When die-casting production plants encounter scrap products in die-casting parts, they rarely analyze the rationality of mold release agent selection and the correctness of spraying technology. When using a new type of release agent, if it cannot accommodate traditional experience and operating habits, it will be immediately rejected. So there is often a confusing situation: when casting the same type of castings, one company is adept at using a certain release agent, while the other company complains that it is not easy to use. The reason for this is still due to insufficient understanding of the characteristics of release agents, neglecting the issues that should have been paid special attention to. The following four aspects should be noted.
1. The correspondence between mold temperature and type of release agent
The basic components of release agent are mineral oil and paraffin wax, and the suitable mold surface temperature varies depending on the ratio. Taking aluminum alloy release agents as an example, they are currently mainly divided into three categories according to mold temperature requirements: low temperature (below 200 ℃), medium temperature (200-250 ℃), and high temperature (above 250 ℃). From the characteristics of film formation, it can be divided into adhesion between active ingredients and mold cavity, dryness of film, and influence on casting coating. If non silicone release agents are widely used for castings with high coating requirements, but if the mold temperature is not well controlled, their expertise in this area cannot be fully utilized. Although the classification difference of mold temperature only varies within 20% of the mold temperature range, it does not prevent the formation of a film, but has a significant impact on the demolding performance, surface quality, and mold life of castings.
2. The relationship between water blending rate, mold temperature, and adhesion amount
Only a fraction of the water-based release agent truly adheres to the surface of the mold cavity during spraying, and most of it is scattered by the phenomenon of vapor film. The experiment shows that ensuring the effective solid matter content (mass fraction) is not less than 0 2 %～0. Under the condition of 3%, the greater the dilution rate and the greater the spraying amount, the more effective adhesion will be, and the larger the adhesion area. This can explain why a low water mixing rate can lead to mold sticking and waste production. Meanwhile, as the mold temperature increases, its adhesion amount and adhesion area decrease. Experience has shown that the ideal mold temperature after spraying should be below 250 ℃, preferably between 180-200 ℃. A film is formed within 1 second of spraying at a mold temperature below 270 ℃.
3. The relationship between spray technology and film quality
In order to ensure the uniform formation of the film, the spraying process is very important. To achieve ultra-fine atomization, uniform dispersion, and strong adhesion. At the same time, optimize the spraying distance. The distance is too small, and due to the high spray velocity, the release agent rebounds and causes loss; If the distance is too large, the mist release agent will merge into large droplets, and the impact force when it falls may damage the uniformity of the film. Due to the high mold temperature during spraying and the low mold temperature during film formation, condensation may occur. Therefore, spraying should not be used as a means to reduce mold temperature, but rather to minimize the mold temperature difference from spraying to film formation as much as possible. Experience has shown that the ideal spraying distance is 100-200 mm, not greater than 250 mm. For necessary point spraying, such as cores and runners, it can be shortened to 70 mm. For large molds, using a device that can automatically track the trajectory of the nozzle is more effective.
4. Water quality issues
The quality of water used for diluting water-based release agents is easily overlooked. Release agents such as LEVENIT and MARBO chemical manufacturing companies in Italy not only have a complete production process and quality testing system, but also strictly control the purity, hardness, pH value, and mixing water temperature of water quality. Because if unqualified water is mixed into the release agent, some of its characteristics will be lost. For example, when the number of bacteria in 1 m3 of water reaches 105, the release agent may deteriorate, causing an increase in the scrap rate of some sensitive die-casting parts. For example, when water containing impurities or impure components is added to the original concentrated solution, the gas content in the die casting increases, which has a significant impact on the production of castings with air tightness or weldability requirements. As a general rule, the original imported release agent should be promptly mixed with qualified water after opening the lid and used up within one week.
