Ductile iron pipes on pipe quality control is the key, nodular cast
iron pipe is different from the forging of the gray cast iron
pipe, it is cast pipe industry of high-tech goods, it from raw material selection and quality control of every work has strict request.
Raw material request, nodular cast iron containing phosphorus 0 or less.
1%, sulfur 0 or less.
015%, otherwise there dephosphorization and desulfurization method.
Again, hot metal melting of cast iron, improvement in electric furnace hot metal temperature of 1550 ℃ or so.
Cerium, increased magnesium, calcium, such as alkaline earth metal or rare earths nodularizer, make arrange from flake graphite in cast iron containing a ball;
, increase the nodularizer quickly examine the molten iron in molten iron should with the spectrometer after first the content of chemical elements and metallographic analysis.
If the primary chemical element content conforms to the request (
6 to 3.
8 ~ 2.
Manganese 0 or less.
Phosphorus 0 or less.
Sulfur 0 or less.
03 ~ 0.
Rare earth element 0.
01 ~ 0.
According to the GB9441 -
Requests for metallographic examination, 88 specification nodulizing grade is given priority to with secondary;
Spheroidization rate more than 80%;
Graphite intrusive for 6 ~ 7 magnitude (
400 times in the field of view, the ball diameter is 1.
5 ~ 4毫米)
, the graphite count up to 600 ~ 800 / was;
Cementite 1% or less;
Small-bore tube ferrite 90% or higher, large diameter pipe is approximately 85% (
Light gymnastics ball within 8 ~ 12%)
, after the rapid inspection qualified, the molten iron in 10 -
15 minutes in steel centrifugal forging into the pipe.
After heat treatment, the tube billet must into ductile nodular cast iron pipe (
Medium and small diameter tube elongation should be 10% or higher;
The large diameter pipe elongation should be 7% or higher)
According to ISO2531 -
91 international standard request, the mechanics performance of ductile iron pipes are as follows: tensile strength 420 mpa or greater;
Bending strength 590 mpa or higher;
The yield point strength 300 mpa or greater;
Brinell hardness of 230 or less.
On the basis of ISO8179 -
1995 specification, and the coating should be zinc + asphalt, spray should be in tubing looks clean, to the hot conditions, rules of spraying zinc, 130 g/m2 or bitumen coating layer thickness is about 0.
Now many users ignore the spraying zinc this request, clearly put forward abroad as long as the zinc layer combined with tube appearance as a whole, then spraying asphalt to supply useful maintenance of pipes.
On the basis of ISO4179 -
1985 specification, the pipe appearance shall be cement mortar lining, Japan also in unsaturated resin mortar exterior spray cleaning level.
, tubing pressure testing before delivery by root examination, socket to remove iron tumor, polishing processing, brush clean level of epoxy resin, proposed the tube diameter 400 mm or more during the transport and deposition, should add the socket end support.
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