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Seal selection – part 2

Choosing bespoke, machined sealing solutions

Industrial Seals Expert turns its attention to machined seals in the latest installment of the blog series “seal selection.” Discover how seals are machined, the benefits of customizing seals to order, and – above all – which machined solutions are best suited to your application.

Over 30 years ago, SKF developed its Machined Seals Concept (MSC) and opened up a host of opportunities for engineers and maintenance technicians alike. Experience has shown that ready-made, off-the-shelf seals are not always a suitable option in an emergency or when creating a prototype. With the MSC, operators can choose from around 170 standard sealing profiles and 26 standard (and over 50 additional) materials to develop bespoke solutions. This enables rapid production of seals for any conceivable application, regardless of dimensions and design.

Made-to-order solutions

The SKF SEAL JET system makes this possible. Rather than waiting on parts to be manufactured and delivered, unique designs can be realized in minutes. But when selecting any critical engineering component, it’s vital to cover all the necessary bases. When selecting your seal profiles and sealing materials, consider the following:

  • Movement during operation: linear or rotating?
  • Temperature range
  • Speed: stroking or circumferential and rotational
  • Pressure differentials
  • Fluid media: type and viscosity
  • Surface specifications
  • Environment: contaminants, abrasives, external temperatures

Before deciding whether to deploy a linear or a rotary seal, one should be able to determine the difference between the two. To put it simply, rotary seals are only suitable for applications with rotating parts and are designed specifically for that purpose. Components with a linear motion – a one-dimensional movement along a straight line – are sealed with a linear solution (piston seal, rod seal, wiper seal).

For more on what the SKF SEAL JET system can do and to see it in action, watch the video below:

SKF Machined seals concept - Production of machined seals

Piston seals

Piston seals – both single- and double-acting – can be machined for a variety of applications. Found in various industrial machinery and off-highway equipment, agricultural environments, as well as energy-generating applications such as wind and hydro power, they are prone to high pressure and contact forces which can be countered with the appropriate sealing surface properties.

Whether your seal should be machined with an unloaded or a loaded lip seal design rests entirely on the intended application. Unloaded lip seal designs can minimize friction, are focused on leak tightness, and are normally intended for applications with frequent movement. Loaded lip seal designs are best installed in applications with high sideload and low temperatures. SKF also recommends choosing X-ECOPUR as slide ring material when preparing to machine a piston seal, as it will support static sealing behavior.

Rod seals

Selecting profiles and materials for a rod seal is a complex task as there are many different cylinder designs and application criteria combinations possible. That said, the ability to machine rod seals on site with the SKF SEAL JET system can help speed up lead times. Normally housed between a cylinder head and a piston rod, rod sealing systems can consist of two different seal types, a rod seal and a buffer seal, or a just a rod seal – but always in combination with a wiper seal.

As with piston seals, rod seals are fitted with either a loaded or unloaded lip seal. They are also normally single-acting solutions. That means that fluid pressure acts from inside the cylinder on one side of the seal. Pressures acting on the rod side of the piston can be more than 400 bar, but pressure peaks can be even higher. Therefore, getting rod seal material selection right is key to engineering success. Choose a wear-resistant seal material and a surface material that meets your application’s surface specifications.

Wiper seals

It is a wiper seal’s job to ensure dirt, moisture, or other abrasives are clear from piston rods. And again, these solutions can be applied to many industries. It’s imperative that operating conditions and sealing materials are assessed in great detail before machining starts.

Single-acting designs can be machined for hydraulic or pneumatic applications. In medium-to-heavy duty hydraulic applications, the SKF SEAL JET system can machine a double-acting design to help prevent leakages. Double-acting wiper seals for pneumatics are used as a complete solution for light duty applications where the function of the rod and the wiper seals can be combined.

Rotary seals

Single-acting shaft seals, double-acting slide ring rotary seals, v-rings, and all their various modifications fall into the machined rotary family of solutions. The main purpose of shaft seals is to maintain grease and oil in rotating equipment, but they are also built to withstand pressure differentials. V-rings provide an additional barrier against contaminants. Double-acting slide ring rotary seals can withstand higher pressure differentials and, for example, can be used in rotary distributors for mobile hydraulic equipment to separate different media.

All varieties of rotary seals can be customized with flexible or pressure-resistant sealing geometry to compensate for misalignments and run-outs. As rotary seals are subject to lengthy operating phases, heat dissipation capacity is a vital aspect of rotary seals and has a significant impact on sealing performance.

SKF’s Machined Seals Catalogue and Machine Seals – Selection guide provides in-depth selection guidance on the many possibilities when machining a rotary seal for industrial use. From here, you can discover how other machined solutions, such as guide rings, static seals, and back-up rings can open a wealth of benefits for operators and end-users.

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Seal selection – part 1
Find the right seal for different operating conditions