Phase Change Madness!

There are metal alloys which will melt at 70^oC... here

You can make joke tea spoons out of it.

Del

Hello anchange

Will solid CO₂ do the job for you?

I must admit it was the first thing which sprang to mind.

Kind Regards....

Don't think so, it will be too hard to get from liquid to solid Someone told me that Naphthalene and Menthol could be possibilities anyone know how I can get phase change date on those / at what pressure (assuming room temp) do they perform sublimation? Also are they expensive or cheap to buy like 20lbs worth.

Hello again, anchange

Napthalene would do the job, but avoid contact, and the vapours are toxic and flammable, so it's not really an option.

Napthalene is slow to sublime at room temperatures (Remember those mothballs in Grandma's wardrobe).

Iodine crystals, pressed into shape, but avoid skin contact, would do the job.

Do not breathe the Iodine vapour, you would need a proper fume hood, and pass the extracted air through water to stop toxicity for the neighbourhood.

Iodine crystals pressed into solid form, will take much longer than CO₂ to sublime.

As I said earlier, solid CO₂ would satisfy the temperature requirements, is non-toxic, but remember you need Oxygen to stay alive, and you can normally obtain local supplies of solid CO₂ from a maker of liquid CO₂.

The solid CO₂ is normally sold in the form of flakes, shaved off a larger block, but have a chat to potential suppliers, and you may well obtain solid blocks of CO₂, which can fuse together, will need to be worked with quickly, or it will all sublime.

Commonly wax was used for the interior mould, but you have not advised your casting metal.

You haven't advised the shape of that interior mould, and perhaps it is very intricate.

Do you have multiples of the completed casting to make, or is a One-Off project?

Further details would assist.

Kind Regards....

What about Ice-Water-Steam?

Wow thanks for all the help. Basically what I'm trying to do is to do a similar kind of casting as wax loss casting except I don't want to coat the molding material with ceramic and then burn out the wax. I'm looking for something that I can mold, place directly into my casting sand and then vaporize leaving a cavity directly in my casting sand that I can then pour metal into. It would be a mix between the principles of wax loss casting and foam loss casting used for quick and dirty repeatable castings from a master negative mold. Sparkstation (or anyone else) have any ideas?

Hi !! You can try using Thermocol material to produce shape you want to cast and put it in the moulding Box, Put Foundry Sand around leaving space for sprue to pour the metal and after some time Burn the Thermocole

Cavity thus created can be poured with desired metal to get One off Casting

It is very cost effective solution . Giving Shape to thermocole material / Sheets is very easy -- you can glue sheets to get desired thicknerss and remove unwanted material of thermcole you may use heated thin needle which can be pierced in and moved as long as needle is hot. Re- heat the needle and proceed from where you left,until desired shape is made

I do not know if this is right solution for your needs but this has been quite successful method for our occassionl requirement of one off requirement of metal pieces when making pattertns are costly and time consuming.

Thanks

Udayan

Bradley,

I presume you are expecting uneven cooling of mould during casting.

This is a major worry for intricate castings as material at the periphery tends to cool faster as compared to the one which is at the interior. Other problem faced is 'flow' of material during casting as solidification process starts in the areas near to the exterior walls.

One method which enables the temperature to 'even out' is by inserting heat pipes in to the mould. Heat pipe is a device having heat transfer rate thousand of times better than copper conductor of same size. It works on the principle of evaporation and condensation of a liquid which is inside the heat pipe which is under vacuum allowing the liquid to change its phase from liquid to vapour and by doing so it transfers the latent heat from one end of heat pipe to the other end. By doing so, you are able to even out the temp with in the mould. I suggest you visit www.capri.co.in to understand the working principle of heat pipe.

Typically, a water filled heat pipe works in temperature range of 30 to 200°C.

There are Phase change materials available known as PCM which store latent heat at a given temp and can be sourced commercially. They change phase from solid to liquid on seeing a certain pre-determined temp and when the temp falls, they pick up latent heat from atmosphere and solidify - ready for next cycle.

So you have a combination of PCM (solid to liquid to solid) and heat pipes (Liquid to vapour to liquid).

PCMs and heat pipes are not toxic too.

I hope I was of some help.

Try these folks.

http://www.pcm-solutions.com/response1.html

j.

I saw a magazine article a while back about a a boat motor manufacturer that uses styrofoam. It's rigid enough to hold up while making the sand mold and vaporizes quickly when the molten steel is added. Google "lost foam casting"

This was my comment; I forgot to log in. On thinking about it, I believe they were pouring aluminum (aluminium or you in the UK), not steel. I'm surprised they don't have porosity problems, but it does work.

I think I've confused people. What I'm trying to do is find a substance that can be easily cast from a mold and then it can be easily dissolved/vaporized. I've done a lot of foam casting before but the problem with that is that you can't mold the foam at home you have to cut it up to make your shape. Thermocol/Polystyrene can't be cast at home (Polyurethane can but it then wont dissolve well). I'm trying to find something that I can place into a mold, pop it out, pack casting sand around it, let it vaporize, and then have an empty cavity to pour metal into. Any thoughts?

Bismuth has a low melting point (under 100 F IIRC), but you might have environmental issues using it.