The Shop > Metal Stuff

Casting a Model Westinghouse-Type Twin Steam Engine in Iron

<< < (10/11) > >>

Steve I'd happily do it, but my tester is intended for aluminium alloys so I don't think that we'd learn much sadly.

Didn't realize that, Andrew!   :doh:

I think on today's menu, we will re-melt the last casting, sprues and riser and try again. I will have to make up the roughly 20% loss with new scrap. Choices are:
radiator iron
left over disk rotor iron
or a combination

I'm favoring using more of the disk rotor iron attempting to reduce shrinkage. But that probably will also reduce carbon (already reduced from a second melt, as well) so maybe add some plumbago (graphite) to the charge?

The big question is how much ferrosilicon to add.
Normal is  .25%,
disk rotors (Ironman) .35%,
last pour (gray iron) .45%

Since re-using the last pour metal, it may have a reasonable amount of silicon in the iron already, but I've also heard somewhere that ferrosilicon's benefit only lasts about 5 minutes after addition. And re-melting the last pour will cook it for a lot longer than that. So do I trust that It is okay now to add none, or 25%, or .35%  (I'm guessing .45% won't be necessary.)  :scratch:

Well, let's pick a number..........ehhhhh  .35% ..........let's go for it

eh, no good. Really bad melt. Crucible tipped to one side of the furnace, and I didn't notice until near the end. Also lots of clumpy sticky slag that stuck to the walls of the crucible. Maybe it was sand in the sprues, maybe it was the plumbago, too. Anyway, slagged it twice, but then watched bits of slag detach from the walls of the crucible while pouring and slide down the sprue. I'm sure this casting will be scrap, even without breaking the mold open. Bummer!

Well, I ain't quittin'!  :dremel:

I have to check the condition of the furnace because I think I'm getting some leakage through the lining in one area. Anyway, next time, all new metal.

Post Mortem:
Yup to the plumbago being a problem. It was found in a clump in the bottom of the crucible -- still powder ---which is odd because it is far lighter than iron and should have floated. It was at an angle and the only thing I can figure is since the crucible was tipped over against the wall of the furnacethere was a cold pocket of slag and colder metal trapping it.

I cleaned out the crucible thoroughly.

Also yup to the furnace having leaks. I found some cracks in the hotface near the bottom, and oil under blower pressure was building up in the blanket insulation behind. This led to copious long lasting smoke through a few small holes in the stainless steel jacket after the furnace was shut down. It also meant difficult to control mixture settings while burning. And loss of fuel and heat.

I patched the interior with ganister and then satanite, and did a small wood burn to set them.

Finally late today I decided to re-melt the metal from the last pour to see if the problems were external, and not the actual metal itself. I put sprue, casting and riser back in the newly cleaned crucible, and added 2.5 more pounds of mixed disk rotor and radiator metal to bring it to 7 pounds again. I added 14 g of ferrosilicon and poured into two vertical bar molds, one round (1.335" dia.)  and one rectangular (1"x2" section). The melt went much better, slag was manageable. Melt took 1/2 hour. The furnace hardly smoked, and seemed to heat more quickly.

I'll be interested to see how much shrinkage I get in these test pieces and how hard the resulting metal is, and how much slag got in. Yesterday was a major disappointment, but today, i feel like I'm back on track, and there's the possibility of not only salvaging the metal from last time, but getting some more useful stock out of it. Fingers crossed!

ps. On the off chance that one more try might soften up the hard spots on casting #3, after the pour, I put the casting in the empty crucible and fired up the already hot furnace for a couple minutes, then shut it down and covered the openings. Couldn't hurt!

Well great day in the mornin'! June 1st and all the castings did well, but especially Westinghouse Twin #3, which was fully annealed by the last (and third) go at it. I was able to machine all mating surfaces with absolutely no chill hardness anywhere.

What was different? Well putting it in the furnace immediately after another iron melt, inside the crucible, and then giving it more blast for about 5 minutes really heated it up. Then shutting the furnace down and plugging the exhaust with a brick, and the ituyere with a rag. Then leaving it overnight to cool.

That was a real demonstration of the furnace's blanket insulation's efficiency, because when I took the casting out it was still quite warm after 20 hours of cooling! There's not a large amount of thermal mass in this furnace. It's really the insulation doing the job of heat retention.

What was different than the other attempts at annealing this same block?

Well, the in the first annealing attempt I added it to the furnace after a melt, but didn't fire up again, thinking that residual heat would be enough.

The second time, I heated the part up in the furnace from cold -- it was a brief firing to get the part cherry red, and hadn't been preceded by a melt, so the walls of the furnace hadn't stored much heat. Instead, I buried the part in a bucket of wood ashes to slow cooling.

So the third time was the charm, and lots of initial heat in a sealed furnace overnight seems to work the best.

As for the other two castings using "bad metal" from the fourth Westinghouse casting attempt....well the metal wasn't all that bad after all. Must have been the operator. in the photo are the resulting two bars. The round one cleaned up nicely to 1.25" with only a few tiny slag imperfections. Little slag at the very top. No apparent shrinkage. Nice gray iron easily machined. Certainly useful as a post for a Drummond style QCTP, etc.

The rectangular bar shows a little more shrinkage mainly because the center cools slower than the faces and corners. This results in slightly concave sides near the top, reducing as you get to the bottom. Not a lot of shrinkage but some. Little slag near the top. I haven't machined it yet, but expect it will be similar to the round bar, if not better. It would probably be fine to make a couple of tool holders to fit the above Drummond style post, or any other similar purpose.

Anyway a red letter day -- where everything that seemed to be going wrong last week did an about face, and went right!  :ddb: :beer:


[0] Message Index

[#] Next page

[*] Previous page

Go to full version