How to control the TORCH nozzle and electrode

[howied]

Dear all,

I would like to know how do you guys control your plasma spraying torch electrode and nozzle; are there any established criteria for electrode and nozzle replacement? Something like to verify nozzle bore diameter against nominal one, if it is oversize (bigger, smaller?) above certain persent, then we shall replace. what about electrode?

How much wear rate of the nozzles electrode, I must replace new.


This is a NADCAP AC 7109/1 requirement.

thanks.
Howied

[Gordon]

Hi Howied

Good question, but probably not easy to answer. I only know of the rather subjective visual examination, water leak test and monitoring of voltage. The problem is erosion/wear of nozzles and electrodes is rarely even, usually it is a localised scar or gouge that ends their lives, which is difficult to quantify. Obviously you want to get the longest life from your nozzles/electrodes, but this needs to be balance with the risks to deterioration of coating quality and also damage to the plasma gun if a nozzle 'blows'. It really comes down to the experience of your people to judge at what point a nozzle/electrode becomes too risky to use.

I know we have a few members that must go through large amounts of nozzle/electrode consumables, and probably have a lot of experience with this problem. Comments and feedback more than welcome

[Alexangel1226]

Howied,

Best practices:

Nozzles:

1. Rotate the nozzle body in quadrant (~90deg) each time you spray 1~2 parts, depend on the spraying hrs too, tried more than 3 parts, the erosion happen too deep in and the rotation will not be effective after that. it seems that the more eroded area gets the attack more frequently. by rotating regularly, you will see an even erosion on ID of nozzle bore.
Well, marking on each rotation may help. Try it out. Also you may wanna develope your own guideline to show your guys on how a well rotated nozzle scrapping condition look like, or some kinda comparator, to show the condition. Theses visual comparator will assit the experience in determining what's good and what's bad.

2. Also to check on your chilled water conductivity, the higher it gets you will notice drop in cooling effect which result in faster wear rate. You will see formation of oxidized or carbon like material on the nozzle body if you were to remove the body from the shell. To change the water regularly once it exceed the limit. Else u will need to remove the nozzle more frequently to remove the carbon like material. But the former is the most recommended and convenient.

For electrode, pls check out the previous link.

hope this help

Alexangel1226

[Gordon]

Hi Howied & Alex

Good advice from Alex . I've always tried to rotate nozzles at regular intervals, believing that to be good practice and it sounds logical. But to be honest I can't claim in my case a big difference, because I hav'nt really been involved much with repetitive production spraying to analyse the effect on nozzle life. I do know that once a nozzle becomes gouged (localised attack) nozzle rotation has little effect, the plasma arc appears to be attacted to this area and will follow any rotation. So my advice would be to make sure you rotate the nozzles regularly from early on and not to wait for the first signs of scarring.

[Alexangel1226]

Gordon,

I believe you will not see much difference if you do not run the parts of same set-up, powder type or production in badge. Different power type spraying will give different wear rate, it's hard to quantify or measure, but by experience we can see it happening. Thus, it will be cost effective (material or man hr) to run all similar parts in lots, or back to back without having to change much powder type.

Then the nozzle or electrode will last longer. Also depending on the number of ignition and duration of spraying does play a main part of the wear rate. The number of ignition seems proportional to the wear rate. Compare operation which need longer spraying time, more frequent strat-up ignited ones though clock same running hrs will have worse wear condition.

Also last thing is we find, using Argon gas as primary process gas compared to nitrogen...is again a difference in nozzle shell life. Seems argon/helium gas is "mild" not attacking the nozzle as fast as nitrogen/Hydrogen. Also increasing 2nd gas will see a faster nozzle wear rate.

Regards,
Alexangel1226

[Gordon]

Hi Alex

I agree with your comments. Also, you made an important observation on the effects of different plasma gas compositions on nozzle wear. To add to this, the presence of oxygen, water or other contaminants can have a very dramatic effect, which leads us to your new thread today: Process Gasses Purity Impact towards Plasma Spray Process, equipment or outcome

[amycheung83]

Dear all,

I would like to know how do you guys control your plasma spraying torch electrode and nozzle; are there any established criteria for electrode and nozzle replacement? Something like to verify nozzle bore diameter against nominal one, if it is oversize (bigger, smaller?) above certain persent, then we shall replace. what about electrode?

How much wear rate of the  nozzles electrode, I must replace new.


This is a NADCAP AC 7109/1 requirement.

thanks.
Howied

Hi Howied,
Nice to meet you!
This is Amy,we are professional manufacturer for plasma spray nozzles and electrodes of F4,F1,SG100,9MB/7MB/3M7,F210,100HE,Sinplex,Triplex,etc.
If any need and question,welcome to consult with us any time.

My whatsapp&wechat:+86 15200507438
Email:amy@rheniumcn.com

Have a good day!
Amy

[amycheung83]

Dear all,

I would like to know how do you guys control your plasma spraying torch electrode and nozzle; are there any established criteria for electrode and nozzle replacement? Something like to verify nozzle bore diameter against nominal one, if it is oversize (bigger, smaller?) above certain persent, then we shall replace. what about electrode?

How much wear rate of the  nozzles electrode, I must replace new.


This is a NADCAP AC 7109/1 requirement.

thanks.
Howied

Hi Howied,
Nice to meet you!
This is Amy,we are professional manufacturer for plasma spray nozzles and electrodes of F4,F1,SG100,9MB/7MB/3M7,F210,100HE,Sinplex,Triplex,etc.
If any need and question,welcome to consult with us any time.

My whatsapp&wechat:+86 15200507438
Email:amy@rheniumcn.com

Have a good day!
Amy

[ServiceTech]

Measuring the nozzle/electrode comes down to performance and visual examination.  Years ago, I set out to remove the subjective nature of this particular issue during my days at Metco and finally have settled on a method that has proven effective over a period of time in the current industry I work, aerospace.

I will provide the Readers Digest version of the methodology, if you will.  

Step 1 - Install hour meters in the spray consoles that count hours while gun is in operation.
Step 2 - Spray test specimens with new gun nozzle and electrode.  Record the hour meter reading prior to spraying.  Also record voltage.
Step 3 - Start spraying production parts with same nozzle and electrode, keeping track of the hours and number of ignitions.  Do not adjust secondary gas flow for voltage drops.  
Step 4 - Spray test specimens and monitor results every hour of spray time.  Keep track of voltage.
Step 5 - At some point in your process, you will notice either a coating degradation, voltage instability, or drop, or gun hardware degradation.  In our shop, we noticed hardware degradation before any coating issues.  Your mileage may vary due to parameter type, water quality, and production circumstances.  However, I suspect your coating quality will not suffer before gun hardware becomes worn.
Step 6 - When gun hardware, voltage stability or coating quality starts to creep in, note the hours, voltage drop, and number of ignitions. 
Step 7 - Repeat the process.  Check for consistency.  You must use the same parameters and do not make secondary gas flow or amperage adjustments or nozzle and electrode life will be negatively impacted and your test is invalid.  What you are looking for is a production hour point at which the gun hardware or coating quality starts to deteriorate.  
Step 8 - Record all data and analyze results.  Once you have determined the hour usage point where gun hardware requires change, commit to changing the hardware at a time limit of your choosing.  You want to obviously change gun hardware at a reasonable and comfortable time before any issues settle in.  For example, if the time to reach some point of degradation is 12 hours, change the hardware at 10, or 11 hours or whatever your choice.  But be conservative.  This will take the guess work out for your operators and also bring consistency to your process, make the QC department and auditors happy too. 

Also, this is a very intricate and deep issue with many factors in the works and I've only really touched on the basic idea.  Exceptions will apply from shop to shop, parameter to parameter, production parts, gas quality, water quality, ignitions, ramp up performance.  You'll just have to test in situ and determine what's right for your situation.

Check's in the mail.