Improving Surface Roughness of Polypropylene and Measuring Surface Rou 3

[KatRawlings]

Hi everyone,

I was just wondering if anybody can offer me any tips or advice for a project I am working on at the moment. We have been carrying out shot blasting using various abrasives to improve the surface roughness of some polypropylene parts that we are making for the medical industry (1m to 2.5m diameters). Various abrasives have been tested such as garnet, glass bead AB 177-297 and 801 AC, brown aluminium oxide 80/100 and 180/220, white aluminium oxide 70, 120 and 180/220, kiln dried sand, blasting grit (came free with the Sealey shot blasting gun), Honite 13 glass bead, Type 2 plastic media (Urea Formaldehyde) and Type 5 plastic media (20/30 and 30/40 acrylic).

White aluminium oxide 180/220 and acrylic blast media gave us the best results. However, when an electron microscope was used to find the surface roughness of some polypropylene samples that had been blasted with aluminium oxide 180/220, we found that the surface roughness was around 2.5 microns Ra, when it needs to be 0.8 microns Ra.

We therefore still need to improve the surface finish considerably. Does anybody have any suggestions of how we can do this? We are currently carrying out more shot blasting testing with aluminium oxide and plastic media. We are also looking into dry ice blasting.

Also, we would like to be able to measure the surface roughness of our samples on-site while we are carrying out trials. I am therefore looking into hiring/buying a surface roughness testing machine. Can anyone recommend UK companies who might be able to help with this?

Thanks

Kat

 

[HDS]

For those volumes you may have to polish by hand but it will be hard to prevent contamination.

 

[MikeHalloran]

It goes without saying, ... so I'll say it, that the cutters/ bits/ tools used on plastic:
- should be sharp enough to draw blood at the slightest touch.
- should NEVER be used to cut any other material.


A corollary of the first statement above is that if you are using carbide tools, you might get better results with 'microfine' carbide, and still better results with high speed steel, because of the edge radius attainable.

A corollary of the second statement above is that the tools used for plastic should be segregated, marked, and locked away when not in use so they don't get accidentally used on somebody's home project.



Mike Halloran
Pembroke Pines, FL, USA

 

[KatRawlings]

HDS, we may well end up polishing by hand. This was done last week and it took about 2 days for somebody to do. We have not carried out any roughness testing yet on this part but it looks like it might be ok. This may be the route we take.

Mike Halloran, we are a plastics company who specialise in fabricating plastics so we are currently getting the best finish we can with the tooling and our tools are only used for plastics. Thanks for your advice though, all comments are appreciated.

 

[HDS]

Katrawlings

You probably already know of Onsrud but if you don't they would be a big help with this project. They specialize in bits for cutting plastic some of which are very unique.

It is not normally done because it takes lots of machine time but you can put polishing bits in a CNC. They do not have the visual feed back of hand polishing so the program will need refinement and there will be spots that need touch up by hand. However,you requirements are high enough to justify the effort.

 

[sreid]

Possibly, Plasma Etching.

http://www.plasmatechnology.com/

 

[KatRawlings]

Thanks, I’ll look into it.

 

[sreid]

You might find this link useful; Medical Design News.

http://medicaldesign.com/

 

[unclesyd]

Here is another process (SpongJet) you may want to look out or file in file thirteen. I haven't used it but have seen the results achieved by the process.

Here is another possible process using a Bias Style Airway Brush
from Reliable Buff.

http://www.spongejet.com/index.php

http://www.reliablebuff.com/products.htm

 

[KatRawlings]

Thanks Unclesyd, I’ll look into these.