Sand Mold Casting Problems

[jimsshop1]

Hey Jim - I'm pretty sure the ally would melt.

I echo what Oilmac said about getting too hot - that's happened to me several times, and one or two folks have said to me that those pits are to do with dissolved hydrogen.

Have you had a go pouring brass yet? Seems like a good idea while you have the kit laying around. I found advice on-line to throw some glass in which forms a sticky-toffee lid - it's meant to hold the zinc from burning off, and to give the dross something to stick to. Make your rim a bit big so you can clean it up in the lathe, and *make sure you have a good bit of sprue sticking up* (Oilmac's extended risers are a good idea) since the brass will cool at the edges of the sprue and feed down the middle as the interior cools, leading to a kind of 'tube' forming in the sprue.

Oh - and the advice you read about having a fat riser coming off heavy bits in the pattern is good - I suffered from shrinkage problems by not doing that, recently - easily forgotten.

Hold your breath around it - zinc fumes coming off are best left un-breathed!

cheers
Mark

After two attempts at casting a brass ring I got a good one. The first one failed because I did not have large enough gates and the melt cooled before it got all the way around the mold You could see the rolls in the ends where it cooled like lava. Second mold I had the gates as deep as the ring and much wider. I also made a 2" cup riser like Mark suggested and an 1-1/4" vent riser 180 degrees from the pouring gate. I also poked 1/8" vent holes at 4 evenly spaced marks in the ring pattern. I had the brass actually boiling when I took it out of the furnace and poured immediately. Wow was it hot! When the brass flowed up the vent like a volcano I new I had a complete ring cast. But as I watched it cool I was amazed how much it shrunk in the risers again like Mark said. I was afraid it would shrink all way down to the ring and leave a bad spot there. It finally stopped and hardened in the spout. When I broke the sand off I had a good brass ring 9- 1/2" in dia , 1-1/4" thick with thickheavy gates,4, 1/8" **** about an inch long sticking up where I poked the holes. So it went well and hopefully it will machine well. I forgot my camera but will take pics Thursday when I go back to work. Thanks Mark and myfordboy for all the wonderful helpful youtube posts.

Jim in Pa

 

[jimsshop1]

No one seems interested in this thread but I said I would post a picture of the cast Brass ring so here it is partially machined I still have about a 1/4" to take off the inside to get close to my flywheel size.

 

[jimsshop1]

From viewing your experience I am glad that I decided to build it from bar stock instead of using castings. Making the casting patterns takes as much time as actually making flat stock blanks and the final machining is pretty much the same whether you are using flat stock or castings and the flat stock has square edges to index from and hold in the milling vise. Fly wheels are available from Martinmodel.com for $50 to $65 which would work. I realize that you wanted to gain a new skill which I can appreciate because I have done the same thing.

Hi Gordon,

Did you ever finish your engine?

Thanks,

Jim

 

[Cogsy]

It's interesting to me - I've never really cast anything that's turned out useable yet, but I plan to keep trying.

 

[Pierkemo]

How is your furnace look like?
I'm an absolute beginner, i will make an oven fot 1.8 Liter crouse.
Can you give me some indicators??
Thanks,
Pierre

 

[Gordon]

Hi Gordon,

Did you ever finish your engine?

Thanks,

Jim

I have everything made and assembled but not spit and polished. I am running the engine with an electric motor per Gingery's suggestion to seat the rings. Actually I have been sidetracked the last couple of weeks but I hope to get back at it this week.

 

[maker]

Take a picture.
It sounds like a draft problem on your pattern.

I am building the Atkinson Differential Engine with my own aluminum castings. This is my first time at casting and so far have all the parts cast except the flywheel. The castings are not the best I've seen but they are usable. My problem is with the 6 spoke flywheel. I have cast it 3 times but am having problems with the mold when I take the patterns out of each half. The sand edges of the spokes keep breaking off so my impression seems to deteriorate as I try to clean it up. I can not get the sand to hold it's form. I am using fine play sand and ground up kitty litter as my green sand and I know that is not the best way to go but it's all I have. I can form a turd shape in my hand and it breaks clean without crumbling so I think I have the mix close to correct. One thing I noticed when using talc for parting agent is it dries out the sand around the pattern so I am only using it between the 2 flasks so they separate better. I have watched myford but he uses oil base sand. Can anyone please give me some tips to get good crisp edges around the impressions? I'm sick of playing in the sand>:wall:

Thank you,

Jim in Pa

 

[jimsshop1]

Take a picture.
It sounds like a draft problem on your pattern.

Flywheel is finished. I had plenty of draft on all parts as per instructions in the book.

 

[jimsshop1]

How is your furnace look like?
I'm an absolute beginner, i will make an oven fot 1.8 Liter crouse.
Can you give me some indicators??
Thanks,
Pierre[/QUOTE
My furnace is home made from rolled steel and is lined with a 1" thick fire proof ring I got locally. It is fired with propane with a burner of my own design. I will try to take some pictures later for you. It will melt aluminum in 10 min. and brass in about 45 min. I have done about 12 melts on a 20# prop. tank. Pierkemo, where are you located?

Thanks for the reply.

Jim

 

[Pierkemo]

Hello Jimsschop1, i'am living in Belgium.
I think you have also a good burner, and short melt times.
How big is your crusible?
Thank you,
Pierre

 

[jimsshop1]

Hello Jimsschop1, i'am living in Belgium.
I think you have also a good burner, and short melt times.
How big is your crusible?
Thank you,
Pierre

I will take some photos later and post them along with some measurements for you. Welcome to the best model engine forum.

Jim

 

[Cogsy]

I have everything made and assembled but not spit and polished. I am running the engine with an electric motor per Gingery's suggestion to seat the rings. Actually I have been sidetracked the last couple of weeks but I hope to get back at it this week.

Are you using cast iron rings? If so, the best way to 'seat' them is to try and start it. The extra force (in the right position) from combustion forces produces the best seal quite quickly. If run too long without combustion forces it may be impossible to ever get the rings to seal properly.

 

[kadora]

I agree with Cogsy the best way to seat rings and valves is to run engine.

 

[Gordon]

I am turning it with the electric motor but have the fuel and ignition also working. It is starting to sputter but the compression is still to low for a good firing. I am using CI rings. It is improving but I have only been running it for less than an hour. Gingery says he ran it that way for as long as 40 hours.

 

[stragenmitsuko]

I've learned over the years when casting ali , there's scrap and there's Scrap .
Best results I ever got was using old scuba tanks as material to melt .
Cut them into rings on the bandsaw , then crushed the rings on a hydrualic press to make
them fit the crucible . Sadly I only had two , and can't get any more .

I've also been told alloy car wheels make great castings .
So that will be my next attempt .

I've had far less luck with the "usual" aluminium scrap .
It caused a lot of hydrogen inclusions , pitting , altough I degassed the crucible 2 sometimes 3 times .

Pat

 

[jimsshop1]

I've learned over the years when casting ali , there's scrap and there's Scrap .
Best results I ever got was using old scuba tanks as material to melt .
Cut them into rings on the bandsaw , then crushed the rings on a hydrualic press to make
them fit the crucible . Sadly I only had two , and can't get any more .

I've also been told alloy car wheels make great castings .
So that will be my next attempt .

I've had far less luck with the "usual" aluminium scrap .
It caused a lot of hydrogen inclusions , pitting , altough I degassed the crucible 2 sometimes 3 times .

Pat

Al my ali has been billet or precast

 

[jimsshop1]

Hello Jimsschop1, i'am living in Belgium.
I think you have also a good burner, and short melt times.
How big is your crusible?
Thank you,
Pierre

Pierre,
I made the furnace from 1/8" rolled steel. It is 13" high and 13" around. The top is 2" high hinged to the bottom and with wool type fire proof insulation. There is also insulation in the bottom under the plate riser the crucible sets on. The burner is made from a 2" tee bushed down to a 1" pipe 10" long. There is an .068 orifice in the tee. I have 2 crucibles I made. 1 is a 3" pipe 5" long and the other is a 4" pipe 9" long. Both have 1/4" steel plate welded in the bottom. I had access to a rolls set at work to roll the plate and my own welder for the rest. I am very pleased with the speed this melts ali and brass and how little propane is used. If you have more questions, please ask. Have a nice day.

Jim in Pa

 

[Rocket Man]

I have 2 of those 9" flywheels I made 15 years ago then lost interest in the project. Remember the physics of casting, small areas like spokes cool & contract first sucking liquid material form the still liquid sections of the part like the center hub & outer part of the wheel. Hub & wheel both need large risers that will not freeze off as the hub & wheel cool first. As hub & wheel cool and contract it needs to suck in liquid metal from the larger risers. The flywheel has to freeze in stages and liquid needs to come from other areas of the part as it freezes in, 1, 2, 3, order. Good sand, good draft, good vents, make a big difference. My flywheels still may become a project some day but not likely.

 

[jimsshop1]

Pierre,
I made the furnace from 1/8" rolled steel. It is 13" high and 13" around. The top is 2" high hinged to the bottom and with wool type fire proof insulation. There is also insulation in the bottom under the plate riser the crucible sets on. The burner is made from a 2" tee bushed down to a 1" pipe 10" long. There is an .068 orifice in the tee. I have 2 crucibles I made. 1 is a 3" pipe 5" long and the other is a 4" pipe 9" long. Both have 1/4" steel plate welded in the bottom. I had access to a rolls set at work to roll the plate and my own welder for the rest. I am very pleased with the speed this melts ali and brass and how little propane is used. If you have more questions, please ask. Have a nice day.

Jim in Pa

I have 2 of those 9" flywheels I made 15 years ago then lost interest in the project. Remember the physics of casting, small areas like spokes cool & contract first sucking liquid material form the still liquid sections of the part like the center hub & outer part of the wheel. Hub & wheel both need large risers that will not freeze off as the hub & wheel cool first. As hub & wheel cool and contract it needs to suck in liquid metal from the larger risers. The flywheel has to freeze in stages and liquid needs to come from other areas of the part as it freezes in, 1, 2, 3, order. Good sand, good draft, good vents, make a big difference. My flywheels still may become a project some day but not likely.

Flywheel turned out great. Only took 2 tries after I figured out exactly what you just said. The first one stopped flowing half way because my exit riser was too small and the path from the pour riser to the mold was too small also. I also think the liquid was not hot enough. The second pour was really, really hot! I think it was boiling when I poured it. Very scary when you think what could go wrong in less than a second!

 

[dottedline]

Have you thought about using the Williams "saved wax" sand casting technique? It produces highly accurate product. It will even show fingerprints in the casting if they are not removed prior to casting.