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.
[Illustration: Figure 6]
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.