What is the Slickest Most Adhesion Resistant Prep for Sodium Silicate Core Boxes?

I have just revamped a Baltic birch core box that I have been using over the last 3 years. It is 18” long and triangular in cross section with letter located near its interior apex.

A seemingly good approach to coating it has been to spray it with a couple coats of shellac and then a few coats of sprayed while lacquer. The lacquer tends to reveal any surface dents or high spots which I then either sand off or fill with spotting putty or slightly thinned Bondo two-part putty.

Then I have used Johnson’s past wax and sometimes have used silicone spray (I am uncertain how much this helps) and some of the time I have applied graphite. Overall the wax and graphite work pretty well. But I wonder if an automotive wax would be more durable or slicker. And would there be some other coatings that would be superior?

I have noticed that spray shellac left as the final surface coat does not seem to release nearly as well as does the lacquer.

I will soon be making an aluminum casting of the corebox in hopes of improving its durability. So it will need some sort of coating/polishing/talc/graphite/other treatment as well.

Suggestions for both the wood and metal boxes?

Denis

 

One ask this guy in the most appropriate video
https://www.youtube.com/channel/UChF0g3BAJwfO1I5237iNBOQ/videos?view=0&sort=dd&shelf_id=0

in the Navy the pattern shop had two things Sandable sealer, and Spray Lacquer,
the closest thing I have found to sand sealer is autobody primer , it comes in 3 colors and two varieties, small filling, and heavy filling obviously works on wood and metal, fillers, wax you name it , steel wool it fow a crazy slick finish, you can steel wool it with graphite for a slick slick slick finish, or just steel wool it , then lacquer, go easy with the laquer, this is a bad time to get a run

for the finished core box , we used some commercial product, which looked very much like fireclay, graphite, in alcohol , probably with something to keep it in suspension, we sprayed it in the core box, it would dry in a few minutes, make your core, the core would come out of the box with most of the release agent on the core (it was bright silver)

Here is a link to a commercial product, there is some real interesting stuff there

https://generalchem.com/category/cold-box-mold-release-agents

a google search for core box release gives some neat info


V/r HT1

 

HT1,

I.t looks like the linked core release agents contain large proportions of silicone. I have sort of a love/hate relationship with silicone though I have only used it as a spray mold release. Probably would be better in the linked higher concentration products.

My beef with silicone is that I not infrequently like to make some modification to a corebox. That means repainting it with lacquer. Silicone raises havoc with lacquer as it causes fish-eyes even after a fair bit of sanding. I try to get around that by using a sealing coat or two of shellac which seems relatively insensitive to silicone contamination. But even that is imperfect. Wax seems to cause little trouble with fish-eyes and that may reflect its tendency to not be as adhesion resisting (have higher surface energy) than silicone and therefor be not quite as good a release agent as silicone. Graphite does not seem to cause trouble with fish-eyes either. What I would like to find is a wax that is significantly better than Johnson’s so that I could avoid silicone. But, if the core release agents are really superior, then I will knuckle under and use them.

Thanks.

Denis

 

I'm not going to say I have a solution but have you ever "polished" your paint with your fingers?
After the proper drying time I rub my patterns hard. There is a noticeable difference in slickness.

 

I have certainly polished it with 600 and 1000 grit Si-C paper. You can see where that knock the tops off the inevitable hills in the paint. And then I wax and then I rub in graphite with my fingers and a brush. The result is pretty good. I am just looking to make it better.

This morning I tested Meguiars car wax, Johnson Paste wax and Johnson Paste wax to patches of melamine. On the second Johnsons patch I sprayed some silicon. Then to all three areas I pressed on a 1” square patch of Bondo polyester filler and let it set up. Then I did a peel test.

The Meguiars was a little stickier than the Johnsons and the Johnsons plus silicone released the easiest. The differences were not huge but definitely noticeable.

Looks like Johnsons plus silicone is the way to go for what I have in the shop right now. But getting some mold release should be something to look at, unless I get some other better suggestions. Makes me curious as to how much better the proprietary mold release is compared to wax plus spray silicone.

Denis

 

I have noticed that aluminium gets attacked by sodium silicate, not surprising for an alkaline substance. Most of my patterns are coated in an aluminium paint based release agent for resin sand use: the stuff lasts for 50+ moulds before needing a recoat but sodium silicate sticks to it and pulls it off the pattern in sheets. I have some fibreglass mould release wax that seems to be silicone and wax based, it needs to dry for about 30 minutes before polishing and can be built up in layers, they recommend six coats for a new mould. It would work for sodium silicate but probably wear off fast, I was thinking a mix of wax and graphite might be suitable for sodium silicate use, maybe melt some floor polish and stir in graphite powder. At least with that combo you'd get a visual cue on when to recoat it as it wears off.

https://www.trmoldrelease.com/shop-category/paste-wax/

 

Interesting point about sodium silicate's affinity for aluminum. My plan is to cast my present pattern in aluminum and save the original pattern using it as a master for casting working patterns as needed in the future. Maybe I'll need to lacquer the aluminum pattern to protect it from silicate. I am hoping to use it as raw metal thinking the metal will be less prone to flaking and denting.

Denis

 

It could be possible to anodize the aluminium to give a porous but hard wax holding surface too. That would be a hard crust of aluminium oxide, or sapphire in other words so it would be very abrasion resistant.

 

Just throwing this out, anyone know if polyvinyl alcohol mold release might be suitable for this application? It's relatively cheap, easy to apply

 

I don't think that would be a problem. If you use an appropriate amount SS solution, the sand is barely damp and still more or less free flowing.

 

Kelly made some interesting points about PVA in post 10 above. I did try it a bit with Bondo on melamine with somewhat disappointing results. I am not sure I used it correctly though as it seems like it should have worked well. I might revisit it.

And, dang it Kelly, your idea for iron as a pattern is not a bad one. Indeed, I may find aluminum to be too soft. If it is, I will use the master I will be setting aside and make an iron pattern. I think the aluminum one should be adequate since I have used wood to this point with only a few handling-damage repairs needed. The pattern gets used a few times per month, not ten times a day.

Here is a video of my latest demolding operation after I was quite careful to get a few good coats of lacquer onto the mold. Then I waxed it with Johnson's a couple times and buffed it a bit. Then I took some graphite and worked it into the surface with my fingers, a brush, and a paper towel. I have to confess to not always being so meticulaous about surface prep and the inside of the wood corebox had been modified a few times with some repainting that could have been sanded out better etc. Some of the disatifaction I was experiencing with separation of the core was, in retrospect, self-induced.

Here is the video that is a few minutes in length. In summary, the core separated very nicely.



Here are a couple stills:
This is the box after waxing and working in the graphite. My fingers are "slightly" dirty.

This is the box after waxing but before graphite.


Denis

 

Sodium silicate will chemically bond to iron or steel. It is actually used to make laminated steel.
Sodium silicate reacts with aluminum to create flammable hydrogen gas.
Best choice as a core box material for silicate bonded sand is cast or machined urethane. Dusting with talc is all you need as a release agent.
If you have a wood core box, the best paint is epoxy paint. It is both durable and chemically resistant.
If you are using a self setting silicate, the only paint that will work is epoxy paint. The ester catalysts can be strong solvents for all other paints.
Silicone does not work well. If the core box material is porous, fill up the pores with paste wax or epoxy paint.

 

Tom, as you could see in the video linked in post 12 I got a nice release from the lacquer/WAX/graphite combo. Maybe the wax is key to preventing the silicate from attacking the lacquer. Anyway, I'll see what I can find in the way of epoxy paints in less than gallon (100 dollar roughly) quantities. I assume that epoxy paints have less viscosity than the West System epoxy I already have in the shop. That stuff is pretty viscous and I think would tend to blur out letter that I include in my patterns. I do use West System epoxy for filletting long stright inside corners and love it for that purpose.

Denis

 

You can buy epoxy spray paint at Home Depot or Lowe’s.

 

How do they manage to put an epoxy paint (usually two-part) into a spray can? I’ll check it out.

Denis

 

A one part epoxy contains a ketamine or similar amine that reacts with the moisture in the air to polymerize the epoxy. Been around for years!

 

That clue caused me to look up single-part epoxy coatings. For the curious I found this brief background page:

https://roboticsandautomationnews.c...oating-and-technology-across-the-years/36472/

I was struck by the use of ketamine in epoxy when I was much more familiar with its use in humans and animals as an anesthetic agent and, in humans, a psychoactive agent. Near as I can tell we are talking the same compound and not a class of compounds loosely referred to as “ketamine.”

Denis