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Is this bad casting from soft/degraded investment?


#1

Love the new forum format. It’s the same one used by Trimble (Sketch Up Pro), and Google.

I believe these argentium castings are coming out rough because either I’m mixing too much water or not mixing well enough… or I’m holding my high temp. too long on my small flasks. I was wondering if anyone experienced may be able to tell by seeing the crusty/porous look on most of the surface? I’m using Satin Cast for now but was told that UltraVest Max is good for castable resin and will not degrade as fast at high temps.

My flask is only 2.5 inches in diameter by 4 inches high. And a friend says he thinks my investment is degrading from how I described it. I took some pictures tonight. I’m using castable resin from FormLabs and the flask is bone white before I spin cast. I do not think the burnout is incomplete due to the bone white top and bottom of the flask.

There are parts of the castings that have the perfect model surface recreated, but much of the model surface is really rough as you can see from this one.

I am concerned that since I don’t use a graduated cylinder, I am not mixing the exact amount of water required and think I’m adding a little too much water in my mix. Other then that, what else in my routine looks like it could be a problem?

I mix for a minute in a bowl with a whisk. I vacuum for 1 minute. I pour into my flask with models. I vacuum for 3 to 5 minutes. I let it sit for 1.5 hours. (My flask is only 2.5 inches in diameter by 4 inches so I don’t think it needs 2 hours). Then I follow the castable resin instructions for ramping and temps… which includes holding at the maximum for 1 hour. (I held for 2 hours the first time, but held only for 1 hour the second time and still got the same exact kind of rough castings). I’ll spare you the details but both castings each took from 5 to 8 hours of ramp and hold times. I highly doubt my flasks needed more burnout time so I’m screwing something else up I think.

Could it be a combination of too much water in my investment and I should hold my max temp. for less time because my flask is kind of small?

It’s hard to tell from this picture, but in the front, the casting has the correct surface in a small place, but the rest of the casting shows a poor surface. Most of my models all had this typical mixture of really rough poor surface and a few nice surfaces that were identical to the models.

Thanks for any ideas.
Rick


#2

I mix my investment for 3 minutes, vacuum in the bowl for 20 seconds, pour into the flask and vacuum the flask 60 to 90 seconds. All of this is as manufacturers instructions. I use Kerr’s Satin Cast.
I have a paper on this here some where on Ganoksin. I think it may be titled “Silver Casting”.
I have specific instructions on mixing the investment in my paper. Some casters boo hoo the strict measurements, but since I have used this procedure I don’t have any bad castings.
Again all of my processes are as manufacturer’s recommended procedures.
Good luck.


#3

This looks like investment that was to wet during the burnout procedure.
The moisture starts to boil or simmer depending on the used heat and ramp causing this rough effect.


#4

Temperatures are very important as well as being very strict with yourself over mixing investment

Most investment plaster will oxidise at temperatures at / above 750C and become porous. this will also happen if you heat soak at 750C for to long.

The other thing is sprue length. Making your sprue gates to short will impact a casting run in a large way especially if you are not in total control of your metal temperature. To short a sprue will create turbulence, allow the metal to hit hard in the mould cavity and cause a massive amount of porosity. Think of it like pouring a beer to quickly and hitting the bottom of the glass. It will create a huge amount of head. The easiest way to fix this is to allow the head to form further away from the cavity.

so here is my suggestion.

Drop your top temp by a few degrease to stay below 750 especially if you are using old investment. allow for a nice long burnout time 2 to 2.5 hours and 3 if your have more than 2 flasks in the kiln. Allow your kiln to drop to just below 500C and let it sit for an hour before placing in your centrifuge. Lengthen your sprue gates to 10mm on base and 5mm off the tree. Don’t skimp on the vents and use lots of borax in your crucible.

It could be lots of things but this might give you start. I have had castings come out this way in various metals and it usually boils down to letting the kiln get to hot and or casting at to high a temperature.

If you have stable investment you can let your kiln drop to 425 and still get very nice complete castings in silver and gold.

Les


#5

Thank you for all the tips. My sprues are pretty short and combine that with too much water… I think you are correct. I will make the adjustments and try again. Thank you everyone.


#6

Richard-So far some excellent ideas put forth about your investing and
spruing procedures. I’d definitely try a longer sprue.
However the key words may be castable resins. Do you have the same casting
issues with wax? I’d try both in the same flask to see if it might be the
resin.
James Binnion presented an excellent paper at the Santa Fe Symposium as
well as the Portland Jewelers Symposium about issues with resin castings
and how to make them burn out and cast cleanly. The paper is available for
free online through the Santa Fe Symposium web site.
Have fun and make lots of jewelry
Jo Haemer
www.timothywgreen.com


#7

Thanks. I am kind of new to both resin and wax. My printer is experienced in curing the resin so I’m probably not burning it out right and having too wet of investment…too short. I got a lot to try but will do it all.


#8

I really like Les’s suggestions. In addition to making sure my investment has less water than what I did…would letting my flask sit after mixing for more than 1.5 hours help? My workshop is normally warm and humid. About 88 degrees this time of year. I wonder if letting it sit for 3 hours would let the investment harden before the burnout so the steam does not break the investment up? Or would 1.5 hours of sitting suffice as long as the initial ramp up is not too hot? I’ll read Binnions paper which may address it.


#9

You vacuum times seem a little long. Once the investment starts to boil you only need to vacuum about 15 to 30 seconds beyond that, once in the bowl and twice in the flask. Your investment should be the consistency of pancake batter, thick but pourable. allow 2 hours before putting in the kiln.
The problem with resins is that they can expand before they melt and burn. Wax melts and is not strong enough to expand and damage the investment. So your investment needs to be stronger. Also take the resin sprue off and replace with a large wax sprue. The wax melts out early and allows the hot air to act on the resin more quickly.


#10

My experience that I just got back to recently is that it’s important to
mix your investment as close to the gloss off point as you can. I’ve been
getting way better casts with smooth surfaces. No water marks. The
investment is different for the resins. They require a longer burnout and
our brand (which I can tell you the brand but not at the moment cause it’s
not in front of me) it doesn’t gloss off for 14 minutes so it needs do be
mixed and vacuumed for about 13 minutes and poured at the last minute.
Our satin cast for wax is about 9 min. Mix. If you pour the flasks too
soon the water separates and causes crappy surfaces. That is a part I
always rushed because of impatience. It pays off though I if you follow
through. Just do some stretching and squats to pass the time while your
mixing investment.


#11

yes

I cure my investment for at lease 4 hours before submitting it to heat.

Plastic and resin take a bit longer to evacuate from moulds as well. The don’t flash burn like wax and need a bit more time to melt and ooze.

Try a first stage at 300C for 2 to 3 hours. the more solids you get out from melting will make the burning easier.

Carbon protects and holds things in a solid mass so if there is to much solid material in the mood cavity when the heat is turned up you will need longer for the burn.

Think of it this way. Put one bit of paper into a fire and it goes up quickly but when you put in a whole stack it takes forever and sometimes you are still left with bits of unburned paper.

Les


#12

Thank you so very much. I also just realized that since I close my kiln for all the way after 1100F…I don’t have a lot of air flow which I read helps resin burn out. Maybe I just keep the door a little open while its hotter. I’ll report my results.


#13

A lot of good input here. It looks to me that the cause of the rough castings is caused by the investment breaking down. I think it’s from multiple causes, which may include incorrect proportions, temperature of the investment and water, timing of mixing and vacuuming and burnout times and/or temps. Investing isn’t rocket science and none of the steps are absolutely critical, but it is important to be at least in the neighborhood.

You don’t have to use a graduated cylinder to measure your water, you can weigh the water. 1CC at standard conditions weighs 1 gram, so it’s a direct computation. If your 40/100 calls for 100CC of water, 100 grams will be pretty close to right. I know there are chemists that will tell you that’s not entirely correct, but for investing purposes, it works fine.

I tried to upload a PDF of Kerr’s instructions for use with Satin Cast 20 and 2000, but it wouldn’t copy. A search for instructions for the investment you’re using should lead you straight to them. Follow all of the instructions as close to the letter as possible. Like I said, no one step is absolutely critical, but until you have a baseline, you won’t know which step is causing you grief.

Casting resin can be problematic, but it shouldn’t cause that much of an issue. You said in an earlier thread that creating such a tree would be impossible without printing the whole thing. I disagree, In fact, I think that may be part of, if not the entire cause of your problems. I’ve done hundreds if not thousands of trees of tiny pieces using nothing more than a wax pen and sprue wax. Something that may help you is to print the individual pieces and then gate them using sprue wax in the traditional manner. Sprue wax melts at a lower temp than injection or carving wax, the theory being that it will melt and run out of the gate before the model does, giving the model room to expand and flow out without restriction. It is just possible that having the entire tree made from resin may be preventing the models from properly flowing out of the gate as they melt and vaporize. I think I would also extend the burnout time so that each 200F step is held for 2 hours so as to allow everything time to break down and exit the flask at a slower rate.

When all else fails, read the instructions :wink:

Dave Phelps

Good luck


#14

Rick,
I’ve only read a couple replies to your original post so please excuse me if I repeat other peoples advise & suggestions. First, the comments from Dave Phelps, are spot on. I’ve been casting for 45 years mostly golds, in earlier years silver plus lots of platinum. I use a Torit, vertical machine with vacuum assist.

Looking at the photo of your casting it’s a classic example of several things; too wet investment plus degraded most likely as even new investment is very forgiving mixed a little wet. Also, the photo looks like your burnout temp / time is a little fast. Something Dave, also mentioned. Another very important point Dave, noted about the main tree sprue needing to melt out first allowing the mode wax / resin to have an open passageway to drain out. That is important!

Last thing I say your 2nd vacuum time is really long at 3 to 5 minutes. Even 3 minutes is long on such a small volume flask. I’d go maybe 2 minutes tops with that size flask.

Richard


#15

I can report that I got better results by using less water for the Satin Cast. My casting today still was a little rougher than the original resin model but the improvement made it usable.

I believe now that the only problem is that Satin Cast is too soft when the resin expands. (It greatly expands compared to wax before it melts). When I mixed too much water before, it only made it worse. Today, I used slightly less water than recommended for heavy castings, and the Satin Cast is still too weak for the resin expansion in my opinion.

I’ll get the PlastiCast by R and R which is supposed to help with the expansion problem. A friend reports that the Ultra Vest also works well.


#16

Hi Rick,
I normally check the if the resin is cured perfectly or not. My experience being if the resin is uncured the casting are invariably rough even with R&R Plast. We use R& R Plast. De- mineralized waterFrom: Richard Powell <orchid@ganoksin.com>Sent: Mon, 17 Oct 2016 06:41:56 To: umeshgchavan@rediffmail.comSubject: Is this bad casting from soft/degraded investment? [Jewelry Discussion] [Ganoksin Orchid]

          RickPowell
          

          October 17

I can report that I got better results by using less water for the Satin Cast. My casting today still was a little rougher than the original resin model but the improvement made it usable.

I believe now that the only problem is that Satin Cast is too soft when the resin expands. (It greatly expands compared to wax before it melts). When I mixed too much water before, it only made it worse. Today, I used slightly less water than recommended for heavy castings, and the Satin Cast is still too weak for the resin expansion in my opinion.

I’ll get the PlastiCast by R and R which is supposed to help with the expansion problem. A friend reports that the Ultra Vest also works well.

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#17

Thanks. I am wondering if my FormLabs castable resin models are cured properly. My friend prints the models for me and says he cures them. But how does one check if the resin is cured enough?

I guess I could leave the models in the window for a few days before I cast them.


#18

Richard- It could be several things. I still think it may be the resin in
the models. There is so much importance in proper curing of models and the
old ways seem to not work as well as they should. I’d recommend that you
share the following info with your model maker.
Here is the latest Santa Fe Symposium paper from James Binnion. Worth the
read. Jim really knows his stuff.


Jo Haemer
www.timothywgreen.com


#19

I think of casting as a series of steps each of which contains a number of variables.
Things can go amiss at one or several points in each step.

-Improper spring can lead to miscasts (non filled areas), porosities, hot tears and even spalled investment (should a little finger or fin of investment break off in the stream of incoming metal).
-Poorly mixed, mis-measured or old investment can lead to spalling, investment inclusions, cracked molds or rough surfaces.
-Burn out is another area that can go wrong. Too high a burnout can lead to investment breakdown, rough castings or even brittle castings. Too low can lead to miscasts and brittle metals.
-Contaminated metal—solder, a stray bit of other metal and even leftover pickle can lead to brittle, porous or cracked castings.
-Too hot a melt has it’s own set of problems.
-Even the temp at which the flask was cast—in relation to the mass it contains—can lead to non fills and shrink spot (spongy) porosity which is often the result of poor spruing or a large object cast too hot and so allowed to cool too slowly.

I think that it’s useful to narrow down where in the process the flaw occurred. This can help diagnose where and how the problem developed and ultimately eliminate it. I’ve found that even the shape and character of pitting can greatly help to clarify things.

I have no doubt that it could be a poorly cured resin that is causing the problem but I would be curious at to what that mechanism is. At what point in the multi step process that is casting does the uncured resin begin to affect things?

I love a good mystery.

Take care, Andy


#20

It’s interesting as well to note where on the cast object the porosity is…