# How to calculate how much an aluminium tube can hold?

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1. Jul 11, 2016

### Satvir

Hi all,

I'm going to make a roller shaft for a roller mixer. I will be using a aluminum tube of length 900mm placed horizontally and the two ends will be help in a bearing. An another pipe will be placed side by side to the first pipe with a bit of space in the middle and held the same way as the first. A 10Kg paint can (5L) that's filled 75% will be placed horizontally in between the two pipes. (See the attached image of the design).

Currently I'm looking at this pipe to buy http://uk.rs-online.com/web/p/tubing-struts/4355837/# . It's 1000mm but it will be reduced to 900mm.

Could anyone tell me a formula to calculate how much weight can the aluminum tube hold.

Many thanks

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2. Jul 11, 2016

### Nidum

Bare Aluminium tube does not usually perform very well long term when used in this sort of application .

Consider using a cover sleeve or spaced rubbing bands or maybe a smaller diameter solid shaft with several solid rollers .

Calc is easy enough though . What are the dimensions of the can ?

3. Jul 11, 2016

### Satvir

Would Steel be a better choice and if aluminum were use then how long would you say it would last taking into mind it will be spinning around to keep the paint mixing at very low speed.

The paint can dimension:
Height: 25cmn
Diameter: 18.4cm

Could you please post the formula so in the future I can calculate it myself.

Thank you

4. Jul 11, 2016

### Nidum

Just the one can on each pair of rollers or two or three ?

5. Jul 11, 2016

### Satvir

Ideally looking for a max of 2 per pair of roller

6. Jul 11, 2016

### Mech_Engineer

What the O.P. has described is a classic beam bending strength calculation, described in Wikipedia as Flexural Strength (but with a circular cross-section instead of rectangular), or more generally a simply-supported (or possibly fixed-support) Beam Bending problem. Calculated stress is covered in the Beam Stress section of the article, maximum stress occurs at the points furthest from the beam's center line for a given bending direction.

I agree with @Nidum that mild Aluminum won't exhibit particularly good strength properties, you're probably better off with a mild steel such as A36. If weight of the long roller is a concern, that might be when you consider implementing a material with a higher stiffness-to-weight ratio such as aluminum 6061 or similar.

Keep in mind also for your application maximum load may not matter as much as deflection; it's likely the bearings you mount the tube in will only allow a certain level of angular load, and as such stiffness of the material and its associated deformation under load will matter more than stress.

7. Jul 11, 2016

### Nidum

One of the problems with Aluminium in this sort of application is that it has near zero abrasion resistance . A few hours of rolling and the tube surface will be covered with rubs and scratches .

8. Jul 11, 2016

### CWatters

I think you will need to cover the rollers in rubber to get some traction on the can anyway. Especially if the contents has a high viscosity or can settle out.