Reuasbale Offset Pouring Basin

It's a 60lb pale of Refcotec Poly Cap 600. It was $81. Refcotec is a sister company of my local refractory supplier and for some reason they had a 5gal/60lb unit on hand. I was told there may be a 10 pale minimum if I want more.

Yes, that's a lot of sprue to eat.

Best,
Kelly

 

That coating does look nice. Is it brush able??

 

Haven't tried it yes but the manufacturer says it is brushable. When I mixed it, I could tell it was lower viscosity than the mud coatings I brush and perhaps comparable to a little thinner than those I dipped with mud.

They also say coating thickness may need to be tailored to each application by viscosity and number of applications. Not sure how I'd increase the viscosity other than leave the lid off the container for a week. It can be reduced with water.

It's pretty darn tough to beat dipping for speed and uniformity of coating but for large parts and/or selective surface application.......= Brush.

We'll see how it behaves during casting. I really need to make a permeability tester so I can compare it with mud otherwise I'm just feeling around in the dark.

Best,
Kelly

 

For the substrate, I was just going to screen the fines out (I have lab sieves) of my mold sand to get a narrower range of particle size, repeatable open area, and pressure drop across the test sample substrate, probably 35-50 mesh. I'd bind that with sodium silicate or polyester resin and pack that into a short section steel tube, perhaps the ID of radiator hose so it could be easily sealed and pneumatically connected. The coating could be deposited on the substrate and then baked. An uncoated substrate could be tested for a baseline but I think the only relevance is the reduction in open area, not the permeability of the substrate itself which will likely be order(s) of magnitude greater than the coating. Quantifying the rate of permeability could be useful but the relative comparison between coatings is probably more useful.

Once you have samples, I'd orient them so the pressure drop is from the coating to the substrate so the coating is supported. To measure the permeation flow through the sample, I'd plumb the downstream end to the inside of a balloon inside a volume of water. I'd connect a piece of clear rigid acetate tubing with graduation marks to the water volume. When the sample is exposed to differential pressure, the balloon will inflate and you can measure the amount of displaced water into the graduated tube over time to obtain the permeation flow rate, and this can be related to the surface area of the sample to obtain average flux in volumetric flow/in2 for a given differential pressure. You may need to just collect the displaced water and measure the volume in a second step because as the displaced column height grows, the differential pressure across the sample is reduced by that head which may significantly change the differential pressure through the test duration.

For differential pressure across the sample, I'd say 1-5 psi with most interest between 0-1.5 psig. Aluminum develops about 1 psi per 10" of head. For gravity fed parts, my molds range from 10"-27" of head at the deepest point. The reason I stated 1-5 psi is the possible addition of vacuum. I can add about 3.5psi of additional differential pressure with vacuum, up to even ~7psi. To incorporate this into the tester, I'd just plumb the opening of the displaced water to the vacuum source.

I do have a very small 1-5 psig regulator. I'd probably need to build a u-tube manometer to accurately measure < 1-2 psig which is no big deal with a piece of clear hose attached to a board, & some water with food coloring. I already have one on my dust shop collection system. The vacuum motors I use can easily generate these pressures/vacuum. They have very fine pressure/vacuum control when I put a router speed control on them.

You could also burn a cubic inch of foam inside a tube and use the water displacer to measure the volume of gas it decomposes to and potentially relate that to the surface area and coating permeation rate.......and declare yourself to be Dr. Science!......or just screw it and experiment with castings.

It sounds involved but I built such an apparatus once before for use at higher differential pressures and it worked well. I think I could prep samples and rig up a tester in a day........problem is finding the day to do it. I'm oversubscribed as it is.

Best,
Kelly

 

Can't disagree with that and would add that I don't think I've ever regretted or not enjoyed a performance improvement using purpose formulated commercial foundry supplies over home brews, but it's rare they are available in quantities that are practical for home and hobby use. I'll reserve judgement on this material until I get some experience with it but even if its great, buying $800/600lbs of it isn't in the cards for me without cost sharing.

If you have other recipes, I'd be interested in seeing them. That one has been floating around the web for a long time. Have you ever used it? I have all the constituents except I never did find nor anyone who had ever hear of Bindal H. I made several variants on that recipe several years ago. I didn't find it to be any better/worse than drywall mud in how it performed with aluminum lost foam castings and all variants applied much worse than drywall mud. A couple of comments would be:

1. They refer to how combinations of refractory materials can affect permeability but make little to no mention of how/why. No particle size relationship, no formula....nada. I can tell you just selecting low density refractories usually mean they are porous and will be more permeable.
2. The recipe says 35-40m for grain size and that is too coarse.
3. If you use Dextrin as the formula suggests, also add a small amount of bleach or your slurry will have a mold bloom within a week.
4. That formula needs a surfactant. If you try to use it at a viscosity and water content that can be dipped, it will never wet polystyrene nor wax, and the CMC wont get.

For the Refoctec product above, they have a very good surfactant and flow modifying agent that makes the coating coat thicker than the viscosity would suggest and wet better than the water content would otherwise allow. About the only way you are going to vary permeability is with the porosity of the refractory and coating thickness, and that can be hard to control. Once you choose the refractory your pretty much limited to coating thickness when it comes to permeability unless you add an organic actively that burns away in use. For aluminum, degree of refractory is not much of an issue.

FWIW, I 'd hazard a guess to say this material are the same basic materials they use for permeable mold and core washes, probably (but not necessarily) with the flow modifiers and surfactants, and might be a little less viscous (more water content) for dip coating.

Best,
Kelly

 

Guess I’ll have to add dries very well to the list for the Refoctech coating. After 24 hours the interior of the tubes are dry. Dipped drywall mud would still be wet inside.



I experimented with a chip from the drips. Based upon how it brakes I'd say it is similar to drywall mud in strength.



Best,
Kelly

 

Thanks Denis, I try.

I'm going to pour those two parts and see what can be learned and how it seems to behave and compare to past practice.

I've reached the point with LF where I an cast parts with a very high success rate that are cosmetically quite satisfactory and I suspect the same mechanically compared to most hobby casting. It's very fast and effective for one-offs and small quantities of parts. For technical and highly stressed parts, everything matters and even quantifiably measuring what has been accomplished can be a challenge. That water neck isn't critically stressed but must be hermetic at 3/16-1/4" wall so that's why it was my choice.

From a lot of reading, my assumption is I need to get good control of the coating permeation (higher) rate to get the result and control for technical castings. For this water neck, the fill times and the volume of the part suggest average velocity of the metal front to be at most 2 in/sec and more commonly <1"/sec. This is completely paced by the evaporation of the foam and permeability of the coating. So all of the portion of the Bifilm thread addressing the parameters of naturally pressurized feed systems really doesn't apply, but preventing aspiration and turbulence in the cup and any gas that doesn't escape in a controlled manner through the coating wall does.

The offset basin seemed to have real benefit in my first attempt using it but less so in the second attempt. As mentioned, that may have been due to factors other than pouring basin and the basin needs to work in concert with the rest of the system, in this case the foam coating and gating system. We shall see. I wont be able to work on for a while but will get there.

Best,
Kelly

 

I poured the two water neck castings coated with the commercial Refcotec coatings today. I video’d the pour of the one with the top sprue. I’d post the video but it was virtually identical to the one in post #1 of this thread. That part was dipped in the thinned drywall mud. Both this pour and the one in post #1 were about 31 seconds long give or take a second. Both had a couple very subtle puffs of flame above the sprue and both produced a very nice part. Here’s today's part.



I poured and video’d the bottom sprued part but the video was interrupted so I don’t know the duration of the pour but it was very long, Especially the initial part of the pour. I’m guessing it was between 45 & 60 seconds. It poured short. Can’t say I’m surprised. Anytime I get a total travel length >14” I seem to run into that problem and with the sprue length, I was well beyond that territory and there was only 4" of head left by the time the melt reached the end of the road. Both parts were poured at 1575F.




I could probably add a little vacuum or increase the pour temp but not sure I see an advantage over top sprue pours. In fact, since the two top sprue pours were nearly identical, I cannot honestly say I saw a difference or any particular advantage to the commercial coating over drywall mud, at least in regard to how they poured. The commercial coating did coat and dry very nicely.

Best,
Kelly

 

The pouring basins do look like they offer improvement over just a Kush cup and my transitional conical foil sprue, and they reduce labor and molding time. Besides the visual affect of how they pour, there seems to be very little if any dross on top the basin after the pour whereas the Kush cups usually have a 1/2" of foamy/drossy crud. I think this is caused by the tendency for the round Kush cup and funnel to aspirate compared to the offset pouring basin. I have about 6 pours on the first reusable basin and it looks like I may get a lot of service out of them. There is a residual foil left on the inner surface of the basin after the pour which canned easily be pulled off after it cools. Only down side is they do generate more sprue/cup stock for small pours, but since it is clean, probably well worth it.

On the commercial coating, I'm trying to decide whether I'm happy or disappointed with the results. It's only a sample size of one (not counting the bottom sprue short pour) but it was uncanny how virtually identical the commercial coating pour was compared to dipped drywall mud. I would infer the identical pour times suggest identical permeability. I guess I was hoping for higher permeability and some wow moment. It looked more impressive with how well it wetted, flowed, and uniformly coated the part after dipping, but not radically better than the dipped mud. I may be able to modify mud with flow agents to achieve same. After the pour, I'd say the two coatings produced very comparable if not identical results at least cosmetically and maybe mechanically.

Best,
Kelly

 

You could make a foam pouring basin but it is extra foam to melt and doing so can be hard to control. I've seen people just stick a conical piece of foam on top the sprue. Heck, I've seen people just pour on top the sprue level with the top of the sand and get complete parts.......not necessarily what I would recommend but it's been done.

I made the basin because all hell seems to break loose initially with the lost foam pours and that can create a lot of turbulence, oxides, and entrained air.

Best,
Kelly