Replace PTFE Mixer and Agitator Bearings with Vespel® CR-6100 for Maximized Performance and Service Life
Mixers and agitators typically have shafts 5 to 7 meters (15-20 feet) long with large propellers designed to mix the process fluid. The shafts are often supported by only two bearings—one at the top and one at the bottom. These bearings must withstand significant radial loads, in addition to a wide range of temperatures and chemicals.
Mixers and agitators are frequently built with PTFE or filled-PTFE shaft bearings. PTFE-based materials are used because they offer excellent chemical resistance and low friction. Unfortunately, these materials have significant shortcomings in their dimensional stability.
Vespel® CR-6100 offers similar chemical and frictional performance, combined with excellent dimensional stability.
The Weakness of PTFE
PTFE agitator and mixer bearings wear prematurely for several reasons. It is well-known that PTFE-based materials tend to cold-flow and creep. So, when radial loads are applied to the bearings, the PTFE will deform under load. Over time, the bearing clearance increases, allowing the shaft to move, increasing radial loads and accelerating wear.
Compounding the problem, PTFE-based materials typically have a very high coefficient of thermal expansion. In elevated temperature service, the clearance at the bearing will change with temperature, making the bearing clearance dependent upon operating temperature.
Finally, PTFE can be abrasive to the mating metal surface, causing wear of the metal part.
The Strength of DuPont™ Vespel® CR-6100
Vespel® CR-6100 mitigates all of the above issues. Vespel® CR-6100 does not cold flow or creep and experiences minimal deformation under load. The mixer or agitator bearing acts like a bearing and keeps running. The material can withstand very high loads with minimal wear and continue running.
Beyond that, Vespel® CR-6100 has an extremely low coefficient of thermal expansion. When a mixer or agitator bearing with Vespel® CR-6100 is properly designed, the clearance at the bearing remains constant over a wide temperature range, allowing the bearing to function as designed in any temperature up to 260 C (500 F).
Furthermore, Vespel® CR-6100 generally does not cause damage to mating metal parts, allowing the bearing to maintain minimal clearance for a very long run.
Consider the photo above from a sulfuric acid mixer. The top shafts were running against glass-filled PTFE mixer bearings. The bottom shaft was running against Vespel® CR-6100. After 3.5 years, there was no damage to the shaft under the Vespel® CR-6100. The shafts running against glass-filled PTFE were severely worn.
For many years, Vespel® CR-6100 has been used for mixer and agitator bearings with excellent results. Process fluids have included, acids, bases, aromatics, hydrocarbons, and specialized chemicals. If you are experiencing premature wear of any mixer or agitator bearings in your plant, contact your local Boulden representative to discuss an upgrade to Vespel® CR-6100.