A patented lip design and the patented combination of PTFE sealing lip and sliding bearing in the lip seal element provide the new dry running seal “SeccoLip” from EagleBurgmann with particularly high flexibility. These technical features help the lip seal compensate directly and safely radial deflections of the shafts in agitators, mixers and reactors.
The sliding bearing tracks the complete lip seal element to the shaft movements. Since the lip and bearing are in one element, the sealing gap between the rotating shaft and the sealing lip remains virtually constant and the seal remains tight over the long term. Compensating elements such as O-ring, expansion washer or metal bellows are not required for reliable operation.
The modular seal was specifically designed for the operating conditions in the chemical, pharmaceutical, food industry as well as in water and wastewater technology. One or more sealing elements are combined in different possible arrangements to comply with the requirements.
Connections for a supply system are available. Due to the design features, a rolling bearing is not necessary but is optionally available.
The cartridge design makes the SeccoLip easy to install and safe to use. It is particularly suitable for a sliding velocity of up to 2 m/s (6 ft/s) and a pressure range of -1 to 6 barg.
Today 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.
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.
As 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.
In 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.
PTFE 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.