Heating investment mold for better results?


#1

I will be receiving my Form 2 in a couple of weeks and was wondering if heating up the investment mould to the same temperature as the metal would produce better results.

To try this, I would first have to replace the rubber seals on my Investment Vacuum machine with something that can stand the extra heat. Is there anything else I should consider?

Has anyone tried this and did it make a difference?


#2

Interesting idea. There was quite a bit of testing and process experimentation to define the Formlabs recommendations for the Castable Resin burnout curve. To the extent that we know/tested, this is the best process. There’s always room for improvement, so hopefully other casters can share whether they’ve tried alternatives with heating the investment.


#3

Hi Marco,

If you are using Formlabs castable resin then you should be using lost wax investment casting powder such as plasticast investment casting powder to make your moulds. Then you need to burn out the resin in a kiln for around 8 hours with the temperature slowly rising to about 730 degrees C hold that for an hour or perhaps two then you should drop the temperature slowly to the casting temperature which as a rue of thumb should be about half your molten metal pouring temperature. So if you were poring metal at 1000 degrees C the mould temperature for thinnish objects should be about 500 degrees C. Thick objects require a lower mould temperature. Pouring hot metal into a completely cold mould is not likely to yield good results.


#4

If you’re doing fine parts like rings and jewelry you might want to consider looking into a spin caster. It uses centrifugal force to pull the molten metal throughout the entire cavity.


#5

Thanks Stephen and Hillzzz,
I do intend using Formlab’s castable resin and lost wax investment casting powder, and following the recommended burnout curve. The only difference will be the adding of a final “increase temp to metal casting temperature” step so as to have no temperature difference between the metal and the mold when pouring.


#6

Thanks pemcmo,
Have you found the centrifugal machine superior to the Vacuum Machines for rings and jewelry? Do you have any photos that you can upload that show how they come out of the spinner before polishing, please? I would really appreciate seeing them.


#7

Do you have a website with some samples of your work, please?


#8

You actually don’t want the mould to be at the same temperature as the poured metal in fact if you were poring sterling silver at 980 degrees C and you heated the plaster mould to 980 degrees C then you would be in trouble because Gypsum Sulphate based mould powders can’t cope with temperatures above 800 degrees C and begin to break down above that temperature.
You would need the more expensive phosphate based powders for temperature above 800. You will also need mechanical vacuum mixing machines because the phosphate bonded powders are too stiff to mix by hand.
I seriously suggest you do away with the final increase in temperature - you don’t need it.


#9

Thank you for that information Hillzzz! I didn’t know you couldn’t heat it past 800°C, there is no max heating info on the packet so I assumed it was safe. From now on I will check everything.

I am still wanting to heat the mould up to the casting temperature, because I only have a kiln, so I was planing on placing the metal in with the mould after the burnout process to keep the mould hot.

I have found specialised investment that is rated for well above the melting temperature. It is not that much more expensive and you can mix it by hand. As I said, I do have a vacuum machine to get the bubbles out.

Is there anything else that I have overlooked that might make this a bad idea? If so, then I will buy a seperate melting furnace.

I really appreciate your time and your experienced advice.


#10

I just use a crucible and an oxyacetylene torch setup (Smith Little Torch with bud tip) to heat the metal, but I think my limit with that is about 3 ounces of silver. I don’t have a crucible…yet. I’m using a KayaCast vacuum casting setup, although my old setup I had when I was a teenager was a basic vacuum caster and small kiln that cost $99! http://www.katkramer.com/jewelcast

The rubber rings that came with my casting setup are meant to be in contact with the hot flask…

I gave this advice to a friend who’s new to jewelrymaking yesterday who is trying to reinvent the wheel on pretty much everything…people have been casting and making jewelry for thousands of years. It’s been done, so it doesn’t make sense not to follow the usual methods.

I would definitely follow the advice of the folks here who have been successful. :slight_smile:


#11

katkramer I can’t agree with you more.

It is great to learn from the wealth of experienced artisans here. There is no sense in starting from scratch by reinventing the wheel and repeating all the mistakes that was necessary for the historical journey.

It is only once you achieve the competence levels that others like yourself have reached, should one think outside the box and make your own mistakes with untried techniques, in the hope that one day you might contribute to the evolution.

I am an beginner, and although I love learning about all the methods out there and seeing other people’s work, I also know how hard it is when you have so much enthusiasm, not to skip steps in the learning process and to wait before doing your own exploratory innovation.

BTW, I checked out your link to see some of the beautiful objects that you have created. Nice work!


#12

Thanks, Macro!

Yes, I actually got that casting set from my parents back in the mid 1980s. I only wish I had the horribly awful things I made with it! Incomplete casts of nugget rings, rings with shanks that were way too thick. I was casting in the kitchen, burning out with a kiln on the glass cooktop. I had no idea what I was doing…but had that great instruction booklet! I actually scanned it a couple of years ago for someone on a forum who had found one of the casting boxes and didn’t know what to do with it.

Since then I’ve been doing more fabrication from sheet and wire, and bought the casting setup a couple of years in hopes I could do a little more mass production. But I struggled with the wax. I took a class from a master of wax, Kate Wolf, and finally “got it.” I can tell you I have over a thousand bucks in wax and it was all trial and error. In a couple of years, I made one thing. I feel like was is becoming almost a lost art, and I struggled to find any information on how to do it. My best “teacher” before Kate was the old University of Michigan Dental School video archives. I can tell you I was definitely trying to reinvent the wheel!

Anyway, I have a tech background and graphic design background, so this seems like a natural extension of a bunch of random skills…I’m pretty excited about it, and got the okay from my better half to get the printer today. But I can tell you the weak spot is my knowledge is the actual casting. I’ve cast a few things successfully, and glad I have the larger vacuum setup so I can use the perforated flasks. I do also cast glass, and some glass artists use the R&R brand of investment. I do know with glass casting the investment can cause a very bad surface on the sculpture if not cured correctly. I currently cast with Kerr Satincast.

But things like cleanup of the models and even time-efficient cleanup of the actual castings are still quite unfamiliar. So I’m thankful for the forum and the opinions of the more experienced folks. There’s another forum about casting jewelry (he spells it “jewellry” in the title) that has some good info. I’m getting the feeling that some of his poor results are from curing the models in the sun instead of a UV curing unit.

Anyway, I can’t wait to see where you go with this! :slight_smile:


#13

Yes, curing it properly is very important. I am building a 108W curing station out of two of these just to make sure.

Also, I am not sure if it is just marketing, but it seems like the investment for resin pattern moulds needs to be different from the investment used for wax patterns.

This company has one for each. Here is what they say about the specialised stuff:
Omega+ has been designed to withstand the challenges of SLA master model casting, both in terms of expansion of the pattern within the mould and carbon removal.


#14

Can’t wait to see the UV curing unit. I noticed the one at the distributor today had lamps on the top and on both sides, but it was about $70 at a local beauty supply. It seemed like it would be a little small for curing more than about 10 jewelry models, though.

Yes, it sounds like the investment is different. I would guess if the pattern expands quickly, it can crack the investment mold. Being a glass artist, expansion is a big deal and can damage our kiln shelves (I cracked a 24" square one…expensive mistake!). I haven’t heard of Omega+…looks like you might be in the UK? Can you get the R&R investment recommended on the burnout schedule page here on the Formlabs site?


#15

10 moulds at a time, impressive! I guess you need a good income so you can get all the equipment (toys) needed for the art.

I will post a picture of my Frankenstein contraption on the strike of the first lightning bolt.

I live in Australia and I haven’t yet found a local distributer for the recommended R&R investment: just kangaroos.


#16

That’s awesome! Actually, 10 models at a time, so like 10 rings. Not too much room!

I can only imagine the shipping to Australia. I just found it for $54 USD at a couple suppliers, but the shipping ranged from $27 to $55…quite a bit!

I’m guessing taking it on a plane will raise some eyebrows…the drug authorities might stop you with your box of “white powder.” :smiley:


#17

Yes, exactly LOL! That’s why I go with other brands. :runner:

It only costs around $10 Australian (USD $7) to deliver a 22.5KG sack of investment from a local dealer. (No, not that type of “investment” or “dealer”).


#18

My first casting set-up was a 8 inch square flat piece of steel plate with a 1/4 inch pipe welded into the middle. Connected to the pipe was a vacuum pump I got from a petrol station pump i found in a rubbish skip. I used steel tubes as my flasks and after burning out in the kiln I stood them on a heat proof rubber gasket over the hole. turned on the vacuum and poured the molten metal in. The vacuum sucked the metal in to the mould and job done.

It worked quite well and cost very little to make.