Chemical Mixing Agitator

Not enough information... need a picture.

Is it a stirrer, mixer?... agitator implies oscillation?

Our parent company had one rotary mixer design with a stupidly long shaft which relied one extra bearing and the motor bearings. It had a two blade propeller blade on the end. It wobbled like mad and wore out motor bearings.

It's a matter of implementing simple common sense mechanical design to solve the problems. (Mind, common sense is rather rare...)

I told 'em to extend the casting that the motor bolted to and add a second bearing a couple of inches from the first. That removed all the problems.

Length and diameter of shaft, rpm and pitch of propellor are also worth looking at if it is this sort of design.

Del

i contacted the manufacturer he recommended mounting the flange of the agitator with a PTFE gasket which has 5 degrees inclination, i did and nothing was solved. even if i'm not convinced with that solution.

Need more information before anyone can make a suggestion.

1. Are the bearings any good?
2. Is the shaft/impeller bent?
3. What are you blending?
4. Is the vibration always there or at a certain RPM?
5. Is the impeller turning the right direction?
6. Are the mounting bolts tight?
7. Is the mounting flange cracked?
8. Do you have the right voltage/frequency for the motor

We need input from you.

1- it only has one ball bearing Z2 and its okay

2- i removed the shaft and checked the run out it was 0.35 mm , and i corrected it to 0.07 couldn't correct it more

3- some sort of chemicals , their specific gravity is nearly 1.02

4- the agitator shaft is directly coupled to the motor shaft no change in rpm and yes the vibration is always there.

5-i checked the rotation it was correct.

6- yes

7- nope but i noticed that it has a small thickness dunno if that will affect or not.

8- ye the motor is consumes the correct power.

OK - Calm down. Do you have a graphics program that you can use to show the problem? It will help to know, semi-quanifiably, what you're dealing with!

i just ordered for a vibration monitoring device , i will do the trial run today and inform u back with the results

Suggest to contact manufacturer and ask for customer support.

Further suggest to give more information on this agitator, a picture as indicated tells a lot more than what you write - maybe.

Suggest to look for a replacement mixer until the problem is sorted.

Further I suggest to read the manual and make sure all maintenance was carried out properly and it was used within specification. Any miss-use would void warranty and any damage will mean you have to either live with the vibration or you have to replace the mixer.

The small shaft diameter sounds like a contributor to this problem. Your questions and investigations seem good, so keep pursuing those. Welcome to CR4, and good luck in resolving the issues being faced.

It could be anything, what kind of agitator, (Lighting?),

Is the agitator shaft or any part of it bent?

What is the viscosity of your product?

You really don't have enough information.

Sounds like exactly what I described in my first post, which seems to have been ignored...

It was funny, I visited the factory where they were testing the new mixer. It was stirring a big vat of stuff which I'd assumed was water.

There were loads of us all wearing suits being shown round.
I took off my jacket, rolled up my sleeve and put my arm into the tank and carefully held the shaft .
They all looked on horrified!

I could feel it was running smooth.
I pulled out my arm, now dripping with thick gloop!

"Yes that's much better" I said.

The MD of the outfit hastily told one of the underlings to fetch some paper towels for me.

My quick check was better than all their messing about without actually testing anything.

I'm also illustrating why a vibration monitor is a waste of time and money... you know it's vibrating already!

Del

(Please don't lecture me about the obvious safety problems with what I did)

I knew a guy once in an electroplating plant who had no qualms about reaching into 17% sulfuric acid tanks.... Not me.

The plant in question was Hytek Finishes in Kent, WA, USA (Seattle suburb). One of the contracts they had was with Ray Carver stereo components, which had some exacting standards about the blackness of their anodized aluminum housings. That required some fairly close temperature control. At the time, I was working for Seattle Refrigeration, which furnished some chillers and controls for such purposes.

well, I didn't expect details,.....

In the food industry, they use alkalies and acids for clean up,..... I think these clamped down since then, but in the early 90's people would test it with their fingers......

If its tacky.... its an acid, if its slimy it an alkaloid.

Here are a few items to consider:

Too many paddles? Or not enough paddles? Is the paddle pitch angle too steep?

Are there cross braces and/or other devices that are creating unwanted patterns in the liquid?

Is the agitator rotating too fast for the length of the drive shaft to stay stable?

Is the agitator mounted too close to an tank intake or discharge outlet?

Is the agitator quality too poor or of the wrong design for the application?

well , the liquid inside the tank is water mixed with some chemicals, the specific gravity of those chemicals is almost 1.02

secondly, the rpm is 1500rpm and i cannot ensure about this , maybe from the DCS i can check later.

i cannot also measure the pitch angle of the propeller.

i told the customer u can mix it by a piece of wood :D

Like Del mentioned, excessive shaft overhang. Can you put a speed control on the motor?

something like a VFD?? , i requested the electrical team to do so , they said it's not possible cause we may need a larger frame motor. i will consider that also thanks

Do you have compressed air available? I use air motor powered mixers. These can be easily speed controlled with a simple valve(which will likely come with the mixer same as mine did). The units I use do have a phenolic bushing about 1/4 of the way down the shaft. Running if free air, they do vibrate, but when immersed the vibration cannot be noticed.

Terry , that is a good way to solve the issue, i'll note your suggestion and i will try to talk with my team about it cause u know there are many parties involved

Well put, Terry. You recommended good troubleshooting procedure instead of shooting in the dark.

My first thought after reading what had been verified so far is a critical speed issue. IN another lifetime I used to design and analyze rotating equipment and an overhung shaft (as most mixers are) is one of the worst case designs in terms of sensitivity to critical speed. A slender shaft is subject to gyroscop8ic action, especially when the load from the mixing of a viscous liquid is applied.

If that is the case, one possible solution is to add a weight to the end of the shaft to increase mass and reduce gyroscopic effects.