Success with Vespel? CR-6100 Agitator Bearings

A major chemical company assembled an engineering team to increase the life of the main agitator in their reaction unit. The reactor consists of an 18.5 meter (60 feet) high agitator with 5.3 meters (18 feet) diameter blades. It runs at 27 rpm in a mix of phosphoric acid. This machine is the heart of the production unit and the plant engineers needed to extend the maintenance intervals to a minimum of 12 months to coincide with planned stops in the process.

The weak link was the agitator’s bottom steady bearing. The original manufacturer’s design used a 300 mm (12”) long SBR rubber bearing, running against a 175 mm (7”) diameter sleeve. In spite of being cooled to 65 C (149 F) with a water flush, the bearing would fail every 6-10 months—usually breaking free from the metal housing. Each failure required emptying the reaction tank, costing significant time, lost production, lost profits, and increased risk of shaft failure—which would create severe production impact. Painfully, it was a problem that had persisted for more than 20 years.

In their search for alternatives, the engineers were introduced to Vespel? CR-6100 as a potential bearing material. Vespel? CR-6100 is chemically resistant to the process fluid and has a temperature limit of 260 C (500 F), eliminating any concerns about compatibility—even if the water flush was lost. It also has a low coefficient of friction, excellent dimensional stability, and a high load limit. Vespel? CR-6100 had all the characteristics of an ideal solution. Working with Boulden, the plant engineers designed a mechanical method to fix the Vespel? CR-6100 in place--eliminating the need for the bonding agent which was a failure point in the original bearing. The team worked hard to convince management and other site personnel who were wary of changing to a “non-OEM” bearing. Finally, they received the green light to go ahead and the new bearing went into service in early 2021.

One year later, the design was proven successful during a planned shutdown. Not only did the bearing last the full year between planned shutdowns, inspection of the bearing showed dramatically lower wear compared to the old design. This allows the plant to continue uninterrupted production between planned shutdowns without expensive and time-consuming bearing failures. When results of the success were communicated through the company, the team received widespread congratulations for solving a difficult and challenging problem. “Literally Champions!” one of their colleagues commented.