Lexan for Fume Box Slide

[TyG]

I have been told plexi/acrylic gets eaten up by the iodine & bromine when used in fume box. But, what about Lexan? I came across an old post by Jonathan D. where he mentioned using it. Any other thoughts? I know about Teflon/PTFE, but it is not cost effective.

Thanks, Ty

[Andy Stockton]

Hello Ty-

Here is a link to a useful chemical resistance of plastics chart.

http://k-mac-plastics.net/chemical-large.htm

You can find plastics that are resistant iodine and bromine. Those that are resistant to both are pretty spendy. In the cheaper realm acrylic does fine with Iodine (I currently have an acrylic iodine fuming box). On the Bromine side Type II PVC is supposed to work. I have not yet personally tested that although I have a box built. I have not charged it with bromine yet.

One thing you might consider is laminating Teflon to cheaper plastics. I have done that with acrylic and it works well and saves a lot of money. There is an etched Teflon sheet available that glues nicely with cyanoacrylate to acrylic. Because the sheet is quite thin it is much less expensive. 12x12x1/16th About $30

Here is a you-tube video of the Acrylic & PVC box I built a while back.

http://youtu.be/moUfrlAQGFw

[photolytic]

Thanks for the excellent idea Andy.

While cheaper plastics have a distinct initial cost advantage over Teflon, the low coefficient of friction of Teflon should also be a considered. Cyanoacrylate gluing is an excellent idea but its long term adhesion to Teflon or even Plexiglas should be tested.

In planning a Daguerreian darkroom one should also consider how many Dags you plan to make before trading in your old 3G fuming box for the faster 4G model. You may fume several hundred or even several thousand Dags during your Daguerreian career.

Operating the sliding drawer on the fuming box puts a lot of wear on the plastic underside of the drawer. Eventually grooves will be worn in the plastic surface and the seal will be lost.

No plastic will hold up as well to this wear as well as glass. This is why many fuming box makers still use glass. My 14 year old glass lined boxes are still performing like they did several thousand plates ago.

[Andy Stockton]

Thanks photolytic – I am looking forward to the day I finally have enough time to fume “many tens of plates” much less being able to equal your “thousands”. Needless to say wearing out the plastic hasn’t been an issue yet. I couldn’t agree more that glass is the proven performer in fuming boxes. Nothing contains iodine and bromine better. I have experimented with alternate materials mostly because I find it fun. I started out with wanting to make a box with no metal at all since some early boxes I had suffered severe corrosion of their metal parts. The rest of the current design was the result of an over-active imagination.

So far the adhesion of the etched Teflon to the acrylic has been holding up. When I was in the initial design phase I glued two sample pieces together and after a twenty-four hour cure I was unable to separate them even with a knife blade and a lot of pressure. Since cyanoacrylate is an acrylic polymer I would imagine the bond on the acrylic side is a true weld. The particular glue mix I use was formulated by the company selling the etched Teflon specifically for strong adhesion to their product. The etching forms an anchor point for a mechanical bond as well as the glue supposedly having properties that allow some level of bonding with the Teflon. Of course as you point out degradation over time may occur, chemicals do break down.

The one issue that I have had with the etched Teflon is that it comes from the supplier with the non-etched surface a bit scratched and beat-up. I ended up sanding it to a pretty smooth state, but I don’t think it seals quite as well as a flat ground glass-glass joint. I don’t think it leaks much more than the boxes I had before however. If I put a piece of bare mild steel in with either box in an enclosed space, I see evidence of metal corrosion within a week. The plan for that is a plastic box to contain the plastic box. I also haven’t tested the bromine side of the box yet either. Robinson’s Quick – here I come.

On another note entirely, I have thought about making one of my double sliding boxes with glass liners in the boxes and a glass surface laminated to the lid. I just haven’t identified a suitable glue – although I have been thinking of doing a test with JB-Weld. I continue to be attracted to making my own boxes partly because I never seem to find existing glass containers that are exactly the shape and size I want. Fortunately this is a field where we are free to inflict weird idiosyncratic approaches on our selves at any time.

[photolytic]

Andy, Cyanoacrylate will bond Plexiglas and Teflon but it does not dissolve either one.

To form that kind of bond, usually referred to as a weld; you need an actual solvent for acrylics such as methylene chloride. Unfortunately Teflon does not dissolve in common solvents.

That is why you need to roughen the surface to create more area for a mechanical bond.

[TyG]

McMaster-Carr sells PTFE teflon sheets that are adhesive-backed. As far as adhering glass to wood; I have had good success by grinding (ground glass) the surface to bond to the wood and using gorilla glue (poly glue). Thin coat and clamp so that when it foams, it doesn’t push glass away from wood.

[TyG]

CA glue actually becomes brittle after a few years and easily breaks. A whole bunch of woodworkers are just figuring this out; as a few years ago, the woodturners got the bright idea of using CA glue for dang near everything. I am in a woodworking club, and quite a few of them have had things done with CA just simply fall apart.

[TyG]

So, lexan and plexi will not work at all? or not very long?

[Andy Stockton]

jgmotamedi has posted in the past about having used some acrylic/plexiglas in his fuming boxes. This post from a year ago has some discussion although the links to the pictures are now broken.

http://www.cdags.org/dagforum/topic.php?id=215

He may have the longest term experience on longevity of plastic unless someone else chimes in. For what it is worth my acrylic and teflon box has been charged with iodine for about six months. It has gotten little use unfortunately, but I looked it over recently and the plastic has no visible signs of deterioration and the seal continues to be adequate.

I was also interested in your comment on CA glue failure. I did some web searching on the woodworking forums and saw a lot of divided opinions on the issue. Some saying they had no such problems and others contending the glue fails with age. Have you experienced failures? I suppose all glues fail eventually, perhaps these failures are related to varying product formulations or perhaps other factors like cleanliness of the joint or moisture and such?

Andy

[Andy Stockton]

photolytic – your comment about the lack of a true weld between acrylic and cyanoacrylate inspired me to do some further reading. Amazing stuff. I now see where I went wrong – I had assumed that since one of the main ingredients of “superglue” was Polymethyl methacrylate (Acrylic) that there was probably solvent present (which would have caused a weld). With further reading I see that superglue is actually a solvent free glue held in a non-polymerized state with a stabilizer like Hydroquinone. Apparently water molecules start the polymerization process in the Polymethyl methacrylate and Ethyl 2-cyanoacrylate. No solvent, no weld. (At least if I have fully understood what I read).

Very basic info here: http://adhesive-formula.blogspot.com/2010/08/alkyl-cyanoacrylate-adhesives.html

My purpose in posting this however is not to show my advanced ability to cut-and-paste other people’s science knowledge, but to mention that one article stated that the cyanoacrylate polymer is rather brittle and that usually a plasticizer is added to the adhesive formulation. Perhaps the failure of some cyanoacrylate joints is from gradual loss of the plasticizer from the cured adhesive?

[TyG]

Andy, you asked if I have ever had experience in CA glue failing. I very rarely ever use it, and only in places where I only need to hold something for a brief moment to final assemble by other means. What John about “welding” of acrylic is what I want in every adhesion I make. Wood glue; I use either a water-based titebond or elmer’s white glue which raise the grain of wood and then each grain is inter-locking and glued. For acrylic/plexi, I use Weld-On products which melt and re-join the pieces essentially forming the chemical “weld.” For other crap that just plain get broken, etc, I will use a two-part epoxy for stuff like that.

[TyG]

Also, the commonly known method for model makers and such to break a CA glue bond is to put the glued pieces in the freezer for a couple hours or more and it just comes apart. That should tell enough about the structural integrity of CA glue.

[Andy Stockton]

Interesting discussion. Thanks for the responses. I realized I wasn’t really clear about one thing with the acrylic fuming box I made. The only use of cyanoacrylate in that box is to laminate the thin Teflon layer to the acrylic piece that functions as the top lid. Everything else is joined traditionally with solvent based Weld-On products.

The cyanoacrylate was sold by the same company that sells the etched Teflon. I use the Teflon for it’s reduced coefficient of friction, its’ resistance to Iodine and Bromine and because it has a little bit of “give” that I think results in a better seal than would acrylic/acrylic.

Time will tell if my Teflon delaminates or if the Acrylic and PVC break down from exposure to the fuming chemicals. That’s why I store the box outside of my living space.

[jgmotamedi]

Ty built a pair of boxes for the Center for Alternative Photography, where I have taught and will be offering a course on both Becquerel and Mercury development with another member of this forum (this is still not finalized, so no announcements yet) sometime next year.

The boxes are great, but my concern was that the workshop participants would crack the glass slide. They can be rather rough on equipment. Ty and I were thinking about alternatives. I use a 1/8″ PTFE slide between the wood top and glass insert in my boxes at home, but it seems that the price has risen sharply. One alternative to PTFE is acrylic, but my experience is that acrylic eventually breaks down under bromine. It takes a while to show the damage. More importantly it just doesn’t seem to seal as well as PTFE. I get leaks when not using PTFE slides between the acrylic top and the glass liner.

[fluidrive]

Hello,

I have been using corian for about 4 years without any issues.

It seems to work well as a slide and although the Iodine has stained the one pull, it has not shown any signs of deterioration.

As well it is quite durable and almost bullet proof.

c

[Author]

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