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Testing for Aluminium Oxide
4

Testing for Aluminium Oxide

Testing for Aluminium Oxide

(OP)
Hiya everyone,

I was just wondering if anybody knows how I can test for the presence of aluminium oxide? We have been shot blasting plastic with an aluminium oxide abrasive, so bits of this abrasive will be left on the surface of the plastic. We believe that we can remove this aluminium oxide using acetic acid (white vinegar). However, it is essential that there is no aluminium oxide left on the surface of the plastic. We therefore need some way to test for this.

Thanks

Kat

RE: Testing for Aluminium Oxide

I think your best bet would a microscopic examination.
You could locate some particles embedded in the plastic and have a lab verify that it is Al2O3.  

RE: Testing for Aluminium Oxide

xray diffraction technique should be able to identify. As a suggestion,why do you need to blast a soft plastic with a hard abrasive? This is bound to embed.

RE: Testing for Aluminium Oxide

(OP)
Thanks for advice, so i could try microscopic evaluation or XRD. A chemical analysis company has suggested XRF.
@arunmrao: We have tried about 15 abrasives on about 7 different plastics and aluminium oxide has been giving the best results.

RE: Testing for Aluminium Oxide

XRF can be portable (hand-held), so this may be an advantage over XRD.  Either way, a microscopic evaluation, even at 10x magnification, will probably be very helpful in understanding what the surface looks like after abrasive blasting.

RE: Testing for Aluminium Oxide

How serious and expensive are the consequences of remaining aluminum oxide?

If you can't tolerate the presence of aluminum oxide embedded in your surface then the best course of action is not to blast the surface with aluminum oxide.

You will NEVER be able to test all the aluminum oxide away.

Do you seriously think that it's realistic to test and confirm the absence of aluminum oxide on every square millimeter of every part?

You are starting down a path that will be excessively time consuming and expensive and also guaranteed to fail.  You should rethink.
 

RE: Testing for Aluminium Oxide

I agree with MintJulep.

Acetic acid will not remove aluminum oxide.  Al2O3 is inert to acetic acid, so you aren't doing any better than soap and water would do (actually, soap and water may do better).  Strong caustic (pH > 10) will dissolve Al2O3, but it may damage the palstic and will certianly damage any human tissue it comes into contact with (it is very dangerous), so a caustic wash may not be the best solution.

The best solution would be use a abrasive that is compatible with the product and processes

rp

RE: Testing for Aluminium Oxide

Perhaps you need to review what you are trying to achieve with the shot blasting.  This is seems to be a rather crude approach to achieving whatever your goal is.  I'd imagine that the part in question is not that expensive, and the cost of inspection would most likely blow the price through the roof.

TTFN

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RE: Testing for Aluminium Oxide

I've never sandblasted plastic with aluminum oxide but I do have some experience sand blasting tungsten carbide with aluminum oxide.

Aluminum oxide splits and shatters in sandblasting. It does this even when sandblasting a soft medium because the particles impact one another. One of the shapes formed with regularity could be described as 'spears'. These aluminum oxide 'spears' penetrate and become embedded in tungsten carbide.

I would suspect that the spears formed by the breakdown of aluminum oxide grit would become deeply embedded in the plastic.

You may be able to find the report on this on the Internet.  I remember seeing it because there was a lot of commotion about whether the aluminum oxide on the surface of tungsten carbide would interfere with brazing or not. Once we establish that the aluminum oxide penetrants occupied a miniscule percentage of the available bonding area I pretty well lost interest in the whole thing.
 

Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.    

RE: Testing for Aluminium Oxide

(OP)
Thank you all for your replies. 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 hydrofluoric and phosphoric acids as suggested. Thank you for your help.

RE: Testing for Aluminium Oxide

What's the intent of the shot blasting?  One who think that a plastic could be made with the desired surface qualities in the first place, avoiding any further processing such as this.  

Again, I caution you about HF, since it's extremely toxic and hazardous, and not necessarily something you want to be handled by untrained personnel.

TTFN

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RE: Testing for Aluminium Oxide

Have you considered shot blasting with dry ice?  Leaves no residue.

RE: Testing for Aluminium Oxide

I echo the warning on the use of HF acid unless you have been properly informed about its properties.
It is insidious as one drop on the skin especially the finger nails is quickly absorbed with resulting pain that feels like being pounded with a hammer.  The affected area will take long medical and healing process.
It has to use in a fume hood. The use of an acid proof fume hood is very desirable.
It can not be worked in metal tanks.


Here two suppliers of plastic bleat media.   Checkout both to see how it used, especially the Maxiblast Application

http://www.maxiblast.com/applications/

http://www.optiblast.com/products.asp


You could look at soda blasting, wet or dry.
  
 http://www.armex.com/?gclid=CNGt88jjvaYCFQrt7QodCzRbGg


You could also try corn cobs or walnut shells.

http://www.kramerindustriesonline.com/blasting-media.htm


Or water ice blasting.

http://www.iceblast.net/faq00.htm
 

RE: Testing for Aluminium Oxide

(OP)
Thanks for all the suggestions and also thanks for the HF warnings.

@ Ron: Do you have any experience with ice blasting plastics. I have already been talking to some companies about dry ice blasting. The general feel I'm getting is that it probably isn't right for achieving a good surface finish on plastics. A couple of companies have said I can send samples for testing so I am currently waiting for some samples to be prepared so I can send them off. However, even if this works it looks as though it is going to cost far too much for us to start using this process. We would have to send samples off to one of these companies to blast for us, as we do not have the capabilies on-site.

@ Unclesid: I am going to buy some bicarbonate of soda at the weekend so I can test out soda blasting. With regards to ice blasting our on site air capabilities are not adequate so it would be very expensive for us. Thanks for the plastic blast media links and also the natural abrasives link, very helpful.

Kat

RE: Testing for Aluminium Oxide

Regular baking soda will work on some projects, but I don't think it will work your project.  Here is the link to Armex Abrasives where we bought all our soda blasting media.
The second link is to grit-o-cob blasting media
 
http://www.armex.com/

http://www.gritocob.com/product-list.aspx

If you are in the US and live near a Harbor Freight Store they carry the Armex material as we a soda blasting pots.

RE: Testing for Aluminium Oxide

(OP)
Thanks, I am in the UK so I will try to find a UK company that sells soda blasting media. Will that work with my shot blasting gun that I have been using? Or will I need to purchase proper soda blasting equipment?

RE: Testing for Aluminium Oxide

It should work and if doesn't all you will have to do is change the nozzle.  Keep the air as dry as possible.

RE: Testing for Aluminium Oxide

(OP)
@unclesyd: Thanks, I'll post when I have tested with soda blasting media to let you know how it goes.

@IRStuff: The plastic cannot be made this way in the first place. It is complex engineering and must be cut and machined etc. There might be alternatives to shot blasting but the results that shot blasting has given are billiant. We therefore need some way to improve surface finish to this standard without using aluminium oxide, or alternatively we need to find a way to remove the al oxide afterwards. Maybe shot blasting with plastic blast media will work as our results for this are quite good. I'm sure we'll get there in the end.

RE: Testing for Aluminium Oxide

Well, now you've got everyone curious.
Plastics are ordinarily used where the geometry is complex enough to make machining prohibitively expensive, so you put the expense in a mold and make the plastic parts from the mold by means of a relatively primitive process...

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Testing for Aluminium Oxide

Even still, it might be easier, overall, to make the part as an assembly of several parts, and allow the individual components to be molded.

Additionally, machining can entail using other tools that may allow you to get the surface properties you desire directly on the machine.  It would seem to me to be cheaper to switch out a machine tool bit than to install the part on another machine, blast it, and then clean it, and the inspect it.

As I mentioned, if you tell everyone the entire problem, there may be another solution.  By holding back you potentially deprive yourself of all the help you could be getting.

TTFN

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RE: Testing for Aluminium Oxide

(OP)
I am not meaning to hold back, we are under confidentiality aggreements with the company we are producing the part for so I can't really go into too much detail. It is a 1m disc with lots of circles cut into it and thin ribs/veins that lead into the centre. It has really small tolerances so maybe this is why it isn't moulded, I'm not sure. It is definitely not going to be possible to make the parts separately and join them together anyway because there are over 100 of these veins/ribs.

It is not a cheap piece of equipment so we are trying to find the best way to make it, not the cheapest. We basically need some sort of way to remove machine marks and to deburr this plastic while not effecting tolerances. It also needs to not contaminate the part. For example, we could shot blast with a plastic media, but the results just aren't as good as they were with aluminium oxide.

RE: Testing for Aluminium Oxide

One of them brain things hit me, we used the SS White machines to finish some small and large parts.  If I remember correctly the process is very easy to control and can be automated.  The first link is Airabrasives (SS White) while the second is to information on the suction type blast cabinets.
There are also many things to test like liquid blast with Al2O3 or others.
Continue blasting as you are and followup with a second blast media for a 2 stage process..
Change the angle of attack of the nozzle for your existing equipment.
If you can get access to a good microscope , preferably a metallurgical, you can probably be able to see the Al2O3 by varying the light.

http://www.airbrasive.net/

http://cmvblasting.com/index_ing.html

RE: Testing for Aluminium Oxide

(OP)
Sorry for any confusion. My orignial aim of posting on this forum has now changed due to information from elsewhere and also posts on here. This is where we are currently:

We are shot blasting to remove machine marks and to deburr so that we have a smooth, even finish across the entire 1m diameter sample. We have achieved this surface finish with aluminium oxide and the customer is happy with this.

However, due to it being for a medical application we cannot use aluminium oxide. This is why I was asking about testing for aluminium oxide and removing aluminium oxide.

It appears as though there will still be traces of aluminium oxide whatever we do to the samples, so it doesn't look like we will be able to use aluminium oxide at all. The problem now is therefore different to the problem in my original post; we now need to find a different technique to give us the same surface finish. One possibility is therefore to blast with a different abrasive that wouldn't need to be removed before the part is used in the medical industry. Our main areas of focus are therefore currently dry ice blasting, soda blasting and blasting with acrylic media. If anybody has any tips for any of these 3 areas or any suggestions of alternative techniques that would be brilliant.

Has anyone used dry ice blasting or soda blasting for plastics?

RE: Testing for Aluminium Oxide

Perhaps the machine tool bits need to be changed for something different.  We diamond-turn various materials for lenses, and it used to be a requirement to hand polish to remove the machine marks.  However, improvements in the cutting technology have minimized those requirements.  

Have you consulted with others about using a different tool or cutting process that will not tool marks?

TTFN

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RE: Testing for Aluminium Oxide

Are the "veins" a hollow structure running parallel to the large dimension (diameter) of the disk?

If not, small grooves and small ribs in the surface of a part, no matter how large, are certainly moldable.  Even Teflon compression molding will give very good tolerances and surface finishes.

RE: Testing for Aluminium Oxide

Have you considered flame polishing? It will give you a glossy rather than matte finish, but it remove tool marks and leaves no residue. You can find videos of the process on You-Tube.

RE: Testing for Aluminium Oxide

(OP)
@Btrueblood: It is small grooves and ribs in the surface but we are a plastics engineering company and we are not capable of molding so we will definitely not be molding this part. I do not know the reasons that this company has chosen us to make their parts rather than a molding company but I am sure they have thought about this. Even if they haven't then it is not my place to lose business for my company by suggesting they go elsewhere for these products. I have simply been asked to investigate improving the surface finish of these parts after the current process has been carried out.

@Compositepro: Thanks, I will have a look into flame polishing.

@IRstuff: Yes I have consulted with others about using a different tool or cutting process and this is not going to happen. We have a good process in place and the customer is happy with this. We just need a way to improve the surface finish at the end of the process. We have had some good results after shot blasting with plastic media so it is possible that we will use this.

RE: Testing for Aluminium Oxide

(OP)
@Compositepro: I have had a quick look into flame polishing and it appears as though it is mainly used on acrylic. We are working with polypropylene and I can't seem to find any information on flame polishing polypropylene. Also, it appears as though a high level of skill is necessary to use this technique and to avoid causing damage to the plastic. Due to this parts being made in a long, complex, expensive process, I would not want to risk damaging one. Thanks for the suggestion though, it's always good to think about new ideas.

Kat

RE: Testing for Aluminium Oxide

Can you solvent polish PP?

RE: Testing for Aluminium Oxide

Here are some other ideas.  it would be not problem if the part was not circular.  

Brush finishing is used for plastics
 
http://www.curtinhebert.com/deburring_machinery.asp?source=ssi_gaw_deburring&gclid=CPLR6PS41aYCFUHt7QodiCtpGw

Here is a different media you may want to look at. There is a lot of good information on other media.

http://finishingassociates.thomasnet.com/viewitems/abrasive-media-and-deburring-polishing-compounds-/zinc-base-shot
blasting-abrasives-briteshot-reg-#s

You may have to cut and paste the links.

RE: Testing for Aluminium Oxide

(OP)
Thanks Unclesyd.

RE: Testing for Aluminium Oxide

Just wanted to keep you busy. The lead for this approach was TV program that showed a flour sifter and since we had a 18" vibrating pad lap there ought to be bigger ones.

Here is another approach that you may want to investigate if the quantities are high enough.  The Covington Reciprol Laps go to 36" and it looks like it would not be a problem to enlarge the pan to accommodate your part.  Very little additional weight is involved.

http://www.covington-engineering.com/rociprolaps.htm

http://www.lortone.com/laps.html

http://www.diamondpacific.com/moreproducts.html

I polished to mirror finish about 2,000 CS 1" dia disks. on our machine.
 

RE: Testing for Aluminium Oxide

(OP)
@unclesid: I think our parts will be too large to use the technique mentioned above. They are between 1m and 2.5m diamter. Thanks anyway.

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