WO2019201179A1 - 球墨铸铁管及城镇高压燃气管线用球墨铸铁管的制备工艺及城镇高压燃气管线用球墨铸铁管 - Google Patents

球墨铸铁管及城镇高压燃气管线用球墨铸铁管的制备工艺及城镇高压燃气管线用球墨铸铁管 Download PDF

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Publication number
WO2019201179A1
WO2019201179A1 PCT/CN2019/082500 CN2019082500W WO2019201179A1 WO 2019201179 A1 WO2019201179 A1 WO 2019201179A1 CN 2019082500 W CN2019082500 W CN 2019082500W WO 2019201179 A1 WO2019201179 A1 WO 2019201179A1
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WIPO (PCT)
Prior art keywords
iron pipe
ductile iron
iron
ductile
gas pipeline
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PCT/CN2019/082500
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English (en)
French (fr)
Inventor
王宇新
孙二考
李建民
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广东北晟益通实业有限公司
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Publication of WO2019201179A1 publication Critical patent/WO2019201179A1/zh

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L9/00—Rigid pipes
    • F16L9/02—Rigid pipes of metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D13/00—Centrifugal casting; Casting by using centrifugal force
    • B22D13/02—Centrifugal casting; Casting by using centrifugal force of elongated solid or hollow bodies, e.g. pipes, in moulds rotating around their longitudinal axis
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/10—Making spheroidal graphite cast-iron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/10—Cast-iron alloys containing aluminium or silicon

Definitions

  • the invention belongs to the technical field of preparation of ductile iron pipes, and relates to a preparation process of ductile iron pipes, in particular to a preparation process of ductile iron pipes which can be used for laying high-pressure gas pipelines in cities and towns.
  • the natural gas pipelines laid in the city, the high-pressure section ( ⁇ 2.5 ⁇ 4.0MPa) and the secondary high-pressure section ( ⁇ 0.8 ⁇ 1.6MPa) all use seamless steel pipes and welded steel pipes, but at present these gas pipeline steel pipes have the following problems:
  • ductile iron pipe Since the steel pipes are not resistant to corrosion and do not have the ability to withstand strong earthquake damage, some developed industrialized countries have started to use urban ductile iron pipes to build urban gas pipelines since the 1970s. Because ductile iron pipe has the same strength and toughness as steel pipe, it has strong corrosion resistance, especially in terms of resistance to electric corrosion. The ductile iron pipe is more than ten times that of steel pipe. Therefore, the safe service life of ductile iron pipe can be Up to 100 years. The ductile iron pipe is connected by a rubber ring sealing socket type flexible interface, which can dissipate the destructive force of the strong earthquake to the underground pipeline, keep the pipeline intact and maintain normal gas transmission capacity, thus avoiding earthquake secondary disasters in the city and ensuring the city.
  • ductile iron pipe produced in China has many defects in its own quality, mainly due to the common existence of sand holes, pores, slag eyes, cold partitions, uneven wall thickness, and bearing. Casting defects such as internal shrinkage and shrinkage of the mouth end severely reduce the airtightness of the pipe, and it is also necessary to set up a welding repair process to repair the pipe with leakage defects. Therefore, the ductile iron pipe produced in China is only suitable for the laying of water supply and drainage pipes.
  • One of the objects of the present invention is to provide a preparation process of a ductile iron pipe, and further provide a preparation process of preparing a ductile iron pipe for a high-pressure gas pipeline in a town according to the above preparation process, to provide a ductile iron for a high-pressure gas pipeline in a town. At least one of the above technical problems is solved.
  • a process for preparing a ductile iron pipe comprising the steps of:
  • Preparation of molten iron The furnace charge is smelted into the original molten iron and superheated to not less than 1500 ° C, and the chemical composition of the original molten iron is adjusted according to the set value of the chemical composition of the molten iron.
  • S2 spheroidization treatment: spheroidizing the original iron liquid with adjusted chemical composition by spheroidizing agent, and injecting the spheroidized iron liquid into the special casting electric furnace of spheroidal graphite cast iron, using iron casting furnace for special casting of ductile iron The pouring temperature of the liquid is maintained not less than the critical temperature of the molten iron;
  • the molten molten iron in the preparation process of the present invention, is superheated to 1500 ° C or higher, and the molten iron is superheated to a temperature of not less than 1500 ° C in the preparation stage of the molten iron, which may promote The carbon exerts a deoxidizing and purifying action on the molten iron to achieve a pre-spheroidizing treatment effect on the original molten iron, thereby facilitating spheroidization of the graphite; further, in the preparation process of the present invention, according to the set value of the chemical composition of the molten iron The chemical composition of the original iron liquid was adjusted.
  • the raw iron liquid having a temperature of 1500 ° C or higher and having a chemical composition adjusted is spheroidized, and the spheroidized molten iron is injected into a cast iron special cast electric furnace (Inventive Example)
  • the cast iron special casting electric furnace mentioned in the above is the casting electric furnace equipment disclosed in the patent CN101658901B), and the spheroidized molten iron is injected into the special casting electric furnace of the ductile cast iron, on the one hand, the molten iron can be further desulfurized and deoxidized, on the other hand
  • the amount of residual Mg in the molten iron can be stabilized, thereby avoiding the spheroidization of the molten iron, ensuring the spheroidization level of the produced ductile iron pipe, and stabilizing the mechanical properties such as toughness and strength; and simultaneously pouring the molten iron It is always kept at a temperature range not less than the critical temperature of molten iron (ie, 1420 ⁇ 1480
  • the ductile cast iron pipe blank is prepared by the hot die centrifugal casting process, and the centrifugal casting process is started when the centrifugal force of the pipe mold reaches the centrifugal force setting value, and the preparation process enables The casting process is started under suitable centrifugal force according to requirements, thereby controlling the shrinkage of the prepared ductile iron pipe blank.
  • the centrifugal casting process adopts a high-speed large centrifugal force casting process, which ensures that the high-temperature molten iron for casting is gradually solidified under the action of large centrifugal force (this In the embodiment of the invention, it is preferred to start pouring when the centrifugal force of the tube mold reaches 80-110 G, and the centrifugal force of the tube rotation of the Bid Lavo method is increased by about 1 time, so that the high-temperature molten iron is always in a large centrifugal force in the tube mold.
  • the pressure self-feeding of the ductile iron liquid in the porridge solidification and graphitization expansion coincidence stage thereby ensuring the dense structure of the ductile iron tube
  • the thickness of the thick-walled part is uniform and there are no casting defects such as shrinkage holes and shrinkage.
  • the wall thickness is also very uniform and compact, and there is no inclusion. Therefore, the prepared ductile iron pipe has good airtightness.
  • the appropriate carbon equivalent of the molten iron is combined with the instantaneous incubation, so that the matrix structure of the as-cast as-cast ductile iron pipe blank has no free cementite.
  • the invention adopts the hot mold centrifugal casting process of the coating, and the preheating coating needs to preheat the tube mold to 200-220 ° C before spraying, which can ensure that the insulating coating can be quickly dried during spraying, and can be avoided when the molten iron is injected into the tube mold.
  • the tube mold is ablated and damaged by the molten iron due to the detonation of the heat insulating coating, thereby causing a production interruption accident.
  • the iron liquid having the S content of not more than 0.12% can be directly injected into the induction heat preservation furnace without the external desulfurization treatment, and the chemical composition of the original iron liquid is not required to be adjusted.
  • the S content because: 1) The desulfurization effect of the spheroidization treatment is very good, and the high temperature and high sulfur iron liquid with a sulfur content of not more than 0.2% and a temperature of 1500 °C can be processed into a qualified ductile iron liquid.
  • the sulfur content of the spheroidized iron liquid can be removed to a level less than 0.01%; 2) the cast iron special cast electric furnace allows the spheroidization treatment to be directly carried out without slag treatment, and directly spheroidizes the MgS slag in the package
  • the MgO slag is directly poured into the furnace, and the S 2- and O 2 - anions in the slag are removed by direct current electrolysis.
  • the Mg 2+ cation in the slag is reduced to Mg when it contacts the molten iron as the cathode.
  • the molten iron forms a dynamic balance with the escape loss of Mg from the molten iron, stabilizes the residual amount of Mg in the molten iron, avoids the spheroidization decay, and makes the MgS slag and the MgO slag harm, thereby realizing the circulation of the magnesium metal. use. This also simplifies the production process and improves the consistency of the mechanical properties and quality of the prepared ductile iron pipe.
  • one of pig iron, scrap steel, iron filings, carbon-free bricks and recycled materials (mainly the pouring riser of pipe fittings or other castings and a small amount of non-conforming products of ductile iron pipes and fittings) may be selected.
  • the possible loss of chemical composition during the smelting process and the set value of the chemical composition of the molten iron so that the composition of the chemical composition of the molten iron after smelting is close to its setting. Value, simplifying the process of chemical composition adjustment of molten iron.
  • the process of melting the furnace material into the original iron liquid may adopt a cupola-induction electric furnace double smelting process, or a blast furnace pig iron liquid into the frequency conversion coreless induction furnace to adjust the chemical composition of the "short process" smelting process.
  • the molten iron liquid is superheated to not less than 1500 ° C, and the furnace charge can be smelted by using a cupola furnace.
  • the temperature of the original molten iron directly reaches 1500 ° C and above (that is, the tapping temperature of the original molten iron is not If it is less than 1500 ° C), the molten iron may be superheated in an induction furnace by using other melting methods, so that the temperature of the original molten iron reaches 1500 ° C and above (that is, the induction furnace holding temperature is set at 1500 ° C and above).
  • the flow treatment of the molten iron can promote the graphitization, prevent the spheroidization of the molten iron during the pouring process, and avoid the generation of free cementite.
  • the inoculant used in the inoculation treatment is a conventional inoculant, which may be one of a ferrosilicon inoculant, a silicon germanium inoculant or a combination thereof, preferably a 75FeSi inoculant, and the amount is 0.2 to 0.4 of the weight of the molten iron. %.
  • the cooling treatment performed on the tube mold during the pouring process is preferably a shower water cooling treatment.
  • the solidified shaped ductile iron pipe blank can continue to cool the pipe mold during the cooling process; the large-diameter thick-walled ductile iron pipe with relatively slow cooling rate after solidification can accelerate the cooling speed and can also be used in the pipe mold.
  • the solidified ductile iron pipe blank is subjected to air blowing or water spray.
  • the spheroidizing treatment of the raw iron liquid having the adjusted chemical composition is preferably a feeding method or a subcontracting method which does not affect the iron carbon equivalent and has a remarkable desulfurization effect.
  • the centrifugal force setting is no less than 80G and no greater than 110G. Since pouring at a small centrifugal force causes shrinkage and shrinkage defects, and the centrifugal force is too large, the tube mold and the equipment are deteriorated due to excessively high rotational speed, and the safety of the device is deteriorated. Therefore, the centrifugal force is set.
  • the fixed rotation speed is set to 80G ⁇ 110G (the centrifugal force of different diameters of ductile iron pipe is different, among which, the value of small diameter pipe is close to the upper limit value, and the value of large diameter pipe is close to the lower limit value), which can avoid loosening and shrinking. At the same time of defects, the stability of the operation of the equipment and the tube mold is ensured, thereby ensuring the quality of the manufactured ductile iron pipe and ensuring production safety.
  • the set temperature of the ductile iron tube blank solidified in the tube mold can be cooled to a temperature of 760 to 830 °C.
  • the extubation temperature is higher than 850 °C, the strength of the ductile iron pipe is insufficient. At this temperature, the pipe drawing tends to deform the ductile iron pipe during the extubation process, and when the extubation temperature is lower than the temperature of the eutectoid point (about 730 ° C)
  • the ductile iron pipe will undergo eutectoid transformation, which leads to the lattice transition causing the volume transition, which makes the ductile iron pipe expansion cause difficulty in extubation. Therefore, controlling the extubation temperature at 760-830 °C can prevent the difficulty of extubation and avoid deformation of the ductile iron tube.
  • step S2 the pouring temperature of the molten iron is kept not less than the critical temperature of the molten iron by using a cast iron special casting electric furnace, and the holding temperature in the special casting electric furnace of the ductile iron can be set to 1430 to 1480. °C achieved.
  • the holding temperature in the cast iron special casting electric furnace is set to 1430 to 1480 ° C, so that when the molten iron in the cast iron special casting electric furnace is injected into the pipe mold, the molten iron is kept non-oxidizing clean iron liquid, thereby It can ensure that the molten iron has sufficient fluidity, and it can ensure that the molten iron in the tube mold can still maintain a liquid time under the action of high centrifugal force after the pouring, thereby avoiding the pouring of the ductile iron pipe, cold separation, shrinkage,
  • the casting defects and waste products such as shrinkage cavities, blisters, slag eyes, pores, and uneven wall thickness are dense, uniform, defect-free, and airtight.
  • the spheroidizing agent may be a magnesium ingot, and the set value of the chemical composition of the molten iron may be: C is 3.4 to 3.7%, and Si is 2.0 to 2.6%.
  • Adjusting the chemical composition of the original molten iron according to the set value of the chemical composition of the molten iron includes:
  • the mass fraction of carbon and silicon in the original molten iron based on the above set values, so that the mass fraction of carbon in the original molten iron is not higher than 3.7%, and the carbon equivalent reaches the eutectic composition (ie, the carbon equivalent is 4.26%). Or the carbon equivalent can reach 4.1% to 4.3%. Therefore, the spheroidal graphite cast iron tube forming and the obtaining of the free cementite spheroidal graphite cast iron blank in the matrix structure can be favored in the process of the hot-melt centrifugal casting process of the coating of the invention, and the quality of the spheroidal graphite tube blank can be ensured Simplify the subsequent annealing process.
  • the use of magnesium ingot as a spheroidizing agent can greatly reduce the cost of the spheroidizing agent on the one hand, and avoid the influence and interference of the elements such as Si in the rare earth ferrosilicon spheroidizing agent on the iron component on the other hand. Save a lot of valuable rare earth elements.
  • the raw iron liquid having the adjusted chemical composition may be spheroidized by a subcontracting method, wherein the amount of the magnesium ingot spheroidizing agent is 0.10 to 0.20% of the weight of the original molten iron. .
  • the spheroidization treatment is carried out by the subcontracting method, and the spheroidization treatment effect is good, and the speed of vaporization of the spheroidizing agent in the reaction chamber of the subcontracting is controlled without explosion.
  • the amount of the spheroidizing agent is 0.10-0.15% of the weight of the original molten iron, which can ensure that the Mg content in the molten iron is not less than 0.04% after the spheroidizing treatment is completed, and the ideal spheroidizing effect is achieved, when the S content in the original molten iron is greater than 0.12.
  • the amount of the spheroidizing agent may be increased to 0.18 to 0.20% by weight of the original molten iron as needed.
  • a process for preparing a ductile iron pipe for a high-pressure gas pipeline in a town comprising the following steps:
  • the test pressure is set, and the spheroidal graphite cast iron is finished according to the set test pressure.
  • the tube blank is subjected to a gas tightness test in which the test pressure is not less than 1.20 times the designed conveying pressure of the gas line to be laid.
  • the finishing processing includes the inner grinding of the socket, the outer grinding of the socket, the inner wall grinding, the pipe cutting, the chamfering, and the flange drilling of the sealed interface ductile iron pipe of the S type and the N type.
  • the internal grinding of the socket and the external grinding of the socket are to improve the surface finish of these parts, so that the sealing pressure of the ductile iron pipe can be further improved when the sealing rubber ring is matched during the connection of the ductile iron pipe.
  • the airtightness test on the production line of the ductile iron pipe for the high-pressure gas pipeline of the town generally adopts a test method in which the test pressure is not less than 5.0 MPa and the pressure holding time is not less than 20 seconds.
  • the qualified ductile iron pipe can continue to complete the subsequent internal and external coating, final inspection, spray mark and digital marking, and then be bundled into the warehouse to become the finished ductile iron pipe for urban high-pressure gas pipeline.
  • the preparation process of the ductile iron pipe for the high-pressure gas pipeline of the invention can effectively avoid the casting defects such as slag eye, subcutaneous pores, blisters, under-filling, cold partitioning, shrinkage, shrinkage, etc. in the preparation process of the ductile iron pipe.
  • Uniform wall thickness wall thickness error can be controlled at ⁇ 0.3mm
  • high density of pipe body structure high density of pipe body structure
  • good air tightness Therefore, this ductile iron pipe has a high-pressure section A ( ⁇ 4.0MPa) for laying urban gas pipelines. Quality requirements.
  • the following steps may also be included before the annealing process:
  • Ultrasonic non-destructive testing of the ductile iron pipe blanks after cleaning and purging the outer wall is carried out to determine whether the spheroidizing grade of the ductile iron pipe blank is qualified and whether the ductile iron pipe blank body has casting defects and other damage defects.
  • the actual temperature of the molten iron injected into the tube mold during casting is sufficiently high (for example, not lower than 1400 ° C)
  • the insulating coating sprayed on the inner wall of the tube mold is almost entirely hung on the ductile iron.
  • the outer wall of the tube blank is taken out. Therefore, the outer wall of the spheroidal graphite tube blank needs to be cleaned and then purged to clean the residual heat-insulating paint on the outer wall of the spheroidal iron tube blank.
  • the purge preferably uses high pressure steam to purge the outer wall of the ductile iron pipe.
  • ultrasonic nondestructive testing of the ductile iron tube blank is required to determine whether the spheroidization level of the ductile iron tube blank is qualified, and whether the ductile iron tube blank body has slag eyes, subcutaneous pores, blisters, and cold.
  • Other damage defects such as casting defects, heavy skin, shrinkage holes, shrinkage and other casting defects and damage cracks.
  • Ductile iron pipe blanks with spheroidal grades and no casting defects and damage cracks are recorded as qualified, and unqualified ductile iron pipe blanks are recorded as unqualified and directly remelted as furnace charge.
  • Ultrasonic testing of ductile iron pipe blanks can quickly complete the non-destructive testing of ductile iron pipes, and comprehensively test whether ductile iron pipes have casting defects and internal damage defects without impairing or affecting the performance of ductile iron;
  • the ultrasonic wave is used to determine whether the spheroidizing grade of the ductile iron pipe is qualified.
  • the detection efficiency is much higher than the traditional metallographic detection method, and even the different components and content of the ductile iron pipe base can be quantitatively determined.
  • ultrasonic waves are used.
  • the detection of the ductile iron tube blank can realize the continuous on-line detection of a large-volume ductile iron pipe of a single specification, which is beneficial to the automation of the ductile iron pipe production line.
  • the annealing treatment may have an annealing temperature of 780 to 850 ° C and an annealing time of 20 to 40 min.
  • the invention has the following obvious advantages: 1) The spheroidal graphite cast iron tube blank prepared by the preparation process of the invention does not contain free cementite, but the tube body is Normalizing occurs in the air. The eutectoid transformation at this time will cause the pearlite to exceed the standard. Therefore, it is only necessary to eliminate the low temperature annealing of the pearlite cast iron tube to obtain the high elongation and high toughness of the ferrite content.
  • Ductile iron tube which can significantly reduce the annealing temperature (from the traditional 980 ⁇ 1050 ° C to 780 ⁇ 850 ° C); 2) the annealing process of the present invention eliminates the high temperature annealing phase of the removal of the Leysite and the middle of the annealing kiln
  • the fast water-cooled (or air-cooled) structure simplifies the equipment structure of the tunnel annealing kiln, shortens the annealing time, reduces the energy consumption of the annealing treatment, and prolongs the life of the refractory material in the annealing kiln; 3) avoids the ductile iron pipe due to The risk of burnt and deformation (ie, the ductile iron pipe becomes elliptical) and the loss of waste; 4) Because the wall thickness of the ductile iron pipe is uniform, the annealing process is smooth and smooth, and can be completely avoided. Serious consequences brought fracture (fracture ductile iron pipe clogging in the anne
  • the following steps may be further included:
  • the outer surface of the annealed ductile iron tube blank is sprayed with zinc.
  • zinc spraying may be achieved by means of hot-spraying zinc, cold-zinc coating, etc., and the thickness of the zinc layer is preferably not less than 40 ⁇ m.
  • Spraying zinc on the outer surface of the annealed ductile iron pipe blank is beneficial to improve the ability of the ductile iron pipe surface to withstand electrical corrosion. At the same time, it can avoid the subsequent ductile iron pipe blank during the airtightness test due to the spheroidal ink.
  • the cast iron tube blank body is in contact with water and causes the surface of the tube to rust.
  • the following steps may be further included:
  • the inner and outer walls of the ductile iron pipe blank acceptable for the airtightness test are coated with a protective and functional coating, wherein the coating material of the inner wall protective coating may be one or more of epoxy resin, polyurethane or urea resin.
  • the coating material of the outer wall protective coating may be one or more of epoxy asphalt paint, polyurethane, and polyurea.
  • a ductile iron pipe for a high-pressure gas pipeline for a town prepared by the above-described process for preparing a ductile iron pipe for a high-pressure gas pipeline in a town is provided.
  • the ductile iron pipe for urban high-pressure gas pipeline provided by the present invention can be applied to a town gas pipeline with a conveying pressure of 0.4 to 4.0 MPa.
  • the ductile iron pipe for urban high-pressure gas pipeline provided by the invention can be safely used for high-grade section A (2.5-4.0 MPa), high-pressure section B (1.6-2.5 MPa), sub-high-pressure section A (0.8-1.6 MPa) And the laying of gas pipelines of Class B (0.4 ⁇ 0.8MPa) of the secondary high pressure section; if there are special needs, it can also be used for the laying of gas pipelines of not more than 6.0MPa.
  • the high-pressure gas pipeline of the town may be connected by a ductile iron pipe, and the flexible mechanical seal interface may be used.
  • the interface may be an S-type mechanical seal interface, a N 1 mechanical seal interface, and a K II mechanical type.
  • Sealing interface, K-type mechanical sealing interface, S II mechanical sealing interface, and T-type sliding-in sealing interface (T-type interface is limited to sub-high pressure gas pipe below 1.6MPa); material of sealing rubber ring used for connection
  • Hydrogenated nitrile rubber, acrylate rubber, fluororubber, fluorosilicone rubber or polytetrafluoroethylene can be selected according to the environmental conditions and the design life of the gas pipeline.
  • S1 preparation of molten iron:
  • the chemical composition of molten iron is set to: C: 3.4 ⁇ 3.7%, Si: 2.4 ⁇ 2.5%.
  • the raw iron, scrap steel and ductile iron pipe are used as the charge, and the charge after batching is 40t/h.
  • the slag iron is separated by a siphon type slag iron separator, and the original iron liquid is injected into the 60t large-capacity core induction heat preservation electric furnace by the siphon type tap hole of the cupola.
  • the set temperature of the induction holding furnace is 1500 ° C and kept at a constant temperature.
  • the cup furnace melting process is set according to the set value of the chemical composition of the molten iron, so that the iron temperature of the molten iron is greater than 1500 ° C, and the chemical composition of the original molten iron is ensured.
  • the set value range if the set value range is exceeded, the original molten iron is injected into the variable frequency coreless induction furnace, and the mass fraction of carbon and silicon in the original molten iron is adjusted according to the set value of the chemical composition of the molten iron. So that the mass fraction of carbon in the original molten iron is not higher than 3.7%, and the carbon equivalent is 4.2% to 4.3%;
  • S2 spheroidizing treatment: Put the magnesium ingot with 0.16% weight of the original molten iron into the reaction chamber of 1.5t subcontracting, inject the original molten iron of the induction holding electric furnace into the subcontract for spheroidization treatment, and spheroidize the molten iron.
  • the residual amount of Mg is ⁇ 0.04%
  • the chemical composition of the molten iron includes: C: 3.4 to 3.7%, Si: 2.2 to 2.4%, Mn: ⁇ 0.3%, P: ⁇ 0.07%, S: ⁇ 0.01%, spheroidization treatment
  • the spheroidized molten iron in the sub-container is directly injected into the 12t ductile iron special pouring electric furnace by using a 5t rotary forklift (to ensure the production is not interrupted, one set of special casting electric furnace needs 2 sets) 1.5t subcontracted 5t rotary forklift supply of molten iron), in order to keep the pouring temperature of molten iron not less than the critical temperature of molten iron, the holding temperature set in the special casting electric furnace of ductile iron is 1430 °C;
  • S3, hot-die centrifugal casting spraying the heat-insulating paint on the inner wall of the heat pipe mold which has been preheated to 200 ° C and cleaned the inner wall. After the heat-insulating paint is completely dried, the pipe mold is moved to the upper core station, and the robot is used to bear the mouth. The core is installed at the tube mold socket; after the core is completed, the tube mold is moved to the pre-rotation station of the centrifugal unit, and when the tube mold is pre-rotated to 85% of the set speed, the tube mold is moved to the centrifugal casting station (the tube mold is centrifuged).
  • the pre-rotation station of the unit When the pre-rotation station of the unit is pre-rotated to 80-90% of the set speed and then moved to the centrifugal casting station, the time for the centrifugal casting station to increase the speed of the tube mold can be saved, and the production efficiency can be improved); after moving to the centrifugal casting station Quickly increase the speed of the tube mold to the maximum value (centrifugal force reaches 90G), and then start pouring.
  • the iron liquid with a temperature of 1430 °C in the cast iron special casting electric furnace is injected into the tube mold by the quantitative solution, and the weight of the molten iron is 0.3%.
  • the 75FeSi inoculant is incubated with the flow, and at the same time, the tube mold is sprayed and cooled; after the iron liquid is solidified, the tube mold is moved to the cooling station (the mold spray water can be continuously cooled, and the tube mold can be cooled at the same time) Spray water mist to accelerate red hot ductile iron The cooling of the blank), and then the tube mold is moved to the extubation station.
  • the tube extruding machine extracts the ductile iron tube blank from the tube mold; and pulls out the ductile iron tube The empty tube mold of the blank, and then through the cleaning station, the spraying station, etc., clean the residual paint on the inner wall of the tube end of the tube mold, re-spray the insulating coating and dry, and then recycle again for the preparation of the ductile iron tube;
  • the heat-insulating paint is a water-based paint, which is composed of diatomaceous earth and bentonite in a weight ratio (15-20):1, and the coating thickness can be 0.6-1.2 mm.
  • the diatomaceous earth and the bentonite in the water-based diatomaceous earth paint are disposed at a weight ratio of 18:1, and the coating thickness is 0.9 mm.
  • the core of the socket adopts the cold box process and uses the core of the automatic core shooting mechanism.
  • the brushing machine is used to clean and heat the heat-insulating paint brought out from the outer wall of the ductile iron tube blank drawn from the tube mold, and completely remove the sticking on the outer wall of the ductile iron tube blank. Residual insulation coating;
  • Non-destructive testing After the brush tube and the purge are completed, the spheroidal graphite tube blanks that have been cleaned and purged on the outer wall are subjected to ultrasonic non-destructive testing to determine the spheroidization level of the cast tube blank, whether there are casting defects or other damage defects.
  • the qualified ductile iron pipe that has passed the inspection enters the next process, and the ductile iron pipe which is judged as waste is remelted as the charge of the charge (normally, the scrap rate here does not exceed 0.2%);
  • the qualified ductile iron pipe blank is transferred into the tunnel annealing kiln annealing, the annealing temperature is controlled at 780-850 ° C, the annealing time is 30 min, and the kiln temperature is 680 ° C;
  • finishing processing finishing the spheroidal graphite cast iron blank after the spraying of zinc, including: grinding socket and socket, grinding inner wall, cutting ring chamfering, flange drilling, etc.;
  • air tightness test airtightness test of the ductile iron pipe blank after finishing processing, the test pressure is 5.0MPa, the dwell time is >20s; the ductile iron pipe qualified by the airtightness test enters the next process, The ductile iron pipe judged as waste is remelted as a charge (normally, the scrap rate here does not exceed 0.1%);
  • ductile iron pipe coating protection electrostatic spraying protective coating on the inner wall of ductile iron pipe blank qualified for air tightness test, the coating material is polyurethane, the coating thickness is 70 ⁇ m; the ductile iron pipe qualified for airtightness test
  • the outer wall of the blank is electrostatically sprayed with a protective coating on the zinc layer.
  • the coating material is polyurethane, and the coating thickness is 100 ⁇ m.
  • the ductile iron pipe prepared in this embodiment has no casting defects such as blisters, slag eyes, pores, cold partitions, shrinkage, shrinkage holes, etc., and the metallographic and mechanical properties are tested by the body sampling, and the spheroidization level is high and stable.
  • the matrix structure is ferrite-based P15, the elongation is 18-22%, and the tensile strength is 440-480 MPa.
  • the ductile iron pipe prepared in this embodiment is suitable for laying a high-pressure Class A gas pipeline of a city with a conveying pressure of 4.0 MPa, and the ductile iron pipe is an S-type flexible mechanical seal connection, and the sealing apron material used is preferably polytetrafluoroethylene.
  • S1 preparation of molten iron:
  • the chemical composition of molten iron is set to: C: 3.4 ⁇ 3.7%, Si: 2.4 ⁇ 2.5%.
  • the raw iron, scrap steel and ductile iron pipe are used as the charge, and the charge after batching is 40t/h.
  • the slag iron is separated by a siphon type slag iron separator, and the original iron liquid is injected into the 60t large-capacity core induction heat preservation electric furnace from the tap hole, and the induction heat preservation furnace is set.
  • the constant temperature is 1500 ° C and the temperature is kept constant.
  • the cup furnace melting process is set according to the set value of the chemical composition of the molten iron, so that the iron output temperature of the molten iron is greater than 1500 ° C, and the chemical composition of the original molten iron is within the set value range. If it exceeds the set value range, the original molten iron is injected into the variable frequency coreless induction furnace, and the mass fraction of carbon and silicon in the original molten iron is adjusted according to the set value of the chemical composition of the molten iron to make the original molten iron The mass fraction of carbon is not higher than 3.7%, and the carbon equivalent is 4.2% to 4.3%;
  • spheroidizing treatment Put the magnesium ingot with the weight of 0.12% of the original molten iron into the reaction chamber of 1.5t subcontracting, inject the original molten iron of the induction holding electric furnace into the subcontract for spheroidization treatment, and spheroidize the molten iron.
  • the residual amount of Mg is ⁇ 0.04%
  • the chemical composition of the molten iron includes: C: 3.2 to 3.6%, Si: 2.4 to 2.5%, Mn: ⁇ 0.3%, P: ⁇ 0.07%, S: ⁇ 0.01%, no slag is required.
  • the spheroidized molten iron in the subconductor is directly injected into the 8t ductile iron special casting electric furnace by the 5t rotary forklift, in order to keep the pouring temperature of the molten iron not less than the critical temperature of the molten iron, the special casting electric furnace of the ductile iron is set.
  • the set holding temperature is 1440 ° C;
  • the iron liquid with a temperature of 1440 ° C in the cast iron special casting electric furnace is injected into the tube mold by the quantitative solution, and the weight of the iron solution is 0.3% of the 75FeSi inoculant.
  • the tube puller extracts the ductile iron tube blank from the tube mold.
  • water is used as a paint carrier, and diatomaceous earth and bentonite are prepared at a weight ratio of 20:1 to prepare a heat insulating coating having a coating thickness of 0.4 to 0.8 mm.
  • the coating thickness is preferably 0.6 mm. .
  • the core of the socket adopts the cold box process and adopts the core of the automatic core shooting mechanism.
  • the brushing machine is used to clean and heat the heat-insulating paint brought out from the outer wall of the ductile iron tube blank drawn from the tube mold, and completely remove the sticking on the outer wall of the ductile iron tube blank. Residual insulation coating;
  • Non-destructive testing After the brush tube and the purge are completed, the spheroidal graphite tube blanks that have been cleaned and purged on the outer wall are subjected to ultrasonic non-destructive testing to determine the spheroidization level of the cast tube blank, whether there are casting defects or other damage defects.
  • the qualified ductile iron pipe that has passed the inspection enters the next process, and the ductile iron pipe which is judged as waste is remelted as the charge of the charge (normally, the scrap rate here does not exceed 0.2%);
  • the qualified ductile iron pipe blank is transferred into the tunnel annealing kiln annealing, the annealing temperature is controlled at 780-850 ° C, the annealing time is 30 min, and the kiln temperature is 680 ° C;
  • finishing processing finishing the spheroidal graphite cast iron blank after the spraying of zinc, including: grinding socket and socket, grinding inner wall, cutting ring chamfering, flange drilling, etc.;
  • air tightness test airtightness test of the ductile iron pipe blank after finishing processing, the test pressure is 5.0MPa, the dwell time is >20s; the ductile iron pipe qualified by the airtightness test enters the next process, The ductile iron pipe judged as waste is remelted as a charge (normally, the scrap rate here does not exceed 0.1%);
  • ductile iron pipe coating protection electrostatic spraying protective coating on the inner wall of ductile iron pipe blank qualified for air tightness test, the coating material is epoxy resin, the coating thickness is 100 ⁇ m; the spheroidal ink qualified for air tightness test The outer wall of the cast iron tube blank is electrostatically sprayed with a protective coating on the zinc layer.
  • the coating material is polyurethane, and the coating thickness is 100 ⁇ m. After that, the final inspection is performed, and the trademark and the quality of the qualified product are tracked, and the spheroidal graphite cast iron is obtained. Finished product.
  • the ductile iron pipe prepared in this embodiment has no casting defects such as blisters, slag eyes, pores, cold partitions, shrinkage, shrinkage holes, etc., and the metallographic and mechanical properties are tested by the body sampling, and the spheroidization level is high and stable.
  • the matrix structure is ferrite-based P15, the elongation is 18-22%, and the tensile strength is 440-480 MPa.
  • the ductile iron pipe prepared in this embodiment is suitable for laying a high-pressure B-class gas pipeline of a town with a conveying pressure of 2.5 MPa, and is an S-type flexible mechanical seal connection.
  • the material of the sealing rubber ring used is preferably a fluororubber.
  • the chemical composition of iron liquid is set to: C: 3.4 ⁇ 3.7%, Si: 2.3 ⁇ 2.6%, using pig iron, scrap steel, carbon-free non-burning iron oxide brick and recycled material as charge, ingredients
  • the furnace charge is smelted into the original iron liquid in a 30t/h large-scale furnace-rich oxygen-rich cupola
  • the slag iron is separated by a siphon type slag iron separator, and the original iron liquid is injected into the 53t large-capacity cored induction heating furnace from the tap hole.
  • the set temperature is 1500 ° C and maintain a constant temperature.
  • the cup furnace melting process is set, so that the iron output temperature of the molten iron is greater than 1500 ° C, and the original guaranteed molten iron is ensured.
  • the composition of the chemical composition is within the set value range. If it exceeds the set value range, the molten iron solution will be melted in a 10t variable frequency coreless induction furnace and injected into a 53t large-capacity cored induction heating furnace to ensure the above chemical composition of the molten iron.
  • the set value is reached so that the mass fraction of carbon in the original molten iron is not higher than 3.7%, and the carbon equivalent is 4.2% to 4.3%;
  • spheroidizing treatment Put the magnesium ingot with 0.14% of the weight of the original molten iron into the reaction chamber of 1.5t subcontracting, inject the original molten iron of the induction holding electric furnace into the subcontract for spheroidization; after spheroidizing, the Mg in the molten iron The residual amount is ⁇ 0.04%, and the chemical composition in the molten iron includes: C: 3.4 to 3.7%, Si: 2.2 to 2.6%, Mn: ⁇ 0.3%, P: ⁇ 0.07%, S: ⁇ 0.01%; spheroidizing treatment After the molten iron is not treated by slag, a 5t rotary forklift is used to directly inject 8t spheroidal graphite cast iron special casting electric furnace. In order to ensure the high enough casting temperature required for the quality of this small-diameter ductile iron pipe product, the spheroidal cast iron is specially cast in the electric furnace.
  • the set holding temperature is 1460 ° C;
  • the iron liquid with a temperature of 1460 °C in the special casting electric furnace of spheroidal graphite cast iron is injected into the tube mold, and the iron alloy weight is 0.3% of the 75FeSi inoculant.
  • the tube extruding machine extracts the ductile iron tube blank from the tube mold; the empty tube mold of the ductile iron tube blank is pulled out, and then passes through the cleaning station, Spraying station, etc., leaving the inner wall of the die end The paint is cleaned, re-sprayed and dried, and then recycled for the preparation of ductile iron pipes;
  • water is used as a paint carrier, and diatomaceous earth and bentonite are disposed as a heat insulating coating at a weight ratio of 20:1, and the coating thickness is 0.4 mm.
  • the core of the socket adopts the cold box process and adopts the core of the automatic core shooting mechanism.
  • the brushing machine is used to clean and heat the heat-insulating paint brought out from the outer wall of the ductile iron tube blank drawn from the tube mold, and completely remove the sticking on the outer wall of the ductile iron tube blank. Residual insulation coating;
  • Non-destructive testing After the brush tube and the purge are completed, the spheroidal graphite tube blanks that have been cleaned and purged on the outer wall are subjected to ultrasonic non-destructive testing to determine the spheroidization level of the cast tube blank, whether there are casting defects or other damage defects.
  • the qualified ductile iron pipe that has passed the inspection enters the next process, and the ductile iron pipe which is judged as waste is remelted as the charge of the charge (normally, the scrap rate here does not exceed 0.3%);
  • the qualified ductile iron pipe blank is transferred into the tunnel annealing kiln annealing, the annealing temperature is controlled at 780-850 ° C, the annealing time is 30 min, and the kiln temperature is 680 ° C;
  • finishing processing finishing the spheroidal graphite cast iron blank after the spraying of zinc, including: grinding socket and socket, grinding inner wall, cutting ring chamfering, flange drilling, etc.;
  • air tightness test airtightness test of the ductile iron pipe blank after finishing processing, the test pressure is 5.0MPa, the dwell time is >20s; the ductile iron pipe qualified by the airtightness test enters the next process, The ductile iron pipe judged as waste is remelted as a charge (normally, the scrap rate here does not exceed 0.2%);
  • ductile iron pipe coating protection electrostatic spraying protective coating on the inner wall of ductile iron pipe blank qualified for air tightness test, the coating material is epoxy resin, the coating thickness is 80 ⁇ m; the spheroidal ink qualified for air tightness test
  • the outer wall of the cast iron pipe blank is coated with a protective coating on the zinc layer by an electrostatic spraying process.
  • the coating material is epoxy asphalt paint with a coating thickness of 100 ⁇ m; then the final inspection is carried out to mark the quality and quality of the qualified product.
  • the digital code is the finished product of ductile iron pipe.
  • the ductile iron pipe prepared in this embodiment has no casting defects such as blisters, slag eyes, pores, cold partitions, shrinkage, shrinkage holes, etc., and the metallographic and mechanical properties are tested by the body sampling, and the spheroidization level is high and stable.
  • the matrix structure is ferrite-based P5 with an elongation of 18 to 24% and a tensile strength of 420 to 450 MPa.
  • the ductile iron pipe prepared in this embodiment is suitable for laying a sub-high pressure A-class gas pipeline of a transmission pressure of 1.6 MPa, and is a T-type flexible sealing connection.
  • the material of the sealing apron used is preferably hydrogenated nitrile rubber.
  • the production line of the ductile iron pipe for the high-pressure gas pipeline of the present invention can be automated or semi-automatic, such as: (1) In the preparation process of the molten iron, the cupola can be intelligently controlled by the expert system to realize the furnace working condition and The whole process of the smelting parameters is automatically controlled; (2) during the spheroidizing process, the molten iron in the subconducting bag can be spheroidized, transferred to the special casting electric furnace, etc. on the rotary forklift; (3) Insulation coating During the preparation process, the centrifugal system can automatically prepare the mixing system to be ready for use by the mixing system; (4) The installation of the socket core can be performed by a robot or a robot. Thereby, it is beneficial to save manpower and material resources and improve the production efficiency of the ductile iron pipe.

Abstract

一种球墨铸铁管的制备工艺，包括铁液制备、球化处理和涂料热模法离心铸造等工艺步骤，制得的球墨铸铁管基体组织以铁素体为主，无游离渗碳体，珠光体含量低，延伸率大于18％，抗拉强度高，无渣眼、砂眼等铸造缺陷，气密性好。还提供了一种城镇高压燃气管线用球墨铸铁管及其制备工艺，该城镇高压燃气管线用球墨铸铁管无渣眼、皮下气孔、砂眼、浇不足、冷隔重皮、缩孔、缩松等铸造缺陷，管壁厚度均匀、管体组织致密度高、气密性好，具备铺设城镇燃气管线的质量要求，适用于铺设输送压力为0.4～4.0MPa的城镇高压、次高压燃气管线，如果有特别需要，也可以用于不大于6.0MPa的燃气管线。

Description

球墨铸铁管及城镇高压燃气管线用球墨铸铁管的制备工艺及城镇高压燃气管线用球墨铸铁管 技术领域
本发明属于球墨铸铁管制备技术领域，涉及一种球墨铸铁管的制备工艺，具体涉及一种可用于城镇高压燃气管线铺设的球墨铸铁管的制备工艺。
背景技术
目前城市铺设的天然气管线，高压段(≮2.5～4.0MPa)和次高压段(≮0.8～1.6MPa)全部使用无缝钢管和焊接钢管，但目前这些燃气管线钢管存在以下问题：
(1)由于钢管的耐腐蚀性差，特别是耐电腐蚀能力很差，尽管在安装现场采取了种种防腐蚀处理措施，其设计寿命也仅有15年；而在一些土壤盐度较高的地区，实际使用寿命都不足15年，许多甚至寿命只有4～5年；这极易造成天然气的泄漏，特别是遇到地震、地面沉降等地质灾害时，往往会引发爆炸、起火等造成严重的人员伤亡事故的“次生灾害”，威胁到城市的生命财产安全；
(2)钢管需要运到现场后再进行焊接、试压、作防腐蚀处理等，操作复杂，土方挖掘量大，施工周期长，管道综合造价高，日常检测维护工作量大，且每隔几年就需要挖开道路重修，加重了市政工程建设的投资负担；
(3)由于燃气管线是由一段段钢管焊接连接起来的，即为刚性连接安装的，而经过几年腐蚀，管壁变薄后，管子的强度韧性都会明显降低，此时如果遇到地震、地面沉降等地质灾害时，管子受到拉伸、挤压、扭曲和重物砸碰冲击，管子很容易开裂、破坏断裂，致使天然气突然大量泄漏而引发爆炸、城市大火等严重次生灾害。
因钢管不耐腐蚀、不具备抵御强地震破坏的能力，一些发达工业化国家自上世纪七十年代起，开始陆续使用球墨铸铁管建设城市燃气管线。由于球墨铸铁管具有与钢管等同的强度和韧性，但其耐腐蚀性强，尤其是在耐受电腐蚀能力方面，球墨铸铁管是钢管的十几倍，因此，球墨铸铁管道的安全使用寿命可长达100年。球墨铸铁管采用胶圈密封承插式柔性接口进行连接，能够化解吸收强地震带给地下管线的破坏力，保持管线完好和维持正常的输气能力，从而避免城市发生地震次生灾害，确保城市减灾；并且铺设球墨铸铁管线的施工快捷简便，管线综合造价一次性投入与钢管线基本持平，而管线使用寿命超过钢管七倍以上，因此性价比大幅度超越钢管管线。到上世纪八十年代末，欧美日等一些国家的城市地下燃气管线的建设，已普遍采用了 球墨铸铁管作为燃气管线用管。
目前一些国家如德国、英国、法国的城镇燃气管道用球墨铸铁管，其最高使用压力只有1.6MPa。而我国的京、沪、广、深、津、成、渝等超大城市的人口数量都在千万级以上，燃气用管的使用压力只有1.6MPa是不够的，因此我国制订的城市燃气管线标准规定的最高输送压力在4.0MPa，目前在世界上是最高的。
然而，我国生产的球墨铸铁管由于工艺设备技术的局限，球墨铸铁管产品的自身质量多存在缺陷，主要是管子普遍存在砂眼、气孔、渣眼、冷隔重皮、壁厚不匀，以及承口端内部缩松、缩孔等铸造缺陷，严重降低了管子的气密性，并且还需要设立焊补工序对有渗漏缺陷的管子进行修复。因此，目前我国生产的球墨铸铁管只适用于给排水管道的铺设，而当球墨铸铁管需用于铺设城镇燃气管线时，国家标准《城镇燃气设计规范(GB50028-2006)》规定球墨铸铁管只能用于中压段(≤0.4MPa)，甚至江苏等省市已完全弃用国内质量不可靠的球墨铸铁管，在中压段也使用焊接钢管。可见，我国目前生产的球墨铸铁管由于质量缺陷，使其完全无法满足我国的城市燃气输送压力要求，致使目前国内燃气球墨铸铁管的生产已全部停止，甚至国内球墨铸铁管行业正计划与球墨铸铁管的国际标准ISO2531分道扬镳，在国家标准GB/T13295(水及燃气管道用球墨铸铁管、管件和附件)中将燃气管道用球墨铸铁管剔除出去，只剩输水用球墨铸铁管，这将对我国球墨铸铁管行业的发展带来了严重的技术障碍和不良影响，而钢管由于不耐腐蚀、寿命短、需要经常维修和更换、不具备抵御强地震破坏的能力等自身固有缺陷，其大量使用也为城市安全埋下重大隐患。因此，迫切需要研发一种能够完全克服上述球墨铸铁管质量缺陷的新工艺技术，以使球墨铸铁管能够满足高输送压力的城镇燃气管线标准要求。
发明内容
本发明的其中一个目的在于提供一种球墨铸铁管的制备工艺，并根据上述制备工艺进一步提供一种制备城镇高压燃气管线用球墨铸铁管的制备工艺，以提供一种城镇高压燃气管线用球墨铸铁管，解决上述技术问题中的至少一个。
根据本发明的一个方面，提供了一种球墨铸铁管的制备工艺，包括如下步骤：
S1、铁液的制备：将炉料熔炼成原铁液并过热至不小于1500℃，根据铁液化学成分的设定值调整原铁液的化学成分组成。
S2、球化处理：利用球化剂对已调整好化学成分组成的原铁液进行球化 处理，并将球化处理后的铁液注入球墨铸铁专用浇注电炉，利用球墨铸铁专用浇注电炉将铁液的浇注温度保持不小于铁液的临界温度；
S3、涂料热模法离心铸造：对喷涂的绝热涂料已干燥的热管模完成上承口芯后，驱动管模转动，并在管模转动的离心力达到离心力设定值时，将球墨铸铁专用浇注电炉中的铁液经定量包注入管模中，并在浇注过程中对铁液进行随流孕育处理和对管模进行冷却处理，浇注完成后，待凝固成形的球墨铸铁管毛坯冷却到设定温度时，将球墨铸铁管毛坯从管模中拔出。
首先，本发明的制备工艺中，在铁液制备时是将熔炼出的原铁液过热到了1500℃及以上，由于在铁液制备阶段将原铁液过热至不小于1500℃的温度，可以促使碳发挥对铁液的脱氧净化作用，达到对原铁液的预球化处理效果，从而有利于石墨的球化；此外，在本发明的制备工艺中，还根据铁液化学成分的设定值对原铁液进行了化学成分组成的调整，由于球墨铸铁管口径规格及相应壁厚的不同，使不同规格的球墨铸铁管浇注后在凝固时间与冷却速度上存在差别，为防止球墨铸铁管的铸态毛坯出现游离渗碳体，对铁液碳当量的控制会根据不同口径、壁厚的球墨铸铁管的要求加以区别，给出不同的化学成分和碳当量的设定值，并据此进行调整；加之内壁喷涂了绝热涂层的热管模可以避免铁液激冷，从而能够避免在离心浇注过程中球墨铸铁管的铸态毛坯出现游离渗碳体，形成白口组织。
其次，本发明中是对温度在1500℃及以上且调整了化学成分组成的原铁液进行球化处理，并且将球化处理后的铁液注入到了球墨铸铁专用浇注电炉中(本发明实施例中提及的球墨铸铁专用浇注电炉为专利CN101658901B公开的浇注电炉设备)，将球化处理后的铁液注入球墨铸铁专用浇注电炉中，一方面可以进一步对铁液进行脱硫、脱氧，另一方面可以稳定铁液中的残留Mg量，从而避免了铁液球化衰退，保证了制得的球墨铸铁管的球化级别，并稳定了其韧性、强度等机械性能；同时将铁液的浇注温度始终保持在不小于铁液的临界温度(即1420～1480℃)的温度范围，使铁液始终为非氧化性的洁净铁液，避免了球墨铸铁管在离心浇注过程中产生砂眼、渣眼等铸造缺陷，这保证了铁液的浇注温度始终维持在稳定的高温水平，有利于消除气孔、砂眼、渣眼等夹杂缺陷，高温还使铁液的流动性得以大幅度提高，避免了产生带有冷隔、浇不足等缺陷的球墨铸铁管废品。
再次，本发明制备工艺中，采用涂料热模法离心铸造工艺制备球墨铸铁管毛坯，并且是在管模转动的离心力达到离心力设定值时，再开始离心浇注过程，这样的制备工艺，使得能够根据需求在适合的离心力下启动浇注过程，从而控制制备出的球墨铸铁管毛坯的缩松情况。例如为了克服球墨铸铁凝固时的缩松缩孔倾向产生的内部疏松，离心浇注过程采用高转速大离心力的浇 注工艺，这保证了浇注用的高温铁液始终在巨大离心力的作用下逐渐凝固(本发明实施例中优选在管模转动离心力达到80～110G时开始浇注，比德·拉沃法的管模转动离心力40～50G提高1倍左右)，使得高温铁液在管模内始终在巨大离心力的作用下向管模内壁挤压，而不能向管模中心方向自由膨胀，实现了球墨铸铁铁液在粥状凝固及石墨化膨胀重合阶段的压力自补缩，从而保证了球墨铸铁管组织致密，厚壁部位厚度均匀且无缩孔、缩松等铸造缺陷，还保证了壁厚非常均匀与致密，无夹杂，因此制得的球墨铸铁管气密性好。此外，铁液合适的碳当量加上瞬时孕育，使制得的铸态球墨铸铁管毛坯的基体组织无游离渗碳体。
另外，本发明采用涂料热模法离心铸造工艺，绝热涂料喷涂前需先将管模预热至200～220℃，可保证喷涂时绝热涂料能迅速干透，在铁液注入管模时可避免由于绝热涂料起爆而导致管模被铁液烧蚀损坏，从而造成生产中断事故。
本发明实施例的铁液制备过程中，对S含量不大于0.12％的铁液均可以不经炉外脱硫处理直接注入感应保温电炉中，在调节原铁液的化学成分组成时，也不需要刻意对S含量进行控制，这是因为：1)球化处理的脱硫效果很好，对硫含量不大于0.2％、温度为1500℃的高温、高硫铁液都能处理成合格球墨铸铁铁液，并且可将球化后铁液的硫含量脱至小于0.01％的水平；2)球墨铸铁专用浇注电炉允许在球化处理后不必扒渣处理，而直接将球化处理包内的MgS渣和MgO渣直接倾入炉内，在直流电解的作用下将渣中的S 2-和O 2-阴离子脱掉，渣中Mg 2+阳离子在接触到作为阴极的铁液时被还原成Mg重新进入铁液，与Mg从铁液中的逃逸损失形成动态平衡，稳定了铁液中的Mg残留量，避免了球化衰退，并使MgS渣和MgO渣化害为利，实现了金属镁的循环利用。而这也简化了生产工艺，提高了制备出的球墨铸铁管的机械性能和质量的一致性。
本发明实施例中，可以选用生铁、废钢、铁屑、含碳免烧砖和回炉料(主要为管件或其它铸件的浇冒口和少量球墨铸铁管与管件的不合格品)中的一种或多种作为炉料，根据不同炉料的化学成分组成、熔炼过程中化学成分可能存在的损耗和铁液化学成分的设定值进行配料，使熔炼后的原铁液化学成分的组成接近其设定值，简化铁液化学成分调整的工艺处理。
本发明实施例中，将炉料熔炼成原铁液的工艺可以采用冲天炉-感应电炉双联熔炼工艺，也可以采用高炉生铁铁液进入变频无芯感应电炉调整化学成分的“短流程”熔炼工艺。本发明实施例中将原铁液过热至不小于1500℃，可以是通过利用冲天炉对炉料进行熔炼，在熔炼后原铁液温度直接达到1500℃及以上(即原铁液的出铁温度不小于1500℃)实现的，也可以是通过 采用其他熔炼方式，将熔炼后的原铁液在感应电炉中进行过热，使原铁液温度达到1500℃及以上(即，感应电炉保温温度设定在1500℃及以上)实现的。
本发明实施例浇注过程中对铁液进行随流孕育处理可以促进石墨化、防止浇注过程中铁液球化衰退，避免游离渗碳体的产生。本发明实施例中随流孕育处理所用孕育剂为常规孕育剂，可以是硅铁孕育剂、硅钡孕育剂中的一种或其组合，优选75FeSi孕育剂，用量为铁液重量的0.2～0.4％。
本发明实施例中，浇注过程中对管模进行的冷却处理优选为喷淋水冷却处理。凝固成形的球墨铸铁管毛坯在冷却过程中，可继续对管模进行冷却处理；对凝固后冷却速度相对较慢的大口径厚壁球墨铸铁管，为加速其冷却速度，也可以对管模内已凝固的球墨铸铁管毛坯采取吹风或喷水雾措施。
本发明实施例中对已调整好化学成分组成的原铁液进行球化处理的工艺优选是对铁液碳当量不发生影响且脱硫效果显著的喂丝法或转包法。其中，需通过调整球化剂用量，使球化处理后铁液中Mg的残留量不小于0.035％。
在一些实施方式中，离心力设定值不小于80G，且不高于110G。由于在离心力较小时进行浇注会导致缩松、缩孔缺陷，而离心力过大时管模会因转速过高而使管模及设备的稳定性和设备安全性变差，因此，将离心力的设定转速设置为80G～110G(不同口径的球墨铸铁管离心力取值不同，其中，小口径管取值接近上限值，大口径管取值接近下限值)，可以在避免缩松、缩松缺陷的同时，也保证设备与管模运转的稳定性，进而保证生产出的球墨铸铁管的质量和保证生产安全。
在一些实施方式中，管模内凝固成形的球墨铸铁管毛坯冷却到的设定温度可以为760～830℃。拔管温度高于850℃时，球墨铸铁管强度不足，此温度下拔管易导致球墨铸铁管在拔管过程中变形，而当拔管温度低于共析点的温度(约730℃)时，球墨铸铁管会发生共析转变，导致晶格转变引发体积跃迁，使球墨铸铁管膨胀造成拔管困难。因此，拔管温度控制在760～830℃可以防止拔管困难和避免球墨铸铁管变形。
在一些实施方式中，步骤S2中，利用球墨铸铁专用浇注电炉将铁液的浇注温度保持不小于铁液的临界温度，可以是通过将球墨铸铁专用浇注电炉中的保温温度设定为1430～1480℃实现的。将球墨铸铁专用浇注电炉中的保温温度设定为1430～1480℃，可以使球墨铸铁专用浇注电炉中的铁液注入管模中时，保持铁液为非氧化性的洁净铁液，由此既可以保证铁液有足够的流动性，又能保证浇注结束后管模内的铁液还能在高离心力作用下仍保持一段液态时间，从而避免球墨铸铁管产生浇不足、冷隔、缩松、缩孔、砂眼、渣眼、气孔、壁厚不均等铸造缺陷和废品，制得的球墨铸铁管管壁致密、均匀、无缺陷、气密性好。
在一些实施方式中，球化剂可以为镁锭，铁液化学成分的设定值可以为：C为3.4～3.7％、Si为2.0～2.6％，
根据对铁液化学成分的设定值调整原铁液的化学成分组成包括：
基于上述设定值调整原铁液中的碳和硅的质量分数，以使原铁液中碳的质量分数不高于3.7％，且使碳当量达到共晶成分(即碳当量达4.26％)或使碳当量达到4.1％～4.3％。由此，有利于本发明涂料热模法离心浇铸工艺处理过程中球墨铸铁管成形和获得基体组织中不含游离渗碳体的球墨铸铁管毛坯，在保证球墨铸铁管毛坯质量的同时，还能简化后续的退火工艺。同时，采用镁锭作为球化剂，一方面可以大幅度降低球化剂成本，另一方面也避免了稀土硅铁镁球化剂中的Si等元素对铁液成分的影响和干扰，还可以节约大量宝贵的稀土元素。
在一些实施方式中，步骤S2中，可以采用转包法对已调整好化学成分组成的原铁液进行球化处理，其中，镁锭球化剂的用量为原铁液重量的0.10～0.20％。采用转包法进行球化处理，球化处理效果好，且球化剂在转包的反应室中汽化的速度受控而不会发生爆炸。球化剂的用量为原铁液重量的0.10～0.15％，即可保证球化处理完成后铁液中Mg含量不小于0.04％，达到理想的球化效果，当原铁液中S含量大于0.12％时，球化剂的用量可根据需要增加到原铁液重量的0.18～0.20％。
根据本发明的另一个方面，提供了一种城镇高压燃气管线用球墨铸铁管的制备工艺，包括如下步骤：
利用上述球墨铸铁管的制备工艺，制备球墨铸铁管毛坯；
对球墨铸铁管毛坯进行退火处理；
对退火后的球墨铸铁管毛坯进行精整加工；
根据待铺设燃气管线对球墨铸铁管的压力要求(通常为0.4～4.0MPa)，即待铺设燃气管线的设计输送压力设定试验压力，并根据设定的试验压力对精整加工后的球墨铸铁管毛坯进行气密性试验，其中，试验压力不小于待铺设燃气管线的设计输送压力的1.20倍。
球墨铸铁管毛坯从管模中拔出后，由于管体温度高，可能会在冷空气中发生正火而产生大量珠光体，造成球墨铸铁管毛坯的延伸率下降，因此需要进行消除珠光体的退火处理。
本发明实施例中，精整加工包括承口内磨、插口外磨、内壁修磨、切管、倒角，以及S型、N型等密封接口球墨铸铁管的法兰钻孔。承口内磨、插口外磨是为了提高这些部位的表面光洁度，从而使其在球墨铸铁管连接过程中与密封胶圈配合时可以进一步提高球墨铸铁管的密封压力。
为了确保产品的高可靠性，本发明实施例中，城镇高压燃气管线用球墨 铸铁管生产线上的气密性试验一般均采用试验压力不小于5.0MPa、保压时间不小于20秒的检验方式，试验合格的球墨铸铁管可以根据需求继续完成后续的内外涂覆、终检验、喷商标和喷数字化标记等工序，然后打捆入库成为城镇高压燃气管线用球墨铸铁管成品。
本发明城镇高压燃气管线用球墨铸铁管的制备工艺可以有效避免球墨铸铁管在制备过程中产生渣眼、皮下气孔、砂眼、浇不足、冷隔重皮、缩孔、缩松等铸造缺陷，管壁厚度均匀(壁厚误差可控制在≯±0.3mm)、管体组织致密度高、气密性好，因此这种球墨铸铁管具备铺设城镇燃气管线的高压段A级(≮4.0MPa)的质量要求。
在一些实施方式中，在退火处理之前还可以包括如下步骤：
对制备的球墨铸铁管毛坯的外壁进行清刷、吹洗；
对外壁清刷、吹洗干净后的球墨铸铁管毛坯进行超声波无损检测，确定球墨铸铁管毛坯的球化级别是否合格以及球墨铸铁管毛坯管体是否有铸造缺陷和其它损伤缺陷。
如果浇注时注入管模的铁液的实际温度足够高(例如不低于1400℃)，球墨铸铁管毛坯从管模中拔出时，喷涂在管模内壁的绝热涂料会几乎全部挂在球墨铸铁管毛坯的外壁被带出，因此，需要对球墨铸铁管毛坯外壁进行清刷，再进行吹洗，将球墨铸铁管毛坯外壁残留的绝热涂料清洗干净。吹洗优选采用高压蒸汽对球墨铸铁管外壁进行吹洗。
刷管与吹洗完成后，需要对球墨铸铁管毛坯进行超声波无损检测，确定球墨铸铁管毛坯的球化级别是否合格，以及确定球墨铸铁管毛坯管体是否有渣眼、皮下气孔、砂眼、冷隔、重皮、缩孔、缩松等铸造缺陷和损伤裂纹等其他损伤缺陷。球化级别合格且无铸造缺陷和损伤裂纹的球墨铸铁管毛坯记为检验合格，而不合格的球墨铸铁管毛坯记为检验不合格，直接作为炉料回炉重熔。采用超声波对球墨铸铁管毛坯进行检测，可快速完成球墨铸铁管的无损检测，在不损害或不影响球墨铸铁使用性能的前提下，全面检测球墨铸铁管是否存在铸造缺陷和内部损伤缺陷；并且，将超声波用于测定球墨铸铁管的球化级别是否合格，其检测效率远高于传统的金相检测等方法，甚至还可以定量判定球墨铸铁管基体的不同组份及其含量；此外，采用超声波对球墨铸铁管毛坯进行检测，可以实现单一规格的大批量球墨铸铁管的连续在线检测，有利于实现球墨铸铁管生产线的自动化。
在一些实施方式中，退火处理的退火温度可以为780～850℃，退火时间为20～40min。与传统德·拉沃法退火工艺相比，本发明具有以下明显优势：1)本发明制备工艺制得的球墨铸铁管毛坯的基体中不含游离渗碳体，只是拔管后由于管体在空气中发生正火，此时发生的共析转变会使珠光体超标，因 此，只需要对球墨铸铁管进行消除珠光体的低温退火，即可获得铁素体含量合格的高延伸率、高韧性的球墨铸铁管，这样可以明显降低退火处理的温度(从传统的980～1050℃降低到780～850℃)；2)本发明退火工艺取消了消除莱氏体的高温退火阶段和退火窑中间的快速水冷(或风冷)结构，简化了隧道式退火窑的设备结构，缩短了退火时间，降低了退火处理的能耗，延长了退火窑中耐火材料的寿命；3)避免了球墨铸铁管由于过烧而变形(即球墨铸铁管变椭圆)的风险和废品损失；4)由于球墨铸铁管的壁厚高度均匀，保证了退火过程的平稳流畅，可完全避免因个别球墨铸铁管局部壁厚过薄在加热后发生断裂带来的严重后果(断裂的球墨铸铁管堵塞在退火窑中，会引发连续式隧道退火窑设备故障，甚至引发停产事故)。
在一些实施方式中，在所退火处理之后、精整加工之前还可以包括如下步骤：
对退火后的球墨铸铁管毛坯的外表面进行喷锌。
本发明实施例中，喷锌可以是通过热喷锌、冷涂锌等方式实现，锌层厚度优选不小于40μm。对退火后的球墨铸铁管毛坯的外表面进行喷锌，有利于提高球墨铸铁管表面耐受电腐蚀的能力，同时，还可以避免后续球墨铸铁管毛坯在进行气密性试验过程中，由于球墨铸铁管毛坯管体与水接触而导致管体表面生锈。
在一些实施方式中，在对精整加工后的球墨铸铁管毛坯进行气密性试验之后还可以包括如下步骤：
对气密性试验合格的球墨铸铁管毛坯的内壁和外壁涂覆防护及功能性涂层，其中，内壁防护涂层的涂覆材料可以为环氧树脂、聚氨酯或脲醛树脂中的一种或多种，外壁防护涂层的涂覆材料可以为环氧沥青漆、聚氨酯、聚脲中的一种或多种。由此，可以减小流体输送的阻力，提高球墨铸铁管的耐腐蚀能力，延长球墨铸铁管的使用寿命。根据球墨铸铁管的不同用途和对外部防腐蚀条件等的不同要求，可以选择不同的涂覆材料对球墨铸铁管的内壁和外壁涂覆防护及功能性涂层，喷涂方式和涂层厚度可以根据不同的涂覆材料按需设置。
根据本发明的另一个方面，提供了上述城镇高压燃气管线用球墨铸铁管的制备工艺制得的城镇高压燃气管线用球墨铸铁管。
在一些实施方式中，本发明提供的城镇高压燃气管线用球墨铸铁管可以应用于铺设输送压力为0.4～4.0MPa的城镇燃气管线。本发明提供的城镇高压燃气管线用球墨铸铁管可以安全用于城镇高压段A级(2.5～4.0MPa)、城镇高压段B级(1.6～2.5MPa)、次高压段A级(0.8～1.6MPa)和次高压段B级(0.4～0.8MPa)燃气管线的铺设；如果有特殊需要，也可以用于不大 于6.0MPa的燃气管线的铺设。
在一些实施方式中，城镇高压燃气管线用球墨铸铁管连接时可以采用柔性机械密封接口，例如，其接口形式可以是S型机械式密封接口、N 1型机械式密封接口、K II型机械式密封接口、K型机械式密封接口、S II型机械式密封接口，以及T型滑入式密封接口(T型接口仅限于1.6MPa以下的次高压燃气管)；连接时所用密封胶圈的材料可以依据使用环境条件和对燃气管线设计寿命的要求，选用氢化丁腈橡胶、丙烯酸酯橡胶、氟橡胶、氟硅橡胶或聚四氟乙烯。
具体实施方式
下面结合具体实施例对本发明的实施方式作详细的说明。
实施例1 城镇高压燃气管线用球墨铸铁管的制备
生产规格为DN600×6000mm，PN＝4.0MPa的城镇高压A级燃气管线用球墨铸铁管，包括如下步骤：
S1、铁液制备：铁液化学成分的设定值为：C：3.4～3.7％、Si：2.4～2.5％，选用生铁、废钢和球墨铸铁管回炉料作为炉料，配料后炉料在40t/h大型长炉龄富氧冲天炉中熔炼成原铁液后经虹吸式渣铁分离器将渣铁分离，原铁液由冲天炉的虹吸式出铁口注入60t大容量有芯感应保温电炉中，感应保温电炉的设定温度为1500℃并保持恒温，根据铁液化学成分的设定值设定冲天炉熔炼工艺，使铁液的出铁温度大于1500℃，同时保证原铁液的化学成分组成在设定值范围内，若超出设定值范围，则将原铁液注入变频无芯感应电炉中，根据上述铁液化学成分的设定值调整原铁液中的碳和硅的质量分数，以使原铁液中碳的质量分数不高于3.7％，且使碳当量达到4.2％～4.3％；
S2、球化处理：将原铁液重量0.16％的镁锭放入1.5t转包的反应室，将感应保温电炉的原铁液注入转包中进行球化处理，球化处理后铁液中Mg残留量≥0.04％，铁液中化学成分组成包括：C：3.4～3.7％、Si：2.2～2.4％、Mn：＜0.3％、P：＜0.07％、S：＜0.01％，球化处理后的铁液无需扒渣操作，将转包内球化处理后的铁液用5t旋转叉车运载直接注入12t球墨铸铁专用浇注电炉(为保证生产不中断，1台专用浇注电炉需要用2台配1.5t转包的5t旋转叉车供应铁液)，为使铁液的浇注温度保持不小于铁液的临界温度，球墨铸铁专用浇注电炉中设定的保温温度为1430℃；
S3、热模法离心铸造：在已经预热至200℃、且内壁清刷干净的热管模内壁喷涂绝热涂料，待绝热涂料彻底干燥后，将管模移至上芯工位，由机器人将承口芯安装在管模承口处；上芯完成后，将管模移至离心机组预转工位，管模预转至设定转速的85％时，移至离心浇注工位(管模在离心机组预转工 位预转至设定转速的80～90％时再移至离心浇注工位，可以节省离心浇注工位提升管模转速的时间，提高生产效率)；移至离心浇注工位后，迅速将管模转速提升到最大值(离心力达到90G)，随即开始浇注，将球墨铸铁专用浇注电炉中的温度为1430℃的铁液经定量包注入管模中，同时加铁液重量0.3％的75FeSi孕育剂进行随流孕育，并且同时对管模进行淋水冷却；铁液凝固成形后，将管模移至冷却工位(可继续对管模喷淋水冷却，同时可向管模内喷水雾，加快红热球墨铸铁管毛坯的降温)，随后管模移至拔管工位，待管模内球墨铸铁管毛坯冷却至830℃以下时，拔管机将球墨铸铁管毛坯从管模中拔出；拔出球墨铸铁管毛坯的空管模，再依次经过清刷工位、喷涂工位等，将管模承口端内壁残余涂料清刷干净，重新喷涂绝热涂料并干燥后，再次循环用于球墨铸铁管的制备；
其中，绝热涂料是水基涂料，由硅藻土和膨润土按重量比(15～20):1配置而成，涂层厚度可以是0.6～1.2mm。本实施例中，水基硅藻土涂料中硅藻土和膨润土按重量比18：1配置，涂层厚度是0.9mm。
承口芯采用冷芯盒工艺，用自动化射芯机制芯。
S4、刷管与吹洗：利用刷管机对从管模中拔出的球墨铸铁管毛坯外壁带出的绝热涂料进行清刷及高压蒸气吹洗，彻底清除粘在球墨铸铁管毛坯外壁上的残余绝热涂料；
S5、无损检测：刷管与吹洗完成后，对外壁清刷、吹洗干净后的球墨铸铁管毛坯进行超声波无损检测，判定铸管毛坯的球化级别、有无铸造缺陷或其他损伤缺陷，检验合格的球墨铸铁管进入下一工序，判断为废品的球墨铸铁管作为炉料回炉重熔(通常情况下此处废品率不超过0.2％)；
S6、低温退火：经检验合格的球墨铸铁管毛坯转入隧道式退火窑退火，退火温度控制在780～850℃，退火时间30min，出窑温度为680℃；
S7、喷锌：利用喷锌机对退火后的球墨铸铁管毛坯的外表面进行热喷锌，锌层厚度为40μm；
S8、精整加工：对喷锌完成后的球墨铸铁管毛坯进行精整加工，包括：磨承口与插口、磨内壁、切环倒角、法兰钻孔等；
S9、气密性试验：对精整加工后的球墨铸铁管毛坯进行气密性试验，试验压力为5.0MPa，保压时间＞20s；经气密性试验合格的球墨铸铁管进入下一工序，判断为废品的球墨铸铁管作为炉料回炉重熔(通常情况下此处废品率不超过0.1％)；
S10、球墨铸铁管涂覆防护：对气密性试验合格的球墨铸铁管毛坯的内壁静电喷涂防护涂层，涂层材料为聚氨酯，涂层厚度为70μm；对气密性试验合格的球墨铸铁管毛坯的外壁，在其锌层上静电喷涂防护涂层，涂层材料 为聚氨酯，涂层厚度为100μm；之后再进行终检验，对合格品喷商标和质量跟踪数字码，即得球墨铸铁管成品。
经检测，本实施例制得的球墨铸铁管无砂眼、渣眼、气孔、冷隔、缩松、缩孔等铸造缺陷，经本体取样进行金相和机械性能检验，球化级别高且非常稳定，基体组织为铁素体为主的P15，延伸率为18～22％，抗拉强度为440～480MPa。本实施例制得的球墨铸铁管适用于铺设输送压力4.0MPa的城镇高压A级燃气管线，球墨铸铁管为S型柔性机械密封连接，所用密封胶圈材料优选聚四氟乙烯。
实施例2 城镇高压燃气管线用球墨铸铁管的制备
生产规格为DN300×6000mm，PN＝2.5MPa的城镇高压B级燃气管线用球墨铸铁管，包括如下步骤：
S1、铁液制备：铁液化学成分的设定值为：C：3.4～3.7％、Si：2.4～2.5％，选用生铁、废钢和球墨铸铁管回炉料作为炉料，配料后炉料在40t/h大型长炉龄富氧冲天炉中熔炼成原铁液后经虹吸式渣铁分离器将渣铁分离，原铁液由出铁口注入60t大容量有芯感应保温电炉中，感应保温电炉的设定温度为1500℃并保持恒温，根据铁液化学成分的设定值设定冲天炉熔炼工艺，使铁液的出铁温度大于1500℃，同时保证原铁液的化学成分在设定值范围内，若超出设定值范围，则将原铁液注入变频无芯感应电炉中，根据上述铁液化学成分的设定值调整原铁液中的碳和硅的质量分数，以使原铁液中碳的质量分数不高于3.7％，且使碳当量达到4.2％～4.3％；
S2、球化处理：将原铁液重量0.12％的镁锭放入1.5t转包的反应室，将感应保温电炉的原铁液注入转包中进行球化处理，球化处理后铁液中Mg残留量≥0.04％，铁液中化学成分组成包括：C：3.2～3.6％、Si：2.4～2.5％、Mn：＜0.3％、P：＜0.07％、S：＜0.01％，无需扒渣操作，将转包内球化处理后的铁液用5t旋转叉车运载直接注入8t球墨铸铁专用浇注电炉，为使铁液的浇注温度保持不小于铁液的临界温度，球墨铸铁专用浇注电炉中设定的保温温度为1440℃；
S3、涂料热模法离心铸造：在预热至220℃、且内壁清刷干净的热管模内壁喷涂绝热涂料，待绝热涂料彻底干燥后，将管模移至上芯工位，由机器人将承口芯安装在管模承口处；上芯完成后，将管模移至在离心机组预转工位，管模预转至设定转速的85％时，移至离心浇注工位，迅速将管模转速提升到最大值(离心力达到98G)，随即开始浇注，将球墨铸铁专用浇注电炉中的温度为1440℃的铁液经定量包注入管模中，同时加铁液重量0.3％的75FeSi孕育剂进行随流孕育，并且同时对管模进行淋水冷却；铁液凝固成形 后，将管模移至冷却工位(可继续对管模喷淋水冷却，同时可向管模内喷水雾，加快红热球墨铸铁管毛坯的降温)，随后管模移至拔管工位，待管模内球墨铸铁管毛坯冷却至830℃以下时，拔管机将球墨铸铁管毛坯从管模中拔出；拔出球墨铸铁管毛坯的空管模，再依次经过清刷工位、喷涂工位等，将管模承口端内壁残余涂料清刷干净，重新喷涂绝热涂料并干燥后，再次循环用于球墨铸铁管的制备；
其中，本实施例中，以水作为涂料载体，将硅藻土和膨润土按重量比20：1制备绝热涂料，涂层厚度为0.4～0.8mm，本实施例中，优选涂层厚度为0.6mm。
承口芯采用冷芯盒工艺，采用自动化射芯机制芯。
S4、刷管与吹洗：利用刷管机对从管模中拔出的球墨铸铁管毛坯外壁带出的绝热涂料进行清刷及高压蒸气吹洗，彻底清除粘在球墨铸铁管毛坯外壁上的残余绝热涂料；
S5、无损检测：刷管与吹洗完成后，对外壁清刷、吹洗干净后的球墨铸铁管毛坯进行超声波无损检测，判定铸管毛坯的球化级别、有无铸造缺陷或其他损伤缺陷，检验合格的球墨铸铁管进入下一工序，判断为废品的球墨铸铁管作为炉料回炉重熔(通常情况下此处废品率不超过0.2％)；
S6、低温退火：经检验合格的球墨铸铁管毛坯转入隧道式退火窑退火，退火温度控制在780～850℃，退火时间30min，出窑温度为680℃；
S7、喷锌：利用喷锌机对退火后的球墨铸铁管毛坯的外表面进行热喷锌，锌层厚度为40μm；
S8、精整加工：对喷锌完成后的球墨铸铁管毛坯进行精整加工，包括：磨承口与插口、磨内壁、切环倒角、法兰钻孔等；
S9、气密性试验：对精整加工后的球墨铸铁管毛坯进行气密性试验，试验压力为5.0MPa，保压时间＞20s；经气密性试验合格的球墨铸铁管进入下一工序，判断为废品的球墨铸铁管作为炉料回炉重熔(通常情况下此处废品率不超过0.1％)；
S10、球墨铸铁管涂覆防护：对气密性试验合格的球墨铸铁管毛坯的内壁静电喷涂防护涂层，涂层材料为环氧树脂，涂层厚度为100μm；对气密性试验合格的球墨铸铁管毛坯的外壁，在其锌层上静电喷涂防护涂层，涂覆材料为聚氨酯，涂层厚度为100μm；之后再进行终检验，对合格品喷商标和质量跟踪数字码，即得球墨铸铁管成品。
经检测，本实施例制得的球墨铸铁管无砂眼、渣眼、气孔、冷隔、缩松、缩孔等铸造缺陷，经本体取样进行金相和机械性能检验，球化级别高且非常稳定，基体组织为铁素体为主的P15，延伸率为18～22％，抗拉强度为440～480 MPa。本实施例制得的球墨铸铁管适用于铺设输送压力2.5MPa的城镇高压B级燃气管线，为S型柔性机械密封连接，所用密封胶圈的材料优选为氟橡胶。
实施例3 城镇高压燃气管线用球墨铸铁管的制备
生产规格为DN100×6000mm，PN＝1.6MPa的城镇次高压A级燃气管线用球墨铸铁管，包括如下步骤：
S1、铁液制备：铁液的化学成分的设定值为：C：3.4～3.7％、Si：2.3～2.6％，选用生铁、废钢、含碳免烧氧化铁砖和回炉料作为炉料，配料后炉料在30t/h大型长炉龄富氧冲天炉中熔炼成原铁液后，经虹吸式渣铁分离器将渣铁分离，原铁液由出铁口注入53t大容量有芯感应保温电炉中，感应保温电炉的设定温度为1500℃并保持恒温，根据铁液化学成分的设定值设定冲天炉熔炼工艺，使铁液的出铁温度大于1500℃，同时保证原保证铁液的化学成分组成在设定值范围内，若超出设定值范围，则将使用10t变频无芯感应电炉熔化铁液并注入53t大容量有芯感应保温电炉中进行调整，以确保上述铁液化学成分达到设定值，以使原铁液中碳的质量分数不高于3.7％，且使碳当量达到4.2％～4.3％；
S2、球化处理：将原铁液重量0.14％的镁锭放入1.5t转包的反应室，将感应保温电炉的原铁液注入转包中进行球化处理；球化后铁液中Mg残留量≥0.04％，铁液中化学成分组成包括：C：3.4～3.7％、Si：2.2～2.6％、Mn：＜0.3％、P：＜0.07％、S：＜0.01％；将球化处理后的铁液不经过扒渣处理，用5t旋转叉车运载直接注入8t球墨铸铁专用浇注电炉，为保证这种小口径球墨铸铁管产品质量所需的足够高的浇注温度，球墨铸铁专用浇注电炉中设定的保温温度为1460℃；
S3、涂料热模法离心铸造：在预热至220℃、且内壁清刷干净的热管模内壁喷涂绝热涂料，待绝热涂料彻底干燥后，将管模移至上芯工位，由机器人将承口芯安装在管模承口处；上芯完成后，将管模移至在离心机组预转工位，管模预转至设定转速的85％时，移至离心浇注工位，迅速将管模转速提升到最大值(离心力达到110G)，随即开始浇注，将球墨铸铁专用浇注电炉中的温度为1460℃的铁液经定量包注入管模中，并加铁液重量0.3％的75FeSi孕育剂进行随流孕育，并且同时对管模进行淋水冷却；铁液凝固成形后，将管模移至冷却工位(可继续对管模喷淋水冷却)，随后管模移至拔管工位，待管模内球墨铸铁管毛坯冷却至830℃以下时，拔管机将球墨铸铁管毛坯从管模中拔出；拔出球墨铸铁管毛坯的空管模，再依次经过清刷工位、喷涂工位等，将管模承口端内壁残余涂料清刷干净，重新喷涂绝热涂料并干燥后，再 次循环用于球墨铸铁管的制备；
本实施例中，以水作为涂料载体，将硅藻土和膨润土按重量比20：1配置成绝热涂料，涂层厚度为0.4mm。
承口芯采用冷芯盒工艺，采用自动化射芯机制芯。
S4、刷管与吹洗：利用刷管机对从管模中拔出的球墨铸铁管毛坯外壁带出的绝热涂料进行清刷及高压蒸气吹洗，彻底清除粘在球墨铸铁管毛坯外壁上的残余绝热涂料；
S5、无损检测：刷管与吹洗完成后，对外壁清刷、吹洗干净后的球墨铸铁管毛坯进行超声波无损检测，判定铸管毛坯的球化级别、有无铸造缺陷或其他损伤缺陷，检验合格的球墨铸铁管进入下一工序，判断为废品的球墨铸铁管作为炉料回炉重熔(通常情况下此处废品率不超过0.3％)；
S6、低温退火：经检验合格的球墨铸铁管毛坯转入隧道式退火窑退火，退火温度控制在780～850℃，退火时间30min，出窑温度为680℃；
S7、喷锌：利用喷锌机对退火后的球墨铸铁管毛坯的外表面进行热喷锌，锌层厚度为40μm；
S8、精整加工：对喷锌完成后的球墨铸铁管毛坯进行精整加工，包括：磨承口与插口、磨内壁、切环倒角、法兰钻孔等；
S9、气密性试验：对精整加工后的球墨铸铁管毛坯进行气密性试验，试验压力为5.0MPa，保压时间＞20s；经气密性试验合格的球墨铸铁管进入下一工序，判断为废品的球墨铸铁管作为炉料回炉重熔(通常情况下此处废品率不超过0.2％)；
S10、球墨铸铁管涂覆防护：对气密性试验合格的球墨铸铁管毛坯的内壁静电喷涂防护涂层，涂层材料为环氧树脂，涂层厚度为80μm；对气密性试验合格的球墨铸铁管毛坯的外壁，在其锌层上通过静电喷涂工艺涂覆防护涂层，涂覆材料为环氧沥青漆，涂层厚度为100μm；之后再进行终检验，对合格品喷商标和质量跟踪数字码，即得球墨铸铁管成品。
经检测，本实施例制得的球墨铸铁管无砂眼、渣眼、气孔、冷隔、缩松、缩孔等铸造缺陷，经本体取样进行金相和机械性能检验，球化级别高且非常稳定，基体组织为铁素体为主的P5，延伸率为18～24％，抗拉强度为420～450MPa。本实施例制得的球墨铸铁管适用于铺设输送压力1.6MPa的城镇次高压A级燃气管线，为T型柔性密封连接，所用密封胶圈的材料优选为氢化丁腈橡胶。
在一些实施例中，本发明城镇高压燃气管线用球墨铸铁管的生产线可以实现自动化或半自动化，如：(1)铁液制备过程中，冲天炉可以由专家系统智能控制，实现炉子工况和熔炼参数的全程自动控制；(2)球化处理过程中， 转包内的铁液可以在旋转叉车上完成球化处理、铁液转运、向专用浇注电炉内倾倒等动作；(3)绝热涂料制备过程中，可以由离心机组自带的涂料自动化配置搅拌系统加工成合格涂料随时备用；(4)承口芯的安装可以通过机器人或者机械手进行等。由此，有利于节省人力物力，提高球墨铸铁管的生产效率。
以上所述的仅是本发明的一些实施方式。对于本领域的普通技术人员来说，在不脱离本发明创造构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。

Claims (14)

  1. 球墨铸铁管的制备工艺，其特征在于，包括如下步骤：
    S1、铁液的制备：将炉料熔炼成原铁液并过热至不小于1500℃，根据铁液化学成分的设定值调整原铁液的化学成分组成；
    S2、球化处理：利用球化剂对已调整好化学成分组成的原铁液进行球化处理，并将球化处理后的铁液注入球墨铸铁专用浇注电炉，利用所述球墨铸铁专用浇注电炉将铁液的浇注温度保持不小于铁液的临界温度；
    S3、涂料热模法离心铸造：对喷涂的绝热涂料已干燥的热管模完成上承口芯后，驱动管模转动，并在管模转动的离心力达到离心力设定值时，将球墨铸铁专用浇注电炉中的铁液经定量包注入管模中，并在浇注过程中对铁液进行随流孕育处理和对管模进行冷却处理，浇注完成后，待凝固成形的球墨铸铁管毛坯冷却到设定温度时，将球墨铸铁管毛坯从管模中拔出。
  2. 根据权利要求1所述的球墨铸铁管的制备工艺，其特征在于，所述离心力设定值不小于80G，且不高于110G。
  3. 根据权利要求1所述的球墨铸铁管的制备工艺，其特征在于，凝固成形的球墨铸铁管毛坯冷却到的所述设定温度为760～830℃。
  4. 根据权利要求1所述的球墨铸铁管的制备工艺，其特征在于，步骤S2中，利用所述球墨铸铁专用浇注电炉将铁液的浇注温度保持不小于铁液的临界温度，是通过将球墨铸铁专用浇注电炉中的保温温度设定为1430～1480℃实现的。
  5. 根据权利要求1～4任一项所述的球墨铸铁管的制备工艺，其特征在于，所述球化剂为镁锭，所述铁液化学成分的设定值为：C为3.4～3.7％、Si为2.0～2.6％，
    所述根据铁液化学成分的设定值调整原铁液的化学成分组成包括：
    基于上述设定值调整原铁液中的碳和硅的质量分数，以使原铁液中碳的质量分数不高于3.7％，且使碳当量达到共晶成分或使碳当量达到4.1％～4.3％。
  6. 根据权利要求5所述的球墨铸铁管的制备工艺，其特征在于，步骤S2中，采用转包法对已调整好化学成分组成的原铁液进行球化处理，其中， 镁锭球化剂的用量为原铁液重量的0.10～0.20％。
  7. 城镇高压燃气管线用球墨铸铁管的制备工艺，其特征在于，包括如下步骤：
    利用权利要求1～6任一项所述的制备工艺，制备球墨铸铁管毛坯；
    对所述球墨铸铁管毛坯进行退火处理；
    对退火后的球墨铸铁管毛坯进行精整加工；
    根据待铺设燃气管线的设计输送压力设定球墨铸铁管毛坯的试验压力，对精整加工后的球墨铸铁管毛坯进行气密性试验，其中，试验压力不小于待铺设燃气管线的设计输送压力的1.20倍。
  8. 根据权利要求7所述的城镇高压燃气管线用球墨铸铁管的制备工艺，其特征在于，在所述退火处理之前还包括如下步骤：
    对制备的球墨铸铁管毛坯的外壁进行清刷、吹洗；
    对外壁清刷、吹洗干净后的球墨铸铁管毛坯进行超声波无损检测，确定球墨铸铁管毛坯的球化级别是否合格以及球墨铸铁管毛坯管体是否有铸造缺陷和其它损伤缺陷。
  9. 根据权利要求7或8所述的城镇高压燃气管线用球墨铸铁管的制备工艺，其特征在于，所述退火处理的退火温度为780～850℃，退火时间为20～40min。
  10. 根据权利要求9所述的城镇高压燃气管线用球墨铸铁管的制备工艺，其特征在于，在所述退火处理之后、精整加工之前还包括如下步骤：
    对退火后的球墨铸铁管毛坯的外表面进行喷锌。
  11. 根据权利要求10所述的城镇高压燃气管线用球墨铸铁管的制备工艺，其特征在于，在对精整加工后的球墨铸铁管毛坯进行气密性试验之后还包括如下步骤：
    对气密性试验合格的球墨铸铁管毛坯的内壁和外壁涂覆防护及功能性涂层。
  12. 根据权利要求7～11任一项所述的城镇高压燃气管线用球墨铸铁管的制备工艺制得的城镇高压燃气管线用球墨铸铁管。
  13. 根据权利要求12所述的城镇高压燃气管线用球墨铸铁管，其特征在于，所述城镇高压燃气管线用球墨铸铁管应用于铺设输送压力为0.4～6.0MPa的燃气管线。
  14. 根据权利要求12所述的城镇高压燃气管线用球墨铸铁管，其特征在于，所述城镇高压燃气管线用球墨铸铁管连接时采用柔性机械密封接口，连接时所用密封胶圈的材料选自氢化丁腈橡胶、丙烯酸酯橡胶、氟橡胶、氟硅橡胶或聚四氟乙烯。
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