Shielded impellor casting in iron.

Discussion in 'Sand Casting' started by Ironsides, Dec 17, 2017.

  1. Ironsides

    Ironsides Silver

    I have made another video this time it is about using fiberglassing resin to make the core for a shielded impellor in iron.

    This casting can be very unforgiving if you make a mistake. I made two.

    1. Gating was too small restricting the flow into the mold

    2. Not aiming my pouring trolley right and hesitating while pouring.

    For the first try I used resin to make the entire mold. I have only make small cores in the past so hand mixing is not an issue but mixing sand for the entire mold was a long process.

    Another benefit of using self setting sand is I only needed one box for the three parts to the mold. Not wanting to mix a large amount of core sand by hand again I made two other boxes and did the rest in green sand.

    As I machine all my castings the cores have to peel away from the surface without any sand sticking to it. The resin does a great job of that. Using only 1.5% by weight of resin and hardener it will survive many hard blows with a hammer to remove the patterns.

    Have a look at the video.

     
    Al2O3 and _Jason like this.
  2. Jason

    Jason Gold

    Impressive. Lot's of important steps.... You make it look easy and I know it's not!
     
  3. _Jason

    _Jason Silver

    Do you have to dispose of the resin bonded sand after the pour? Or can you mull it and recycle it?
     
  4. Ironsides

    Ironsides Silver

    Yes I do, to reuse it has to be burnt until all the resin and hardener are gone. Not worth the trouble!
     
  5. I've been taught to rap the sides of the wooden pattern box before the resin cures to create a slight clearance between the sand and the pattern. That and the aluminium "slipcote" paint on the pattern lets the sand come off the pattern fairly well. I'm just wondering what would be a good substitute for the slipcote: it's a fine aluminium powder with just enough binder to hold it on the patterns yet come off if your finger rubs the surface, maybe a weak nitrocellulose binder would work.
     
  6. Tobho Mott

    Tobho Mott Gold Banner Member

    Too bad you had to do it twice. I've never yet poured anything that was too heavy to use my handheld crucible tools, but it seems like a good idea to use a trolley like that if you don't have enough hands to use 2-man crucible tools.

    Seems like you've been having a bit of bad luck aiming it in the past couple of videos though. I wonder how that could be avoided?

    Really cool casting though, I like how you molded it, clever.

    Jeff
     
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I like it Ironsides.

    Can you elaborate a little more on the core sand and how you prepped and mixed it? Approximately what was the mesh size of the sand? What mixing method did you use? Did you catalyze the resin before mixing it with the sand or introduce resin and catalyst to the sand separately? How long did it take for the resin/sand to kick?

    Best,
    Kelly
     
    Melterskelter likes this.
  8. Melterskelter

    Melterskelter Gold Banner Member

    Ironsides, thanks for the very instructive video. Beautiful work. And I learn a lot more from videos where things don’t go perfectly than from those where everything progresses without a hitch. This is especially true when the cause of the problem is discussed and adjustments are made to overcome whatever the hangup was the first go-around.
     
  9. Ironsides

    Ironsides Silver

    Mark

    I have rapped the pattern in the past but what happens is rapping causes tiny cracks in the core sand because it has no strength then molten cast iron seeps into those cracks. The next time I use that resin I will rub the pattern with graphite.

    Jeff

    Both those videos were the same pour. The very first pour was the impellor pour. That is why I was so cross because I knew I had make another mold of the impellor.

    Kelly

    No idea on sand grain size but the sand is weighed then resin and hardener are added. Two parts resin to one part hardener. I use a small plastic tub and mix with a plastic spatula. The second time around I used green sand to speed up molding. If I warm the sand it takes one hour to set but as it takes so long to mix by hand it will take hours to set which is fine by me. The resin and hardener seem to mix very well when the sand is added. If I don't mix it properly it will collapse when the pattern is removed.
     
  10. Jason

    Jason Gold

    Ok... everyone throw a buck in the hat, we are going to get 'ol Ironsides a funnel and some new dollar store glasses for Christmas! :D
     
  11. Tobho Mott

    Tobho Mott Gold Banner Member

    Same pour, makes sense - the similar (actually identical) way the iron dripped out from below the mold weight in the two videos was what made me think to ask! :D

    I can see why you'd be annoyed to have to remake such a complicated mold.

    Jeff
     
  12. Ironsides

    Ironsides Silver

    Jason

    Yep, this is what happens when you get older!
     
  13. PatJ

    PatJ Silver

    I just got around to watching the video in-depth.

    That is a nice part and pattern.

    I have used quite a bit of 3-part commercial resin binder, which is the resin, the hardener, and a catalyst (to fine tune the set time), so I will add some comments for comparison with an expoxy binder.
    (This is a bit of a long-winded post, but for those who want to use resin binder, some of this may be relevant, so I will post what I have learned).

    The resin binder has a "set" time, and a "strip" time.
    The set time is when the mold gets hard enough to handle without disfiguring.
    If you handle the mold too soon (before the set time), it will warp and/or sag.

    The strip time is how long you have to pull the patterns out of the sand before they get permanently glued into the mold.
    I found out the hard way about the strip time when I left some patterns in the sand overnight. I ruined half the patterns the next day trying to pull them out of the sand.

    I use OK-85 sand, which I think is at least 100 mesh, perhaps a little finer.
    The sand has to be completely dry, and I think it has to have less than 1/2 of 1% of moisture; in other words the sand has to be baked in the oven if it does not come dry already.

    OK-85 and and resin binder are designed to work with iron and other metals, and they work extremely well with iron.
    You can make the molds very thin, sometimes 0.75" thick in places.
    I generally add spacers in the flask at the corners, etc. to minimize the sand/binder usage (I don't recycle the resin sand).
    Generally I like to keep the thickest part of the mold at 1" maximum. Any thicker than 1" and you are just wasting sand and resin. From a strength standpoint the mold is very rigid once it sets and very strong even at 0.75" thick.

    Since the resin is basically a glue-type material, the patterns have to be waxes (or otherwise coated with something) to allow them to be pulled out of the sand once it sets.
    I wax my patterns every time I use them, just before I ram the sand.
    I don't rap the patterns before the sand sets because as ironsides mentions, you get cracks in the sand, but also one of the benefits of resin sand is that the patterns can be made to a very close tolerance with very little machining tolerance added, and the cast part is very accurate since there is no distortion of the sand from ramming or from rapping on the pattern.
    For small engine parts, this added accuracy is a very nice feature, and it simplifies machining quite a bit since the cast parts are perfectly round and match the pattern exactly, and thus are easy to center in a 3-jaw lathe chuck.
    And I use less draft angle, and sometimes no draft angle at all, and generally don't have a problem removing patterns from bound sand.
    Patterns with at least 3% draft angle do pull from the sand much easier with no danger of damaging the sand, but I have printed 3D patterns and forgot the draft, and for 1/2" thick parts, I could still pull the part from the bound sand.
    And even if the edge of the resin-bound sand does break off a bit (depending on exactly where this occurs), generally this is not a problem, and it typically occurs on an outside edge, which results in just a little more flash that must be ground off.

    The method I use to remove the patterns from the mold is with a small automotive slide hammer.
    A light impact of the hammer will break the pattern out of the mold very nicely and quickly.
    Without the impact, the patterns are very difficult to remove.
    Patterns that are repeatedly used with resin sand are best made from steel or other durable material. Wood patterns tend to wear out from the slide hammer pulls if you use them too much.

    I generally use a catalyst ratio that gives a 15 minute or less set time, since I can generally ram a mold in less time than that, and mixing a batch at a time, ie: the drag sand first, then ramming it, letting it set, and then mixing the cope sand, ramming that against the set drag sand.
    I generally break the pattern/pattern half lose with the slide hammer in the drag before I ram the cope (the pattern does not have to be pulled out of the sand, just barely broken lose), so that only one side of the pattern is stuck in the sand at a time.

    I carve the alignment holes as you did in the drag, but generally only use two.

    Sometimes I include the runner(s), basin, gates, etc. on the molding board with the pattern half, but for one-off items, I use a round rotary wood rasp bit mounted in a cordless drill to carve out runners, basins, sprue holes, etc., and a small saw to cut the gates.

    The very fine OK-85 sand makes for a very good finish on the cast parts, but the combination of fine sand and resin means that the sand is not very permeable, and the time (once) I have forgot to add vent holes at the high points in the cope mold caused large air bubbles, which ruined the part.

    I use a commercial mixer, and the instructions that came with the resin binder mention mixing the resin into the sand first (2.5 minutes), then mix in the hardener and catalyst.
    The hardener and catalyst are pre-mixed together in a cup, and only a small amount of catalyst is needed per part of hardener.
    I have seen a concrete mixer (with the baffles removed) used to mix resin sand, and that works very well too. They uses a couple of window-sash 1/2 weights in the mix.
    A muller could also be used to mix resin sand, but the parts need to be scraped after each use and before the resin sets, to prevent sand build-ups.
    I can mix about 40 lbs of sand per batch, but if more than that amount of sand is needed for a mold-half, then I can stretch out the set time and mix in two or more batches.

    Resin-bound sand makes excellent molds and cores.
    The cores should be vented. I use a 1/4" dowel rod in the center of round cores, and then vent the ends of each core vertically up and out the top of the cope mold.

    I use snap flasks only for resin molds (I never pour with the flask attached to the sand, since I use wood flasks), and I glue the cope mold to the drag mold using a thin layer of furnace cement around the outside joint.
    Generally the thin layer of furnace cement will harden in about 1/2 hour, and allow a pour within that time without using an weights on top of the mold, but I have started adding a few weights on top because I did have one joint fail.

    The resin-binder instructions mention that the molds should be allowed to season for several hours before pouring, but I have never done that, and never had a problem.
    Resin-bound molds can be lightly flamed if there is a concern about them not being fully cured, but I generally don't do that unless it is a very small and critical core piece that cannot be vented.
    Sodium silicate molds can also be lightly flamed to help prevent them from out-gassing.
    If anyone is still reading this, type in "Chatty Cathy" in a comment below.


    The idea of using epoxy for resin is a good one (in my opinion; I have not tried it yet), since epoxy is readily available in small quantities and is somewhat inexpensive (I will have to compare the price to sodium silicate).
    The commercial resin binder requires the use of a good respirator that is designed to remove the chemicals that are in the resin.

    Epoxy does not seem to have nearly the amount of fumes that resin-sand binder does, although a suitable respirator is probably still a good idea.


    So the questions that come to mind are:

    1. What is the absolute minimum amount of epoxy that can be used to make a resin-bound mold? I am assuming the limit is about the 1.5% that you mention in the video.

    2. Can the set time be varied by varying the amount of hardener? (the epoxy system being two parts, resin and hardener, and the commercial resin-binder being a three-part system of resin, hardener and catalyst).
    I am assuming that using more hardener than is recommended (the epoxy I purchased a few years ago used a 1:1 mixture) would reduce the strength of a normal fiberglass part, but since this is a one-time-use mold, then this is probably not a factor; you only need enough strength to hold the sand together for a short period of time.
    The short set times are very handy, and allow for an almost continuous molding process.



    I have been transitioning to sodium silicate for molds, but have not tried them with iron.
    I have had one source mention that sodium silicate will work with iron, and another mention problems with gassing when using sodium silicate with iron (perhaps the gassing was due to the mold not being lightly flamed first?).
    If the sodium silicate does not work for me with iron, I am going to try the epoxy for iron molds, since I am almost out of commercial resin-binder and it is nearly impossible for the little people (like me) to purchase commercial resin-binder.

    The benefit of using bound sand is that you don't need to condition/mull your sand (but you do need to mix the resin into the sand with a mixer).
    The downside of bound sand is that generally it is not worth trying to reuse the sand.
    I am going to try to recycle the sodium silicate sand, and using 3% or less of SS seems to help when you have to break it up, and really helps when breaking out cores.
    The trick with using 3% or less SS is to NOT over-gas it with CO2. Five seconds of CO2 makes a very hard and durable SS mold that will last for months or more. Ten seconds or more of CO2 will make a mold that crumbles before you can use it.
     
    Last edited: Dec 31, 2017
    Jason likes this.
  14. Jason

    Jason Gold

    WOW! Chatty Cathy. :p
     
  15. I'm looking for cheaper alternatives for resin bonded sand too. We get a three component resin from a nearby iron foundry but the product is tuned for their iron casting system and takes 30-45 minutes to cure enough to remove from the pattern. We've tried to speed it up but no real improvements and would prefer a two minute setting time. Watching Olfoundryman's videos has given a few local resin supplier leads I can try in the new year. I'm also thinking of trying an off the shelf two component urethane resin with added cross-linker as the third component. An isocyanate cross linker greatly increases the cure speed and heat resistance of a resin. The isocyanate cross linker has a short shelf life before it reacts with moisture and also with light to break down into water and CO2. I understand it's toxic and can cause asthma and irritation of the eyes and lungs in an occupational exposure environment when exposed to it for long periods of time. It's used a lot for wetsuit glues and belt grinder tape joins as it increases strength, moisture and heat resistance. https://www.glueguru.co.nz/shop/PRODUCT+TYPES/PRIMERS++ACTIVATORS/B050232.html

    Pat is right about the advantages of using resin: it's fast, has a great finish and is strong enough that no flask is needed when pouring. With some changes to the patterns it's great for a small one man foundry to do low run production casting.
     
  16. PatJ

    PatJ Silver

    I always start out with the intent of typing a few comments, and when I finish typing, there is this book.
    Not at all intentional, but that is what comes out.

    Sometimes it gets so long that I have to imbed crazy phrases in the middle of it just to see if anyone actually is reading it all.
    Ah, I see it worked.
     
    Last edited: Dec 31, 2017
  17. Jason

    Jason Gold

    It's all good Pat. Good info, I'm forever learning.
     

  18. That text colour barely shows up on my monitor....I missed it.
     
    Last edited: Dec 31, 2017
  19. Ironsides

    Ironsides Silver

    PatJ

    Here are the answers to your questions

    1. What is the absolute minimum amount of epoxy that can be used to make a resin-bound mold?

    1.5% is the minimum I would use for cores for cast iron. Cores have a tough time in molten iron, they dangle out in the breeze and are mostly surrounded by molten iron. If the complete mold is made from resin then the 1.5% can be lowered a lot because molten iron flows over only one side of the mold. If you are making molds for aluminium castings you could lower it again because it is poured at half the temperature of molten iron. Bronze and brass comes in between the last two metals.

    2. Can the set time be varied by varying the amount of hardener?

    To tell you the honest truth I don’t know if using more hardener will speed up the setting time. When I first saw two part resins in the hardware section of my local supermarket I purchased those twin syringe type dispensers and tried it on some sand at home. It worked really well but I used too much resin, having never tried this before I started with a large amount and then lowered the sand to resin ratio. The resin I used at the time was the 5 minute kind but the sand went hard a little too quickly for my liking. I then changed over to the slower setting resin. So there you go, resin setting times can be changed but you would have to talk to an industrial chemist specializing in adhesives to find out how they speed up the setting time.

    You said that round cores need to vented, watch this video. It shows me using a core made from epoxy resin with no vents. After the casting had cooled down it was machined all over and then cut in half to see if the unvented core made blowholes in the casting.
     
  20. PatJ

    PatJ Silver

    The proof is definitely in the pudding, and you don't seem to have any problems with core venting or venting the high points of the mold.

    I did get some large air bubbles in the high points of a mold I made, but I was using 100% resin sand and aluminum, not iron, so perhaps the difference is the density of iron forces the air out through the (green) sand, or perhaps making the entire mold from resin-sand makes it less porous.

    I like to err on the side of more venting than I need since it is a bit of a pain to remake a resin-sand mold, and the sand and resin material is wasted if the pour does not go right the first time, and I did ruin a very nice engine base casting with trapped air at the high points of an all-resin mold (no core).

    That is a great video with lots of useful information; thanks much for that.

    I hate seeing that beautiful cylinder cut in half like that, but good that you made extras, and it is good to see verification of a solid casting with no chill.

    Good iron castings for me have been so rare that I would never section one, but perhaps this will be the year of iron for me.
    I need an iron breakthrough, and I am banking on the new furnace delivering for me.

    I have seen porositymaster break a few myths too.
    Last November (2017), he used the dirtiest scrap iron, some of which had perhaps 1/4" thick rust and scale on it, and I asked him about cleaning the metal before melting it, and he said "It is not necessary", and indeed he was correct, he poured the cleanest iron I have seen anywhere using the worst looking scrap iron I have ever seen (some of it looked like it had been in a bucket of water for 20 years).
    So much for wasting time cleaning iron scrap (what I use to do).


    I am formally declaring 2018 "The Year of Iron".
    Gentlemen, get your iron furnaces ready; this year we master iron.
     

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