Casting a windmill gear in grey iron

Denis - If you want a new half, let me know. I have the stripper for ESC printed and printing one gear half now.

Someplace, Andy recently mentioned that he added in a couple of small thick walled pulling holes like you mention above. Also, wall thickness & infill can be increased, and layer height can be decreased (finer ridges). I have left my settings somewhat stock since I am still learning the printing world.

Also, I remember too where Myfordboy made a bound sand (maybe even plaster) mold that he melted out the pattern, then put the mold in a greensand flask. I'll have to look for that video. It was for an aluminum pour but could apply to a similar situation … like when Pat was trying with no draft.

 

Thanks, Ed.

I failed to mention that the silicate molds will be placed in green sand to form the sprue, runner and vertical gate.

If this one pours OK, I’ll be happy and a bit surprised. If not, I’ll be begging for a new pattern half.

Denis

 

I print 1/8" diameter 1/2" deep holes in my patterns for pulling points. That automatically gives you the thickened shell around the hole. Started that from my second printed pattern.

Edit: Sorry I didn't see Ed's post.

 

Well I melted 20 pounds of iron—-twice what was needed this afternoon. Looks like it filled OK. Too hot to really clean it up now.

Really made me think as I was packing the silicate mold in green sand—the first I’ve tried that.





Denis

 

Great casting. What's with the dip in the runner?

I hope Ed will take some side by side pictures to compare surface finish. Your's looks great.

 

Nice pour Denis.
Did you dust the mold with graphite, or is that the coal in your mix? That surface finish is what I get when I use the aerosol graphite.

 

Thank you.

I did not dust the surface. The finish is the result of adding 5% coal to the sand both in the green sand (runner, sprue, basin) and the gear/riser which was sodium silicate bound. I used a dusting of graphite on the pattern as a lube to provide slip for the pattern.

What brand aerosol graphite do you like? How heavily do you apply it?

Denis

 

Thank you, OIF.

What is a good runner if not graceful?

The dipsy doodle in the runner is the result of me using a 2” high pattern in an existing 2.5” high cheek. The silicate mold was embedded in green sand with its upper surface level with the upper surface of the cheek. I cut the lower surface of the cheek green sand down to the silicate mold like cutting down a part line. The runner was cut into the top of the cope whose contour followed the cutdown lower cheek surface. Does that make any sense at all?

Denis

 

Denis what method did you use to clean up the casting after the initial breakout? In the after cleanup pic, is the surface wet? Or is that shine from your superb finish?

I started a bit of machining on Andy #2 last night, but will hold off on any more until I have Denis' gear and take a side by side pic.

ESC - Your parts are printed (striper plate included). Hoping to get to post office yet this morning.

 

I use NAPA aerosol graphite. I made a mask so I could coat just the head cavity in the linseed oil bonded mold.

 

After spraying the graphite, does the mold look barely greyed, light grey, nearly black. Pics? Just trying to get a sense of how to use it. Do you make multiple applications allowing drying between applications? So many questions....sorry.

Denis

 

I just used a little metal modeling (clay) spatula and a wire whisk broom. I also sprayed it with water and I suspect it may have had some residual water when photographed but had some natural shine too as seen when just breaking out of the sand. If the silicate binder had not been weakened with sugar, I’d have needed a chisel to laboriously chip off the concrete-like mold.

Denis

 

Denis, I just give it a light coating and it shows grey to black with just one coat. The fins are very thin and I didn't want to restrict them any further. I couldn't find any pictures, sorry. When I get to the shop I'll see if I have some cores I sprayed.
I must have grabbed a different can the last time I went to the auto parts store. This dry graphite is Blaster brand. Here it is with the mask I used for the head mold.


Gotcha Ed.

 

That looks like good coverage for one coat. I will try that brand. Thank you VERY much.

Denis

Edit: Oh wait, that is the mask, so it has been hit with many coats.

 

Here is a little more info about the gear I cast. Overall I think it will be usable but I do wish I had not accidentally shrunk half the pattern by warming the mold to 150F. That caused some trouble with matchup of the two halves of the gear and resulted in some needless eccentricity of the two halves. To be honest, I was relieved that I my first foray into silicate mold making (I've made lots of cores, but that is somewhat different) resulted in a reasonable if imperfect casting. One unexpected defect were some bubble-like defects in the hub of the gear. See pics. These likely will not affect function, but I am frustrated to have them appear. I have never seen this before! And I made a couple brief slo-mo vids to show the results of initial machining and demonstrate the eccentricity I caused.

I did machine the gear so that Ed will have true concentric surfaces to work from. I bored the gear (the reference surface being so established) as a best fit of the gear teeth. I won't go into detail here unless quizzed, but I was curious to see how the cast iron machined and wanted get an idea of how it would look.




Shoot! I recorded these in Slo Mo but they are playing back at normal speed. Please click the settings gear on the youtube window pane and select playback speed and go to .25 of normal




Denis

 

Denis, those voids will not cause an issue. That hub is used as a positioning and somewhat of a bearing surface. If you need that new half (or both) let me know. It might be interesting to see how this would work if the PLA was heated to a pliable point (200c) and removed vs the high heat melting of true lost PLA. Doing that, I think the pattern surface prep would be a non issue.

Just throwing ideas around in my head.

 

I got my copy of the gear pattern today. I rammed it as received in brand new petrobond and rapped and drew without the stripper plate. It was too wide for the pins on this flask and I didn't want to modify it right now.
There were the same broken edges that Andy experienced, but the center hole with zero draft survived. I may need to taper it there so it will have some strength. It pattern looks nice so we shall see how much finish work is necessary for it to be a usable working pattern.

 

That looks like you got a pretty darn good pull on that pattern. Looks like you may have pinned the smaller diameter bore sand in place---probably a good call given how much tendency it and the larger bore also would have to stick to the pattern.

Denis

 

It sure looks better than my first three or four pulls.