Tangential velocity of work surface
12-18-2012, 06:52 AM,
#1
Tangential velocity of work surface
Hi everyone,
I am a new one to the coating world. When I found this forum, I learned a lot from here.
When doing the plasma spray (APS), we put the repair part on the turntable. We usually set the table speed as 30 RPM. However, the diameter of our part is from 10 inch to 40 inch. The tangential velocity of working surface shall be a lot different. When the diameter is bigger, the tangential velocity is faster. But we always use the same table speed.
I want to ask:
Is the tangential velocity a concern to the coating quality?
What if the tangential velocity is higher or lower than the reference velocity?
If it is a concern, can anyone suggest a reference tangential velocity?
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12-19-2012, 06:33 PM,
#2
RE: Tangential velocity of work surface
Hi Airbin

Sign0016 to the Surface Engineering Forum.

Mostly coatings are applied in multiple thin layers/multiple passes of the gun. The important aspect of this is the thickness of the layer deposited in one pass of the gun. Typically I would advise about 0.0002" (5 μm) per pass for ceramics and carbides and generally less than 0.001" (25 μm) per pass for others. There is always a few exceptions Happy0193 like NiAl bond coats, best applied in one pass only and a few materials that don't mind or benefit from the heavy handed approach.

It is important to match rotation speed to traverse speed so that coating deposition just overlaps slightly with each other on each rotation. Just enough to ensure even deposition and no "barber pole" effect.

Quote:Is the tangential velocity a concern to the coating quality?
Yes

Quote:What if the tangential velocity is higher or lower than the reference velocity?
Assuming rotation is matched to traverse speed then lower than the reference velocity will give higher thickness per pass, higher velocity will give lower thickness per pass.

Quote:If it is a concern, can anyone suggest a reference tangential velocity?
This depends on materials, process, spray rates etc. A good way is to work out your desired thickness per pass and set feeds and speeds accordingly.

I'm sure if you have specific examples, members here may give their recommendations on speeds and feeds. Spray material data sheets and equipment manuals may also give recommendations on speeds and feeds.
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12-21-2012, 10:57 AM,
#3
RE: Tangential velocity of work surface
Thank you, Gordon.
I found most people suggest the surface speed is 45 to 75 m/min.
How does the surface speed affect the coating quality? For example, if the suface speed is 120 m/min, does the coating hardness become harder? or does the coating have fewer porosity?

We spray more than 10 powders, Metco 450NS, 443NS, 45C-NS, 71VF-NS, 52C-NS, 51F-NS-1, 68F-NS-1, etc. Most of our spary data has the same table speed (30RPM) and gun traverse speed (5mm/sec). These data are made more than 10 years ago. The existing engineers and operators don't really know why the data is.

When we spray 450NS with table speed (30RPM) and gun traverse speed (5mm/sec) to our part, we can see stripe on the surface. The senior engineer revised the table spped to 45RPM and gun traverse speed to 3mm/sec, then the stripe situation is improved. The parameter is applied to all size of parts. But I think the surface speed should be considered, not only RPM.
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12-21-2012, 03:31 PM,
#4
RE: Tangential velocity of work surface
Surface velocity is important because it determines how closely particles are deposited on top of/beside each other. If the velocity is too high, the particles will not touch at all. Statistically, this gap will be (partially) filled by particles on the next pass or passes, but there will be some porosity. There will also be an oxide layer which will inhibit bonding, so the coating will not be as strong.

The correct way to set rotational and gun traverse speeds is to first adjust your RPM to achieve your target surface speed. Then, you set your traverse velocity so your gun moves the width of your spray pattern on each revolution. These speeds will be different for each part you spray because each part has a different diameter.
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12-23-2012, 01:11 PM,
#5
RE: Tangential velocity of work surface
(12-21-2012, 03:31 PM)djewell Wrote: Surface velocity is important because it determines how closely particles are deposited on top of/beside each other. If the velocity is too high, the particles will not touch at all. Statistically, this gap will be (partially) filled by particles on the next pass or passes, but there will be some porosity. There will also be an oxide layer which will inhibit bonding, so the coating will not be as strong.

The correct way to set rotational and gun traverse speeds is to first adjust your RPM to achieve your target surface speed. Then, you set your traverse velocity so your gun moves the width of your spray pattern on each revolution. These speeds will be different for each part you spray because each part has a different diameter.
Is there a unique surface speed for all kinds of coating or different speed for each specific coating?
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12-26-2012, 05:56 PM,
#6
RE: Tangential velocity of work surface
Ideal surface speed should be related to particle velocity, ie. your spraying hardware. Contact your gun manufacturer for ideal surface speed.
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03-12-2014, 10:51 PM,
#7
RE: Tangential velocity of work surface
What happens if my piece is a sphere, have many diameters when the gun traverse the surface. I mean i have a diameter 19.05 mm and need cover one half of sphere.

somebody suggest me if i need move only the sphere(rotation movement) or move the sphere and gun together?

thank you for your response.
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03-13-2014, 09:43 AM,
#8
RE: Tangential velocity of work surface
Hi Vicktor

In your case (for sphere), you have to rotate the component and move the gun in such a way that as diameter of sphere reduces the coating gun has to move fastly so that the coating thickness should be equal.

For this type of applications, Robot with Coating Gun is best option (OR) customized setup required.

I personally feel that

IF you are looking good quality of coatings without worrying much about coating cost, then little bit higher surface speeds than optimal will work good.

IF you are looking economical coatings for general engineering applications with acceptable coating quality, then lower surface speeds than optimal will leads to good deposition efficiency and rate.

Thanking you


Regards,

SREENIVAS
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