Honeycomb Filter Coating Structure for Thermal Shock Resistance
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Solution Overview
Problem
Honeycomb filters with outer peripheral coating layers experience thermal stress due to differing thermal expansion coefficients between the honeycomb substrate and the coating layer, leading to potential damage and reduced thermal shock resistance.
Innovation Solution
A honeycomb filter design with an outer peripheral coating layer having a specific inflection point at 1000 to 1500°C, porosity of 36 to 48%, and thermal expansion coefficient of 2.5 to 3.5×10−6/°C between 40 to 800°C, along with a porosity ratio of 0.6 to 0.9 with the substrate, enhances thermal shock resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If an outer peripheral coating layer is provided on the honeycomb substrate to enhance product shape and dimensional accuracy, then the shape stability is improved, but thermal shock resistance deteriorates due to large difference in thermal expansion between substrate and coating layer
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thermal expansion coefficient of the outer peripheral coating layer (2.5 to 3.5×10−6/°C between 40 to 800°C) to match the honeycomb substrate, and by setting the inflection point temperature (1000 to 1500°C) and porosity (36 to 48%) of the coating layer within specific ranges. These parameter optimizations reduce thermal expansion differences and stress generation, thereby improving thermal shock resistance while maintaining shape stability.
Solution Approach 2:
The patent employs composite materials by creating an outer peripheral coating layer with specific composite properties (controlled porosity of 36 to 48%, specific thermal expansion coefficient, and inflection point at 1000 to 1500°C) that are different from the honeycomb substrate. This composite structure allows the coating layer to have matched thermal expansion characteristics while maintaining shape stability, resolving the contradiction between shape accuracy and thermal shock resistance.
2Strength
If the outer peripheral coating layer has high density to improve mechanical strength, then strength is improved, but thermal shock resistance deteriorates due to increased stress from thermal expansion differences
Solution Approach 1:
The patent resolves this contradiction by changing the porosity parameter of the outer peripheral coating layer to a specific range (36 to 48%). This optimized porosity provides a balance: sufficient mechanical strength is maintained while thermal expansion characteristics are improved to match the substrate. The controlled porosity reduces the density difference between coating layer and substrate, thereby reducing stress generation during thermal cycles and improving thermal shock resistance.
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 design suppresses stress and damage from high exhaust gas temperatures, improving thermal shock resistance and catalyst activation, while lowering heat capacity and enhancing isostatic strength.
Implementation Method 1
the outer peripheral coating layer has an inflection point at which expansion in thermal expansion behavior of the outer peripheral coating layer turns to contraction
Data Source
AI summary
A honeycomb filter includes: a honeycomb substrate having porous partition walls disposed so as to surround cells extending from an inflow end face to an outflow end face, an outer peripheral coating layer disposed so as to surround an outer periphery of the honeycomb substrate, and plugging portions that are disposed at any one of ends on the inflow end face and ends on the outflow end face, of the cells, wherein, the outer peripheral coating layer has an inflection point at which thermal expansion in thermal expansion behavior of the outer peripheral coating layer turns to contraction and a temperature T1 of which is 1000 to 1500° C., and the outer peripheral coating layer has a porosity P1 of 36 to 48%, and a thermal expansion coefficient C1 between 40 to 800° C. of 2.5 to 3.5×10−6/° C.