A method for reducing inclusions in the socket of ductile iron pipes

Abstract

A method for reducing inclusions at the socket of a ductile iron pipe comprises the following steps: in step S1, selecting a suitable waste ductile iron pipe (60) according to the location where inclusion defects occur at the socket of the ductile iron pipe; obtaining a required fusible slag blocking ring (10) by axial cutting and mechanical processing of the pipe diameter; in step S2, inserting the fusible slag blocking ring (10) from the end portion of a core head (20) at the socket end and sleeved on the location where the defect occurs on the outer surface of the core head (20) at the socket end to assemble a core head kit for centrifugal casting; and in step S3, installing the core head kit on a centrifugal casting outer mold (30) for mold closing and casting. By utilizing the material, structure, and cost advantages of waste ductile iron pipes, a fusible slag blocking ring of precise size is manufactured and sleeved on the location where stubborn inclusion defects are prone to occur, thereby physically blocking the floating behavior of molten iron slag toward the center and, in combination with the influence on the floating time and the new slag formation mechanism, eliminating the socket inclusion defects of the centrifugal casting product of the ductile iron pipe at a fixed point.

Description

Technical Field

[0001] The invention relates to the technical field of centrifugal casting of ductile iron pipes, in particular to a method for reducing inclusions in the socket of a ductile iron pipe. Background Art

[0002] During the centrifugal casting process of ductile iron pipes, the part most prone to slag inclusions is the socket, especially when large-diameter ductile iron pipes are produced by the hot mold method. This inclusion situation is most prominent and sometimes causes batch quality problems.

[0003] Analysis shows that the reason why batch inclusion defects are more likely to occur in the bell part than in other parts is mainly because the wall thickness of the bell part is larger. Under the action of centrifugal force, the impurities in the molten iron in the thicker wall part have more time to float to the center, which makes the bell part more likely to have slag inclusion problems.

[0004] At present, the strategies adopted in production to solve the problem of inclusions in the socket of ductile iron pipes mainly focus on smelting slag removal and controlling the pouring process, especially reducing the inclusions in the socket by controlling the pouring position and optimizing the pouring time of the socket, but the effect is limited. Summary of the Invention

[0005] Based on the above problems, the present invention provides a method for reducing inclusions in the socket of ductile iron pipes. The material, structure and cost advantages of waste ductile iron pipes are utilized to produce a fusible slag-blocking ring of precise size. Before centrifugal casting, the ring is sleeved on the outer surface of the core head at the socket end, corresponding to the position where stubborn inclusion defects frequently appear in the ductile iron pipe. The fusible slag-blocking ring physically blocks the floating behavior of molten iron slag toward the center, and combines this with the influence on the floating time and the new slag formation mechanism to specifically eliminate the socket inclusion defects of centrifugal casting products of ductile iron pipes.

[0006] The objectives of the present invention are achieved through the following technical solutions.

[0007] A method for reducing inclusions in the socket of a ductile iron pipe comprises the following steps:

[0008] S1. Fabrication of fusible slag ring

[0009] According to the wall thickness of the location where the inclusion defect occurs in the socket of the ductile iron pipe, that is, the distance between the outer surface of the core head at the socket end in the casting cavity corresponding to the location and the inner surface of the centrifugal casting outer mold, suitable waste ductile iron pipes are selected, and the required fusible slag ring is obtained by axial cutting and mechanical processing of the pipe diameter;

[0010] S2. Installation of fusible slag ring

[0011] Inserting the fusible slag ring produced in step S1 from the end portion of the bell end core head and sleeved on the defect occurrence location on the outer surface of the bell end core head corresponding to the defect occurrence location to assemble the core head kit for centrifugal casting;

[0012] Wherein, when the fusible slag-blocking ring cannot be inserted from the end portion of the bell-end core head due to its small inner diameter, the fusible slag-blocking ring is first cut into two half-rings, and then the two half-rings are sleeved on the defect-occurring portion of the outer surface of the bell-end core head corresponding to the defect, and then the two half-rings are connected at the butt joint, or the two half-rings are fixed by relying on the groove on the outer surface of the bell-end core head;

[0013] S3.Mold closing and pouring

[0014] The core head kit assembled in step S2 is installed to the socket end of the centrifugal casting outer mold, the end cover is tightened, the mold is assembled, and preparations are made for pouring; the molten cast iron is poured into the high-speed rotating mold through a ladle. Under the action of high-speed centrifugation, the fusible slag ring acts as a physical barrier to the molten iron slag floating toward the center. At the same time, under the action of the high temperature of the molten cast iron, the fusible slag ring is fused with the molten cast iron, and a complete ductile iron pipe casting blank is obtained after cooling and solidification.

[0015] Preferably, in the above method, in step S1, the location where the inclusion defect occurs in the socket of the ductile iron pipe is one or more locations where the pipe wall at the socket end is thickest.

[0016] Preferably, in the above method, in step S1, the waste ductile iron pipe is first axially cut to obtain a ring piece of suitable width, and then the inner diameter and / or outer diameter of the ring piece is cut to obtain a fusible slag ring suitable for the pipe diameter and wall thickness.

[0017] Preferably, in the above method, during the cutting process, the chips generated by the cutting process are collected, washed and further crushed, the crushed ductile iron fine particles are wrapped with iron sheets and rolled into round bars, the two ends of the round bars are sealed and then bent into a fusible slag-resistant core tube that can be mounted on the outer surface of the core head at the socket end, and the fusible slag-resistant core tube is mounted on at least one defect location corresponding to the outer surface of the core head at the socket end.

[0018] Preferably, in the above method, the at least one defect occurrence location refers to a location where no fusible slag-blocking ring suitable for the pipe diameter is available.

[0019] Preferably, in the above method, the iron sheet used to make the fusible slag core tube has a thickness of 0.6 mm or less, and the ductile iron fine particles crushed from the chips have an average size of 3 mm or more.

[0020] Preferably, in the above method, in step S2, after the fusible slag ring is sleeved on the outer surface of the bell end core head, the gap between the inner surface of the fusible slag ring and the outer surface of the bell end core head at the sleeved position is 1-3 mm.

[0021] Preferably, in the above method, in step S2, the fusible slag-blocking rings with different wall thicknesses are sleeved on the outer surface of the core head at the socket end to correspond to different degrees of defect occurrence, and the degree of defect occurrence at least includes the thickness of inclusions.

[0022] Preferably, in the above method, in steps S2 to S3, in-mold spheroidization is also used to further control the generation of magnesium slag to reduce inclusions.

[0023] Preferably, in the above method, the in-mold spheroidizing means includes clamping a plurality of spheroidizing cored tubes or spheroidizing cored wires axially on the outer surface of the core head at the socket end before or after the fusible slag ring is sleeved.

[0024] Beneficial effects:

[0025] The method for reducing inclusions in the socket of ductile iron pipes provided by the present invention utilizes the material, structure and cost advantages of waste ductile iron pipes to produce a fusible slag blocking ring of precise size. Before centrifugal casting, the ring is sleeved on the outer surface of the core head at the socket end, corresponding to the position where stubborn inclusion defects frequently appear in the ductile iron pipe. The fusible slag blocking ring is used to physically block the floating behavior of molten iron slag toward the center, and the influence on the floating time and the new slag formation mechanism is combined to specifically eliminate the socket inclusion defects of centrifugal casting products of ductile iron pipes. This solves the problem of socket inclusions that has plagued production for many years, improves the as-cast density of the socket part, and ensures the casting qualification rate of ductile iron pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the processing of waste ductile iron pipes in the method for reducing inclusions in the socket of ductile iron pipes provided by an embodiment of the present invention.

[0027] Figure 2 It is a schematic diagram of mold assembly in the method for reducing inclusions in the socket of a ductile iron pipe provided by an embodiment of the present invention.

[0028] Figure 3 It is a schematic diagram of cutting and splicing a fusible slag ring in the method for reducing inclusions in the socket of a ductile iron pipe provided by an embodiment of the present invention.

[0029] Figure 4 It is a schematic diagram of the structure of the fusible slag core tube in the method for reducing inclusions in the socket of a ductile iron pipe provided by an embodiment of the present invention.

[0030] The components represented by the reference numerals in the figure are:

[0031] Fusible slag ring-10;

[0032] Socket end core head - 20;

[0033] Centrifugal casting outer mold-30;

[0034] Fusible slag core tube 40, iron sheet 41, ductile iron fines 42;

[0035] Liquid iron chute -50;

[0036] Waste ductile iron pipe-60. DETAILED DESCRIPTION

[0037] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. It should be noted that these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. The present disclosure can be implemented in various forms and should not be limited by the embodiments described herein.

[0038] Example 1

[0039] See also Figure 1 、 Figure 2 The present embodiment provides a method for reducing inclusions in the socket of a ductile iron pipe, comprising the steps of:

[0040] S1. Production of fusible slag ring 10

[0041] According to the wall thickness of the location where the inclusion defect occurs in the socket of the ductile iron pipe (i.e., the distance between the outer surface of the socket end core head 20 in the casting cavity corresponding to that location and the inner surface of the centrifugal casting outer mold 30), a suitable waste ductile iron pipe 60 is selected, and the required fusible slag ring 10 is obtained by axial cutting and mechanical processing of the pipe diameter.

[0042] The location where inclusion defects occur in the socket of ductile iron pipes is generally the thicker part of the pipe wall at the socket end (such as D3 surface), and there may be more than one location. There may be inclusion defects of varying degrees in one or more parts of the thickest part of the pipe wall, which are manifested in the thickness or looseness of the slag inclusion area.

[0043] In this step, the waste ductile iron pipe 60 is first axially cut to obtain ring segments of appropriate width, and then the inner and / or outer diameters of the ring segments are cut to obtain the fusible slag-blocking ring 10 of appropriate pipe diameter and wall thickness. Waste ductile iron pipes 60 are widely available. If they are rusted and have been stored for a long time, they need to be polished, or a rough machining step can be added during machining to remove the oxide layer.

[0044] S2. Installation of fusible slag ring 10

[0045] The fusible slag-blocking ring 10 produced in step S1 is inserted into the end portion of the bell end core head 20 and is sleeved on the defect occurrence location corresponding to the outer surface of the bell end core head 20 to assemble a core head kit for centrifugal casting.

[0046] Figure 2 Two fusible slag-blocking rings 10 are shown in FIG. 1 , wherein the right fusible slag-blocking ring 10 can be easily inserted into the designated position from the end portion of the core head 20 at the end of the socket, and the left fusible slag-blocking ring 10 cannot be directly inserted from the end portion of the core head 20 at the end of the socket due to its small inner diameter. In this case, Figure 3 As shown, the fusible slag ring 10 is first cut into two half rings, and then the two half rings are placed on the defect location corresponding to the outer surface of the socket end core head 20, and then the two half rings are welded together at the joints. If the two half rings can be naturally fixed by relying on the grooves on the outer surface of the socket end core head 20, welding is not necessary.

[0047] Preferably, after the fusible slag-blocking ring 10 is sleeved on the outer surface of the socket end core head 20 in this step, the gap between the inner surface of the fusible slag-blocking ring 10 and the outer surface of the socket end core head 20 at the sleeved position is 1-3 mm. Such a gap ensures the smoothness of the sleeve and will not affect the socket end core head 20 during the sleeve and the subsequent centrifugal rotation.

[0048] In addition, if Figure 4 As shown, in the process of cutting the inner diameter and / or outer diameter of the ring segment in the aforementioned step S1, the chips generated in the cutting process are collected, washed and further crushed, and the crushed ductile iron fine particles 42 are wrapped with iron sheets 41 and rolled into round bars. The two ends of the round bars are sealed and bent into a fusible slag-blocking core tube 40 that can be sleeved on the outer surface of the socket end core head 20, and the fusible slag-blocking core tube 40 is sleeved on the outer surface of the socket end core head 20 corresponding to at least one defect occurrence site. The at least one defect occurrence site mentioned here refers to a site where there is no fusible slag-blocking ring 10 of a suitable pipe diameter that can be used. In this way, even when there is no suitable section of waste ductile iron pipe available, it is easy to make a useful slag-blocking part. Preferably, the iron sheet 41 used to make the fusible slag-blocking core tube 40 has a thickness of less than 0.6 mm, and the ductile iron fine particles 42 crushed by the chips have an average size of more than 3 mm. The thinner the iron sheet 41 is, the more negligible its effect on the composition of the molten iron is. Here, the average size of the ductile iron fine particles 42 generally refers to the average value of the maximum length. The chips are broken into fine particles larger than 3 mm and will not melt too quickly in the molten iron. The upper limit size of the crushing can be adjusted as long as it does not affect the bending of the fusible slag core tube.

[0049] According to the manufacturing method of the fusible slag-blocking core tube 40 described above, an alternative method to the present invention can also be provided, in which the fusible slag-blocking ring 10 is not manufactured from beginning to end, and only the chips generated by the machining workshop during the processing of ductile iron castings are collected to make the fusible slag-blocking core tube 40 to replace the fusible slag-blocking ring 10.

[0050] Preferably, in this step, the fusible slag-blocking ring 10 of varying widths and / or wall thicknesses is sleeved on the outer surface of the socket-end core head 20 to correspond to varying degrees of defect occurrence, wherein the degree of defect occurrence at least includes inclusion thickness. When a fusible slag-blocking core tube 40 is used, multiple fusible slag-blocking core tubes 40 of varying cross-sectional specifications (not necessarily circular) may also be used.

[0051] S3.Mold closing and pouring

[0052] The core head kit assembled in step S2 is installed to the socket end of the centrifugal casting outer mold 30, the end cover is tightened, the mold is assembled, and preparations are made for pouring; the molten iron is poured into the high-speed rotating mold through a ladle. Under the action of high-speed centrifugation, the fusible slag ring 10 acts as a physical barrier to the molten iron slag floating toward the center. At the same time, under the action of the high temperature of the molten iron, the fusible slag ring 10 is fused with the molten iron, and a complete ductile iron pipe casting blank is obtained after cooling and solidification.

[0053] The mold closing and pouring can be carried out according to the mature process in this field, especially controlling the pouring position of the molten iron chute 50 and the pouring time of the socket end.

[0054] In addition, according to the formation mechanism of molten iron slag, after the cast iron liquid is poured into the mold, a part of the oxidized magnesium elements will form new magnesium slag. Therefore, in addition to the means provided above, it is also optional to cooperate with the in-mold spheroidization means in steps S2 to S3 to further control the generation of magnesium slag to reduce inclusions, especially to grasp the spheroidization timing of the socket end. A scientific method is to clamp multiple spheroidizing core tubes or spheroidizing core wires axially and preferably evenly on the outer surface of the core head 20 of the socket end before or after the fusible slag ring 10 is installed. In this way, the cast iron liquid completes the last step of spheroidization when it contacts the spheroidizing material at the socket end, thereby reducing the magnesium slag that is proliferated due to premature spheroidization timing.

[0055] In summary, the method for reducing inclusions in the socket of ductile iron pipes provided in this embodiment mainly utilizes the material, structure and cost advantages of waste ductile iron pipes to produce a precisely sized fusible slag blocking ring 10. Before centrifugal casting, it is placed on the outer surface of the core head at the socket end, corresponding to the location where stubborn inclusion defects frequently appear in the ductile iron pipe. The fusible slag blocking ring 10 physically blocks the floating behavior of molten iron slag toward the center, and combines this with the influence on the floating time and the new slag formation mechanism to specifically eliminate the socket inclusion defects of the centrifugal casting products of ductile iron pipes. This solves the problem of socket inclusions that has plagued production for many years, improves the as-cast density of the socket area, and ensures the qualified rate of ductile iron pipe casting. According to the cutting inspection of the casting, the method of the present invention can significantly reduce the thickness of stubborn inclusion defects that frequently appear in production to the qualified standard, or even completely eliminate them in some areas. After multiple rounds of testing, no defective areas with a density less than 90% of the theoretical value appear on the entire socket end.

[0056] The foregoing description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed herein are intended to be encompassed within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for reducing inclusions in the socket of a ductile iron pipe, characterized in that: Including steps: S1. Production of fusible slag ring (10) According to the wall thickness of the location where the inclusion defect occurs at the socket of the ductile iron pipe, that is, the distance between the outer surface of the core head (20) at the socket end in the casting cavity corresponding to the location and the inner surface of the centrifugal casting outer mold (30), a suitable waste ductile iron pipe (60) is selected, and the required fusible slag ring (10) is obtained by axial cutting and mechanical processing of the pipe diameter; The location where the inclusion defect occurs in the socket of the ductile iron pipe is one or more locations where the pipe wall at the socket end is thickest; S2. Installation of fusible slag ring (10) Inserting the fusible slag-blocking ring (10) produced in step S1 from the end portion of the bell end core head (20), and sleeved on the defect occurrence location corresponding to the outer surface of the bell end core head (20), so as to assemble a core head kit for centrifugal casting; The fusible slag-blocking ring (10) with different wall thicknesses is sleeved on the outer surface of the socket end core head (20) to correspond to different defect occurrence degrees, wherein the defect occurrence degree at least includes inclusion thickness; Wherein, when the fusible slag-blocking ring (10) cannot be inserted from the end portion of the bell end core head (20) due to its small inner diameter, the fusible slag-blocking ring (10) is first cut into two half-rings, and then the two half-rings are sleeved on the defect-occurring portion of the outer surface of the bell end core head (20) corresponding to the defect, and then the two half-rings are welded to the butt joint, or the two half-rings are fixed by relying on the groove on the outer surface of the bell end core head (20); After the fusible slag-blocking ring (10) is sleeved on the outer surface of the bell end core head (20), a gap between the inner surface of the fusible slag-blocking ring (10) and the outer surface of the bell end core head (20) at the sleeved portion is 1-3 mm; S3.Mold closing and pouring The core head kit assembled in step S2 is installed on the socket end of the centrifugal casting outer mold (30), the end cover is tightened, the mold is assembled, and preparations for pouring are made; the cast iron liquid is poured into the high-speed rotating mold through a ladle, and under the action of high-speed centrifugation, the fusible slag ring (10) plays a physical blocking role against the molten iron slag floating toward the center, and at the same time, under the action of the high temperature of the cast iron liquid, the fusible slag ring (10) is fused with the cast iron liquid, and after cooling and solidification, a complete ductile iron pipe casting blank is obtained.

2. The method for reducing inclusions in the socket of a ductile iron pipe according to claim 1, characterized in that: In step S1, the waste ductile iron pipe (60) is first axially cut to obtain a ring piece of suitable width, and then the inner diameter and / or outer diameter of the ring piece is cut to obtain a fusible slag-blocking ring (10) suitable for the pipe diameter and wall thickness.

3. The method for reducing inclusions in the socket of a ductile iron pipe according to claim 2, characterized in that: During the cutting process, the chips generated during the cutting process are collected, washed and further crushed, and the crushed ductile iron fine particles (42) are wrapped with iron sheets (41) and rolled into round bars. The two ends of the round bars are sealed and bent into a fusible slag-resistant core tube (40) that can be sleeved on the outer surface of the socket end core head (20), and the fusible slag-resistant core tube (40) is sleeved on at least one defect-occurring location on the outer surface of the socket end core head (20).

4. A method for reducing inclusions in the socket of a ductile iron pipe according to claim 3, characterized in that: The at least one defect occurrence location refers to a location where no fusible slag blocking ring (10) suitable for the pipe diameter can be used.

5. The method for reducing inclusions in the socket of a ductile iron pipe according to claim 3, characterized in that: The iron sheet (41) used to make the fusible slag core tube (40) has a thickness of less than 0.6 mm, and the ductile iron fine particles (42) crushed from the chips have an average size of more than 3 mm.

6. A method for reducing inclusions in the socket of a ductile iron pipe according to any one of claims 1 to 5, characterized in that: In steps S2 to S3, in-mold spheroidization is also used to further control the generation of magnesium slag to reduce inclusions.

7. The method for reducing inclusions in the socket of a ductile iron pipe according to claim 6, characterized in that: The in-mold spheroidization means comprises clamping a plurality of spheroidized cored tubes or spheroidized cored wires axially on the outer surface of the socket end core head (20) before or after the fusible slag ring (10) is sleeved.

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