In chemical plants, the ventilation system is very important. Most of the fans that make up the ventilation system are centrifugal fans. However, in the face of the corrosive gas generated by the processing of chemical products, it is easy to cause corrosion of the impeller of the centrifugal fan, which seriously affects the efficiency of the fan. Seriously It will also cause damage to the impeller and affect the production of the product. How to deal with the corrosion of the impeller of the centrifugal fan?
1) Common impeller anti-corrosion measures for centrifugal fans
The corrosion of the centrifugal fan impeller is mainly caused by the corrosive gas contained in the conveying medium, and the types of corrosion caused by different conveying media are also different. In order to prevent the occurrence of impeller corrosion, the following anti-corrosion measures are usually adopted:
1. Impeller with corrosion-resistant material
Austenitic stainless steel (such as 1Cr18Ni9Ti) has low yield strength and is not suitable for manufacturing impellers with high speed. It is suitable for general low-speed fan anti-corrosion impeller materials. When containing CO2 and other media with corrosive gas and smoke, Cr13 stainless steel is mainly used, but stress corrosion should be paid attention to. For fan impellers requiring strong corrosion resistance and high speed, martensitic precipitation stainless steel is widely used, such as 0Cr17Ni4Cu4Nb and FV520B, etc.
2. Plating corrosion-resistant metal layer
The surface of the centrifugal fan impeller can be coated with corrosion-resistant metal materials. The commonly used materials are: thin stainless steel plate, liquid metal, amorphous nickel-phosphorus (Ni-P) alloy, etc. Among them, amorphous nickel-phosphorus (Ni-P) alloy is a relatively successful anti-corrosion coating on the surface of centrifugal fan impellers in recent years. Due to the ideal amorphous structure and alloy properties of the coating, grain boundary corrosion and crystallite The Ni-P alloy coating with coating hardness of HRC50~70 has the characteristics of corrosion resistance, wear resistance, and strong corrosion resistance to hydrochloric acid, sulfuric acid, phosphoric acid and caustic soda.
3. Spray corrosion-resistant coating
The anti-corrosion spraying methods on the surface of centrifugal fan impeller include surface thermal spraying, plasma spraying, etc. The spraying materials include nickel and nickel alloy powder, stainless steel powder, etc. Among them, austenitic stainless steel is mostly used for thermal spraying and has good manufacturability, while nickel and nickel alloy coatings are resistant to hydrosulfuric acid, phosphoric acid, hydrocyanic acid and hydrofluoric acid. The corrosion resistance of media such as acetic acid, ferrous sulfate solution and dry gas is good, but the corrosion resistance of hydrochloric acid, nitric acid, potassium acetate, sulfurous acid and other media is not good. In addition, there are many non-metallic corrosion-resistant coatings composed of paint, rubber, vinyl, etc., which have good corrosion resistance in most oxidizing media and some reducing media.
2) the treatment method of centrifugal fan impeller corrosion
In the actual use of the centrifugal fan, the impeller adopts rubber anti-corrosion paint and epoxy resin paint for anti-corrosion spraying, and in the face of serious corrosion environment, the economy of this material is also better. In most cases, the gas will inevitably cause corrosion to the impeller, so the precise composition of the gas medium must be mastered before the centrifugal fan runs. When the centrifugal fan impeller has corroded, the following measures should be taken to deal with it:
1. Re-analyze the composition of the gas medium and the materials used.
2. If the medium is sulfur dioxide and chlorine gas, the content of mixed water should be detected, and then appropriate treatment measures should be taken. Because the two media are hard to have corrosion-resistant materials except in the dry state.
3. Check the shedding of anti-corrosion materials. If the rotor is unbalanced due to corrosion and causes excessive vibration, the emergency measures of ordinary steel supplementation can be used, but the durable treatment parts must be replaced in a short time.
4. In corrosion, general corrosion is easier to deal with, while local corrosion or pitting corrosion such as trench corrosion and crevice corrosion is faster and more dangerous, so special attention should be paid.
3) Resin anti-corrosion spraying process of centrifugal fan impeller
In the face of the corroded centrifugal fan impeller, the editor takes the relatively economical resin anti-corrosion spraying process as an example to introduce the specific impeller anti-corrosion method, hoping to help everyone.
1. Resin anti-corrosion spraying process
(1) First, polish and sandblast the corroded impeller.
(2) Brush 901 or 470 resin evenly on the impeller body, and use polyester cloth as a primer to bond the impeller surface and impeller blades.
(3) Brush 901 or 470 resin evenly on the polyester cloth again, and bond it with glass chopped strand mat. The bonding surface must be flat and even.
(4) Brush 984 or 470 resin evenly on the bonded chopped strand mat, face it with the talc powder groove, and bond it with glass fiber cloth.
(5) After that, apply a layer of 984 or 470 resin to match with the talc ditch.
2. Treatment after resin anti-corrosion spraying
After the centrifugal fan impeller is anti-corrosion treated according to the above method, it is necessary to wait for 3~6 hours according to the ambient temperature. After the adhesive anti-corrosion material is completely dry, reassemble the impeller part and the centrifugal fan casing at the same time. After the reassembly is completed For Centrifugal Fan Carry out a comprehensive inspection and confirmation. After confirmation, the dynamic balance test is divided into online test and offline test. Then according to the impeller diameter and steering and the angle indicated by the dynamic balance, calculate the added grams and position of the counterweight. From past experience:
(1) Impellers with a diameter of less than 1200mm need to add 20~30g of counterweights;
(2) When the diameter is 1200~1800mm, add 60~80g of counterweight;
(3) When the diameter is above 1800mm, add a counterweight of 90~120g;
It is qualified until the vibration value reaches 3~5mm/s. In this case, the dynamic balancing operation is completed, and then the centrifugal induced draft fan enters the normal operation state.
