Experiment 1. Melting of the Metal:
Put the ladle on an electric cooker or hold it over a gas flame. Adjust to maximum level. Break off a piece of metal and put in the ladle. Within a couple of minutes the metal will reach its melting point. Due to the low melting heat of model metal it will go from solid to liquid within seconds. Keep on heating the metal and you will see a discolouring on the surface. This is oxidization with one of the base metals and the more you heat the more oxidization will form. This is also called dross.
Take the ladle from the heat and watch the metal solidify. Note when the metal reaches its' melting point, it goes pasty before solidifying. The extra heat used at the melting point is now released from the metal keeping it from solidifying, making it pasty. After a few seconds it will be solid again.
Experiment 2. Gravity Casting:
Heat the metal as in experiment 1 and after a few minutes test the temperature of the alloy by dipping a thin wood stick (burnt match), into the metal. Count to seven and take it up. If it smokes lightly the temperature is right for casting, (around 325 C) if it smokes heavily it is too hot. It is important to have the right temperature because if it is too low the metal will solidify before reaching all details or if it is too high it will burn the mould.
While the metal is melting, you will prepare the mould. Dust the inside of the mould with talcum powder to protect the rubber. Put the two halves together and a piece of hard board on each side. Hold the mould together with a clamp in the centre of the mould or with a couple of rubber bands. The mould is now ready for casting.
Pour the metal fast in-to the ingate, all the way to the top. Tap the mould to shake the metal down. The large ingate with gravity pressure will force the metal down into the mould. As it is doing so, the clamp will open up slightly to leave the air out. Now leave the casting to cool for one minute. Open up the mould by pulling the two halves apart. Take out the figure by pulling at its base plate with pliers. The ingate will be cut off with pliers. After trimming with a small knife or file your casting is ready.
Experiment 3. To make a Mould:
One could, make a mould of plaster of parish. It will not be as good as a rubber mould and you will only get a few castings out.
- Select an object to be copied for example a 2c coin.
- Flatten out a piece of the plastesine to about 10mm thickness and about 7cm in length and 4 cm wide.
- Put the coin flat on the plastesine about 3cm from the top. Press it in slightly and work the plastesine with your fingers so it has a tight fit.
- Form an ingate from the top of the mould, which has a diameter of at least 10mm and taper it off to join the coin.
- Make strips of the plastesine about 5mm thick and 50nm wide. Put the strips around your other piece of plastesine to form walls. Make sure you seal all gaps.
- Take Vaseline and brush it very lightly on the pattern and plastesine as a release agent.
- Mix the plaster and pour it on the pattern about 20nm thick. Brush the pattern to make sure that no air bubbles are stuck to it. Leave to set for about 1/2 hour.
- Take off the plastesine but leave the coin sit in the plaster. Form the other half of the ingate and put the wall back again. Brush the mould half with Vaseline.
- Mix more plaster and pour it on about 20nm thick. Brush the pattern to make sure no air bubbles are stuck to it. Leave to set over night.
- Pull the two halves apart and take out the pattern. You now have got a mould. Before using it, it must be dry. If it is the slightest bit damp, it will explode, when you pour in the hot metal. So to be safe leave the mould in a dry place for one week.
- Cast the mould the same way as experiment 2.
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