Sunday, March 10, 2013
|English: A industrial static mixer Italiano: Miscelatore statico industriale in acciaio inox (Photo credit: Wikipedia)|
He was tasked with making a hydro-alcoholic gel that was clear with no air bubbles. The formulation was rather straightforward but scale-up and manufacture was quite difficult. There were a number of problems. First we were supposed to work with existing equipment. This meant that using dish bottomed tanks and poorly positioned high shear mixers. Further, since this was a potential explosion risk we had to use explosion rated mixers.
Our budget was small but there was no way that we could use existing equipment. We had to think of ways to invest in equipment to perform this task that did not require significant capital. Here is what we did.
We fabricated a tall, thin flat bottomed mixer out of rolled steel. It helped that we had a shop that our mechanics and machinists that was so well equipped that they could probably build a spaceship if needed. Second, we ordered a mixing blade that was low shear with high pumping action. The blade was roughly the same diameter as the tank (although slightly smaller). For the mixer we had to purchase an air mixer to meet the explosion proof needs. The results were fantastic. We created an airless gel that looked and performed great. Too bad the project was cancelled before were able to get it launched.
I would love to try to replicate this process with a static mixer someday. I have attached a picture above a static mixer for those of you who are not familiar with these mixers. These mixers were not widely used in pharma the early 1990's when I was involved developing this gel.
Here is a link to Ross who makes a variety of static mixers to meet all needs.
Ross Company Website
Friday, January 4, 2013
|English: Mixing - Axial flow and radial flow. Italiano: Miscelazione - Flusso assiale e flusso radiale. (Photo credit: Wikipedia)|
The cream was made in an eight thousand gallon, jacketed tank with one high shear mixer (a Lightnin A200 if my memory is correct) fitted to the end of a very long shaft. The mixing tanks were built in the 1940's. The mixers were newer, probably manufactured in the seventies. The process was slow to heat and cool. The motor maxed out at 5 horsepower. Typically, 4.2 horsepower was needed to move the material to form the emulsion.
The issue for me was to improve the mixing to increase contact time with the tank walls so that heating and cooling would go faster. Also, increasing pumping action to move the dry adds from the surface to the high shear mixer. There was no budget to change the motor. Changing or adding a mixer would be difficult or impossible without affecting motor load.
That requirement led me to a low shear impeller designs. My goal was to place the impeller midshaft so that material draw-down was improved. I also hoped that a 90 degree pumping action would better supply the hi-shear mixer more efficiently. are intended to impart motion to the product while using the least amount of energy possible. Since I could not exceed 5 horsepower on the motor, I needed to use a low shear, high efficiency hydrofoil which minimized power consumption while keeping the product in motion. I found that in the Lightnin A-310. Here is a site for approximate horsepower conversions: Motor Conversions.
I was able to shave off some the manufacturing time (about 45 minutes) but it was not enough enough to justify the cost of the retrofit and re-qualification needed to make the changes. Still, I liked the "out of the box" approach and it was worth investigating.