Cores

[Powder keg]

Has anyone made cores for their castings? I am working on some patterns that will require cores and I've never made any before. What works best for a binder? What do you use for sand? I use petrobond and I don't want to mess it up.

I'll start a new topic on this engine soon in the work in progress section.

Thanks, Wes

 

[Oldmechthings]

Wes
I ran off copies from my casting manual on making cores and it has already gone off in the mail this afternoon. You should receive it by Saturday. Just use a fine white silica sand, (Places like Home Depot carries it in bags) and mix it with the binder as described in the manual. When I shake the castings out, I attempt to separate as much of the core material out and discard it as is practical. It isn't to difficult because the part that sticks out of the casting is quite chunky, and the part inside the casting has to be reamed out with something like a screwdriver, and that operation can be done over the trash can. The tiny bit that I do not get separated out does not seem to bother the Petrobond enough to be a problem. Of course I separate and remull the layer of burnt Petrobond sand before it is returned to the sandbox anyway, You probably do too.
Birk

 

[Powder keg]

Thanks Birk) Tonight I made the core box on the CNC at school. It turned out really good! I'll take some pictures of them after work. I'm guessing I should paint the two half's? What would be a good way to finish them? I have been using polyurethane on my patterns.

Thanks again, Wes

 

[maury]

Powder Keg, I use sodium silicate binder with fine white silica sand. About 120 to 150 grit.
You will need about 3 - 3.5% by weight, and only mix a little more than you need. You will need CO2 to cure it. You can use a bottle of club soda for the CO2 if you don't have a CO2 bottle. Cork the club soda with a plastic tube through the cork. Put a plastic bag over the core, and run the tube under. This is all with the sand still in the core box.

I finish my core boxes with a couple of coats of thin lacqurer. That is the wooden ones.
I use a bit of johnsons floor wax for the release.

You didn't say what you were casting. If it's aluminum, the metal won't be hot enough to
soften the core. You will probably have to chisel it out. I don't know of a core material, except for baked resin cores which would be more compatible with aluminum. Sodium silicate will work great for bronze.

good luck
maury

 

[tel]

Most of my casting is aluminium, with greensand & I use a brew of sand, flour and molasses water (10% molasses in water) - make 'em in a core box in the usual way and bake 'em til hard. They smell real nice while they're cookin'

 

[Powder keg]

Tel, How hot do you bake them? Do you have to use any type of release so the cores don't stick to the core box?

Thanks, Wes

 

[tattoomike68]

When I worked at a foundry our baked core boxes were sprayed with PAM , the some stuff you use on a frying pan.

We used parting powder on the CO2 hardened cores or the silver never-seize like stuff.

 

[Powder keg]

Thanks Mike! I am getting more ideas to try and see what works best for me)

I have some more drawings done for my next engine. I'll start on the patterns next week. look for another build)

Wes

 

[tattoomike68]

By the way im not sure of the temperature cores were but the core machine did have propane burners shooting flames on the cast iron core boxes but it was made to be quick. I would guess the heat of a torch or BBQ would do the trick on a small core box.

I do miss that foundry work, it was a facinating place.

 

[Powder keg]

Might be to hot for my wood core box) I'm going to try the Co2 cores first I think? I have seen it done. but it was a few years ago.

Thanks, Wes

 

[Powder keg]

Maury, Forgot to mention that I'm casting mainly aluminum. But I'm getting into brass and bronze) tanks for the tips.

Later, Wes

 

[tel]

Tel, How hot do you bake them? Do you have to use any type of release so the cores don't stick to the core box?

Thanks, Wes

I just bake 'em in the kitchen oven (we have a wood burning slow combustion stove), usually for about 1/2 hour or so.

I give the core box a light coat of talcum powder, same as the patterns and they seem to come out alright, I think the design of the core box is probably the more inportant aspect of getting them out, handle with care tho' - they're pretty delicate until baked.

.... AND vent 'em - a bit of fencing wire shoved down the middle (or more for a large one) will save a lot of grief.

 

[Powder keg]

Thanks for the tips Tel. Now for a stupid question, You bake it in the core box, right?

Here is the core box I'm working on. I just have to install the alignment pins and lacquer them.

You can see the taper on each end. That will match the core print on my pattern.

Thanks for all the help, Wes

 

[tel]

Core box is lookin' real good, but no, no NOOOOO - remove the cores from the box before you bake em - if you have 'em rammed up properly they'll hold together so you can arrange a bunch of 'em on a baking tray and pop 'em in the oven - just like cookin' bikkies.

 

[tel]

BTW, I'm really jealous of your patterns, are you using them loose or on a match plate?

I have to do mine the old fashioned way, and it's something I'm not real good at.