RE: Fusing process
Hi Arturas
Yes, propane produces a lot more water as a by-product of combustion than acetylene. I don't think this will be detrimental to the high temperature fusing process, certainly not from a water condensation point of view anyway.
The fact that acetylene requires as little as 45% of the oxygen required for complete stoichiometric combustion, while propane needs at least 75% gives a clue to why propane flames tend to more oxidising. Add to this, that propane produces a broader more tubulent flame and produces a less localised heating effect than acetylene, plus the lower flame temperature results in longer time taken to reach the critical fusing temperature resulting in more oxidation. Basically, similar reasons why acetylene is preferred for welding, brazing and cutting.
The self-fluxing alloy composition particularly the balance of fluxing agents (silicon and boron) and the quality of the as-sprayed coating prior to fusing will also have a big effect. The more porous the coating, the more oxidation will occur during fusing. The self-fluxing agents will mop up the oxidation, but can get exhausted, resulting in raising the melting point/fusing temperature and causing poor fusion. This why the denser/cleaner plasma or HVOF spray coatings tend to fuse easier than conventional LVOF flame sprayed coatings.
Third time lucky I hope! My first two attempts at writing this were cut short by power cuts, probably due to the thunder storms we are having here at the moment.
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