Multi-Stage Glass Tempering with Varying Heat Transfer Rates
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Solution Overview
Problem
Conventional thermal tempering processes are limited in achieving high surface compression and center tension in glass sheets, which restricts the production of highly tempered glass suitable for applications like hurricane-resistant windows and aircraft glass, due to processing methods that do not allow for sufficient heat transfer optimization.
Innovation Solution
A multi-stage tempering process involving quench stations with varying heat transfer rates, where the glass is initially cooled at a first heat transfer rate and then at a higher rate at subsequent stations, allowing for increased surface compression and center tension without causing glass breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional single-stage thermal tempering is used, then the glass achieves basic tempering with moderate surface compression and center tension, but the tempering level is limited and insufficient for high-strength applications like hurricane-resistant windows
Solution Approach 1:
The tempering process is divided into multiple sequential quenching stages, each with different heat transfer rates. The glass sheet passes through several quenching zones where the heat transfer coefficient is progressively increased, allowing the surface compression and center tension to be built up in stages rather than all at once, thereby achieving high tempering levels without excessive process complexity
Solution Approach 2:
The heat transfer rate parameter is systematically varied across different quenching stages. By increasing the heat transfer coefficient from the first quenching stage to subsequent stages, the process optimizes the development of surface compression and center tension, enabling high-strength tempering that cannot be achieved with constant heat transfer rates
2Strength
If higher heat transfer rates are applied throughout the entire tempering process, then higher tempering levels are achieved, but glass breakage increases due to excessive thermal stress
Solution Approach 1:
The first quenching stage applies a moderate heat transfer rate to initially cool the glass surface and establish a controlled thermal gradient. This preliminary action prepares the glass for subsequent higher-rate quenching by reducing the temperature differential gradually, preventing excessive thermal stress that would cause breakage
Solution Approach 2:
The heat transfer rate is made dynamic rather than static, progressively increasing from the first quenching stage to subsequent stages. This dynamic adjustment allows the process to adapt to the changing thermal state of the glass, applying higher cooling rates only when the glass can withstand them, thereby maximizing tempering level while minimizing breakage
3Strength
If multi-stage quenching with varying heat transfer rates is implemented, then significantly higher tempering levels are achieved, but the process complexity and equipment requirements increase
Solution Approach 1:
The quenching system is segmented into multiple independent zones, each capable of delivering a specific heat transfer rate. This segmentation allows the complex tempering profile to be achieved through simpler, modular zones rather than requiring a single complex system, making the increased complexity manageable and implementable
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
The process achieves significantly higher tempering levels than conventional methods, producing glass with enhanced strength and fracture resistance suitable for demanding applications while minimizing breakage and maintaining optical quality.
Implementation Method 1
cooling the glass sheet at a first heat transfer rate, e.g., using a first heat transfer coefficient, at a first quench station, and cooling the glass sheet at a second heat transfer rate at a second quench station
Implementation Method 2
glass sheets are heated to an elevated temperature above the glass strain point near the glass softening point and then are chilled to cool the glass surface regions relatively rapidly while the inner regions of the glass cool at a slower rate
Data Source
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AI summary
A method of tempering a glass sheet heated to a tempering temperature includes cooling the glass sheet at a first heat transfer coefficient at a first quench station and cooling the glass sheet at a second heat transfer coefficient at a second quench station downstream of the first quench station. The second heat transfer coefficient is greater than the first heat transfer coefficient. In a multistage process of the invention, a plurality of quench stations could be used with each downstream quench station having a larger heat transfer coefficient than the previous upstream quench station.