# Calculate drive torque for rotating large drums

• cloznuff_fmwc
In summary: The torque required to maintain that rotational speed.The trunnion bearings will have rolling friction, due to the weight of the drum. What bearings will be used?If the drums are not balanced about the axis, a varying torque will be required to maintain rotation.I'm not sure how you would determine the required torque to maintain rotation. The rollers may have roller bearings against the trunnions. Those bearings will have rolling friction, due to the weight of the drum. What bearings will be used?If the drums are not balanced about the axis, a varying torque will be required to maintain rotation.
cloznuff_fmwc
Hi,

I'm new to the forum so thanks in advance for any help. We would like to make a fixture for rotating large drums in a paint booth. I would like to know how to calculate the torque required at the trunnions to rotate the drum using two drive trunnions (with 2 idler trunnions). I've included a sketch with, hopefully, all the required info. It's been a while since I've done this type of calculating and can't find and specific examples. I'm more looking for HOW to calculate this not just necessarily the answer but the answer would be nice ;-)

Thanks again!

Welcome to PF.

There are two problems here.

1. The torque required to initially accelerate the drum to the required rotational speed will depend on the mass distribution in the wall and the ends of the drum, that is the moment of inertia. Will a drive surface slip, or will the torque be applied through some form of clutch or fluid coupling ?

2. The torque required to maintain that rotational speed.
The rollers may have roller bearings against the trunnions. Those bearings will have rolling friction, due to the weight of the drum. What bearings will be used?
If the drums are not balanced about the axis, a varying torque will be required to maintain rotation.

If the trunnion bearings lock due to a failure at speed of the drive system, will the drum climb the rollers, and so escape to roll free?

Lnewqban
cloznuff_fmwc said:
a fixture for rotating large drums in a paint booth.
Baluncore said:
1. The torque required to initially accelerate the drum to the required rotational speed will depend on the mass distribution in the wall and the ends of the drum, that is the moment of inertia.
I wonder how we can calcuate the MoI of a drum semi-filled with a viscous liquid like paint. It seems like a combination of the MoI of the empty drum plus a term for the torque needed to keep lifting the liquid up some amount as it falls back down inside the drum...

Thanks @Baluncore

The mass is evenly distributed throughout the drum and it is empty when being painted. I did not plan to use a clutch. I'm not concerned if there is slip between the trunnion and drum but with the slow speeds it doesn't feel that would be a problem.

The trunnion bearings will be large PB Tapered Roller Bearings.

Thanks again.

berkeman said:
I wonder how we can calcuate the MoI of a drum semi-filled with a viscous liquid like paint.
I assumed the paint was being applied to the outside of an empty drum.

But then, what is it about the rollers, that prevents damage to the painted surface?

Should the rollers not be mounted at the ends of the drum, where the load will be supported by the end plate, rather than the drum wall?

sophiecentaur and berkeman
cloznuff_fmwc said:
The mass is evenly distributed throughout the drum and it is empty when being painted.
Oh, that kind of paint booth. I misinterpreted it to mean a place where people went to buy cans of paint.

The surfaces where the trunnions set will not be painted. Thanks

berkeman said:
Oh, that kind of paint booth. I misinterpreted it to mean a place where people went to buy cans of paint.
Doh, sorry, I should have been more clear. Yes, we are manufacturing these drums and painting the exterior of them. We would like to be able to rotate them in the paint booth. The surface where the trunnion drives against is a large machined "tire" that will not get painted.

Thanks

berkeman
I hope the "tire" area can reduce the pressure to prevent deforming the tank. I see this as a major torque factor along with F= a*mass imbalance. to with 115,000 lbs per ? sq in. Is most of the mass on the external surface? The Queen Elizabeth QEII ship's prop could be turned with one hand due to low friction. This will not be your case. So the rolling friction must be minimized and determined 1st before the drive torque can be determined by the gear ratio of the respective diameters.

We've got the drum design down, been doing them a loooong time. No fear of deforming the drums, the tires are large enough, trust me! These are massive assemblies ;-)

Just trying to come to a required torque value on the drive trunnions to correctly size the drive components (motor/gearbox/coupling).

Thanks

cloznuff_fmwc said:
The surface where the trunnion drives against is a large machined "tire" that will not get painted.
That all seems good.

Please check the rotation rate of the drum against the separation of the rollers, to verify that safety will not be compromised by a drum escape, else the coroner may later want to examine your design notes and computations.

I was wondering about the flexible term "trunnion", which usually refers to a protruding solid round pin, that rests in a bearing, to support a body. It seems the term "trunnion bearing" has been reduced to "trunnion", and is applied in some industries to include the axle, bearings and roller that a drum rests on.
https://en.wikipedia.org/wiki/Trunnion#Trunnion_bearings

I did not plan to use a clutch. I'm not concerned if there is slip between the trunnion and drum but with the slow speeds it doesn't feel that would be a problem.

Welcome, @cloznuff_fmwc !

That drum can’t weight 58 tons.
If so, you better consider a VFD drive for those motors.

cloznuff_fmwc said:
The surface where the trunnion drives against is a large machined "tire" that will not get painted.
If that "tire" is of a material that deforms under load, you will also have to supply the energy to do that thru the trunions.

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