material can withstand the temperature difference on both sides of the glass due to its flexibility, and overcome the sealing failure problem caused by the temperature difference of brittle sealing materials。
• Ultraviolet radiation: Long-term exposure to the sun will accelerate the aging of materials, and the use of Low-E coating can effectively reduce the impact of radiation。

3. Five technical measures to ensure the life of the vacuum

1. High temperature exhaust and getter technology

Professor Tang Jianzheng's team made a breakthrough in using the "encapsulation" technology to solve the problem of oxidation failure of getter in the process of high-temperature production. The getter used in modern vacuum glass can quickly increase the vacuum level and maintain it for a long time, and its technical principle is in the same vein as electric vacuum devices such as picture tubes.

2. Advanced sealing technology

• Metal edge banding technology: the use of Kovar alloy and other materials through high temperature sintering to form chemical bonding, air tightness leakage rate ≤ 1×10⁻⁻⁹Pa·m³/s, anti-aging ability far beyond organic glue
• Lead-free solder: in line with EU ROHS environmental protection standards, avoid lead contamination and ensure sealing strength

3. All-toughening process innovation

The low-temperature sealing technology realizes the mass production of fully tempered vacuum glass, avoids the annealing of tempered glass, increases the strength by more than 5 times, and resists wind pressure up to 4000Pa.

4. Intelligent manufacturing and quality control

China's first vacuum glass intelligent manufacturing production line uses more than 2,000 sensors to achieve automated mass production, and the key process parameters include:

• The fluctuation of edge banding width is controlled within ±0.1mm
• The spacing error of the support ≤ 0.05mm

The in-house inspection items include heat transfer coefficient testing, support integrity testing, edge banding adhesion testing, etc., to ensure product consistency.

5. Composite structure design

Improve the comprehensive performance through the "vacuum+" composite technology:

• Vacuum + lamination: sound insulation≥41dB, strength up to 3-5 times of ordinary glass
• Vacuum + hollow: The warm edge structure raises the critical temperature of condensation on the window frame to -30°C