During the maintenance process of diesel generator set, the problem of removing carbon deposits is often encountered. Most of the carbon deposits in the engine are accumulated on the valve, piston and cylinder head. The composition of the carbon deposits has a great relationship with the structure of the engine, the location of parts, fuel, lubricating oil types, working conditions, and working hours.
Carbon deposit is a complex mixture of colloid, asphaltene, carboid, lubricating oil, and carbon, which is formed by the incomplete combustion of fuel and lubricants of diesel generator under high temperature. These carbon deposits affect the heat dissipation effect of some parts of the engine, worsen the heat transfer conditions, affect its combustion, and even cause the parts to overheat and form a crack.
At present, mechanical cleaning, chemical and electrolytic methods are often used to remove carbon deposits from the generator set.
It uses a wire brush and scraper to remove the carbon deposits. In order to improve production efficiency, when a wire brush is used, the electric drill can be driven to rotate by the flexible shaft. This method is simple and often used for small-scale maintenance units, but has low efficiency, easily damages the surface of parts, and is difficult to remove carbon deposits.
It can also be used to remove carbon deposits by spraying nuclear debris. Because the nuclear debris is softer than metal, it will deform itself when it impacts the part, so the surface of the part will not be scratched, and the production efficiency is also high. This method uses compressed air to blow dry and crushed peach, apricot pit and walnut hard shell to impact the surface of the parts with carbon deposits, destroying the carbon deposit layer and achieving the purpose of removal.
For the surface of some finished parts, the mechanical method cannot be used, but chemical method can be used. Immerse the parts in a cleaning solution such as sodium hydroxide and sodium carbonate at a temperature of 80-95°C to dissolve or emulsify the grease and soften the carbon deposits. Take out after about 2 to 3 hours, and then remove the carbon deposits with a brush. Add 0.1% ~ 0.3% potassium dichromate in hot water for cleaning, and then blow dry with compressed air.
The alkali solution is used as the electrolyte, and the workpiece is connected to the cathode, so that the carbon deposit is removed under the combined action of chemical reaction and hydrogen stripping. This method has high efficiency, but it is necessary to master the specification for removing carbon deposits. For example, the specification for removing carbon deposits by valve electrochemical method is roughly: voltage 6V, current density 6 A / dm2, electrolyte temperature 135 ~ 14 5°C, and electrolysis time is preferably 5-10min.
All parts of diesel generating set that come into contact with various oils must be cleaned of oil after disintegration. Oil can be divided into two categories: saponifiable oil, which is oil that can interact with strong alkali to produce soap, such as animal oil and vegetable oil; and a type of oil that is not saponifiable, which cannot work with strong alkali, such as various mineral oil, lubricants, vaseline and paraffin. They are not soluble in water, but are soluble in organic solvents. These oils are removed mainly by chemical and electrochemical methods. Common cleaning solutions include organic solvents, alkaline solutions and chemical cleaning solutions. There are two methods of cleaning: manual and mechanical.
(1) Organic solvent
Common are kerosene, light diesel, gasoline, alcohol and trichloroethylene. Organic solvent oil removal is based on dissolving dirt, it has no damage to metal, can dissolve all kinds of grease, does not require heating, easy to use, good cleaning effect. However, most of the organic solvents are flammable, and the cost is high, which is mainly suitable for small-scale units and scattered maintenance work.
(2) Alkaline solvent
It is an aqueous solution of alkali or alkaline salt. The alkaline solution is used to chemically react with the saponifiable oil on the surface of the part to generate soap that is easily soluble in water and glycerin that is not easy to float on the surface of the part, and then washed with hot water to easily remove oil.
In the case where unsaponifiable oil and saponifiable oil are not easy to remove, an emulsifier should be added to the cleaning solution to emulsify the oil and separate it from the surface of the part. Commonly used emulsifiers are soap, water glass (sodium silicate), and gum. Different cleaning fluids should be used to clean parts of different materials. Alkaline solution has different corrosion effect on metal, especially on aluminum.
When cleaning with an alkaline solution, the solution is generally heated to 80 ~ 90°C. Rinse with hot water after degreasing to remove residual alkali solution on the surface to prevent parts from being corroded. Alkaline solution cleaning is widely used.
(3) Chemical cleaning fluid
It is a chemically synthesized water-based metal cleaning agent, which is mainly used as a surfactant. Because its surface active substances reduce interfacial tension and produce wetting, penetrating, emulsifying and dispersing, etc., have strong decontamination ability. It also has the advantages of non-toxic, non-corrosive, non-combustible, non-explosive, non-pollution, having certain anti-rust ability and low cost.
(1) Scrubbing
Place the parts in a container containing diesel, kerosene or other cleaning fluids, scrub with cotton yarn or brush. This method is easy to operate, simple equipment, but low efficiency, and is used for small and medium-sized parts produced in small batches. Under normal circumstances, gasoline should not be used, because it has fat-solubility, which will damage human body and easily cause fire.
(2) Boiling cleaning
Place the prepared solution together with the parts to be cleaned into a cleaning tank of appropriate size welded with steel plate. A heating stove is arranged at the lower part of the pool, and the parts are heated to 80-90°C for washing.
(3) Spray rinsing
Spray the cleaning fluid with a certain pressure and temperature onto the surface of the part to remove oil. This method has good cleaning effect and high efficiency, but the equipment is complex, and it is suitable for cleaning parts with less complicated shape and serious oil dirt on the surface.
(4) Vibration cleaning
It is to place the cleaned parts on the cleaning basket or cleaning rack of the vibration cleaning machine, immerse it in the cleaning liquid, simulate the artificial rinsing action by the vibration of the cleaning machine, and cooperate with the chemical action of the cleaning liquid to achieve the purpose of removing the oil contamination.
(5) Ultrasonic cleaning
It achieves the purpose of removing oil stain of the parts by the combination of the chemical action of the cleaning solution and the ultrasonic oscillation effect introduced into the cleaning solution.
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