The hottest surface treatment method

2022-09-21
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Surface treatment methods (I)

the commonly used surface treatment methods mainly include degreasing treatment, mechanical treatment and chemical treatment. Many factors should be considered in the selection of surface treatment method, including:

(1) types of surface pollutants. Such as animal oil, vegetable oil, mineral oil, lubricating oil, dirt, fluid, inorganic salt, water, fingerprint, etc

(2) physical properties of pollutants. Such as the thickness, tightness or looseness of pollutants

(3) types of bonding materials. For example, alkali solution can be used for steel materials, while mild solution with less corrosion should be considered when dealing with brass and aluminum materials

(4) the degree of cleaning required

(5) cleaning ability of cleaning fluid and equipment condition

(6) danger and price cost, etc

the commonly used surface treatment methods are introduced as follows

I. degreasing treatment method

(I) solvent degreasing method

organic solvents can effectively remove oil stains on the surface. For the organic solvent used for cleaning and degreasing, it is required to have the following properties:

(1) strong ability to dissolve dirt

(2) lower specific heat or latent heat

(3) non combustible

(4) non toxic

(5) stable chemical properties and inert to the treated surface

(6) low boiling point

(7) it is heavier than air in the gaseous state, and it also has a larger density in the liquid structure, which is mainly composed of steel beams, steel columns, steel trusses and other components made of section steel and steel plates

(8) low surface tension, etc

in fact, organic solvents that can meet the above requirements do not exist. Therefore, it is necessary to select a more appropriate solvent

type according to the specific situation. Commonly used organic solvents include acetone, benzene, toluene, xylene, trichloroethylene, carbon tetrachloride, ethyl acetate, banana

water, gasoline, etc. For large-scale continuous production of bonding parts, it is best to use trichloroethylene steam bath to remove grease

on the basis of solvent degreasing and absorption, we should try our best not only to preserve international advanced technology, but also prone to the full diffusion of some pollutants by means of solvent. In this case, the solvent should be changed frequently and cleaned repeatedly. Generally, a small number of times should be used to remove grease

in addition, when degreasing with solvent, there must be necessary drying time, otherwise the bonding strength will be reduced due to the residual solvent on the surface of the bonding part. For the surface of large-area bonding parts, wipe it from top to bottom or from left to right repeatedly until there is no oil stain. Some use solvent to remove grease, and then rinse with detergent

since many organic solvents are inflammable substances, the relevant regulations on the operation of inflammables and explosives must be observed when removing grease with these solvents

if solvent degreasing and ultrasonic degreasing are combined, the treatment effect is better. Table 2 shows the effect of solvent degreasing treatment of steel and its combination with ultrasonic degreasing treatment

Table 2 treatment effect of solvent degreasing

comparison value of shear strength of treatment methods (%). Untreated 28 toluene degrease 93 heptane degrease 93 butanone degrease 94 ethyl acetate degrease 100 trichloroethylene degrease 100 methyl chloroform, ultrasonic degrease 110 methyl chloroform for 5 minutes, ultrasonic degrease 113 methyl chloroform for 13 minutes, Ultrasonic 20min degreasing 114

(II) high temperature degreasing and carbon removal

this method is generally used for degreasing and oil removal of used bonding parts. Due to the long-term use of the bonding parts, the surface is easy to absorb or deposit oil stains. If the oil stains are not removed before bonding, an oil film isolation layer will be formed between the adhesive and the surface of the bonding parts, which will seriously affect the bonding strength

for these bonded parts, if high temperature treatment is allowed, they can be placed in an electric blast drying oven at ° C. If the bonding part is too large to be added to the electric blast drying oven, several red lights or blowtorch can be used to heat locally to make the grease on and around the surface of the bonding part exude, and then wipe it with clean cotton yarn, and then remove the grease with solvent. It must be pointed out that when removing oil with solvent, the solvent must be separated from the fire source to prevent accidents

for the repaired old parts, if there is a tough thin layer of carbon deposit on it, the carbon deposit must be carefully removed before bonding and repairing

carbon deposition is generally composed of complex components such as combustion products, metal oxides, dust, grease and its colloidal sludge deposits. The methods of removing carbon deposits can be divided into mechanical treatment and chemical treatment. However, no matter what method is used, it needs to be degreased in advance

mechanical treatment is mainly scraped by hand tools, such as steel wire brush, copper wire brush, scraper, pneumatic tools, etc. If necessary, soak the workpiece in kerosene for a period of time, and then remove it with abrasive, etc

chemical treatment is divided into alkaline molten salt bath method and solution treatment method

the formula of alkaline molten salt bath is as follows:

sodium chloride 5 sodium hydroxide 6.5 sodium nitrate 30

melt the above mixture, and then place the workpiece in the above molten bath at 250 ° C for treatment. The treatment time depends on the specific situation

the formula and process conditions for removing carbon deposits by solution treatment are as follows:

[Formula 1]

sodium hydroxide 2.5 sodium carbonate 3.5 sodium silicate 0.15 soft soap 2.5 water 100

treatment conditions: ° C, H. Processing object: steel and 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

treatment conditions: ° C, H. Processing object: steel and aluminum

[Formula 3]

sodium hydroxide 10 water 40 xylenol soap 50

treatment conditions: room temperature, 24h, or ° C, 4. Processing object: steel

[Formula 4]

sodium carbonate 1.9 water glass 0.9 soft soap 1 water 100

treatment conditions: ° C, H. Processing object: aluminum

(III) chemical degreasing

if conditions permit, it is best to use chemical degreasing method for bonding parts. The water used in the formula of chemical degreasing method and the chemical treatment method described later is soft water or pure water, that is, distilled water that is generally easy to obtain is used to prepare the treatment solution. Tap water is used for washing

the solution formula used for the chemical degreasing method of steel is as follows:

[Formula 1]

sodium silicate 10 sodium dichromate 30 sodium phosphate 30 sodium hydroxide 30 water 1000

the bonding parts are treated in the above solution at ° C for min, then washed and dried

[Formula 2]

sodium hydroxide 10 sodium carbonate 50 sodium silicate 50 water 1000

treat the bonding parts in the above solution at ° C for 30min, then wash and dry

when washing with water, it is necessary to wash the lye remaining on the surface of the bonding parts for many times, otherwise the bonding strength will be affected. In addition, for bonding materials such as aluminum alloy and Babbitt alloy, it is strictly forbidden to boil with sodium hydroxide solution to degrease and degrease

(IV) ultrasonic degreasing

the usual surface treatment methods are difficult to remove impurities from the fine cracks, low-lying and other dead corners of complex structural components. In this situation, ultrasonic wave can solve the problem ideally

ultrasonic wave is the mechanical vibration energy converted from electric vibration kinetic energy through the combination of high-frequency generator and transducer. When ultrasonic degreasing is used, the transducer is placed in the clean liquid, and the processed parts are placed near it. When the frequency of ultrasonic wave is Hz, there is enough energy to flip the fluid, and at the same time, a great mechanical scouring force is generated on the interface of the surface phase to tear or impact the impurities out of the wall, so the speed of cleaning the pollutants is greatly accelerated. This method is more suitable for small complex parts. If the purified parts are large, the frequency should be reduced accordingly. In most cases, the general parts can get a sufficiently clean surface after being treated in an ultrasonic wave with a power of 20w/cm2 for S. The liquid used should be changed frequently to avoid the formation of pollution film on the surface of clean parts

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