Breaking all the rules.

Discussion in 'Sand Casting' started by Ironsides, Feb 24, 2019.

  1. Ironsides

    Ironsides Silver

    There has been a lot discussion here about spue and gating design.

    Have look at this video

    1. He does not use a tapered sprue

    2. He does not use a pouring basin.

    3. He uses a very high sprue extender.

    His castings turn out really great so he must be doing something right.
     
  2. Petee716

    Petee716 Gold Banner Member

    You can't argue with success. He indeed broke most of the rules and ended up with nice castings. Having the runner in the cope was one that stood out to me but it made his pattern and the molding procedure much simpler for him so I guess it was worth the trade off (assuming it worked the first time). I don't know that the riser was even necessary either.
    There has been some highly specific advise given here recently. It makes sense to take heed of it, but for most of our purposes I doubt following it to the letter would make a lot of difference to most of us.
    I will say for certain though that if I rammed my molds out in the yard I would run out of sand very quickly!

    Pete
     
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Those are some sexy handles and plywood but can't say I think much of his joinery........butt joints and screws parallel to the planes of the laminate? Tisc-tisc.

    Best,
    Kelly
     
  4. PatJ

    PatJ Silver

    For me, aluminum has been one of the most forgiving metals to pour, and when use the correct pour temperature, then I seldom have problems.
    I did overheat one melt, and got a lot of gas pinholes, but I have never had shrinkage or hot tear problems with aluminum castings no matter what I did, and not matter the sprue/runner/gate configuration.
    I did get several large gas bubbles in a casting when I forgot to vent the high points of the cope, with aluminum.

    Brass/bronze, and iron don't seem to be so forgiving, but in the past I have still gotten away with a lot as far as not following any standard with iron.

    I think one of the reasons that the sprue/runners/gates/risers are not as critical for what we do is that the parts are thin, an so the solidification process is relatively rapid, and the chances of shinkage and tears is small.

    As the parts get larger and thicker, it becomes more critical to get at least the riser correct, and I have heard of several iron guys getting hot tears with iron due to the wrong shape of a riser, or the wrong location of a riser, or a feeder solidifying before the riser, etc.

    Most of the work we do is akin to jewelry work, where you have a tiny little mold cavity, and you basically slap the metal into, with nearly instant solidification.

    Porositymaster was having some hot-tear issues on some larger pieces in iron, and he found it very difficult to resolve, but I think he did get it worked out.
    For a solid casting that will not be x-rayed or used structurally, I think shrinkage is the only thing to worry about, and nothing else matters if the mold fills completely and you don't have gassing or a lot of trash in the melt.

    For structural parts of higher thickness/mass, or pressure-tight castings, the bi-film theory needs to be considered, else you may churn up a lot of unwanted oxides into the melt.

    For the drawer pulls, I would guess that the central runner that he is using is acting like a large riser, since it is oversized to the extreme.
    The gating looks pretty good, but I think the gates are also very much oversized.
    Having the sprue at the end of a long runner can be problematic, and in the past with iron, I have had the melt go cold before it reaches the far end of the runner, so I would have used a central sprue.
    He also uses quite a lot of metal filling the runner, and could use less melt metal and perhaps a smaller crucible with a correctly sized runner.

    So yes, you can deviate quite a bit away from standard sprue/runner/gate/riser practices and still have a good casting.
    The key is to not violate one of the major rules of casting, such as an interrupted pour, a pour that aspirates a lot of air into the melt, sand that is not rammed tight enough and erodes when the metal touches it, overheated or underheated melt, gas in the melt.
    He just happens to avoid shrinkage not by design, but by accident with the oversized runner.

    For me, its about finding some base set of equations or guidelines for castings that are up to a maximum of perhaps 100 lbs, and finding out what works (in iron for me), and then trying to adhere to that setup as much as possible.
    If I can get close with a standard setup, then I can tweek things if necessary and hopefully make corrections with minor changes to the layout if I have problems.
    The idea is to get some predictability to the arrangements, with consistent results from one casting to another, and also to use the minimum amount of metal/fuel for each casting.

    To me, there is a big difference between what you can get away with, and what is close to an optimal layout. Proving you can deviate a great deal from an optimal arrangement proves nothing in my opinion, other than the fact that you can have very sub-optimal layouts that still work, while casting in a very inefficient manner.
    You can turn the mixture screw on a carburetor (for cars when they had that), and the car will still appear to run fine, but the engine may build up carbon deposits, and the cylinders may get washed with excess fuel, the spark plugs may foul up quickly, excessive fuel usage, etc, etc., and so what is the point of not adjusting your carburetor as it should be to run optimally? The only thing you have proven is that you don't understand how to adjust a carburetor.

    So I guess everyone in the hobby has to decide what level they take it too because as the video shows, many layouts will work.
    For those who have production runs, or want to have arrangements that could possibly be used for production runs in the future, I think it would pay dividends to understand the process as much as possible, because the idea is minimal fuel usage, minimum melt requirements, and maximum consistent quality with repeatability.
    You can ignore many things and get away from ideal conditions, and still have good castings, but you are not operating under ideal/most economical conditions.

    Just a few things that come to mind when looking at his video.

    .
     
    Last edited: Aug 23, 2019
  5. DavidF

    DavidF Administrator Staff Member Banner Member

    You know, you could pour 10 perfect castings and someone is bound to come along and say that's not how you do it
     
  6. PatJ

    PatJ Silver

    I think it is a matter of what works for the individual, and to some extent whether you are doing one-off castings, or trying to make 100 of each.
    It is surprising how much you can get away with and still get good castings.

    Edit:
    If you look at logical fallacies, you don't want to fall into the "hasty generalization" thing with castings, or perhaps "irrelevant conclusions".
    There are any number of examples of Rube Goldberg machines online that work very well.
    The mistake you don't want to make are the following fallacies:

    1. Rube Goldberg devices work well, and so Rube Goldberg designs must be as good as any other design.
    2. Rube Goldberg devices work well, and so there is really no need to design things differently, since Rube Goldberg proves that the actual design is not really important.

    Proving that Rube Goldberg devices work well simply proves that Rube Goldberg devices can work well, but it does not address the question "Is there a better method?".

    If you are happy with the methods that you are using and the results, then by all means stick with those regardless.
    If you are interesting in advancing your foundry knowledge, then dig a little deeper and try to reach a more in-depth understanding of what is going on, and perhaps try to optimize things.
    In the end, you only have to make one person happy (yourself).
    .
     
    Last edited: Feb 25, 2019
  7. Ironsides

    Ironsides Silver

    I think PatJ was right, those drawer pulls turned out great in the video but a structural/pressure casting can be a much more demanding casting to produce. Why do I say this? because a lot of my early efforts to pour pressure castings would not hold pressure.

    I chose to pour a pressure casting because it is similar to a structural casting, there are a lot of forces pushing and pulling to make it fail if it is not strong enough. A pressure casting needs only one gauge to measure stress all over the casting.

    So a straight sprue was used without a pouring basin and was not kept full during the pour. No air vents were used in the green sand mold and no vents in the resin sand core. The casting was pressure tested and was cut in half to see if I had churned some oxides into the casting and to see if it looked like Swiss cheese.

    I would like say, be careful when pressure testing castings. A lot of the castings I have tested were small bronze steam fittings. So I tried a large iron casting compared to the steam fittings. When it failed it did not fail in the way smaller castings do. It stretched a lot before it failed and opened a large crack. All the smaller castings don’t stretch much and will open a very small crack and will release all the pressure. This large iron casting was 7.6 times the volume of the casting I tested in the video but the same wall thickness. So I found out the hard way that cast iron stretches before it fails. Pumping an insane amount of pressure and thinking that it will fail in the same way as smaller castings do, I learnt a valuable lesson in physics.


     
    PatJ, joe yard, _Jason and 3 others like this.
  8. Chazza

    Chazza Silver

    Well I have been using much the same technique since 1978 and most of my castings have worked first time and I was taught by a pattern maker/ moulder tradesman.

    I usually use a tapered sprue, for no other reason than that it saves moulding time, rather cutting the sprue later as in the video.

    I don't know what a pouring basin is and have never needed one when pouring aluminium.

    In Australia the "sprue extender" is called a bush and is used to make pouring easier and to get a good head of metal pushing the melt into the mould.

    If I was tasked with the same job as in the video, I would not have used an out-gate and neither would I have had feeders along the sides. I think pouring straight into the desired shape would have worked; maybe a feeder in some places may have been needed,

    Cheers Charlie
     
  9. PatJ

    PatJ Silver

    That is one tough (and water tight) casting.
    3,000 psi !!!!
    Holy mother of gosh, I was sweating bullets as that gauge when up and up.
    I was fully expecting one of those "looks like we are going to need another Timmy (another ironsides)" moments.
     
  10. Ironsides

    Ironsides Silver

    I can really relate to the timmy video clip. There is never a dull moment in ironsides foundry.
     
    _Jason likes this.

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