uneven Wc coating thickness
01-11-2012, 05:31 AM,
#1
uneven Wc coating thickness
I am wondering if someone might have some ideas what may cause uneven Wc coating buildup with a tafa jp-5000. It hasn't been a huge issue till now cause we grind all the parts when I am done but it does take me longer to hit my size if the coating is not going on even. I am following all the parameters but I do notice I get nothing registering on the feeder pressure gauge??
The hoses all run straight to the gun and everything is fine when I do a leak test. Not sure if there is more to check with the gun or if it is in the setup or traverse.
It is very frustrating...
Reply
01-11-2012, 07:49 AM,
#2
RE: uneven Wc coating thickness
(01-11-2012, 05:31 AM)Brent Wrote: I am wondering if someone might have some ideas what may cause uneven Wc coating buildup with a tafa jp-5000. It hasn't been a huge issue till now cause we grind all the parts when I am done but it does take me longer to hit my size if the coating is not going on even. I am following all the parameters but I do notice I get nothing registering on the feeder pressure gauge??
The hoses all run straight to the gun and everything is fine when I do a leak test. Not sure if there is more to check with the gun or if it is in the setup or traverse.
It is very frustrating...

It could be a number of things mate.

Check your speeds and feeds are correct

RPM = SURFACE SPEED (M/MIN)
PART CIRCUMFERANCE(M)

TRAVERSE = RPM X STEP DISTANCE / 60

If your traverse is too fast for the rpm it will have a barbers pole effect and cause uneven build up.

If you have a leak in your feed line it will cause poor flow and cause un even build up

Leak check your feed line up to the t-piece (same way you check the hopper but instead of blocking the line at the hopper block it at the t-piece)

Also check the condition of you t-piece sometimes it gets worn where the feed line from the hopper connects to it and could cause carrier gas to leak - this would not show up on a leak check hence the reason to check condition of it.

Have a look at the above and see how you get on.

Cheers

Kev
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01-19-2012, 06:21 AM,
#3
RE: uneven Wc coating thickness
Hi Kev
I have done leak test right out to the gun, looping a line right around from one side of the tee to the other and it holds pressure with no flow.

As far as the traverse goes I don't think its a case of going to fast. My traverse only goes at 22 in/min (.56m/min) and I am using 200sf/sec to work out my rpm which doesn't give me much of an offset. The sleeves I have sprayed have all been low in the middle of a say 6" long spray distance . To keep the part cool I start the powder feed across shut off the powder wait for it too cool. restart the powder and traverse to the start. I almost swear that the powder feed starts strong and seems to slow by the middle of the fit giving it that high on the ends and low in the middle.

Brent
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01-20-2012, 12:34 AM,
#4
RE: uneven Wc coating thickness
(01-19-2012, 06:21 AM)Brent Wrote: Hi Kev
I have done leak test right out to the gun, looping a line right around from one side of the tee to the other and it holds pressure with no flow.

As far as the traverse goes I don't think its a case of going to fast. My traverse only goes at 22 in/min (.56m/min) and I am using 200sf/sec to work out my rpm which doesn't give me much of an offset. The sleeves I have sprayed have all been low in the middle of a say 6" long spray distance . To keep the part cool I start the powder feed across shut off the powder wait for it too cool. restart the powder and traverse to the start. I almost swear that the powder feed starts strong and seems to slow by the middle of the fit giving it that high on the ends and low in the middle.

Brent

A 6" spray distance is a bit short for WC when I used WC Tafa 1350vm (86%WC 10%C 4%Cr) the spray distance used was 14 inches with an 8" barrel. 1900 oxy and 4.6 gph of Fuel. Your carrier flow will depend on the outcome of your spot test (do you carry out a spot test ?) somewhere around 18lpm of nitrogen should be almost there

What is the diameter of your part ?

As far as keeping the part cool you should really have some cooling air on the part especially with that short spray distance the component will be toasting ! Do you keep it below 150°C ? Also if you arrange cooling air make sure that the air does not effect the spray stream.

See how you get on with the above, let me know how it goes.

Cheers

Kev

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01-20-2012, 03:33 AM,
#5
RE: uneven Wc coating thickness
bad post on my part 6" was the width of the area being sprayed not my stand off distance.
What is a spot test??
As far as cooling goes I have a stationary air line wide open about 6" below the part being sprayed
Reply
01-20-2012, 04:13 AM,
#6
RE: uneven Wc coating thickness
(01-20-2012, 03:33 AM)Brent Wrote: bad post on my part 6" was the width of the area being sprayed not my stand off distance.
What is a spot test??
As far as cooling goes I have a stationary air line wide open about 6" below the part being sprayed

A spot test allows you to see you have the correct carrier setting set your spray distance from a peice of plate and set you carrier gasd light the pistol and turn the powder on and pause for 5 seconds the coating spot should be a perfect circle if your gas is too low it will be an oval shape if its too high it will be a figure of 8 shape

I would check over the hopper again, feed rates, carrier flow, Check the powder is not moist, check the condition of the wheel in the hopper etc

Make sure your parameters are correct oxy, fuel, barrel length etc. The barrel isnt loaded or anything silly like that is it ?

What is the diameter of the part you are spraying ?

Cheers

Kev
Reply




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