Plasma Torch for Spraying of Powder Materials
Development and Research of the Method and Plasma Torch for Spraying of Powder Materials by High-Enthalpy Laminar Plasma Flow
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
- PHY-PLS/Plasma Physics/Physics
8 Project completed
Senior Project Manager
Safronova O N
Georgian Technical University, Georgia, Tbilisi
- A&A Company, Inc., USA, NJ, South Plainfield
The purposes of offered Project are: the development and research of the method and plasma torch for spraying of powder materials by high-enthalpy plasma flow, investigation of operating parameters, determination of optimal characteristics for realization of high-quality coating, improvement of stability and economy of the process.
At present the plasma spray deposition of powder materials has been one of the most developed plasma processes. The industrial application of plasma spraying is characterized by great scope of work and wide range of sprayed materials. However, in spite of significant technological and commercial progress and extensive distribution, the conventional methods and plasma torch constructions, based on the utilization of turbulent plasma flow, have a number of disadvantages affecting on the stability of processing parameters and quality of coating.
- In plasma torches with turbulent (swirling) stabilization the repetitive gas breakdown occurs between the arc column and outer electrode - anode. This process, called “shunting”, results in variation of the arc length, voltage and current, as well as the fluctuation of plasma jet temperature and velocity.
- With the coating process, the heated up (molten) powder particles leave the plasma flow having the length of high-temperature zone about of 70-100 mm, then the particles move to sprayed part out of plasma jet in ambient atmosphere. As a result the particles are decelerated and oxidized, that results in decreasing of density and bond strength with substrate.
At turbulent plasma jet outflow, the powder particles are melted and accelerated not only in axial direction, but also in radial direction. Being moved away from jet core, some particles hit the peripheral zone of jet, where the gas temperature and velocity is significantly lower than that in the core. Thus, being in the peripheral zone of jet the powder particles, even preheated up to melting temperature, are cooled, suddenly lose the velocity, jump out from plasma flow and do not participate in surface forming. Thereupon, the sprayed coating properties hardly deteriorate, the powder utilization factor (PUF), density and bond strength decrease.
- For providing completely melted powder of especially high volume fraction refractory metals and compounds, and improving the coating properties with using of conventional plasma torches, today it takes the way of increased plasma torches power. It results in increasing of electric power consumption as well as rising of cost of equipment.
- The known plasma spraying torches are characterized by high noise level reaching 120 dB in the operator’s workplace.
As already conducted analysis has shown, the most prospective technical solution is the proposed method of powder sprayed coating by laminar plasma jet. The main point of the method consists in the following: the melted powder particles motion towards the surface takes place in axial direction inside laminar plasma flow having the length of the order of 500-600 mm in plasma forming gas atmosphere.
The distinguishing feature of the offered method and plasma torch design is the diffusive attachment of arc to the nozzle-anode (it has supposedly been spread on the greater surface of anode), which ensures the improved stability of arc burning on the nozzle-anode.
The elaboration of new method and plasma torch allows to:
· increase the dwell time of powder particles injected in high-temperature zone of plasma flow and its energy content 5-10 times in comparison with known plasma spraying methods;
· increase density, bond strength and surface uniformity;
· decrease power consumption 1,5-2 times;
· reduce the variations and fluctuations of major processing parameters;
· increase the PUF 1,4-1,6 times;
· reduce the noise level from 120 dB to total indoor noise background.
The offered Project leads to creation of principally new and beneficial product, application of which initiates not only essential improvement of plasma coatings quality, but activates also the elaboration of new coatings and materials with improved features and properties.
The offered method and plasma torch design has a strong commercial potential. They may be used in mechanical engineering, aircraft industry, metallurgy, power engineering, and many other fields, where the deposition of high-quality coatings by laminar plasma flow with completely melted and overheated powder particles is required.
The practical application of obtained results will lead to an initiation and creation of new improved technologies and devices in the field of plasma coating, which facilitates the solution of wide range of technical tasks and economically significant problems.
The scope of activities in the given Project includes the following:
- elaboration and manufacturing of plasma spraying torch for deposition of powder coating by laminar plasma flow;
- creation of test stand for investigation works;
- experimental research of plasma torch;
- pilot investigation of plasma torch;
- working out of technical documentation.
As a result of Project completion the following ISTC goals ant tasks will be realized:
- the highly-qualified staff and former "weapon" scientists and experts in the field of plasma treatment of materials and creation of high tech. for civil industry will be engaged;
- Project implementation will promote the integration of Georgian scientists and specialists into the international scientific community;
- Project implementation will contribute in transition to market economy and will solve the line of problems connected with Georgia`s industry, also the Project realization may be promising for other countries when developing the new high-quality coatings.
The competence of Project participants is proved by many-year experience in R&D activities connected with plasma treatment of materials. The Project participants have more than 30 inventions and scientific publications on the plasma treatment of materials..
In the given Project the role of foreign collaborators may consist in information exchange during Project implementation, introduction of comments to the annual reports and potential partnership in commercialisation of Project results.