Gas-Thermal Deposition of Coatings
A Method of Gas-Thermal Deposition of Coatings on the Inner Surfaces of Holes and Its Implementation for Cylinder Blocks of Internal-Combustion Engines
Tech Area / Field
- SAT-SUF/Surface Transportation/Space, Aircraft and Surface Transportation
- MAT-SYN/Materials Synthesis and Processing/Materials
3 Approved without Funding
MISIS (Steel and Alloys), Russia, Moscow
- State Enterprise Krasnaya Zvezda, Russia, Moscow
- Swedish Life Science University / Department of Chemistry, Sweden, Uppsala
Project summaryThe process of gas thermal spraying of coatings on not-easily-accessible internal surfaces of various holes can be successfully used in production of new and reclamation of worn cylinder blocks of internal-combustion engines, including those from aluminium alloys.
At present, more than half of internal-combustion engine cylinders in the world are manufactured from aluminium alloys. However, only 10 to 15% of aluminium blocks are not lined with iron or steel inserts. These 10–15% make use of sufficiently expensive methods to strengthen the working surface, including gas-flame spraying by special costly equipment, which fails to ensure the required quality and requires additional press-fitting. The proposed process makes it possible to solve all these problems by means of a simpler method, which does not require considerable financial investment into the re-equipment of the commonly used facilities.
Its applications are not reduced to mass production only. Repairs of worn engines by the proposed method offer significant advantages as compared with traditional reclamation by boring and lining with iron or steel sleeves. The advantages are high cost effectiveness and simplicity of use. The proposed process does not require developing complex special equipment. It can be realized based on the standard commercial spraying tools equipped with simple accessories.
The process consists in applying a coating by the method of gas thermal spraying on internal surfaces of holes, for instance, of internal-combustion engine cylinders. The components of the coating are silicon carbide, the nickel-based viscous matrix and a solid lubricant based on clad graphite. The composition of the coating is chosen such that to ensure the high wear resistance of the counterbody, i.e., the piston rings.
Rotatable reflecting element with the tilted surface, e.g., shaped as a cone, is positioned before nozzle of the spraying torch; herewith, the axis of the nozzle is shifted relative to the axis of rotation of the reflecting element.
Besides, the method can be realized with additional features shown in the diagrams, namely:
- the nozzle is movable along a preset trajectory relative to the axis of the reflecting element;
- exhaust gas from the side of the treated hole opposite to the nozzle is forcibly sucked off as the coating is applied;
- the reflecting element is forcibly rotated at a speed sufficient to impart an additional pulse to particles of sprayed material to increase their linear velocity;
- the reflecting element rotates under the action of a jet of gas or plasma with sprayed material, or a jet of gas directed from one or several additional nozzles;
- the reflecting element is additionally vibrated in the range of ultrasonic frequencies.
During the operation, the jet with sprayed material successively passes various sections of reflecting element’s working surface. These sections cool down after exiting the zone of heating by the jet.
Besides, the reflecting element can be additionally cooled by cooling gas using one or several nozzles located near the main nozzle. The same gas can be used to remove waste particles of sprayed material. An additional effect is that the flow of sprayed particles is stabilized due to a decreased turbulence and separation (blow-out from the spraying zone) of low-energy particles of sprayed material. The additional nozzles can be also used to rotate the reflecting element, which in this case can be shaped as turbine blades.
The flow can also be stabilized by sucking off waste gas from the side of the treated hole opposite to the nozzle.
The quality of the coating, including its density, can be increased at the expense of rotation of the reflecting element at a rate sufficient to ensure an increase of the linear velocity of the sprayed particles after they are reflected from the reflecting element.
At present, spraying on internal surfaces of holes is performed using complex-shape special torches, which make it possible to direct the flow of sprayed particles perpendicular to the treated surface. This results in considerable additional expenses and problems of technological character.
Besides, a method of thermal spraying of coatings on internal surfaces of holes in component parts is known (US Patent No 5439714, priority date 13/07/1993), which we chose as a prototype for our invention. In that method, the reflecting element having a tilted surface for directing the jet with sprayed material to the internal surface of the hole is placed before the spraying nozzle. The reflecting element can rotate; herewith, the nozzle and reflecting element are located on the same axis of rotation.
However, the given method has a number of drawbacks. As the jet with sprayed material is permanently directed to the same region of the reflecting element, that surface is subject to intensive heating and damage. This effect of the gas jet on the same region of the reflecting element leads to changes in the macro- and microgeometry of the reflecting surface, and to adhesion of sprayed material to the reflecting element. A consequence of adhesion is the nonuniformity of the treated-surface coating and deterioration of its quality. Besides, if the reflecting element is a body of rotation, any microdeviation of the jet of sprayed material relative to the axis of the reflecting element leads to a significant thickness variation of the coating along the diameter of the sprayed surface of the hole.
The method of spraying a coating we propose eliminates all these drawbacks. Practically no special equipment or sophisticated accessories are required to achieve the desired result. Expenses for introducing the process are incommensurably less than the profit from its use.
Current state of research on the project
To date, the process is realized by its modelling for particular blocks using various universal modules. A complex-composition wear-resistant coating has been sprayed and machined on experimental cylinder blocks, including on an aluminium block.
Laboratory studies have shown the possibity of realizing the proposed scheme and producing significant advantages – a low wear of the liner in an internal-combustion engine cylinder and a low wear of the counterbody, the piston rings. It has been found that, as compared with the method of treatment according to the prototype method, the resistance of the reflecting cone increased 2,5-fold; the coating is of even thickness along the diameter of the cylinder, its density increased noticeably.
Technical specifications of the unique equipment used
Along with the common equipment for metallographic analysis (assessment of the quality of coatings), unique equipment for deposition of coatings by the method of powder-cord gas-thermal spraying by Techni-cord (Russia) will be used, with localization, change of direction/acceleration of abrasive-jet and gas-thermal fluxes; honing machines with diamond tooling will also be used.
Aim and tasks.
Aim of the project – Development of a ready-for-commercial-use process of gas thermal application of wear-resistant coatings on the surface of internal-combustion engine cylinders with increased service life, including with the aluminum block.
- Fabrication of an experimental setup.
- Tests of the process parameters and tribological parameters on iron cylinder blocks.
- Tests on aluminum liners and cylinder blocks.
- Refinement of the setup design and process regimes based on the results of the tests.
- Forming patents in the Russia and abroad.
- Development and fabrication of a commercial setup for realizing the proposed process in repairs of worn cylinder blocks.
- Development and fabrication of a commercial setup for realizing the proposed process in full-scale production of internal-combustion engines.
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