Plasma Powder Spray Laser Diffusive Bonding for Boiler Wall Coatings
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current thermal spraying methods, such as plasma spraying, fail to produce a protective layer on metallic walls exposed to hot gases that can withstand increased erosive and corrosive stress due to high internal stresses and adhesion forces, leading to a thin and ineffective coating that may flake off.
Innovation Solution
A thermal spraying method using a plasma powder spraying device with a cathode and anode, combined with a laser beam system, where the coating material is preheated and applied as a powder jet without melting, forming a diffusive bond with the base material using a low-power laser, allowing for a thicker and more durable protective layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plasma spraying is used to produce a protective layer on metallic walls, then the coating provides corrosion protection, but the layer becomes relatively thin and develops high residual stresses that cause flaking
Solution Approach 1:
The invention changes the physical state parameter of the coating material from completely molten (conventional plasma spraying) to preheated but not molten. This parameter change allows the material to be applied without forming a thick, stressed layer that flakes, while still achieving adequate corrosion protection through the diffusive bond formed by subsequent laser treatment.
Solution Approach 2:
The invention replaces the mechanical/thermal bonding mechanism of conventional plasma spraying (relying on molten particle impact and solidification) with a diffusive bonding mechanism activated by laser beam treatment. This substitution eliminates the formation of harmful residual stresses while maintaining adhesion strength.
2Duration of action of stationary object
If the protective layer thickness is increased to meet extended service life demands, then corrosion and wear resistance improve, but residual stresses exceed bonding forces causing the layer to flake off
Solution Approach 1:
The invention applies preliminary heating of the coating material to a preheated but not molten state before application. This preliminary action prepares the material for subsequent diffusive bonding with the base material through laser treatment, enabling thicker layers to be applied without generating excessive residual stresses that would cause flaking.
Solution Approach 2:
The invention substitutes the conventional bonding mechanism (mechanical interlock and adhesion through molten particle solidification) with a diffusive bonding mechanism. This substitution allows thicker protective layers to be applied while maintaining bonding strength, as the diffusive bond does not generate the same level of residual stresses as conventional solidification bonding.
3Device complexity
If conventional plasma spraying is used, then the process is simpler, but the protective layer is too thin to meet increased demands for extended service life under erosive and corrosive stress
Solution Approach 1:
The invention merges the plasma spraying process with laser beam treatment into a combined process. The plasma spray applies the preheated coating material, and the laser beam subsequently creates the diffusive bond. This merging allows for thicker protective layers to be applied while maintaining process efficiency and not significantly increasing overall complexity.
4Quantity of substance
If a thick protective layer is applied using conventional methods, then material coverage increases, but the layer flakes off due to excessive residual stresses
Solution Approach 1:
The invention changes the application parameter from applying completely molten material to applying preheated but not molten material. This parameter change allows thicker coatings to be applied without generating the residual stresses that cause flaking, thereby maintaining coating integrity while increasing material coverage.
Solution Approach 2:
The invention substitutes the conventional solidification-based bonding mechanism with a diffusive bonding mechanism activated by laser treatment. This substitution enables thicker coating applications to maintain integrity, as the diffusive bond accommodates the thicker layer without generating excessive residual stresses that would cause flaking.
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 method achieves a protective layer thickness 100% to 200% greater than previous methods, extending service life and reducing material costs through the use of coarser, cheaper powders, while minimizing heat input and distortion to the base material.
Implementation Method 1
a plasma gas nozzle of the plasma powder spraying device has at least one combined bore which is formed from two nested partial bores which have a common starting point on an outer circumference of the plasma gas nozzle, one of which partial bores is arranged with its central axis perpendicular to the central axis of the other partial bore, so that plasma gas is introduced tangentially to the central longitudinal axis of the plasma powder spraying device into the anode
Implementation Method 2
the plasma gas reaches an arc rotating about the central longitudinal axis of the plasma powder spraying device, wherein the arc is set into rotation with its arc bases on the one hand at the anode and on the other hand at the cathode according to the rotation of the plasma gas
Implementation Method 3
heating of the coating material in the respective plasma jet, whereby the powder does not become molten; wherein each powder jet is formed from a different coating material and is processed with a respective associated laser beam to form the diffusive bond
Implementation Method 4
heating of the coating material in the respective plasma jet, whereby the powder does not become molten
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a thermal spraying process for producing a protective layer using plasma powder spraying on walls of combustion plants, especially waste incineration plants, which are exposed to hot gases, in particular flue gases and consist of a predetermined metallic base material.In order to produce a protective layer with a thickness of 0.6 to 1.5 mm, thereby increasing the service life of, for example, pipe-web-pipe segments, at least the following steps are proposed: cleaning the metallic walls; setting a plasma gas into rotation around the central longitudinal axis (X1) of a plasma powder spraying device (2); internally feeding a coating material as a powder simultaneously through two internal feed openings (24, 26), which internal feed openings (24, 26) are arranged opposite each other with their outlet openings, whereby at least one powder jet (4, 6) is generated; melting the coating material; and bonding the coating material impacting the metallic wall by means of at least one laser beam (11, 12) of a laser beam system (3) to form a diffusive bond between the coating material and the base material of the metallic wall.