HVOF Sparklet and stoppage problem

[attin]

Greetings all,

Our customer remonstrant about HVOF gun stoppage. They are using HVOF coating method, particle size 20-53 micron and powder hardness 45 HRC. Another problem that they have; " which resultant from the gun powder, in time it is outgoing as sparklet. Has anybody had idea this problem? Have a nice day..

Bahattin

[Gordon]

Hi Bahattin

It sounds like your customer is suffering from nozzle fouling. "Sparklets" produced when fouling debris falls back into flame. This issue may be one of HVOF gun hardware/parameter settings and or selection of best powder grade for equipment.

[attin]

Tahnks Mr. Gordon

I guess particle size range is also relationship this problem, they are using another powder from another supplier, but they arent existing any problem with sparklet. 20-53 micron particle size range, is it very narrow size range for HVOF? Thanks for your helps.

[Gordon]

Hi Bahattin

If your customer is spraying both powders with same parameters, it does indicate differences between powders. Though both powders may have same particle size range, there is still a lot of room for differences in particle size distribution within that range, certainly enough to effect optimum spraying parameters. Also the amount of fines that are retained in the powder (particles finer than 20 micrometres) can also have a significant impact. It's not to say your powder is necessarily poorer than the other, just that it may need different spray parameters. Unfortunately, your customer probably will not want to get involve with parameter optimisation and will expect powder to respond exactly the same. Problem here is that you either 1. produce an exact copy of your competitors powder, 2. persuade your customer to invest time and effort into developing new parameters for your powder, or 3. do spray parameter development yourself.

HVOF powders generally require finer and tighter particle size distributions than the lower velocity flame spray processes.