The surfaces of materials like metals and composites can alter due to various factors like the manufacturing process, aging, exposure to the air, handling and so on. Oxidation, oil and grease left on the surface of the material can all severely compromise bonding performance.
Steel sheets with oxidation and greace on the surface
That’s why surface preparation is so crucial to remove oxidation, oil, grease and other contaminants to produce the consistently clean high-quality surface that’s so essential for the best possible bond quality.
By the way, issues with bonding quality can also occur when there’s a change of material supplier, that’s why it’s important to have a requalification of adhesive bonding performance whenever there is a new supplier.
For effective chemical bonding surfaces need to be free of oil, grease dirt and other contaminants to allow for optimal bonding performance. The wettability factor is also important because adhesives more readily and fully cover the surface of the material to be bonded.
Solvent based cleaners like heptane and acetone are often used to remove grease, oil and other contaminants from the surface of metals, while water-based cleaners and alcohol are typically used for removing grease and oil from more sensitive substrates like carbon fibre and plastics. The issue with this method is the use of potentially hazardous and environmentally unfriendly chemicals for the cleaning process, which can be expensive and difficult to dispose of, as well as being harmful to the planet of course.
A mechanical abrasion is usually used after the degreasing process, to remove oxide layers or any remaining dirt from the surface. Dry blasting (or sandblasting), brushing, or other mechanical finishing processes have historically been used for this, but again there are drawbacks. Dry blasting results in the creation of dust which, in addition to being a health and explosion risk, can result in blast media being left on the surfaces to be bonded. If this happens bonding is compromised. The solution to this is to clean the surface again after blasting, but this introduces an additional process step, slowing productivity and hence increasing cost.
Brushing can result in microscopic scratches on the surface which in turn results in a less than perfect ‘wet out’ surface and a weaker bond.
Wet blasting (or vapor blasting) is a surface finishing process that not only removes grease, oil, oxides, dirt and other contaminants, but that also creates a perfectly clean ‘wet-out’ surface to a specific Ra that’s perfect for bonding.
And when it comes to composite bonding, the cushioning affect of water also prevents damage to carbon fibre.
The video below is a good illustration of why the creation of a ‘wet-out’ surface is so important for effective bonding. A sheet of carbon fibre is shown where the top strip of carbon fibre is wet blasted, while the bottom area of carbon fibre, below the blue masking tape, has been left un-finished. Note how the water ‘beads’ up on the un-finished surface, this is typically due to the hydrophobic properties of the grease and oil that remains on the surface. Where the top strip has been wet blasted (or vapor blasted) you can see water evenly spreading across the surface because it’s been rendered hydrophilic by wet blasting it.
Video illustrating the effect of wet blasting carbon fibre
It's for this reason that you will find our wet blasting machines in most of the Formula One racing teams' manufacturing facilities because effective composite bonding is critical to the integrity of the car. Composites are of course widely used in the aerospace industry as well, and again, that is why our machines are installed in many of the leading aerospace manufacturers.
Our wet blasting systems are also found in numerous other industries for the purpose of preparing metal surfaces for bonding.
Vapormatt automated wet blasting systems ensure a repeatable and consistent surface finish on the components’ surface in perfect preperation for bonding. Automation also improves productivity and subsequent ROI.
Vapormatt Puma - wet blasting a composite wheel - wet blasting a carbon fibre component in preperatin for bonding
Our range of manual machines tends to suit users with a lower volume throughput and whose components frequently vary from one to the other.
Process control is another important feature of wet blasting (vapor blasting), in fact process control in wet blasting is significantly better than all comparable processes. Visit our wet blasting education page to learn all about the controllable variables.
Process control allows you to refine the wet blasting (vapor blasting) process to precisely suit your components, which is especially useful when you’re trying to achieve a specific Ra of surface roughness that’s optimum for best bonding performance.
And because there is no dust, explosion risk, or harmful chemicals it’s a surface finishing process that’s significantly more environmentally friendly than most other alternatives. To make this point even more compelling, water used in our wet blasting systems is recycled through the system for rinsing and blast chamber window washing.