Having established that the coatings are a massive
improvement on their conventional counterparts, what
is the downside ? There is obviously a cost to be paid
due to the use of shrouding nitrogen gas. However,looking
at the costing of a typical sprayed coating of Inconel
625 it becomes obvious that the bulk of the cost is
in the material. Our analysis of the costs shows that
PURECOAT is approximately 10% more expensive than
Arcspray and less than 50% the cost of HVOF.
Corrosion Resistant Alloys e.g. Inconel 625
These alloys provide corrosion protection by providing
a resistant barrier layer. They offer protection by
readily forming an adherent oxide film usually of chromium
oxide, on their surface, which inhibits further corrosion.
However this readiness to form oxides mean that normally
coatings will contain oxidised particles, which are
therefore depleted in chromium. Research has shown that
these oxide layers around the particles can act as a
path for further oxidation and penetration of the oxidising
medium to the substrate. The lower the oxides content
of the coating the better. Coating density is also very
important in reducing the paths along which the corrosion
medium can migrate.
High temperature oxidation and sulphidation.
The same factors arise in the protection of components
against high temperature oxidation and sulphidation.
In this case alloys such as Metallisation 78E and 88E
are used to give ten times the resistance of normal
steel. All of these materials rely on providing a dense
resistant barrier of an alloy, which is not degraded
by the spraying process. Normal coatings fail due to
degradation of the alloy and penetration through the
coating. The Purecoat process minimises these deleterious
effects leading to better performance and longer life.
The low level of oxides present in the coating ensures
a much higher than normal electrical conductivity. A
typical sprayed copper coating has an electrical conductivity
around 40% of that of wrought copper. Using the new
process electrical conductivity can approach 90%.
Typical Spraying Parameters
Metallisation Arc Spray Pistol base: 140 or 528E
Primary pressure: 3.0 BAR
Secondary pressure: 2.0 BAR
Tertiary pressure: 0.6 BAR
Current: Dependent on wire size. Must be limited to
300A to maintain high quality deposits.
The coating may be finished in conventional ways. Improved
surface finish may be expected due to the improved coating
Observe normal spraying practices, respiratory and hearing
protection is advised. UV eye protection must be provided
when arc spraying.
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