Fusing process

[Arturas]

Hello,
I hear a lot of speech about fusing process. We do it also in our company. But it is very intresting for my to know : what is difference if I perform fusing with acetylene and if I perform fusing with propane??? I understand that fusing with propane oxidize coating, but is it really make so big influence to wear resistance of the coating???

[Gordon]

Hi Arturas

Welcome to the Surface Engineering Forum. I think you were a regular poster on the old message board. I would be interested in your comments on how the old and the new compare.

Acetylene produces a very intense and localised flame around 3150 C, while requiring relatively small amounts of oxygen.

Propane produces a relatively broad and turbulent flame at around 2800 C while requiring large amounts of oxygen.

From a practical point of view acetylene certainly makes the best flame for control of the final fusing of coatings. Propane though is very good for preheating large parts prior to final fusing.

I think if you are successfully fusing your coatings using propane (fully fused, with no holes, porosity or reduction in hardness) then I see no real problems with coating performance.

Try both approaches to fusing, I think you will soon see the advantages to using acetylene.

[Arturas]

Hi Arturas

Welcome to the Surface Engineering Forum. I think you were a regular poster on the old message board. I would be interested in your comments on how the old and the new compare.

Acetylene produces a very intense and localised flame around 3150 C, while requiring relatively small amounts of oxygen.

Propane produces a relatively broad and turbulent flame at around 2800 C while requiring large amounts of oxygen.

From a practical point of view acetylene certainly makes the best flame for control of the final fusing of coatings. Propane though is very good for preheating large parts prior to final fusing.

I think if you are successfully fusing your coatings using propane (fully fused, with no holes, porosity or reduction in hardness) then I see no real problems with coating performance.

Try both approaches to fusing, I think you will soon see the advantages to using acetylene.

Hello

Thank You for Your answers.

It is very interesting , but what about water which separate from flame during process time. I think that quantity of water is bigger when I use propane gas. And it can lead to corrosion or it is impossible?

Arturas

[Gordon]

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.