styrene pattern for casting

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todd goff
Posts: 128
Joined: Fri Jun 12, 2009 12:59 pm
Location: South Carolina

styrene pattern for casting

Post by todd goff » Tue Apr 13, 2010 8:05 pm

I am a little confused right now about a casting that someone wants me to make. The process that I am using is new to me and I have several questions. What I have is a styrene pattern for a small pulley to go on a lathe and it is not working too well. I use petrobond sand and rammed the core into the pulley with my fingers so that it would not break. The next thing I did was to hand ram (not air ram) the rest of the mold so that it would not break apart. Well, in the end it was disastrous; the styrene pattern split and the rest is history. My goal was to put the styrene pattern in the mold and it would burn out when the metal hit it it would vaporize and leave the casting in its place. I told the guy what happened and he said to use regular sand in the mold and pour it in. Can someone please tell me how to do this? Regular sand will not work in my opinion as there is no agent in it to make it bond together and also regular sand without a binder will wash away if you do not have a binder (lifting force of metal; although al. is very nominal, correct?) Oh well, I am open for suggestions and thanks for the help.

Harold_V
Posts: 17658
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: styrene pattern for casting

Post by Harold_V » Wed Apr 14, 2010 12:07 am

I spoke at length with a guy that was developing casting procedures using styrene beads. I distinctly remember him telling me that all that was required was loose, dry sand.

Do bear in mind, I have no experience with this process. I, like you, don't understand what keeps the sand from collapsing before metal fills the void, but it apparently works that way.

Harold

RONALD
Posts: 556
Joined: Sun Oct 26, 2003 7:27 am

Re: styrene pattern for casting

Post by RONALD » Wed Apr 14, 2010 7:43 pm

I have done many Lost Foam castings over the years, and my preferred molding method/material is the Sodium Silicate/CO2 process. All you do is pack the sand by hand around the pattern, and then you harden it with CO2 gas. Using unbonded sand sometimes will work, but there is a chance it will not. I have used PetroBond sand, and if you don't ram it too much that should work also.

Here are two earlier posts to look at.

http://www.chaski.org/homemachinist/vie ... 14&t=76920

http://www.chaski.org/homemachinist/vie ... 14&t=76146

todd goff
Posts: 128
Joined: Fri Jun 12, 2009 12:59 pm
Location: South Carolina

Re: styrene pattern for casting

Post by todd goff » Wed Apr 14, 2010 7:47 pm

Ah ha, now it makes perfect sense. Thanks for the advice Ronald; the styrene mold didn't play well with the sand when I rammed it even though I only hand rammed it.

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