Close enough.....just go with it. You may already intend to do so, but I would extend the runner to and slightly past bottom of th epattern and that last saddle, even if it further changes the area you mention. You can just glue on the extensioss. The feed system doesnt have to be one piece. I piece them together all the time. Since there is no radius where the runner necks down, I'd just make sure you get good coverage in that corner where the metal must turn. If you have sharp corners it can sometimes get a little sand wash. Otherwise looks pretty good. Take a look at the bonded sand cup Koen made. It looks like a pretty good way to go for you. https://forums.thehomefoundry.org/i...d-for-a-mercedes-om603.2735/page-2#post-52859 How the thick sections in the pattern will fill and freeze is the only concern compared to my typical castings, but I have been amazed at how well lost foam has tolerated such in similar instances for me and avoided shrink defects where convetional sand casting may not have produced such a result. Did you pour the cassette? Best, Kelly
I haven’t cast anything yet as I want to go to the foundry well prepared, use as little of there time as possible and appear well organised and professional to maximise the chances of repeat business. I still need to: extend the runners to the bottom of the pattern (I wasn’t going to but I will after your suggestion), make a pouring basin and coat the pattern. Once this is done it should be go time, I should dry out an extra 40kg of sand to take with me as well. I do have the scrap cassette pattern that lacks the 3mm radius fillets. I could use this for a test pour at work using my steel crucible, unknown aluminium and trying out a pouring basin, I’ll have to make one from fire cement or the like.
Practice can only help. The more massive and conductive the cup material, the more heat it will steal from the melt.....especially the early part of the pour. Best, Kelly
It's probably a statement of the obvious, but don't plan on multiple pours using the same molding sand without allowing it thouroughly cool between sessions. Depending upon ambient temp, I spread the sand thin on my concrete driveway and usually takes 1-2 hours for sufficient coolong for reuse. Warm/hot sand will distort/destroy your pattern. Are you going to mold the pattern at the foundry or bring it already molded? Best, Kelly
They are curious about the moulding process so I will do that on site. I can spend all day there if I want. I’ve had a go at making a basin with some sodium silicate sand cured with co2. Maybe I’m not doing it right but it is still a bit crumbly in spots. I’ll cure this in the oven at work tomorrow. Maybe the co2 soak wasn’t long enough.
I had another read and maybe my SS is too dilute. So I went from 5-6% Upto 11% I also only gassed with a lance for 7-10 seconds about every 2-3 inches. It seems far less crumbly.
Just need to experiment until you get the strength you need. Very dependent upon SS grade and grain size. If your CO2 is welding gas 75/25%, that can require greater exposure cure time. If you are post curing, I wouldn’t think you’d have any problem with the higher SS %. what’s the cup volume? Best, Kelly
Since you don't have to worry about Cleaning that sand out of a complicated Core you can go heavy on the Sodium Silicate with no real downside (If you use welding gas I recommend baking the core/mold afterward to make sure all the SS is catalyzed.) On a few parts where I made the mold out of SS bonded sand.... I did the old "That looks about right" method. Worked just fine. Admittedly it took hammer blows to get the mold apart after casting. But it held up to the pour just fine. I would never use that method with a core that I needed to remove easily
With an unknown sodium silicate, getting the sand to silicate ratio right is guess work and experimentation. I use a silicate available from a local pottery supply place, for my first attempt, I used a 5% ratio, that resulted in a somewhat weak core, I upped the ratio to 6% and that was my sweet spot, the core was strong enough to do its job but weak enough to break out of the casting with ease. This video is of my 3rd attempt at a core, it was used in a successful casting of an intake manifold for a VW.
Thanks for the replies, if I remember correctly the basin will hold 1.6 or so kg of aluminium. I also have no frame of reference how hard the sodium silicate is meant to be prior to baking, it feels harder in some spots than others and can still crumble around the edges. My welding gas is 100% CO2. Cheaper to fill up. I baked the core today but it is still at work so I will let you know how I get on with it as I haven’t handled it since it was too hot. I’m thinking it might be good to fold up a small steel box that permanently encapsulates the SS sand so it is easy to remove from the sprue without damaging it. That’ll be a job for next time though as all this is just an experiment before the important pour. I was watching ‘Engine Taro’ on YouTube, if you’re not familiar he lost foam casts motorcycle parts as well. He uses terracotta pots for his pours but they always crack, I was getting tempted down this path (out of sheer impatience). I’m sure the sodium silicate will turn out much better.
I was not aware of Engine Taro, I'm not sure whether to thank you or curse you, I hadn't planned on spending all morning and part of the afternoon watching his "make your own DOHC head" series. He does really amazing work and it's a fascinating watch so I think I'll go with Thank You.
I don’t think the cracking would be a problem for single use but am not a fan of their mass or shape. I’ve seen his videos. I would have tried to tip him off to the tolerance stack up on his stacked fin approach. Been there done that. There are ways to minimize it. http://forums.thehomefoundry.org/index.php?threads/motorcycle-cylinder-sample.1521/ His pattern work is meticulous but I think he could get much better as machined finishes on his patterns with better cutters, speed/feed and pattern stock. I use wax too but very sparingly and he is right to be concerned about the additional pattern mass to evaporate. His DOHC head turned out well and I wish him success on his 4 cyl 125cc. Best, Kelly
Post bake I’ve found that the basin is hard in some parts and has some small soft spots, probably due to not enough gas coverage, it’ll still work for a pour. I might try some small scale experiments, probably what I should have done in the beginning. I was probably a bit too eager.
If you are just blowing CO2 from the surface with your mig torch that isn’t enough penetration. You need a needle/lance that you can insert into the sand or a way to force the CO2 to flow through the sand like a simple sealing cap for the mold like shown at the end of rocco's video. Best, Kelly
Hi, I've made two hasty movies ( with one hand) to show you how I make the cups. 4% sodiumsilicate and with silica sand ... The gas is carbonic acid... After taking out the styrofaom I give the inside a blast too ... Hope this helps Best, Koen
Thank you, I might give your gassing technique a try if I end up doing another sand basin. I’ve been pretty bogged with work/life things and haven’t had a chance to pour anything yet. Although I did order some ceramic fibre board and an adhesive suited for 1200c. So now I will test the sand pouring basin and the ceramic one at the same time. Hopefully next week I can get into the workshop after hours and get my patterns set up for the testing. I’ll post the results.
I finally tested out the poring basin. The pour turned out almost perfect, I poured using an alloy wheel at 720c. I’ll make some more sand pouring basins and get the rest of the parts poured at the foundry. There were a few tiny leakers, could this be attributed to my low quality refractory?
Nice! Leakers are usually from low sand compression. The coating is to keep the sand from imprinting on the casting.
You're soft spots in the basin after baking were most likely due to not mixing the SS and sand enough. Baking replaces the need to gas (I do both together when using welding gas 75-25). You really need to mix the SS into the sand. I wear a pair of rubber gloves and treat it like it's cookie dough.
