METALS INTERMEDIATE - ALLOY CASTING
HERE'S THE THEORY
If you have not completed metal essentials you will not be able to continue. Please complete metal essentials first.
Alloy Casting Intermediate will teach you the fundamentals of casting low melting alloys. The course starts below by taking you through some basic steps you need to learn to start preparing moulds for casting.
Once you've learnt these steps, you'll be ready to book the practical part of the course. We'll demonstrate how to safely melt and pour molten metal. Please be sure to concentrate when you go through the following points, as you'll need to pass a short quiz. Once you have completed the quiz you can book on to the practical demonstration in which you will need to demonstrate what you have learnt here. You can either bring your own machined mould or you can use one we have prepared.
The booking form immediately follows the quiz - IF you get enough of the answers right!
You should only need about 5 minutes to go through the points, and 5 minutes to complete the quiz
The basic anatomy of a mould:
The Alloy -
An alloy is a combination of more than one metal. This is done to improve certain characteristics or change the appearance. For example rose gold is made by adding copper to gold. What we use is a low melting point alloy. This is predominantly tin with bismuth added for hardness. It melts between 150-180C.
The Mould -
In the Lab we use a high density Polyurethane foam for casting (only the orange coloured Foam is suitable). This means it must be CNC machined.
Unless it is very simple most moulds will need to be made in two parts. In the Digital Machines Template there is instruction on how to do this.
The basic anatomy of a mould:
Pattern / Negative This is the negative space for your alloy to flow into.
Sprue hole These are necessary for trapped air to escape, without these you will have air pockets in your cast.
Cups and Nipples These are registration points that allow you to line the two halves of the mould perfectly.
Using molten metal is extremely dangerous
Hazards.
- Molten metal will give you serious burns.
- If a flux needs to be added toxic fumes can be emitted
Controls
- The correct PPE must be worn. This includes gloves, face shield and full sleeve non synthetic clothing.
- Extraction must be switched on.
- Design your object
- Design the mould. This is the negative form that will contain the positive casting. This will need to include the sprue holes, pour holes and registration cups and nipples.
- Machine your mould. You should do this first in a lower density and cheaper foam to ensure that it machines as you designed it.
- If it is a two part mould secure it together with a g-clamp.
- Put on your PPE. This includes gloves and a face shield in addition to safety glasses.
- Make sure you have everything you need. Once the pot is switched on you cannot leave it.
- Switch on the melting pot and turn the heating setting to 5.
- Always keep the pot at least half full. Add more alloy if needed.
- Move the alloy around with the ladle to help it melt faster and to keep a more consistent heat. Do not get tempted to turn the heat up to melt it faster. This will only destroy the alloy.
- There might be powdery residue on top, this is called dross, scim it from the surface and deposit on the metal plate.
- Once melted, reduce the heat to 2, overheating the alloy will reduce its usable life.
- Pour carefully, observing your sprue holes to make sure there isn’t excessive leakage.
- Switch off when finished.
- Clean up any wasted alloy and return to the reserve pot.
- Wait 45 minutes to unmold.
- Weigh your finished cast and pay for what you use.
If you have not completed metal essentials you will not be able to continue. Please complete metal essentials first.
