Borosilicate Windshield Glass Densification for Thermal Shock
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Solution Overview
Problem
Conventional glass compositions, such as soda-lime glass, are susceptible to thermal shock and cracking when used as thicker outer glass plies in laminates for automotive applications, and they fail to provide adequate impact resistance and fuel efficiency due to their density and thermal expansion properties.
Innovation Solution
A borosilicate glass composition with a minimum of 74 mol % SiO2, 10 mol % B2O3, and Al2O3, resulting in a liquidus viscosity greater than 500 kP and a temperature at which viscosity is 200 Poise at 1725° C or less, is developed for fusion forming, providing enhanced strength and resistance to thermal shock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If soda-lime glass is used as a thicker outer glass ply, then the glass provides adequate optical clarity, but it is susceptible to thermal shock and cracking upon impact
Solution Approach 1:
The patent changes the chemical composition parameters of the glass by incorporating borosilicate glass with specific oxide ratios (SiO2: 70-80 wt%, B2O3: 10-20 wt%, Al2O3: 3-7 wt%). This compositional parameter change results in modified physical properties including lower thermal expansion coefficient and improved thermal shock resistance while maintaining adequate impact resistance for automotive applications
Solution Approach 2:
The patent creates a composite glass material by combining multiple oxide components (silica, boron oxide, aluminum oxide, and controlled amounts of alkali and alkaline earth oxides) to form a borosilicate glass system. This composite material structure provides synergistic effects that simultaneously improve thermal shock resistance and maintain mechanical strength for use as outer glass plies in automotive laminates
2Strength
If a thicker glass ply is used to improve impact performance, then impact resistance is enhanced, but fuel economy deteriorates due to increased weight
Solution Approach 1:
The patent utilizes the lower density inherent in borosilicate glass composition (typically 2.2-2.4 g/cm³ compared to 2.5-2.6 g/cm³ for soda-lime glass) to reduce the weight of thick glass plies. This parameter change in material density allows achieving the required impact performance with reduced mass, thereby improving fuel economy in automotive applications
3Reliability
If borosilicate glass composition is used, then thermal shock resistance and strength are improved, but manufacturing complexity increases due to fusion forming requirements
Solution Approach 1:
The patent optimizes the viscosity parameters of the borosilicate glass composition by controlling the ratio of oxide components, specifically achieving a liquidus viscosity greater than 500 kP and a T200P temperature of 1725°C or less. These parameter changes enable the glass to be successfully fusion formed at relatively large thicknesses (2-6 mm) using conventional manufacturing equipment, thereby reducing manufacturing complexity despite the advanced material composition
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 borosilicate glass composition densifies upon deformation, preventing the spread of cracks and offering improved thermal shock resistance, which enhances the strength and durability of glass plies in laminates, while also offering weight savings for improved fuel efficiency.
Implementation Method 1
The borosilicate glass composition densifies upon deformation, preventing the spread of cracks
Implementation Method 2
the borosilicate glass composition has a liquidus viscosity of greater than 500 kP and a temperature at which a viscosity of the borosilicate glass composition is 200 P of 1725° C. or less
Implementation Method 3
susceptible to thermal shock and to cracking upon impact
Data Source
AI summary
Disclosed herein are embodiments of a borosilicate glass composition as may be useful for windshield and other applications in particular due to unique fracture behavior.