The robotic electrostatic spraying equipment consists of a spray gun, a spray cup, and a high-voltage power supply for electrostatic spraying. During spraying, the spray gun, spray cup, and paint particle component are connected to the negative terminal, while the car is connected to the positive terminal and grounded, creating an electrostatic field between the tip of the spray gun and the car. The paint is mostly a high-molecular-weight organic conductive medium, atomized and sprayed through the nozzle. The particles become charged upon contact with the main needle at the nozzle. Under the influence of the electrostatic field, these negatively charged paint particles move towards the polarity of the car surface and are adsorbed onto the car surface, forming a uniform coating film. However, due to various reasons, uneven spraying can sometimes occur in robotic electrostatic spraying. Below, we share the reasons for uneven spraying in robotic electrostatic spraying.
1. Employee operational skills
A statistical analysis was conducted on the operational qualification certificates and years of experience of the spray painting operators on the production site. All personnel had participated in the training and examinations organized by the training center as required and obtained operational qualification certificates. All personnel had more than 8 years of experience in spray painting. Analysis of feedback regarding uneven spraying failures revealed no clear correlation between the failures and the operators. Insufficient operator skills were not the primary factor.
2. Raw material quality factors
The paint, thinner, and hardener were all tested and qualified before use. No large-area uneven paint application occurred during the spraying process. Therefore, it is considered that the possibility of uneven paint application being caused by substandard raw materials such as paint, hardener, and thinner is relatively small.
3. Compressed air pressure analysis
Insufficient compressed air pressure during spraying can lead to inadequate paint atomization or insufficient spraying power, resulting in uneven spraying. Rotary cup spray gun manufacturers typically require a spray gun pressure of 0.35–0.5 MPa. Electrostatic spray gun pumps have a compressed air pressure indicator to monitor the pressure at any time. Feedback from the field indicates that spraying operations were not performed with insufficient compressed air pressure; therefore, insufficient compressed air is not the primary factor.
4. Analysis of the Influence of Ambient Temperature and Humidity on Spray Gun
During spray painting, ambient temperature and humidity affect the quality of the paint application. If the relative humidity of the work site is too high, exceeding 80% or reaching saturation, a very thin, invisible water curtain will form on the sprayed surface due to the adsorption of moisture on the metal surface, thus affecting the quality of the paint film formation. Therefore, it is recommended that the work site temperature be between 18 and 25°C and the relative humidity between 45% and 65%, with the ambient temperature not exceeding 12 and 30°C and the relative humidity not exceeding 80%. A review of the on-site temperature and humidity records and work logs showed that work was not carried out when the temperature and humidity did not meet the requirements; therefore, the influence of ambient temperature and humidity is not the primary cause of the problem.
