Layered Heater Material Processes for Thermal Stress
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Solution Overview
Problem
Existing layered heaters face limitations due to incompatibility of substrate materials with thick film processes, requiring multiple processing sequences and resulting in inefficiencies, especially with high thermal expansion substrates like 304 stainless steel, and imperfect resistor patterns in thermal spraying processes.
Innovation Solution
The use of different layered processes for each layer, such as thermal spraying for the dielectric and protective layers and thick film for the resistive layer, allows for increased substrate compatibility and reduces processing steps, enabling a synergistic result with a single firing sequence and broader material selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If thick film processes are used for high temperature applications with 304 stainless steel substrates, then the heater can withstand high temperatures, but the dielectric material becomes unacceptably conductive or delaminates due to high coefficient of thermal expansion incompatibility
Solution Approach 1:
The patent uses a composite material system consisting of a metal substrate (304 stainless steel), a metallic bond coat layer (NiAl or NiCrAlY), and a ceramic top coat layer (7YSZ or 8YSZ). This composite structure allows the dielectric layer to adhere to the high thermal expansion substrate while maintaining dielectric properties at high temperatures, resolving the incompatibility between substrate and dielectric material.
Solution Approach 2:
The patent introduces a bond coat layer as an intermediary between the substrate and the dielectric top coat. This bond coat layer serves as a transition layer that accommodates the thermal expansion mismatch and provides a suitable surface for dielectric adhesion, preventing delamination and maintaining performance at high temperatures.
2Manufacturing precision
If multiple drying and high temperature firing steps are performed for each coat in thick film layered heaters, then each layer is properly formed, but the processing sequence becomes complex and time-consuming
Solution Approach 1:
The patent combines multiple separate firing steps into a single consolidated firing sequence. The bond coat layer and dielectric top coat layer are fired together in one high temperature cycle, eliminating the need for separate drying and firing steps for each layer. This reduces processing complexity while maintaining layer formation quality through proper process parameter optimization.
3Productivity
If thermal spraying process is used for resistive layer formation, then rapid deposition is achieved, but the resistor pattern becomes imperfect without shadow masking
Solution Approach 1:
The patent applies a release agent to the dielectric layer surface before thermal spraying the resistive material. This preliminary action creates a patterned surface energy distribution that guides the molten or semi-molten resistive material to solidify only in desired areas, forming precise resistor patterns directly during the spraying process without requiring shadow masks or subsequent etching steps.
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 enhances the applicability and efficiency of layered heaters by allowing the use of previously incompatible substrates and reducing interface stresses, resulting in a more reliable and customizable heating solution.
Implementation Method 1
thermal spraying processes, which may include by way of example flame spraying, plasma spraying, wire arc spraying, and HVOF (High Velocity Oxygen Fuel)
Implementation Method 2
the layers for thick film heaters are typically formed using processes such as screen printing, decal application, or film printing heads
Implementation Method 3
the processes for thick film layered heaters involve multiple drying and high temperature firing steps for each coat
Implementation Method 4
The resistive material is applied to the dielectric material in a predetermined pattern and provides a resistive heater circuit
Implementation Method 5
The dielectric material is applied first to the substrate and provides electrical isolation between the substrate and the electrically-live resistive material and also minimizes current leakage to ground
Data Source
AI summary
A layered heater is provided with a dielectric layer formed by a first layered process, a resistive layer formed on the dielectric layer, the resistive layer formed by a second layered process, and a protective layer formed on the resistive layer, wherein the protective layer is formed by one of the first or second layered processes or yet another layered process. The first layered process is different than the second layered process in order to take advantage of the unique processing benefits of each of the first and second layered processes for a synergistic result. The layered processes include, by way of example, thick film, thin film, thermal spraying, and sol-gel. Additional functional layers are also provided by the present invention, along with methods of forming each of the individual layers.