Hi, new to this forum,

I'm working on a making a ball mill, im trying to use a fan motor (AC 220v 50w) but the rpms are way to fast. It's from a standing fan, I've looked at Triac controllers but they all seem to be too fast, and at low rpm apparently I will lose all my torque. Is there a way to get linear speed control at low end rpm? Or should I just get a different motor? Not very experienced with this either so sorry if my understanding is a bit slow.

Thanks.

 

A lot depends on the diameter of the ball mill but I believe that typical speed of a ball mill varies between 30 RPM to maybe 300 RPM. If it spins too fast, it acts like a centrifuge so the material just sticks to the inside surface - too slow and it just rolls down the side. The optimum speed is such that the material falls away from the inside surface before it reaches the top, so it falls to the bottom. I'm wondering if you could use a truck windshield wiper motor? 24V DC is easier to control and the internal worm gear would probably get you within the right speed range?

 

thats a very good idea, I would like it to be on for long periods of time but to the best of my knowledge that wouldn't be too hard to do. But Ill look into that thank you.

 

Not a thing am experienced either, but would consider a clothesdryer perhaps with a proper layer inside its drum or proper sized balls...
Many discarded daily to junk, for $0

 

might not be a bad idea at all, but way too big for what I’m trying to do .

I built a little set up with the motor and my drum is made of 90mm pvc with size 7 lead sinkers as some of the stuff I’m milling will be flammable, so don’t want any sparks from other metals. Hopefully in the future I can get a rubber lined drum and cast some antimony hardened balls so the lead doesn’t contaminate what I’m milling.

 

Not only RPM must be considered but also Horsepower. My experience has been with large industrial ball mills which were chain driven by a motor with a small sprocket to a larger sprocket on the ball mill for speed reduction. FWIW

 

Hi, new to this forum,

I'm working on a making a ball mill, im trying to use a fan motor (AC 220v 50w) but the rpms are way to fast. It's from a standing fan, I've looked at Triac controllers but they all seem to be too fast, and at low rpm apparently I will lose all my torque. Is there a way to get linear speed control at low end rpm? Or should I just get a different motor? Not very experienced with this either so sorry if my understanding is a bit slow.

Thanks.

I built one that rotates at about 50rpm using a motor geared down with an automotive belt and pulley wheels. The diameter of the container is critical as well as the diameter of the rollers that it sits on. Increasing the diameter of the container will decrease the RPM's of the container. Increasing the diameter of the rollers will increase the RPM's of the container. Motor torque and motor RPM are inversely related, so if you reduce motor RPM's the torque INCREASES. A 1/4 HP motor like I used was probably overkill, but it works great.

 

I built one that rotates at about 50rpm using a motor geared down with an automotive belt and pulley wheels. The diameter of the container is critical as well as the diameter of the rollers that it sits on. Increasing the diameter of the container will decrease the RPM's of the container. Increasing the diameter of the rollers will increase the RPM's of the container. Motor torque and motor RPM are inversely related, so if you reduce motor RPM's the torque INCREASES. A 1/4 HP motor like I used was probably overkill, but it works great.

This is certainly the good solution because along with the required speed reduction you get the torque boost for free.
I have seen ball mills where the tank rests on two small diameter rods, and that idea can simply be scaled up to whatever size you choose. One small pulley on the motor shaft and a much larger diameter pulley on one of the support shafts. That can provide the speed reduction of 100:1 easily, so the 3600 RPM motor will turn the tumble drum at 36 RPM with a lot more torque. (100 times as much in theory). AND that sort of scheme can be less costly, as well.