using Low melting temp alloys for dies for wax models

Cerrobend alloy on eBay.

I often make epoxy cavity moulds from Ceratru alloy. It involves making a highly-polished aluminum positive with only positive drafts, then dipping the cold master in the melted alloy.

It adheres like the chocolate on a dipped ice cream cone, and freezes in a thick enough layer to be mechanically sound when slipped off the master. The epoxy casting is made in the alloy mould, then the mold is gently cracked off the casting, and re-melted.

LLoyd

Sorry... that is Cerrotru, not "ceratru".

I selected it because it has virtually zero dimensional change when freezing.

LLoyd

That's a good idea, dipping the positive I mean. Sorta like what they do with cerramic molds IIRC.

There are several basic procedures, casting, spraying, slush molding, and dipping. Casting and spraying are the most common for injection molds. Casting is usually done using a metal master to take advantage of the chilling effect which gives better surface detail. Spraying can be done on non-conductive masters as long as all areas can be accessed with the spray. To use the molds for plastic injection, cooling must be provided to keep the hot plastic from melting the molds. The plastic temperature can exceed the melt point of the metal if proper cooling is used. Have fun.

Perhaps I should have been clearer in what I want to do. The molds in question are two part molds, the wax is injected into the mold, allowed to cool, the mold is parted and the wax is removed.

I want to learn how to make the mold used in this process. I know that many people use rubber molds, but with belt buckles have trouble keeping the wax to a consistent thickness. I also like the idea that after a short run of a particular buckle the mold is remelted and a new mold produced.

So long as each of the front and back of the buckle have only positive drafts, you should be easily able to make the dipped Cerrotru moulds in front/back halves. It would only involve embedding the master buckle half way into a base material for holding -- say a block of plasticene, and dipping the face of this into the melt.

It would be better to carve/sculpt two "half buckles" in bas-relief in a block of aluminum, and use that as the master -- then you'd get the opportunity to create a sprue, vents, and clamping faces.

LLoyd

For your two part molds, either cast or spay can be used. The choice between the two may be determined by the model or original you plan to use. If your model is metal, then pouring will work well. If the model would be damaged by the heat, then the spray my be better. By the way, a properly made rubber mold should not have the problems you describe. Ridged models have to have draft if used for casting metal molds, an obvious advantage for flexible molds. What are your models made of?

The models are the sterling silver original buckles. could they be bedded in plaster, then the half mold poured? what would one use for parting compound/

It has been a long time since I that material. I wouldn't want to give you wrong info. Check this site and maybe call them for specific info on the alloy you plan to use. They also list all the various alloys with properties and uses.

I seem to recall using a very light application of silicon spray. I think a teflon spray would also work. Are the buckles cast or hand tooled or encraved? Low relief with good draft I hope.

What's the melting temperature of the wax you're using? If it's below roughly 400 degf, you might try Dow Corning's 3110 RTV silicone.

Hul

ol3_m3 wrote:

========= see

Unka' George [George McDuffee]

------------------------------ Watch out w'en you'er gittin all you want. Fattenin' hogs ain't in luck.

Joel Chandler Harris (1848-1908), U.S. journalist. Uncle Remus: His Songs and His Sayings, "Plantation Proverbs" (1880).

OM

========== For more specific advice I would need to know your expected production volumes, amount of capital you wish to invest, and your current technical skill level.

An existing industry that is doing almost exactly what you describe are the dental fabricators/labs, although a belt buckle may be at the upper limit of their capability. Try making contact with your area dental labs. You may get a tour, and even better thay may agree to make some of your castings on a time available basis to improve their machine utilization.

More than likely, elastomeric molds cast from silicone or urathane for detail, possibly backed with plaster for support will prove to be what you want/need. The elastomeric molds will allow negative draft and undercuts, and should be durable [in the range of 50 to possibly low hundreds of wax castings] with high-temp [hard] wax.

There are many "tricks of the trade" to investment casting, so if your local community college or tech center offers a course you will be money/time ahead to take it. This would also let you get some "hands on" before spending any money on equipment and supplies. For your use, it should not make any difference if this is a "technology" or "art" driven course.

If you are near a university with technology or fine arts programs it can be worthwhile to check with these, and generally you can enroll for a single class on an audit basis without the admissions hassle.

Even if they don't have casting class, find out who the more "hands on" instructors are for the "technology" and "fine arts" and talk to them personally. In many cases there is an investment/spin caster setting under a bench and supplies in the cabinet, and they may be looking for extended/adult education class ideas. google on for

55k hits.

take a look at these sites for dental lab equipment. You might email for a list of customers in your area for some leads.

google on for more than 1 million hits.

There are investment casting hobby kits, and the price/size/capability goes up from there. Your belt buckles because of the length and width, not so much the weight may be at the upper limit of the hobby level equipment. Take a look at

also of interest

google on for 152k hits.

Good luck and let the group know how you make out.

If you have [access to] a digital camera, see

for details on how to post pictures. My Logitech webcam will focus close enough for this, so you might check if you have a webcam.

Unka' George [George McDuffee]

------------------------------ Watch out w'en you'er gittin all you want. Fattenin' hogs ain't in luck.

Joel Chandler Harris (1848-1908), U.S. journalist. Uncle Remus: His Songs and His Sayings, "Plantation Proverbs" (1880).

Thanks for the lost wax casting information. I am looking for information on a specific method of mold making in which to inject wax or a wax plastic combination to make the models used in the casting process. The mold making process uses a low melting temp bismuth based alloy to produce a perminate mold. If anyone has any information this process I would like to know of it, Please.

So far I have discovered the alloy used in the process, there are a number of names for it, but it melts at 281 deg, and is fluid at 330 deg. If nothing else can anyone suggest any boks on the subject that might be helpful?

Thanks in advance for your assistance.

OM

There are two alloys with 281 melt, both are tin and bismuth with different ratios. Basic difference is in accuracy; one has a little expansion, the other a little shrinkage. Both have been used for wax molds. The one with less bismuth is more stable. At one time I had casting info but can't seem to locate it. You might just give it a go using some coins or other objects that are expendable. Experience is a very good teacher.

Thanks for the ideas, if you remember anthing additional please let me know

Found out there are two alloys that melt at 281 deg. does anyone know which one is used. still trying to figure out a procedure, any help is appreciated

| > I belive the alloy used melts at 281 deg F, Does anyone in this group | > know the procedure used to produce these dies? | >

| > Thanks | >

| > OM | | Found out there are two alloys that melt at 281 deg. does anyone know | which one is used. still trying to figure out a procedure, any help | is appreciated |

I'm curious why you want to use alloys(metal) to make dies for wax models. Rubber molds are normally used for such purpose in lost wax casting and they are more superior in dealing with design undercuts.