Improving surface finish of polypropylene 1

[KatRawlings]

Hi everyone, I am trying to improve surface finish on polyproylene. We need a surface roughness of 0.8 microns (Ra) or better. The part is going to fully machined on a CNC router and there are lots of veins and gulleys. It has a 2.5m diameter. Any suggestions for improving surface finish of plastic? Are there any chemicals that might work on PP?

Thanks

Kat

 

[MikeHalloran]

I know a guy whose only job is to bring stainless steel pipework from a mill finish to a mirror finish. He averages about an hour per square foot of developed surface. So your reported two days per piece in another discussion is credible.

... and not likely to be reduced much, except by leaving the workpiece in the CNC router, putting polishing tools in the router head, and letting the machine do the work.





Mike Halloran
Pembroke Pines, FL, USA

 

[Demon3]

Can you treat it with a heat gun? I know some plastics like cellulosics are self polishing in that you can bring a shine back with a blast of a heat gun to soften the surface. Or can you spray on a lacquer to give the gloss?

Chris DeArmitt PhD FRSC CChem

 

[ornerynorsk]

What Demon3 said. We flame "polish" olefins quite frequently.

 

[KatRawlings]

Mike Halloran, polishing by hand is possibly the route we will take. However, I have still been told that I need to look into alternatives.

Does anybody know of a chemical that I could use on polypropylene?

Demon3 and ornrynorsk, we carry out flame polishing already on other jobs so there are people with experience here and it will not work on this particular part because of all the intricate parts that must be kept within tolerance. Thanks for the suggestion though.

Kat

 

[HDS]

That is a question best answered by your PP supplier.

 

[btrueblood]

It's unlikely you will get a chemical to improve the surface finish, a.) polypropylene is insoluble to most everything, b.) the things that do "dissolve" PP also tend to destroy it.

 

[cowski]

Any possibility of changing to a molding operation instead of machining?

 

[Demon3]

Try polishing it with a chemical that's similar to PP in polarity so it may soften the surface a little. Suggestions would include squalane and isododecane. No promises but could be worth a try.


You could use atmospheric plasma to deposit an extremely thin, well-adhering topcoat to give shine.

Chris DeArmitt PhD FRSC CChem

 

[KatRawlings]

I’ll get in touch with our supplier to ask for advice.

Thanks btrueblood, I’m guessing you’re right.

No we can’t mold for many reasons, mainly because we will only be making small amounts and the parts will vary in sizes.

 

[KatRawlings]

Thanks Demon3, I'll have a look into what you have said.

 

[ornerynorsk]

A process that I have recently seen involves cryogenically freezing plastic parts so that machining/polishing operations that would not otherwise be possible can be performed effectively.

The rubber molding industry has also been doing this for years to make tumble flash removal a viable process.

I have my skepticism that it would work well on PP, the distortion from the thermal changes might be too much for your tolerance.

Just a notion, thought I'd throw it out there.