Thermal Pre-stressing Small Glass Tubes Using Nested Cooling
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Solution Overview
Problem
Existing methods for thermally pre-stressing small glass objects, such as tubes, ampoules, and syringes, are inefficient due to rapid cooling and difficulty in achieving sufficient temperature differences, especially when using gaseous cooling agents, which limits the strength increase and is unsuitable for objects with small diameters and thicknesses.
Innovation Solution
A device and method that simultaneously directs a cooling agent against both the outer and inner surfaces of small glass objects using a coaxial arrangement of nozzles, with some nozzles angled for improved cooling, and a rotary drive for uniform stress distribution, allowing for effective thermal pre-stressing of small glass objects with gas as the cooling agent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gaseous cooling agents are used for thermally pre-stressing small glass objects, then the process is cleaner and faster, but sufficient temperature differences cannot be achieved due to rapid cooling and small heat capacity
Solution Approach 1:
The patent employs a nested structure with an inner cooling agent guide positioned inside the outer cooling agent guide. The inner guide directs cooling agent through the interior of the glass object, while the outer guide directs cooling agent against the exterior surface. This nested arrangement enables simultaneous internal and external cooling, creating sufficient temperature differences without requiring excessive cooling speeds, thus resolving the contradiction between productivity and temperature control.
Solution Approach 2:
The patent transitions from single-surface cooling to multi-dimensional cooling by introducing cooling agent delivery from both the interior and exterior surfaces. The inner cooling agent guide introduces cooling from the inside dimension, while the outer cooling agent guide provides cooling from the outside dimension. This dual-dimensional approach enables effective temperature control in small glass objects with limited heat capacity, achieving both sufficient temperature differences and efficient processing.
2Device complexity
If cooling air is blown against the outer surface only, then the device structure is simpler, but uniform stress distribution cannot be achieved
Solution Approach 1:
The patent segments the cooling function into two independent subsystems: an inner cooling agent guide for internal cooling and an outer cooling agent guide for external cooling. Each subsystem can be independently designed and positioned, allowing optimized cooling patterns for uniform stress distribution. The segmented structure achieves superior stress uniformity while maintaining reasonable device complexity through modular design.
Solution Approach 2:
The patent applies local quality by positioning cooling agents at specific locations and directions. The inner cooling agent guide introduces cooling at the interior surface, while the outer cooling agent guide positions cooling at the exterior surface. By controlling the local application of cooling agents at different positions and orientations, the patent achieves uniform stress distribution throughout the glass object, resolving the contradiction between device simplicity and manufacturing precision.
3Adaptability or versatility
If thin-walled small glass objects are pre-stressed, then the application range is expanded, but achieving sufficient temperature differences becomes difficult due to small thickness and low heat capacity
Solution Approach 1:
The nested dual-guide structure enables simultaneous internal and external cooling, creating temperature differences throughout the thin-walled small glass objects. The inner cooling agent guide penetrates the thin wall to cool the interior surface, while the outer cooling agent guide cools the exterior surface. This nested cooling approach effectively creates sufficient temperature differences in thin-walled objects with low heat capacity, expanding the application range without compromising temperature control.
Solution Approach 2:
The patent adds the internal dimension of cooling by introducing the inner cooling agent guide that delivers cooling agent through the thickness of the glass wall. This dual-dimensional cooling approach (internal + external) creates effective temperature gradients in thin-walled objects, enabling successful thermal pre-stressing of small glass objects with small thicknesses that would otherwise be difficult to treat due to their low heat capacity.
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 achieves a significant increase in strength comparable to chemical pre-stressing, with reduced probability of failure and local stress variations, effectively pre-stressing glass objects with diameters as small as 1-20 mm and wall thicknesses of 0.5-5 mm, enhancing their durability and resistance to pressure.
Implementation Method 1
In thermal pre-stressing of glass, used especially for flat glass or curved glass, the finished cut plates are conveyed into a device, in suspended or flat condition, where their surface is heated up quickly to a temperature of approximately 150 degrees above transformation temperature. Immediately thereafter, cold air is blown against the glass by a nozzle system adapted to the glass shape. As a result of the quick cooling-down process, the glass surface is frozen in an expanded-grating condition, while the interior of the glass has time to cool down slowly and to contract more effectively. Given the fact that the surface and the interior of the glass form a single unit, the result is a pressure pre-stress in the surface layer and a tension pre-stress in the interior of the glass.
Implementation Method 2
the glass surface is frozen in an expanded-grating condition, while the interior of the glass has time to cool down slowly and to contract more effectively
Data Source
AI summary
A device and a method for thermal pre-stressing lengthy hollow objects, in particular glass tubes, are disclosed. The device comprises a heating device, a fixture for receiving an object, and a coolant feed device comprising an outer coolant feed unit with a plurality of nozzles for feeding coolant against an outer surface of the object, and further comprising an inner coolant feed device for feeding coolant against an inner surface of the object.