(1) The type of surface contamination. Such as animal oil, vegetable oil, mineral oil, lubricating oil, dirty soil, fluids, inorganic salts, moisture, fingerprints, etc.
(2) The physical characteristics of the contaminants. Such as the thickness, tightness, or looseness of contaminants.
(3) the type of adhesive material. For example, alkaline solutions may be used for steel materials, and milder corrosive solutions should be considered when handling brass and aluminum materials.
(4) The degree of cleaning required.
(5) Cleaning fluid cleaning capacity and equipment condition.
(6) Danger and price costs.
The commonly used surface treatment methods are described below.
First, degreasing method
(a) The solvent degreasing method The organic solvent can effectively remove the oil on the surface. The organic solvent used for cleaning and degreasing needs to have the following properties:
(1) Strong ability to dissolve dirt;
(2) Low specific heat or latent heat;
(3) Incombustible;
(4) Non-toxic;
(5) Chemical stability and inertness to the treated surface;
(6) Lower boiling point;
(7) It is heavier than air in the gaseous state and has greater density in the liquid state;
(8) has a low surface tension and the like.
Organic solvents that meet the above requirements do not actually exist. Therefore, according to the specific circumstances, we must choose the more appropriate solvent type. Commonly used organic solvents include: acetone, benzene, toluene, xylene, trichloroethylene, carbon tetrachloride, ethyl acetate, banana water, and gasoline. For large batches of continuously produced adhesives, it is best to use trichloroethylene steam bath to remove grease.
The use of solvent degreasing is also prone to the full diffusion of some of the contaminants by virtue of the solvent. In this case, the solvent should be changed frequently and repeatedly cleaned. Generally, grease should be removed by a small number of times.
In addition, the use of solvent degreasing, must be necessary to dry time, or because the solvent remains on the surface of the adhesive and its adhesive strength decreased. For a large area of ​​the adhesive surface, wipe it from top to bottom or from left to right, and repeat until it is free of oil. There are also some use of solvents to remove grease, and then rinse with detergent.
Since many organic solvents are flammable substances, when using these solvents to remove grease, the relevant regulations for the operation of flammable and explosive materials must be observed.
If the solvent is degreasing and ultrasonic degreasing is used in combination, the treatment effect is better. Table 2 shows the effects of the solvent degreasing treatment of steel and the use of ultrasonic degreasing treatment.
Table 2 Treatment effect of solvent degreasing Treatment method Shear strength Comparative value (%) Untreated 28 Toluene degreasing 93 Heptane degreasing 93 Butanone degreasing 94 Ethyl acetate degreasing 100 Trichloroethylene degreasing 100 Methyl chloroform, Ultrasonic for 5 min Degreasing 110 Methyl chloroform, ultrasonic 13 min degreasing 113 Methyl chloroform, ultrasonic 20min degreasing 114
(B) Degreasing and Decarbonization at High Temperature
This method is generally used for degreasing and degreasing of used adhesives. Due to the long-term use of the adhesive, the surface is easily adsorbed or deposits oil. If the grease is not removed before the adhesive bonding, an oil film separation layer will be formed between the adhesive and the surface of the adhesive, which will seriously affect the bonding strength.
For these adhesives, if high temperature processing is allowed, they can be placed in an electrically heated blast oven at 200-250°C. If the adhesive pieces are too large to be joined in the electric blast drying oven, several red lights or torches can be used for local heating so that the grease on the surface of the glued parts and around it can seep out, and then wipe with a clean cotton yarn and then use a solvent. oil. It must be pointed out that when degreasing with solvent, the solvent must be separated from the fire to prevent accidents.
For reworked old parts, if a thin layer of tough carbon deposits is deposited on top, the coke must be carefully removed before the glue repair.
Coking typically consists of complex components such as combustion products, metal oxides, dust, grease, and colloidal sludge deposits. The method of removing coke can be divided into two kinds: mechanical treatment and chemical treatment. But no matter what method you use, you need to remove oil and grease.
Mechanical treatment is mainly scraped with hand tools, such as cleaning with wire brushes, copper wire brushes, scrapers, pneumatic tools, etc. If necessary, the parts are first soaked in kerosene for a period of time and then removed with abrasives.
Chemical treatment is divided into basic molten salt bath and solution treatment.
The basic molten salt bath recipe is as follows:
Sodium Chloride 5 Sodium Hydroxide 6.5 Sodium Nitrate 30
The above mixture was melted and the part was placed in the above molten bath at 250°C. The processing time was determined as the case may be.
The solution processing method to remove carbon deposit formula and process conditions are as follows:
[Formula 1]
Sodium Hydroxide 2.5 Sodium Carbonate 3.5 Water Glass 0.15 Soft Soap 2.5 Water 100
Processing conditions: 80-95°C, 1-2h. Treatment targets: steel, cast iron.
[Formula 2]
Sodium carbonate 2 Sodium phosphate 1 Water glass 0.8 Soft soap 1 Water 100 Potassium dichromate 0.3 Surfactant 0.5
Processing conditions: 80-95°C, 1-2h. Treatment targets: steel, aluminum.
[Formula 3]
Sodium hydroxide 10 water 40 Xylenol soap 50
Processing conditions: room temperature, 24h, or 60-85°C, 4. Treatment object: steel.
[Formula 4]
Sodium carbonate 1.9 Water glass 0.9 Soft soap 1 Water 100
Processing conditions: 90-95°C, 2-4h. Treatment target: aluminum.
(3) Chemical degreasing If the conditions permit, it is best to use chemical degreasing on the cemented joints. The water used in the chemical degreasing method and in the formulation of the chemical treatment method described later is soft water or pure water, that is, the treatment solution is prepared using distilled water which is generally easily available. Use tap water for washing water.
The chemical formulation used for the chemical degreasing of steels is as follows:
[Formula 1]
Sodium silicate 10 Sodium dichromate 30 Sodium phosphate 30 Sodium hydroxide 30 Water 1000
The adhesive was treated in the above solution at 80-100°C for 10-15 min, then washed with water and dried.
[Formula 2]
Sodium hydroxide 10 Sodium carbonate 50 Sodium silicate 50 Water 1000
The adhesive was treated in the above solution at 80-100° C. for 30 min, then washed with water and dried.
When washing, it must be washed several times, and the remaining alkali liquor on the surface of the cemented joints should be washed cleanly, otherwise the bonding strength will be affected. In addition, it is forbidden to degreasing and degreasing with sodium hydroxide solution for bonding materials such as aluminum alloy and babbitt.
(D) Ultrasonic degreasing
The usual surface treatment methods are difficult to remove the impurities from the dead ends such as the sipes and low enthalpies of the complex structural components. In this case, ultrasound can solve the problem more ideally.
Ultrasound is the mechanical vibration energy converted from the electrical vibration energy through the combination of a high-frequency generator and a transducer. When ultrasonic degreasing is used, the transducer is placed in a clean liquid and the treated part is placed near it. When the frequency of the ultrasonic wave is 20-5000Hz, there is already a sufficiently high energy to turn the fluid, and at the same time, a large mechanical flushing force at the interface of the surface phase tears or impacts the impurities from the wall, thus greatly speeding up The speed of cleaning dirt. This method is more suitable for small and complex parts. If the cleaned parts are large, the frequency should be reduced accordingly. In most cases, it is common for parts to be cleaned with an ultrasonic wave of 20 W/cm2 for 20-60 s. Use liquids that need to be changed frequently to prevent the formation of a fouling film on the surface of the cleaned parts.