The industry list is the wrong shape

The standard version of this article lists industries: construction, transport, automation, electronics, furniture, energy, medical. It is accurate and it answers a question no buyer is actually asking. A buyer knows which industry they are in.

The useful question is different: in this sector, which requirement governs, and what does it force me to specify that another sector could ignore? A section that is entirely adequate for a warehouse cart can be rejected in a food plant for reasons that have nothing to do with strength, and a frame that passes a cleanroom audit can be unsuitable outdoors. The material did not change. The governing constraint did.

We have written separately about the split between industrial and construction acceptance logic. This is the wider map, and it exists because most specification mistakes are made by carrying an assumption across a sector boundary.

Fact one: aluminium is attacked at both ends of the pH scale

Aluminium protects itself with a thin natural oxide layer. That layer is stable over roughly neutral conditions and it is attacked at both extremes. Strong alkalis dissolve it, and strong acids dissolve it. This is why “aluminium does not rust” is a true statement that leads buyers to a false conclusion.

The practical consequence is that several sectors routinely expose aluminium to chemistry that is far from neutral, and the exposure is designed into the process rather than being an accident:

Food and dairy plants clean with alkaline detergents and caustic solutions, and they follow with acid rinses. That is a chemical attack on an untreated or thinly anodised surface, repeated daily, for years.

Construction puts aluminium against fresh concrete and mortar, which are strongly alkaline while they cure. Splash and run-off carry that alkalinity onto the surface, and the resulting staining and etching is often blamed on the coating rather than on the chemistry.

Industrial cleaning in general has moved towards stronger, more alkaline products, for reasons of hygiene and cost. A frame that survived a mild detergent for a decade may not survive the replacement.

The controls are to know the cleaning chemistry before choosing the finish, to specify a coating class rather than a process name, and to remember that cut ends and drilled holes have no coating at all and are the first places the attack shows. Where the chemistry is aggressive, a coating system intended for that exposure, or a different material altogether, is the honest answer.

Fact two: aluminium has no fatigue limit

Steel exhibits a stress below which it can be cycled indefinitely without cracking. Aluminium does not. There is no safe stress; there is only a life, and it gets shorter as the stress range rises.

This matters wherever the load repeats. Transport and vehicle structures, vibrating machinery, equipment on moving floors, anything exposed to wind gusting, and anything that is loaded and unloaded many times a day all fall into this group. In those applications the design question is not “is it strong enough” but “how many cycles, at what stress range, and what life do we need”.

Two practical consequences follow. First, the connection matters more than the section, because fatigue cracks almost always start at a geometric discontinuity such as a hole, a thread root or a sharp change of section. Second, a warranty or a design life stated without a cycle count is not a fatigue statement at all. Where repeated loading is significant, the honest specification asks for the load spectrum, not just the peak load.

The constraint map

The table below is the practical version of “applications across industries”. Read the middle column first: it is the requirement that will decide the specification, and it is the one that has to be stated in the enquiry.

Where the usual answer is simply wrong

Three sectors deserve calling out, because the standard answer fails there in a way that is expensive to discover late.

Food and pharmaceutical plants. The standard advice is that aluminium is hygienic because it does not rust. The actual constraint is that the cleaning regime is chemically aggressive, and that hygiene requirements favour smooth, sealed, easily cleaned surfaces with no crevices. Those requirements can conflict with a slotted section, where the slot is a crevice by design. In these environments the right answer may be a closed profile, or aluminium excluded from the washdown zone altogether.

Construction. The standard advice is that aluminium is light and does not corrode. The actual constraints are thermal bridging and fire. Aluminium conducts heat roughly four times better than steel, so an aluminium frame is a thermal bridge unless it is broken, and it loses strength progressively at temperatures well below melting, so fire performance is a property of a tested assembly rather than of the section. Both constraints are outside the scope of a profile supplier and both have to be owned by the system designer.

Anything outdoors. The standard advice is that aluminium is maintenance free. The actual constraint is that the coating is thin and can be worn or chemically attacked, that chlorides are aggressive, and that dissimilar fasteners create a galvanic couple in rainwater. “Low maintenance” is defensible; “no maintenance” is not.

How to state this in a specification

Once the dominant constraint is identified, the specification becomes short and specific. Three lines do most of the work: the dominant requirement, the acceptance evidence, and the assumptions that were made.

The acceptance evidence line is the one buyers forget. A requirement without a test is a preference. If cleanability matters, the specification should name the cleaning agent and the surface requirement. If continuity matters, it should name the bonding method and how continuity is verified. If long-term exposure matters, it should name the coating class and the thickness test. That is what turns a wish list into something a supplier can be held to, and it is also what makes a quotation comparable between suppliers.

What to send with an enquiry