melting grader slide/wear plates

[coulsea]

I have tried casting with brass? wear plates from a cat grader and seem to be getting a lot of shrinkage.
has anyone else had experience with these.
picture shows a mini anvil in aluminium and brass, the tapered brass sprue has been cut off, the riser is still there. I don't think that air went in with the pour and the riser should vent the whole pattern.
I am a complete beginner so any suggestions welcome.

 

[jkimberln]

Wear plates are generally made of aluminum bronze, not brass. Great material for making an anvil, I'd say. But you might check your pouring temperature.

 

[ddmckee54]

I'd check with the guys over on thehomefoundry.org. Maybe a bigger gate and a bigger riser so that they don't freeze so fast and continue to feed metal into the part as it cools?

Don

 

[darwenguy]

Hi, to avoid this shrinkage you need to make your runner and gating bigger/more mass than the casting. This allows the casting to draw liquid metal from the runner as it cools.
Hard to explain without pics, you can just carve a big hollow or use somthing like a yogurt pot, the sprue goes into this then feeds the casting from there.
Il find some pics if this makes no sense.
Best regards.
Luke

 

[MRA]

Yes - your gate froze but the thick part in the middle of your casting was still liquid. As it cooled, it in turn shrank - but because the gate was already frozen, there was nowhere to pull more metal from, so you ended up with a hole/slump. If you put a riser right on top of the thickest part of your pattern (OK, this makes it more hassle to clean up) - then this will feed the last bit to solidify, and you shouldn't end up with a slump like this.

In brass risers you'll somtimes see the outside goes off first, where the sand cools it - and a hole developes down the middle where the centre stays liquid for longer and feeds the casting underneath. This is the same kind of effect.

cheers
M

 

[coulsea]

I added a lump that would cool last and it made a big difference.
I am still amazed at the amount of shrinkage, is this normal with brass or is this a particularly bad type?.

 

[darwenguy]

yes that looks the job! This is about right, i would say that the alloy you used probably shrinks a little more than brass. Noce job!

 

[darwenguy]

Also you could cast this without the riser, if needed best to put the riser on the sacrificial lump to avoid the extra metal haveing to pass through the pattern and potentialy wash some sand away. The air doesnt trap at all. I like the pouring cup you added to the sprue thats a good thing.

 

[coulsea]

I like the pouring cup you added to the sprue thats a good thing.

I initially thought that air was getting trapped or sucked in with the pour so did a bit of youtube research.
Olfoundaryman has a good video Basin and sprue design - YouTube
I bought a devil forge 10kg for $470 au including freight and am very impressed, melts aluminium in 8 mins and brass in 15 mins.

 

[ddmckee54]

coulsea:

That looks good, just out of idle curiousity how far down the riser did that shrink hole go?

Don

 

[abby]

The transition from liquid to solid results in contraction , this of course is obvious, and for brass it is around 2% by volume.
What we want to achieve in casting is for the contraction to be spread evenly
The shrinkage depression in your casting is due to uneven cooling , the thick part of the casting will freeze last and if it is unable to be fed correctly a contraction depression will result as the metal is drawn away by the outer parts which have frozen first.
A chill , as the name suggests , is a piece of metal , usually steel , that is placed in contact with the thick part of the pattern and is then rammed up with the greensand.
For small castings it might simply be a nail pushed into the sand mould at a strategic point.
The chill causes the thick part of the casting to freeze quickly whilst the feeders are still liquid thus avoiding the depression.
You can also keep the feeder liquid for a little longer by agitating with a piece of suitable rod .
Hope this helps.
Dan.

 

[vk7krj]

coulsea, where did you get your Devil Forge from? I have searched, but can't find anything outside of America, and their ebay shop has no product in it to order.
Ken.

 

[coulsea]

coulsea:

That looks good, just out of idle curiousity how far down the riser did that shrink hole go?

Don

25mm and about 15 round, the riser is 40 high and 60 round

 

[coulsea]

coulsea, where did you get your Devil Forge from? I have searched, but can't find anything outside of America, and their ebay shop has no product in it to order.
Ken.

ebay au from lithuania , just had a look and no listings, maybe they are updating, it only took 10 days to get here.
i looked at it for a few days and they sent me an offer for cheaper.

 

[aarggh]

They're forges are really nicely made, great value I reckon. Pretty quick shipping to OZ too for my one.

 

[vk7krj]

Thanks guys, I have sent them an email for price plus shipping to Tassie. Will keep you posted.

 

[SmithDoor]

I have tried casting with brass? wear plates from a cat grader and seem to be getting a lot of shrinkage.
has anyone else had experience with these.
picture shows a mini anvil in aluminium and brass, the tapered brass sprue has been cut off, the riser is still there. I don't think that air went in with the pour and the riser should vent the whole pattern.
I am a complete beginner so any suggestions welcome.
View attachment 125123

Need a second raise on other side.
The basic formula for one of a kind part is the raisers weight is almost the same weight as part.

Now production they adjust and change the shape to cut down on raiser size.

Dave