Looking for some help

[Former_Member]

I did a casting a few days ago with unfilled results
Bronze
Melted in Melt furnace 1850F I believe
Vacuum Assist -25 #

Did I sprue it wrong?
Metal not molten enough?
Not enough Vacuum?
Other possibilities?
Any help is appreciated
Newton
I'm going to include a few pics
hope they show up

<a href="http://imgur.com/SNbUq8c"><img src="http://i.imgur.com/SNbUq8c.jpg" title="Hosted by imgur.com"/></a>

<a href="http://imgur.com/m8zLZb0"><img src="http://i.imgur.com/m8zLZb0.jpg" title="Hosted by imgur.com"/></a>

<a href="http://imgur.com/jlKntVJ"><img src="http://i.imgur.com/jlKntVJ.jpg" title="Hosted by imgur.com"/></a>

[steedcraft]

Hi Newton, I could not open the photos you gave so am just chatting blind with general guides to be encouraging.

Sprue shape - lots of theories about turbulence and the like in the metal as it flows in I tend to prefer a shorter thicker one purely so the wax is strong and unlikely to break when de bubbling the investment. Button size is typically twice that of the job this is important. As the job cools it will shrink so a reservoir of still molten metal above is needed as some of this is drawn in to the mold to maintain good fill.

I do not use vents with vacuum assist but hey there is no harm in waxing a couple on if you are having trouble

Temperature sounds about right, I think I pour at about 1100 c (I use a thermocouple to check temp but am not sure how accurate it is, and as its a time consuming fiddle dont tend to bother once ive got my eye in) If it is too cool it will be too thick to pour, if it is too hot you will increase the shrinkage as it cools. be sure to have the investment and flask (mold) nice and warm so the metal does not chill on entry.

as long as your investment / sand is pourous enough to allow the air in the mold to escape under vacuum, and your vacuum table supports the investment / sand so it does not blow out you should be ok

sorry for a general sort of answer give it another try and let us know how you get on

all the best and have fun

quin

[Former_Member]

Thanks Steed
If you could copy and paste these

http://i.imgur.com/SNbUq8c.jpg

http://i.imgur.com/m8zLZb0.jpg

http://i.imgur.com/jlKntVJ.jpg

Thanks
Newton

[Former_Member]

You may be able to just click on them
The large upright piece was a coin like medallion
The part that cast has some decent detail, just wish it was all there
Thanks
Newton

[steedcraft]

Hi Newton, saw the pics a treat. erm 2 things spring to mind,

1, metal not hot enough, get a k type thermocouple suitable for 1300 c and pour at 1150c

2 the investment does not seam to be allowing the vacuum to vacate the mold, this could be wax residues left behind blocking it up, so burn out more. it could be the wrong grade investment, or poorly mixed (standard investment is course and more pourous than the finer jewellery silk). could be "fat layer" on investment blocking the vacuum, when you pour the investment and it sets a "fat layer" (just like in concrete) of fine particles comes to the top and is less porous, this needs to be scraped off with a knife. I pour the investment right to the top of the flask so the meniscus is proud of the flask, the fat will settle here and be easily removed giving a good seating for the flask on to the vacuum table.

good luck and enjoy it
quin

[steedcraft]

hi newton me again just having another look at the pic I think the metal is too cool. the little dribble at the button is a tell tale sign, you have a "flat top". when bronze is poured at temperature the metal is nicely rounded a bit like a baked loaf of bread, and the extra dribble seen in your pic would have been drawn in to that. I suggest you try a few test ingots to look for this and test the temperature out
all the best
Quin

[Former_Member]

Howdy Steed
I'm using Kerr Satin Cast Investment

[Former_Member]

The investment was vacuumed and poured in flask with about 1/2 inch proud of the top of the flask, then vacuum, afterwards topping the flask off. So possibly Higher temp melt and scraping fat??
Thanks for your Help and Insight