Hello, Building on a previous post, I would appreciate advice on suitable brands of epoxy resine that can be used as a binding agent for sand cores?
Just use whatever is cheap or already on hand. It's a disposable use so strength or long life is not an issue, it just needs to hold on long enough for the molten metal to begin solidifying and no more. Luckygen1001 has some good casting videos about using cores but I can't find the one about using epoxy binder:
I was a professional boatbuilder in the 70's-80's and the last thing I'd want to do with WEST epoxy is get it all over my hands, and tools and workbench, then burn it out in a furnace while breathing the combustion products. Luckygen1001 also has used simple Portland cement as a core binder, and that is cheap, has no toxicity, and is completely non-polluting by comparison. Low tech rules.
Even the commercial resins for sand give off nasty fumes when filled with metal, you simply stay upwind of the smoke until it cools. The advantages of resin sand is huge, no need for flasks for each mould and no need for ramming the sand either and cure times can be tuned down to a couple of minutes. When the right resin is used for the particular metal, the casting can be dug out of loose sand as the resin has let go fully. Downsides are the cost and availability of the resin and the nasty toxic smoke when the metal is poured into it.
I've really like the results with Portland cement cores. They burn out very nicely, cost is nil. Winds in my area are variable, nothing simple about standing upwind, heh!
BTW, one guy I worked with building boats had contact dermatitis from long term use of W.E.S.T epoxy so bad that he could not even touch cured epoxy without his hands cracking and bleeding. He had to put masking tape on his tools, because they had dried epoxy on them. It made a pretty unpleasant impression. W.E.S.T epoxy is considered to be a relatively benign epoxy type for personal contact. Nevertheless...
Anyone who doesn't wear protective gear while working with resin is asking for trouble: I use phenolic urethane no bake binder and it stains your hands black just like urethane wood glues do, it's a simple matter to put on some disposable gloves. The days of working outdoors in the sun on your boat while handling resin or spraying paint are long over. There's number of spray painters and fibreglassers with long term lung damage from not using protection. You'll notice Luckygen is casting iron which doesn't shrink as much as aluminium which lets him get away with using a rigid binder like concrete, I'd be inclined to add some organic material to allow the binder to disintegrate just like they add a few percent of sugar to sodium silicate to aid shake out after casting. The original poster is making small elbows so he shouldn't get much contraction and may get away with cement binder although an epoxy would certainly let go from the heat to aid any contraction.
Mark Presling on Youtube just did two videos where he used epoxy for cores for casting aluminum within the last couple of weeks.
I cast both iron and aluminum. For iron cores Portland cement binder. For aluminum cores, I generally use traditional molasses baked sand cores. Both work extremely well, are non-toxic, supplies are available everywhere at minimal cost, and the latter is even pleasant to be around while baking. If someone else likes epoxy or phenolic urethane, or water glass and CO2 for cores, and carefully uses protective gear suitable for contact and airborne organic toxins, fine, I have no problem with that. BUT, often amateur and starting casters hit the Internet read a few posts, and watch a video about using commercial foundry resin solutions, and come to believe that they are absolutely required to do a good job. They then go out and spend the money without ever trying anything more traditional, and pass on the same information -- that these resins and techniques are required. Their initial castings are naturally often poor, and they have the usual teething problems due to inexperience that we all have to start out with. Unfortunately they tend to pass on the very same misconceptions they received about what is "required" in terms of materials. Often in Youtube videos, themselves. The answer is, no. Commercial organic resins are not required in the hobbyist foundry -- for either core sand, or greensand (petrobond, et al). In fact many of the fabulous commercial castings created during the last couple hundred years are of absolutely mind boggling quality, yet used the simplest traditional core materials and methods. I'd simply like new people to step back a little and examine what ALL of the DIY options are, and not just assume, from what they've read, or what their 20 year old DIY video influencer with three castings under his belt did, and realize they do not need to start mixing epoxy with sand to get a perfectly usable sand core. If after trying other traditional and non toxic options, they still want to don the gear and go with epoxy, or whatever, hey no problem. To each, his, her, or their own!
I had good luck using sodium silicate that I purchased a from a local pottery supply store and cured with CO2 purchased from a paintball place.
Sodium silicate works well but having a CO2 cylinder handy is another added cost and it is very finicky to get a decent uniform gassing of the sand. I've used it for all sorts of moulds and it's superior to foundry resins for home use in terms of cost and shelf life. Epoxy is commonly available, easier to source than CO2, cheap for small cores and gives a good result without much experimentation. I think it's ideal for someone to dip their toes into casting without having to buy extra stuff. Earlier epoxies and certain paints in the 60's, 70's and 80's had all sorts of wonderful toxic allergy inducing additives that did their function well. I know of one person that gets a whiff of a certain 1980's epoxy paint accelerator/crosslinker and they will be sick immediately. That said, mixing epoxy with some sand is easiest way to get a core without, gasses, recipes, baking in ovens or whatever.
I've had good luck with sodium silicate. I just gassed it with my standard welding gas (75%Argon 25% Co2) then tossed it in the oven for 30-45 min @ 350F. If you have a CO2 tank you could skip the baking step. But I'm not spending $$ on a tank of gas I'll never use all of. (not a beer guy so couldn't even put on a keg in the shop) From doing a bit of Google / you tube searching it seems like folks have had good success with all kinds of modern epoxies (West System, Total boat, no name amazon special) just stay away from polyester. It's the devil!! it's cheap but awefull.
