FAQ's -- Frequently Asked Questions
1. Can the bottom of the
sand molds withstand exposure to the molten bath?
2. Will the metal freeze
to the bottom of the molds?
3. Won't the sliding
molds create loose sand by abrasive action?
4. You can't use mold
vents as they would over-fill and leak with the pressurized filling.
5. Is slow filling
important? I'd always heard you should
fill as fast as possible.
6. Is pressurized
filling important? Does the process
increase my capability and ease of casting?
7. I thought you
wanted higher pressure FEEDING after filling?
And why is that important?
8. Do you really think
this can be done in iron as well as in non-ferrous metals?
9. What if a rupture or
other leakage occurs, or just down-time of the molding machine?
10. Why does the movie
show liquid metal running out at the end of the line?
11. This isn't just
for vertical green sand molding, is it?
12. Does Herron
Casting Services have the staff to help us get up and running?
1. Can the bottom of the sand molds withstand
exposure to the molten bath without scabbing or spalling into the bath?
Absolutely!
Spalling is caused by radiant heat
WITHOUT molten metal contact.
Sand floats, and the molds float and
slide more easily.
Filter cloth holds the sand in place.
Use western bentonite.
2. Won't the metal lose a lot of heat to the
bottom of the sand molds? Will it not
even freeze to the bottom of the molds?
No.
Sand is an excellent insulator.
Radiant heat loss is ELIMINATED in the
contained system.
A thin layer of sand, over the bath, will
dry out completely, then insulate.
The metal will NOT freeze because hot
metal rises and any cool metal falls.
Only an open bath can freeze over, as
radiant heat loss plus air conduction is so powerful. This system produces substantial energy
savings in many ways!
3. Won't the sliding molds create loose sand by
abrasive action?
No.
The sand does not slide nor abrade where
the cloth is present.
(around
the perimeter of the metal chamber)
The sand does not slide over the flowing
liquid.
The sand rides on the cloth and floats on
the metal.
Over the low friction chamber, sliding
takes place beyond the cloth, where each sand grain pushes the next grain, and
all stay in place.
Near the molten metal, no abrasive action
occurs!
Air nozzles should be placed just prior
to cloth dispensing and application
(to
remove any loose sand from molding or pattern stripping).
4. You can't use mold vents, can you? They would over-fill and leak with the
pressurized filling.
Won't you
risk mis-runs?
Actually, the machine can be set so that
pressure is equal to that of a standard sprue.
That is, equal to the mold height, and vents could be used during
filling.
The same risers may be used as in
conventional gravity pouring, and the same coarse sand would create similar
levels of burn-in.
The thin flow-off vents freeze quickly so
you could then go over the high-pressure, solidification feeding chamber in the
optional second operation of dual chambers.
For ultimate advantages however, higher
pressure filling is recommended. Vents
would not be used. The higher pressure
overcomes mis-run even when finer sand is used for
higher quality.
We also have a longer available time for
air to escape through the permeable sand, as the filling time is NOT limited by
mold cycle time anymore.
Vents and permeability are not as
important in this process. Adjustable
filling pressure and design of the chokes, provides wide flexibility and
casting capability.
Thinner walled castings can be filled
like never before, gently, from the bottom, and deliberately slow under
pressure.
5. Is slow filling important? I'd always heard you should fill as fast as
possible.
There is an extreme to be
avoided both ways, too slow or too fast.
The Herron Casting Machine puts you back in control of filling time,
while molds are moving at high speed.
6. Is pressurized filling important? Does the process increase my capability and
ease of casting?
Pressure is always important. The height of your sprue is currently your
available pressure.
Patterns too high in the mold may fill
too slowly or not at all... mis-run! The number one cause of riser connection
shrinkage is actually: poured short
risers mis-run!
With the Herron Casting Process, pressure
may be set at the optimal level to fill those hard to fill castings. The gates are then designed to freeze before
burn-in begins to occur, leaving conventional risers to feed at standard pressures.
YES!
Capability is increased and
ease of casting!
7. I thought you wanted higher pressure FEEDING
after filling? And why is that
important?
By filling at low or
moderate pressure and designing a few seconds of cooling into the length of the
chambers, the casting skin freezes, protecting the surface from burn-in. Now, a higher pressure FEEDING zone is
reached, which will push metal into dendritic voids better than a conventional
riser can with lower head height in the mold.
This has been known for centuries by foundrymen "topping-off"
a riser head, waiting a few moments after initial filling. Modern high quality casting techniques use
this principle (i.e. burst feeding, semi-solid casting, etc.). They just can't do it while molds are moving
like the Herron Casting Machine can!
8. Do you really think this can be done in iron
as well as in non-ferrous metals?
YES! Units can be designed with exposure to the
bath from as little as 10 seconds to as much as 10 minutes! This provides the ultimate in pressurized
feeding. The filter cloth is not
required except in very challenging applications, but quality is improved by
using filter cloth. The cloth makes
possible alloy modification at the point of entry (i.e. sodium or titanium in
aluminum, or graphite or magnesium ferro-silicon in iron, using mold
stitching).
The cloth is leached with
silica for iron applications.
9. What if a rupture or other leakage occurs, or
just down-time of the molding machine?
The patent application
discusses this fully. As in any metal process,
a safety pit or floor dikes must contain any possibility. The VPV or furnace is under constant, steady,
pressure when operating, so that every mold is filled exactly the same (at the
same speed, pressure, and temperature, eliminating variation). If rupture occurs, a valve immediately
releases the pressure and another valve connected to a reserve vacuum tank
immediately withdraws the metal from the mold line.
Furthermore, poor quality
molds cannot push the mold line through the machine. If the molds can enter the machine it is very
unlikely they will rupture. The filter
cloth will not fail, but if it did, it would be a very slow leak and would
freeze off.
10. Why does the movie and the PowerPoint slides
show liquid metal running out at the end of the line?
The sprues, small as they
are, are in constant contact with the bath until exiting over the final
wall. Ingates
above are designed to freeze by this time but the up-sprue may still be
slightly molten. This can be collected
in a separate chamber or caught in ingot molds.
Extended cooling before shakeout is actually desired in most cases but
is not shown.
11. This isn't just for vertical green sand
molding, is it?
No. I want the first units to be vertical green
sand but all the principles could be demonstrated most cheaply with no-bake
molds in a slower set-up without using vacuum and pressure, just a metal
holding vessel. Detailed drawings are
available. Ultimately, this process can
automate the horrendously slow filling processes of lost foam and ceramic
investment casting. Horizontal molds,
even of various sizes, in green sand or no-bake can also be processed. Every foundry will one day use this method,
according to my own and other expert opinions.
Favorable terms and advantages will be allowed to the pioneers.
12. Does Herron Casting Services have the staff
to help us get up and running?
Absolutely. A team of the best independent consultants
and vendors has been prepared and are waiting to put you ahead of the pack in
the competitive world of casting.
Please
write to ask any further questions:
E-Mail:
DHerron@HerronCasting.com
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Copyright© 2001, 2005,
David J. Herron
All Rights Reserved