Question on clarity / surface finish specifications 4

[bnmorgan]

This is related to thread712-847.

We're designing a part where appearance is of high priority. Being run from acrylic. It's partially 'frosted' and the other part needs to be 'high polish' clarity. Could someone tell me where I might find reasonable information on how to fully specify a section that is "frosted" and similar information on "high polish" SPE-SPI's don't help a lot, as the plates we have are black ABS, I need the same information for transparent material.

Thank you much,
Byron Morgan
Tupelo, MS

 

[dwightdixon]

The clarity of the material itself has a great effect. Therefore, I do not think you will get quite the same result. The reflected light scattering that give the dull apprearance to solid material is a bit different than the transmitted light scattering which clear materials will give. The light scattering of a high polished surface is usually measured by a Haze meter, which measures the light scattering of a single beam of light. I would think you could use the same meter to measure the effects of the frosted surface. Depending on the effect you hope to achieve I have seen vapor honed surfaces work as well as sandblasted surfaces or even some form of etching with a specific pattern to give the "right" appearance.

 

[Pressed]

You have asked a sparingly published topic. A large acrylic manufacture might be your best source of info. A plastics trade/eng journal might be another good source for info.

http://www.connecticutplastics.com/understanding.pdf

http://www.connecticutplastics.com/faq/cat1078172496

http://www.predev.com/smg/specification.htm

http://www.devicelink.com/mddi/archive/02/04/001.html

http://www.mmsonline.com/articles/039903.html

http://www.predev.com/smg/intro.htm

http://www.garelectroforming.com/g-4_microfinish_comparator_set.htm

http://www.jitsupplygroup.com/measuring/roughness.pdf

_______________________________________
Feeling frisky.........

http://www.tailofthedragon.com

 

[bnmorgan]

Thank you much,
I think 'polish' may be the wrong term, as these are high rate of production parts, so individual polishing would be rather laborious. We need a way to specify a certain surface finish to be maintained for clarity and also the finish for the frosting area. Direct communication with the molder won’t be a problem, but if the tools get moved to a different vendor then we may run into trouble in the lack of specifications.

 

[opticker]

Your need for a "polished" surface depends greatly on the application of the part - whether imaging or illumination. If yor application involves imaging through the "polished" region, you will neeed to employ optical specification that quantify scratch & dig, power and irregularity, and perhaps haze, coatings and spectral transmission. If it's illumination, we often use the same specifications, but they become much looser to the point that some specification of a "shiny" surface will suffice.

Characteristically, no post molding operation is necessary other than an optical coating process.

 

[bnmorgan]

It's not optical or specificly illuminating, but it's an appearance part of a window blind, where it needs to be smooth and clear, without blush or anything of the like, and then a section of it is 'frosted'.....and we need to know exactly how to specify the 2 surface finishes properly.

 

[Pud]

Try getting one of these EDM reference pieces to decide on frosted portion:

http://www.rubert.co.uk/Comparison.htm

Polish finish is usually specified as "mirror" finish.

Rgds

Harry