DIY Sandblasting: Blasting Plastics

[kat.rawlings]

Kat, if you are new to sand blasting please read up on the health implications of kiln dried sand and free silica.

What surface do you wish to achieve? Surely there's a chemical treatment appropriate to your objective, acid for glass etching or similar. The benefit of a chemical is that there is always (almost) another known chemical to remove unwanted residues.

I'll also add that I'm fairly new to this too and many of the other respondents have years of experience. It's all a learning curve.

Thank you for the safety warning, giving up on the kiln dried sand anyway because it didn't work very well.

We are trying to improve the surface of different materials to improve aesthetics. Basically for some materials it's just a case of we want to remove machine marks and have a smooth, even finish across the entire surface. Also, we have customers who would prefer frosted acrylic to clear acrylic. Blasting the clear acrylic with aluminium oxide seems to be giving quite a nice frosted finish. The part we are looking to do this on is 2x2x1m so I'm guessing blasting would be much quicker and easier than treating with chemicals.

We seem to have learnt a lot since we started last week anyway and we are definately making progress. I went for a demo with Hodge Clemco in Sheffield yesterday who were very helpful. We tried garnet (too course), brown aluminium oxide of various grades (brilliant on acrylic but discolours polypropylene so we have ordered some white aluminium oxide), glass bead (didn't do much) and also an unknown plastic media (worked very well on polypropylene and Hodge Clemco are going to find out what this media is and contact me).

 

[kat.rawlings]

try using baking soda. its very gentle and does not create as much heat. look for baking soda madia on ebay.

So I should try baking soda as an abrasive with the equipment I have got, so all I need to buy is baking soda? Because the website Ratty mentioned (post no. 17) makes it look as though I need to buy equipment…

 

[kat.rawlings]

Pay close attention to what shed or dead said, you don't want silicosis!

The saftigrit should be white, if it's not it's just standard aluminium oxide & will defo discolour your workpiece. Can't remember if they do a coarser version of it. I'd talk to Guyson & tell them what you're trying to achieve & any special requirements like your medical application, they're pretty knowledgeable & will normally have covered something similar in the past.

Guyson gave us brown saftigrit initially but they have now sent some white saftigrit to us to carry on our testing. Hopefully this will work better, fingers crossed!

 

[Ratty]

If you google Dry Ice blasting you get lots of hits, here's one near you that hire equipment http://www.mico-services.co.uk/
I'd never heard of dry ice blasting either, I do love this forum
Looking forward to hearing your progress Kat.

 

[brightspark]

So I should try baking soda as an abrasive with the equipment I have got, so all I need to buy is baking soda? Because the website Ratty mentioned (post no. 17) makes it look as though I need to buy equipment…

use the soda through gun and gear u allready have

 

[kat.rawlings]

use the soda through gun and gear u allready have

Thank you, definately worth a try then coz easy to get hold of and cheap! I'll let you know the results.

 

[Robotstar5]

Thanks I will have a look into dry ice blasting, I don't know anything about it. Is is expensive? Do you know who I could arrange a demo from?

We use a company called Cryogenesis at work, you do need a serious compressor for the air supply though!

 

[kat.rawlings]

We use a company called Cryogenesis at work, you do need a serious compressor for the air supply though!

Thanks, I'll check it out. I doubt dry ice blasting will be the route we take though because it looks expensive!

 

[kat.rawlings]

It doesn’t look like it is going to be possible to use dry ice blasting as the set-up costs and running costs are far too high. Also, when I contacted one ice blasting company I was told that ice blasting might not affect the surface of plastic if it is good quality and that it could even damage the surface of the plastic. We are getting some good results with shot blasting now anyway. I will now provide results for all the media we have tested:

Saftigrit (Aluminium Oxide) 180/220. Good results but discoloured the plastic so tested this in white and also in courser grades.
Honite 13 Glass Bead. Not hard enough to significantly modify the surface.
Blasting Grit. Good results and machine marks etc removed. The surfaces of the samples don’t feel as smooth and soft as when the aluminium oxide 180/220 was used. Again, the samples were discoloured.
Kiln Dried Sand. Results not very good with a rough surface finish and there are also safety issues concerning kiln dried sand and free silica so it is probably best to avoid this abrasive.
White Aluminium Oxide 180/220. Good results with a smooth, even finish, less discolouration than with the brown aluminium oxide but the surfaces of the samples appear glittery. This was the best abrasive for Nylon 66, polycarbonate, cast acrylic, clear PVC and white PVC.
Plastic Media (plastic and grade unknown, waiting for an email). Good result on polypropylene but the other materials feel rough to touch. This was the best abrasive for polypropylene.
Garnet. This abrasive is far too coarse, leaving a deep profile in acrylic. It also discoloured acrylic.
Glass Bead 801 AC. Didn’t have much effect on acrylic even when the psi was increased.
Glass Bead AB 177-297 (courser grade than the one above). Still not hard enough to achieve the desired surface finish of acrylic.
Brown Aluminium Oxide 80/100 (2 grades courser than the Saftigrit 180/220). Results were good but other abrasives were better on all plastics.
White Aluminium Oxide 70. Too course- surface feels rough so the finer grade is better (180/220).
White Aluminium Oxide 120. Again, the surface feels rough so the finer grade is better (180/220). However, this abrasive gave the best surface finish on polyethylene.

We have therefore achieved the desired surface finish on all plastics that we have tested. However, surface contamination will still be an issue for certain applications, particularly when aluminium oxide is used. Can anybody offer any advice on removing this aluminium oxide or on testing to see if aluminium oxide is present on the surface of the sample?

Thanks for your help.

Kat

 

[kat.rawlings]

Also, does anybody actually have an experience of using dry ice blasting on plastics?

 

[pidgeon chit welder]

Stupid as it sounds have you tried to use very small degreased steel ball bearings and sort of shot blast it at a low pressure whilst wearing your normal HASW stuff /breathing gear ?
You should not get any residue other than what you knockoff and that may well be vacuumed off or even ultra sound bath washed in demineralized water perhaps.
Obviously you'll need to also clean and dry the shot as well to keep things super clean.

 

[kat.rawlings]

Stupid as it sounds have you tried to use very small degreased steel ball bearings and sort of shot blast it at a low pressure whilst wearing your normal HASW stuff /breathing gear ?
You should not get any residue other than what you knockoff and that may well be vacuumed off or even ultra sound bath washed in demineralized water perhaps.
Obviously you'll need to also clean and dry the shot as well to keep things super clean.

Thanks I'll look into it.

 

[Balders]

Acetic acid is great for ally oxide removal. Worth a try. Toxicity's very low.
Alot of liquid kettle de-scalers are acetic acid based. So's White Vinegar and it's cheaper

Hope that may help.

 

[kat.rawlings]

Acetic acid is great for ally oxide removal. Worth a try. Toxicity's very low.
Alot of liquid kettle de-scalers are acetic acid based. So's White Vinegar and it's cheaper

Hope that may help.

Thanks, very helpful, I'll be buying some white vinegar!
Does anybody know how I can test to see if there is still aluminium oxide left on the surface of the sample?

 

[Ratty]

We are getting some good results with shot blasting now anyway. I will now provide results for all the media we have tested:
Kat

Thanks for that list Kat, it's great to have test results like that. Good of you to take the time, I've kept a copy for future reference as I occasionally use platics in my work so it could be very useful

 

[kat.rawlings]

So I can probably use white vinegar to remove the aluminium oxide. However, it's important that there is no aluminium oxide left on the surface of the samples, so does anyone know how we can test for this?

 

[Cris B]

How thermally sensitive is your plastic product? If it's robust enough to withstand 100degC without deformation then put the plastic in a non reactive container and add equal parts of white vinegar and boiling water. Let it sit for one hour and rinse it with water. Repeat the process if necessary.

The bigger question here is why having the aluminium oxide particles removed is necessary. If it is cosmetic that's one thing, but if it may then interfere with a possible further process such as chemical bonding, then you are probably best to avoid using it all together as tiny particles invisible to the naked eye may remain in the plastic surface.

 

[Shox Dr]

They are laser welding the items together

 

[kat.rawlings]

They are laser welding the items together

Thanks for that, I had actually forgotten that I had written that in the original post and that is not the case anymore. We are still using blasting in some cases after laser welding so that the joint line is not as visible. Our main aim is currently to remove machine marks and deburr to improve aesthetics.

 

[kat.rawlings]

How thermally sensitive is your plastic product? If it's robust enough to withstand 100degC without deformation then put the plastic in a non reactive container and add equal parts of white vinegar and boiling water. Let it sit for one hour and rinse it with water. Repeat the process if necessary.

The bigger question here is why having the aluminium oxide particles removed is necessary. If it is cosmetic that's one thing, but if it may then interfere with a possible further process such as chemical bonding, then you are probably best to avoid using it all together as tiny particles invisible to the naked eye may remain in the plastic surface.

Thank you for your reply. When I posted originally I was thinking there might be an easy, non-destructive method for detecting aluminium oxide. Our main focus was for a particular medical application where it is essential that there is no aluminium oxide contaminating the products. I was therefore thinking we could remove the aluminium oxide chemically and then test each product to check that all aluminium oxide had actually been removed. From the responses I have had on this forum and elsewhere, it appears as though this will be far more difficult and expensive for us to do this than we originally anticipated, and it doesn’t appear as though this would be feasible. If we shot blast these products with aluminium oxide it is highly likely that there will still be some aluminium oxide embedded in the surface of the plastic, which will not be acceptable. Also, some of the parts have a 1m diameter so it will not be easy to check the entire surface for contamination. For this particular application I am therefore thinking it would be better to use an alternative method to shot blasting with aluminium, so that there is no risk of contamination.

It is possible that there could be a non-medical application where surface contamination wouldn’t be as serious and the removal of aluminium oxide would be mainly for aesthetic purposes. In this case we would be able to try a few different chemicals (and different lengths of exposure etc) to remove the aluminium oxide. I can therefore try the white vinegar and boiling water technique that you suggested. Thank you.