Posted by Alecxei Goncharov (195.96.79.2) on 14:22:37 11/01/06
Hi, I ve read your article Nature of Thermal Spray Coatings with
grate interest and with real pleasure. No doubt, it could be
recommended as a manual for engineers. As I have dealt for a long
period with detonation spraying of coatings, I d like to remark
some points at the mentioned text and to make some proposals.
1. Explaining the nature of coating failure, where the tensile
stresses exceeds that of the bond strength or cohesive strength,
you show two
right pictures, where the bending of the coating is directed to
free surface of coating due to its cooling and solidification. I
would agree with it, if the heat flow has the same direction, what
could be in the case, for instance, if air cooling flow winds to
the sprayed surface. In opposite situation, if cooling flow winds
to the substrate and it s productivity enough for the heat flow to
direct to the substrate, the coating bends tending to snuggle to
the substrate. It s clear, that all said concerns to convex form of
the substrate, which has to be cooled during spraying to achieve
good adhesion strength. In opposite case, if, say, internal
cylinder surface has to be coated, the last must be heated just
before spraying to enable the initial expansion of the hole, which
will follow the shrinkage as well as that of sprayed coating. This
procedure of preliminary heating is necessary to avoid the coating
detach after spraying.
Best regards
Please go to the new Surface Engineering Forum as this old message board is a read only archive. Please copy and paste relevant information or link to the page if you wish to reactivate a thread on the new forum.
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