cleaning up acrylic

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PeterB
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Re: cleaning up acrylic

Post by PeterB » Sat Jun 28, 2014 8:25 pm

Only just found this post, very interesting, when I first started cutting acrylic I used to use surgical spirit to clean it up, and couldn't understand why it kept cracking a few hours later, it was the surgical spirit that was doing it, I now use IPA.
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keithwright
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Re: cleaning up acrylic

Post by keithwright » Wed Oct 22, 2014 3:31 pm

We solved the problem of marks on acrylic by simple NOT removing the protective films before cutting.

Keith

davehills
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Re: cleaning up acrylic

Post by davehills » Thu Dec 04, 2014 2:52 pm

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Last edited by davehills on Thu Dec 04, 2014 2:54 pm, edited 1 time in total.

davehills
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Re: cleaning up acrylic

Post by davehills » Thu Dec 04, 2014 2:54 pm

StarLoc Adhesives wrote:I wouldnt ever put acetone on acrylic of any type extruded or cast it usualy causes micro stress cracks all over the surface and if theres any nicks or deep scratches it can shatter the sheet

Isopropyl alcohol / IPA / isopropanol is fine on it but contact between acrylics and ketones such as acetone should be avoided
I have found that IPA causes cracking, too, especially if the finished part is subject to any sort of stress, such as bending. Have experimented and even vapour from IPA causes it. Take care..

Edit: A good way to test is to fix a strip/offcut of your chosen material such that it is slightly stressed and expose to the cleaning liquid in question. You can do this with a bit of tape, such that the tape and material forms a shallow "D" shape. Then wipe the material with the liquid you want to test.

If the test piece cracks after a period of time you know the liquid should be avoided..

Matrix
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Re: cleaning up acrylic

Post by Matrix » Fri Dec 05, 2014 9:55 am

Further to what Dave has said - if you are working commercially, don't forget to advise your customers about cleaning appropriately!

Just recently we got back some returns - well over 6months after the customer purchased the product. All of them had become extremely brittle at places where we had bent the plastic, and around a some of the laser cut holes - yet, when straight off the production line, they easily pass a 2m drop-test onto a concrete floor.
The customer had been keeping their kit nice and shiny using a generic "bathroom cleaner", which we found was acting in the way Dave mentions. Bear in mind though, that even water vapour can lead to this kind of cracking if there is enough stress within the plastic. Doubling the stress way more than doubles the chance of cracking, so its well worth paying attention to.,

Some tips for reducing the stresses are...
- Bending over a larger radius reduces the stress at bends.
- Using a radius/fillet at internal corners -the stresses get concentrated at 'any sharp internal angle.
- Cutting thick plastic progressively over two or more passes - the faster the laser head moves, the less heat is pumped into the plastic, and it can cool a little between passes.
- Avoiding parts that are very narrow - as the cut nears its end, small parts become tiny 'islands' of plastic, so heat from the laser can't be conducted away by the rest of the plastic sheet.
- Prefer cast plastic to extruded - extruded plastic has stresses 'locked in' by the machines that form it into sheets.
- For very critical applications, the finished parts can be annealed - a special heating and cooling process that 'relaxes' the internal stress.

If you're interested to see the stresses in your (transparent) parts, it's easily done with a pair of polarising filters. You can get polarisers from most camera shops, and many sunglasses have polarised lenses (the ones where you see 'rainbows' in car windscreens). Put one behind the plastic and one in front, and slowly rotate one of them - you will see coloured bands appear in the plastic. They are rather like the contours on a map - closer together = trouble!. If you flex the plastic, you can even see the stresses changing right before your eyes.

PS) Why not treat yourself for Xmas - get some polarisers anyway, the effect looks real pretty!! ;)

Spooky
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Re: cleaning up acrylic

Post by Spooky » Sat Dec 06, 2014 2:52 am

Without disclosing too much I can say for sure StarLoc likely knows more about cleaning agents and solvents than anybody I know :)

This guy isn't the student of solvents, he is the guy the professors go to ;)
Please note I am not employed by HPC, any advice or recomendations I give are based on my own experience and are not necessarily the same as HPC's. First point of contact on any hardware issues should be with HPC
Dave@OpticalPower.co.uk

Dave
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Re: cleaning up acrylic

Post by Dave » Tue Sep 15, 2015 3:18 pm

When I just cut acrylic I leave the protective coating on and just cut through it.

If im engraving I just paint (or airbrush for a fine even cost) the acrylic with washing up liquid. If you leave the white plastic on it you seem to get a white residue off it that melts onto the engraving when doing deep or large engrave areas.

All of the above is trumped if you can get acrylic shipped with a paper based backing with low tack glue however I can’t seem to find it in the UK anymore.

llamalasers
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Re: cleaning up acrylic

Post by llamalasers » Fri Sep 18, 2015 12:47 am

Washing up liquid is a great tip! Thanks for that.
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started out with LS3040

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