Controlling of wobbling in agitator shaft

What is the speed, power, size of shaft, free span between bearings or supports & medium being agitated?

Generally you may consider spider type bearings but more info is required.

For any given size and materials of agitator, in any given medium, there is a critical speed above which instability, "wobble", may be expected.

• Consider slowing the agitator down
• Consider reducing either or both of the density and viscosity of the material being agitated
• Consider adding additional guidance bearings at intervals along the shaft
• Consider contacting the original equipment manufacturer for advice

• Consider increasing the diameter of the agitator shaft
• Consider reducing the diameter, number of blades and/or pitch of the agitator

Are we talking here of an agitator hanging inot a reactor vessel from above, supported purely at the top? consider some kind of spigot to guide it at the bottom or somewhere along it's length?

Or do as suggested and contact supplier! I don't think the arrangement is that uncommon? Are you sure all is in reasonable condition? Has something happened to create an imbalance or distortion of the impeller or shaft?

Just an idea borrowed from an old Porsche car I once owned. Is it possible to use a tubular, rather than solid shaft? The stiffness is really good when compared to a solid shaft, especially over a long span at high r.p.m.'s.

The Porsche 928S used a propshaft that was tubular and small in diameter to transmit more than 300 horsepower. The shaft was contained inside a torque tube that connected the engine (front) to the transaxle (rear) I have no knowledge of any damage ever occurring to these inner shafts, other than the splines could twist from the engine end of the cars that had serious performance upgrades.

Best Regards,

Ing, Robert Forbus

There are other few reasons why your agitator would wobble. You could check any of the following conditions: This assumes that you have a propeller type of agitator.

1) Check if the shaft is not bent or not straight down, you can either take it to the shop or test it right where it is mounted by switching on momentarily when your tank is empty. In some cases, the mounting of the shaft may not be rigid or it is loosely fitted to the reducing gearbox shaft or the motor shaft itself, (if it is of the direct drive type). The agitator should not sway sideways when it is not rotating. Otherwise, you will have to check all the mounting bolts of the gear box or the motor.

2) The agitator or the propeller blade is not balanced in pitch. If your propeller is a double blade or triple blade, each blade must have an equal twist or pitch. A very small variation caused by a bend or damage will result to an unequal load to the blades and force the shaft to wiggle or wobble. You have to check this in a balancing machine or a good size lathe.

Other factors like speed, viscosity, liquid level, size of shaft, diameter of the propeller and likewise the type of agitator that you have installed may have to be considered. But these are given that they are designed correctly for the type of product you have.

The shaft length of 4.5 meters is quite long for an agitator, you might consider using a horizontally mounted type of agitator located on the side near the bottom of the tank. There is a lesser chance for wobbling on a shorter shaft.

Consider balancing the agitator and check alignment of the agitator. Consider installing a stablelizing impeller at the end of the shaft.

I agree with #4,#5 & #6. You need to use a hollow shaft which increases stiffness and also use intermediate bearings at different levels 'cause an unsupported length of 4.5 meters is too long for an Agitator.

You will do well to see if there is wobbling when run without liquid to eliminate other causes such as loose bolts, non-uniformity in blades etc.

Need details of mounting/orientation. Vertical on center? Off center? Angled? Open top? Turbine? Axial/radial? Fluid mixed? Rising or falling level?

if using a hollow shaft use a short solid shaft at the bottom of the agitator with a sturdy stand with a hole in the top, to allow the short staft you inserted in the bottome of the ag. to guide into. I ve seen agitators that were 20 meters use this and works well. solid shafts maybe more rigided but the weight buts more tear on bearings. good luck

Dear Mr.ialmaint,

Many CR4 MEMBERS have given their views. Your question is in broad sense and not specific.

The wobbling may be due to Un-Balance also, and Vibrations have Specific Standards, which involves speed in RPM, Revolving Mass etc. The centre distance between bearings and the agitating arms/disc location also plays a vital role.

Pl. post full information and suggestions will come a lot.

DHAYANANDHAN.S