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Analysis on the control method of thermal spraying coating process!

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Analysis on the control method of thermal spraying coating process!


A new technology which can measure the thickness of thermal spray coating quickly and non-destructive can realize early detection of deviation and correction in the early stage of the process.

When 8 traditional gray iron inserts in the crankcase of the cylinder engine are replaced with hot melt coating, the porosity and mechanical properties of the aluminum castings in the cylinder hole area are very high.

The actual production process mainly includes four steps: precision boring (fine boring), roughening, coating and post-treatment. Between the above steps, tests must be carried out to ensure quality. 100% of the tests must be performed based on the number of parts, applications, and key quality parameters.

The purpose of the fine boring is to align the holes with the crankshaft axis and expand the pores according to the required coating thickness after the final machining. The shape and position tolerances need to be determined and the cylindricity is also generated. For coating thickness, only very limited position tolerances can be corrected subsequently, with a thickness of several hundred microns. Therefore, holes need to be set in place before coarsening and coating.

After replacing 8 traditional gray iron inserts in crankcase of cylinder engine with hot melt coating, the porosity and mechanical properties of aluminum castings in the cylinder hole area are very high.

The purpose of coarsening the cylindrical surface is to produce the required coating adhesion. This procedure can be accomplished by sandblasting corundum, high pressure or pulse low pressure fluid jet or pure machining. It is used to make the surface coarsening to be coated can be used in corundum sand blasting and fluid jet process in separate equipment.

Usually, the mechanical roughening of the crankcase can be carried out after the fine boring in the same clamping. Therefore, the rough profile can be introduced without offset. Then, the optical image recognition technology is used to detect the surface defects and classify the reprocessing. In the case of corundum sandblasting, the surface defects can be embedded in corundum particles; In the case of fluid jet, the main problem is to peel off the phase and expand the hole.

In order to measure the coating thickness, the measuring optical element is inserted into the cylinder hole (upper hole opening), so the coating thickness can be measured reliably at any position of the circumference and the depth in the cylinder.

When roughening, cut the groove profile into the aluminum. The shape of the profile, grooves and metallic glossy surfaces make it unsuitable for detection using camera systems.


Improve the service life of the engine

The thermal spraying process is characterized by the melting of coating materials through heat sources (such as plasma flame) and spraying to components by rotating air flow. The liquid particles suddenly solidify and delamination when they contact the surface, thus producing coating. Almost all materials can be processed by powder based thermal spraying in atmosphere. The spectrum range from thermoplastic, metal and carbide to ceramic. Iron based coating has the required tribological properties, and can be used as wire or powder. Wire arc spraying, plasma transfer arc (ptwa) and rotating single wire (RSW) are examples of wire coating process.

Besides metal, powder based plasma coating provides the choice of ceramic material spraying. Low alloy carbon steel is mainly used for coating the surface of gas and diesel engine. The coating is not uniform and consists not only of molten and solidified particles. In the coating, oxides and carbides and holes accumulate, making the frequency between 1% and 4%, which depends on the process parameters and the selection of process. These holes are honed to serve as a lubricant reservoir and hold the lubricant in the specified position. Therefore, the friction between piston ring / piston and cylinder wall is reduced, thus reducing fuel consumption and improving the service life of the engine.

Realize the measurement of coating thickness in one second

The thickness of the thermal spray coating that is not yet machined must follow a narrow allowable range. Any deviation from the specified tolerance may result in subsequent reprocessing and destruction of honing tools during subsequent machining.

Measuring the coating thickness early in the process can eliminate any subsequent processing steps in the value-added chain, such as too low coating thickness. For the rough spray surface, the traditional coating thickness measuring instrument has low repetition precision, so it is not suitable for quality assurance. Random examination by micrographs is time consuming and seamless and non-destructive inspection of coating process is not allowed.

The instrument is designed based on the process of thermal coating testing. The light source of the device heats the coated surface for several milliseconds to several degrees Celsius. The film thickness of thermal spray coating is measured by photothermal method and the difference of thermal conductivity between coating and substrate.

Measure the thickness of the coating in the working surface of the cylinder from the bottom to the top at the opposite point (a, b).

The measuring point 1-15 is crankcase 1, and the measuring point 16-30 is crankcase 2

The light source used in the device is similar to the flash of the camera and will not cause any harm to human body or environment. Each measurement process analyzes more than 100000 temperature readings and then determines the coating thickness. It can be measured at a distance of up to 1 m and an area of 2 to 50 mm diameter of the surface can be measured. The error of a single measurement is usually less than 1%. The coating thickness can be recorded at frequencies up to 2 Hz. Through optical measuring probe, the measuring points of the working surface distribution of the whole cylinder are automatically measured and the thickness is recorded automatically.

Reduction of surface roughness

In the final honing process, the rough structure of the spray surface should be removed, so the surface roughness should be reduced to the average roughness within 5 microns.

Above is Huaian metal spray company for you to introduce the process control of thermal coating, hope to help you!


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