Pouring cup or pouring down the downsprue?

I've been experimenting on the best way to make a detailed, logo casting in aluminum. I have tried 4 methods to date! All are using new ingot aluminum, Petrobond , the same parting dust, cope and drag, propane burner, etc.

Method one was with the pattern facing down in the drag like a tea cup would normally sit, pour down a down sprue the height of just the cope. Have a smaller riser, opposite the down sprue, to know when full. Results were hit and miss and main issue was the logo was not "filling up" with good strong detail. See picture labeled "Second Try"

Second method was lost wax from a silicone mold made of my logo cup/cover. The down spure was in the middle of the back of the cup, which was facing downward and the logo details were OK, but not great. A lot of time and energy spent on this one! Was hoping for near perfect detail, but did not get it. Possibly due to the charge going straight into the invested part and possibly splashing around, inside the empty investment mold? Next set of investment molds, I tried the cover/cup facing down, and have the pouring sprue come in from the side, rather than from straight above the middle of the pattern. These were terrible. No detail at all and everything seemed smoothed over. The removed investment showed EVERY detail? See Investment picture.

Third way was based on the suggestion of a good metal caster. Sand cast, turn your logo cup facing up, fill from the side down and use an elevated pouring sprue. Good details but a fair number of pin holes in the casting. More than on other tries. I believe the extra pour sprue height added a good head of pressure to fill the cavity and resulted in good detail. But the splashing down the higher pouring sprue may have allowed air/gas to enter the liquid metal? See June 29-2022 picture.

Fourth method tried today was using the up turned logo cup but with a pouring basin with small hill before the down sprue. I was easily able to keep the basin full and it seemed like it was working but the detail is bad! Not even worth saving. BUT there is no sign of porosity or pinholes. Surface finish is good on the entire part. See pouring cup picture.

So what is the best method for getting fine detail? I have used facing sand and saw little difference. Any constructive suggestions appreciated. Jgaertner

 

At this stage I would be trying a different alloy.

 

OK, can you recommend a source and type of alloy to use for fine detail? I never gave the aluminum much though other than making sure it was new, not salvaged and of a know quality.

 

Hello Kelly, Yes, I am afraid it has to be aluminum because they will be used as axle covers on real aircraft. Originals were cast in aluminum.

 

I was trying to find my invoice for the aluminum ingot I bought. It was several years ago! I did not realize it was so long ago.
I think the ingot was A356? It says CLARK or something similar on the ingot.

I generally try to pour my charge at 1350F measured with a digital pyrometer. I always remove the little dross there is while still in the
furnace (top of the furnace removed, obviously) and then lift the crucible out and pour immediately.

I preheated the investment shells to 1250F before placing them in a bed of sand and pouring.

 

I am pretty sure I ordered this aluminum from Small Foundry Supply company near St. Louis, MO. Jgaertner

 

you could get a piece of cast scrap aluminium which you will know has good casting properties and test this to see if it improves your results. Then you will know if you A356 ingots are not what they claim to be.
Theres nothing wrong with using scrap. The part it comes from will give you a good indication of what its capable of casting wise

 

Hello Kelly, I have a run of the mill digital pyrometer with a contact K-type thermocouple with ceramic shell from McMaster Carr.

I did not know about the mold temperature issue with investment. It was Suspend-A Slurry. It made beautiful impressions as seen
in the picture below. Castings were very poor. Very frustrating for the time involved. If I try it again, I will keep the temperature
lower. I use my electric burn out oven to heat the empty shells. Digital PID controlled.

I use propane in my furnace. I will admit I have no idea about how one tunes the furnace output? Any suggestions or comments
would be appreciated. It works very well. It came from Foundry101.com

 

John,

Kelly uses mostly resistive furnaces. I burn fuel (diesel) but the principle is the same. I like a reducing flame for iron and, as Kelly recommends, lean for aluminum. To make a reducing flame (rich) start fuel flow and add some combustion air and then back off the air and you should see a fairly good-sized yellowish flame coming out of the vent. Put a piece of metal in that flame and it will soot up proving it is a reducing flame. Now increase the mix of air to fuel until the flame disappears and again try the clean piece of metal in the flame. It should no longer soot up. You are just into the oxidizing range (lean) of combustion. I run my burner for iron so I can just see a hint of color in the flame---that is close to optimal for heat and still in the reducing range. The other issue is to not blast too much fuel and air through the furnace regardless reducing vs oxidizing as that wastes fuel and results in lower than optimal flame temperature.

Denis

 

Hello Denis, Thanks for this helpful suggestion. I guess I have to figure out whether my propane furnace can be enriched or leaned? Its pretty rudimentary.
See my picture, attached. Open on one end, outside the furnace with a single pin hole for propane introduction. It would be very easy to make a flap to control the incoming air. which might allow me to enrich or lean the air/fuel mixture. Would be worth a try.

Jgaertner

 

I'll only speak to the petrobond ,
Detail always goes in the drag, unless you are worried about it washing, you do not have that issue at all in aluminum

in the nicest way possible, that petrobond look awful course, like 60GFN sand. it should be at least 120, 160 would be better, it would help to see your rammed up mold, but you can only get as much detail as the sand will pick up, good petrobond will get GREAT detail, more then you need,
what did you use for parting? parting compound slathered on reduces the detail transferred from the pattern to the sand, in a case like this you might want to just rub the piece down well with powdered graphite in a parting bag and forgo sprinkling parting at all

V/r HT1

 

Hello HT1, I have tried installing this pattern, both facing into the Drag and more recently, facing up, into the Cope. I am using 130 for my facing sand. Straight from a brand new bag. The parting powder I am using very sparingly and always sprinkled on the pattern and backing board and then gone over with a cosmetic brush. I have not experienced any issues as far as I can tell with the parting powder. It was purchased from Small Foundry Supply. I am sure leaving too much behind would hurt the detail, but my details are either not filling or the parts come out with pin holes.

 

Thanks Jeff, I think this is a good detail to work on. I have an entire machine shop, so building a shutter for the inlet will be a piece of cake. I can probably get this done in a few days and test just the burner connected to the furnace's tweer. I would like to lean the burn as right now I think its too rich. Yellow flame (???) Jgaertner

 

ok terminology ! your PART is filling, , but the detail it's just not up to the standard you require, so the issue is

1) your pattern : Does the pattern have as much detail as you require???
or
2) your mold : is the detail transferring from the pattern to the sand , ram up the mold and look at it NO REALLY LOOK get a flashlight and a magnifying glass if you need to!

the metal having pin holes is entirely a separate issue

ok I think I have went over this many times, I promised a video that I have not done, donrt rub the pattern with parting compound, you rub the pattern with powdered graphite this makes the pattern slippery
the the pattern gets dusted with parting compound, the graphite stays on the pattern, the parting compound stays with the sand, if you need to use a brush you have TOO MUCH COMPOUND !!! dust, you want a fine even dusting , if you blow out the mold and parting comes flying out you USED way too much, and your surface finish will suffer, Tobho has a great picture of how bad parting compound use messed up an axe,

now just for aluminum because of it's high surface tension, you get more detail if the temperature is higher, but you get a better overall surface finish if the temperature is lower in the pouring range , but with that big clunky part you need to be low in the pouring range or you will get other issues

as always you pick up more detail if the head pressure is higher , that's half the reason for putting the detail in the drag , so you might consider a taller cope , but I dont think it is necessary

V/r HT1

 

John, if you have a yellow flame then it's on the rich side. A flap will only restrict more air making it richer. It looks like you have a nipple threaded into the reducer, try removing it to get more air. Otherwise you'll just have to reduce the gas input.

 

Your burner is self aspirating. So, as it is, you could choke it down some---make it richer---by applying a simple shutter to the open end of the 2" (or so) pipe. BUT, you could also lean it out if you attached a blower of some sort with a shutter. Then you could control the air/fuel mix. Folks have used all sorts of blowers. Generally a relatively low-powered blower will be all you need. Set up the blower with a simple blast gate for a shutter and run flexible tubing from the blower to the burner. Most likely you will be closing the shutter to reduce the output of the blower. I use a repurposed electric leaf blower for my setup. I shutter it down quite a bit.

Denis

Keyboarding while Bonz was posting. Fortunately our "stories" line up. ;-)