Separation technology is an extremely widely applied technology, suitable for various industries such as medicine, chemical industry, metallurgy, textile, environmental protection, food, military, etc. It uses centrifugal force as a driving force According to the physical characteristics and different separation requirements of Zaogu and other suspensions or emulsions, a device that achieves different separation purposes. Due to its simple structure and high efficiency, the pure physical separation process can fully ensure the characteristics of the separated materials. Therefore, the market application of centrifuges is extremely wide, especially for imported products like Thermo brand.

In recent years, China's national economy has continued to develop, new technologies and new processes have been presented endlessly, and the application range of centrifuges is more extensive; however, in this process, most manufacturers are more concerned about the separation performance and strength of the centrifuge Requirements, the impact of corrosion factors are often not paid enough attention, which brings some negative effects. This article makes some analysis and explanations on this issue for everyone to discuss.

As we all know, the harm of corrosion is extremely huge. There are many examples in the world that can illustrate that a centrifuge is a high-speed rotating equipment, and its safety requirements are as important as pressure vessels. Most centrifuge manufacturers are designing, selecting and In the application, more consideration was given to the influence of uniform corrosion on the strength parts, neglect of the adaptability of the structural design, processing technology, etc. to the corrosive environment, leading to some serious consequences. Not only the parts have a tendency to corrode and pollute the separated materials; more seriously, they even cause machine damage and death.

1. Centrifuge environment

Centrifuges are divided into different types of equipment according to function and structure, but all have common characteristics:

1. The drum is a high-speed rotating part;

2. Take the drum as the main body to form the separation space;

3. The drum has a special-shaped structure;

4. There are other couplings or supporting parts in the drum.

These characteristics of the drum show that the core part of the centrifuge is a stress part, and its special-shaped geometry leads to the multi-region stress distribution of the part and the coordination of multiple parts, which makes the possibility of forming a galvanic pair possible. , These are some situations worth noting.

2. Possible corrosion phenomena

The forms of metal corrosion are mainly divided into two categories: uniform corrosion and local corrosion. The former is easy to find because of the apparent phenomenon, and it is clearly stated in most manual data. It is not detailed here, only the latter is discussed.

Local corrosion only occurs locally, and it is an extremely serious and harmful damage, such as pitting corrosion, crevice corrosion, intergranular corrosion, stress corrosion, wear corrosion, etc. In centrifuges, local corrosion is widespread and should be Focus on the analysis of its formation mechanism, take measures to overcome it.

1. Porosity is a highly corrosive phenomenon, which mainly exists in metals that are easily passivated, such as stainless steel. Due to possible defects on the surface, there are active ions in the solution that can damage the passivation film (such as halogen Ion), the passivation film is partially destroyed, thereby forming galvanic pairs, causing pitting corrosion. After the formation of pitting corrosion, due to the effect of centrifugal force, the dynamic process of the galvanic couple in the hole will be accelerated to ensure the continuity of the pitting corrosion until the perforation, which is different from the pitting phenomenon under static conditions.

2. Intergranular corrosion will cause parts to lose strength and elongation, causing parts to break brittlely. It is a kind of harmful damage that develops inward from the surface along the grain boundary and has no signs of corrosion on the outer surface.

3. Wear and corrosion means that the surface of the parts suffers from both wear and corrosion.

4. Stress corrosion is the damage caused by a certain tensile stress in a corrosive environment. It has the following characteristics: residual tensile stress, applied tensile stress, corrosive penetration environment, local defects.

The above-mentioned four kinds of corrosion are extremely serious to the centrifuge and may cause serious consequences.

3. Measures

1. Different materials and separation requirements require different models. After the model and main parameters are determined, according to the corrosion resistance of different materials in different environments, the physical and chemical characteristics, cost performance and other factors are combined to determine the strength part material from the basic level. From the point of view of the material itself, the target material it targets is safe, so the selection of materials should follow the following principles:

a. There is no absolute universal anti-corrosion material, you must fully understand the application environment, and select materials, such as stainless steel is not suitable for concentrated carbon sulfate steel but suitable.

b. Stainless steel is not stainless, but only in air and other adaptive environments.

c. In the same environment, choose the same material or materials with similar equilibrium potentials as much as possible to avoid causing galvanic couples to the environment.

d. Comprehensive price-performance ratio, with special attention to the influence of processing technology.

2. Structural design

An excellent design can extend the service life of the equipment and ensure the safety of the equipment. For structural design, the design defects that are most likely to accelerate corrosion are the stress concentration tendency and the crevice environment. Sometimes the corrosion rate is small despite the metal immersion solution; Because the chemical and electrochemical state of the internal solution has changed (PH and potential drop), it will cause severe crevice corrosion, so the design should pay attention to:

a. Try to avoid the occurrence of gaps;

b. Try to use the same material in the same environment;

c. Ensure the uniformity of parts or increase compressive stress;

d. Avoid forming dead angles to ensure smooth flow of fluid.

3. Surface protection measures

A basic idea for controlling corrosion is to isolate the corrosive environment. In the design of centrifuges, surface treatment methods are often used, such as flanges, galvanization, chromium plating, electroless plating, etc. These methods are effective in many environments, but for rotating parts, an important phenomenon must be noted: the substrate The material and the coating are two kinds of materials, and their coefficients of linear expansion are different. When the rotating member is elastically deformed, a different amount of deformation will be generated, resulting in a large number of micro-cracks. If the aforementioned phenomenon exists, it will accelerate corrosion formation. Therefore, the surface protection method for rotating parts should be used with caution.

4. Corrosion inhibitor

The centrifuge itself involves multiple disciplines. In order to use the centrifuge well, in addition to the above measures, you should also pay attention to study its application environment. The application of corrosion inhibitors is also widely used in practical applications. For some harsh environments, the use of appropriate corrosion inhibitors can bring parts to a suitable level. As long as the process permits, the use of corrosion inhibitors should be an effective way for centrifuge applications.

5. The correct process method design is correct, and the material selection is reasonable, which is only a prerequisite for solving the corrosion of the centrifuge; the correct application of the processing technology also affects the anti-corrosion ability of the centrifuge to a certain extent. Processing methods usually leave many defects on parts or equipment, such as misalignment, local stress, etc. Misalignment may cause gaps, unreasonable clamping positioning methods may lead to eccentric parts, unreasonable tooling may produce rough surfaces, and assembly may not Appropriate, unreasonable welding, heat treatment, uneven tightening bolt force, etc. will cause local stress concentration.

Therefore, finding the correct processing method is also an effective way to prevent corrosion.

The corrosion problem of the centrifuge is a comprehensive and complicated problem, because the working environment of the centrifuge is quite different from the data obtained in the static state of the general information manual. Therefore, when referring to the relevant data, in addition to the above analysis, the influence of many factors such as dissolved oxygen in the solution, temperature, high-speed fluid, and flow state changes in the separation zone should be considered, and appropriate measures should be adopted to ensure the safe and reliable operation of the centrifuge.

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