F4 Nozzle/Electrode Wear

[Rich]

Hi all, I'm using a Sulzer F4 APS gun with 7MC cabinet and experiencing premature electrode wear/failure resulting in 'spit' marks on coatings during trials. I've attached some photos and would appreciate some pointers, based on the photos, of what to investigate first regarding the short electrode life. I'd prefer to hear your comments before stating the operating paramaters in use. The photos show a typical nozzle/electrode which has been in use for approximately 30 hours with 60 start-ups. Each start-up is at a lower current that operating current and gradually increased to operating current over the course of 5-10 seconds, i.e. not starting at full whack!

   

   

   

   

   


Thanks for any comments you may have.

[LEN WOOD]

F4 is an excellent gun!

Just a few questions:

• Are all gases pure enough/uncontaminated and all supply lines and hoses free from leaks?
• Do you see white or yellow flashes/sparks in the plasma stream (more visible with powder off) long after the new electrode 'bedding in' period?
• Have you checked the gun for water leaks?
• Leaving the heat exchanger/chiller on for extended periods will cause condensation to form on the electrode, chamber interior, etc. If the gun is not adequately purged then this will seriously shorten life.
• Is the coolant changed fairly frequently and the heat exchanger tank/reservoir and lines free from any corrosion and contaminants?
• Do you ramp the system/gun down (Secondary gas off then Amps down) and allow the Primary gas to purge a short while before shut off? If not then pieces of electrode will be lost on next run and will be seen in the coating as the Tungsten breaks away.
• Has the system been calibrated recently so you know that you're parameters/settings are fairly accurate?
• Are you burner cables in good condition and free from obstructions?
  

Have you always experienced short hardware life? If not then what has changed, supplier or configuration or?

Using an electrode alignment/centring tool will help achieve optimum life of hardware. But obviously isn't the issue here.

Sorry for the 'patronising' list but it saves time!

Let me know

[loriolo]

why do not try with original spare parts before, the same productor of spares could have low cost spares and very high quality spares, you must choice......, and then we can analyze the problem, as well as I agree for all said by Len Wood.

[Rich]

Thanks for the list, it's not patronising at all, especially as I'm fairly new to thermal spraying. I'll fill in what I can now and find out the rest when I get a chance.

• As far as I know, yes.
• No, generally the plasma jet is fairly stable and spark free. More sparks/streaks noticed towards end of electrode life, as well as falling voltage.
• Yes, it's been re-built many times for new nozzle/electrode, and each time checked for leaks. Leaks are quite rare.
• Not sure about the chiller and how often it runs/is left on for after coating. What do you mean by purging the gun?
• I can't remember when the coolant was last changed. Are you hinting that the gun may be overheating due to poor cooling? Is it normal to see cracks in the electrode as seen in the last picture above? How often would the coolant require changing? Weeks, months or years!?
• We do run the gun down, but possibly not in the way you describe. I'll investigate!
• Yes all gauges are currently in calibration.
• What do you mean by burner cables?
  

(03-02-2010 12:31 PM)LEN WOOD Wrote:  Have you always experienced short hardware life? If not then what has changed, supplier or configuration or?

The first nozzle/electrode that was in the gun when it was first used recently (it's been in storage for a few years apparently) lasted a long time. Since then we've had problems. No idea what has changed since then at all! All process controls are the same.


Another issue, but most likely related, is possibly with the 7MC cabinet. The F4 has been run at 700 amps but recently we've used 650 amps. (The electrode life issue was apparent before we changed the current.) At 700 amps the hardware was tripping out, possibly on over-temp. Could this be related to cooling issues as mentioned earlier?

Thanks for your help, really appreciated and I've got a lot to learn!





Loriolo - I would like to source some OEM spares but until I can prove that the issue lies there, I don't think I'll have much luck unfortunately.

[derek]

F4 gun has been in use for approximately 30 hours with 60 start-ups, the condition of your nozzle is normal. I bet after you shut off the gun you don't have Ar keep running. It will protect you electrod. We replace the nozzle and electrode every 40 houres in use.

[Rich]

Sorry guys, I've been out of the loop the last week or so. Thanks again for all the info here - there's a lot to think about and experiment with when I get the time. And thanks especially to Len for a few extra pointers too. I'll have a play and let you all know how I get on!

Sure I wrote this all out yesterday but it seems to have disappeared, or I didn't press the right 'post reply' button!

[LEN WOOD]

G'Day Rich,

Thanks for the thanks. I'm always happy to help, especially those that appreciate real and practical support in a field where vendor support is lacking!

Let me know how you get on.

[Diucky]

Hi,


Just keep in mind that a F4 running at 700 A could not be use at more than 65 V(Ar/H2) otherwise the electrode will burn and shows crack as i can see on your picture.

One clue : 7M starting device should be adjusted because as far as i know the initial configuration is for 9MB gun, if this is not adjusted this will reduce your anode/electrode lifetime.

Regards
Diucky