One of the important processes of surface treatment
These pollutants includeantirustOil, lubricating oil, animal and vegetable oil, etc. used in drawing, machining or forming must be removed before coatingContaminants。Degreasing is one of the important processes of surface treatment.Because oil stain will reduce the adhesion of the film and affect other properties of the film, it must be cleaned.
Remove the oil stain on the surface of parts by chemical or other methods.Common methods include alkaline degreasing, organic solvent degreasing and metal cleaner degreasing.
Also called degreasing.The process of removing the oil stain on the metal surface to provide a clean surface and implement protective measures.It mainly includes: ① immersion method, soaking and washing the metal surface with solvent or alkali solution; ②Spray cleaning method, spray degreasing agent to the metal surface; ③Brushing method: brush the metal with degreaser.Remove the oil stain on the surface of parts by chemical or other methods.Common methods include alkaline degreasing, organic solvent degreasing and metal cleaner degreasing.
Oil removal purpose
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In the process of storage, handling and processing, the surface of metal is inevitably polluted by some external pollutants.
Oil removal is a treatment process for oil-water separation and oil recovery of oily wastewater.Oily wastewater comes from oil fields, oil refineries, petrochemical plants, meat, fish, poultry processing plants, grease plants, leather factories and other industrial and mining enterprises.The medicament treatment of oily sludge is a method to achieve the purpose of oil removal by using the oil removal mechanism of chemical agents such as rolling up, emulsification, dissolution and solubilization.According to the types of agents, the author summarized the research status of the treatment of oily sludge agents at home and abroad in recent years, including surfactant washing for oil removal, demulsifier demulsification for oil removal, alkaline water washing for oil removal, flocculant flocculation for oil removal, and compound oil removal between agents.These methods were evaluated and compared, and suggestions on the future research direction of oily sludge treatment technology were put forward.[1]
Physical degreasing method
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The physical degreasing method is a method of washing away oil stains by using solvents that have solubility to oil stains (animal and vegetable oils or mineral oils).This method is fast, but the degreasing effect is not very good, and most solvents are flammable and explosive, with certain toxicity, which is not safe to use.This method is applicable to stamping parts, castings, aluminum, copper and their alloy processing parts and die castings of iron and steel materials.It is suitable for mineral oil and serious grease that are difficult to be removed with alkaline solution.
The organic solvent used for degreasing should consider the solvent with strong solubility, good volatility, low toxicity, difficult ignition, low price and no corrosiveness to the coated material.Recently, benzene, ether, ketone, phenol and chlorinated solvent are mainly used.The most common degreasing solvents areTrichloroethane、Trichloroethylene, perchloroethylene, etc.The steam degreasing method is adopted, which is characterized by fast degreasing speed, high efficiency, clean and thorough degreasing, and very good degreasing effect for all kinds of oils.Adding a certain amount of emulsion into chlorinated hydrocarbon has good effect on spraying and soaking, but due to toxicity, it is rarely used except for cleaning a few parts in the electronic industry.
The processes of solvent deoiling include scrubbing, steaming and dipping.In order to make the degreasing more thorough, it is better to clean twice and change the solvent in time to ensure the degreasing quality.Because most organic solvents are toxic and easy to burn, safety and ventilation should be considered during use and storage.[2]
Chemical degreasing
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Composition of degreaser
According to the type and nature of grease, degreasing agent includes two main components, alkali detergent andsurface active agent 。
Alkali
The common alkali detergent aids aresodium hydroxide, soda ash, sodium silicate andSodium tripolyphosphate。As alkaline agents, sodium hydroxide and soda ash are the cheapest. Wastewater is difficult to treat. Sometimes, the washing objects are damaged due to the strong alkalinity. On the other hand, sodium hydroxide and soda ash are notEmulsificationIt has no effect on mineral oil cleaning;
Sodium silicate and sodium tripolyphosphate can provide both alkalinity and certain emulsifying power, and are widely used in variousDegreasing cleaning agentEspecially alkali sensitive degreasing process.The biggest defect of using sodium silicate is that if you do not wash it first with hot water after degreasing, it is difficult to completely clean the residual sodium silicate by direct cold water washing, and the residual sodium silicate will react with the acid in the next process to generate firmly adhered silica gel, thus affecting the adhesion of the coating;Sodium tripolyphosphate is mainly concerned about phosphorus pollution and environmental damage.[3]
surface active agent
Surfactant is the core component of degreaser, and early degreaser is mainly emulsified by emulsifier, such asFatty alcohol polyoxyethylene ether(AEO) series, alkyl phenol polyoxyethylene ether (TX, NP) series, etc.Excessive use of emulsifiers will emulsify and solubilize the fallen grease in the working fluid, resulting in a gradual decline in the oil removal capacity of the working fluid, which requires frequent replacement of the working fluid.
However, with the rise of surfactant price, it is increasingly required to reduce the amount of surfactant used and improve the rate of oil removal, which requires that the oil removal agent has good dispersion and anti secondary deposition performance, stripping the fallen grease from the metal surface, not emulsifying and saponifying in the solution, but floating on the solution surface, to maintain the clarity and continuous oil removal capacity of the tank liquid.
On the other hand, the surfactant suitable for degreasing is generally non-ionic product, and non-ionic products are generally of high price. In order to reduce the cost of degreasing agent, anionic products will also appear in the formula of degreasing agent, especially those with non-ionic propertiesAnionic surfactantFatty acid methyl ester ethoxylate sulfonate(FMES), with excellent characteristics of "dispersion and rolling off", is helpful for non emulsified stripping removal of oil and grease.
Intercept and degrease
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Interception and degreasing is a new concept of oil-water separation technology different from "adsorption and degreasing". It is based on a compound modified "HK" special material developed by chemical methods. This space state interception membrane has the following special functional properties under the condition of water saturation:
It is extremely sensitive to oil and water;
It has the rebound ability to resist oil adhesion;
When one-way water pressure is applied to the barrier membrane, the water particles can be displaced in a guided way, thus showing the special functional barrier effect of "water can not pass through oil".
Bidun HY series high-efficiency oil removal device is based on the principle of "intercepting oil removal", and adopts HK intercepting units with different accuracy levels, so as to achieve the purpose of quantitative control of oil removal accuracy.
Electrochemical degreasing
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Electrochemical degreasing method is to use electrolysis to place the coating on the surface filled with degreasing liquidElectrolytic cellAs the anode (or cathode), and then the DC power is applied in a short time to reduce the surface tension of the oil and solution interface. At the same time, because bubbles are separated from the electrode, the oil film is also cleaned, which makes the oil film fall off from the coating to achieve the purpose of oil removal.
Electrochemical degreasing is carried out after general organic solvent degreasing or chemical degreasing.The electrochemical degreasing of steel parts is also generally based onsodium hydroxideMainly, the electrochemical degreasing solution of aluminum, copper and other materials is generally sodium carbonate, trisodium phosphate.It is not suitable to add in the electrochemical degreasing solutionsurface active agent This is because the surfactant has foaming property, which will generate foam containing a large amount of hydrogen and oxygen mixed gas in the cathode and anode during electrolysis, which may cause explosion.
Whether chemical or electrochemical degreasing, the coating must be strictly cleaned in cold water or hot water to clean the residues such as lye and surfactant adsorbed on the surface of the coating.It is better to use flowing clean water for water washing. In order to ensure the quality of water washing, special attention should be paid to the purity and quality of cold water and hot water, and the water in the water washing tank should be replaced regularly to improve the quality and effect of water washing.
