Buderus Manual on Trenchless Installation of Ductile Cast ... - Duktus

Properties of ductile cast iron pipes
2.2 How the pipes are produced
Casting techniques of the kind which had been developed in the Middle Ages, above all
for casting works of art and bells and also for casting guns, were a prerequisite for the
development of a technology for producing high-quality pipes. Initially pipes were cast
in horizontal moulds where the moulds were also split horizontally. This meant that
there was a limit to how long the pipes could be, given that at the casting temperature
of some 1300°C and under their own weight, the cores used to form the hollow centres
of the pipes would bend, which also limited the uniformity of the wall thickness of
the pipes. Pipes dating from this early period of manufacture can be recognised by the
two lines of flash on opposite sides of their outer surface, which formed in sand moulds
on the plane marking the division between the top and bottom halves of the moulds
(Fig. 2.9).
With the increasing demand for cast iron
pipes for supplying water and gas in the
rapidly expanding towns and cities in the
second half of the 19th century, the carousel
casting process was introduced, in
which the sand moulds were arranged
upright in casting carousels in such a way
Fig. 2.9
that a semi-continuous procedure became
possible. In this process, the moulds, in
the form of undivided metal mould boxes
matched to the shape of the pipe, were
initially placed in position individually and
later on in rotary racks, to allow work to
go on in a continuous flow. The cores to
produce the hollow centres in the pipes
were rammed onto metal core spindles
with the help of metal core bushes. There
was an increase in the overall length of the
Fig. 2.10
pipes and the flash at the mould division
disappeared. This process was used by <strong>Buderus</strong> from the time when pipe production
began in 1901 until 192 . Hundreds of thousands of kilometres of pipes dating from this
period of production are still giving faithful service below the ground.
A particularly important milestone in the course of further development was the invention
of the centrifugal casting process (Fig. 2.11). In 192 , this process was successfully
introduced throughout Europe, including at <strong>Buderus</strong>. One of its principal features is
12