Nanomaterials with grain size ranging from 20 nm to 100nm can be used to prepare nanomaterials, but there are still many technical problems in the wide application of nanomaterials in thermal sprayingpowder. The research on it is not deep enough. At present, the coating particles of nanostructure prepared by thermal spraying are mostly submicron particles of 100 ~ 200nm. Did not really reach the nanometer level, coating density is not high enough. The particle size that produces the small-size effect at room temperature is less than 100nm, and the particle strength generally abides by the hall-petch relationship, the smaller the particle is. The higher the intensity. In this sense, there is no breakthrough in the performance of nano-coating at present, and there is still a lot of room for development.

Another important problem is that nano powder cannot be directly used in thermal spraying. Because too fine powder will produce burning and flying problems, and powder delivery is very difficult, deposition efficiency is also affected. Generally, the particle size range of spraying powder is -140 ~ +500 mesh. The solution is to prepare nanomaterials into micron-scale nano-structures that can be directly thermally sprayed. At present, liquid dispersion spray method and mechanical grinding synthesis method are mainly used to prepare nano-structure feedstock. But it also brings the problem of complicated process and increasing cost. Therefore, the study of high quality, high performance or with special structural properties of nano powder or nano composite powder is a very important direction of nano thermal spraying research, but also the power of thermal spraying technology development.

The research time of nano thermal spraying technology is not long, there are many topics need further research and discussion. Such as:

(1) study on the structure and characterization of nano thermal spraying powders;

(2) research on quality control of thermal spraying structure coating;

(3) study on the melting, cooling process and corresponding mechanism of nanomaterials in spraying;

(4) research on the behavior characteristics of nano thermal spraying coating during use;

(5) research on computer control of nano thermal spraying.

As an important application field of nanomaterials, the research level of thermal spraying technology in China is still far behind that in the United States, Japan and other developed countries. The research ofthermal sprayingpowdersis still in the experimental stage. But from the results of existing research. Nano-structure coating prepared by thermal spraying technology has excellent antisepsis and wear resistance, and has a good application prospect. Although the cost of coating preparation and some technical problems still limit the wide application of this technology, its application has a broad prospect. With the development of nanomaterials, advanced thermal spraying equipment, advanced thermal spraying technology development, nano thermal spraying technology will be developed and widely used.

Posted by: hannahgwendolyn at 09:37 AM | No Comments | Add Comment
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For micro/nano particles in the process of the thermal spraying processcontrol measures, according to the principle of similarity, in thermal spraying workshop for prototype, combining the theory of gas-solid two-phase flow, thermal spraying workshop similar experimental model is established, under the condition of different ventilation and dust removal of micro/nano powder in thermal spraying workshop movement and the diffusion regularity of experiment research. The results show that mechanical ventilation can significantly reduce the concentration of micro-nano dust particles in thermal spraying workshop. The higher the ventilation flow per unit time, the lower the concentration of micro-nano dust particles in the respiratory layer of the workshop, and the shorter the removal time. Under the condition of the same ventilation rate, the combination of the bottom and the side of the workshop is more beneficial to the removal and settlement of the respirable layer micro-nano dust particles than the side strong ventilation alone.

The diffusion process of micro-nano dust inthermal sprayingpowderworkshop is essentially gas-solid two-phase flow. According to the motion law of gas-solid two-phase flow and the analysis of basic motion equation, the physical quantities involved mainly include air density, gas pressure, airflow velocity, aerodynamic viscosity coefficient, particle size, particle density, particle velocity, particle movement time, gravity acceleration, geometric size, etc.

Based on the principle of dimensional analysis, seven similarity criterion Numbers are derived: stokes criterion number, homogeneity criterion number, euler criterion number, froude criterion number, Reynolds number number, gas-solid phase density criterion number, and motion criterion number.Generally limited by actual experimental conditions, it is often difficult or difficult to realize that similar model and prototype meet all similar criteria at the same time. Therefore, under the condition of ensuring sufficient accuracy, the number of similar criteria is simplified according to the actual situation, that is, the approximate similar model is established.

Considering the actual movement of micro/nano dust particles in thermal spraying workshop, the similarity criterion number can be simplified as the geometric similarity criterion number and the ventilation rate ratio of the exhaust outlet.

The layout of similar experimental model (referred to as "experiment box") in the thermal spraying workshop is consistent with the actual workshop structure. There are 8 air inlets on the upper end and 3 air outlets on the side, and the remaining surfaces are sealed. All sides of the experiment box are made of colorless transparent acrylic sheets (commonly known as "plexiglass"), and all sizes are designed according to similar models. Micro-nano particle dispersion device is installed on the left side of the experiment box to simulate the dust source in the process of thermal spraying. Honeycomb floor is adopted at the bottom of the workshop, and the whole system is relatively complex, so it is simplified. 9 air outlets are set at the bottom of the experimental box, and centrifugal fan is adopted at one end as the negative pressure source.

Posted by: hannahgwendolyn at 10:20 AM | No Comments | Add Comment
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