Supporting > Casting
Casting Gray Iron
Dick Morris:
Thanks for writing this up. It was very interesting. Having cast aluminum and bronze, this looks very doable.
Jasonb:
--- Quote from: Alyn Foundry on July 14, 2024, 12:18:25 PM ---
We made several engine kits before deciding it was too labour intensive to carry on, as we were all in full time employment. Today, my kit lies idle. The advent of CAD and the 3D printer have rendered the Aluminium master pattern redundant.
:cheers: Graham.
--- End quote ---
That is assumming the person wanting the patterns can use CAD, there are many that have no idea how to produce a 3D model of a pattern and for those owning a 3D printer is limited to printing downloaded toys from the net. Unless they can get someone to do the CAD work for them then traditional methods may be all they can use.
When it comes to master patterns as opposed to the one off home casting there is still a need because the 3D printed pattern is not durable enough, think of the Nattie Flywheel pattern for example due to it's thin spokes I did not even want to make that from wood, a plastic print would be even weaker. An alternative to aluminium are the modern 2 part resins where a 3D print could be used to make a mould and then PU resin patterns cast from that which can be bonded to a match board, often several cast patterns of the same part on one board.
CI:
I have had some 3D printed patterns break up, especially the ones with thin infill and walls.
I use a small automotive slide hammer to pull patterns from bound sand, and if you don't exceed the strip time, then the adhesive bond between the sand mold and the pattern can be broken with a light tap of the hammer.
I forgot to pull the patterns one time, and left them in the mold overnight.
The patterns were effectively glued into the bound sand mold.
I damaged most of the patterns trying to get them out of the sand that time; destroying about half the patterns.
I have seen the resin pattern casting material, and hard resin master patterns that can be cast from that mold.
I am not really keen in stocking more resin material though, since it will have a finite shelf life.
Since I am set up to melt alumium, and have quite a few 256 ingots, it would make sense for me to cast permanent patterns, such as for the Ball Hopper Monitor.
Aluminum is easy to melt and pour, since the temperatures involved are so low compared to iron.
With cast aluminum permanent patterns, you can always use JB weld to touch up any bad spots, or to add a bit here or there to the pattern.
And you can epoxy additional pieces onto a cast aluminum pattern; I have seen that, where sometimes adjustments must be made after the pieces are adhered to the matchplate.
I am not a fan of matchplates, since they are really not required with bound sand.
I did use some matchplate arrangements for the green twin engine, and that did work well.
It is very easy to add runners, gates, risers, etc. to bound sand after it has set.
If there was a production run, it would pay to create matchplates.
Edit:
One advantage of the poured resin product to create hard plastic permanent patterns is that the resin will exactly mimic the smooth surface of the pattern.
With a permanent cast aluminum pattern, ceramic mold coat will help get a very smooth surface finish, but the aluminum casting will still probably need to be buffed out with a fine ceramic buffing disk.
I am not sure how stable the hard plastic permanent patterns would be, but I would think they would last a long time, and would never oxidize.
.
bent:
Very cool writeup CastIron, thanks! :DrinkPint:
I am in the process of retiring (currently working half time and training a new hire to take over) from being the valve design engineer at my company, where I've been designing bronze and ductile iron castings for production, and then lately forged brass valve bodies too. I've had the privilege of watching a large foundry here in Washington state operate their jolt-squeeze molding machine and pour our valve castings in ductile iron. I'm always a bit in awe of real foundrymen, there is a lot of art as well as science to the trade. We were lucky that for a time, their foundry business was slow, and so for a few years we had them use our parts as fill-in work for their production line. Then, they got busy with their in-house products again, and we were politely asked to take our products elsewhere.
:-\
our local foundry:
https://www.romac.com/foundry
Mcgyver:
Good stuff! Thanks for posting it.
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