Seal reduces vacuum dryer cycle time by 50%
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Meco Shaft Seals product story
Edited by the Engineeringtalk editorial team
Nov 24, 2005
A US manufacturer of powdered paint pigments had to solve a leakage problem on its rotary vacuum dryer. It used an air-purged EAS (externally adjustable, split) model seal to solve the problem.
A US manufacturer of powdered paint pigments had to solve a leakage problem on its rotary vacuum dryer.
The products are fine, mildly abrasive powders.
The process calls for moisture content in the powders to be reduced from 30-35% down to 1-2% in the finished product.
The dryer is steam-jacketed and operates at a temperature of 338F.
The machine's horizontal shaft turns at 6 rev/min and is 160mm in diameter.
Vacuum is held at 25 inches.
To seal the product and hold vacuum inside the vessel, maintenance personnel had been using both packing and conventional, spring-type mechanical seals on the shafts.
Neither of these sealing methods worked for long and when the seals failed, both product and vacuum were lost.
The loss of vacuum caused the batch cycle to run for eight hours per day to achieve the desired product dryness.
Over time, as product escaped between the shaft and the seals, abrasion wear to the shaft occurred.
In an attempt to prolong seal performance, maintenance workers resorted to winding heavy gauge plastic sheeting into the seals when they failed.
They eventually decided that the seals they were using were not effective enough to continue replacing them.
They contacted the regional representative for MECO seals, who suggested they use an air-purged EAS (externally adjustable, split) model seal to solve the problem.
The patented EAS seal design is based on the use of a driving elastomer, which wraps around and grips the shaft.
This both protects the shaft from abrasion damage and blocks product migration along the shaft, even if it is scored or pitted.
Through friction, the elastomer turns with the shaft and drives sacrificial rotors to turn against stator plates, forming the seal interface.
No relative movement takes place between the shaft and any of the rotating seal components, so all wear is limited to the seal interfaces between rotors and stators.
The seals are able to accommodate thermal growth of the shaft during the process, as well as shaft runout of 0.25in TIR and more.
The factory representative helped to install the MECO EAS seals on the first dryer.
Because of the seals' split design, installation was quick and painless; the bearing and drive did not have to be removed.
Once the air pressure was correctly set, the seals held the vacuum completely in the dryer and the drying time for most of their products was cut in half: from approximately 8 to 4 hours.
From a housekeeping point of view, the seals completely contain the product in the dryer and workers are pleased with the absence of leakage around the vessel's shaft.
An additional benefit of the seal conversion is that the need for expensive re-shafting was avoided because shaft wear was eliminated on this machine.
The company was so pleased with the seals' performance that it installed them on a second dryer later in the same year.
Both machines run without trouble, requiring only routine monitoring of purge air pressure and occasional seal face adjustment.
This adjustment can be done while machinery is running, reducing downtime for seal maintenance.
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Contact Meco Shaft Seals
Tel +1 207 371 2210
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