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 Post subject: Acrylic glue cracks
PostPosted: Fri Oct 29, 2010 8:07 pm 
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Hi

I have had some shapes cut out of 5mm acrylic using a laser cutter.

I was advised to use bison acrylic glue at the place i bought the acrylic.

When it came to using the glue, as soon as i put it on, loads of little hairline cracks appeared along the glued surface.
I'm a bit worried about them....
Will they weaken the bond/structure? Or are they just cosmetic?

Many thanks!


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 Post subject: Re: Acrylic glue cracks
PostPosted: Fri Oct 29, 2010 10:06 pm 
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STRESS IN ACRYLIC SHEET
Stress is a phenomenon which can affect many materials including
acrylic sheet. It is produced by the application of force and, if excessive,
can result in total mechanical failure. Long before these limits are
reached with acrylic sheet the appearance of fine crazing or stresscracking
can occur over time which, at best, is unsightly and at worst,
can reduce the mechanical properties of the material.
Stress may be generated by thermoforming at too low a temperature, by
the application of mechanical force or by the generation of heat during
fabrication, eg machining and drilling. Crazing is induced by the release of
stress, especially inherent stress, brought on by exposure to chemical
solvents (environmental stress cracking), cements, screen printing ink or
exposure to high energy radiation. It is therefore important to ensure that
only the minimum stress is induced in acrylic sheet when fabricating or
thermoforming and that component parts are designed to prevent
excessive mechanical loads being applied during service. Extruded acrylic
sheet has a lower stress level tolerance than cast sheet and particular
attention must be given to design parameters when using this material.

Taken from here-

http://www.ultimatehandyman.co.uk/perspexmanual.pdf

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 Post subject: Re: Acrylic glue cracks
PostPosted: Sat Oct 30, 2010 12:13 am 
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I take it this is bad then?

Image

Would it be weakened? It feels pretty sturdy.
Looks really messy there but its actually quite a neat job.

What would i have to use in future? I still want to laser it to get the perfect shape
But what should i use....Cast acrylic sheet? What glue?
I don't want any crazing at all

Many thanks


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 Post subject: Re: Acrylic glue cracks
PostPosted: Sat Oct 30, 2010 12:13 pm 
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If i did the following, would it still get crazing? :

*Order some cast acrylic instead of extruded
*Still get the 10mm and 5mm laser cut
*Use a different glue, suggestions?

Its for a water proof camera housing so needs, well to be water proof.


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 Post subject: Re: Acrylic glue cracks
PostPosted: Sat Oct 30, 2010 6:18 pm 
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Tensol 70 can be used to glue cast acrylic and can be used out doors-


Two sheets of PERSPEX may be laminated together using the
solvent-free clear adhesive TENSOL 70 from the EVO-PLAS range.
TENSOL 70, applied with the appropriate EVO-PLAS application kit,
will produce a bond which is durable in external applications, has
excellent optical clarity and good mechanical strength.


Again taken from the Perspex workshop manual.

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 Post subject: Re: Acrylic glue cracks
PostPosted: Mon Nov 01, 2010 3:45 pm 
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But if i use cast acrylic laser cut will i still get crazing?


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 Post subject: Re: Acrylic glue cracks
PostPosted: Mon Nov 01, 2010 6:08 pm 
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I can't say for certain, you would have to test it out.

Perhaps the heat from the laser is contributing to the crazing

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 Post subject: Re: Acrylic glue cracks
PostPosted: Sat Nov 13, 2010 3:29 pm 
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I have just used cast acrylic instead of extruded.

I still got crazing but loads better than the extruded. However, over time it's getting marginally worse.
I again used the bison glue.

Has anyone got any experience of this and would tensol 70 be better to reduce crazing?


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 Post subject: Re: Acrylic glue cracks
PostPosted: Sat Nov 13, 2010 5:50 pm 
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Can't help with the acrylic, just wondered - are you Brisa from Finland?

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