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Author Topic: Getting Good Lead Castings  (Read 510 times)

Bob La Londe

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Getting Good Lead Castings
« on: April 03, 2018, 07:07:03 AM »
Some molds just pour perfectly as unboxed. 

Others can be quite finicky.  Especially those with lot of hardware and inserts in the mold.  Others with fine detail or bottle necks to flow can be a problem. 

Sometimes preheating the mold is the trick.  Other times preheating the hardware.  If preheating is the trick then a hot plate can be the answer.  I know one fellow spreads out hooks on a hot plate and picks and places them into his mold with pliers.  I have one spinnerbait mold I pour where I hang half dozen hooks at a time on the side of my lead pot to warm up. 

Playing with heat isn't always the answer.  Sometimes the mold needs something to help it flow better.  An old trick from the days of yore is to soot up the cavities with candle smoke. I think it was popular because at one time most of us had a few candles in our home.  It was just something we had on hand and it helped a little... sometimes.  It does work as a mold release.  I don't think it works as well as some other things.

Graphite spray is very popular these days.  It does work well as a mold release, and because it acts as a thin layer of insulation it may also help the lead flow better in some molds.  It takes the lead a fraction of a second longer to freeze off which allows it to fill details better.  Sometimes this really is the answer.  Atleast good enough.  There are graphite sprays sold for casting, but I have not noticed much difference between those and aerosol graphite lubricants available at your local big box hardware store.  There may be some but I have not really been able to put my finger on it. 

Talcum powder.  (unscented baby powder) No kidding.  It might have some insulating properties, but that is not what makes it work.  The fine particles break up the surface tension of the lead as it flows into the mold.  The results are almost always better than without.  I would suggest wearing a dust mask to reduce inhalation.  Its very light fine powder, and breathing in any kind of hard particle in volume isn't good for your lungs.  I keep a small round dish with just a little baby powder in it on my test bench for when I am testing molds.  I use a cheap flux brush to dust powder into the cavities of the molds, and tap out the excess.  I buy bags of the brushes for a couple dollars for painting on resins too.  Talcum powder works very well. 

(Note:  A light dusting of talcum powder has a similar affect on resin castings.)

Lead quality.  I get it all the time that people have a pile of cheap "lead" alloy of unknown provenance and they can't get it to pour well.  I test molds with 99.5% pure I get from a well known metal vendor.  I don't get any discounts.  Wheel weights use to be popular, but they now are pretty hard to get without contaminating your batch with zinc.  Old roof flashing and plumber's lead are still being salvaged from time to time and seem to mostly be pretty good.  Even when you switch to good known alloy you may have problems if you haven't cleaned out your melting pot "pretty good."  Pure lead isn't necessary for good castings.  Sometimes you want a tiny amount of tin or antimony alloyed into your mix for different properties, but pure lead is a good place to start when you are having problems. 

Head pressure.  I've found I get better pours out of my bottom pour lead pots when they are full.  More lead in the pot means more weight (pressure) at the spout.  I also get better pours from a bottom pour lead pot than I get from a ladle. 

If you are making your own molds another place to think about head pressure is in the mold itself.  A little bit deeper sprue can make a difference in how well your cavities fill sometimes.  There is a reason high volume lead casters tend towards spincasting.  The centrifugal force provides the equivalent to head pressure, but in a lateral direction as the mold will be laid out that way. 

I am sure there are other tricks I don't know or have forgotten to mention.  Please if you know something else or have an opinion comment below. 

If you know ANYBODY who might benefit from this post please share it with them, personally or via social media. 
« Last Edit: April 03, 2018, 11:11:11 AM by Bob La Londe »