Why we use aluminium track and not mild steel
Mild steel costs less per kilo, which is why it turns up in lower quotations. But the track is a running surface carrying a moving load inside a warm, humid, dusty building. Here is what the material choice actually changes.
The track is not only structure
It is easy to think of the track as the frame that holds everything up. It is that, but it is also a running surface. Wheels roll along it continuously, under load, for years.
So the material has two jobs at once. Carry the load without excessive deflection, and stay a good running surface in a building that is warm, humid and full of cotton dust.
Those two requirements decide the material. Not the price per kilo.
The shape matters more than the metal
This is the part that gets missed most often.
Aluminium track is extruded. The metal is pushed through a die, which means the cross section can be whatever the design needs it to be. Material goes exactly where the bending stress is highest and is left out where it does nothing. Running surfaces, mounting features and stiffening ribs can all be part of one continuous section.
Mild steel track is generally fabricated from standard rolled sections, or folded from sheet. You are choosing from shapes that already exist for other purposes. If the ideal section for the load path is not one of them, you take the nearest available shape and either add material or accept more deflection.
A section designed for the job will out-perform a general purpose section of similar weight. That is the main reason we use aluminium. It is an argument about design freedom rather than about metallurgy.
| Extruded aluminium | Fabricated mild steel | |
|---|---|---|
| Cross section | Designed around the load path | Chosen from shapes that exist |
| Running surface | Formed as part of the section, consistent along its length | Depends on the fabrication and the coating |
| Humid mill conditions | Forms its own protective oxide layer | Needs a coating, and coatings wear where wheels run |
| Weight for equivalent stiffness | Lower | Higher |
| Cost per kilo | Higher | Lower |
Corrosion, and where it actually hurts
A spinning mill is humid by design. Add cotton dust and traces of oil and you have conditions mild steel does not enjoy.
Mild steel can of course be protected. Paint, galvanising and plating all work. The difficulty is the one place you cannot protect properly, which is the surface the wheels run on. Coatings wear away where there is rolling contact. That is simply the nature of the thing.
Once the running surface begins to corrode you have two problems instead of one. The wheels wear faster against a rougher surface, and the corrosion products come away as fine particles. In a building where the material passing underneath is roving, particles falling from overhead are not a small matter.
Aluminium forms a thin oxide layer by itself, and that layer re-forms when it is disturbed. It is not immune to everything, but it does not shed rust into your material path.
Weight, which shows up in the structure
Aluminium is lighter for the same stiffness, and that has effects beyond the track itself.
Lighter track means lighter supporting steelwork and fewer or lighter fixings into the building. It is easier to handle during installation, which matters when sections are being lifted into position above running machines. On modernisation work in an older building, where the roof structure was never designed to carry a transport system, this can decide what is possible at all.
The honest part
Mild steel is cheaper per kilo and a mild steel track will appear in a quotation at a lower number. That is a real difference and we are not going to pretend otherwise.
What we would ask is that the comparison is made across the life of the installation rather than at the delivered price. The questions worth asking are how the section performs under your loads and your spans, what the running surface looks like after some years in your particular building, and what it costs to replace a section once the mill is running.
If you are holding two quotations with different track materials, send them to us. We will tell you what the difference means for your spans and your loads, and we will tell you if it does not matter much in your case.
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