Adhesives have seen extensive use in the space sector, replacing rivets, screws and welds. Not only do they improve aesthetics, they also offer superior stress distribution across joints, make stiffer structures and use lighter materials. Standard adhesive practice involves using a wet chemical surface treatment process that often includes chromates and other hazardous materials. Chromates are a class of toxic substances used in coatings that has been proven to be very harmful to human health. The EU is currently implementing Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) regulations to restrict the use of these chemicals. This is where the EU-funded OSMOSIS project comes in. “Utilising ENBIO’s patented CoBlast technology, OSMOSIS offers new coatings with exceptional adhesion onto a wide variety of substrates, including titanium, aluminium and steel,” notes project engineer Lorcán Byrne. CoBlast is an environmentally friendly, dry process that does not rely on hazardous wet chemicals such as chromates. The technology has existing heritage in space and has solved mission critical problems for the European Space Agency. ENBIO has now modified this process, allowing a direct primer to bond to the metal with excellent adhesion properties.
One-step metal transformation process
CoBlast not only eliminates the need for hazardous chemicals, it also transforms surface treatment to a simple one-stage process that reduces cycle time in the factory floor space. In particular, it uses conventional grit/micro-blasting equipment to remove a metal’s natural oxide layer and replaces it with a desired functional coating. Abrasive and coating powders are simultaneously blasted onto the metal surface from a single nozzle. The abrasive mechanically wears down the substrate, exposing active chemical bonds to which the coated particles adhere before an oxide layer can re-form. The inert nature of the abrasive ensures that it does not easily form chemical bonds, so that the process results in a coating with excellent coverage, with little or no abrasive remaining on the surface or embedded in the substrate. The level of coating substrate integration achieved by this process is far beyond most coating methods. CoBlast skins integrate exceptionally well even with substrates that normally suffer poor coating adhesion, thanks to the simultaneous roughening, chemical activation and coating deposition. Furthermore, it can be applied to almost any substrate geometry, as the nozzle is easily mounted on standard industrial robots and other automation equipment. This line-of-sight process allows for convenient masking of uncoated sections.
Inching a step closer to space
The key goal of OSMOSIS was to bring a viable chromate-free adhesive primer to the European space market. The technology has been shown to match or exceed the strength of chromate alternatives under a variety of conditions. Bonded metal joints demonstrated comparable strength retention following exposure to thermal cycling, humidity and other corrosive conditions. The technology is undergoing the final stages of qualification, with flight heritage expected later in the year aboard EIRSAT-1, Ireland’s first autonomous satellite.
OSMOSIS, coating, space, CoBlast, substrate, chromate, abrasive, surface treatment, adhesive, ENBIO, primer