Who dreamed up the term pressure casting

[Mike W1]

Now I'll grant that it works, some moulds apparently need that technique but you sure as heck can't be increasing the pressure of the alloy into the mould whether you dip or bottom pour. Gotta be a better term for it than that doesn't there?

[Tdart]

By pressure casting you are using the weight of all the lead in the ladle to push lead into the mold as opposed to just using gravity to pull the lead in that will become the bullet. From a fluids perspective (I'm a physicist), pressure casting puts the cavity at the bottom of a fluid. Pressure at the bottom is higher than the top, so pressure casting makes sense to me. But I have been wrong before...

[MT Gianni]

It wasn't dreamed up in this century and perhaps not even in the previous one. If it ain't broke.......................

[MtGun44]

Yes, it DOES increase the pressure. The column of molten lead above the mold applies substantial
pressure due to gravity, just like a water column, but much more pressure for a given height of
material due to the high density of the lead. A 33 ft water column applies 14.7 psi, I bet a
6" column of lead applies a few psi of pressure.

Bill

[theperfessor]

If my assumption for the density of lead is correct, a column of lead has a pressure at the bottom that is equal to about .4 psi per inch of column height, so a 6" high column has a pressure at the bottom of slightly less than 2.5 psi.

[44man]

I have always had a problem with the term "pressure" when casting. You can't compress the molten lead or get more in the mold by a long column. You just force the air out. You will not change a thing if a ladle is full or half full or if the level in the pot is 2" or full.
I ladle cast with the spout in the plate with no leakage for two reasons, first, I don't make a mess and the most important is I keep feeding the boolit with molten lead from the ladle as the boolit shrinks instead of from a sprue that can fail to feed a large boolit before it hardens.
If you get whiskers, something is plainly too hot. I can get whiskers with a half full Lyman ladle and slowing down will stop it.
If you bottom pour from a height, everything must be hotter.

[Mike W1]

This is along the lines of what makes sense to me also but I've also been wrong before!


I have always had a problem with the term "pressure" when casting. You can't compress the molten lead or get more in the mold by a long column. You just force the air out. You will not change a thing if a ladle is full or half full or if the level in the pot is 2" or full.
I ladle cast with the spout in the plate with no leakage for two reasons, first, I don't make a mess and the most important is I keep feeding the boolit with molten lead from the ladle as the boolit shrinks instead of from a sprue that can fail to feed a large boolit before it hardens.
If you get whiskers, something is plainly too hot. I can get whiskers with a half full Lyman ladle and slowing down will stop it.
If you bottom pour from a height, everything must be hotter.

[theperfessor]

I agree that you can't get more than a fixed maximum amount of lead in a mold cavity. Nor will the molten lead compress to any measurable degree at the pressures we are talking about. I will offer the opinion that the extra pressure DOES HELP overcome the surface tension that some lead alloys in combination with some molds seem to have. Pressure casting can yield bullets that are filled out sharper than non-pressure cast bullets.

Like everything else about casting use whatever works for you. And it isn't always the same thing that works every time for every problem.

[Trey45]

Yes, it DOES increase the pressure. The column of molten lead above the mold applies substantial
pressure due to gravity, just like a water column, but much more pressure for a given height of
material due to the high density of the lead. A 33 ft water column applies 14.7 psi, I bet a
6" column of lead applies a few psi of pressure.

Bill

This is called head pressure and it certainly applies to casting.

[44man]

I have always accepted the term "pressure" because there is no other way to describe it although I think quantity of lead needed is how I feel about it.
I can fill a big .500 boolit with half a ladle full but the huge .45 BPCR boolits need more in the ladle.
I usually cast the first cavity with a full ladle, let it just set and finish the ladle in the next cavity without refilling it, no difference in the boolits. The large boolits just need more lead in the ladle so I dip some more.
The few times I got the bottom pour to work, I tried the pressure thing and found no difference in boolit weight from one cast with half a ladle.
Now those huge brass and 6 cavity molds need worked faster then a Ladle can handle.
Most times I use two double cavity molds at once with a ladle and have used three. Just pre heating the molds is a problem but once there casting goes fine.

[cbrick]

Does holding the ladle spout or bottom pour spout against the sprue increase pressure as opposed to holding the sprue plate away from the source?

Yes, of course it does, it has to. If your holding the ladle in direct contact with the sprue plate your "adding" the weight of alloy in the ladle (or pot) to the flow into the mold. If you hold the ladle away from the sprue plate your using only the weight of alloy in the stream going into the mold. I think the term "pressure" casting is correct because you are adding the weight of alloy in the ladle going into the mold.

Does it matter? Well, that's another question. As the Perfessor says, not all situations are the same and it could be a benefit for some alloys & molds.

Rick

[theperfessor]

I have one mold that I have to pressure cast with, I hold it up to the nozzle and fill 'er up, hold for a second or two, and then drop the mold a little to get a little puddle when I pull away. Could I make it work another way? Probably. I could change alloys, add more tin, change temperatures, cast faster or slower, or dance naked in the moonlight. Or just keep doing what I do with that mold.

[BAGTIC]

You are increasing the pressure due to the momentum of the moving fluid. The faster it flows the more momentum.

[BAGTIC]

Spanish for "I am wax" is 'estoy cera', not 'soy wax'.

[bangerjim]

I agree that you can't get more than a fixed maximum amount of lead in a mold cavity. Nor will the molten lead compress to any measurable degree at the pressures we are talking about. I will offer the opinion that the extra pressure DOES HELP overcome the surface tension that some lead alloys in combination with some molds seem to have. Pressure casting can yield bullets that are filled out sharper than non-pressure cast bullets.

Like everything else about casting use whatever works for you. And it isn't always the same thing that works every time for every problem.

+1 on this!

A better term would be "injection molding" ..........that is REALLY what we are doing!


The head pressure of the pot forces the NON-COMPRESSBLE liquid lead into the cavities faster and better than just letting gravity trickle it in on some molds.........as I have found out this week.

Lead and mercury are pretty close, so using inHg (which has charts & conversions everywhere) will give you an idea of the head pressure you are forcing the lead into the cavity.

Hg = 13.5 g/cm3
Pb = 11.38 g/cm3

Close enough for what we do ( and for gubmint work!) :cbpour:


bangerjim

[dondiego]

Spanish for "I am wax" is 'estoy cera', not 'soy wax'.

OK......good to know............I think. This may need to go to the FLUX thread.

[williamwaco]

I first heard it in 1956 when I learned to cast

And by the way?

Forcing the air out is the primary goal of bullet casting.

zero air = perfect bullet.



.

[williamwaco]

If my assumption for the density of lead is correct, a column of lead has a pressure at the bottom that is equal to about .4 psi per inch of column height, so a 6" high column has a pressure at the bottom of slightly less than 2.5 psi.


I didn't do the math and I concede you are always correct, but - that really sounds too light to me.

[Old Caster]

Simple. Just look up how much lead weighs per cubic inch and the column height of the lead in the pot or ladle will tell you how many pounds or portions of a pound the pressure it is exhibiting per square inch. When pressure pouring in a bottom pour pot, the pressure is probably about 6 times as much as a ladle because the lead is about 6 times as high when full. It is not compressing the lead but giving a more complete fillout or in other words moving the air out of the mold replacing it with lead more completely. Simple physics.

[theperfessor]

Well, let's work through the math. As has been stated, the pressure at the bottom of a column of fluid is the density multiplied times the height. I couldn't find a density for liquid lead but I did find a density of solid lead - 711 lb/ft^3. Divide by 1728 to convert to lb/in^3 and you get .411 lb/in^3. Multiply by the height in inches and you get lb/in^2 which is a pressure term. Each inch of column height raises the pressure by .411 lb/in^2.

My figure for the density is probably off a little, thus my statement of an approximate answer.

[Garyshome]

I use it but only when the mold needs more pressure to fill out quick enough that I get good boolits. Also I don't want the stream exposed to any more oxygen than necessary [impurities and other bad stuff]. It's just another tool in the box!

[sljacob]

You are increasing the pressure due to the momentum of the moving fluid. The faster it flows the more momentum.

exactly..As I see it, without a seal between the ladle and the sprue plate there is no pressure coming from the weight of the alloy in the ladle. Any added pressure would just widen the column with. It is all about the momentum.

[MtGun44]

My estimate was "a couple of psi" - pretty close to 2.5 psi, I'd say. This pressure pushes
the alloy into the corners better and pushes out the air - overcomes the surface tension
more than with no pressure.

Bill

[williamwaco]

OK,

I give.

[Old Caster]

If you had a column height of a couple of feet you would quickly find out what pressure pouring was. Water pressure in your house is usually caused by it coming from a water tower but lead being a lot heavier, would have tremendous pressure at that height.

[FAsmus]

Gentlemen;

Enter the term "Wosikia pressure-wave casting".

This technique will provide additional pressure at the fill-hole without the usual spout-to-the-sprue-hole and turn your wrists procedure.

Here it is, try it and see what you think:

With the mold sitting upright on the side of your open-top pot of alloy bring the pour spout of the ladle up out of hot alloy and start pouring before you even get to the fill-hole. This nearly eliminates any slag or other foreign material from getting into the cavity. As the stream of alloy reaches the fill hole direct its flow toward one side or the other of the angled sprue hole. This creates a swirling action to the hot alloy such that as it enters the cavity it will drive out the air more effectively. You will note that as the alloy enters the fill-hole that it will build up a 'wave' of metal over the fill-hole. This indicates that the flow of material has reached a certain level of pressure greater than merely the weight of metal coming behind it in the flow from the ladle. Keep on pouring for a second or two after the cavity is filled. This will guarantee that all air is driven out of the cavity and you will get absolutely square corners on all grooves and bases.

In my endeavors to make good bullets I have tried many techniques. At the end of it I brought in my electronic scale and weighed each bullet as it was cast. I learned a lot.

The Wosika method worked best. I could grain a full grain of bullet weight by using it over the turn-fill method. Same day, same alloy - same everything else. Just the difference in technique. Mind; do not just 'trickle' the alloy into the fill-hole. Rather HIT it hard and let the excess alloy run off, back into your pot.

Good evening,
Forrest

[44man]

Slag floats! A good ladle has no slag at the spout, only clean lead. When you tip, it stays at the top.

[Old Caster]

Slag does float but it also sticks to metal like the ladle, pot, or needle in the bottom pour pot. If slag couldn't be at the bottom of a pot, the spout would never clog.