mecheng55
Mechanical
- Sep 30, 2009
- 1
We just completed some injection mould tools that have an EDM surface finish of Ra(µm) 1.5-1.7.
The parts are then painted for final finish but we have just been requested to go with a higher gloss "piano black" finish.
Our supplier has said to achieve this without visible defects they need to have a SPI A1 polished mould surface but can only achieve B1 with the current tool steel.
I found on the internet that A1 is Ra(µm)~0.01-0.02 and B1 is Ra(µm) ~0.05-0.1.
Since I am not familiar with painting plastic I have some questions that hopefully someone here can answer:
1. Isn't the point of painting at 50(µm) to cover any defects in the surface where the paint is ~30x the EDM surface finish? (and help cover moulding defect as well)
2. If answer to (1.) is true why would the difference between A1 and B1 matter?
3. Why would we need a smoother mould surface to achieve a higher gloss paint surface? My only paint knowledge is that you need a "rough" surface for the paint to adhere. Of course I'm not sure if that also applies to plastics.
4. Could polishing the existing mould be enough of a dimensional change that the current tools may need to be scrapped? Does anyone have experiacne with how much they need to take off the mould surface? (guessing 0.01 -0.05???)
Thanks
The parts are then painted for final finish but we have just been requested to go with a higher gloss "piano black" finish.
Our supplier has said to achieve this without visible defects they need to have a SPI A1 polished mould surface but can only achieve B1 with the current tool steel.
I found on the internet that A1 is Ra(µm)~0.01-0.02 and B1 is Ra(µm) ~0.05-0.1.
Since I am not familiar with painting plastic I have some questions that hopefully someone here can answer:
1. Isn't the point of painting at 50(µm) to cover any defects in the surface where the paint is ~30x the EDM surface finish? (and help cover moulding defect as well)
2. If answer to (1.) is true why would the difference between A1 and B1 matter?
3. Why would we need a smoother mould surface to achieve a higher gloss paint surface? My only paint knowledge is that you need a "rough" surface for the paint to adhere. Of course I'm not sure if that also applies to plastics.
4. Could polishing the existing mould be enough of a dimensional change that the current tools may need to be scrapped? Does anyone have experiacne with how much they need to take off the mould surface? (guessing 0.01 -0.05???)
Thanks
