Casting Question

[rlb]

Question for those with experience casting:

 

I am going to try casting my anchors for Oneida.  It will be the first time I have tried casting.  I'm using the Micro-mark 280 metal (280 degree melting point).

 

How should I orient my anchor patterns in the mold?

 

As on the left, or as on the right?

 

Ron

 

Edited April 4, 2020 by rlb

[wefalck]

As on the left. If you make it as on the right, the metal with rise out of the vent before the mold is completely filled. Also the vents in the mold on the left should go up to the level of the funnel for the same reason.

[rlb]

Thanks much, wefalck.

[druxey]

In addition, make the filling vent area larger: the weight of the head of metal will help ensure good filling of the mold.

[rlb]

Thanks druxey!

[druxey]

And, of course, the excess metal is completely recyclable for the next casting....

[steamschooner]

Depending on the size of the anchors the low temp alloy my not flow into the mold. You may have to use some centrifugal force to fill the mold. Has to do with surface tension of the material I believe. 

Steve

[rlb]

Druxey, I will make the filling vent/funnel larger, it's good I can recycle the metal!  I think I need to get a larger crucible.  I am doubting that the spoon/ladle that came with the casting "kit", will hold enough metal.

 

Steve, I have wondered about this.  They will be long, narrow pieces to cast.  I was puzzling over whether a lower melting point was better or not, as it's not as big a delta from the mold (maybe won't cool down as fast as a higher temp metal?).  I have also read that heating the mold before pouring can help, and I will talcum powder the mold also.  I don't think centrifugal force is an option, unless there is a safe way to do this by hand.  Is a higher melting point alloy better for this type of casting?

 

Ron

[steamschooner]

Ron, What type of material is the mold made of? rtv, plaster,? Heating it should help and the talcum also. I find that the low temp alloy cools very quickly.  you can "cook" the alloy if you try and use to much heat. If you look in scratch build logs pg 11 is my build log of the John Cudahy. On the 7th page of that log you will see my casting efforts for my anchors.   post #182  I use Cerro cast a low temp alloy and vulcanizing rubber in a two piece mold. Again depending on the size of the part to be made will be a factor in weather you can just pour the metal in or not. Using high temp metal you still run into the problem of surface tension not allowing the metal to flow in to small areas.

Steve

[rlb]

Steve,

The molds will be rtv silicone rubber.  I was able to find your build log--a sweet model!  I definitely can't manage the centrifugal casting arrangement you showed.  I'll see how it goes.  If I am not able to cast them well, I'll do the anchors another way.

Ron

[druxey]

I think you should be OK after the first casting or two, when things have warmed up. Don't pour too slowly - be intentional! Certainly talc will help flow.

[Dr PR]

I have a friend who has been making HO scale kits for decades. He taught me how to cast the low temperature metals. He uses some home made centrifugal rigs to spin the mold while he is pouring to be sure the metal flows to the ends of the cavities and to expel air from small cavities. A centrifuge isn't essential, but if you will be doing a lot of castings it might be worthwhile.

 

I have an ancient laboratory centrifuge that was used in school chemistry and medical blood test labs. It has a nice shield around it in case the hot metal leaks from the mold. You can pick these things up pretty cheap and replace the centrifuge head with a plate to hold the mold. It has a variable speed motor control and a lid.

 

The molds are flat, with the poring funnel in the center and the mold cavities arranged around it. Here is an example, with the brass originals below on the left and the cast pieces on the right. Note that some of the pieces are cast with an angled tab on one end.

Notice that there are no vents for simple pieces like these. The mold halves are not clamped very tightly so the air escapes easily. A bit of flash might exist on some pieces but it is easily removed.

 

A trick he uses is to dissolve hand soap (he used Ivory soap) in water and paint this on the mold surfaces. It reduces surface tension and sticking to the RTV, and it washes off with water.

Edited April 6, 2020 by Dr PR

[wefalck]

Just a thought: we all love the challenge of mastering a new technology, but it may be worthwhile to ask oneself, if this technology then provides really the advantages sought for. Most ships have at maximum two anchors of the same type and size. So, unless you are building a series of models, it is rather unlikely that you will ever need that anchor in exactly that size again in your lifetime. In order to replicate it by casting, you have to fabricate a master first. Fabricating another copy of the master is probably less work than taking a mold and then casting it ...

 

Incidentally, printing anchors could be one of the few useful application of filament-printers. The slightly rough surface of the prints might be well-suited to the quite rough forgings of the anchors.

[rlb]

Thanks for all your advice, druxey.

 

Phil, your centrifugal casting technique looks good, thanks for the tip.  Probably won't try it this time around, but if I see an old centrifuge for cheap, I might go for it.

 

wefalck--yes, mastering a new technology is probably the primary reason for me wanting to cast the anchors.  There will be four, each a different size, and I am making the masters out of wood.  I could more easily just paint the wood masters, and not cast anything.  That is my back-up plan if I'm not able to get a good result casting.   I had bought a piece of brass the thickness of the biggest anchor, but thinking about cutting 4 anchors out of brass, and filing them all down by hand seemed even more work than the casting.   Making the forms out of wood vs. brass is definitely easier for me.

 

Printing these, and the many other parts that could use that technology kind of defeats the purpose of the hobby for me.  I guess casting is kind of analogous to printing, but it still seems more of a by-hand process, which appeals to me.   

 

Ron