motor selection guide

[Gorpomon]

Hello,

This is a basic question and while I did do a search beforehand, none of the answers really helped.

I need to select a motor to drive a sheet rolling application. The motor spins the shaft, which is initially empty and then gradually it rolls up sheet material until its around 250lbs heavy.

The only other requirement is the sheet must be fed in at 100fpm. Which for an empty roller equates to 107rpm, and when the roller is full of sheet material, it seems like 25rpm would be the required speed.

It has been so long since I've even looked at motors, where do I begin selection? What factors do I consider? This doesn't seem to complicated but I'm at a loss as where to begin.

Any guidance (links to pertinent answers, faqs, etc) will be really appreciated.

Thanks!

 

[Skogsgurra]

This used to be a typical DC motor application. But that has changed so that induction motors with standard VFDs are now used. If you go to ABB, AB, Siemens, Rockwell and such companies, they have standard inverters with standard software for that.

I see no reason not to use a standard solution here. Or do you have very special demands?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MiketheEngineer]

Those are commercially available - often used on slitters. Google that or check w/ Braner Engineering in Chicago or Red Bud Industries in Red Bud, IL.

 

[Gorpomon]

Outside of the 100fpm and be able to roll 250lbs there are no special demands.

I was hoping this was something where I could just get a motor, pulleys and belts at my local Grainger and then machine/weld the fixtures for it? Is that not possible?

What I was really hoping for was a guide on how to go from knowing my basics like weight and speed up to what style of motor to get from a really common industrial supplier like Grainger. Is there a sort of guide like that out there anyone has seen?

 

[Skogsgurra]

Yes, I think it is possible. But you have to do some studying to make it run well. Some of the winder software is really tricky. Siemens is the most complete and also the trickiest with all compensation for inertia, acceleration, windage and other factors.

If you want a really simple solution and don't have high web tension or fast acceleration, you could use a standard induction motor and an adjustable friction coupling.

If you want to automate it, just let the friction coupling be controlled by a dancer roll. Very common on small take-up reels.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Gorpomon]

I think you got exactly what I want, but how do I go about selecting a "standard" induction motor?

For example, when I go to a website like Grainger, I see a list of AC motors and there's several types and each type has 20 - 30 different motors. I have a feeling the ability to know exactly what you need is out there, I just can't find a guide to that (I even looked in my old machine design books and didn't find much guidance).

 

[Skogsgurra]

We need the web tension and the linear speed. Say that you want to keep the web at 500 N (around 100 pounds) and that your maximum web speed is 100 m/minute (around 300 FPM). Then the work done is 500*100/60 (divide by 60 to get m/second), which is a little more than 800 watts (833.33 W). That is the minimum power you need to do the work.

Then look at your reel and see what diameters it moves between. Lets assume a mandrel diameter around 20 cm (8 inches) and a maximum reel diameter around 60 cm (24 inches). Then your motor needs to run at around (100/60)/(.2*3.14) = 2.65 RPS or 160 RPM.

Assuming (again) that you do use an adjustable clutch, your maximum torque will be web tension times maximum reel radius. Torque = 500*.3 = 150 Nm.

Maximum output from clutch will then be torque times speed (Nm and rad/s) which is 150*2.65*2*3.14 = 2500 W.

You have losses and you also need a safety margin. So, I think that a geared motor with around 5 HP and output speed around 160 RPM will do the job.

For other web tension, speed etcetera, plug in your data.


I didn't do a second check on this. Someone may want to do that.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Gorpomon]

Thanks so much, my math had come to around a 7HP motor with around 175RPM output. However do you know of any standardized resources like a machine design handbook that could walk me through those calculations like you did? Can someone recommend one?

Furthermore, if I want your 5HP/160RPM motor, how do I go about getting it? What type to do I search for? Is any 5HP/160RPM output motor ok or do the different types of motors really affect my performance?

 

[Skogsgurra]

There are not much difference between motors. It is mostly about number of poles and rotor type. But as long as you get the correct output speed and horsepowers, you really do not need to care about that. You will probably find that a four-pole motor is a good choice. Go to your sparky and ask him to get you a suitable geared motor. If he is any good, he will find one that suits your application. He may also be able to fill in the details so you feel more confident and informed.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Gorpomon]

Well that's good to know that I'm sort of on the right path. Only problem is there are no sparkies for miles around me.

 

[Skogsgurra]

Sorry. I am a few thousand miles away. Can't help.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...