Aluminum windows are competing with uPVC windows and often become a choice product of many homeowners. When it comes to finishing of aluminum windows, there are several options available in the industry.
Aluminum window profiles are can be anodized, or painted either by powder coating or have baked on enamel coating.
Anodizing process was first applied back in the 1920’s – it is an electrochemical procedure which creates a protective aluminum oxide coating on the aluminum surface. Lifetime of such protective finish varies depending on how thick is the anodic coating.
Aluminum oxide is known for excellent durability and weather resistance, therefore it protects the metal quite well. The anodized coating can be either dyed into a desired colour, or naturally produce bronze tones as a result of diffraction phenomenon.
A great advantage of the anodized coating is that it is an integral part of the base metal and therefore it does not peel or flake. The thicker anodic coating is, the more durable and more long lasting it is.
Colour range and physical properties of anodized profiles
Anodizing produces a rich lustrous metallic appearance effect, it is translucent and the base metal is visible underneath.
Anodized aluminum profiles are not afraid of sunlight, unlike painted aluminum finish which will fade with years as a result of exposure to UV rays. Anodic coating is very thin comparing to powder painted one. Thus, even the best grade anodic coating is only required to be .0007″ thick, which is 3 times thinner than paint or powder.
Anodized colours are quite limited though. You may find anodized aluminum windows in the following finishes: clear, champagne, copper, light bronze, medium bronze, dark bronze, black.
If this suits your architectural requirements, then you should consider anodized aluminum windows with their durable, non-peeling, UV resistant finish.
Maintenance of anodized surfaces
Interestingly, anodized surfaces can be renewed and rejuvenated – with years they may start looking dirty and show stains, but this issue can easily be resolved by using mild detergent and abrasive cleaning. Once this is done the result will impress you – you will see a renewed surface which can last for the next couple of decades. This is quite different from painted aluminum, because if its coating fails, the only solution would be to repaint the surface.
Anodizing method is environmentally friendly as it produces no volatile organic compounds (VOCs) and used no heavy metals in the process. Also, anodizing produces chemicals which can be used by waste water treatment plants.
An alternative to electrochemical anodizing would be application of organic coatings. Organic coating is a type of coating which contains compounds with some carbon bonds. Paint, powder, lacquer, enamel are all organic coatings. Paint can be liquid or powder.
While liquid paint consists of pigment, resin and solvent, powder paint does not have solvent component, it is just pigment and powdered resin.
There are many types of resins available, including acrylics, polyesters, polyurethanes, urethanes, PVDF etc. However, very few of them will exceed lifespan of 5 years.
If the same kind of resin is used in both powder and liquid paint, then there will be no difference in the coating’s performance. The decision which one to use is simply determined by which application technique is more convenience to use.
However the most important advantage of powder paint is reduced air pollution. Powder paint is known to emit no VOCs while being cured by heat in the oven.
Powder coating is usually manufactured in large batches, and requires expensive grinders for the process, so custom colours can be quite expensive. While solvent based paints offer convenience of small batches and lot of flexibility for both painters and customers.
Each resin type is not available in both powder and solvent-based formulation, but rather in one of them. This happens because some resins are more easily manufactured as powders, and others – as liquids.
Solvents pollute the air. Some countries are considering prohibiting spraying of solvent-based coatings without special environment control equipment, which will imminently increase the cost of solvent based coatings. Therefore powder coatings are becoming more competitive then ever before, since they do not pollute the air.
Powder coating process
In aluminum window industry, polyester powder coating is considered to be one of the most durable and weather resistance finishing types. It is available in a wide range of colours. It is also easy to clean and maintain as it will not require any painting from you. Powder coated aluminum windows are well protected from UV exposure and other unfavourable environmental conditions.
Powder coating is done through electrostatically charged particles of dry paint applied to aluminum surface.
Powder coating of aluminum window profiles is a 3-step process involving pre-treatment, powder application and curing.
The first step is to thoroughly clean the aluminum surface – all grease, soil, oxides etc. must be removed and it can be done both chemically and mechanically. The quality of any organic coating depends on pretreatment. Quality pretreatment of aluminum surfaces is essential in receiving of high performace coating. That is why liquid and powder painting should always be factory applied.
After pre-treatment step, the aluminum profile is placed in a special machine where powder particles are being sprayed with compressed air through an electrostatic tool thus receiving a positive electric charge. The aluminum is being heated and the powder melts, developing a uniform film. It will then be cured at a special temperature for a specific amount of time and cooled to become a hard coating.
Powder coating vs. baked enamel
The main difference between powder coating and baked enamel finishing is that the latter is a solvent based paint which produces VOC’s when being cured.
Also powder coating is known to produce a smoother and more uniform finish than baked enamel.
You may sometimes hear that powder coating is more advantageous in terms of producing a harder and more lustrous coating, but in fact, this is just the characteristics of the resin itself, and not the method of application.
In order to choose the right aluminum window finishing type it is recommended to see actual samples of aluminum profiles. Contact one of our representatives to make an informed decision.