From the Perspective of Glass Factories: A Full-Chain Effort to Safeguard the Safety of Curtain Wall Glass
As the core material manufacturer for glass curtain walls, glass factories are not only the creators of the "crystal clothing" for modern buildings but also bear the crucial responsibility of ensuring the safety of glass curtain walls and preventing the risk of glass breakage. Strict control over every link, from raw material selection and production process management to quality inspection and technological innovation, directly affects the safe service life of downstream glass curtain wall buildings. Faced with the hidden dangers of glass breakage caused by factors such as thermal stress and nickel sulfide impurities, glass factories need to build a safety defense line with a full-chain mindset, ensuring that every piece of glass leaving the factory can withstand the test of the natural environment and time.
Raw Material Control: Eliminating "Invisible Killers" from the Source
The quality of glass starts with the purity of raw materials. For curtain wall glass, impurities in raw materials (especially nickel sulfide) are "invisible killers" that lead to subsequent glass breakage, and the raw material control system of glass factories is the first line of defense against this risk. In the raw material procurement process, we have established a strict supplier qualification system. For core raw materials such as quartz sand, soda ash, and dolomite, we require suppliers to provide third-party inspection reports, with a focus on verifying the content of nickel and sulfur elements (nickel content must be controlled below 0.005% and sulfur content not exceeding 0.01%). Raw materials that do not meet the standards are firmly rejected for storage.
After raw materials are delivered to the factory, they must undergo a "secondary screening": X-ray fluorescence spectrometers are used to test the composition of each batch of raw materials to ensure that the content of trace elements meets the standards accurately; for quartz sand that is prone to impurity contamination, a dual process of magnetic separation and water washing is adopted to remove foreign substances such as metal particles and slag that may be present in the raw materials. In addition, during the raw material mixing stage, we have introduced "homogenization control technology". Through a computerized automatic proportioning system, different raw materials are mixed in precise proportions and undergo more than 3 homogenization treatments to avoid fluctuations in the internal composition of glass caused by uneven distribution of raw materials, thereby reducing the probability of nickel sulfide impurity formation at the source.
On one occasion, the nickel content of a batch of quartz sand was close to the critical standard. Although it did not exceed the national standard, we resolutely sealed this batch of raw materials and negotiated with the supplier for return or replacement to ensure absolute safety. "Prioritizing the elimination of hidden dangers over securing orders" is a principle we have always adhered to in raw material control. Because we are well aware that a raw material defect in a single piece of glass may lead to a high-altitude glass breakage safety accident after several years or even decades.
Process Optimization: The "Technical Code" for Resisting Thermal Stress
Thermal stress is one of the core causes of glass curtain wall breakage, and the production process of glass factories directly determines the ability of glass to resist thermal stress. To address this issue, we have focused on two key links—glass forming and tempering—and improved the thermal stress resistance of glass through process optimization.
In the glass forming stage, we adopt the "float glass ultra-thin tin bath control technology". By accurately adjusting the temperature gradient in the tin bath (controlling the temperature difference within ±2°C), we ensure that the temperature of the glass ribbon is uniform during the cooling process, avoiding internal stress caused by local rapid cooling. Meanwhile, after the glass exits the tin bath, a "slow cooling annealing process" is introduced: the glass is slowly sent to an annealing furnace and cooled from 600°C to room temperature at a rate of 5°C per hour, allowing the internal stress of the glass to be fully released. The float glass treated with this process has an internal residual stress value that can be controlled below 15MPa, far lower than that of glass produced by ordinary processes (residual stress is approximately 30MPa), laying a solid foundation for subsequent processing into curtain wall glass with excellent thermal stress resistance.
For tempered glass commonly used in curtain walls, we have further upgraded the tempering process parameters: the heating temperature of the tempering furnace is stabilized at 680-700°C (compared to 650-670°C in traditional processes), and the heat preservation time is extended to 5 minutes to ensure the full uniformity of the internal crystal structure of the glass; in the cooling stage, the "graded air quenching technology" is adopted. Through computer control of the cooling air speed in different areas (the air speed at the edges is 15% higher than that at the center), we avoid "edge stress concentration" caused by uneven cooling of the glass—a key pain point that makes the edges of glass prone to cracking under the action of thermal stress. Tests have shown that the tempered glass after optimization has a 25% improvement in thermal shock resistance and can maintain structural stability even in a sudden temperature change environment from -20°C to 80°C, effectively reducing the risk of glass breakage caused by thermal stress.
Quality Inspection: Issuing a "Safety ID Card" for Each Piece of Glass
"Every piece of curtain wall glass leaving the factory must be accompanied by a 'safety ID card'." This is a rigid requirement we have for the quality inspection process. To fully identify potential hazards of glass, we have built a "three-level inspection system" to achieve full-process and gap-free monitoring from production to finished products leaving the factory.
First Level: Online Real-Time Inspection — During the glass forming process, laser thickness gauges and surface defect detectors are used for real-time monitoring of glass thickness deviation (controlled within ±0.2mm), surface scratches (depth not exceeding 0.01mm), and bubbles (bubbles with a diameter larger than 0.3mm are not allowed). If any problem is found, the machine is shut down immediately for adjustment to prevent unqualified glass from entering the next process.
Second Level: Offline Special Inspection — For tempered glass, 3% of samples are randomly selected from each batch for "homogenization treatment testing": the samples are placed in a homogenizing furnace at 290°C for 2 hours to accelerate the phase transformation of nickel sulfide impurities. If there is a nickel sulfide hazard, the glass will break in advance during the test, and the entire batch of products must be re-inspected. At the same time, the samples are subjected to bending strength testing (the applied force must reach more than 120MPa) and thermal stress simulation testing (repeatedly soaking in 80°C hot water and 20°C cold water for 5 times, with no cracks as the qualification standard) to ensure that the mechanical properties and thermal stress resistance meet the requirements.
Third Level: Finished Product Delivery Inspection — Before each piece of curtain wall glass leaves the factory, it must undergo "identity coding": laser marking technology is used to mark the production batch, production date, and inspector number on the corner of the glass for easy subsequent traceability. At the same time, quality inspectors conduct a re-inspection of the appearance and a review of the dimensions, and issue a "Product Quality Certificate" containing all test data. Unqualified products are destroyed without exception and are never allowed to enter the market.
In 2023, a construction enterprise purchased a batch of curtain wall glass for use in coastal areas from us. During the offline inspection, 2 samples showed tiny cracks in the homogenization test. We immediately conducted a full inspection of the 1,200 pieces of glass in this batch, and finally identified and destroyed 8 pieces of glass with nickel sulfide hazards. Although this resulted in a loss of nearly 100,000 yuan, we believe this is the responsibility that glass factories must bear—because we cannot allow any piece of glass with hidden dangers to become a "sharp blade" falling from high altitudes.
Technical Services: From "Selling Products" to "Solving Problems"
With the diversification of glass curtain wall application scenarios (such as coastal areas with high temperature and humidity, and plateau areas with strong sunlight), a single type of glass product can no longer meet the safety needs in different environments. For this reason, we have transformed from a "product supplier" to a "technical service provider", providing downstream customers with customized glass solutions to help them avoid the risk of glass breakage from the design stage.
For areas with strong sunlight where thermal stress is a prominent issue, we recommend the "Low-E coating + insulated glass" combination solution to customers. The Low-E coating can reflect more than 60% of infrared rays, reducing the heat absorbed by the glass and lowering the temperature difference between the inside and outside. The insulated layer is filled with inert gas (such as argon) to further improve thermal insulation performance, controlling the temperature difference between the inside and outside of the glass within 20°C and significantly reducing the probability of thermal stress generation. At the same time, we provide detailed technical parameter manuals to guide customers in selecting the appropriate glass thickness (for example, 8mm or thicker tempered glass is recommended for east-facing curtain walls) and insulated layer thickness (12mm or thicker is recommended) based on the building orientation and local climate conditions.
In the installation process, we also send technical engineers to the site to provide guidance: regarding the gap between the glass and the frame, the thermal expansion coefficient of the glass (9.0×10⁻⁶/°C for ordinary glass) is used to calculate the expansion and contraction amount in different temperature ranges, and customers are advised to reserve a gap of 12-15mm (20% more than the conventional standard); regarding the selection of structural adhesive, compatibility test reports are provided to ensure that the bonding strength between the structural adhesive and the glass reaches more than 0.6MPa, avoiding glass displacement and breakage caused by adhesive layer failure.
In addition, we have established an "after-sales tracking system"—for curtain wall glass leaving the factory, free performance sampling inspections are conducted every 3 years (using drones equipped with infrared thermometers to detect the internal stress distribution of the glass), and maintenance suggestions are provided to customers (such as the replacement cycle of aged sealant and precautions for glass surface cleaning), forming a closed loop of "production-service-maintenance" to ensure that customers can use the products with confidence and for a long time.
Future Directions: Strengthening the Safety Defense Line through Innovation
Faced with new challenges in the field of glass curtain wall safety, glass factories have never stopped innovating. Currently, we are focusing on research and development in two major directions to fundamentally solve the problem of glass breakage from a technical perspective.
The first is the research and development of "intelligent stress-monitoring glass". During the glass production process, micro-fiber optic sensors are embedded inside the glass. These sensors can collect real-time data on thermal stress and mechanical stress inside the glass and transmit the data to a cloud platform via wireless signals. When the stress value approaches the critical point, the platform will automatically send an early warning message to the customer, reminding them to replace the glass in a timely manner. At present, this product has been applied in a pilot project, with a monitoring accuracy of ±5MPa, providing a new "real-time monitoring" solution for the safety of glass curtain walls.
The second is the exploration of "self-healing glass materials". A special polymer repair coating (mainly composed of epoxy-based siloxane) is applied to the glass surface. When tiny cracks (with a width of less than 0.1mm) appear on the glass, the active components in the coating will automatically polymerize under ultraviolet radiation to fill the crack gaps and prevent crack expansion. Experimental data shows that the crack resistance of glass coated with this coating is improved by 40%, and it can effectively delay glass breakage even under repeated thermal stress effects.
The research and development of these innovative technologies are not only aimed at enhancing product competitiveness but also at fulfilling the social responsibility of glass factories. We hope that through technological breakthroughs, glass curtain walls will no longer become urban safety hazards due to issues such as thermal stress and impurities, and that the "crystal clothing" of every high-rise building can remain shiny and safe at all times.
Conclusion: Guarding the Urban Skyline with Dedication
From raw material selection and process optimization to quality inspection and technical services, every effort made by glass factories is adding to the safety of glass curtain walls. We are well aware that a small piece of glass not only meets the aesthetic needs of buildings but also is related to the lives and property safety of countless people. In the future, we will continue to take "zero defects" as our production goal, driven by innovation, control every link from the source, provide safer and more reliable curtain wall glass products for downstream customers, and work together with construction enterprises and regulatory authorities to jointly guard the safety and beauty of the urban skyline. Because we firmly believe that only when every piece of glass can withstand the test can the "crystal clothing" of the city truly become a safe "protective clothing".
