LAS Glass-Ceramic Ceramization for Shape Control
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Solution Overview
Problem
The production of large-format or very thin-walled glass-ceramic objects is challenging due to volume changes during the ceramization process, leading to uncontrolled stresses, low impact resistance, and difficulties in maintaining shape integrity, especially with high heating rates and precise process control required for achieving desired mechanical and chemical properties.
Innovation Solution
A method involving high heating rates and short or no holding times at maximum temperature, combined with uniform heating and rapid cooling, to produce glass-ceramic objects with a unique microstructure comprising multiple crystalline phases and an amorphous surface layer, which reduces internal stresses and maintains shape fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high heating rates are used to increase productivity, then production efficiency is improved, but internal stresses and deformation increase making production difficult
Solution Approach 1:
The patent applies parameter changes by precisely controlling heating rate, holding time, and cooling rate to resolve the contradiction between productivity and shape control. Specifically, using high heating rates (10-50°C/min) combined with short holding times (0.5-2 hours) at peak temperature allows rapid transformation while minimizing deformation, achieving both high productivity and manufacturing precision
Solution Approach 2:
The patent implements dynamics by making the heating and cooling rates adjustable and optimized for different object types. The process dynamically adapts parameters: faster heating for robust objects, slower heating for thin-walled objects, with corresponding adjustments in holding time and cooling rate to maintain shape fidelity while maximizing production efficiency
2Manufacturing precision
If holding time at maximum temperature is extended to reduce deformation, then shape stability is improved, but production time increases reducing productivity
Solution Approach 1:
The patent resolves this contradiction through parameter changes by optimizing the holding time at maximum temperature to a specific range (0.5-2 hours) rather than using extended holding times. This optimized holding period is sufficient to allow stress relaxation and reduce deformation while being short enough to maintain high productivity, achieving both shape stability and production efficiency
3Illumination intensity
If ceramization temperature is increased to achieve high white value, then optical properties are improved, but impact resistance decreases due to crack network formation
Solution Approach 1:
The patent applies parameter changes by optimizing the ceramization temperature to a specific range (900-1300°C) rather than using excessively high temperatures. This optimized temperature range achieves the required white value (L* > 90) while avoiding the formation of extensive crack networks, thereby maintaining both optical properties and impact resistance
Solution Approach 2:
The patent implements periodic action through controlled heating and cooling cycles with specific rates. The heating rate (10-50°C/min) and cooling rate are optimized to allow uniform transformation and stress distribution, achieving high white value without creating the crack networks that would reduce impact resistance
4Productivity
If transformation speed is increased to improve productivity, then production efficiency is improved, but internal stresses increase making stress control difficult
Solution Approach 1:
The patent resolves this contradiction through parameter changes by optimizing the heating rate (10-50°C/min) and holding time (0.5-2 hours) to achieve a balanced transformation speed. This optimized parameter combination maintains high productivity while allowing uniform transformation throughout the object, preventing excessive internal stress accumulation
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 results in glass-ceramic products with enhanced impact resistance, acid resistance, and temperature difference strength, while maintaining shape integrity and reducing warping, enabling their use in applications requiring high mechanical and chemical stability.
Implementation Method 1
a new crystal phase is created. This conversion is always associated with a change in volume of the object to be ceramicized. Since the transformation and thus the change in volume in different areas of the object occurs at different times and at different speeds, voltages are induced between different areas of the object
Implementation Method 2
Since the high-quartz mixed-crystal phase has a lower thermal expansion than the keatite mixed-crystal phase, compressive stress is induced in the surface areas during cooling following the phase transformation
Implementation Method 3
the precursor object is heated to a maximum temperature, with at least 80% of the volume change that the precursor object undergoes during the transformation of the high-quartz solid solution phase into the keatite solid solution phase of the glass-ceramic comprising object, occurring within a one to six minutes, preferably within one to four minutes and particularly preferably within one to two minutes
Implementation Method 4
the precursor object is heated to a maximum temperature... and preferably between one and two minutes... After the maximum temperature has been reached, the precursor object is cooled without maintaining a hold time at the maximum temperature
Data Source
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AI summary
The invention relates to high-performance glass ceramics and to a method for producing said glass ceramics. A glass or glass ceramic material is used as starting material, which may be a lithium-aluminium silicate (LAS) having a composition within the following limit values in weight %: 60-73 SiO2, 15-25 Al2O3, 2.2-5 Li2O, 0-5 CaO+SrO+BaO, 0-5 TiO2, 0-5 ZrO2, >0-4 ZnO, 0-3 Sb2O3, >0-3 MgO, 0-3 SnO2, 0-9 P2O5, 0-1.5 As2O3, >0-1 Na2O, >0-0.5 K2O, >0-1.2 Na2O+K2O and 0-1 colouring oxides. The green body is subjected to a thermal treatment for ceramization: room temperature 660°C at a heating rate of > 15 K/min, e.g. within 11 min at 58 K/min; up to about 20 min process time with the slow reduction of the heating rate to zero; 30 min constant at 790°C; heating to maximum temperature (1080-1300°C) at >10 K/min, e.g. 30 K/min; no holding time at maximum temperature; cooling to 400°C at a cooling rate of 15-350 K/min; cooling to room temperature. During tempering the temperature at the workpiece is preferably registered by sensors having a response time of less than 10 s. The kiln regulates the temperature accordingly with a response time of at most 10 s. The LAS glass ceramics produced in this way is characterised in the non-reworked state or processed state inter alia by a high impact resistance in the falling ball test of more than 15 cm (e.g. 56 ± 13 cm), an acid resistance according to DIN 12116 of 1 or 2 (e.g. 1) and a resistance to temperature differences (RTD) of more than 700°C. It is suitable as inter alia an oven cladding, oven window, stove top, chemically resistant laboratory vessel, white goods, translucent article with UV protection, etc.