What's wrong with these pictures?

[nzfinescale]

I offer the following disasters for learned comment from the group gurus.

The following are cast from Emerald prints cured under UV overnight in water. Prior to curing they were given a quick isopropanol rinse followed by around 10 minutes ultrasound with detergent. 252525 prints. Prints were excellent without any obvious problems. I've reviewed the STLs and these appear to be OK. These models did seem difficult to get free of uncured resin.

A similarly treated, but much lighter and thinner model cast well in the same run, with no issues at all. I have no control over the casting process as it has been done by a casting house who have been uncooperative to date on matters such as investment and burnout details. I'm working on that.

The first casting is 12mm diameter. For much of the cast the surface is good and smooth, but parts have blown out, there is a black residue and the fine details at the top have disappeared, to be replaced by a kind of scintered metal sponge. In the blown out area there looks like some structure under the surface - no idea what that would be.

The second casting is 8mm in diameter. Surface quality is mostly excellent, but again black residue and that large hole (which also appears on the opposite side and has appeared in previous casts too). The model is hollow but wall thickness is about 2mm. The acorn at the top has also begun to suffer the sponge-like scourge.

Given the fine casting (not shown) went well I'm assuming its the resin models rather than the casting process - so presumably a curing issue?

It's driving me crazy - the best patterns I've ever had thanks to the Solus, and the darn things won't cast!

Lawrence

[rkundla]

Not knowing what it was supposed to look like before casting, I can only assume that the investment gave out and broke apart during burnout.

What metal is that? If it is silver, did you try to get rid of the black marks by putting it in pickle? The other pits look to be caused by either ash or broken investment. Can you mechanically remove the black marks with sandpaper or polishing wheels?

What does the underside of the hollow second model look like? Does it have surface issues on the interior as well?

[Jewelermdt]

My guess is it didn't burn out fully and large ash still in cavity. I hear heaver models need longer burn out at top temp.

[GSJ_NZ]

Hi Lawrence,
Are you using Morris & Watson? I’ve had a couple of fairly successful Emerald casts from them, mostly in Stg silver though. A palladium one initially looked great, but was pumice-like through its core, a bit like the top section of larger one of your casts. They did a fairly large (4cm3 of resin) stg silver ring mount the other day that apparently cleaned up nicely.
They’ve been keen to give the resin a go, and helpful, but also don’t want to modify their casting procedures to suit the resin.

My curing process is not as controlled as yours, but here it is for what it’s worth:
First zap in the ultrasonic in a bag of detergent and water for 5 mins, rinse in warm water, leave in sunlight (ok, maybe not today!) for a few hours but moving it around to try and get an even exposure, and 3x lots of microwave cure @ 2mins 20 sec each in a beaker of baby oil. Remove supports, file and emery to tidy up the support areas, back into a clean ultrasonic bath, rinse, back into the microwave, wash in warm water to remove the oil. I did 4x lots of microwave cure for the big one due to its increased size and volume.
The Emerald seems to harden up nicely after being in the microwave in oil.
Gary

[nzfinescale]

Hi Gary

Yep you called it - M&W. These are cast in bronze by the way - forgot to add that to my original post.

I talked to Grant George there who was quite willing, although ultimately not definitively helpful. They use UltraVest with the recommended burnout for that investment. I have yet to check out what that is but I gather the ramp is quite slow. Based on my conversation with him and gleaned knowledge from this forum it seems likely that resin expansion during burnout is causing investment to spall away. Those bits are eventually falling to the lowest point in the final cavity causing voids (if large), or that spongy effect if there's a volume of small particles.

I don't think this is a curing issue as the best bits of the castings are the bulky bits (if anything least cured) and it is the details at the low points that suffer (Presumably the best cured).

My next step is to persuade M&W to try Plasticast. I'm a very small customer though, so I'm only going to get traction on that if they are feeling generous, curious or getting pressure from others.

Other thoughts:
1. M&W did do some casts from Jesse Taylor in Cherry for me that worked well. So I guess Cherry is an option.
2. Does anyone have feedback on Yellow or an Emerald/MJWax mix specifically on the expansion during burnout question? Maybe this would also be an option. Any castable resin that works with UltraVest would be good to know.
3. Anyone casting bronze or brass from Emerald on a contract basis? Any recommendations on this would be most welcome.

Frankly I'm feeling a bit disheartened. I've laid out a lot of cash (for a hobbyist), it all works great on the modelling and printing side, but it looks like I might be in for a long road to get to the casting endpoint I was after.

Moulds are certainly an option, but direct casting has advantages for some tasks that I would like to take advantage of.

Lawrence

[Archerm]

UV overnight no water.
Microwave your models in distilled water for 2 1/2 min to 3 min let cool and repeat two more times before you invest them.
Make sure your bottom is large enough to control porosity. total weight break down for bronze 40% model 60% sprue and button.

[nzfinescale]

Thanks Archem

Will give the microwave a go. I've avoided it to date as the domestic authority takes a dim view!

In terms of the casting this is in a large commercial flask on a significant tree. So while there is no 'button' per se, there is a large mass of metal serving that function. I don't have control on that point, but my caster is doing this daily and has done for years so I'm as confident as I can be on that aspect (and in no position to alter it anyway).

L

[M-Williams]

Most probably the cause of this failed casting is "curing".