[Biggermens]

Hello everyone

I need some help here i am trying to make a heat sink. so i made my pattern and it is nice and smooth, i pack my sand around it and i can never get it out of the sand all the sand stays stuck in the fins.
And i use baby powder on the pattern also

Anyone know what i am doing wrong, or is it too much to ask to sand cast this would it be better to use lost fome casting ???


Thanks eveyone
Biggs

[DMF_TomB]

sand casting sand i am always adjusting

1) regular grit sand ( often kid play box sand at Home Depot)
2) fine sand (also usually at Depot)
3) Bentenite clay (pottery supply places sell dry clay in bags)
4) Fire clay (pottery / craft places sell dry bags)
5) water content
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too much clay and fine sand and it will definitely stick together and take a shape but sometimes the water / dampness is tricky and during casting if it cannot vent through the sand and it will go through the molten metal leaving a swiss cheese casting.
.
grab a handful of sand and squeeze. it should take an impression of you fingers and within reason if you shake one end it should hold together.
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aluminum is easy but finding sand for cast iron is tough as sand melts from heat, sticks to casting and leaves a rough finish.
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petro bond sand is a oil / chemical mixed with sand. red when new and sand turn black from use (probably carbon soot). petro bond burns and smokes when molten metal poured in it but i got to say in general a easier sand to mold with and leaves a better as cast finish
PetroBond Foundry Casting Sand
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it is hard getting foundry supplies in small quantities try budgetcastingsupply. most foundry supply places don't want to deal with less than ton or pallet size quantities. i even had a place tell me it was $200 to fill out paperwork for an order this was not even counting the cost of buying anything.

[Biggermens]

Thanks for your help Tom

this is what i am using
10 lbs 4.5 kg sand
1 lbs 0.45 kg Bentonite
1 lbs 0.45 kg water

it works well i sqwees it in my hand and holds very well and i brake it and it brakes very nice it dont fall apart, i did a few other paters it works well but i cant do that heat sink.

am i trying to do the imposible ?? or is it posible to cast this in sand ??

Also my sand sticks to my fingers when i work with it , is that normal ??

Thanks
Biggs

[DMF_TomB]

depends of grit of sand, some sand is coarse and needs extra clay. if it has more clay it can be used a little drier and it is less sticky to your fingers and the pattern.
......not that you should have too but i have heard of some people spraying a little Pam spray cooking oil on a pattern. Sort of like spraying silicone oil on something so stuff don't stick to it as much.
......also it is normal to screw into wood pattern a screw eye or regular screw and tap on it in all directions. this pushes the pattern in the sand back and forth to give a little extra clearance on pattern sides. the you can grab the screw to help pull pattern out. sometimes it is easier to use 2 screws.
...... for parting dust i use diatomaceous filter medium in an old sock that i shake and it come out through the sock (use in aquarium filters) although budgetcastingsupply sells parting dust and graphite powder and a liquid mold release...... my guess is you can buy $5 of diatomaceous powder at a pet store and it will last you a lifetime.

[Biggermens]

My sand is play sand from the home depot and i pass it in a 40 mesh sreen for sreen printing t-shirts i find it nice and fine enought for me, i also have a 100 mesh screen but i only get 1 pound out of a 50 pound bag hehe so i used the 40

I have tyed the pam it helped a little bit but i was getting better resaults from the baby powder

I do use screws in my paters i put 4 in them and i hade a little steel stick hit the screws to loose it up and it come out nice

I just cant get the heat sink to come out nice like in the pictuer attatch on the first post

Do you find diatomaceous powder workes better then baby powder ???

Thanks very much
Biggs

[fastleather]

How much draft do you have on your pattern? Is your sand fine grain and stiff enough to make your mold? Wiil need a release on your mold to pull it from your sand. You will need some sort of riser for the casting to draw from as it cools.

[DMF_TomB]

i suspect you need more clay and finer sand mixed in with you sand.
i have never used baby powder.
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like i said if sand too fine or too much clay you may have venting problems when casting and may get steam bubbles in you metal casting. always where protection for example face shield and welding jacket when pouring molten metal