# Torque required to spin a hollow cylinder

• Slikatel
In summary, the conversation is about a problem with sizing an AC motor to rotate a load. The load is a hollow cylinder with specific dimensions and weight. The formula for inertia is discussed, as well as the torque required for acceleration and external resistances. It is suggested to contact an electric motor manufacturer for motor sizing.
Slikatel
TL;DR Summary
Hello all and thanks for viewing this, I am in need of some assistance to solve a problem to size an AC motor rotating this load (power transmission will be trough belt & pulley).
Hello all and thanks for viewing this, I am in need of some assistance to solve a problem to size an AC motor rotating this load (power transmission will be trough belt & pulley).

I have a hollow cylinder (pipe) that needs to spin 25 RPM:

- OD = 50 mm
- ID = 48 mm
- M = 200 kg
- Total length = 40m

The formula for inertia (Z-axis) i found when searching for a hollow cylinder = I = M * r^2 this gives me a solution of I = 0.1201 kg/m²

If i put this in the torque formula of T = I x angular acceleration = 0.1201 kg/m² x 2.618 rad/s2 (25RPM - 1 sec - ) = 0,3144218 Nm?

I'm stuck here :) would like to have some advice in where to search. Thanks so much for the advice.

The torque you calculate from your I equation is the torque required to accelerate (or decelerate ) the rotational speed of the pipe from one rpm speed to another rpm speed; but, must also include any external rotational resistances, such as the pipe's supporting roller's contact and bearing frictions (which for the support of 40 m long pipe could be significant).

Once your cylinder is rotating at a fixed rpm speed (i.e. 25 rpm) then the only torque required to keep it rotating at that speed is the torque to resist forces applied to the cylinder from the external effects, such as the pipe's supporting roller's contact and bearing frictions and any external forces from whatever is being done to the pipe while it is rotating.

Then with that information your best route is to contact an electric motor manufacturer/supplier for motor sizing.

Last edited:
Hi JBA and thanks for the reply, greatly appreciated.

So if i read your message correctly you are saying that for starting of the rotation (from non-turning formula) i need another formula?

## 1. What is torque?

Torque is a measure of the force that causes an object to rotate around an axis. It is typically measured in units of newton-meters (N*m) or foot-pounds (ft-lb).

## 2. How is torque related to spinning a hollow cylinder?

In order to spin a hollow cylinder, a torque must be applied to overcome its inertia and cause it to rotate. The amount of torque required depends on the size and shape of the cylinder, as well as the material it is made of.

## 3. What factors affect the torque required to spin a hollow cylinder?

The torque required to spin a hollow cylinder is affected by its mass, radius, and shape. A larger and heavier cylinder will require more torque to spin, while a smaller and lighter cylinder will require less torque.

## 4. How can the torque required to spin a hollow cylinder be calculated?

The torque required to spin a hollow cylinder can be calculated using the formula T = I * α, where T is the torque, I is the moment of inertia of the cylinder, and α is the angular acceleration. The moment of inertia can be calculated using the formula I = ½ * m * r^2, where m is the mass of the cylinder and r is the radius.

## 5. How can the torque required to spin a hollow cylinder be reduced?

The torque required to spin a hollow cylinder can be reduced by decreasing its mass or radius, or by changing its shape to one with a lower moment of inertia. Additionally, using lubricants or reducing friction between the cylinder and its axis can also reduce the torque required.

Replies
5
Views
2K
Replies
10
Views
5K
Replies
8
Views
2K
Replies
7
Views
19K
Replies
3
Views
3K
Replies
10
Views
13K
Replies
5
Views
3K
Replies
5
Views
8K
Replies
5
Views
2K
Replies
18
Views
7K