Part 3

An easy way to test the temperature of the melted lead is to insert the end of a pine stick for a moment. When the wood blackens or burns, the lead is hot enough to pour.

Whenever the lead is in melted form and exposed to the air, as in the iron pot, there will be a slight oxidation take place which appears as a yellowish-red scum. Do not confuse this with the dross and dirt which is to be skimmed off, but if the scum gets thick, then skim it off before pouring any of the metal.

PREPARING THE MOULD

One of the greatest difficulties in making lead castings has been to get the metal to completely fill the mould. There are several reasons for this, but they can easily be overcome.

If the mould, which is generally made of iron, is very cold, it will chill the melted lead and cause it to become solid before it has reached all parts.

The surface of a cast iron mould is very porous, and the melted lead, partially entering the pores of the iron, is held back long enough to chill and set.

To remedy these faults, it is sometimes advisable to heat the mould in order to get perfectly shaped castings.

To close the pores of the iron moulds they are sometimes “smoked” with a flame like that of “Prest-O-Lite” gas or else dusted with graphite.

The AMBU mould compound has been developed to eliminate the necessity for heating or smoking the mould—it remedies all the pouring troubles and in addition, has chemical ingredients that aid in preventing the mould from rusting. AMBU mould compound is placed in a little sack, contained in each can, and the surface of the mould dusted with the sack, as shown in Figure 6.

The compound completely fills the pores of the iron, produces perfect castings with a cold mould and prevents the finished part from sticking. It does not wear off as quickly as the “smoke,” and dusting from time to time, while castings are being made will produce a high polish on the mould surface which will result in even better castings.

The mould in Figure 6 is the new AMBU Washburn combination link mould, which casts 15 parts, being reversible much like the ordinary “waffle iron.” The side being “dusted” casts four top connectors of different lengths.

POURING THE LEAD

Placing the mould as in Figure 7, the lead is poured in the four openings until the metal projects slightly above the top.

To pour properly first skim the dross as previously explained, then with the ladle, push the film of oxide away and dip into the clean pure lead. Pour steadily until the mould is filled and the metal projects slightly above the top. As it cools there will be quite a little contraction which takes up most of the excess lead.

=Never=, under any conditions, stop pouring with a mould partially filled. Always be sure there is enough melted lead in the ladle to completely fill the mould, before starting to pour.

The mould can now be easily opened by pulling on the handles especially if it has been properly dusted with the Ambu Mould Compound.

After the mould is opened, Figure 8, the castings are easily removed, without damage to either the mould or the casting proper. The workman does not, at any time, handle the hot parts of the mould or the hot castings.

The mould weighs 25 pounds, and is large enough to absorb sufficient heat to allow continuous pouring without becoming overheated. It is solid enough to be used without the need of a vise.

IMPORTANT INSTRUCTIONS

In all lead moulding, there are several important points to remember:

1. Never put anything in the lead pot that is not perfectly dry. A few drops of water in a pot of melted lead will cause an explosion and the hot lead will be thrown all over the shop burning and perhaps blinding the workman.

2. Have all moulds clean and dry.

3. Keep the melted lead in the lead pot clean at all times.

4. Always completely fill each mould at one pouring.

5. Dust moulds well with Ambu mould compound before pouring.

6. When castings “shrink” and crack, add pure lead to that in the pot until the trouble is remedied.

7. Be sure melted lead is of proper temperature, by pine stick test, before starting to pour.

8. Remove castings as soon as they set, to prevent the mould from becoming too hot.