Ever heard the expression ‘We tend to receive what we expect’? Well this sentiment doesn’t always apply when mill finish aluminium is being considered.
In Google terminology it is a generally accepted ‘knol’ (unit of knowledge) that aluminium is a long lasting lightweight metal with minimal on-going maintenance requirements.
There are many different surface finishes that can be applied to enhance the appearance of aluminium; anodising, powder coating and satin brushing are just three examples. However mill finish aluminium is not one of them! Mill finish is not an applied finish but simply untreated aluminium.
For whatever reasons some names just stick; Escalator for moving stairway; JCB for excavator etc., and mill finish for unfinished aluminium. This term often raises expectations and mistakenly leads the unwary into expecting an immaculate surface finish. So let’s attempt to close the knol gap when it comes to the appearance of mill finish aluminium.
For those with the time and inclination to study this issue in detail the Aluminum Association of America publish booklets detailing numerous examples of aluminium’s surface finish attributes. However for a brief overview please read on.
Aluminium Mill Finish
Once the extrusion or rolling mill has manufactured the aluminium into the desired shape and size the material is said to be in the mill finish condition.
So what are the visual characteristics of untreated aluminium? Extruding aluminium, as opposed to rolling sheet, produces differing surface finish effects so let’s consider them separately.
Aluminium extrusions are produced by either pushing or pulling the material (in a heated/softened state) through a hardened steel die. This process produces both simple geometric shapes (aluminium angle, channels, etc.,) and the more complex ‘purpose made’ designs. All of these forms normally display longitudinal lines of varying width, texture and tone. Various surface abrasions may also be apparent. The standard architectual grade (6063) is normally quite shiny and this tends to highlight such features.
Despite these factors there are many instances where mill finish is successfully incorporated into a large number of projects (both seen and unseen). It is usually only when surfaces are going to be viewed at close quarters, either in aesthetically demanding situations or in particulary ‘aggressive’ atmospheres , that this industrial finish benefits from a finishing operation of some kind.
Aluminium sheet is produced in a similar way to flattening pasty with a rolling pin. The constant backwards and forwards rolling process reduces the material to the required gauge thickness and temper (hardness) and in so doing the sheet becomes ‘polished’ to some degree. The alloy mix of the aluminium will also effect the materials’ brightness and reflectivity. Sheets will sometimes display rolling bands or stripes and may also commonly possess a grainy type finish.
A finer surface appearance can normally be achieved by selecting anodising or architectural quality aluminium. Our industry recognises that items required for these applications require a higher surface finish standard as opposed to general commercial applications.
In summary, aluminium materials that are going to be closely scrutinised would usually benefit from an applied surface finish. However there are many applications where mill finish is perfectly acceptable.
Interestingly, mill finish aluminium sheets with variable surfaces, including patterned, perforated and textured designs often prove an exception to the above rule by lending themselves to a wider use of mill finish due to their surface topography and consequent distorting optical effects, where marks and blemishes are often disguised.
Before reaching a final decision on surface finish our Free Samples Service is available to provide a range of alternative finishes.