Choice material
The quality of ductile iron pipes depends
on the composition of the raw material - pig
iron. We carefully choose low phosphorous
and low sulphur pig iron and inspect each
batch of raw material so as to ensure its
carbon, phosphorous and sulphur contents meet
our requirements.
Molten iron spheroidization
We treat molten iron with spheroidizing agent
to adjust its composition so that it meets
process requirements.
Molten iron quality control
Quality and temperature are strictly controlled
in each link in preparation of molten iron.
Composition analysis is done for every heat
of molten iron to ensure it meets the requirements
for centrifugal casting.
Centrifugal casting
Water-cooled metal mould process is adopted
in casting, which is done on a centrifuger.
Molten iron in the cupola is heated by an
electric furnace. After being spheroidized,
it is continuously cast into a pipe mould
turning at a high speed. Cooled down by water,
the molten iron sets into a ductile iron pipe.
Quality control
The ductile iron pipes are inspected for superficial
cast imperfections as soon as they are cast
so as to ensure the quality of the centrifugally
cast ductile iron pipes.
Annealing treatment
Then the qualified cast ductile iron pipe
is put into an annealing furnace. It is fully
annealed there to attain the required metallographic
structure of ductile iron.
Property inspection
Appearance inspection,
hardness test,
metallographic
examination
and tension
test are immediately
performed on
annealed ductile
iron pipes.
Any pipe that
fails in tests
is rejected.
Weighing
Every ductile iron pipe is weighed to ensure
the weight of the pipe conforms to quality
standard requirements.
Dressing
Inspection of imperfections on both
internal and external surfaces is done for
each ductile iron pipe out of the annealing
furnace. The socket and spigot of each pipe
is dressed and cleaned.
Hydraulic test
Hydraulic test is performed on each ductile
iron pipe to ensure there is no leak in
the pipe.
Cement mortar lining
Cement mortar is lined onto the internal
surface of each ductile iron pipe to prevent
water from being polluted.
Conditioning
A ductile iron pipe lined with cement
mortar will be conditioned for a period
of time.
Zinc spraying
A casting ductile iron pipe will be sprayed
with zinc as per customer request.
Bitumen coating
Every ductile iron pipe is coated with bituminous
paint to prevent corrosion and give the
pipe a good look.
The following factors ensures precision
products casting
◎High quality pig iron, proper casting
temperature, and good flowability of molten
iron.
◎A quality pipe is built from a quality
finishing line, such as zinc spraying and
internal and external coating to ensure
high corrosion resistance.
◎Reliable quality control and testing
means are required to ensure accurate joint
dimensions and even wall thickness.
◎Wall thickness and pressure are
calibrated.
Features of ductile iron pipe processes
◎Advanced duplex cupola and electric
furnace process is adopted to effectively
ensure the composition of molten iron and
the temperature of casting.
◎Water-cooled metal mould centrifugal
casting technology is adopted to minimize
deflection and deformation of long pipes
and ensure homogeneity and compactness of
castings.
◎The cast pipes are treated with
annealing after they are formed to attain
stable and homogeneous metallographic structure
and maintain higher elongation.
◎Pipe surface is sprayed with zinc
and coated with bituminous paint to make
it more corrosion-resistant.
◎Every pipe undergoes severe hydraulic
test.
◎Every pipe for gas delivery undergoes
gas-tight test. |
