The Expert's Corner
Simplify your High Viscosity Dispersion Process
March 5, 2020
A manufacturer of high-performance epoxy coatings was utilizing a two-step process to effectively mix the base material of a rebuilding compound design for corrosion and abrasion protection.
The first step was to disperse powdered fiberglass and fumed silica into a resin using a large saw-tooth disperser. The pre-mix was then transferred to a vacuum-rated planetary mixer where the operator would add a hardener material and inert ceramic microspheres to create a finished product. After a total batch time of one and a half hours the final product would have a viscosity of up to 1.5 million centipoise and a specific gravity of 1.5.
We suggested that the customer test their application on a Ross Model PDM-40 PowerMix Planetary Disperser in our Test and Development Center. The PowerMix is hybrid planetary mixer utilized for creating fine dispersions in viscous mixtures - typically within the viscosity range of 100,000 to 2 million centipoise - more efficiently. It consists of a high speed disperser blade and a planetary blade that revolve on their own axes while orbiting the vessel on a common axis. By constantly advancing both agitators into the batch material, the PowerMix applies intense mixing action while preventing localized build-up of heat. Solids are quickly incorporated into the viscous bulk material and agglomerates are dispersed regardless of product flow characteristics.
For the test, we loaded all of the ingredients into the vessel at once; which included the resin, fiberglass, fumed silica, hardener, and microspheres. We began by running the planetary blade at 18 rpm and the 8" disperser blade at 600 rpm. Then we gradually increased the speed of the disperser blade during the first few minutes and begin pulling vacuum. By the 7-minute mark, we are running the disperser blade at full speed (1,850 rpm) and have established a deep vacuum at 29.5" Hg. After only 12 minutes, all raw materials looked fully incorporated, so we stopped mixing to inspect the batch. Samples revealed a specific gravity of 1.47 and a 5.5 reading on a Hegman draw down gauge. Measured viscosity also fell well within the expected range. The PowerMix efficiently completed a satisfactory batch in record time and without any transfer step.
The customer was impressed with the results of the test and purchased a new 40 gallon PowerMix along with a matching Ross Model DS-40 Discharge System. The DS-40 allows the operator to quickly and efficiently discharge the viscous mixture from the mix can, optimizing yield and simplifying clean-up.