Help! Ordered acrylic, got polycarbonate - The Planted Tank Forum
 
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post #1 of 12 (permalink) Old 10-19-2011, 09:54 PM Thread Starter
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Help! Ordered acrylic, got polycarbonate

I've spent the past week gathering tools and supplies to build an acrylic sump tank. On Friday I ordered my acrylic sheets from the local glass shop. Unfortunately, the receptionist was used to the terms "Plexiglass" and "Lexan"; so even though I had written down acrylic she told the guys in the shop to cut Lexan. I went ahead and accepted the polycarbonate since they gave it to me at the same price as acrylic and threw in a couple of good sized extra pieces that I can experiment with (or possibly build a rack for my CO2 bottles). The good news is that the polycarbonate should be easier to drill and machine. The bad news is that I have a bottle of Weld-On #4 ordered and have spent the past two weeks preparing to weld together an acrylic tank.

I know people have made sumps and even aquariums out of polycarbonate, but I have no idea how to weld/glue it together. If there is a tutorial out there it would be really helpful (I haven't done a lot of searching yet). Does anyone know if polycarbonate can be welded together in a similar manner to acrylic, or does it have to be glued/sealed like glass? I have MDF cut up for building jigs, so I can hold things square. What I don't have are clamps long enough to span the length of the tank, and I'm not sure about the height (width is no problem).

I ordered the acrylic slightly over-sized so I could router the edges to get them smooth and square. The edges on the polycarbonate are already quite smooth, so now I'm not sure whether or not to cut things down. I'll have to trim the bottom and end pieces down to keep the tank from being too wide, but if the sides and ends are the same height do I need to router the top and bottom edges? Do I still assemble the four sides first, and then set them on top of the bottom pane? I know with commercial glass tanks the edges are assembled around the bottom piece; although those have a frame added afterwards. I realize I'm sort of rambling here; but the situation caught me unprepared and I'm an anal retentive bastard when it comes to design (occupational hazard when you've spent over a decade as a design engineer and mistakes can cost thousands of dollars or more).

At this point, any information would be appreciated. I was hoping to be ready to assemble the tank by this weekend; but I'd much rather wait a week or two and get it correct. Thanks.

Sean
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post #2 of 12 (permalink) Old 10-19-2011, 10:08 PM
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Do not trust it with Weld-On #4. Maybe there is a glue that will work, but none that I've ever seen that I would trust at all. I know enough about polycarbonate to know that it does not bond nearly as strong as acrylic using any method I've ever heard of. I may be wrong but I think this won't be trustworthy long-term.

Also, polycarbonate scratches way easier than acrylic. It's stronger, but it's more flexy and it's also just way more scratch prone.

Polycarbonate, if I understand my plastics, is a whole different animal than acrylic, such that it does remelt in solvent to make a durable chemical weld like acrylic will.
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post #3 of 12 (permalink) Old 10-19-2011, 10:18 PM Thread Starter
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I know it's softer, which means it will scratch and bow easier (although some types of polycarbonate have a scratch resistant coating that is quite hard). I'd never use it for a display tank; but for a sump the appearance isn't a big deal and it won't be holding enough water that I have to worry about bowing. You are correct that polycarbonate and acrylic are quite different. They are however both thermoplastics, which means you can melt them and reform them with heat; unlike thermoset plastics which once cooled cannot be melted or easily recycled. Whether or not you can chemically "melt" polycarbonate to weld two sheets together is something I'm still trying to determine. Essentially, this is how superglue works, so I'm hopeful there is an industrial adhesive that will work with Lexan?

Last edited by smannell; 10-19-2011 at 10:20 PM. Reason: forgot about anti-scratch coating
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post #4 of 12 (permalink) Old 10-19-2011, 10:28 PM Thread Starter
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OK, according to wikipedia, Dichloromethane can be used to chemically weld polycarbonate. Now I just have to find an adhesive based on that and determine if the capillary welding method will work.
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post #5 of 12 (permalink) Old 10-19-2011, 10:43 PM Thread Starter
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Sites that sell Weld-On products claim Weld-On #3 & #4 will weld polycarbonate; however its active ingredient appears to be methylene chloride and I have yet to find anything that indicates how well it works with polycarbonate. Has anyone actually used either of these on polycarbonate (Lexan)? Sorry for the rapid posts, I'm still in panic mode.

OK, it appears that methylene chloride and dichloromethane are the same chemical, so I'll shut up now and wait for advice.

Sean

Last edited by smannell; 10-19-2011 at 10:48 PM. Reason: found new information
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post #6 of 12 (permalink) Old 10-19-2011, 10:50 PM
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The shop that cut this stuff for you should be able to answer this question....
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post #7 of 12 (permalink) Old 10-19-2011, 11:11 PM
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Oops, just saw that you found out they are the same thing. good luck and don't spend much time breathing those vapors - not good for you.

Last edited by billb; 10-19-2011 at 11:12 PM. Reason: slow reader
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post #8 of 12 (permalink) Old 10-20-2011, 01:07 AM
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"Essentially, this is how superglue works, so I'm hopeful there is an industrial adhesive that will work with Lexan?"

I've used Weld-on for Lexan, works fine. How thick are the sheets? I'm using a pc 3/8 as a battery tray in my car. ! year later still straight & strong.
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post #9 of 12 (permalink) Old 10-20-2011, 01:08 AM
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We use weldon 4 for lexan at work, can't speak to how strong the bond is though, we use it on low impact medical devices.
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post #10 of 12 (permalink) Old 10-20-2011, 02:37 AM
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If I remember right polycarbonate is UV sensitive and having strong lights on it for too long will make it degrade...
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post #11 of 12 (permalink) Old 10-20-2011, 04:09 AM
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Quote:
Originally Posted by smannell View Post
I know people have made sumps and even aquariums out of polycarbonate, but I have no idea how to weld/glue it together. If there is a tutorial out there it would be really helpful (I haven't done a lot of searching yet).
you need to use an resin and literally melt it together.

I seen lots of people design crazy PC reserviors with poly, and each time they put up a post they would rant because if u mess up the resin you need to start all over again.

This might help.. its by one of my friends who designs crazy reserviors with poly for PC's.
http://www.xtremesystems.org/forums/...Fall-Reservoir

As u can see you need to melt the parts together:
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post #12 of 12 (permalink) Old 10-21-2011, 02:20 AM Thread Starter
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OK, it looks like I can essentially proceed as I originally planned. I have a couple of questions for anyone with experience fabricating acrylic/polycarbonate tanks. First, Weld-On is designed for acrylic so it contains small amounts of acrylic monomers and polymers to help bond the two pieces together. Since I'm bonding polycarbonate should I add a small amount of router chips to the Weld-On so it will contain some polycarbonate, or just leave it be and hope the trace amounts of acrylic work. Second, is a .030" gap too large for capillary action to pull the solvent into the gap? I'm working with 1/4" thick sheets. I have a bunch of small, smooth paperclips I was going to use as shims, but if .030" is too large a gap I can probably get some small piano wire at Home Depot. Thanks for all the suggestions.
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