Glass Plate Tempering via Internal Heating for Deep Compressive Stress
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Solution Overview
Problem
Existing glass tempering methods, such as physical tempering, face challenges in forming deep compressive stress layers without compromising surface quality, especially when dealing with glass plates having coatings or chemically strengthened layers, and struggle to achieve balanced stress distribution across the plate thickness.
Innovation Solution
A method involving internal heating of a glass plate with a single matrix composition to at least the annealing point while maintaining the surface temperature above the strain point but below the annealing point, followed by controlled cooling, to create a deep compressive stress layer without surface deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the glass plate is heated to near the softening point for physical tempering, then a compressive stress layer is formed at the surface, but the surface quality is lowered due to traces of cooling medium or contact traces
Solution Approach 1:
The patent applies local quality by creating a temperature gradient within the glass plate thickness direction, where the surface temperature is maintained below the softening point while the internal temperature reaches near the softening point. This localized temperature distribution allows the interior to generate sufficient thermal stress for compressive layer formation while the surface remains cool enough to avoid quality degradation from cooling medium traces or contact marks.
Solution Approach 2:
The patent transitions from conventional uniform surface heating to internal heating by introducing a dimensional aspect to the temperature distribution - the temperature varies significantly through the thickness dimension of the glass plate. By heating the interior to near softening point while keeping the surface cooler, the method creates a three-dimensional temperature field that resolves the contradiction between stress formation and surface quality.
2Strength
If the glass plate is heated to near the softening point, then tempering is achieved, but coating films or chemically strengthened layers are altered and surface quality is lowered
Solution Approach 1:
The patent maintains different temperature conditions at different locations within the glass plate. The surface region, where coating films and chemically strengthened layers are present, is kept below the softening point to preserve their integrity. Meanwhile, the interior region is heated to near the softening point to achieve the necessary tempering effect, thus locally differentiating the thermal treatment to protect sensitive surface layers while still achieving bulk tempering.
3Strength
If the entire plate thickness is stress-relaxed before quenching, then uniform tempering is achieved, but the compressive stress layer depth is limited to about 1/5 of the plate thickness
Solution Approach 1:
The patent creates a non-uniform stress distribution by maintaining different temperature states across the plate thickness. The interior is heated to near the softening point where stress relaxation occurs, while the surface is kept cooler to maintain higher stress. This localized stress relaxation in the interior region allows for deeper compressive stress layer formation (at least 1/4 of plate thickness) while maintaining overall stress balance, thereby achieving both deeper compression layers and controlled stress distribution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for the formation of a deep compressive stress layer that extends to at least 22% of the plate thickness, enhancing the glass's resistance to flaws while maintaining high surface quality and compatibility with various surface treatments.
Implementation Method 1
an internal heating step of heating the internal temperature of the glass plate to be at least the annealing point, while maintaining the surface temperature of the glass plate to be higher than the strain point and at most the annealing point within 10 minutes
Implementation Method 2
a cooling step of cooling the glass plate... a physical tempering method for forming a compressive stress layer at the surface layer of a glass substrate by quenching the surface of the heated glass substrate
Data Source
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AI summary
To provide a method for tempering glass to obtain tempered glass having high surface quality and a deep compression stress layer. The present invention relates to a method for tempering a glass plate comprising a preparation step of preparing a glass plate having a surface temperature of at most the strain point, an internal heating step of heating the internal temperature of the glass plate to be at least the annealing point, while maintaining the surface temperature of the glass plate within 10 minutes, or to be at most the strain point, and a cooling step of cooling the glass plate.