DIY Sandblasting: Blasting Plastics

[mill]

Just do not hold or have the shot blast gun to near, to plastice, can blow holl very fast, pont to lower air presher needed, if not you see less of it,

 

[Shox Dr]

Have you looked at using a needle scabling gun on the surface, this would give a preened finish, not unlike blasting, but without the inclusion

 

[berni29]

Hi There

A very interesting thread. Thank you for sharing your results.

If blasting plastic with aluminium oxide, will it need cleaning with the vinegar before painting? I am guessing yes!

Many tks... Berni

 

[atconut]

have you tried baking soda yet ? it just washes off with water

 

[kat.rawlings]

Have you looked at using a needle scabling gun on the surface, this would give a preened finish, not unlike blasting, but without the inclusion

Thanks, I will have a look into needle scaling.
Kat

 

[kat.rawlings]

Hi There

A very interesting thread. Thank you for sharing your results.

If blasting plastic with aluminium oxide, will it need cleaning with the vinegar before painting? I am guessing yes!

Many tks... Berni

Thanks.

It will need cleaning before painting but vinegar would not necessarily be needed. After blasting with aluminium oxide the surface appears glittery. Washing with washing up liquid and hot water removes this glittery appearance and excess material, leaving a smooth finish that I guess would be adequate for painting.

Kat

 

[kat.rawlings]

have you tried baking soda yet ? it just washes off with water

I will buy some baking soda at the weekend and once we have carried out testing I will post the results.

Kat

 

[gavuk]

Hi Kat ,sorry i've missed this thread ...we used to use a company called vixen,for blasting supplies and equipment....VIXEN ....we used to blast alluminium and changed to their aqua blast system,they had a trailor set up for demonstrations maybe they could suggest a different approach .....good luck

 

[kat.rawlings]

Hi Kat ,sorry i've missed this thread ...we used to use a company called vixen,for blasting supplies and equipment....VIXEN ....we used to blast alluminium and changed to their aqua blast system,they had a trailor set up for demonstrations maybe they could suggest a different approach .....good luck

Thanks Gav, I'll have to have a chat to Vixen when I get chance. Feels like I have a million jobs on at the moment!

 

[kat.rawlings]

I still need to carry out some on-site soda blasting and speak to Vixen about their aqua blast system so these are both on my list of things to do. I just think I should post an update at this point explaining what my current position is regarding this testing.

When I started this thread originally I didn’t have any experience with shot blasting and didn’t really know where to start with it all. I have carried out lots of testing and posted the results (mainly in post #29).

We are now looking at using shot blasting to improve the surface finish of polypropylene for a specific product for use in the medical industry. This means that surface contamination is an issue so we can only use abrasives that will be suitable for use within the medical industry. We are therefore carrying out testing with plastic abrasives.

However, although we thought we were achieving a good surface finish using white aluminium oxide 180/220, when samples were tested using an electron microscope it was discovered that the surface roughness of these samples was still far too high, as they had a Ra of 2.5 microns when it needs to be 0.8 microns or less. To help improve surface finish we are trying a finer plastic media and we have added an attachment to our shot blasting gun to alter psi (I am thinking lowering the psi could give a smoother surface).

I am therefore currently looking for tips on improving the surface finish using shot blasting and also on testing the surface roughness after blasting. I am thinking we will need to hire/buy a surface roughness testing machine of some sort. Any ideas where I can do this?

Thanks for all your help so far everyone.

 

[pidgeon chit welder]

Would making a simple pulley and weights device with high quality abtec bearings ( or even air bearings allow you to carry out coefficient of friction tests ie a known weight dragged over a surface from first movement to stopping using a standard set pulling force /weight ?

Could you use a microscope to measure the peaks and roots of the abraided cross sections in microns of the various materials and then make up your data charts from both readings ?

If it were a set magnification and presented on a Monitor screen via a camera set up you should be able to work out the measurements especially if you graduate the screen view with a know scale derived from using a known test piece thickness

 

[Wedg1e]

I am therefore currently looking for tips on improving the surface finish using shot blasting and also on testing the surface roughness after blasting. I am thinking we will need to hire/buy a surface roughness testing machine of some sort. Any ideas where I can do this?

Thanks for all your help so far everyone.

I work for an NDT supply and service company and we occasionally get asked for surface roughness standards - but they're usually for checking machined finishes, nothing as fine as you're asking. However, I can do some digging tomorrow and see what I can find. I'm guessing there'll be some optical magnification involved but it may still be an operator's personal judgement, rather than an absolute measurement, kind of technique.

Vixen at Thornaby is only a couple of miles from me; they've always been extremely helpful when I've needed abrasives, or parts etc..

 

[kat.rawlings]

Would making a simple pulley and weights device with high quality abtec bearings ( or even air bearings allow you to carry out coefficient of friction tests ie a known weight dragged over a surface from first movement to stopping using a standard set pulling force /weight ?

Could you use a microscope to measure the peaks and roots of the abraided cross sections in microns of the various materials and then make up your data charts from both readings ?

If it were a set magnification and presented on a Monitor screen via a camera set up you should be able to work out the measurements especially if you graduate the screen view with a know scale derived from using a known test piece thickness

Thanks for your suggestions.

The pulley and weights device wouldn’t work because there are ribs and grooves on the part and I will need to measure the surface roughness on these ribs and in the grooves (as small as 5mm). Maybe I should have mentioned this, sorry :s

Our customer used an electron microscope to measure the Ra but it will be expensive for us to buy a microscope or even to send our samples off for someone else to do every time. I am currently in contact with some companies who sell surface roughness testing equipment about purchasing or hiring something. It looks as though the Surtronic 25 (http://www.spectrum-metrology.co.uk/surf25.htm) might be suitable for our needs so I am currently speaking to Spectrum Metrology about this. I will post with progress we make on buying/hiring equipment to test surface roughness.

 

[kat.rawlings]

I work for an NDT supply and service company and we occasionally get asked for surface roughness standards - but they're usually for checking machined finishes, nothing as fine as you're asking. However, I can do some digging tomorrow and see what I can find. I'm guessing there'll be some optical magnification involved but it may still be an operator's personal judgement, rather than an absolute measurement, kind of technique.

Vixen at Thornaby is only a couple of miles from me; they've always been extremely helpful when I've needed abrasives, or parts etc..

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

Vixen has been mentioned a few times, I definitely need to contact them to ask for some advice.

 

[rtbcomp]

As well as advice on roughness testing these firms may be able to give advice on treatment, or at least point you in the right direction, worth asking them.

 

[kat.rawlings]

As well as advice on roughness testing these firms may be able to give advice on treatment, or at least point you in the right direction, worth asking them.

Thanks, it will be worth asking.

 

[kat.rawlings]

Just to update everyone on where I am up to at the moment:

As I have mentioned previous aluminium oxide 180/220 gave the best results but the surface roughness is still not good enough. We have therefore tested the following 3 plastic abrasives:

Type 2 Urea Formaldehyde (Guyblast) Size 20/30. This blast media didn’t really affect the surface of the acrylic or polypropylene samples so it appears as though something coarser is needed.
Type 5 Acrylic (Avialite) 30/40. This abrasive barely affected acrylic. The surface of the polypropylene sample was improved but machine marks were still visible and the samples don’t feel very smooth.
Type 5 Acrylic (Avialite) 20/30. The 20/30 acrylic gave very similar results to the 30/40 acrylic media on polypropylene samples. It therefore appears as though plastic media will not give good enough results on polypropylene.

This means we still need to improve the surface finish. I’m currently thinking we could try a finer grade of aluminium oxide to achieve a smoother surface finish but then I will still have the problem of contamination. So maybe we could try a courser grade of acrylic. Or does anyone have any suggestions for a different media?

We are also altering the pressure on the blasting gun to see how this affects things. Can anyone think of any other parameters that would be easy to modify?

 

[Shox Dr]

Have you looked at using steel shot,*



*without going back over to see if I have already suggested it,

 

[pidgeon chit welder]

I mentioned the steel shot earlier , plus cleaning and drying it before each recycle event .

One last thing that comes to my mind is very high pressure water through a masking slot perhaps & rinse off with de mineralized water in a ultrasound bath if small enough or an attached ultra sound device and light pressure spray across the part affected . At least it should solve the contamination probs and leave a rough surface

Ultra sound is often used in small parts cleaners to help the muck lift and slide off using nothing but soap and water or de mineralized water.


Can I ask a question?

Is the idea to almost polish a cut edge or to roughen an area ?
Several things come to mind for the former and one or two common products for the later.
How big is the area involved and what shape is it? Will there be repetitions ie a production run or just a one off ?

 

[kat.rawlings]

The idea is to polish a cut surface.

The part is a 1m diameter disc that has ribs and grooves leading into the centre. There will be repetitions but we would maybe be making around 20 a year so there will not be large volumes. The discs will be made in different sizes and could be as large as 2.5m.

We are trying to make the surface smoother as our customer requires the part to have a Ra of 0.8 microns (even in between the ribs, which is around 5mm thickness). Aluminium oxide 180/220 gave the best results but when the samples were tested under an electron microscope the Ra was 2.5 microns. We therefore need to make the surface even smoother than this.

Would steel shot not make the surface rougher than al oxide did? I’m thinking a finer grade al oxide could work? Or we could try a different media that might give a finer finish?

Thanks for your help. Let me know if there are any more questions.