Hi All,

Looks like the summer has finished here.. oh well back to work then
I'm plying around Metco 450NS and not having much look. The powder was pulsing but that was down to insufficient carrier gas flow.

The trouble now is the flame seems to be sitting too low. It is as if the powder is being pushed too far into the flame but the feed rate is spot on and if I reduce the flow it starts to pulse. I've got the correct powder port and the equipment seems fine. Any ideas?

The other thing I'm slight confused about is the amount of material being deposited per pass. The tech sheet says apply 0.004-0.006" in a pass. I'm only managing one Speeding the turn table up doesn't help. Any suggestion?

Thanks guys
Jim

Hi Jim

Carrier gas flow is a critical parameter for injection of the powder into the right area of the plasma jet. I am assuming you are using flow rates above those recommended in order to get a smooth non-pulsing powder flow. Unfortunately, this may lead to the larger particle size fraction of your powder to be injected to far through the plasma jet, resulting in poor heating, low deposit efficiency and reduced coating quality. Sounds like you will need to revisit your powder feeding problem, but this time curing the pulsing problem, while maintaining the recommended carrier gas flow.

If you are using Metco 450 as a bond coat, this is usually best at a thickness of 0.004-0.006" for optimum bond strength and best applied in one single pass. This means using much slower gun speeds/feeds than you would typically use for the top coat material.

Hope your problems are not as grim as the UKs summer weather

Hi Gordon,

I was actually using the recommended flow rate (5.9 nlpm) to clear the pulsing issue. I've reduced it down to 2 nlpm and the flame sits happy in the middle of the plasma and doesn't seem to be pulsing. Strange.
As for build up I've managed 4-5 thou a pass so thats good too The micro structure had a lot of oxides but I think thats down to the powder being a bit cold/damp and maybe a little too much heat due to the slower feeds. Still better than yesterday I'll try again on Monday!
thanks
Jim

Hi Jim

I would suggest you do not stray too far away from the recommended carrier gas flow. It is normal to get some "target point deviation" with the 3/7/9MB type guns, where the actual spray stream may kicked off gun axis by may be as much as 5 -10 degrees on the opposing side of the powder port. With argon plasma, you may also get a small rotational offset about the gun axis as well due to the plasma gas swirl.

Here is a great base to start with....

3/7/9mb gun (I like the 9mb)
argon/hydrogen
GH nozzle
#6 powder port(this will keep the powder from injecting thru the flame)
feed rate - 60+/- 5 gm/min
4.0" standoff
4.75 frontal intersect @ 60psi cooling
Primary- 100psi / 80flow
secondary 60psi / as required... do not excede 20flow
500amp / 70volt

Put on a helmet and make sure the powder port is centered with the gun and powder flowing... BE VERY CAREFUL.

4mp feeder carrier -- 34flow
9mp feeder carrier -- 12.5 flow

Try to run about 350 surface feet per min.

let me know if you try.

Erick