Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines
Builds, Repairs, Show Your Machines! => Technical Tips, Builds, and Help => Topic started by: PatJ on November 03, 2020, 10:55:17 pm
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Thanks for sharing your knowledge! Know it is appreciated.
Len.
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Thanks much.
I hope to rope some more folks into making their own engines/castings some day, and thus the article of how to do that.
Pat J
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Congratulations on making it into Live Steam...!!!
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I finally got published in Live Steam.
What an incredible amount of work that was.
The most difficult thing was that so much of what I did was for the first time, and I was not set up to do much of that work at the beginning, such as not having a foundry, not being set up to take good photos in a light booth, not knowing how to set up the camera, not having good machining skills, etc.
I was not really sure about how to write the article, or whether the focus should be on the foundry work, or the machining work.
It was like plowing frozen ground, but I finally got it done.
It just goes to show what you can make if you keep at it.
If I were to do another article, I would have a much better idea of how to go about doing it.
Disclaimer:
I did not receive any compensation from Live Steam for this article, and it is not meant to be an advertisement.
The article was provided to Live Steam for free, and the intent was to advance the state of the art of model steam engine design.
I am in this hobby because I like to build steam engines, and my motivations are as simple as that.
I have always been a big fan of Live Steam Magazine, as was my dad who built numerous models after being inspired by Live Steam, so this is my way of giving back to them for publishing so many great steam engine build articles.
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What an interesting thread, thank you.
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Interesting reading, I have fond memories of my father melting aluminium scrap in tin cans with a carbon arc torch and then turning that chunk of metal on his lathe.
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An excellent thread. 👏👏👏👏👏
A lot of lessons learned.
Sadly, the videos won’t load. Message says you closed your YouTube Account.
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Thank you for this very honest and educative writeup, really enjoyed the read.
Am certain this will save some newbies (like myself) from quite a few bumps while raising a casting skill :)
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After several attempts at casting parts, I visited the nearby Metal Museum located in Memphis, Tennessee, and they have foundry there.
I was very glad to meet these wonderful folks, and they filled me in on many of the do's and don'ts of metal casting, as well as showing me how to make bound sand molds.
This was a golden opportunity for me to learn how metal castings should be made, in order to get high quality castings, and this knowledge solved many of the problems I was having.
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Here is the video for the flywheel above.
Another example of me just blindly stumbling through the process, and getting just lucky enough to get a good flywheel casting.
Many of the other parts in this mold where thinner, and they were hard like tool steel, and a power hacksaw had no effect on them, other than to remove all the teeth from the blade.
Luckily the flywheel was thick enough that it did not have any hard spots in it.
https://vimeo.com/user82094693 (https://vimeo.com/user82094693)
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Melting aluminum can be a rather casual affair, and a steel crucible can be used, a temporary brick furnace, a rudimentary burner, propane, and the burner does not have to be fine tuned in order to get aluminum to pour temperature.
Almost anyone can melt and pour aluminum, although it is a step up from pouring the lower temperature metals such as lead-free pewter or similar metals that pour at perhaps 450 F ?
Many people use aluminum extrusions, and aluminum cans, and neither of these are very good for engine castings.
The best aluminum to use for casting engine parts is alloy 356, which is generally the material used for auto engine blocks, and aluminum auto rims.
To melt iron, it is easiest to use an oil burner, and forced combustion air is required.
And the burner has to be adjusted somewhat accurately in order to get iron to pour temperature, which is perhaps 2500-2600 F.
I was able to cast a second flywheel in gray iron, but I did not understand the iron casting process, or the correct burner settings, and was having great difficulty, and so after this second flywheel in iron, I cast the remaining parts for the green twin oscillator in aluminum 356.
At the time I made this flywheel casting, I was not sure if I would ever be able to make another casting of this quality.
I had a poor understanding of the entire casting process, especially the iron casting process.
I now cast iron routinely, and all my final engine parts are in gray iron.
I still cast permanent patterns in 356 aluminum sometimes, when I intend to cast multiple pieces, and want a more durable pattern.
This second flywheel turned out with no defects, and I was very proud of this.
I sent this flywheel off to my Canadian buddy for him to use on his green (he painted his engine gray) twin oscillator.
It took several more years of experimentation in order to find the correct burner setting in order to get consistent and high quality iron castings.
And I had to change to a bound commercial sand mold in order to get the quality I wanted.
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The video of the above iron pour is located here:
I had rather a critical mass of junk in the driveway at the time, and such a clutter.
I have since cleaned things up, and I highly recommend not trying to cast metal in a cluttered area, and never pour molten metal in lace-up shoes like you see me wearing in this video.
I am lucky to still have toes ! Yikes, the dumb mistakes I made in the beginning.
I suspect that the iron I poured that day was at about 2500 F.
Iron-rated pyrometers are extremely expensive, and so I don't use one, and luckily you don't really need one with iron.
https://vimeo.com/478658289 (https://vimeo.com/478658289)
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This was my first attempt at an iron pour, and I learned lessons #5 (don't pour iron into petrobond, although some folks successfully do this), and lesson #6, don't open the mold soon after pouring iron into it, because a cloud of smoke will rise up out of the sand, and will combust, and burn all the hair off of your face, and potentially blind you.
I was not wearing a face mask when I broke this mold open, since I assumed the dangerous part was over, and so I was met with a ball of fire in the face.
I saw it coming, and closed my eyes, but burned off some of my eyebrows.
My wife yelled "What the heck just happen? Where did all that smoke come from?".
"Just a minor scratch" I yelled back (I always say that regardless of the injury; its a marital thing).
The petrobond began to fail as the iron filled the mold, and so I had some sand inclusions in the rim.
I did not know if I would ever succeed with another iron casting, so I decided to repair the flywheel and use it, and it is the flywheel that is seen in my final green twin oscillator engine photo. I turned the flywheel to hide the repair, and the repair did not affect the flywheel structurally.
So I succeeded with my first attempt at an iron casting, and not because I understood how to cast gray iron, but more through luck and chance.
Casting gray iron involves some procedures that are not necessary with aluminum, and so it can be tricky to cast if you are not aware of exactly what to do, and when to do it.
Luckily the casting turned out to be easily machinable with no hard spots, in spite of me not using ferrosilicon additive, which I was not aware of at the time.
For iron castings that are thinner than this piece, using ferrosilicon is a must to prevent the iron from becoming very hard like tool steel.
So I lucked out and got a usable iron casting on the first try.
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Another attempt at a flywheel in aluminum 356.
Lots of flashing on this one, not sure exactly why the fit was so poor between the mold halves.
Not really what I would consider a usable casting.
I was using an excessively tall sprue, which is the vertical hole into which you pour the metal.
Live and learn.
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My Petrobond (this is a tradename for an oil-based foundry sand) was beginning to dry out, and so I made the mistake of adding oil to it.
This ruined my sand, and ruined the casting also.
Lesson #5: Don't add oil to your petrobond. Add alcohol.
So I was just stumbling along, learning as I went.
I was getting close to creating usable parts, but still experiencing lots of blunders, and it seemed like I may be up against an infinite learning curve.
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My next attempt was another engine base, and this time I poured a little too cold, probably around 1340F, and should have been at more like 1350F.
The cooler the pour, the better the surface finish, but the metal must be hot enough to completely fill the mold cavity before it begins solidifying.
I think this defect is called a "cold shut"?
I call it a partial mold fill.
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My next casting was a demonstration for my brother's friend, and I learned lesson #4, which was use different size pins on either side of the flask.
The flask consists of the upper section called the cope, which is just an open box, and a lower section called a drag, which is also just an open box.
I made the drag mold, then made the cope mold, separated the mold halves, removed the pattern, and then unintentionally rotated the cope 180 degrees when I put it back on top of the cope.
Lesson learned again.
Trial by fire as they say.
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My next aluminum casting was a frame for a small engine that my dad once contructed.
I made a 3D model of the frame, printed it, and then filled it with spackling compound, with a final coat of paint.
The casting turned out pretty well, with a few sand inclusions at the top of the piece.
I never built this engine; it was just a proof of concept of 3D printing my own pattern, filling it to make it a bit more convex, and then casting it.
Again I had no idea about more generally used runners, gating, risers, etc., and so was just forging ahead in a trial-and-error fashion.
My machining skills at this time were about like my casting skills; ie: very poor.
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My next casting used a core, and the sand I used for the core was sandblasting sand that was adhered using a sodium silicate binder.
I thought the sandblasting sand would be sufficiently fine, but it turned out to be rather coarse material.
I did not know that the top of the flask had to be weighted, and so the mold halves separated, and the aluminum 356 partially ran out.
Lesson #2: Add weights on top of the flask before pouring metal.
Lesson #3: I made the pattern for this casting out of thin balsa wood, and that turned out to be a mistake because after several uses, the pattern broke into numerous pieces. Don't make patterns from balsa wood unless they will be a one-time use application.
And although the core remained in place pretty well, but was not mechanically fixed in position in the mold, so it probably shifted a bit during the pour.
The top of the casting turned out fairly decent.
The bottom was another disaster.
At the time, I had no idea about how to set up gates, runners, riser, etc. in a more standard configuration that is often used in foundries.
Fortunately the exact setup of gates, runners, risers, etc. is not critcal, and I almost got a usable casting.
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My second flywheel casting attempt turned out better.
I had some flash around the molt join, where the metal ran out along the joint a bit.
And a bit of distortion of the mold as the pattern was rapped a bit side to side to allow it to be withdrawn from the sand.
But definitely an improvement from the last casting.
I tried to maintain a pour temperature of about 1350 F.
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The top of the flywheel casting had some sand inclusions, where the sand mold broke off and fell into the molten metal, and this defect leaves a hole in the casting.
The bottom of the flywheel was destroyed when the residual alcohol burned and gassed as the hot metal ran into the mold.
Lesson #1 learned: No alcohol/graphite spray on petrobond.
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I had heard that one could spray an alcohol and graphite mixture onto sand molds to make the surface finish better, and so I made the mistake of spraying that onto petrobond, which was a huge blunder, and one of many blunders I made while learning how to cast metal.
Here are the results.
Top looks ok.
Bottom was a disaster.
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I had discovered 3D modeling, and had created a model for the green twin oscillator that I built.
My buddy in Canada found a 3D printing place in a nearby city, and so he sent my 3D model to them, and they printed it, and sent the pattern to me.
This is the pattern I received, and I was most impressed with it.
I did not know how to add draft angle in Solidworks at the time, and so I had to glue some wood onto the outside of the rim, and sand it down a bit.
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I purchased some fire bricks in 2012, and a propane burner, and some petrobond sand, intent upon making my own engine castings.
Someone directed me to this video, and this is what got me started with pattern making.
https://www.youtube.com/watch?v=-sQCJ6rv54s
I was anxious to cast something, anything, and so I cut a round shape out of a piece of plywood, and made some crude spokes.
I pressed these objects into the sand, melted some aluminum 356 in a steel crucible, and did an open-face pour.
I still have the crude spoke casting, since it was my first attempt to cast anything, and a reminder of where I started.
The furnace was just stacked hard fire bricks, with a few soft fire bricks behind (I had no idea what I was doing, and so just stumbling along).