The finer the salt spray particles in the salt spray test chamber, the larger the surface area formed, the more oxygen is adsorbed, and the stronger the corrosion. In nature, more than 90% of the salt spray particles have a diameter of less than 1 micrometer. The research results show that the amount of oxygen adsorbed on the surface of the salt spray particles with a diameter of 1 micrometer and the amount of dissolved oxygen in the particles are relatively balanced. No matter how small the salt spray particles are, the amount of oxygen absorbed no longer increases.
The traditional spraying methods include air pressure spraying method and spray tower method. The most obvious disadvantages are the poor uniformity of the amount of salt spray deposition and the large diameter of the salt spray particles. The ultrasonic atomization method uses the principle of ultrasonic atomization to directly atomize the salt solution into a salt mist and enter the test area through diffusion, which solves the problem of poor uniformity of the amount of salt mist sedimentation, and the diameter of the salt mist particles is smaller. Different spraying methods will also affect the pH of the salt solution.
The working principle of ultrasonic atomizationThe working principle of ultrasonic atomization in the salt spray test chamber is to use the ultrasonic generator and the transducer to generate self-oscillation, radiate strong ultrasonic waves into the water, and the ultrasonic waves pass through the water and the semi-permeable membrane to act in the atomizing cup. The salt solution to be atomized causes the micro-bubbles existing in the salt solution to vibrate under the action of the sound field. When the sound pressure reaches a certain value, the micro-bubbles expand rapidly and then close suddenly, generating shock waves when the micro-bubbles are closed. This series of dynamic processes such as expansion, closure, and oscillation is called acoustic cavitation. Under the effect of acoustic cavitation, the liquid is dispersed in the gas phase and forms a fine mist flying on the surface of the liquid. Under the driving of the flowing gas, the fine mist continuously flows out of the atomization cup to achieve ultrasonic atomization. In the whole process, there was only physical reaction, but no chemical reaction.
Control of the amount of salt spray deposition in the ultrasonic atomization method The ultrasonic atomization method is easy to control the salt spray settlement rate. Factors affecting the salt spray settlement rate are: temperature, pressure, salt solution concentration, salt spray particle diameter, atomization speed, etc. The diameter of the salt spray particles has the following relationship with the ultrasonic frequency: Ultrasonic frequency;: Density of the salt solution;: Surface tension of the salt solution can be seen. When other conditions are constant, the salt spray sedimentation rate can be adjusted by adjusting the diameter of the salt spray particles. The higher the ultrasonic frequency, the finer the salt mist produced and the lower the salt mist sedimentation rate. The purpose of controlling the settling rate of salt spray can be achieved by adjusting the ultrasonic frequency.
The atomization speed is closely related to the power of the ultrasonic wave, and the salt spray sedimentation rate can be adjusted by adjusting the power of the ultrasonic generator. Thus, the sedimentation rate per unit time is controlled. The output of salt mist can also be adjusted by adjusting the amount of air entering the air inlet of the atomizing cup. When the air intake is large, the micro-bubbles existing in the liquid will increase, and it is easy to form more fine mist. At the same time, the flow rate of salt mist will be accelerated due to the increase in pressure difference, and the amount of mist entering the test area will increase.
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