Using Epoxy (and maybe polyester) to Make Cores

Discussion in 'Sand Casting' started by Melterskelter, Sep 11, 2021.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    The acetone might be a bit hard on anything but metal tooling.

    I have an 8kw resistive electric, lift off furnace, that has A20 capacity and really like it. I've been threatening to reconstitute a build thread here as the original went down with AA, alas the dead link in my signature. Here was the latest low mass version of the refractory liner. There's a whole thread but this is the cut-to-the-chase conclusion.

    ......and the controller:

    Do you have a build thread on your furnace here? Maybe we could discuss it there. -Back to regularly scheduled programming......core binders!

  2. DavidF

    DavidF Administrator Staff Member Banner Member

    It's been years since I fooled around in the composites industry and back when I was doing it for a living I would order 500 lb drums at $1200.00 each. That was for derakane 411.
    US composites was my go to supplier, but I was looking a few years back and found a place that was selling smaller quantities. I might have them saved on the computer, I'll have to look when I get a chance.
    Mix ratios varied depending on temperature and what rate of cure I needed. Alot of times I worked on "hot" lines that were leaking and would mix up for a hot patch that would kick in just a few seconds (like 4 seconds) to stop the initial leak so it could be over wrapped. For that kind of cure I would use about 15 cc cobalt, 15 cc dimethylene, and 20 cc mekp to 8 Oz of resin.
    General work would use about 5 to 10 cc cobalt and 10 cc mekp to a quart of resin.
    Most of the work I did was "fast" but did occasionally lay up stuff bigger than a tractor trailer.
    Those days are pretty much gone for me now, but I still have a boat mold that I made years ago that one day I plan on laying up a few of one day and building electric yatch tenders. Like I don't have enough projects going
  3. Smoking Shoe

    Smoking Shoe Copper Banner Member

    Now you have done it! A month just turned into 5 weeks - or more.
    Your YouTube videos were what led me down the electric path, after doing some math, rather than the typical hydrocarbon fuel route. I had a lot of new propane related hardware leftover from my last planed upgrade but the castings I plan to do will need to be high quality/hydrogen free. With electric I can pump in an inert gas and I even considered vacuum for a brief time. The math indicates the cost to melt should be cheaper as well - so the decision to go electric was made.

    I don't have a build thread ...... yet. I am still in the process of finishing the work space needed before winter sets in. Now that I've found your build here I'll probably be changing a few details of the design. Low mass was one desired parameter from the start. A quick scan tells me that there may be a better way to build the wall to support the heating coils than I have planned.

    The electronics/control are, for me, the easy part.
  4. Melterskelter

    Melterskelter Gold Banner Member

  5. MortyNTenon

    MortyNTenon Copper

    Linocure Part B from Ask Chemicals has Cobalt naphthenate as an ingredient. Don't know if its available separately or just with the other two parts.
  6. DavidF

    DavidF Administrator Staff Member Banner Member

  7. Melterskelter

    Melterskelter Gold Banner Member

    Well, I can get Cobalt Naphthenate locally for about ten bucks for 4 ounces—-enough to treat a lot of vinyl esther. The same company sells vinyl esther without added cobalt.

    And there is a source of cobalt I found online as well. The stuff is fairly toxic. So, it ships UPS/FedEx but not USMail.

    In addition I bought some epoxy accelerator not “authorized” for use in West System epoxies. But it was relatively cheap and the 5:1 epoxies are similar in formulation. So, there is a good chance it will work. I mixed up a small test batch half an hour ago and will report on what happens. The SDS suggests the hydrochloride acid is a primary ingredient.

    You can see some initial cloudiness of the epoxy with the X-55 on the right.

    After 1/2 hour the mixed epoxy was noticeably more viscous and just slightly warmer than the unmixed and most of the cloudiness was gone. I’ll check in an hour or so and see how the coating and pot are curing. I expect the pot to cook off in that time. The shop temp was about 72 F.

    It is the same local company that has the vinyl esther and the cobalt.

    The online cobalt source is

  8. Melterskelter

    Melterskelter Gold Banner Member

    Major fail: The X-55 did nothing good for West Systems 1:5 epoxy. I think it initially speeded the reaction just a bit based on a small viscosity change seen at 1 hour after mixing. But there was no real acceleration of the epoxy cure and this morning practically no difference in the 2cc plug or epoxy that was in the mixing cup in the X-55-added batch vs the standard mix. This is NOT a criticism of the makers of X-55 as it is sold for use in their Resin Research Brand 1:2 ratio epoxy. I noticed after the fact that RR’s epoxy intended for this accelerator is a 2:1 mix and not 1:5. So, it should not be surprising that the formulation is significantly different than a 1:5 epoxy.

    No big deal. There is some value in having explored an avenue in just knowing it is a dead end.

    I will add that, if you go to and look at Resin Research resins, the company offers some interesting options for cure rates, optimization of cured resin qualities and so on not seen with System Three or West System.

    If I want to pursue acceleration of epoxy or silicate core (I use propylene carbonate) cure times will be to place my packed core on a seed germination warming pad. Something like this

    In the summer, I just set my uncurled core in the sunlight, which does a nice gentle job of warming. But “them days are gone” here in the PNW until sometime in May.

    I could place the cores in an oven, I know. And set it on low. But, accidentally burning up a tuned core box with many many hours of work invested just is not an option for me. A simple box—-sure. But not a straight edge core box that could easily have 30 or more hours building and tuning invested in it.

  9. MortyNTenon

    MortyNTenon Copper

    I have an old electric grille that I rig up on low to warm cores up. The Linocure instructions even mention heating to improve strength and remove some gasses. It does smell when up to temp.
  10. Melterskelter

    Melterskelter Gold Banner Member

    On Saturday I cast a couple more 26” prism/straight edges. This time one of them had an 1.5% epoxy-bound core to which I added 2% sea coal. The sea coal was added to see if I could get a nicer sheen on the core surface as the silicate bound core using 5.5% sea coal had a bit better finish. The added coal did indeed produce a shinier surface that is just right I think. As before, both cores fell out of the casting easily post pour. The epoxy core was very soft and nearly was loose sand. This quality would be very desirable on cores contained in somewhat inaccessible cavities as removal of the sand would be very easy.

    The other desirable quality for epoxy cores is higher strength than for silicate.

    However, I think detail rendition is just slightly better for silicate. It could be that the epoxy breaks down just a bit as the iron flows. This is a subtle difference. But, for the casting I am making, I will likely stay with silicate. I do have a new design coming up that will need max strength and for that will go with epoxy. It’s nice to have choices.

    Here is the slightly crisper silicate core.

    This is the epoxy core.

    Added 10-19-21: I just flipped the labels on the two pics. I posted using my phone and when I looked on my PC I could see that I had them backwards. The difference is not great, but I do think it is noticeable. Such a gentle group for not contesting my labels...

    Last edited: Oct 19, 2021
    Tobho Mott likes this.
  11. MortyNTenon

    MortyNTenon Copper

    Thanks for testing

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