Grease sticking to the workpiece can be divided into two categories, the first category for animal and vegetable oils, they can be decomposed under the action of alkali, known as saponification class grease. The second category for different viscosity (liquid or solid), different composition (hydrocarbon) of mineral oils, such as gasoline, petroleum jelly, paraffin, lubricants, etc., in the role of alkali does not decompose, known as non-saponification class.
There are too many oil-contaminated parts, before chemical degreasing should be pre-washed with benzene, trichloroethylene, gasoline or other organic solvents to wash away excessive oil. Whether saponification class or non-saponification class grease are insoluble in water, so it must be in a certain composition of the solution with chemical treatment to remove from the metal surface. For the saponification class of grease can be used saponification reaction and emulsifier adsorption method to remove; non-saponification class can be used to remove the emulsifier adsorption method.
1, saponification in addition to oil
Use of alkali solutions such as NaOH, KOH or alkaline salt solutions such as Na2CO3, Na3PO4, K2CO3, NaCN, etc. and saponification class of grease and saponification reaction occurs to produce a colloidal solution of sodium stearate or glycerol dissolved in water and removed from the surface of the metal,
Reaction in the heating of the fast, sodium stearate and glycerol easily dissolved in hot solutions. Glycerol is easily soluble in hot solution, so the oil removal should be heated to keep the temperature of the oil removal solution within the range of 80℃～boiling point.
Saponification reaction of NaOH concentration should not be too high, because the concentration of high can promote some easy to oxidize the generation of oxide film of metal, therefore, de-oiling tank caustic soda concentration should not exceed 100g / L. If you are afraid of corrosion, can be used to dissolve in water to produce hydrolysis of alkaline salt solution such as Na2CO3, Na3PO4, etc., the concentration should also not exceed 150g / L.
2, Emulsifier adsorption degreasing
Workpiece surface of non-saponifiable oil and grease, can not be removed by alkali, but under certain conditions, add emulsifier, so that the oil droplets and alkali to form an emulsion, can be removed from the metal surface.
Emulsifiers, such as water glass, soap, sodium stearate, fatty acids, and so on.
There are the following points that must be noted when chemically removing oil.
①Should be based on the type of workpiece oil to formulate the composition of the oil solution
Degreasing can be added to the caustic soda, but should not be too much, not more than 100g / L, add the amount of alkaline salts should not be more than 150g / L, generally 60 ~ 80g / L, emulsifiers are generally controlled in the 0.5 ~ l0g / L.
② Degreasing process to be heated
Heating can promote the saponification reaction, promote the dissolution of emulsifiers, and promote the flow of the solution, so the heating can be shortened processing time, the general working temperature should be more than 80 ℃.
③ Should stir the solution or brush the workpiece, can make the metal surface around the emulsifier update, so that the oil droplets from the metal surface through the mechanical action removed.
④ Degreasing should be constantly replenished drug consumption and removal of soap scum and floating oil layer.
General chemical degreasing time according to the degree of oil contamination of the workpiece, the composition of the degreasing solution, temperature, stirring and scrubbing degree of different and different, usually 10 to 30 minutes.