Materials are the deciding factor for how much wear, corrosion, and temperature a seal can withstand. This article introduces the main material groups used in mechanical seals so that you can better understand the technical specifications and choose the right seal.
A seal set consists of many parts made from different materials, each part withstanding a different type of load. If just one material is not compatible with the medium or temperature, the entire seal set can fail prematurely, even with a good design.
Is a soft, self-lubricating material that can withstand short-term dry running and does little damage to the mating face, so it's often used as a soft face. Carbon is impregnated with resin or metal like antimony to increase durability, tightness, and wear resistance. The limitation is that it's difficult to withstand strong oxidizing agents and can swell or crack if impregnation is not suitable.
Silicon carbide (SiC) is very hard, wear-resistant, has good thermal conductivity, and can withstand most chemicals. The reaction-bonded type contains free silicon, so it's cheaper but less durable with strong alkalis, while the sintered type is more resistant to chemicals. Alumina ceramics are cheaper, suitable for water and light chemicals, but less resistant to thermal shock. Silicon nitride is also used when high impact resistance is required.
A hard alloy consisting of carbide particles bonded by cobalt or nickel. Very impact-resistant and able to withstand heavy loads, suitable for media with solid particles and high pressure. The type using nickel as a binder is more resistant to corrosion than the type using cobalt.
Diamond or DLC coating reduces friction and increases the ability to withstand dry running, while hard coatings like chrome oxide or stellite increase wear resistance for shaft sleeves and metal parts.
Most gasket materials are elastomers, each suitable for a group of media and a temperature range (changing depending on the formula):
PTFE is inert to most chemicals and can withstand temperatures of around 260 degrees C, often filled with glass, carbon, or graphite to reduce deformation. PEEK has high mechanical strength, used for bearing rings and load-bearing parts.
Stainless steel 316 and 316L are used for most applications, duplex for chloride environments like seawater. Nickel alloys like Alloy 20, Hastelloy, or Inconel are used for strong acids and high temperatures, titanium for special corrosive environments.
Hardness determines wear resistance, thermal conductivity helps to dissipate heat at the seal face, the coefficient of expansion affects deformation when the temperature changes, and the PV limit (pressure multiplied by sliding speed) indicates the load that the seal pair can withstand. Chemical compatibility needs to be looked up in the manufacturer's table.
Choosing materials only by price, ignoring the actual concentration and temperature of the medium, forgetting that dry running damages hard seal pairs, or using EPDM for media containing oil. Please provide full information to SNS-VN for advice on suitable materials and a quote.