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Batch time cut 80% with dual drive coaxial disperser
(Reprinted from August, 1983 CHEMICAL PROCESSING)

STEVE BOYKO
Production Manager
Loctite Corporation
Newington, CT

With CP Staff

New Solutions to Plant Problems

Problem: Loctite Corporation in Newington, Conn., needed an efficient, high capacity dispersing system to provide increased production output of anaerobic adhesives. Formulation of the adhesives requires the incorporation of rubbers and an inorganic filler into a solvent base. Up to 4017(, of an adhesive formulation may be rubber compounds which must be ground and dissolved in the high viscosity batch. The time required for dispersing and dissolving the rubbers in the 90,000 cps viscosity material was as long as 3-4 days. Other adhesives go as high as 2,000,000 cps.

Solution: About a year before the increased production capacity was scheduled, Loctite began working with an equipment manufacturer to design a custom mixer which would provide all the process requirements for production of adhesives. These requirements included:

High shear for dissolving the rubber and dispersing the filler
Bulk mixing for batch uniformity
Vacuum capability for degassing
Pressure capability for transferring the finished batch from the disperser
Cooling to remove the heat generated by the high speed dispersion head.
By early 1982, the design and fabrication was completed and a custom designed dual drive coaxial disperser with vacuum vessel was installed at Loctite. The unit features:

A high speed disperser head powered by a 60 hp motor
A butterfly sweep system, powered by a 30 hp motor, to force the high viscosity material into the dispersing head. provide bulk mixing, and aid in heat transfer
Side wall & bottom vessel scrapers
A 300 gal mixing vessel capable of full vacuum and pressure up to 100 psi
A dimpled jacket on the vessel to provide batch cooling.
The original design called for placing the mechanical seal for the disperser close to the high speed head to reduce the effect of deflection of the high speed shaft. However, initial operation of the equipment showed this design to be unsatisfactory. The carbon in the mechanical seal face in contact with the adhesive mass actually catalyzed polymerization of the adhesive. Although the catalytic effect was not sufficient to solidify the entire batch and seize all moving parts, it was sufficient to destroy the seal.

A major redesign effort was then launched which resulted in providing the mechanical seal far enough up the disperser shaft to be out of contact with the batch. The design is believed to be the first of its type for a coaxial disperser. The mechanical seal is protected from contact with batch materials by a gland type seal and a slinger.

Results: The dual drive coaxial disperser produces 4x the volume per batch as the previous system and does so in less than 1/5 the time. Batch times have been cut from several days to approximately a half day. The system, though capable of investing up to 90 hp, has never drawn more than 60 hp. Thus, there is sufficient safety factor to assure long equipment life and process flexibility. Since the redesign of the seal system, the equipment has operated for over a year without maintenance downtime. The design, redesign service, and operating productivity have provided a very effective process system for Loctite.

Dual drive coaxial disperser vessel has a dimpled jacket for cooling and is capable of full vacuum and pressure to 100 psi

Disperser head and butterfly sweep system lifts out of the vessel for cleaning and to allow the vessel to be tilted to remove batch

Dual drive coaxial disperser with "out of-batch" mechanical seal was designed and built by Schold Machine Company, 10590 Oak St. N.E., St. Petersburg, FL 33702.