Keep hearing about this whole reading. What exactly is it ? Benefits? Cons ?
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Keep hearing about this whole reading. What exactly is it ? Benefits? Cons ?
The mold is held tight against the spout of a bottom pour pot for a few seconds then a puddle is poured on top. Advantage: it works for me. Other folks have just as good of results with different methods. Use what you like that gets results that satisfy you.
I use it on most of my molds as it gives a good fill out.
However the pressure casting will cause fining where the extra pressure will push the lead into the vent lines.
I think It`is when the mould won`t fill out very well ,you stick the mold up against the nozzle of bottom of the Pot of Lead (where the lead comes out) using the weight of the alloy in the pot to feed into the mould, instead of holding the mould a few inches below the nozzle. Helping the to mould fill out better I could be wrong Maybe someone will chime in .
Yeah, it's just a method of getting better fillout with an alloy or mold that gives some problems with doing it on it's own.
Do you get air voids on molds that are not well vented?
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It can be done with a bottom pour or a ladle pour.
I always try it, every casting session. Sometimes it works better, sometimes not. I think the variables involved are particular mold, particular temperature, particular alloy, -- and maybe even phase of the moon. (yeah, that's too many variables) Soooo I guess I don't really know why it sometimes works better and sometimes not, but I always try it. jd
Actually, you'd have less problems since the pour has the pressure from all the molten Lead above it pushing the air outQuote:
Originally Posted by 7br
harder than pouring with the air gap under the nozzle.
Also--
When you clean your molds, scrub the vent lines with a old tooth brush, and you'll never have to worry about it.
You'll often get a faster, and better fill out.Quote:
Originally Posted by Wolfdog91
Dress for the occasion--
When the mold is full, but the Lead can't quite over flow making a sprue puddle,
I have had teeny, tiny Lead splatter balls bounce up and hit my hand/arm.
And,,,,,,,,,,, they're HOT!
I have done it with a bottom pour, but, the pressure of a full pot is too much. The lead gets into all the vent 'lines'.
The 'best' way to pressure cast is with a Lyman ladle. The one with a spout on one side. Fill the ladle, turn the mold 90deg and 'fit' it to the spout. Turn spout and mold upright. When the mold is full you can just leave the ladle in place or move it up a bit and let the lead pour over the mold. If you are really coordinated you can do this with multiple cavity molds. I am not :)
I pressure with a bottom pour pot by holding the mold snug against the bottom of the nozzle. Wear a glove, when the cavity is filled, hot lead will spurt as has already been mentioned. The sprue plate might stick to the nozzle at that point and a little twist to break it loose while continuing to pour a sprue puddle is very helpful to allow molten alloy to draw into the cavity as it cools and shrinks.
A full pot gives a lot of pressure, so as already mentioned, you may need to reduce the level in the pot a little to get the best result. Another benefit when pressure filling in cold weather is the stream has no time to give off heat between the nozzle and the sprue plate. Just another technique that might improve your product when casting.
I’ve always used a Lee bottom pour pot and never had to pressure cast with any of my molds (40+). I heat the mold up really good on a hot plate and run my PID at 707° to control the melt temp.
One thing I don't like about mold/nipple contact, is that the sprue puddle is small, and tends to stick to the sprue cutter instead of dropping clear.
More often than not I end up using the no/contact method and trying for a steady stream to fill, and stop the flow just when there is a small rounded button on the sprue plate. -- I only have one and two cavity molds. jd
Once I learned to properly clean moulds, use a good alloy at correct temp, use correct tempo cast properly with ladle or bottom pour I've never had to pressure cast again. It's a band aide solution to another problem that should be remedied.
I get my best boolits (near as perfect as possible) with a Lyman Spouted Dipper ... it has a open bowl and a little side spout .
Fill the bowl , hold mould sideways , press side spout to sprue hole and invert mould and spout to right side up ... count 1, 2 , 3 and while holding mould level roll spout off sprue hole and leave a nice large uniform sprue puddle . Repeat if mould has more than one cavity and I like to start filling the cavity farthest away from the hinge and keep a slight downhill tilt so sprue metal doesn't run into a unfilled cavity .
You Do Not need a bottom pour pot to pressure cast ... it's easier and I find better to use a Lyman Spouted Ladle / Dipper . Too much pressure behind that stream of lead causes more problems than it solves .
Gary
The RCBS pot has a thumb screw that allows you to control the flow of lead coming out of the spout. I find that pressure casting works well with it. Lee pots lack that feature and I got whiskered boolits from lead going into the vent lines with them. It was very hard to control the flow rate. I did see an article once where a guy used a Z shaped of metal to make a flow rate regulator for the Lee pot. The lister leg of the Z was screwed to the pot using one of the existing screws. The upper leg had a hole drilled and tapped for a thumb screw that would limit the amount of travel for the rod that opened the spout. It allowed for consistent flow of metal out of the spout. FWIW.