I'm new to this "art" and have searched the Internet for info on my
problem but haven't yet found much help so I turn here.

My problem is what appears to be sand inclusions due to breakdown of
the sand when hot. I'm trying to cast some relatively thin parts and
found the only way to get the mold full is to pour a bit hotter than I
normally do. Don't have a pyrometer yet so I'm kind of guessing.

The inclusions are on the top side of the casting (floating) and
appear to just be in the flow stream above the entrance to the mold.
The last parts of the mold filled are defect free, which makes me
think that it is sand cooking and flaking of the runners after
upstream sand has had a chance to heat.

I'm using western bentonite, around 10%, and relatively coarse sand
(70). My muller isn't able to properly mix Petrobond or K-bond sand
so until I can upgrade I'm stuck with water bonded sand.

What I would like to know is if there is some kind of modification I
can make to my Gates, runners, chokes, etc that might eliminate the
problem, or trap the floating sand before it gets to the mold? Is
there some readily available additive I can use to increase the hot
strength of the sand? More watter? I have no steam problems - yet.

=========================
Leon McAtee

On 28 Feb 2004 09:36:34 -0800, (Leon McAtee)
wrote:

===I'm new to this "art" and have searched the Internet for info on my
===problem but haven't yet found much help so I turn here.
===
===My problem is what appears to be sand inclusions due to breakdown of
===the sand when hot. I'm trying to cast some relatively thin parts and
===found the only way to get the mold full is to pour a bit hotter than I
===normally do. Don't have a pyrometer yet so I'm kind of guessing.
===
===The inclusions are on the top side of the casting (floating) and
===appear to just be in the flow stream above the entrance to the mold.
===The last parts of the mold filled are defect free, which makes me
===think that it is sand cooking and flaking of the runners after
===upstream sand has had a chance to heat.
===
===I'm using western bentonite, around 10%, and relatively coarse sand
===(70). My muller isn't able to properly mix Petrobond or K-bond sand
===so until I can upgrade I'm stuck with water bonded sand.
===
===What I would like to know is if there is some kind of modification I
===can make to my Gates, runners, chokes, etc that might eliminate the
===problem, or trap the floating sand before it gets to the mold? Is
===there some readily available additive I can use to increase the hot
===strength of the sand? More watter? I have no steam problems - yet.
===
============================
===Leon McAtee

If you mixed your greensand correctly I would not fool with it. When
you cut your sprue and gate and runners are you slicking them down and
making it so there are no sharp projections into the mold cavity that
can get washed off. At the bottom of the sprue you need to make a
deeper impression so the turbulance of the molten aluminum does not
cause the sand in this area to get erroded away. Simply make a deeper
cavity below the bottom of sprue and also below the bottom of any gate
or runner. I think the 10% of bentonite to sand is in the ball park.
70 mesh is pretty coarse so you may want to add just a touch but not
all that much more bentonite.

Another last ditch effort is to make a vent riser equal in size to the
fill sprue, and tilt your mold so this vent riser is at the higest
portion so any loose floating sand is floated up and out this vent
riser. Its not a cure but a possible work around. Make sure your
ramming the mold sufficiently and slick down the edges of the pattern
/ mold at the parting line so it does not contribute to loose sand in
your mold.

Pouring thinner sections hotter is the normal proceedure.
Visit my website: http://www.frugalmachinist.com
Opinions expressed are those of my wifes,
I had no input whatsoever.
Remove "nospam" from email addy.

check your gating system. Are you using a pressurized or non-pressurized
gating system? What's your ratio for downsprue: runner : ingate?

Tricks to help can include:
* reduce pouring height
* put bigger well at bottom of downsprue
* go to non-pressurized system
* put traps at end of runners
* dog legs in runners/gates
* minimize turbulance and metal veloceties in gating system

You can get some good books/training courses at the following:
http://www.afsinc.org

"Leon McAtee" wrote in message
om...
I'm new to this "art" and have searched the Internet for info on my
problem but haven't yet found much help so I turn here.

My problem is what appears to be sand inclusions due to breakdown of
the sand when hot. I'm trying to cast some relatively thin parts and
found the only way to get the mold full is to pour a bit hotter than I
normally do. Don't have a pyrometer yet so I'm kind of guessing.

The inclusions are on the top side of the casting (floating) and
appear to just be in the flow stream above the entrance to the mold.
The last parts of the mold filled are defect free, which makes me
think that it is sand cooking and flaking of the runners after
upstream sand has had a chance to heat.

I'm using western bentonite, around 10%, and relatively coarse sand
(70). My muller isn't able to properly mix Petrobond or K-bond sand
so until I can upgrade I'm stuck with water bonded sand.

What I would like to know is if there is some kind of modification I
can make to my Gates, runners, chokes, etc that might eliminate the
problem, or trap the floating sand before it gets to the mold? Is
there some readily available additive I can use to increase the hot
strength of the sand? More watter? I have no steam problems - yet.

=========================
Leon McAtee

"Smelly Belly" wrote in message ...
check your gating system. Are you using a pressurized or non-pressurized
gating system? What's your ratio for downsprue: runner : ingate?

Tricks to help can include:
* reduce pouring height
* put bigger well at bottom of downsprue
* go to non-pressurized system
* put traps at end of runners
* dog legs in runners/gates
* minimize turbulance and metal veloceties in gating system

You can get some good books/training courses at the following:
http://www.afsinc.org

Thanks for the link. I suspect the last parameter is the one giving
me the problems. My ingate is quite small due to the thiness of the
casting. Metal velocity at that point is probably high. I also was
trying to keep the hydrostatic pressure high to help fill. My first
attempt only filled partialy - but had no sand includions.

check your venting.

What is the smallest cross section of your casting? Can you move the
ingate? Faster fill doesn't always make a better fill.

What's the height of your cope?

"Leon McAtee" wrote in message
om...
"Smelly Belly" wrote in message
...
check your gating system. Are you using a pressurized or
non-pressurized
gating system? What's your ratio for downsprue: runner : ingate?

Tricks to help can include:
* reduce pouring height
* put bigger well at bottom of downsprue
* go to non-pressurized system
* put traps at end of runners
* dog legs in runners/gates
* minimize turbulance and metal veloceties in gating system

You can get some good books/training courses at the following:
http://www.afsinc.org

Thanks for the link. I suspect the last parameter is the one giving
me the problems. My ingate is quite small due to the thiness of the
casting. Metal velocity at that point is probably high. I also was
trying to keep the hydrostatic pressure high to help fill. My first
attempt only filled partialy - but had no sand includions.

"Smelly Belly" wrote in message ...
check your venting.

The venting on this part has consisted of several small(3/32") vents
at the top most portions. They have never fully filled. One can see
that the ones closest to the ingates fill to a greater height (around
2 inch) than the colder ones.

What is the smallest cross section of your casting?

Size and general shape of a bread pan - about 4mm thick the piremeter
has a section only about 1.5mm thick which has been limiting my gate
size. There is a way I can gate to a more substantial portion of the
patern but it will take a bit more creativity - and my first attempt
at making a core.

Can you move the
ingate?

Yes. Tried one at one edge and then one on each end. The attempts
with 2 had sand inclusions (if that is what they really are) on only
one side, and seemed to be of less total volume.

Faster fill doesn't always make a better fill.

That has been my limited experience. The slower and the colder I can
pour and still have a fully filled mold seems to give the best
results.

What's the height of your cope?

About 6 inches total - 3 inches above the top of the casting. I also
tried swapping the cope and drag relative to the pattern with little
differance.

Will probably try again this weekend with larger runners, bigger sump
under sprue, a sand trap before the gate, and larger gates. I've had
good luck with other patterns using a slanted sprue. Seems to allow
the metal to flow in with less turbulance. But the flask I have been
using is a bit small to try that with this pattern. I have made a
slightly larger flask and will use it next time.

On 2 Mar 2004 18:14:07 -0800, (Leon McAtee) wrote:

snip
What is the smallest cross section of your casting?

Size and general shape of a bread pan - about 4mm thick the piremeter
has a section only about 1.5mm thick which has been limiting my gate
size. There is a way I can gate to a more substantial portion of the
patern but it will take a bit more creativity - and my first attempt
at making a core.

snip

What about using a runner and multiple ingates around the edge?

This advice is worth what you paid for it... my foundry work, so far,
comprises reading about it


Mark Rand
RTFM