Category Archives: rotary seals

Preliminary Considerations for Spring-Energized Seals

springsealsToday we’ll continue our look at spring-energized seals by exploring some of the preliminary considerations to made when working with these seals.

A spring energized PTFE seal is selected to fit an exact set of service conditions found in your application.

Gallagher Fluid Seals recommends conducting a review of the entire sealing environment. You should use the Engineering Action Request (EAR) form before selecting a seal design.

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PTFE Radial Lip Seal Applications

dieselToday we’ll conclude our series of blog posts on PTFE by discussing some PTFE radial lip seal applications, as well as a brief look at wear sleeves.

PTFE has superior mechanical and physical properties and chemical resistance, which means the areas where PTFE radial lip seals are used is growing. These areas include:

Diesel Engine Applications

These consist of the front and rear crankshaft, accessory drive, and blower and thermostat seals. PTFE seals are used and tested in these areas because they can meet the performance and life requirements of modern engines.

Minimum wear, performance at high temperatures with limited lubrication, resistance to abrasive contaminants and fluid compatibility are the main factors for PTFE’s use in these applications.

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PTFE Rotary Seals: Housing, Pressure and Shaft Run-Out

rotary7Today we’ll continue our look at PTFE rotary seals by focusing on three areas: housing/bore considerations, pressure and shaft velocity and shaft misalignment and runout.

Housing/Bore Considerations

Typical PTFE rotary lip seals are pressed into the bore to assure proper OD sealing and seal retention in the housing. Most seal and housings are made from steel and cast iron. Take care when softer materials – aluminum, bronze, plastic – are used for the housing. Aluminum has a thermal expansion rate almost double that of steel. Metal case designs can lose the required press fit in an aluminum housing when they go through thermal cycles due to the higher rate of thermal expansion of aluminum.

A finish range of 32 to 63 μin Ra (0.8 to 1.6 μin Ra) is recommended for service pressures up to 3 psi (0.20 bar). For thicker fluids such as grease, a 125 μin Ra (3.17 μin Ra) finish would be acceptable with no system pressure.

A lead in chamfer is strongly recommended for all seal housings. The chamfer aligns the seal during installation and helps keep the seal from cocking. Both corners of the chamfer should be free of burrs or sharp edges. For pressurized rotary applications, take additional precautions to ensure the seal isn’t pushed from the housing.

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PTFE Rotary Seal Shaft Considerations

shaft table 3As we continue this blog’s PTFE series, we’re going to take a closer look at PTFE rotary seal shaft considerations.

In rotating applications, proper surface finish is crucial for getting positive sealing and the longest seal life possible. Rotating surfaces that are too rough could create leak paths and can also be very abrasive. Unlike elastomer contact seals, PTFE lips can run on very smooth surfaces regardless of lubrication.

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PTFE Rotary Lip Seals: Definitions

rotaryseal2Over the past few weeks, we’ve gone into a lot of detail about how PTFE rotary lip seals work.

Today we’ll offer up a short glossary of some of the terms used when discussing these seals. We’ll also break down some of the factors affecting PTFE rotary lip seal design.

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PTFE Radial Lip Seal Design Principles

Over the past few weeks, we’ve been discussing the basics of PTFE rotary seals. In today’s entry, we’ll take a look at PTFE radial lip seal design principles.

PTFE radial lip seals generally incorporate a uniformly thin element cross section, made to compensate for the high flexural modulus of PTFE, especially in cases of severe shaft run-out. The thin sections also minimize thermal expansion and compressive “creep” and their effects on maintaining a controlled contact pattern on the shaft surface.

Most PTFE seal constructions have the “body” portion of the element clamped between the two metal cases. To maintain proper retention pressure on the element, a thin element keeps compression set and “creep” at a minimum.

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PTFE Radial Lip Seal Design

rotarydesignIn the newest installment of our series of blog posts on PTFE rotary seals, we’re going to take a closer look at PTFE radial lip seal design.

Before selecting a seal type and the filled PTFE compound to be used in a proposal, it’s important to have a thorough understanding of operating conditions and how they affect the seal performance.

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Fillers Employed in PTFE Resins

PTFE resinIn our last few blog entries, we’ve discussed PTFE rotary seals and how they work. In this post, we’ll look at the fillers employed in PTFE resins.

In its virgin form, PTFE resin isn’t the best sealing material for dynamic shaft applications. Therefore, different fillers are added to achieve the desired results. The most common fillers are fiberglass, graphite, carbon, coke flour and molybdenum, although any filler can be added to virgin PTFE resin as long as the material can withstand maximum sintering temperature of 710-730 degrees F.

In order to develop lip seal products properly from PTFE resins, it is vital that the engineer understands the favorable and unfavorable characteristics of the resin.

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How Do PTFE Rotary Seals Work?

How Do PTFE Rotary Seals WorkIn our last blog post, we talked about some of the benefits and uses of PTFE rotary lip seals.

But how do PTFE rotary seals work? In this post, we’ll try to answer that question in more detail.

Rotary shaft seals work by squeezing and maintaining lubricant in a slim layer between the lip and the shaft. Sealing is aided by the hydrodynamic action caused by the rotating shaft, which creates a slight pump action.

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What is a PTFE Rotary Lip Seal?

PTFE rotary lip sealsPTFE resin was discovered in 1938, but it wasn’t until the 1950s that it gained notice as a possible rotary lip seal material. However, PTFE (polytetrafluoroethylene) seals fell out of favor in the 1950s and 1960s, as they were shown to be unreliable performers in a number of applications.

In more recent decades, there has been significant progress in the areas of PTFE lip seal design and material processing.

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