In order to effectively seal shafts in applications involving high fluid levels – in other words where the fluid level touches the seal – rotary shaft seals with an active sealing mechanism are needed. Using machine manufactured PTFE sealing lips as a basis, new manufacturing processes have made it possible to fabricate sealing lips with an integrated pump-back helix.
The authors: Christian Geubert Technical Support Europe, Freudenberg Process Seals Thomas Pauly Head of Regional Development, Merkel Freudenberg Fluidtechnic Bianca Wolf Regional Development, Merkel Freudenberg Fluidtechnic
With the introduction of the Simmerring Radiamatic HTS II over ten years ago, Freudenberg Process Seals created a PTFE shaft seal that delivers highly reliable, minimum-friction performance without the need for a spring. Originally intended for demanding applications in process plants, it is now broadly used in all industry segments. Owing to its dead space-free design, however, it has above all remained the number one choice for manufacturers of mixers in the food, beverage and pharmaceutical sectors. The HTS II is characterised by five main advantages:
- Patented sealing lip offers low-friction sealing over a broad pressure range
- Processed media only comes into contact with a homogeneous PTFE surface
- Made of food-safe materials
- Easy installation: the seal is pressed into an open housing bore
- Modular structure for flexible designs that can easily be adapted to the available installation space
For plant operators, choosing the Radiamatic HTS II means a far longer seal service lifetime; they also praise its very low friction, extremely low heat build-up and high durability, even under extreme operating conditions. The patented sealing lip of the Radiamatic HTS II is designed to ensure that the precisely aligned contact surfaces and angles remain almost constant under any operating conditions. As a direct result, friction and wear are so effectively reduced that the HTS II guarantees maximum service life, even in dry operation and when used with unhardened shaft surfaces. The standard version of the Simmerring is intended for sliding speeds of up to 18 m/s and temperatures from -70 to +200 °C. By varying the materials and the seal geometry, this operational window can also be significantly extended.
Selected high-performance materials
The Simmerring is currently available in six major PTFE compounds, permitting a broad spectrum of application-optimised versions. The clamping ring, which is made of acid-resistant, grade 316Ti stainless steel and positioned on the seal side not exposed to the media being produced, provides the necessary tension in the installation space. The resulting secure fit ensures that the seal remains firmly in place in open installation spaces, even at high temperatures and pressures up to 6 bar. In combination with the flexible requirements for shaft hardness, this gives plant operators altogether affordable machinery configuration options.
One special advantage of the Radiamatic HTS II is its modular design, which makes it possible to tailor the materials, type and configuration of the sealing lip to virtually any application scenario. In addition to the sixty standard sizes available, application-specific variants can be supplied to deliver peak performance on specific machinery.
The pump-back helix
The original configuration of the HTS II could not be used if the fluid levels were high enough to constantly cover the seal. With PTFE seals, this problem can only be successfully coun-tered by integrating a specially designed helix in the sealing lip. As the shaft rotates, this helix actively “pumps” the medium to be sealed back into the fluid space. The integrated helix technology for PTFE Simmerrings has proven its value in millions of automotive engines and transmissions.
Freudenberg Process Seals has now succeeded in making this special pump-back helix machine manufacturable for the PTFE HTS II. As the shaft turns, the fluid is actively pumped back out of the sealed space, meaning that even applications involving high oil levels or completely submerged components can in future be reliably and lastingly sealed. The direction of the helix – which is determined by the direction of shaft rotation – is marked on the body of the seal directly during the manufacturing process.
The particular appeal of this tool-free production method lies in its flexibility in responding to the varying needs of plant operators and manufacturers. Even the smallest batch sizes are easy to produce, with extremely short turnaround times. This approach also offers substantial benefits, for example when refitting mixers or stirrers equipped with older, non-FDA-compliant shaft seals. Thanks to the Simmerring Radiamatic HTS II, existing facilities can be brought up to speed by replacing the legacy systems with FDA-compliant sealing elements.
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