Powder coating quality control

[caddone]

Guys,
Is there a way to keep the consistency between 2 different powder coating vendors in terms of color and texture?

What are the methods to control the quality during production?

Thanks
C1

 

[caddone]

May be this isn't enough information. Here is what I am upto. I have an assembly of several parts that are supplied by couple of different vendors. They are externally visible and it's important to appear same color and texture. Say for instance I ask for RAL 9007 (grey aluminum). Can it appear different from different vendors?
Also, How the texture finish be specified and measured?

Please help.
Thanks
C1

 

[mcgyvr]

I find the best way is to specify an exact powdercoat spec from a specific paint vendor..
Like "Finish with Sherwin Williams PES8-C6148 Safety Orange"

Then providing a paint chip or sample and simply talking to both vendors and explaining the situation is the best method.

A color is just a color. Textures/Gloss,etc.. will all cause it to look different from another part of the same color.

 

[IRstuff]

I think there is still not sufficient information regarding how "different" can the coatings be? Is it simply an esthetic thing, or is there an objective specification on how closely matched the colors have to be? Are these parts replaceable? Would the replacement part have to match the original parts?

There is no question that any approach that you use, short of painting everything yourself with a single batch of paint, can result in both colorimetric and textural differences. No matter what you specify, say, even Federal Standard 595B, color 36320, which is one type of battleship gray, there can rarely be perfect matching, even with the same manufacturer's paint. One possible option is to have the disparate vendors stop prior to powder coat, and send everything to a single vendor for the final finish. Note that a single manufacturer's paint can change over time, when their own internal processing may dictate using different materials or different pigments. Note also, even if colors are matched by colorimeters, that only ensures that the colors match for the conditions imposed during the colorimeter measurement.


TTFN
faq731-376

 

[mcgyvr]

interesting...
I have NEVER had a problem with visual differences between vendors when they use the exact same powder from the same manufacturer.

 

[IRstuff]

Obviously, manufacturers desire and intend to keep consistency, but there's no guarantee of that.
Here's an article talking about how color variations arose from using different types of curing ovens on the same powder:

http://www.precisionquincy.com/articles/PrecisionQuincyinPowderCoatingmagazine.asp

this one has a paragraph on how they control their color:

http://www.btdwoodpowdercoating.com/design-options/coating-colors/

and this one talks about how the color difference is measured and specified:

http://www.colorwiki.com/wiki/Delta_E:_The_Color_Difference

TTFN
faq731-376

 

[TomDOT]

Delta E is an excellent way to define how much variance you will allow in color. Handheld instrument. You will need to specify illuminant. I can generally see a Delta E of 1 or more pretty easily. Others don't consider it a big difference. Gloss is also easily measureable - you just need to get the right (handheld) instrument.

In the world of color and texture, how much of a difference is acceptable varies HUGELY between different applications or inspectors. That's why an actual numerical value is important.

 

[caddone]

Guys,

Thank you for sharing these information. Here is what I came across. I saw a product from X-Rite

Link :

http://www.colorhq.com/x-rite-SP62-Portable-Spectrophotometer-p/sp62.htm

This is a equipment that can be used to read a color and store all the information about it. It can later compare this to another color and tell how close it its to the original specimen. This is an expensive equipment (~$8000).

Any of you guys know of any other way to compare? or any other equipment that's less expensive.

Thanks
C1

 

[TomDOT]

Caddone,

There are cheaper colorimeters out there, in the "few hundred dollars" range. Adequate for some applications. The real professional ones do tend to be around $7000-$8000.

You can also compare color by eye - but it takes a good eye

 

[caddone]

I think a measuring gadget is very much necessary to tell by how much its off.

Say for example RAL 8007 & RAL 8011 appear to be same. But in reality they are different.

 

[TomDOT]

That's where we differ - I looked up those two RAL colors online*, and they are quite readily discernable to me. 8011 is darker and less yellow, more of a "true" brown than 8007. Based on what my (uncalibrated) monitor is showing me, I'm eyeball estimating a delta E in the 2-3 range.

*I don't use RAL much. I have the US Fed Std 595C color deck on my desk. Yes, I've been looking at and comparing paint colors for a long time. I think my wife is pickier more discerning than I am. Painting a wall in my house is an adventure

 

[mcgyvr]

I looked up those two RAL colors online*

Viewing a color "online" is totally different from looking at 2 color chips in front of you.. There are many colors that monitors/browsers just don't produce properly and it can be totally different from one screen to the other.

 

[IRstuff]

Not to mention that color, in isolation is also a function of the illuminant. So even though the colors look different on a monitor, that doesn't mean they'll necessarily look as different under particular lighting conditions. In fact, that something else that would need to be properly specified, i.e., under what lighting conditions are the different colorants supposed to look "identical?"

TTFN
faq731-376

 

[TomDOT]

mcgyver - I thought I was being pretty plain with "Based on what my (uncalibrated) monitor is showing me..."

I'm well aware of the issues with displaying colors on any monitor (heck, RGB monitors can't even show the whole color space the human eye sees) - but for this rough purpose "I can see the difference" a decent LCD monitor is more than adequate.

If you would like to supply the two RAL color cards under discussion, I'd be happy to look at them directly, either under a darn good D65 bulb, an F11 bulb, or using actual indirect natural light through a north window. I'll then use one of those $8,000 colorimeters to give a numerical delta E and will report it.