risers on iron castings

[ironman]

Hi everyone

About a month ago vtsteam gave me the measurements to make a pattern exactly the same as his. I wanted to have a go at casting it using my methods and materials. I made a video of how the mold was made and poured. 

   

Risers generally need to be placed on top of a casting but there are two reasons why I put mine on the side of the casting.

1. As metal flows through the mold it cools down and as it fills up the riser is less effective. When a riser is placed on the side and all the metal has to flow through it the riser will be more effective. To make the top riser work better, fill the mold until it just starts to fill the riser up and then pour directly into the riser with hot metal.

2. It is a lot easier to cut of a riser on the side than on top.
 
Photo 1 shows a wire placed in the shrinkage cavity in the riser.

photo 2 shows how deep the shrinkage cavity is.

photo 6 Shows the metal I used to melt down for that casting. It is mostly 25mm (1") thick and produces very little slag.

[tom osselton]

Good video I was wondering why you curved your gate but then realized it would let the metal flow more natural through the channel,  what I couldn't figure out is the purpose of the wire.

[doubleboost]

Very well shown 
I was surprised at how shallow your flasks were
But it gave a good casting with no shrinkage
John

[ironman]

doubleboost

A lot of backyard casters use really deep flasks and then use pouring cups to get enough head pressure so the casting won't shrink.

 In every case I have seen they use too small sized riser and still get shrinkage in the casting.

If a decent size riser is used like mine very tall flasks are totally unnecessary.

[vtsteam]

Thanks so much Ironman for taking the time to cast that block and make a video of how you did it. 

I think I cast that pattern maybe 10 times before I got a good one. I tried no riser at first, then several tries with a side riser on the opposite side of the pattern from the sprue. My first success was a somewhat different pattern, when I moved the riser on top -- per a suggestion of yours earlier. However when I returned to the block pattern, that didn't work as well.

Finally, and coincidentally, I tried a side riser fed by the sprue and that finally gave me a perfect casating -- almost identical to the layout you show (see photo below). The only difference was that I had added an extension to the runner which I had read would help trap slag -- another problem for me because of the metal I am using is not as clean as yours. The trap seemed to work, and I'm sure the riser trapped slag as well. Another small difference -- in mine the runner runs tangential to the riser instead of feeding directly into it -- this is also supposed to direct slag down the runner trap.

Riser size: I had heard back when first casting with aluminum that a riser should always be wider in diameter than the deepest part of the casting is deep. So I used a 1-1/2" diameter (76 mm) riser dowel -- the casting was an inch deep.

I always learn new things from your videos -- the 14mm sand depth was a surprise to me too -- I thought sure you'd have doubled up your drag flasks. But your single thickness drag worked perfectly. I can definitely see why you use a metal bottom plate and clamps, though!

All the little details are good to see -- in the past videos they often are cut out in the interest of saving time. But it is helpful to see just exactly how you cut your sprue basin, and press down the top of your cope by hand after ramming, and how you cut that off with a metal ruler. Also how you press facing sand onto the sides of the pattern by hand. Small things, but the details are very much appreciated.

Your sand looks wetter than mine -- I might try a little more moisture in future to make cutting runners and gates less crumbly. Also the pattern hollow would erode less. We'll see if I get a return to blowholes with maybe another percent of water.

Thank you again for showing us all how you cast, in detail. 

[ironman]

For this video I had a helper come around to film the birds eye view when pouring. It is so everything I can see you will see.

You mentioned that my sand looks wet, it has the standard 4% moisture. You probably noticed I don't use a vent wire and still get blowhole free castings. Sand has to have enough porosity to prevent that.

Have a look at my video where the casting is knocked out, you will notice the sand is very wet where the cast iron weight prevents the steam from escaping to the air. When I see that I know that the sand has enough porosity.

About 23 years ago I toured through the Cat engine foundry in Peoria Ill. They used a large machine to compact the engine block molds. I saw no vent wires being used. The molds were closed and went to the pouring station. The tour guide told me that the sand moisture content was strictly controlled to prevent defects.   

[vtsteam]

MIne tested to 2.5% moisture, so I think I can try to come up a percentage point with it and see what happens.

[Meldonmech]

Hi
      What is the black facing sand you use?   Has it a plumbago content?

                                                                Cheers David

[ironman]

The sand is black because coal dust has been added.