Choosing the correct seal is essential for the operation of the entire hydraulic or pneumatic system.

After checking the dimensions by measuring the groove, internal and external diameter, it is good to focus on choosing the most suitable material for the specific use. This choice is rather complex as it is necessary to orient oneself among a multitude of polymers with different characteristics and functions.

 

To identify the correct material it is important to know the characteristics of the sealing system. More specifically, it is good to check:
 

- the chemical compatibility between the seal and the fluid or working environment

- the level of friction and wear

- the mechanical properties that define the resistance to stress

- resistance to extrusion

 

Many polymers are used in the production of the seals; among the most common ones we include Polyurethane, POM, PTFE, Phenolic Resin, NBR, FKM or Viton and TPE.

 

Polyurethane is one of the most used materials in the production of seals. It is a compound with excellent mechanical resistance, high elongation at break and excellent resistance to abrasion and cutting. It is suitable in the presence of mineral oils, petroleum derivatives and hydrocarbons. However, it is not resistant to brake fluids, chlorinated hydrocarbons and alkaline solutions.

 

POM, or Polymethyloxide, is commonly known as acetal resin. It is extremely compatible with most lubricating oils and fluids in general. It is typically used in the construction of bushings, anti-extrusion rings and sliding guide units in cylinders. It also has excellent resistance to traction and impact, a low coefficient of friction and a high elastic modulus.

 

PTFE has a very low coefficient of friction and is characterized by excellent resistance to aging and static and dynamic stresses. It also has high resistance to chemical agents and fire, not propagating the flame. These characteristics remain unchanged in a range of temperatures between -80 ° C and 260 ° C, making it suitable for the most varied uses in the industrial, electrical, chemical, hydraulic, pneumatic and food sectors.

 

The phenolic resin is unsuitable for food use due to its chemical composition. It is a synthetic material obtained from the chemical reaction between phenol and formaldehyde with which cotton or polyester fibers are impregnated. It has high toughness and resistance to traction and wear and a low coefficient of friction. It has good resistance to acid and alkaline solutions and - such as NBR - to mineral oils and fats.

 

NBR has good resistance to mineral oils and greases, such as engine oils, gear oils, differentials. It ages quickly when exposed to sun, air or atmospheric agents in general. It is extremely versatile from an application point of view thanks to thermal compatibility and stability of mechanical characteristics suitable for temperatures ranging from - 40 ° C to 120 ° C in its various formulations. It is mainly used in the production of seals and o-rings.

 

FKM is also known as Viton: it is a synthetic rubber that is very resistant to heat, oils, aliphatic and aromatic hydrocarbons and chemical agents. This material is perfect for the production of o-rings or seals where stability and elastic memory at high temperatures is required.

 

TPE, or thermoplastic elastomer, is a polyester resin available in different degrees of hardness. It is a flexible material like elastomers and has mechanical properties similar to plastics. It has excellent resistance to cutting and abrasion and high chemical characteristics. It is compatible with lubricating oils, hydrocarbons and many fluids such as acids and bases. TPE is suitable for hydraulic applications, especially for support and anti-extrusion rings.

 

In conclusion, the choice of material must take into account:
 

- characteristics of the sealing system

- physico-chemical properties of the material
 

Finally, it is important to ensure that assembly, storage and handling are carried out with care and attention, always taking into account the characteristics of the material and of the sealing system.