Corrosion-resistant magnetic pumps refer to fluoroplastic magnetic pumps and stainless steel magnetic pumps based on fluoroplastics and stainless steel. Let’s first talk about the selection guide for fluoroplastic magnetic pumps.
The flow-through parts of the fluoroplastic magnetic pump are F46, and the remaining materials include the main shaft of silicon carbide, the pump body static ring, the impeller rear ring, the sliding bearing; and the fluororubber sealing ring for sealing.
It is well known that F46 can withstand the corrosion of the medium, but the silicon carbide material has a tolerance range. Considering economic factors, the silicon carbide that comes standard with the fluoroplastic magnetic pump is reaction-sintered silicon carbide, with a purity of generally 93% to 95%, and the remaining 5% is mainly silicon dioxide crystals. Silicon carbide is also very stable at room temperature, but silicon dioxide will react with many media at room temperature, such as caustic soda, hydrofluoric acid, phosphates, etc. The chemical reaction equation is as follows:
Reaction of caustic soda and silicon dioxide: SiO2+2NaOH=Na2SiO3+H2O
Reaction of hydrofluoric acid and silicon dioxide:6HF+SiO2=H2SiF6+2H2O
The above reaction will destroy the main structure of silicon carbide, increase the surface roughness of silicon carbide, turn it into a frosted state, and accelerate the wear rate of the wear parts. Therefore, the corrosiveness of the conveying medium must be studied when selecting materials, otherwise the service life of the corrosion-resistant magnetic pump will be shortened.
When conveying media such as nitric acid and organic solvents, fluororubber sealing rings cannot be selected, and fluorine-coated sealing rings should be used, because fluororubber sealing rings will swell and lose elasticity in nitric acid and organic solvents, affecting the sealing performance.
Let’s introduce the selection points of stainless steel-based magnetic pumps in corrosion-resistant magnetic pumps.
Stainless steel magnetic pumps are mainly based on austenitic stainless steel. Austenitic stainless steel magnetic pumps have poor corrosion resistance in acidic media, but are inert in alkaline corrosive media. Therefore, stainless steel corrosion-resistant magnetic pumps are generally selected in solutions containing alkaline media.
In addition to the austenitic stainless steel of the flow-through parts, the remaining materials immersed in the medium are: SIC, cemented tungsten carbide, austenitic stainless steel after ion nitriding; and all-PTFE sealing gaskets.
The reaction of silicon carbide in alkali solution is as mentioned above. Cemented tungsten carbide, ion nitrided stainless steel, etc. are inert in alkali solution. Therefore, when conveying caustic soda and other media, cemented tungsten carbide wear parts are generally selected.