Low RPM motor question

[northstarmatt]

Hi guys, I have what is probably a pretty simple question but I want to make sure I get the right thing. My company has large liquid mixing tanks that are powered by hydraulic motors. I've been asked to make a portable mixing tool that will mount on a 275 gallon tote and be easily removable. I have the mechanical part designed (very simple - just a bracket with a coupler and a shaft with paddles that will go down into the container.), what I need to figure out now is what motor to buy. It will be operating at very low speeds of ~60rpm or less, and the liquid is basically water (minimal viscosity) so I don't anticipate a lot of torque. We'll need the motor to operate for 5 or 6 hours at a time to ensure our batches are adequately mixed. I'd also like to be able to plug it straight into a standard US 110V outlet. Does anyone have any suggestions on what motor I should use? I really appreciate any help or guidance!

Matt

 

[jraef]

A gear motor. Standard AC induction motors rotate at a speed based on the supply frequency. You can increase the number of electrical "poles" in the motor design to drop the shaft speed, but that becomes ridiculous to try to get to something like 60RPM (120 poles!). You can get what are called "Variable Frequency Drives" that change the voltage and frequency together so that you can effectively run the motor at any speed, but if you are not going to VARY the speed, this solution, for a 115V plug-in device, is going to be expensive compared to just buying a simple little gear motor. A gear motor is a standard motor with a close coupled gearbox attached to it so that the final shaft speed is whatever you need it to be, without going to the expense of any electronics.

The other alternative would be a small "universal" AC/DC motor, similar to what is in a drill motor or an appliance. They are inexpensive, but would need regular maintenance (brush replacement), something unlikely to happen on a portable mixer.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Compositepro]

http://www.indco.com/shop/industrial-mixers/ibc-tote-mixers

 

[jraef]

Gearmotor, 60RPM, 115VAC example

"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[MikeHalloran]

Because you apparently intend to cantilever the impeller and shaft from the gearbox bearings, and because you haven't given us a clue about the impeller size or measured its torque demand, I'd suggest a bigger gearmotor, maybe up to 1/2HP, which gets you more torque and bigger bearings than a 1/12HP gearmotor of similar ratio.

Pick out half a dozen from the Grainger catalog, then go to the store. They won't have any of the catalog units in stock, but they'll have some PSC POS that will work ok at some cost in efficiency.



Mike Halloran
Pembroke Pines, FL, USA

 

[jraef]

I wasn't picking out a size, there was no information given for that. I was just showing an example.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[MikeHalloran]

And it was a fine example of a stock gearmotor, Jeff.

I wanted to gently point out that our OP may have underestimated the severity of the bearing situation.

By which I mean that stock gearmotors of all sizes have output shaft bearings that are sized for a modest radial pull from a chain or belt located just a shaft diameter or two from the distal bearing, and not much thrust load at all.

Whereas, mixers intended to twirl a propeller at the end of a long-ish shaft in a tub of goo typically have sturdy shafts and housings and bearings, and typically cost a lot more than stock gearmotors.

Therefore, if one is determined to 'save money' by using a stock gearmotor to twirl an unbalanced (or at least unspecified) impeller at the end of a long shaft, it makes sense to use one of the bigger stock gearmotors that can run from the specified power source. It still won't last as long as a real tank mixer motor, but maybe it will last long enough to gather some data.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

There are no decent/large illustrations on this page, but this is representative of a small top entry mixer:

http://www.spx.com/en/lightnin/pd-mp-small-top-entering-mixer-classic/

Mike Halloran
Pembroke Pines, FL, USA

 

[northstarmatt]

Thanks for the input guys! based on what i'm hearing I think this will work for me. any thoughts?

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