Rotary & Shaft Seals

Machines with many moving parts often use oil to lubricate and protect mechanical components. However, when using oil, it’s important to take steps to prevent costly and potentially hazardous leaks. Oil seals offer a simple but effective solution, closing spaces between mechanical components to prevent lubricants from escaping. As an added benefit, oil seals also prevent moisture or chemical contaminants from breaching gaps in the machinery.

MSP Seals offers a full range of oil seals to prevent oil leaks and protect sensitive machinery from damage.

What Are Oil Seals?

Oil seals, alternatively known as rotary shaft seals or lip seals, are flexible rings of elastomer that secure the boundaries between stationary and moving components in a machine. These rings are flexible but durable, resisting wear from friction and exposure to oil. These properties allow oil seals to keep lubricants in a machine while keeping contaminants out. In doing so, oil seals prolong the working life of rotating shafts and precision bearings, ensuring that moving parts retain the lubrication they need for smooth performance.

MSP’s oil seals are designed to withstand extreme working environments, offering excellent durability and low friction properties to promote long working life. Our oil seals are lightweight and have a long shelf life, so they won’t become brittle or interfere with machine operation. Compared to standard seals, they offer improved performance in a convenient and easy-to-install form, making them the perfect solution for rotary shaft sealing.

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What Is The Best Material for an Oil Seal?

Oil seals can be made from several types of polymers, but the most effective is polytetrafluoroethylene, or PTFE. PTFE has exceptionally low friction, allowing it to resist abrasion and retain its integrity over time. PTFE is also resistant to high temperatures and chemical solvents, and it requires minimal lubrication, making it ideal for almost any operating environment.

Although PTFE is an excellent general-purpose oil seal material, other elastomers can also be appropriate, including silicone, nitrile, and EPDM. Materials are often chosen based on specific application requirements, such as the need to withstand specific chemicals. The mechanical properties of the rotary shaft, including shaft hardness and roughness, can also impact the selection of an oil seal elastomer. For instance, a softer metal shaft often requires a softer seal material than PTFE.

An infographic that explains what rotary

Why Does Rotary Shaft Roughness Matter for Oil Seals?

Although the physical properties of the seal are important, the properties of the rotary shaft can also affect performance and longevity. One primary consideration in this respect is rotary shaft roughness, which refers to the surface unevenness of the shaft. Rotary shafts can have different degrees of roughness based on their machined tolerance. Smoother shafts have more even surfaces with finer machined tolerances.

Rotary shafts with the appropriate surface finish promote even sealing and limit premature wear due to abrasion. Generally, oil seals perform better when they are paired with smooth, properly finished rotary shafts. However, some surface roughness is desirable as it allows a film of lubricant to flow between the seal and the shaft, extending the longevity of the oil seal.

A rotary shaft that is too smooth exerts extra friction on the oil seal since this lubricant film cannot form. By contrast, a rotary shaft that is too rough can abrade an oil seal, causing it to fail and leak oil.

Why Does Rotary Shaft Hardness Matter For Oil Seals?

Rotary shaft hardness refers to the shaft’s resistance to indentation, which is important to consider when selecting an oil seal elastomer. The seal must always be softer than the rotary shaft to avoid damaging or wearing down the metal, leading to mechanical failure. As mentioned above, this means that softer metals are not always compatible with PTFE, which has a higher hardness relative to other polymers. PTFE seals can erode softer metal components, despite their otherwise favorable performance characteristics.

In general, harder metals are preferable for rotary shafts than softer metals, since increased hardness usually corresponds to more durable shafts and seals. However, the ideal hardness depends on a number of application-specific variables like rotation speed and pressure.

The lowest speed and lowest pressure applications can handle softer metal shafts, but hardness should still be at least 35 on the Rockwell C scale with high lubrication. When speeds or pressures are higher, the ideal rotary shafts might have hardness levels of 60 or 70+ Rc. The ideal oil seal material changes accordingly.

Despite the overall performance advantages of hard shafts, one benefit of softer rotary shafts is that they offer more leeway when working with durable oil seals. A PTFE oil seal polishes underlying metals that have hardness levels below 45 Rc, refining the surface finish for a better seal and less friction.

At higher hardness levels, this polishing effect disappears, so excess surface roughness can be more problematic. Thus, the higher the hardness required for the application, the smoother the rotary shaft needs to be to protect the working life of the oil seal. Even with proper surface finishing, seals used with very hard rotary shafts may wear out faster simply because there is less room for imperfections in the surface finish.

Oil Seal Types

Rotary Shafts & Oil Seals by MSP Seals

Whether your application uses harder metal shafts or softer ones, MSP Seals can help you identify the most appropriate oil seals for your application. Our personalized customer service team works with each client to determine your application’s key constraints, using these factors as a guide for material selection.

As experts in all manner of rotary and shaft seals, MSP offers a diverse range of oil seals and other sealing solutions, including:

  • Grease Seals
  • Shaft Seals
  • Mechanical Seals
  • V-Seals
  • Braided Packing

We offer both standard and custom configurations for all of our sealing products, with standard and custom sizes measured in inches (SAE, ARP) and metric (JIS, DIN).

While PTFE is our preferred material for performance oil seals, we also manufacture seals from a wide variety of hard and soft materials. Some of our material capabilities include:

  • Carbon
  • Ceramic
  • Nitrile Butadiene Rubber (NBR, Buna-N)
  • EPDM (EP)
  • Butyl Rubber (IIR)
  • Fluorocarbon (V, FKM, FPM, FFKM, FFPM)
  • Neoprene / Chloroprene (CR)
  • Fluorosilicone (FSi)
  • Polyacrylate (ACM)
  • Silicone (Si)
  • Polyurethane Rubber (AU, EU)
  • PTFE
  • Stainless Steel (304, 316, 316L, etc)
  • Carbon Steel
  • Brass
  • Bronze

Our comprehensive sealing offerings include manufacturing, packaging, and labeling, as well as inventory and total cost management for clients seeking full-service sealing partners.

To learn more about MSP Seal’s ISO 9001:2015-certified seal manufacturing, contact our team today. Our PTFE and sealing specialists are on hand to answer your questions and help you identify the best oil seals for your application.

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