How to carry out post-treatment after blackening surface treatment in Dalian?

1、 Cleaning process

Hot water cleaning

Purpose: After blackening surface treatment in Dalian, there will be residual blackening solution on the surface of the workpiece. The main purpose of hot water cleaning is to preliminarily remove residual chemical substances on the surface of the workpiece. Hot water can accelerate chemical reactions, allowing some easily soluble substances to detach from the surface of the workpiece more quickly.

Temperature and time: The temperature of the hot water for cleaning is generally between 60-90 ℃. Low temperature, poor cleaning effect; Excessive temperature may have adverse effects on the workpiece and the formed oxide film. The cleaning time is usually 3-5 minutes, and the specific time can be adjusted appropriately according to the size, shape, and degree of blackening treatment of the workpiece.

Operation points: Fully immerse the blackened workpiece in hot water and stir it appropriately to ensure that all surfaces of the workpiece can fully contact the hot water, in order to achieve uniform cleaning effect.

Cold water cleaning

Purpose: After hot water cleaning, there will still be some impurities remaining on the surface of the workpiece. Cold water cleaning is mainly used to further rinse off these residual substances and reduce the temperature of the workpiece, creating suitable conditions for subsequent processing steps.

Temperature and time: The temperature of cold water is generally around room temperature, and the cleaning time is about 5-10 minutes. For workpieces with complex shapes, many pores or concave parts, the cleaning time can be appropriately extended to ensure thorough cleaning.

Operation points: Use flowing cold water for cleaning, which can better remove residual impurities. During the cleaning process, the workpiece can be gently brushed by shaking or using a soft bristled brush (for workpieces that are allowed to be brushed) to help remove impurities from gaps and corners.

2、 Passivation treatment

Passivation principle

Passivation is the formation of a more stable protective film on the surface of the blackened workpiece, enhancing the corrosion resistance of the oxide film. During the passivation process, chemical reagents react with metal atoms on the surface of the blackened oxide film to passivate the active sites on the surface, forming a dense and chemically stable passivation film. This passivation film can further prevent corrosive media such as oxygen and moisture from coming into contact with the metal substrate, thereby improving the rust prevention ability of the workpiece.

Selection of passivating agent

Chromate passivator: Chromate passivation is a traditional and effective method. It can form a passivation film containing chromium on the surface of the workpiece, which has good self-healing ability and corrosion resistance. However, due to the presence of hexavalent chromium in chromate salts, they pose certain hazards to the environment and human health. Therefore, strict compliance with environmental regulations is required during use, and their use is restricted in some areas with high environmental requirements.

Chromium free passivators: With the increasing environmental requirements, chromium free passivators are gradually being applied. For example, passivators based on components such as molybdate, tungstate, silicate, etc. These passivators can form a protective film on the surface of the workpiece as a substitute for chromate passivation film. Although their rust prevention performance may be slightly inferior to chromate passivation, they have environmental advantages.

Passivation process parameters

Concentration and temperature: Taking the common chromate passivation as an example, the concentration of the passivation solution is generally around 3-5%, and the temperature is controlled at 30-50 ℃. For chromium free passivators, their concentration and temperature should be determined according to the specific product manual, and different chromium free passivators may have significant differences.

Time: The passivation treatment usually takes 2-5 minutes. If the time is too short, the passivation film may not be fully formed; If the time is too long, it may cause the passivation film to become too thick, resulting in peeling or detachment.

3、 Oil immersion treatment

Oil immersion purpose

Rust prevention: Soaking in oil can form a layer of oil film on the surface of the workpiece, which can effectively prevent oxygen and moisture in the air from contacting the surface of the workpiece, further improving the rust prevention ability of the workpiece. Especially for some workpieces used in humid or corrosive environments, oil immersion treatment is a very important rust prevention measure.

Lubrication: For some workpieces that require certain lubrication properties, such as shafts, bolts, etc. in mechanical parts, oil immersion can provide preliminary lubrication and reduce friction and wear during subsequent use.

Oil selection

Rust proof oil: Rust proof oil is a commonly used oil in oil immersion treatment. According to the usage environment and requirements of the workpiece, different types of rust proof oil can be selected. For example, for workpieces stored indoors for a short period of time, soft film rust proof oil can be used; For workpieces that are used outdoors for a long time or in harsh environments, it is necessary to use hard film rust proof oil.

Lubricating oil: If the workpiece needs to have good lubrication performance in addition to rust prevention, a suitable lubricating oil can be selected. For some precision mechanical parts, lubricating oil containing additives can be used to improve their wear resistance and oxidation resistance.

Key points of oil immersion operation

Temperature and time: The oil immersion temperature is generally at room temperature or slightly higher than room temperature. The immersion time depends on the size and shape of the workpiece, usually 3-10 minutes. For large or complex shaped workpieces, the immersion time can be appropriately extended to ensure that the oil can fully infiltrate all parts.

Drain and dry: After soaking in oil, remove the workpiece from the oil and let the excess oil drain naturally. If you need to accelerate the drying speed, you can use clean compressed air to blow dry or dry in a low-temperature environment, but be careful to avoid damaging the oil film due to high oil temperature or high drying temperature.

4、 Drying treatment

Natural dryness

Applicable scenarios: For some workpieces with low drying speed requirements and simple shapes, natural drying can be used. This method is easy to operate, cost-effective, and can avoid problems such as workpiece deformation or oil film damage that may occur due to high temperatures or forced drying.

Environmental requirements: Natural drying should be carried out in a well ventilated and dry environment, avoiding drying in damp or dusty areas to avoid affecting the quality of the workpiece. The drying time depends on factors such as the size of the workpiece, humidity and temperature of the environment, and may generally take several hours or even a day.

Drying treatment

Applicable scenarios: For mass-produced workpieces that require rapid drying or high cleanliness requirements, drying treatment is a more suitable method. For example, in automated production lines, in order to improve production efficiency, drying is usually used to process blackened workpieces.

Temperature and time control: The drying temperature is generally controlled between 80-120 ℃ for 10-30 minutes. Excessive temperature may lead to a decrease in the performance of oil film or oxide film, while low temperature may result in slow drying speed. During the drying process, attention should be paid to controlling the air circulation inside the drying equipment to ensure that all parts of the workpiece can be evenly dried.