Transfer of boric acid (H₃BO₃) through chemical pumps requires special attention to the selection of mechanical seals, as this substance is not aggressive like many other acids, but still requires materials with good chemical resistance and wear resistance.
1. Seal materials:
Mechanical seal faces:
Ceramics (silicon carbide, aluminum oxide): These materials have excellent wear resistance and chemical resistance, making them a good choice for working with boric acid. Ceramics withstand the effects of chemicals, providing reliable sealing.
Graphite: Graphite also has good chemical resistance and is often used for sealing materials in the chemical industry. However, it needs to be protected from mechanical wear, as graphite is a fairly brittle material.
Stainless steel (316, 904L): Stainless steel is a good choice for metallic seal parts, as it has good resistance to boric acid. For enhanced corrosion protection, more specialized steel grades or coatings can be used.
PTFE (Teflon): This material has excellent chemical resistance to boric acid and can be used for various sealing rings and components that come into direct contact with the liquid.
Elastomers:
FKM (fluoroelastomer, Viton): This material has good resistance to organic acids, including boric acid, and is suitable for use at high temperatures.
EPDM (ethylene-propylene-diene monomer): EPDM is used for seals that come into contact with diluted acids. It is resistant to the effects of boric acid and suitable for lower temperatures and concentrations.
PTFE: This material is suitable for various sealing elements, as it has excellent chemical resistance and good wear resistance, but may have limitations in mechanical strength.
2. Types of seals:
Mechanical seals: This is the most preferred type of seals for chemical pumps transferring boric acid. Mechanical sealing provides reliable sealing, preventing liquid leakage and maintaining the required pressure in the system.
Wet seals: This solution can be used to prevent overheating of the seals or to provide cooling during operation. This is suitable if boric acid is used in concentrated form and the operating temperature is elevated.
Dry seals: Can be used when a seal is required without the need for cooling. They can be effective if temperature and pressure are controlled and within acceptable limits.
3. Design and additional mechanisms:
Dust seals and protective rings: These elements help prevent the entry of contaminants and solid particles into the sealing area, reducing the risk of wear and extending the service life of the seals.
Lubrication and cooling systems: In case the temperature or concentration of boric acid is sufficiently high, a lubrication or cooling system may be necessary to maintain the normal operation of the seals and prevent overheating.
Seal condition monitoring: To ensure durability and reliability, it is recommended to use seal condition monitoring systems to timely detect wear and prevent leaks.
4. Operating conditions:
Temperature: Boric acid is usually used in the temperature range from -10°C to 80°C, depending on the concentration. The seal must be resistant to these temperatures.
Acid concentration: Boric acid is most commonly used in diluted solutions. However, for high concentrations, materials need special resistance to chemical attacks.
Pressure: The pressure at which the pump operates is also important. The mechanical seal should be designed for the working pressure corresponding to the process of transferring boric acid.
5. Recommendations:
Ceramics or PTFE are ideal materials for mechanical seal faces, as they have excellent chemical resistance and resistance to boric acid.
FKM (Viton) or EPDM can be used for sealing rings, especially at lower acid concentrations.
Stainless steel (316L or 904L) is a good choice for metallic seal parts if the concentration of boric acid is not too high.
Conclusion:
For the transfer of boric acid, it is necessary to choose a mechanical seal that provides reliable sealing with moderate chemical activity of the substance. Ceramics, PTFE, graphite, and stainless steel are ideal materials for seals. FKM and EPDM will provide reliable sealing in cases of low acidity of the solution. The selection of materials depends on the concentration, temperature, and pressure, as well as other operating conditions of the system.