The quality of degreasing mainly depends on four factors: degreasing temperature, degreasing time, mechanical action, and degreasing additive.
1. Degreasing temperature Generally speaking, the higher the temperature, the more thorough the degreasing is. This is due to three reasons. Firstly, temperature changes the physical properties of oil stains, such as high drop point rust preventive grease, petroleum jelly, solid paraffin, etc., which are difficult to clean even with high concentrations of alkaline solution at lower temperatures. However, when the temperature of oil stains is increased, their viscosity decreases, and even droplets form, which is beneficial for removal. Secondly, promote the progress of chemical reactions. Generally speaking, for every 10 degrees increase in temperature, the rate of chemical reactions doubles. Thirdly, accelerate the movement of surfactant molecules, thereby promoting wetting, emulsification, dispersion, and other effects. As the temperature increases, the solution's ability to dissolve pollutants also increases. However, not all situations require higher temperatures. Various degreasing agents have their own suitable temperature range. In degreasing solutions that use certain types of surfactants, excessive temperatures can cause the surfactant to precipitate and aggregate like oil droplets adhering to the surface, causing uneven blooming of the phosphating film. 2. Degreasing time During the degreasing operation, it is necessary to ensure sufficient degreasing time. The pressure jet degreasing time is generally 1.5-3 minutes, and the immersion degreasing time is 3-5 minutes (depending on the type and amount of oil contamination). Increasing the degreasing time means prolonging the contact time between the degreasing solution and oil stains, thereby improving the degreasing effect. The more oil stains, the longer the degreasing time is required. In assembly line operations, it is often not allowed to use too long a time, so it is generally first used to degrease by spraying for 1 minute, and then by impregnating for 3 minutes. 3. Mechanical action In degreasing, the use of mechanical actions such as pressure spraying or stirring is very effective, because during spraying, fresh degreasing solution is forced to have good contact with the surface of the part, and the content of the entire degreasing solution is uniform, which is conducive to improving the degreasing effect; During spraying, mechanical force is used to promote the penetration of degreasing agent and damage the oil film, effectively forcing oil stains to detach from the surface of the parts; When spraying, it promotes the emulsification and dispersion of oil stains separated from the parts in the degreasing solution, preventing oil stains from adsorbing onto the cleaned surface of the parts. Mechanical action is particularly important in medium to low temperature degreasing. Generally speaking, pressure spraying is more than twice as fast as impregnation degreasing. The injection pressure is usually (0.1~0.2) Mpa (the degreasing agent used for pressure injection must be low foam to avoid excessive foam affecting normal operation and the loss of degreasing liquid), and the degreasing by impregnation cannot be considered as static impregnation. A circulating pump must be equipped to keep the solution stirring, and the circulating amount per hour is about 5 times of the tank liquid volume.
4. The effect of degreasing additives on the degreasing effect
The composition and usage of degreasing agents have a significant impact on the degreasing effect. For example, the degreasing effect of alkaline solution containing surfactants is better than that of alkaline solution alone. For solid or semi solid fats with high drop points, solvent cleaning is more effective than other degreasing methods. In order to improve the emulsification and dispersion ability of oil stains, it is effective to appropriately increase the content of surfactants in the degreasing agent. Different types of surfactants and different alkaline substances can cause certain differences in the degreasing effect. Good degreasing agents are determined through extensive experiments and repeated screening of their component matching ratios. For alkaline degreasing agents containing surfactants, the most effective cleaning effect is at the upper limit of the critical micelle concentration of the surfactant. During use, the degreaser will continue to be consumed, causing a decrease in concentration. Therefore, it is necessary to regularly supplement the degreaser to maintain the necessary concentration. The degreasing effect of a degreasing agent is not linearly related to its concentration. Therefore, for situations with high quality requirements for degreasing, a significant increase in concentration should not be adopted, but a secondary degreasing method should be used. The two degreasing solutions can be the same and there is no need to increase the concentration additionally.
In practical use, it is necessary to consider various factors to control them in the optimal state and achieve satisfactory degreasing results.
