Heat Transfer during the Solidification of Hot Dip Aluminizing Coating

Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity. Although the pulling speed is one of the most important parameters to control the coating thickness of aluminizing products, however, there are few publications on the mathematical modeling of pulling speed during the hot dip process. In order to describe the correlation among the pulling speed, coating thickness and solidification time, the principle of mass and heat transfer during the aluminizing process is investigated in this paper. The mathematical models are based on Navier-Stokes equation and heat transfer analysis. Experiments using the self-designed equipment are carried out to validate the mathematical models. Specifically, aluminum melt is purified at 730 degrees C. The Cook-Norteman method is used for the pretreatment of Q235 steel plates. The temperature of hot dip aluminizing is set to 690 degrees C and the dipping time is set to 3 min. A direct current motor with stepless speed variation is used to adjust the pulling speed. The temperature change of the coating is recorded by an infrared thermometer, and the coating thickness is measured by using image analysis. The validate experiment results indicate that the coating thickness is proportional to the square root of pulling speed for the Q235 steel plate, and that there is a linear relationship between coating thickness and solidification time when the pulling speed is lower than 0.11 m/s. The prediction of the proposed model fits well with the experimental observations of the coating thickness.