Stop a mixer from swaying during operation.

[Mixmasterintraining]

Hello,

I am currently mixing 4 tons of product with a density of 8.4lb/gal that is very sensitive to over mixing. My current mixer design has reliability issues. There are two counter rotating agitators in the tank which are about 8' long by 5' wide. While running the agitators sway due to either fabrication quality or design flaws. I currently have 2" and 4" shafts extending down from the gear box into the tank. I am being sold on two different design options:

1: Add a steady bearing to bottom of tank to reduce movement and my issues with this are the following.
a. Ability to CIP
b. Have not corrected the problem just hid they symptom.
c. Failure of the tank due to shaft hitting steady bearing in the repeatedly in the same place.

2: Increase the size of the shaft to 6" and 3" my issues are the following:
a. Work required to perform repair (cut off top of tank and replace with new cover)
b. Cost associated with new gear box installs.

My question is for this application in a pharmaceutical environment, what would be the best course of action? Is there any published literature on the subject? Lastly are these design solution accurate or should I be looking at other alternatives?

Thank You,

 

[ash9144]

You are correct about adding a steady rest bearing. Larger shaft also does not correct the problem.

If these agitators are from a reliable source (Chemineer, Lightnin, etc) have them take a look and see what is wrong.

If they are counter flow they are probably fighting each other causing your deflection issues. Maybe they should be ran cocurrently with proper baffle design.

I would turn one off and see if it corrects the problem. You may also try slowing down the agitators.

 

[gr2vessels]

One small correction to the above reply;- I would check the design of the agitator with competitor design, particularly if the original design if comming from not always reliable source like Chemineer or Lightnin. I would also check the reinforcement on the vessel to evaluate the support provided to the agitator. Quite often, the agitator loads are underestimated. Finally, I would check the As Built drawings and re-check the shafts and blades for compliance with the original design.
Good luck,
gr2vessels