The speed of epoxy cure can be varied for some brands by selecting faster or slower curing hardeners. For instance, I have used both the fast and slow hardeners (and they also make a very slow hardener) supplied by West Systems for their epoxy resins. Take a look at this link: https://www.westsystem.com/the-105-system/ I would suspect other manufacturers also supply various hardeners that affect cure rate. Obviously temperature also affects cure rate and the exothermic nature of the chemical reaction can come into play big-time when epoxies or polyester resins are used in thick section. But, cooling the sand and resin prior to mixing could dramatically slow cure rates. I have kept mixed resin in an ice bath on hot summer days to lengthen open time. (There is a risk condensation in humid conditions.)
It's a bit of a misnomer that epoxies have one component labelled a "Hardener" you really need both components in the correct ratio for a proper cure as they react with each other and there will be leftover uncured resin if the ratio is out. One product I used, stated that a 3% mismatch in the two components reduced the ultimate strength to 50% of properly mixed cured resin. There is a chemical known as DMP that will reduce the cure time to 10% if 1% is added to your epoxy mix, I understand it does two things one of which is generate heat, so you have to be careful and it also reduces the strength and life of the epoxy. I heard about it for pattern making purposes. It also works as a catalyst for urethane resins and I see it available online cheaper than the chemical supply companies sell it for. Apparently there are better accelerators for epoxy but this is the most common and oldest one. http://www.chemcoms.com/Tris(dimethylaminomethyl)phenol.html
chatty Cathy I have used SS with a 60 min Catalyst, I have only used the wax once and it was to prevent the sand from sticking to the pat. I mix the SS and Cat in a small cement mixer with the vanes removed and mulling balls in the sand i mix about 45lbs per mix The largest mold i have ever made weighed 275 lbs. I'm using Lane MT 70 sand it is about 100 grit. Ln Mt also has a 125 which is 125- grit, it is air stream filtered rather then screened. I had to buy 5 gallons of the catalyst at a cost of $170 for the cat, the foundry grade SS was only 30.00 for 5 gallons, it cost more to ship then the cost of the SS. I have always tapped the pat for removal but maybe that isn't necessary with the wax. Art B
I reskimmed the thread but i didn't see a supplier for the resin bonder. I haven't ever used epoxy so i don't really know where to look. is just liquid fiberglass????? Art B
"Fiberglas" is an Owens Corning proprietary name for a combination of glass fiber and a setting resin either epoxy or polyester used to form all manner of boats, pipes, panels, sporting goods etc. The name has become commonly used as a generic term rather than a proprietary term in a way similar to the use of the term "Xerox" has come to mean a form of document copying. You can buy polyester or epoxy resins at most hardware stores, home improvement stores, on the Web, etc. If you search on epoxy resins and polyester resin you will find hundreds of articles concerning their use. YouTube has hundreds of videos on their use and relative benefits. West Systems is a maker of epoxy resins that I have used and trust. Their website is informative. Wiki has good introductory information as well: https://en.wikipedia.org/wiki/Fiberglass Denis
thanks,I guess my question was could we use the fiberglass resin as a bonding agent in the sand and have it hold up for aluminum casting/ or will it burn up???
In post #1, ironsides uses epoxy (same as fiberglass resin I guess) as a sand binder for a mold he poured in cast iron. If it worked well for him with cast iron, it will be extreme overkill for aluminum. Sodium silicate is an inexpensive and effective way to make bound sand molds and cores for aluminum, so unless you are having some sort of serious issues with SS, then there is no need to use epoxy as a sand binder. Would you agree?
I came across this video about a 3D printer making a very complex core for an impellor. After my effort making cores I am beginning to wonder why I bother using primitive methods to make a impellor core. This must be the way of the future, why stop at the cores just make the whole mold with a 3D printer without patterns. What does everyone think?
I think it has a place for making moulds that would otherwise be impossible with a pattern but it would come in distant second place time-wise compared to a resin bonded sand mould that can be made with a conventional pattern in about four or five minutes. Also surface finish will be an issue dependent on the resolution of the printer, which is not so much of a problem with a pattern. A 3D printer will take time to print a sand mould, dependent on how fine your desired surface finish is. It has the advantage of ignoring conventional rules about having draft on patterns, so it has some of the advantages of investment casting but uses sand. Probably faster than investment casting but slower than conventional resin bonded sand and with a rougher finish which could be mitigated with a ceramic wash. Edit: The resin print head technology will be fun for home users to duplicate on a budget too. These guys have an interesting approach: they use 3D sand printing along with 3D scanning to prototype a sand mould to ensure dimensional accuracy of the finished casting. I expect that once a prototype casts accurately they then hand it over to conventional resin bonded sand casting techniques if the multi-part mould they used is anything to go by.
I started making patterns using a 3D printer a few years ago, and got some pretty good results. I did have a lot of problems with the 3D printer and the software, so many problems that I ended up tossing the whole affair into a dumpster. I now have the skill to manually make patterns from wood, and while I like 3D modeling work, I also like to hand-make patterns too. Myford seems to be trending in the opposite direction, going from hand-made patterns to 3D printed ones. More power to him; there are no rules in the backyard casting world; you only have to please yourself and have fun with however you are doing it.
Mark I have seen that before but it is still very interesting to watch. Did you get some resin to experiment with?
I have a friend with a small commercial foundry so all I ever get to use is 3 component urethane resin. Even my pattern making is based around using it, the current product is a bit slow it takes half an hour to go off and is intended for large cast iron moulds with plenty of time to work with it.
