The design and composition of mating faces in all mechanical seals are usually taken for granted but are crucial with respect to the prime objective—to prevent leakage reliably. To accomplish this, different materials are used—including silicon carbide, tungsten carbide, aluminum oxide, hard coatings and metals, mechanical carbon graphite with antimony, or resin impregnation. The first three ceramics are referred to as hard-face materials, among which silicon carbide is used most frequently.
If one intends to eliminate every chance of a premature seal failure and give prolonged life to all seals, they should select an appropriate mechanical seal face material.
Let’s look at some seal face materials along with their applications.
Glass filled PTFE (or Teflon R)
It offers the chemical resistance of PTFE. However, to put a stop to cold flow issues related to PTFA and to give hardness to the face, glass must be added.
Ni-resist
It’s stainless steel with a nickel to reduce the friction that the rotating face generates. It’s not just perfect for freshwater application but is also quite an affordable seal face.
Tungsten carbide
Similar to silicon carbide, this seal is also very versatile. Yes, it has the hardness of a silicon carbide, but it’s quite heavy to the touch. This means, distinguishing it from silicon carbide isn’t difficult. As a result of its high modulus of elasticity, distortion can be prevented. This is why it’s best for high-pressure applications. To reuse tungsten carbide, it can be polished and re-lapped.
Silicon carbide
Both silicon carbide and tungsten carbide are versatile seal face materials. While it’s also a hard material, it’s blue and is lighter to the touch. Compared to most mechanical seal face materials, the lubrication qualities of silicon carbide are easily the best. Alpha sintered silicon carbide is usually used in high-temperature sealing environments and is most suited for chemical applications. Contrary to tungsten carbide, silicon carbide is quite hard. If dropped or contacted with force, it may crack or shatter.
Ceramic
With 99.5% aluminum oxide, ceramic offers incredible wear characteristics as a result of its hardness. It applies to almost every product and is chemically inert. However, ceramic can’t deal with the thermal shocks that 17-4 seats or Ni-resist can. If your drop ceramic on concrete, it will also shatter.
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