motor cooling fan

[dallen]

here is a fan that I casted yesterday in a moment of boredom. Actually its off my milling machine, and its broken.
Questions

Was I too cold when I poured.

This part is only about 3/32 thick.

Question
How could I pour this to get more head pressure to the fins, or should I use a wire to vent the fins from the insied so they will have a better chance of filling.

[Harry]

Are you using greensand or petrobond? The greensand would probably benefit from vents because of the volume of steam created.

I would say more head pressure and a little on the hot side since that is pretty thin but should pour fine. For more head take a piece of pipe and pack it with sand and use your sprue cutter to punch a hole through it. Then just place it over the sprue hole on the mold and that will give you more pressure.

Another thing you could do is cut a round runner around the perimeter about 1/4" outside of the part and gate each fin into this runner. This will let the metal flow through fins easier.

[dallen]

greensand, thats one reason I am building a muller, if the thing don't take as long as my roaster did to build. Naw I am about half way done on the muller about ready to flip it and cut the pipe off at 12 inches. This fan isn't something that I have to have it just started because I opened my big mouth so I could insert both my feet at once kinda deal, but it would be nice to know I can do that thin of work.

the sand was pretty wet from some rain water that got into the tub from a rain storm that came throu here the other day.

It would help if the fins came down square to the edge of the base, but they taper up from for about 3/4 of an inch out form the edge.

I need to give the sand a couple days to dry out some more, or just go cast big hunks of something and dump the dry cand back in the tub to soak up the moisture. anyway looks like I will be home all week with the grass so I may try it again in the evening to see if I can do it differantly.

Thanks for the lookse

David

[Nudge]

the sand was pretty wet from some rain water that got into the tub from a rain storm that came throu here the other day.

Get a rosting pan or some other tray and put it over the vent of your furnace (while it is running) put your sand in and keep moving it around. I have done this a few times when I have over done the water.

If the sand was too wet when you did that casting that will be the biggest problem when trying to get it to fill and get a good finish.

3/32 thick (2.3mm) that IS quite a thin casting it will be good to see it come out well Good luck with it.



Just another tip, when taking pics of Alli castings try turning the flash off and take the pic with the light behind you.

[dallen]

hey Nudge, this was one of those lets do this now type deals, killing time on a sunday. It was more of an excersize in molding then casting but now I want the thing to turn out like it should be.

I normally only post the good picture but since neither was that great I decided I would let someone else judge which one I sould leave on here, guess I get to redo the picture like I do the casting, .

I am thinking about doing this again with Sodium Silicate and Sand to see if I can get better results, I do know that the sand was way too wet, I did try micing it with dryer sand but it didn't work so good, I get my muller finished I should be able to tweak the sand around better then.

Anyway it is going to be fun to see if I can do this becasue its sort of an odd part to mold up, its thin, has no strength so that I can ram down hard on it due to it being plastic and its cracked and taped back together, has all these fins on it that need to come out clean and smooth. it it was just a 32th thicker it would be easier to get the metal toflow.

Anyway have to run into town take care of some business, then maybe i can get something done around here.

David.

[Nudge]

put a few layers of tape on the thin bits and build it up a bit if needed

[dallen]

now thats an idea, will try that, I have a guy sending me a new fan, or anyway a good fan that isn't cracked, hopefully I can try when it gets here. I want to make a good casting out of this now just to prove to myself that I can. Even if it means I have to hand mix petrobond I have the stuff to di it with. But the muller isn't that far off from being done. I get it ready I plan on mixing up a couple hundred pounds.

I figured out how to fill the bottom so it won't crush when I ram it up hard, now that I have a good blade coming for a pattern, I can get some bondo and see if it will harden on it without melting the plastic.

[Nudge]

Just test it on the old fan first. it should be ok but I would put tape on it then put the bondo on it that way you can take it off after doing the casting

[dallen]

well i took a shot at ramming up the fan blade again last night, only did the topside, side with fins. I rammed it a lot harder as the moisture in the sand had lessened up a bunch, I let the tub set in the blazing Oklahoma sun all day yesterday so the top couple of inches was pretty dry, and by mixing it up with what was underneith I got a pretty good bond out of it.

Anyway the part rammed up ok, still had some problems with pulling the pattern out, becasue the fins I have to cope down (I think is the right term) had to dig the edge of the fins out as they are not even with the bottom edge of the fan blade. this worked pretty but there was some crumbling in the sand around the edge due to it not packing tight enough against the blade, cure is to use a rammer with a smaller end so it will fit between the blades and use sifted sand. I need to order a seive with a bigger weave in it.

Found a Recipe for what is being called Moonsand, sand and cornstarch with some water, may give it a try, if it will pack tight enough I can use it to face the blade with and then finish up the mold with regular greensand to hold it in place. something to try when the sun goes down.

David