Metal Casting Zone

I have a garden cart with nylon gears - same one goes down have to buy whole transmission - thought I would cast replacement. Did lost wax - no resin stong enough - going up to brass. Used investment - burnout mold loooks good - keep it warm, turn digital oven to 1960 degrees, (artcaster bronze D from Contenti). Melt, slag pour - gears all look melted and no detail. Too hot - too cold? impossible? Someone can likely tell from photo what I am doing wrong. I appreciate suggestions.

Thanks to the kindness of strangers,

Bob Lanier Fort Worth

If I had to venture a guess, I would say cold metal or cold mold. You say the mold was at 1960 F, do you know what temp the metal was.

I really like that site for the Bronze D. They seem to have everything for casting small stuff. I just typed in Contenti.

Was that an open-faced mold? That flash looks like where you poured the metal in and some dripped over the side. That looks to me to be a combination of lack of head pressure and shrinkage. You need to have either gravity or centrifical force to help the metal overcome the surface tension to get in to those details, and you need a sufficient mass of metal in the feeding sections (read: sprue that you pour the metal down and gating to the part) to compensate for shrinkage as the metal cools. Just having the mold and the metal hot ain't gonna cut it.

hi bob and welcome to the forum. thanks for the pic! i think like jammer that the metal may have been a bit cold but it looks like gas was trapped in the mold. hence the rounded edges. this gas may have come from the mold or the wax????? personally i would give green sand a go!i havent cast any cogs yet but small pulleys and wheels is what i do in green sand. if you were to give your casting ways another go i think you you need to vents and a riser to combat shrinkage upon cooling.

Yes, head pressure would probably help a lot.

And, Welcome to the forum.

definetly either low pressure or cold pour, why not try casting in zinc first?

thats a good idea ! try zinc. if it was plastic before then zinc would suffice.

yes open faces - small gear down so no bubbles form. I thought maybe metal was too hot- it gasses when I pour
Thanks

where would one acquire zink? Why would it be better
Thank you

Zinc is commonly found in 1983 and newer pennies, the copper plate will float off as slag. the reason it would be better is that its melts at a lower temp and is easier to pour to get to fill a mold cavity, basically it is more fluid. Since your mold was an open face i would think that is most of your problem. You need the weight of molten metal to push the metal into the fine detail areas.....