DIY Sandblasting: Blasting Plastics

[Shox Dr]

Have you thought of heat, to blend or smooth out the surface

 

[kat.rawlings]

Shox Dr, I was just wondering if you think I should still try steel shot after I have made my requirements more clear? Because I could probably give that a go quite easily if you think it will work? I just thought it would give a rougher surface finish than the al oxide.

I’m not sure heat would work. The tolerances are really small so I would worry about deformation of the 3mm ribs. What do you think?

 

[Shox Dr]

You have nothing to lose, have you. I don't think it will give a rougher surface, more of a preened finish, with the added benefit of no inclusion, but then I could be totally wrong.

Give it a go.

 

[kat.rawlings]

You have nothing to lose, have you. I don't think it will give a rougher surface, more of a preened finish, with the added benefit of no inclusion, but then I could be totally wrong.

Give it a go.

Thanks I'll order some

 

[Shox Dr]

Kat when I say steel shot I don't mean shot blasting shot, I'm talking about round steel balls like very small ball bearings.

 

[kat.rawlings]

I thought you meant steel shot like "Turbobead carbon steel shot blast media":
http://www.guyson.co.uk/consumables/media.html
They are spherical.
Do you mean something different? And if so then what sort of place would I buy some?

Thanks

 

[Shox Dr]

Looking at Guysons site I would call them and ask about the Metalic range, Flexgrain or better still Turbonox looks like a good media to try.

Have you spoken to them at all?

 

[kat.rawlings]

Looking at Guysons site I would call them and ask about the Metalic range, Flexgrain or better still Turbonox looks like a good media to try.

Have you spoken to them at all?

Yes I have spoken to Guyson many times about our requirements, and some of the abrasives that I have tested (aluminium oxide brown and white, honite, type 2 plastic media) are samples that we recieved from Guyson. In return I sent them a review of our results. I will contact them again about steel. The minimum purchase is 25kg so if I'm lucky I might get another sample and then we can purchase some if it works well.

 

[Shox Dr]

Sorry that last question, was not meant to read as it did. Clearly you have spoken to them I just surprised they haven't had similar requests in the past.

 

[kat.rawlings]

I didn’t take offense or anything, don’t worry about how the question was asked, you’ve been helpful

Guyson originally recommended Honite, which didn’t really affect the surface at all, and aluminium oxide 180/220. Since then I have asked them for different grades of aluminium oxide and the plastic media. They were also helpful near the beginning when I was buying equipment to get set-up. Steel shot has not been suggested but I’ll have a chat to them tomorrow and I’ll let you know.

 

[Wedg1e]

Thanks, it would be great if you could let me know if you found out anything from work.

PM sent

 

[pidgeon chit welder]

Ok another avenue to try.

Helicoptor cockpit bubbles & old fashioned aircraft used to be a made of a perspex material.
Air maint guys would use something akin to jewelers rouge to polish scratches out of the bubble and keep it transparent whilst still retaining the optical properties it was originall designed to have.

Another avenue to perhaps explore is Specsavers or Vision Express , where they have the lense grinding machines . Spectacles with plastic lenses are ground and polished on site or used to be when my eldest daughter worked in Vision Express 18 yrs ago .

They may or may not be bothered to help /advise youiin a shop but their HQ might .

I picture your wheels looking like a small millstone wheel though not knowing how many groves you have around it.

Could you try this rouge type polishing out /off with a dremmel type tool or even a CNC made jobby programmed to do the work to get the desired finish and then wash it with low pressure warm denatured water spray to remove anything left on the surfaces & use a cool air fan shaped jet to blow off all particles of abrasive & water .

 

[kat.rawlings]

I have now found a local company who will measure surface roughness for us, so we do not need to purchase or hire roughness testing equipment. So now I just have the problem of achieving the correct surface finish.

Pidgeon chit welder, I will look into your suggestions when I get chance. I now have a long list of things to try so I will post an update when we have done some more testing. The discs in question are 1m to 2.5m in diameter so I don’t think we would be able to use a grinding/polishing wheel. Also, we need to improve the surface finish in the grooves, as well as on the top surface, so we wouldn’t be able to get into these grooves with a polishing wheel. There are 3mm thick ribs all the way around. In between each rib there is a groove, which is 5mm wide at the centre of the disc and obviously wider around the edge of the disc. Sorry it’s hard to describe the part and I can’t provide a picture for confidentiality reasons.

A Dremmel tool might work if there is one that fits in the grooves, I’ll look in to this more at some point. Thank you for your help.

 

[Shox Dr]

To save me rereading the whole thread how are you making these

 

[kat.rawlings]

To save me rereading the whole thread how are you making these

I'm not sure what I'm actually allowed to say because of a confidentiality agreement with our customer. I will hopefully get chance to have a chat to my manager at sometime today. If not then I will reply on Monday.

 

[kat.rawlings]

They are being fully machined on a CNC router using standard slot drills.

Thanks

 

[kat.rawlings]

For those of you who are interested: I have spoken to Vixen and they think they can help and will be in touch by the end of the day I am also waiting for Guyson to get back to me so hopefully someone will be able to help.

 

[Maverick.uk]

They are being fully machined on a CNC router using standard slot drills.

Thanks

Hi Kat

I think that is part of the problem! Your specification is a grinding tolerance and the process being used to machine is milling. Depending on the speeds and feeds in use at the milling stage will depend on the results obtained. But they will be prob be going for material removal rather than surface finish.

The spec of 0.8Ra is a bearing grade finish.

Check here

http://icrank.com/cgi-bin/pageman/pageout.cgi?path=/data/surface_finish.htm&t=2

Cheers

Kevin

 

[kat.rawlings]

Hi Kat

I think that is part of the problem! Your specification is a grinding tolerance and the process being used to machine is milling. Depending on the speeds and feeds in use at the milling stage will depend on the results obtained. But they will be prob be going for material removal rather than surface finish.

The spec of 0.8Ra is a bearing grade finish.

Check here

http://icrank.com/cgi-bin/pageman/pageout.cgi?path=/data/surface_finish.htm&t=2

Cheers

Kevin

Thanks for the link Kevin, a very useful page. We are using milling to make the part because we are going for removing material at this stage in the process. We are starting off with a sheet of PP which we are then milling to make a disc with lots of intricate details on the surface. Due to this material removal (which is necessary) the surface of the polypropylene is then left with machine lines. It also needs deburring around the features. We have therefore been looking at blasting to remove the lines and deburr, and we have achieved this, and when looking at the product it appears to be smooth. However, it is not quite smooth enough when surface roughness testing has been carried out. We are therefore continuing our grit blasting trials and trying to tweak various parameters to get a finer finish.

I am also looking into alternative techniques to blasting such as using chemicals, so any suggestions would be welcome

In a worst case scenario we will be sanding the part down by hand, which will take a few days.

 

[brightspark]

Thanks for the link Kevin, a very useful page. We are using milling to make the part because we are going for removing material at this stage in the process. We are starting off with a sheet of PP which we are then milling to make a disc with lots of intricate details on the surface. Due to this material removal (which is necessary) the surface of the polypropylene is then left with machine lines. It also needs deburring around the features. We have therefore been looking at blasting to remove the lines and deburr, and we have achieved this, and when looking at the product it appears to be smooth. However, it is not quite smooth enough when surface roughness testing has been carried out. We are therefore continuing our grit blasting trials and trying to tweak various parameters to get a finer finish.

I am also looking into alternative techniques to blasting such as using chemicals, so any suggestions would be welcome

In a worst case scenario we will be sanding the part down by hand, which will take a few days.

just a thought cant the blasting be done in 2 stages with diffrent grade media . one to take the marks and rough edges off then a finer media to smooth off.