Metallization – the ideal technology for the best anticorrosive protection
08.10.2018
The metallization ensures the anticorrosive protection and prolongs the lifetime of series of products that are ususally exposed to hostile environmental and working conditions.
In our days there are several metallization techniques, but they can all be grouped in mainly 2 big categories. The first one includes solutions for finishing, decoration and anticorrosive purposes and the second one consists of technologies meant to ensure the resistance in time of the parts, or to create thermal barriers where needed.
The metallization is the recommended solution for series of anticorrosive applications or for technological ones, as they are needed in the oil and gas industry, on petrochemical area or in the maritime domain.
How does thermal spraying work?
All metallization methods imply covering an area with melted metal particles that are supposed to create a protective coverage while adhering to the surface they got thermally sprayed on. For melting purposes, a heating source is necessary along with a material to be sprayed and a method for projecting the melted particles. When touching the surface to be treated the particles solidify and mechanically adhere initially to the first layer of the covered area and afterwards between them, building up the anticorrosive protection.
Due to the fact that that energy necessary for heating the particles is not relevant in comparison with the one needed for spraying, during metallization only a small amount of heat in transferred to the surface to be processed. As long as the differences of temperature between the sprayed particles and the part to be treated are irrelevant, there is no risk of thermal deformation as it would be in case of galvanizing.
The flame spraying systems are usually the option when specific levels of anticorrosive protection are to be obtained. In their case a wire is transferred through the flame system in order to get melted and sprayed afterwards onto the surface to be protected. Through the nozzle of the equipment a strong airflow is pushed for atomizing and spraying the melted particles. The transfer of the wire is usually ensured with an air engine and a gearbox that are part of the equipment gun. Wires of 1.6mm to 4.76mm can be used.
In case of electric arc metallization systems, two wires electrically charged are manipulated in such a way so that they will converge at some point creating in electric arc. An air nozzle will atomize the particles and sprays them onto the surface to be treated. The transfer of the wire through the system is done with the help of an air or electric engine and of a properly assembled gearbox.
Choosing one or another metallization method depends on each project in part. For instance the protections created with electric arc spraying systems while using aluminum wires are 2.5 times more adherent than the ones created while using the flame spraying method. The choice takes into consideration other aspects as well such us: storage capacity, ease of operation, safety, maintenance costs and time, the desired finishing and the automation level of the process.
The efficiency of protections created through metallization
The thermal spraying process itself is not really new. The technology became extremely efficient on a large scale during the 90s, when it was used in series of protective applications from gas turbines to metal benches in parks. When it comes to protecting steel structures, metallization is the best and most recommended solution as it offers 20 years guarantee for all processed parts even if these are exposed to aggressive working conditions like the ones in the maritime industry and other similar domains.
Metallization is usually done while using Zinc, Aluminum, or alloys (85% Zn and 15% Al). Choosing the right material is based on series of environmental aspects (corrosive atmosphere, temperature etc), legal specifications and norms into force, lifetime expectations of the processed parts, wished adhesion degree, availability of coverage material.
As a general rule, Zinc protection is mostly used in case of applications where the expectations related to anticorrosive protection are low (for example: water tanks, some bridges and metal structures in general). Aluminum is normally used in situations in which there is a high need of anticorrosive protection (for instance when parts are exposed to salted water or to aggressive actions).
Furthermore, Aluminum is used in case of high temperature applications like the ones in offshore projects, or oil and gas industry.
The alloys are used when the corrosion resistance of Zinc is the admitted limit for the part to be processed.
For finishing purposes other materials and alloys can become options– Copper, Aluminum Bronze, Phosphor – Bronze.
