Ceramic Heater Recessed Resistor Thermal Stress
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Solution Overview
Problem
Conventional ceramic heaters are prone to cracking due to thermal stress caused by significant differences in thermal expansion coefficients between the heat generating element and the base body, especially under abnormal conditions of substantial electric current flow.
Innovation Solution
The ceramic heater design features rectilinear portions with concavely recessed inner elliptical arc sides, which increase the opposing surface area and distribute stress through a cushioning effect, preventing cracks by relaxing thermal expansion stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the heat generating element and base body are made of materials with different thermal expansion coefficients, then the heater can be constructed with conventional materials, but thermal stress causes cracks in the base body
Solution Approach 1:
The patent changes the geometric parameters of the heat generating element by forming recesses in its outer peripheral surface. This parameter modification allows the element to accommodate thermal expansion differences without generating excessive stress, thereby preventing cracks while maintaining conventional material selections.
Solution Approach 2:
The recesses are pre-formed in the heat generating element before assembly with the base body. These recesses act as cushioning features that absorb thermal expansion stress during operation, preventing stress concentration and crack formation at the interface between the heat generating element and base body.
2Power
If substantial electric current flows under abnormal conditions, then the heater can provide sufficient heating power, but great thermal stress develops causing cracks
Solution Approach 1:
The recesses in the heat generating element serve as pre-designed stress-absorbing features that become particularly effective under abnormal high-current conditions. When substantial current flows and generates excessive heat, the recesses cushion the resulting thermal expansion stress, preventing crack formation even during transient overload conditions.
Solution Approach 2:
By modifying the geometric parameters of the heat generating element through recess formation, the patent creates a structure that can handle both normal and abnormal operating conditions. The recesses increase the surface area and create stress distribution paths that prevent crack initiation during high-power operation.
3Device complexity
If the inner sides of rectilinear portions are straight lines, then the structure is simple, but stress from volume expansion concentrates causing cracks
Solution Approach 1:
The patent replaces straight-line inner sides with curved surfaces featuring recesses in the heat generating element. This curvature modification allows stress from volume expansion to distribute more evenly along the curved surface, preventing stress concentration at sharp edges or corners that would occur with straight-line geometries.
Solution Approach 2:
The invention changes the geometric parameters of the heat generating element's inner surface from linear to curved with recesses. This parameter change maintains relatively simple manufacturing processes while dramatically improving stress distribution characteristics and preventing crack formation.
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 design effectively suppresses crack development in the ceramic base body, enhancing the heater's durability and reliability under sudden voltage applications.
Implementation Method 1
a heat generation section (2) composed of a bend portion (2c) and two rectilinear portions (2a and 2b)
Implementation Method 2
since the material of construction of the heat generating element is commonly greater in thermal expansion coefficient than the material of construction of the base body, there is the possibility that a crack will appear in the base body due to a thermal stress generated between these materials
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
[Problem] Provided is a highly durable ceramic heater capable of suppressing development of cracks in a base body resulting from a difference in thermal expansion between the ceramic-made base body and a heat generating element. [Solution] A ceramic heater of the invention includes a ceramic base body (1) and a heat generating resistor including a heat generation section (2) composed of a bend portion (2c) and two rectilinear portions (2a, 2b) extending from opposite ends of the bend portion (2c), respectively, the heat generating resistor being embedded within the ceramic base body (1). The two rectilinear portions (2a, 2b) include inner sides opposed to each other in a transverse section, and the inner sides include recesses (5) in at least a midportion.