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| Green sand molding methods |
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| vtsteam:
--- Quote from: ironman on April 12, 2013, 02:23:05 AM ---A very cheap alternative is portland cement for cores and molds. Use about 8-10 % cement and about 4% water then wait for 3-5 days to set. --- End quote --- Thanks Ironman, I'm going to have to try that! I'd been using molasses water and wheat wallpaper paste and baking them. But the baking part is tough to arrange with SWMBO, and energy wasteful unless you have a lot of cores -- I don't usually. I guess the cement just calcifies at high temp. Does it work for aluminum castings , too, or just iron? |
| ironman:
vtsteam It works with both and I use coal dust in cores for iron castings. awemawson I did purchase sodium silicate with molasses mixed in and found it caused blowholes when used as cores. The sodium silicate I purchased before and after the molasses batch never gave any problems with blowholes in cores. It has to be purchased from a foundry supplier which are not friendly to backyard casters so now I experiment glues or binders that can be purchased from my local hardware shop. |
| doubleboost:
This method works for me I have bought some sodium silicate but not used it yet John |
| vtsteam:
--- Quote from: ironman on April 12, 2013, 02:23:05 AM ---Meldonmech A long time ago I used Co2 cores but lost interest because of cost and very poor post casting breakdown. A very cheap alternative is portland cement for cores and molds. Use about 8-10 % cement and about 4% water then wait for 3-5 days to set. --- End quote --- Ironman, I'm about to make some cores following your recipe -- just wondered, are your mixing proportions by weight, or volume? Also same question for your greensand mix given on Youtube for iron casting -- weight or volume? (I'm also thinking about making a power muller similar to yours in the video. I think I have a similar big cast roller in my scrap pile) Thanks! |
| vtsteam:
Update on the above -- I was impatient to try it, so I thoroughly dried out some sand -- spread out on a board in the sun, weighed it and added 9% by weight Portland cement and 4% by weight water. I then tried to extrude a 5/8" x 5" cylindrical core using a piece of PVC pipe split on one side as a core box and the slit closed up with two hose clamps, per Doubleboost's video. I used a 1/2' dowel to ram the mix, and to act as a plunger when trying to push out the core after the clamps were released. I had little luck -- if I rammed it hard it wouldn't extrude at all. If I rammed lightly and it did extrude, it had no wet strength and crumbled to bits. I played around with more water and cement, and got a little better wet strength, and I widened the slit in the pipe with a hand saw which made extruding a little more likely -- but still was unable to get a single solid core. I suppose I could widen the slit further -- the only problem with that is, the clamps make the finished core diameter smaller in inverse proportion to the size of the slit -- the bigger the slit, the smaller the core. I wanted one about 5/8" -- which is just about exactly what you get from a 1/2" nominal water pipe here. So, questions: I'm wondering if the mix recipe assumed damp, instead of thoroughly dry, sand (which would have increased the proportion of both water and Portland cement). Or was based on volume instead of weight? Also whether this type of core actually needs to come out of a mold before curing? Maybe extruding is the wrong idea. Since it is Portland cement based, it can cure in an enclosed space -- so maybe that's what ironman does.... ? |
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