Metal casting

[4V50 Gary]

Not gun related, but its application can also be used to fabricate gun parts or accessories. We did something similar at WKU (National Muzzle Loading Rifle Association sponsored class held at WKU) in their brass casting class.

https://youtu.be/gImHcPMhnok

Unfortunately, they don't tell you what type of sand, or describe their process. They also don't show the creating of the flow holes that they pour the molten metal into.

[HiBC]

Quite a while back,I'm thinking sometime in the 1980's or late 1970's.I worked in a foundry.
This foundry was more about wo5rking with sculptprs,making parts to restore old fancy cash registers,antique lock ,door and cabinet hardware,etc.

They made some parts for a blacksmith supply,Yant,I believe. The blowers.

They did a great,detailed,legible job of casting reproductions of old brothel tokens.

We dd not cast iron. We did yellow brass,red brass,silicon bronze,and aluminum.

That black sand appears to be commercial foundry sand.Not the best for artisan gun stuff,as in for muzzle loaders.

Here is where I have a problem. This family jealously guarded the trade secret of their sand.

I recall the sand either came from a river in Missourri,or from the Missourri river.
It was fine grained..if I had to guess,about 180 to 240 grit? It was buff colored,about like coffee with lts of cream. No asphalt or oil.

I think before I time out here,I'll start a new post

[HiBC]

That sand was trated very special.It was worked on the floor,as a pile,but kept very clean from contamination.It would get sieved regularly,and moisture content was carefully controlled. A fist full had to "pack" and hold shape.

Very careful consideration had to be given the part to be cast. Remember,it has to be pulled from the packed sand,without disturbing the cavity.

Sort of like pulling a glass bedding job. You must define a parting line at the widest cross section of the part. Everything must be drafted from there.

Sculptors pattern wax can be modeled into an original part. Of course,patternmaking is a highly skilled art. The patterns traditionally are wood,smoothly,cleany finished and shellacked to fine gunstock standards.

To be continued...

[HiBC]

The chase,or frame. Two square or rectangular frames,to make a box to hold the sand mold. Typically,horizontal corrugations help hold the sand in the frame

One side has alignment bushings,the other,pins. Typical of about any mold.

On a flat,solid table,1/2 of the frame is placed...now,forgive me,I had my own tasks around managing the fire,pot,and melting the metal.Cutting sprues,and filing the raw castings.

They were keen to keeping their process.If I was standing and watching generally it was a sign I needed something more to do.

So,I'm unclear about some things I was around 40 years ago.

I might get some of this wrong.

Sand would be shoveled into the frame and tamped.A double ended wooden tool was used,potato masher blunt tamper on one end ,wedge shaped on the other.the sand had to be packed to a degree it would stay in the frame.

That may have been done with the parting line of the mold down on the table.Actually,the part pattern may have been laid down on the table That would give a a well packed chase and a nice flat parting line. .This would be the bushing,as opposed to the pin,side of the chase. Then the packed sand is carefully struck off lever with the chase.That way when the mold is turned over,the sand is supported by the table.

So now lets do that...turn the mold over

To be continued

Then the chase is turned over,supported on the table.,with the part buried near the parting line,and the sand packed tight to the pattern

[HiBC]

OK,so now you are looking at the flat sand of the parting line with a buried part.

The next phase is a carefull excavation of the part down to the level of the pattern parting line. We want it to look like the part is half buried in a sand dune or mud flat. Like inletting a stock,smoothly carve away sand down to the parting line.Don't remove sand to expose the walls of the chase

There you have the half mold.Smooth the surface,gently blow loose sand clear.

Now,a dry dust called "parting sand" is sifted over the entire mold surface,,This will alow the mold halves to be separated.Place the other half of the chase in place A sieve is then used to sift sand over the part till it is buried.

Then more sand is added and packed,till the chase is overfilled,packed,and struck off level.

More incomplete knowledge here. I'll try. Venting,spue,and runners.

I'll undoubtedly get some of this wrong. I was not apprenticed,I have not done it,I'm sharing fragments of memory.

If you are a foundry hand,please correct me.Also,please don't attack me.

I;m doing the best I can.

The pattern is still in the sand. At some point,we need a path for the metal to be poured in. There is air in the mold. We must vent the mold to allow the air to escape. There will also be steam from the moisture in the sand. The mold will not fill properly without venting.

Now,also consider...imagine the mold filling in terms of being trapped in a submerged car. As the car,or mold fills,at the high points,you might find trapped air to breath. These same air pockets will prevent mold fill. They must be vented.

So,how??? To be continued

[HiBC]

Well,whatever works. A decision has to be made about venting,gating,sprue,etc while the pattern is in the mold or after its been removed. Poking around in the unsupported sand cavity can make for a crumbly mess.

While tools can be used to cut runners and sprues,etc,pre-planning can add those features to the part pattern,so they are already in the sand,to be removed with the pattern.

With the part in the sand,still,a cork borer,or icepick,or wire can be used to probe vents down to the part pattern. Placing the vent locations blind might be tough.
Actually, wires can be placed and packed in the sand and pulled out before the mold is parted,I suppose paper straws could be used and left in place...oneway or another,vent your mold,thinking about the material flow.

Getting the material in

First,a good cast part has fairly uniform wall sections.To go from liquid metal to solid,the heat is conducted into the mold.As metal solidifies,it shrinks.

The metal cools and hardens at the outer skin first in contact with the mold.

It will be liquid under that skin as it cools,shrinks,and hardens.

Now get this,the shrink will be drawn fom what is liquid.Least resistance. So while the outer skin is hard,the tickest cross sections,is where the shrink will be pulled. You will have porosity and voids,and maybe large,brittle crystals. Plus a lot of stress.

To be continued

[HiBC]

Getting the material in:

Now,most of my knowledge is from plastic injection molding. Its not the same as sand casting. I don't know to what degree the rules overlap.

I'll try my best. You want the material to be delivered to the part by a generous ,continuous ,uninterrupted flow. Lets call that the Runner. Its best to add vents to the runner. Why not?

We don't want the part to deal with the cooling and shrinkage problems of the runner,so we use a "gate" You might scoop a gate into your sand cavity after is done,or add it as a feature to your part pattern...but a caution. You are soon going to have to pull that pattern out of the sand.Complexty can mess with the release.

In plastic,we might use a gate 70% of the thickest wall.That will get you a fill,but its best the gate freezes off first.

You can cut a fairly generous sprue as the main line to feed the gate.

As the part fills,you may want to add "Risers" Risers allow extra material to flow through the mold,and then back up. When the risers at the far end of the mold fill,you can stop pouring.

The spue is where you pour the pot into the mold.Think of a coffee cup.Think of a glowing red crucible of molten metal,maybe a gallon,and enough radiant heat hitting you that denim turns a toasted brown and crumbles.

During all that,a steady,smooth supply of molten metal is important. That sprue helps achieve that.

Exactly how? I have not built a sand mold. Experience and references,your research will tell you.

To be continued

[HiBC]

Now,you have some idea about the additional features in the sand you will need.

But for now,you still have your part pattern in the sand.

If we did well and get lucky,the parting sand will work,and we can carefully lift to top half off the mold. It needs to be a clean,straight motion with no bumps remember,its just a pocket in sand

Place it on the bench

The Old Man,generally might have a couple of 6-32 screw holes in the top of the part. One factor in cleanly pulling the part from the sand is having something to get hold of.. Another tool he used was a pneumatic little round buzzy vibrator dookickey. About 2 in diameter and an inch thick.

With a gentle pull on the part pattern,some vibration helped the part break free.

Now you have the mold apart.doing as little damage as possible clean up any stray sand. Its best you already have most of the other carving and scooping done.

Now the mold halves are placed back together.

We had a chunk of steel catwalk laid on the floor,filled with sand.That is what we placed the molds on.

Next,furnace and crucible

[HiBC]

Our furnace was round,firebricked.. A sort of swingin lid with about an 8 inch center hole.. It had roughly the equivalent of a leaf blower type air feed,,but maybe not that intense.And propane was the fuel.

A square of cardboard big enough to set the crucible on was placed in the unlit furnace. The crucible was placed on that. The cardboard jept any vitreous material from gluing the crucible to the firebrick.

The crucible was placed in te furnace,still unlit.

Then it was filled with whatever metal we were going to pour.Bronze for sculpture was the nicest to work with..
Put a ball of burning paper in the furnace,turn on the air,then turn on the gas,as I recall. Nothing much to do but melt it and pour it
Aluminum was OK. Like with bullets,a little dross and skimming.

Brass is problematic. At casting temps,the zinc catches fire. Nasty fumes,like welding galvanized but worse.Then there is whatever other metals,like lead,that may be in there.

I was to toss 2 beer bottles in the crucible with the brass.The glass melted and put a cap over the melt. I don't know if it kept all the toxic metal in,but it kept the oxygen out. No burning zinc.

Till we actually poured the melt into the mold. Then we pierced the glass with a poker. The brass was flaming and fumng as we poured.

It was about 40 years ago, I ain't dead,but the owner and son are. I don't recommend pouring brass without some good respirators.
Its dangerous work. Face shield,welder gloves,leather apron,etc.necessary.

When the spues were good and solid,you could dump the mold and see your parts. Sprues would be cut on an abrasive chop saw.

A big Baldor buffer was fitted with a fluted rubber contact wheel.A backstand idler wheel was attached to the wall, I'd guess the abrasive belts were maybe 3 inch by 10 feet. That was used to clean up the castings.

It was a job for a while when I needed one

Consider this post some raw ore. Its not refined. Pan it,keep the nuggets and dust,throw the rest back.

I hope that helps,Gary.

[4V50 Gary]

Thank you HiBc for that insightful dissertation on casting. I've only done a few things myself and most of my time was spent tool making.

[woodnbow]

I’m not even going to attempt casting anything but lead but this was a very interesting post. Thank you for taking the time!

[Old No7]

While I will likely not try to duplicate that process... (never say "never"...)

KUDOS's to HiBC for those really interesting and informative replies!

Those prove the value of the internet. Well done, thanks for sharing.

Old No7