Overview
Designing the ideal heating element configuration (HEC) for gravity bending requires understanding of infrared (IR) heating physics and the specific product parameters. A well-designed HEC achieves the required glass shape efficiently, with high quality, and reliably reproduces results.
Core Physical Principles
- IR radiation impact to glass is challenging to estimate, especially across varying distances.
- Heating element output doesn’t linearly translate to radiation power the glass receives, further complicating control.
- Higher general bending chamber ambient temperatures increase localized IR power requirements.
- Roof heating elements affects multiple glass areas due to scattered radiation.
- IR penetrates the very surface of the glass only influencing temperature distribution through the thickness.
Key HEC Influencing Factors
- Product Characteristics: Complex shapes and thicknesses demand fine HEC tuning. For example:
- Thick Glass: Needs more heating time, and mass complicates handling and increases over-bend risks.
- Thin Glass: Needs more attention to glass temperature and profile stability. Especially, in asymmetric solutions to avoid over heating causing optical and glass stress issues, even spontaneous glass breakages.
- Special Glass Types: For example, borosilicate, and aluminosilicate, behave differently under IR-heating and require different type of processing temperatures but also heating element configurations.
- Complex Edges: Require corner-specific heating element set-up to retain shape.
- Furnace Design: Each furnace, even in the same facility, has unique traits impacting HEC. For single-chamber furnaces, characteristics may vary at the wagon level.
- Mold Tooling: Mold mass and design influence HEC. Initial HEC trials must account for these features.
Designing Initial HEC
Start with an evaluation of the product’s distinct requirements:
- Glass Type, Thickness and Geometry: Deep sagging shapes often need more intense IR heating and longer bending times.
- Printed Areas: Large printed zones absorb more heat, demanding HEC adjustments to prevent overheating.
General HEC Guidelines
Excessive general heating complicates precise IR-heating control, risking quality degradation. Opt for targeted heating to maintain shape without increasing bending time or final temperatures, which can reduce transmission optical quality and create tension related issues.
Summary
There’s no formula or software for automatic HEC setup; successful configuration relies on understanding IR heating principles and iterative adjustments. Each bending furnace and product design requires unique HEC calibration to achieve optimal results.
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