Plasma Spray Chamber Gas Recirculation for Substrate Cooling
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Solution Overview
Problem
Existing plasma spray processes, particularly vacuum and low-pressure plasma spraying, face challenges with high temperatures and limited cooling efficiency due to low-pressure environments, leading to substrate overheating, reduced productivity, and increased costs from using expensive inert gases like helium.
Innovation Solution
A plasma spray apparatus and method that recirculates and cools inert gases at or above normal pressure, using a closed-loop system with heat exchangers and compressors to enhance cooling efficiency and allow higher gas flow rates, enabling the use of cost-effective silicone masking tapes and reducing substrate temperature exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If vacuum or low-pressure plasma spraying is used to produce high-quality coatings, then coating adhesion and mechanical strength are improved, but substrate temperature control deteriorates due to limited cooling efficiency
Solution Approach 1:
The invention changes the pressure parameter from vacuum/low-pressure to super-atmospheric pressure (above 1 atm), which fundamentally alters the cooling efficiency of the inert gas. At super-atmospheric pressure, the inert gas achieves superior heat transfer coefficients, enabling effective substrate temperature control while maintaining the inert atmosphere necessary for high-quality coatings.
Solution Approach 2:
The invention implements periodic cooling cycles where inert gas is continuously supplied to the substrate surface during plasma spraying. This periodic action of cooling gas flow maintains substrate temperature within acceptable ranges throughout the coating process, preventing thermal damage while allowing continuous deposition.
2Temperature
If helium is used as cooling medium in low-pressure plasma spraying, then cooling capacity is improved, but process cost increases due to expensive gas consumption
Solution Approach 1:
The invention changes the pressure parameter to super-atmospheric conditions, which dramatically improves the cooling efficiency of inexpensive inert gases like nitrogen or air. This eliminates the need to use expensive helium while achieving superior cooling capacity through enhanced heat transfer at high pressure.
Solution Approach 2:
The invention replaces expensive cooling media (helium) with inexpensive inert gases (nitrogen, air) by operating at super-atmospheric pressure. The high pressure compensates for the lower intrinsic thermal conductivity of these cheaper gases, making the overall process cost-effective while maintaining high cooling efficiency.
3Temperature
If high flow rate of cooling gas is used in normal-pressure plasma spraying, then substrate cooling efficiency is improved, but oxygen contamination increases leading to coating embrittlement
Solution Approach 1:
The invention maintains a controlled inert atmosphere (nitrogen or other inert gas) at super-atmospheric pressure throughout the spraying chamber. This inert environment prevents oxidation of the molten feedstock and coating materials, eliminating embrittlement issues while allowing high flow rates of cooling gas to be used for effective substrate temperature control.
4Temperature
If longer pauses are introduced between coating layers, then substrate temperature is controlled, but productivity decreases
Solution Approach 1:
The invention enables continuous plasma spraying operation without pauses between layers by implementing efficient substrate cooling at super-atmospheric pressure. The enhanced cooling capacity allows the substrate to dissipate heat rapidly, maintaining acceptable temperature levels throughout continuous deposition, thereby maximizing productivity.
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 solution achieves high-quality coatings with improved temperature control and productivity, maintaining substrate integrity and mechanical properties while reducing process duration and costs compared to conventional methods.
Implementation Method 1
the feedstock in form of a powder is heated by a plasma jet, emanating from a plasma torch
Implementation Method 2
the material is melted and propelled towards a substrate
Implementation Method 3
one or more ducts in which a cooling gas is blown toward the substrate with a high flow rate
Implementation Method 4
a first heat exchanger for cooling down the inert gases, communicating with the working chamber
Implementation Method 5
oxygen is a very reactive element which oxidizes the heated feedstock and introduces brittle phases in the metallic matrix
Implementation Method 6
a compressor for increasing the pressure of the gases
Implementation Method 7
a second heat exchanger for further cooling down the gases
Data Source
AI summary
Plasma spray apparatus for coating substrates, including at least a working chamber including a plasma torch and at least a substrate support, in which an inert gas or a mixture of inert gases is contained at a pressure which is close to the normal pressure, and at least a gas circuit, in communication with said working chamber, including recirculating means of the inert gases contained in said working chamber. The recirculating means include a closed loop, including a blower and a first heat exchanger communicating with said working chamber for extracting the inert gases and supplying a first fraction of the cooled inert gases back into a first portion of the working chamber, and at least a path, communicating with said closed loop and including a compressor and a second heat exchanger for supplying a second fraction of the cooled inert gases into a second portion of the working chamber.