I've been tossing around ideas for gluing polystyrene foam board together for casting purposes. Hot melt glue seems to be the standard as it's fast to use and it melts away when hot metal gets poured on it. Just about every other glue has problems: PVA wood glue is slow to dry, cyanoacrylate melts foam and gives off toxic fumes, possibly cyanide based, epoxy and urethane would have to physically burn away. Waxes have been mentioned and that may be a good glue when fed into a temp controlled hot melt glue gun. I should jury rig a temp controlled glue gun and run some wax-glue and hot melt glue and maybe melt some styrene through a glue gun and see if that can work. Hmmm 3D printer filament plastic might be an option too.
Wax works in glue guns if use a dimmer switch/rheostat to control temp. Otherwise it will just run out of the nozzle. You can extrude wax stock for the gun. You can also use a plastic syringe with about any low/moderate melt temp wax you want, just place it in a cup of warm water on a coffee cup hot plate and put the dimmer switch on that to control temp. It will take a while to melt initially but you just return it to the warm water after each use to keep it at temperature. I've used this to apply wax for filleting with fillet tools before I bought preformed fillet. Best, Kelly
Cured and uncured, uncured is worse, just take a look at how vapours condense and give nearby parts a white frosted appearance and imagine the same liquid being heated and giving off clouds of vapour, that stings the eyes and burns the throat/lungs.
I fitted a controller unit I had lying around, so far the gun runs fairly hot, I have it dialed down to about 5% and it still melts glue ok but is still a bit hot for XPS foam. I'll play around some more and see if I can get a good setting, the glue gun has a fair bit of thermal inertia so i have to make a change and come back later to test at that setting.
So the test results are in: for my particular glue gun and glue combo, eighty degrees C (176 deg F) is about the sweet spot between having a liquid glue and melting the XPS foam board coupons. The glue is clear when melted and milky when cool. At the temperature the gun was set at, it was going from clear to milky quickly but if slathered on too thickly it would melt the XPS foam a bit. Glue gun with the home built PWM controller board (Model No. Illudium Q-36) which runs from 1% duty cycle to 99% duty cycle, it's set very low. Some slight melting is visible and the join sets/cools quickly. Eighty degrees C does the job!!!
Very consistent with what I have found Mark. My glue gun was $8 at a hobby store purchase and has a dual range Hi/Low switch. I think you can buy them on Amazon for half that. Here is the glue I use but if you search "cool shot hot melt" or any (ultra) low melting point hot glues..........you will find many. It's hard to maintain glue gun temperature unless you are using it continuously. If you let the gun sit unused, they heat up as most don't have any active temperature control so if you have a delicate joint you may want to push some glue through the gun before applying it.....and like I said, thin lines not globs and quickly smear the joint to prevent heat distortion and create a thin homogenous joint. This minimizes risk of casting defects. A big blob of glue imbedded inside the foam pattern can create defects. Though Polystyrene melts at 240c, heat deflection temps are as low as 90c, and most EPS/XPS has recommended max service temps <80c. The cellular wall of XPS foam is so thin, if it gets anywhere near the deflection temp, it immediately slumps and deforms. A drop of solvent eats through it like aggressive acid. When you experiment with Polyvinyl Acetate glues, there are a myriad of types marketed under different purposes but I'd tell you they all behave about the same with foam. The only exception is the so-called "Fast Grab Tacky Glue" variant. That does have high enough initial tack/grab that often times you don't need tape or fixtures while it cures. I got this sample pack off Amazon for $2.75 delivered. The Fast Grab Tacky Glue was the only thing of interest, the rest......just disappointing marketing. Best, Kelly
You could add a temp controller to the glue gun. A MYPIN programmable temperature controler is about $25.
I did whip up a design based on the ESP8266 and a MAX31855K thermocouple interface, so with that I could have wifi connectivity to my glue gun . https://forums.thehomefoundry.org/index.php?threads/wifi-temperature-sensor-project.693/#post-14627
Was reading this thread and had a thought. How about using a temperature controlled hot plate and brushing a thin coating of wax on it. Then quickly rub the part against it and press the parts together. This way the whole joint gets done at one time.
I think I've seen that or something very similar done. There's a guy on youtube goes by the name Luciano who has a number of lost foam videos, in one of them, he rubs what looks like a glue stick, might be wax, on a hot plate then uses it to bond two pieces of foam in exactly the manner you suggest. Edit: found the video, https://youtu.be/0NE4EoY82Ns?t=340 looks like he adjusts the temperature of his hot plate using a router speed controller. As a side note, this guys uses a mixture of latex primer, water and plaster or drywall compound powder to coat his foamies. Anyone got thoughts on that?
The use of PolyVinyl Alcohol as a possible polystyrene glue was brought up in a previous thread some time ago (sorry, can’t remember by who). It is a common barrier coat for mold release agent. It’s also used as a 3D printing filament. Since it is suspended in alcohol, it won’t attack polystyrene. My interest would be a glue for laminating 2” boards into thicker board. I applied two coats with a foam brush to a sample piece, allowing each to dry, and then misted some alcohol on the surfaces and stuck them together. They were tacky enough to stay together but a relatively weak initial bond. I clamped the pieces together and let them sit for 24 hours. My shop is only 60F and some heat would have helped but the bond was strong on the sample block. So I sand the edges of the sample block on the belt sander and it did not smear or load the abrasive belt. It is a nice thin glue line and the surface sanded evenly around the glue joint and looked good. So then I hot-wired off four ¼” thick slabs. It hotwired fine but I definitely could feel some more resistance as I passed through the PVA joint……but it cut cleanly without incident. I broke the four samples. Even though they did break on the glue joint, the bond was quite strong and you can see on the one sample that the PVA adhered to both sides of the joint. I machined the sample with a router bit and the glue joint did not load up the bit. I think this is encouraging but as the surfaces get larger, it will be more difficult to evaporate the alcohol across a long thin glue joint, but I was think of vacuum bagging to clamp the pieces together and high vacuum might be help that alcohol find it’s way out! Best, Kelly
That might have been me in your Two Barrel carb thread although I brought it up in a somewhat different context.
Ah yes, I believe you were talking about coatings for surface finish. I'm not sure I would advocate for that just yet. The joint seems to be remarkably thin yet still noticeably different passing through the hot wire so still quite dense......and maybe higher melting temp. That would certainly create a diffusion path but my aim is to have the least detectable glue joint possible so it can be machined and abraded and evaporated with properties near foam as possible, so disturbing the surrounding foam would be a bit counterproductive. I'd much rather not have a glue joint at all. I can buy thick EPS and XPS billets. Although EPS is available in differing densities, it does not machine and finish as well as XPS. The sources for thick XPS billet I've found are usually 2/bs/ft3 or higher density. I've been using 1-1.3lb/ft3 density foam. There are thicker Dow and Owens Corning XPS sheets (like in the retail stores) commercially available but only by the truckload so unless you know a commercial contractor using it, that's out. Best, Kelly
I still have to go visit that guy with an enormous pile of extruded 4" think foam. I was told I can take what I want.
