Let me tell you about chemical information of degreasing
1、 Overview of chemical degreasing
From the composition of degreasing agents, degreasing agents are divided into three categories: one is organic degreasing agents, such as kerosene, gasoline, trichloroethylene, carbon tetrachloride and other degreasing agents. These degreasing agents are only crude degreasing, and can not be directly electroplated after degreasing. The second type is water-based degreasing agent, which is composed of inorganic alkali, salt and surfactant. This kind of degreasing agent is the main body of electroplating degreasing agent. It is mainly used for chemical degreasing, and a small amount is also used for electrolytic degreasing and ultrasonic degreasing. The third type is the mixed degreasing agent of inorganic and organic matter, also known as emulsion degreasing. It is mainly composed of surfactant, kerosene or gasoline and water to form emulsion, but it is seldom applied in production.
According to different principles of chemical degreasing, water-based degreasing agents are divided into three categories.
The first type is saponified degreasing agent. The oil on the metal surface saponifies with the alkaline substances in the degreasing agent, and finally turns the oil into fatty acid salt soluble in water, so as to achieve the purpose of degreasing. This kind of degreasing agent has a certain selectivity for oil. For example, animal oil and vegetable oil can undergo saponification reaction, but this degreasing agent is powerless for mineral oil.
The second type of emulsified degreaser is the surfactant with the function of emulsified oil added to the first type of degreaser. Under the synergistic action of inorganic salt and alkali, surfactant emulsifies and disperses the oil into water to remove the oil on the metal surface.
The third type of degreaser is displacement degreaser. Its composition is similar to that of the second kind of emulsified degreasing agent, and the difference lies in the difference of surfactants. This kind of degreasing agent has strong permeability. It penetrates and separates the grease and metal surface by surfactant molecules. The grease floats out of the metal interface under the action of gravity. Displacement degreaser has poor removal effect on wax.
2、 Mechanism of chemical degreasing
The three types of degreasing agents are not isolated, but interrelated. For example, adding NaOH and Na3PO4 into water? 12H2O and Na2CO3 (Na2SiO3 can also be added) form saponified degreaser. When the degreaser is used when the temperature rises above 70 ℃, the oil will saponify with the degreaser. When surfactant (OP-10) is added to the degreasing agent and the temperature reaches 50 ~ 70 ℃, the oil will be emulsified and removed by emulsifier, and the degreasing agent will become emulsified degreasing agent. When some surfactants are added to this degreasing agent, it becomes a displacement degreasing agent, which can be used at 10 ~ 50 ℃.
Traditionally, degreasing above 70 ℃ is called high-temperature degreasing, because at this time, paraffin and stearic acid (the main component of polishing paste) can be melted and easy to be removed; 55 ~ 70 ℃ is called medium temperature degreasing. At this time, most lipids, such as calcium base grease (commonly known as butter), reach the melting point temperature; The temperature below 55 ℃ is called normal temperature degreasing, also known as low temperature degreasing.
In terms of degreasing principle, above 70 ℃ is the necessary temperature for saponification reaction. Below 70 ℃, saponification reaction is difficult to occur due to insufficient activation capacity. The optimum temperature range of emulsion degreasing is 55 ~ 70 ℃. Below 55 ℃ is the use of displacement degreasing.
Chemical degreasing is the synergistic effect produced by the saponification of alkali on oil and the emulsification, wetting, penetration, coiling and diffusion of surfactant on oil, so as to achieve the effect of oil removal. The specific process is: diffusion → penetration → wetting → roll off.
3、 Constituent elements
In combination with the amount of grease, viscosity and curing (aging) degree on the parts, the soaking and degreasing time is usually long. Therefore, the slot body is mostly one slot with two positions. The tank body should be made of iron material, and the heating equipment is heating pen.
