Sand Mold Casting Problems

[jimsshop1]

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

 

[maury]

JimShop, can you give us more info? I don't like your sand, but it might work. What does your pattern look like? gating, risers? Aluminum needs risers! also, does your gating minimize turbulance in the mold? Post some pictures of your parts and the patterns.

maury

 

[vederstein]

I had the same issues casting my flywheel last winter. Eventually I gave up and made a three spoke pattern. That one came out usable. Not great, but usable.

http://www.homemodelenginemachinist.com/showthread.php?t=27224&page=9

 

[Jack3M]

I found that the home made stuff just doesn't work well. I also found the oil based works better, but adding more oil to it helps. (Petrobond) Also, make sure you have plenty of air relief vents throughout and at least 3 risers over and above your pour riser in the center. And make sure your molten metal is at it's maximum pour range temp as it cools very quickly with so much distance to travel.

Also, if there is mold failure to the outside of the part, it is just extra filing and more metal used in the process.

 

[jimsshop1]

JimShop, can you give us more info? I don't like your sand, but it might work. What does your pattern look like? gating, risers? Aluminum needs risers! also, does your gating minimize turbulance in the mold? Post some pictures of your parts and the patterns.

maury

For the 9" flywheel I am using a sprue right in the center hub same size as the pattern hub. For venting I am poking holes with 1/8" wire from back side of the pattern between the spokes and 4 places around the rim through to the side I am pouring from up top. This has worked fine for all the other pieces. When breaking open the molds the ali has followed up the holes. There are some on here that have proven that vents are not necessary but I want al least the small holes I poke. My metal is flowing fine throughout the pattern but my edges are coming out rough and sand seems to fall into the impression no matter how careful I am. I am thinking about mixing more clay powder and making the sand mix wetter. Thank you for trying to help. I have attached some pics.

 

[girle]

Add Bentnite relieve with graphite

 

[oilmac]

As an ex moulder , maybe my past experiences may be of some assistance, When you come to ramming up your mould in the case of these delicate flywheels etc, it is a good idea to make up an "oddside" or false cope This is the top half rammed up on flat board or plate, Your pattern is set into it down to its half way point or joint line, with a delicate pattern take care you do not press your little pattern into the sand too heavily or you will damage it. Held loosly in this section, , as when you ram your bottom half mould on top of this , you want your pattern to be held securely in the drag half when you turn over the moud, and you remove this sacrificial top half of the mould mould from the bottom half, the pattern stays in the drag.

Now I think we are coming to the stage in the process which is causing you grief, Place your drag half moulding box on top of your "dummy top part or oddside , whatever you want to call it!," When you start ramming this half section, put some sand through your fine sieve, and taking handfulls of the sand , throw it into the middle of your wheel , This will give an even ram in this section, Then sieve on more sand on the rest of the mould face, and ram up your mould., Turn it over and remove the oddside.

Now when I look at the joint face of the moulds, that some of you guys call a proper joint line, I could scream, Finish the joint line with your trowel and other small tools to a nice smooth finish, Get rid of the rocky mountains and grand canyons, In other words polish it, It should be exactly on the parting line of your pattern, Note-- If you have made a split pattern, you do not need a false cope Placing your half pattern on the moulding board is easier.

Now for the part of the excercise where I believe you folks find a problem cropping up, Thus your rough mould edges breaking away, Forget dusting the mould joint face with talc, Rubbish ! This is causing your edge breaking problems My old works foreman would have had an apaplectic fit with temper if he had seen any one using talc as a parting medium,, Use a sprinkling of the following --, Lightly through your fingers sprikle on some dry fine sand, play sand for the kiddies is excellent stuff, This creates a lovely barrier , moulders have been using this grade of fine sand, as a parting medium for hundreds of years, The brass moulders tend to take a fine muslin bag , containing about a handful of nice dry fine powdered lime, just a light application of this stuff works a treat, A lovely waterproof joint face, Using these materials as a parting medium , you should get a lovely joint face free from broken lumps falling into & washing away with the molten metal.

The rest of the project is per verbatim, Ram up top mould as per bottom, lift off your top half, And now for the sneaky part, Creep into the house , steal one of your good lady's nice make up brushes designed for applying Talc to her skin, Wonders will never cease!

Using the brush, gently apply a moist brush around your pattern ( Don't Give it a Bath) This will strengthen you edges , Close your mould & cast .

 

[jimsshop1]

This morning I got set up at work and very carefully prepared my mold for the flywheel making sure to do everything in sequence and being ever so careful not to disturb the mold cavity and keep things as clean as possible. I am quite happy with the results and should be able to progress with this build. I am sure I will never attempt this whole casting thing again with this many parts to do. I am 71 and it has been a great learning experience for me and a couple of my coworkers but also has been an exhausting one for me what with all the sand mixing and failures along the way. I will keep my home made forge since it works so well and maybe melt and cast some small brass parts since that is the reason I built it in the first place until I saw the Atkinson Dif. engine. The pic attached is of the best side but the other only has a few more sand pits in it but it gives it character I think.

You all have a great day,

Jim in Pa

 

[jimsshop1]

As an ex moulder , maybe my past experiences may be of some assistance, When you come to ramming up your mould in the case of these delicate flywheels etc, it is a good idea to make up an "oddside" or false cope This is the top half rammed up on flat board or plate, Your pattern is set into it down to its half way point or joint line, with a delicate pattern take care you do not press your little pattern into the sand too heavily or you will damage it. Held loosly in this section, , as when you ram your bottom half mould on top of this , you want your pattern to be held securely in the drag half when you turn over the moud, and you remove this sacrificial top half of the mould mould from the bottom half, the pattern stays in the drag.

Now I think we are coming to the stage in the process which is causing you grief, Place your drag half moulding box on top of your "dummy top part or oddside , whatever you want to call it!," When you start ramming this half section, put some sand through your fine sieve, and taking handfulls of the sand , throw it into the middle of your wheel , This will give an even ram in this section, Then sieve on more sand on the rest of the mould face, and ram up your mould., Turn it over and remove the oddside.

Now when I look at the joint face of the moulds, that some of you guys call a proper joint line, I could scream, Finish the joint line with your trowel and other small tools to a nice smooth finish, Get rid of the rocky mountains and grand canyons, In other words polish it, It should be exactly on the parting line of your pattern, Note-- If you have made a split pattern, you do not need a false cope Placing your half pattern on the moulding board is easier.

Now for the part of the excercise where I believe you folks find a problem cropping up, Thus your rough mould edges breaking away, Forget dusting the mould joint face with talc, Rubbish ! This is causing your edge breaking problems My old works foreman would have had an apaplectic fit with temper if he had seen any one using talc as a parting medium,, Use a sprinkling of the following --, Lightly through your fingers sprikle on some dry fine sand, play sand for the kiddies is excellent stuff, This creates a lovely barrier , moulders have been using this grade of fine sand, as a parting medium for hundreds of years, The brass moulders tend to take a fine muslin bag , containing about a handful of nice dry fine powdered lime, just a light application of this stuff works a treat, A lovely waterproof joint face, Using these materials as a parting medium , you should get a lovely joint face free from broken lumps falling into & washing away with the molten metal.

The rest of the project is per verbatim, Ram up top mould as per bottom, lift off your top half, And now for the sneaky part, Creep into the house , steal one of your good lady's nice make up brushes designed for applying Talc to her skin, Wonders will never cease!

Using the brush, gently apply a moist brush around your pattern ( Don't Give it a Bath) This will strengthen you edges , Close your mould & cast .

Oilmac, Great explanation and help if I do this again. My pattern was a split design. I posted the pic before I saw your post. Thank you, sir!

 

[Herbiev]

Great instructions there Oilmac. Many thanks.

 

[oilmac]

Jimsshop,

for a home workshop enthusiast, you are doing very well, your flywheel is acceptable, Practice makes perfection, Keep at it and finish your engine, Lots of folks think anyone can make a mould, It is not as easy as it looks, Practice and more practice, If I may say your patternmaking is first class,
I meant to say in my article to everyone, the parting material should just be a dusting and no more,

Oilmac.

 

[maury]

Jims, not bad for a first try.
A few hints:
the pock marks are from dirt washing into the mold, either because the sand was not tight enough or it didn't have enough binder, or it could be from turbliance in the mold from the metal washing the sand loose. On your next flywheel you might try gating the flywheel from the outside at 2 or 3 places around the rim, and putting a large riser on the hub. Put the runners and gates in the drag and make them about 3-4 x as wide as they are deep. I have had success doing this with my flywheels.

I suggest you try Petrobond using fine sand, say 120 grit. Your castings will turn out great. With aluminum, don't forget to add plenty of risers on the thick sections.

maury

 

[Gordon]

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.

 

[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.

Gordon,

My plan at first was to use flat stock as I have built engines in the past from bar and you are correct, at least you have a straight edge to start with. But, since I had designed and built a successful forge to melt brass my best friend who thinks I can do anything said "I bet you can cast it all in aluminum, it should be easy for you" Well you know how it goes with friends, you can't let them down. So I made the patterns first and was very careful to make them with square edges and keep the draft at the proper degree so they would release from the mold easy. They actually came out really close to the patterns so by just cleaning off the flash they clamped very true in my mill vice. At my age, 71 and with advanced R.A I doubt I will ever do this again at this level, it hurt me bad. Thanks for the comments and I will keep posting as the build progresses.

 

[jimsshop1]

Jimsshop,

for a home workshop enthusiast, you are doing very well, your flywheel is acceptable, Practice makes perfection, Keep at it and finish your engine, Lots of folks think anyone can make a mould, It is not as easy as it looks, Practice and more practice, If I may say your patternmaking is first class,
I meant to say in my article to everyone, the parting material should just be a dusting and no more,

Oilmac.

Thanks for the praise, the patterns took many, many hours, believe me.

 

[Wizard69]

Thanks for the praise, the patterns took many, many hours, believe me.

No doubts here! By the way nice looking flywheel.

There is a reason pattern makers are a skilled job classification all on their own. It is a very interesting and challenging occupation.

 

[jimsshop1]

No doubts here! By the way nice looking flywheel.

There is a reason pattern makers are a skilled job classification all on their own. It is a very interesting and challenging occupation.

Well going into this casting as a first time greenhorn redneck I figured if I had any chance of success at all I had better start with the best I can do on the patterns. BTW The flywheel does not look as good on the other side but nothing a little bondo won't take care of. Did I mention in another venture I learned how to do body work and painted a few cars? Oh well, on with the build. I don't know if I should go on from here about this build or go back to my original thread where I started.

Thanks again,

Jim

 

[oilmac]

Hello again Jimsshop and others,
Looking at your casting Jim, It was a good attempt, but the following info may be of some help to you all, I tend to think looking at your work folks that you tend to cast your metal too hot, If you stew your aluminium too much in the pot one tends to build up hydrogen in the metal thus the black specks in your cast metals when yo start machining

As home foundry work, Is a "different Kettle of fish" from the luxury of industry, where I had pyrometers for temperature checking +nitrogen degassing etc. However on a simplified method of working at home with limited resources , I tend to do the following upon getting the metal molten, a good casting temperature is a mild pink color going to a nice silver like mercury, Time to pour your mould, In the case of very thin section castings like Jims bedplates? a little hotter.

Now a way to cut down on dirt wash The premise is-- "Cleanliness is Next to Godliness," In the case of Jims Flywheel type of casting (or similar) a centre downgate is usually O.K. In my young days I used to cast big aluminium pulleys and the principal gate was on the centre boss, But due to pretty heavy rims, to negate hot tears and shrinkage we used to ram up pices of polished steel plates placed on the underside of our pattern rim, These acted as chills , Care hads to be taken to cast our moulds pretty sharpish in case moisture gathered on the face of the chills , Thus creating an amatuer version of Mount St Helens, With the risk of a sore burn or worse, From you folks point of view I would stick to risers on my rim.
Now back to my homily on cleanliness , When I look at the top of your moulds, after it is closed' That believe it or not could be a source of problems round the sprue head there is a lot of loose sand particles, These can be picked up and swept down the runner on casting, to negate this problem before drawing the sprue bar out, take your trowel and give around it a smooth polish, (Reasonable but not like an ice rink) Draw you bar , open your mould , draw pattern, , dust mould surface with your talc, and take another of your good lady's make up brushes and dust the sprue hole, and around its top edge with powdered talc You are now ready to close your mould and cast.
Another excellent hint is to make the bars you use for forming your sprues from a larger diameter piece of timber , Turn the bar with a generous taper (cone shape ) too about one third distance down its length , Thus you have a nice reservoir of feed metal , and it is easier to pour the metal into.

In my own moulding methods I make up "Head Bushes " these are produced from shallow Heinz bean tins , both ends cut out thus leaving a ring , into which I put a handfull of sand and deftly using my fingers make a pouring cup to match the top of the sprue, This deft action requires skill to get right , and the ends of the tins have to be cut correctly on a mechanised tin opener , One does not want a nastily gashed finger .
Like Jim , my age is not kind to me , I am 79, So my days of metal pouring are rapidly drawing to a close

 

[jimsshop1]

Hello again Jimsshop and others,
Looking at your casting Jim, It was a good attempt, but the following info may be of some help to you all, I tend to think looking at your work folks that you tend to cast your metal too hot, If you stew your aluminium too much in the pot one tends to build up hydrogen in the metal thus the black specks in your cast metals when yo start machining

As home foundry work, Is a "different Kettle of fish" from the luxury of industry, where I had pyrometers for temperature checking +nitrogen degassing etc. However on a simplified method of working at home with limited resources , I tend to do the following upon getting the metal molten, a good casting temperature is a mild pink color going to a nice silver like mercury, Time to pour your mould, In the case of very thin section castings like Jims bedplates? a little hotter.

Now a way to cut down on dirt wash The premise is-- "Cleanliness is Next to Godliness," In the case of Jims Flywheel type of casting (or similar) a centre downgate is usually O.K. In my young days I used to cast big aluminium pulleys and the principal gate was on the centre boss, But due to pretty heavy rims, to negate hot tears and shrinkage we used to ram up pices of polished steel plates placed on the underside of our pattern rim, These acted as chills , Care hads to be taken to cast our moulds pretty sharpish in case moisture gathered on the face of the chills , Thus creating an amatuer version of Mount St Helens, With the risk of a sore burn or worse, From you folks point of view I would stick to risers on my rim.
Now back to my homily on cleanliness , When I look at the top of your moulds, after it is closed' That believe it or not could be a source of problems round the sprue head there is a lot of loose sand particles, These can be picked up and swept down the runner on casting, to negate this problem before drawing the sprue bar out, take your trowel and give around it a smooth polish, (Reasonable but not like an ice rink) Draw you bar , open your mould , draw pattern, , dust mould surface with your talc, and take another of your good lady's make up brushes and dust the sprue hole, and around its top edge with powdered talc You are now ready to close your mould and cast.
Another excellent hint is to make the bars you use for forming your sprues from a larger diameter piece of timber , Turn the bar with a generous taper (cone shape ) too about one third distance down its length , Thus you have a nice reservoir of feed metal , and it is easier to pour the metal into.

In my own moulding methods I make up "Head Bushes " these are produced from shallow Heinz bean tins , both ends cut out thus leaving a ring , into which I put a handfull of sand and deftly using my fingers make a pouring cup to match the top of the sprue, This deft action requires skill to get right , and the ends of the tins have to be cut correctly on a mechanised tin opener , One does not want a nastily gashed finger .
Like Jim , my age is not kind to me , I am 79, So my days of metal pouring are rapidly drawing to a close

Oilmac, you have given so much good Information to me and others that will follow in my footsteps. I doubt I will ever do this again as all my castings came out useable but with a lot of clean up and fussing around with some bondo and sanding-painting. I wish they would have turned out good enough to leave as bare cast but oh well at least I can continue on with the engine build. I really want to see this thing run. I do have a question if you don't mind. I have it in my feeble brain to shrink a brass ring around the flywheel. Now here is the dumbest question you've probably ever been asked. Is it possible to make a circle mold in aluminum and pour it full of molten brass or would that be a big bang thing?:fan:

Thank you again,

Jim

 

[MRA]

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