It has been about 20 years since John Campbell published his first book on casting, yet I rarely see examples of his guidance being applied.
Here is an example of
casting the John Campbell way. Only worth watching the firs half.
I have John Campbell's book, which contains the 10 rules for good castings.
There are John Campbell believers/followers, and John Campbell's detractors.
However you feel about Campbell, I feel his 10 rules are important to making consistently high quality castings.
One summary of the 10 rules is here:
http://pmt.usp.br/ACADEMIC/martoran/NotasFundicao/JOM-CampbellRules.pdf
and another link here: (click on the NEXT link on the lower left side to go to the next rule)
http://www.atlasfdry.com/10rules.htm
As with all things foundry, I use a hybrid of rules.
1. Many use a pour basin; I do not; I pour right down the sprue, while keeping the sprue as short as possible.
Sometimes I use a ring of steel sitting on top of the mold, but it is not what I consider a pour basin, but rather a spill container.
I don't try to keep the ring of steel full, but rather focus on keeping the sprue full.
I keep the lip of the crucible as close to the sprue opening as possible, sometimes resting the lip of the crucible on the top of the mold (you can do this with bound sand).
Pours are not linear, and you have to be able to quickly adjust the pour rate during the pour.
Typically the flow is fast as you are filling the runners, and then slows as the gates begin to regulate the metal flow.
I often see folks spill metal all over the side of the flask when the runner(s) get full, but that can be anticipated and minimized; you don't have to spill any metal while pouring a mold.
2. I keep the sprue and runner about the same size (sometimes I oversize the runners), and try to make a smooth transition from vertical sprue to horizontal runner(s).
3. I use a spin basin at the end of each runner, with the runner entering the spin basin on the tangent.
My spin basins open to the top of the mold. The spin basin(s) stop the bounce wave that occurs with dead end runners. The bounce can eject metal through the gates in a sudden spray, which is undesirable.
4. I use gates at the top of the runner(s), with both the gates and runner(s) typically located in the drag or bottom half of the mold.
5. I initially pour quickly to fill the sprue, and then be sure to keep the sprue full at all times during the pour.
If you pause slightly during a pour and interrupt the pour, you will probably have a cold joint in the casting where the fill was interrupted and then restarted.
6. I don't use tapered runners.
7. The mold does not begin to fill until the entire runner system is full, and any impurities in the mold such as loose sand are swept into the spin cavity, along with theoretically any floating slag, and air-entrained metal caused by the turbulence of filling the sprue.
8. The gates control the flow into the mold cavity, and the gates tend to scrap any slag from the metal flowing down the runner (another reason to put the gates at the top of the runners).
The gates should be sized to allow a complete mold fill at pour temperature with the sprue/runner/gate size you select.
The gates should be sized to reduce the metal velocity to obtain a fill that is free of turbulence.
I often fill the mold cavity upwards, and use the gates at the bottom of the mold cavity (one of John's rules I think, don't waterfall into the mold cavity).
Molds will fill upward. With bound sand, you need small vent holes at the high points in the cope, else you will trap air.
And cores should have vents in them/through them, with the ends of the core vented out the top of the mold.
9. I use smooth curves and transitions in the runners. No sharp corners.
I often oversize the runners a bit to get a really hot flow of metal running down the mold before metal begins to fill the mold cavity.
Some folks do not use runners at all, but rather feed directly into the mold cavity from the sprue. I think this is asking for problems.
10. High velocity and turbulence are two things to avoid when metal casting.
11. I use risers in strategic locations when I feel like there may be shrinkage in the part.
Keeping the ferrosilicon to a bare minimum keeps shrinkage to a bare minimum.
12. I keep the iron castings in the mold overnight, until they cool naturally.
Pulling iron castings out of the mold when they are hot can make the metal very difficult to machine.
13. Another of John's rules concerns keeping the thickness of the part even if possible (old castings generally have a consistent thickness).
If the casting has thick and thin sections, then the thin sections will solidify first, and then draw from the thick sections, which can cause hot tears.
14. Sharp corners should be avoided in castings/patterns.
Sharp corners often set up high stress points, which can turn into cracks/points of failure.
The methods above work well for me, and after I adopted them (after reading John's book) have provided very consistent and high quality iron castings that are easily machinable.
Everyone has their own sprue/runner/gate/riser layout favorite methods, and there is no one exact method that works universally.
If you come up with your own system, and it consistently produces high quality castings, then it really does not matter too much what that system is.
Generally speaking though, I think if you are producing high quality castings, chances are you are following many if not all of the 10 rules, and perhaps a few of your own.
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