'S
HOME FOUNDRY'S
HOME FOUNDRY
CREATED 01/11/01
LAST UPDATED 18/11/01
***WARNING***
Please note, the information, techniques and idea's expressed on this site are undertaken with safety as the foremost priority. Metal casting is extremely dangerous, care and common sense must be exercised at all times. I do not take responsibility for those who apply the methodology's as outlined here. Users of information on this site do so at their own risk.
My home foundry began about 14 years ago when I decided I wanted to build my own wobbler steam engine. The drawings described how to silver solder all the components together to build up the body. It looked a bit fiddly to me so I made up some patterns and hunted around for someone to cast them for me. Because of its size no one was interested, so out of frustration I decided to have a go at casting it myself. I found an ad in the Model Engineering Magazine for a home furnace and sent away for the plans. It was a coke burner with an old Hoover vacuum cleaner for the blower. I used a light dimmer switch to control the speed and away we went. Unfortunately coke was rather scarce and expensive to purchase so I converted it to a gas burner, knowing what I now know this burner was a very inefficient design, with the wealth of information now available on the internet things have now been rectified.
BASIC INFO AND ENVELOPE DIMENSIONS OF MY OLD FURNACE.
The barrel is made up of two 20 liter oil drums riveted together
Outside diameter - 280mm
Wall thickness- 50mm
Overall height - 430mm
Lid thickness - 60mm
Exhaust Diameter - 75mm
Center post diameter 70mm
Air inlet - 1" BSP nipple
Refractory - 1550 deg C castable
Holds up to a No 6 crucible.
Kao wool lining between castable and barrel.
Click the thumb nail to view full size.
CLICK here to see a sectional view of the coke furnace.
This shows the original setup when this furnace was a coke burner. The blower hose is attached into the base of the furnace. There is a circular chamber inside with a castable grate which allowed the air to pass up through the coke. The crucible sat on a circular post and had coke packed around it.
This furnace had a nice feature which allowed easy removal of a steel crucible. A vee is cut in the front at the top. The lid has a mating male vee. A small gap is left in the bottom of the vee, this allows a handle that is welded to the crucible to fit in. No need for tongs, just lift and pour.
The small hole on the side is used to fit the thermo-couple into the furnace. The larger hole half way up at the rear is the gas burner inlet. The blower is an old Hoover Upright. A light dimmer switch is used to adjust the force of the blast.
This is a plan view of the furnace. The base is almost burnt out, this is a high temp fiber board that covers the old grate when I converted it to a gas fired furnace. The center post that the crucible sits on is visible here.
That was the old furnace, CLICK here to see the new furnace.
BURNERS
The furnace contains and reflects the heat into the crucible to melt the metal. That's half the story, a method of delivering that heat efficiently and effectively is also required. Below are two examples of my burners, one good, the other not so good.
This was my first attempt at designing and building a gas burner. The pipe at 90 deg is the air inlet. The rear pipe is the gas inlet, it could be moved in and out to tune the flame. Didn't work all that well.
It's pretty rusted but the small nipple screwed into the front has three holes drilled around the hex. These holes were to large and the entire assembly didn't allow for proper mixing of the gas and air.
Things have progressed along way since my discovery of the internet. There is an absolute wealth of information on furnace and burner design. My current burner as shown below is based on information gathered from the web page of Ron Reil.
If you are just beginning in the home foundry game and want some real quality info, check his site out.
This burner is a normally aspirated, i.e. - it draws in it's own air via the induction developed from the high entry velocity of the gas into the burner venturi. This is unlike the burner above which relies on a blower to produce a forced draft. Being in a buildup area and not wanting to upset my neighbors with the deafening roar of a melting furnace, the blower style burner had to go. The new normally aspirated burner is relatively quite to the extent I can have a normal conversation without having to raise my voice over a deafening roar. My wife is starting to accept her backyard being turned into a hobby foundry from time to time, but I still gotta get the washing of the line before I start.
View of the burner assembly
View showing the gas inlet end
This view shows the gas injection tube removed. The end of the tube has a Tweco Tip with a 0.9mm (0.035") orifice. Check out Ron Reil's site for more info.
The Burner in action at about 15 psi of back pressure.
If you would like a copy of drawings for the above burner click the thumbnails.
These drawings are done in ISO format, all dimensions are in millimeters, to convert to imperial units i.e. inches divide by 25.4.
Note - You may need to apply best fit in your viewer to see the complete page.
The photo and sketch above shows the beginnings of my next project, a TILT FURNACE. (click and take a look at the progress) I'm planning on running this furnace on transmission oil. This will require a blower so I made up patterns and cast the housings and fan. The blades are around 1/32" thick with very little draft on the pattern. This was an extremely hard component to mould and cast, the phrase "learn by your mistakes" certainly applied here. The actual burner will be based on the best of a number of designs I've seen, one of which can be found in Steve Chastain's latest book, building an aluminum tilt furnace. I will post more pictures and description as progress is made.
SAND PREPARATION
This is probably the one thing that turns most people off when they think about casting at home, but it is probably the most important thing to get right if you are going to produce quality work. I used to dread the thought of mulling sand by hand using almost every part of my body until I ached. Stomping with feet kneading with hands and punching with knees to get the perfectly tempered sand. Four hours of hard yacka for a 30 minute pour and then start the whole process all over again.
Enough was enough, there had to be a better way. After visiting a foundry I discovered a machine that produced perfectly tempered sand in a fraction of the time I spent. In fact it did in 10 minutes what it would take me 4 hours to do.
Click here and have a look at the MULLER that I designed and manufactured to make life just a little bit easier.
PATTERNS
Patterns are used to form the sand mould. They are placed inside one half of a flask. they then have the tempered sand packed around it. When the pattern is removed from the sand, an exact impression is left. It is this impression that the molten metal is poured into, through runners and gates that gives us the finished product.
Patters can take on many different forms, they can be made from virtually anything from foam to timber, even an original casting can be used with some modification. CLICK and have a look at some of the patterns that I've used.
An addition to the above is a couple of points that should be highlighted when making your own patterns, "draft" and surface finish. Some patterns that I have been supplied with are totally unsatisfactory for sand molding and require some heavy modification before they can be used. This can be difficult to bring up as often the person supplying the pattern has put endless hours into its manufacture. The more draft the better but no less than 3 degrees for Green Sand and no less than 1 1/2 degrees for Co2 Sand. I use the analogy of the sand bucket making sand castles, impossible or at least very hard to do without draft. Surface finish, firstly make sure the patterns are sealed, unsealed timber soaks up the sands moisture and makes the sand stick to the pattern, not to itself. All surfaces should be smooth and consistent. That means, no undercuts especially around fillets, it will tear the sand when removed. Take care with your patterns, it may be a tedious and fiddly job, but it will reflect in the finished product.
FLASKS
These are also called the Cope and Drag. A flask is made up of two halves which can be accurately aligned together. CLICK and have a look at some of the types of flasks I use.
THE SHOW
What actually happens during a casting session. Have a CLICK and see what its all about.
CASTINGS
Well you've seen some of the equipment I use to produce my castings take a CLICK and look at some of my more recent work.
A DAY OUT AT THE RMIT
Checkout how the professionals do it. CLICK and enjoy
A DAY OUT IN THE VALLEY
A recent trip to the Latrobe Valley with my good friend Ian Arstall to collect 2 tonne of coke turned out to be more than I ever dreamed. CLICK and see what I mean.
MISCELLANEOUS
The Cupola and the Molding Shop construction. CLICK and see what's been happening lately.
INDUCTION FURNACE
Finally got some pictures of Rob Walkers Induction Furnace at the annual Bendigo Model Engineers Exhibition CLICK and have a look.
LARGE OIL FIRED FURNACE
Well the large oil fired furnace is complete and christened with cast iron CLICK and have a look at the final product
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TO BE CONTINUED
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