Centrifugal casting ductile iron pipe tube mold forming mold and method

Abstract

The application provides a pipe mold forming die and method for centrifugal casting nodular cast iron pipe, and belongs to the technical field of nodular cast iron pipe production. The pipe mold forming die comprises a upsetting punch, an extrusion punch and a concave die. The forming cavity of the concave die comprises, from top to bottom, a socket forming area, a straight section guiding area and a spigot forming area. The inner surface structure of the socket forming area is matched with the outer surface structure of the pipe mold socket end. The outer surface structure of the upsetting punch is matched with the inner surface structure of the pipe mold socket end. The socket forming area and the upsetting punch form the pipe mold socket end in the upsetting process. The bottom of the spigot forming area is detachably connected with a pad. The spigot forming area and the pad form the pipe mold spigot end and inner flange plate in the upsetting process. The straight section guiding area and the extrusion punch form the pipe mold straight pipe in the reverse extrusion process. The application can realize one-time forming of the pipe mold socket end, spigot end and inner flange plate, greatly shortens the production cycle and guarantees the pipe mold forming quality.

Description

Technical Field

[0001] This invention belongs to the field of ductile iron pipe production technology, and particularly relates to a pipe mold forming die and method for centrifugal casting of ductile iron pipes. Background Technology

[0002] Centrifugally cast ductile iron pipes are core components of modern water supply and gas transmission pipeline systems, and their production relies on high-precision, long-life metal pipe molds. Traditionally, large-diameter (typically ≥DN800) pipe molds are manufactured using a "split forging + welding assembly" process: the pipe mold is disassembled into a straight section and a flared socket end for free forging, then welded together, and finally the inner flange structure of the spigot end is welded.

[0003] Using the above process, the complex inner flange structure at the spigot end cannot be directly formed by free forging and must rely on subsequent welding. However, the heat-affected zone of the weld is prone to becoming a weak point in the microstructure and properties. Under the periodic impact of high-temperature molten iron and thermal fatigue loads of rapid heating and cooling, cracks are easily initiated in the weld area, becoming the main risk point leading to the early failure of the pipe mold. Summary of the Invention

[0004] To address the deficiencies or shortcomings in existing technologies, this invention provides a pipe mold forming die and method for centrifugal casting of ductile iron pipes, which can achieve one-time forming of the pipe mold socket end, spigot end and inner flange, significantly shortening the production cycle while ensuring the forming quality of the pipe mold.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, embodiments of the present invention provide a pipe mold forming die for centrifugal casting of ductile iron pipes, including an upsetting punch, an extrusion punch, and a die. The die has a forming cavity inside, which, from top to bottom, comprises a socket forming area, a straight section guiding area, and a spigot forming area. The inner surface structure of the socket forming area is adapted to the outer surface structure of the socket end of the pipe mold, and the outer surface structure of the upsetting punch is adapted to the inner surface structure of the socket end of the pipe mold. The socket forming area and the upsetting punch form the socket end of the pipe mold during the upsetting process. A pad with an outer contour adapted to the inner flange is detachably connected to the bottom of the spigot forming area. The spigot forming area and the pad form the spigot end and the inner flange of the pipe mold during the upsetting process. The straight section guiding area and the extrusion punch form the straight pipe of the pipe mold during the reverse extrusion process.

[0006] Furthermore, the straight section guide area is located below the socket forming area and is smoothly connected to the bottom of the socket forming area. The inner diameter of the straight section guide area is the same as the outer diameter of the straight pipe of the pipe mold.

[0007] Furthermore, the insertion forming area is located at the bottom of the forming cavity, and the inner diameter of the insertion forming area is the same as the inner diameter of the straight section guide area.

[0008] Furthermore, the pad is a cylindrical structure, the outer diameter of the pad is the same as the inner diameter of the socket forming area, and the upper surface of the pad is provided with an inner flange cavity that matches the outline shape of the inner flange.

[0009] Furthermore, the upsetting punch has an inverted frustum structure, the taper of the upsetting punch is adapted to the taper of the die socket forming area, and the maximum outer diameter of the upsetting punch is smaller than the maximum inner diameter of the die socket forming area.

[0010] Furthermore, the upsetting punch consists of an upsetting section and a forming section along its axial direction from bottom to top. The upsetting section has a cylindrical structure with a flat bottom surface, and the outer wall contour of the forming section is the same as the inner wall contour of the mold socket.

[0011] Furthermore, the extrusion punch consists of an extrusion section, a transition section, and a straight rod section along its axial direction from bottom to top. The extrusion section has an inverted frustum-shaped structure, the transition section has a cylindrical structure, the diameter of the transition section is smaller than the inner diameter of the straight section guide area of ​​the forming cavity, the bottom end of the straight rod section is connected to the top surface of the transition section, and the top end of the straight rod section is connected to the movable crossbeam of the extruder.

[0012] Furthermore, the upsetting section of the upsetting punch and the extrusion section of the extrusion punch satisfy the length condition a = kb, where a is the length of the upsetting section, b is the length of the extrusion section, k is the filling guarantee coefficient, and k ≥ 1.1.

[0013] Furthermore, an ejection mechanism is provided below the die cavity. The ejection mechanism includes an ejector rod and a driving device. The bottom end of the ejector rod is fixedly connected to the output end of the driving device. An ejection hole is provided at the bottom of the die cavity. The ejection hole is coaxially arranged with the molding cavity, and the inner diameter of the ejection hole is smaller than the inner diameter of the molding cavity. The ejector rod passes through the bottom ejection hole, and the top end of the ejector rod contacts the bottom surface of the pad block.

[0014] Secondly, embodiments of the present invention provide a method for forming a pipe mold for centrifugal casting ductile iron pipes, utilizing a pipe mold forming die for centrifugal casting ductile iron pipes as described above, including the following steps: Step 1: Sawing to obtain a cylindrical billet, heating the billet to ensure that the core and surface temperatures of the billet are uniform and reach the initial forging temperature; Step 2: Place the pad at the bottom of the forming cavity, place the heated blank inside the forming cavity, spray lubricant evenly on the upper and lower end faces of the blank, and the upsetting punch moves down to upset the blank, forming the socket end, spigot end and inner flange of the tube mold. After upsetting is completed, the upsetting punch returns. Step 3: Replace the extrusion punch and position it in the working position. The extrusion punch moves down to perform reverse extrusion on the upset billet. After extrusion reaches the set stroke, it stops to form a straight tube of the tube die. After extrusion is completed, the extrusion punch returns. Step 4: Eject the formed tube mold along with the spacer block from the cavity mold, remove the spacer block, and perform heat treatment and finishing on the formed tube mold.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: To achieve one-time forming of the socket end, spigot end, and inner flange of the pipe mold, the forming cavity inside the die of this invention consists of a socket forming area, a straight section guiding area, and a spigot forming area arranged axially from top to bottom. The inner surface structure of the socket forming area is the same as the outer surface structure of the socket end of the pipe mold, and the outer surface structure of the upsetting punch is the same as the inner surface structure of the socket end of the pipe mold. A pad with an outline that matches the inner flange is detachably connected to the bottom of the spigot forming area. The socket end, spigot end, and inner flange of the pipe mold can be formed in one step during the upsetting process using the upsetting punch, and the straight pipe of the pipe mold can be formed during the reverse extrusion process using the extrusion punch. This eliminates the need for welding the socket end, spigot end, and inner flange of the pipe mold as in the prior art, thus achieving one-time forming of the socket end, spigot end, and inner flange of the pipe mold. This significantly shortens the production cycle while ensuring the forming quality of the pipe mold. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the molding die in Embodiment 1 of the present invention; Figure 2 This is a front sectional view of the die in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the upsetting punch structure in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the extrusion punch structure in Embodiment 1 of the present invention; Figure 5 This is a comparison chart of the simulation results of the forming process under different k values ​​in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the tube mold forming process in Embodiment 2 of the present invention; Among them, 1. Upsetting punch; 101. Upsetting section; 102. Forming section; 2. Extrusion punch; 201. Extrusion section; 202. Transition section; 203. Straight rod section; 3. Die; 4. Spacer block; 5. Forming cavity; 501. Socket forming area; 502. Straight section guide area; 503. Insert forming area; 6. Ejector rod. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Example 1 A typical embodiment of the present invention provides a pipe mold forming die for centrifugal casting of ductile iron pipes, such as... Figure 1 As shown, it includes an upsetting punch 1, an extrusion punch 2, a die 3, a pad block 4, and an ejection mechanism. The die 3 has a forming cavity 5 extending through its upper and lower end faces. The forming cavity 5 is designed according to the geometric characteristics of the final die, such as... Figure 2 As shown, it is divided into three functional areas from top to bottom along its axial direction: socket forming area 501, straight section guiding area 502, and spigot forming area 503.

[0019] The socket forming area 501 is located at the uppermost end of the forming cavity 5 and is in the shape of an inverted cone flare. That is, the top opening diameter of the socket forming area 501 is larger than the bottom opening diameter. The inner surface structure of the socket forming area 501 is the same as the outer surface structure of the pipe mold socket end. It is used to accommodate and constrain the compressed metal in the upsetting process, so that it forms a preset flared shape, thereby integrally forming the socket end of the pipe.

[0020] The straight section guide area 502 is located below the socket forming area 501 and is smoothly connected to the bottom of the socket forming area 501. This section is a cylindrical straight hole structure, and its inner diameter is the same as the outer diameter of the straight pipe of the mold body. The straight section guide area 502 is not only used to define the outer contour of the middle section of the forming mold, but also to precisely guide the downward movement of the extrusion punch 2 during the reverse extrusion process to ensure coaxiality.

[0021] The spigot forming area 503 is located at the bottom of the forming cavity 5, and its diameter is the same as that of the straight section guide area 502. A pad 4 is placed and positioned at the bottom of the spigot forming area 503. The spigot forming area 503 and the pad 4 cooperate with each other to form the spigot end of the pipe and the inner flange.

[0022] The pad 4 is detachably installed in the insertion forming area 503 of the concave mold 3, and different pads 4 can be replaced according to the specifications of the pipe.

[0023] Specifically, the pad 4 has a cylindrical structure, and the outer diameter of the pad 4 is the same as the inner diameter of the insertion forming area 503 to ensure the positioning accuracy of the pad 4 under high pressure. The pad 4 can be inserted into the forming cavity 5 from the top opening of the forming cavity 5.

[0024] The upper surface of the pad 4 is provided with an inner flange cavity at the center. The outline shape of the inner flange cavity is perfectly matched with the geometric features of the inner flange at the end of the mold to be formed. Specifically, the inner flange cavity includes an annular groove for forming the radial protrusion of the flange and a tapered guide surface for forming the inner hole of the flange. The bottom of the inner flange cavity is a plane, corresponding to the bottom surface of the inner flange.

[0025] The design of the inner flange cavity allows the metal at the end of the billet to flow into and fill the cavity under the pressure of the upsetting punch 1 in the early stage of the upsetting process, thereby pre-forming a complete inner flange structure. This fundamentally changes the traditional manufacturing mode in which flanges are connected by welding or machining after the straight pipe is formed.

[0026] This invention utilizes an upsetting punch 1 to form a tapered socket through an upsetting process, and then uses an extrusion punch 2 to simultaneously extrude the straight section of the tube body and the inner cavity of the spigot end through a reverse extrusion process, achieving seamless overall forming.

[0027] Among them, such as Figure 3 As shown, the upsetting punch 1 has an inverted frustum structure. The taper of the upsetting punch 1 matches the taper of the socket forming area 501 of the die 3. The maximum outer diameter of the upsetting punch 1 is smaller than the maximum inner diameter of the socket forming area 501. Specifically, along its axial direction from bottom to top, there are upsetting section 101 and forming section 102. Upsetting section 101 has a cylindrical structure with a flat bottom surface. The outer wall contour of forming section 102 is the same as the inner wall contour of the pipe mold socket. In the initial process, the upsetting punch 1 descends vertically. The bottom surface of upsetting section 101 impacts and compresses the heated blank placed in the forming cavity 5, causing the blank to undergo upsetting deformation. The top of the blank forms the pipe mold socket contour under the extrusion of the outer wall of forming section 102 and the inner wall of the socket forming area 501, realizing the integral forming of the pipe mold socket.

[0028] like Figure 4 As shown, the extrusion punch 2 is a long rod-shaped structure, and its length is greater than that of the forming cavity 5. The extrusion punch 2 consists of an extrusion section 201, a transition section 202, and a straight rod section 203 along its axial direction from bottom to top. The extrusion section 201 is an inverted frustum-shaped structure. During the reverse extrusion stage, the lower surface of the extrusion section 201 contacts the billet and extrudes the billet. The conical lower surface of the extrusion section 201 can reduce the resistance at the initial contact and guide the metal flow. The transition section 202 is a cylindrical structure. The top of the extrusion section 201 is smoothly connected to the transition section 202. The diameter of the transition section 202 is smaller than the inner diameter of the straight guide area 502 of the forming cavity 5, so that a uniform annular gap for reverse extrusion of metal is formed between the two. The diameter of the transition section 202 is equal to the diameter of the upsetting section 101, so that the transition section 202 can be inserted into the forming hole formed by the upsetting punch 1 in the billet, which facilitates reverse extrusion of the billet. The bottom end of the straight rod section 203 is connected to the top surface of the transition section 202, and the top end is connected to the moving crossbeam of the extruder. After the upsetting process is completed, the extrusion punch 2 is driven to extend into the center of the billet, and the straight section of the tube mold body and the inner cavity of the spigot end are formed by reverse extrusion.

[0029] To ensure the continuity of molding and overcome the "inward curling (folding) of metal ends" defect commonly found in traditional reverse extrusion processes, the upsetting section 101 of the upsetting punch 1 and the extrusion section 201 of the extrusion punch 2 satisfy a specific proportional relationship in length, namely a = kb, where a is the length of the upsetting section 101, b is the length of the extrusion section 201, k is the filling guarantee coefficient, and k ≥ 1.1.

[0030] The physical meaning of this geometric constraint is that when the upsetting process is completed, the upsetting section 101 (length a) of the upsetting punch 1 occupies the main forming space of the upper part of the die 3, and presses the top of the blank into a plane through its end face. When the upsetting punch 1 is pushed upward and the extrusion section 201 (length b) of the extrusion punch 2 enters downward, since a≥1.1b, it means that the axial space occupied by the upsetting section 101 of the upsetting punch 1 is greater than the space occupied by the extrusion section 201 of the extrusion punch 2.

[0031] This spatial misalignment and redistribution of metal volume ensures a clear direction for metal flow during the transition from upsetting to reverse extrusion. Specifically, as the extrusion punch 2 descends, the metal at the top of the billet does not lose support due to the abrupt spatial change; instead, it is guided into the annular gap by the guiding cone surface of the extrusion punch 2. Because the filling guarantee coefficient k≥1.1 provides sufficient metal volume reserve, the radial extrusion force on the end metal is greater than its tendency to contract towards the center, effectively suppressing the defect of inward curling and folding of the metal.

[0032] Specifically, when k < 1, it means that the upsetting section 101 of the upsetting punch 1 is shorter than the extrusion section 201 of the extrusion punch 2. In this state, the volume of metal entering the top of the forming cavity 5 during the upsetting stage is insufficient, and a metal layer of sufficient thickness cannot be formed at the top of the forming cavity 5. When the extrusion punch 2 moves downward to perform reverse extrusion, due to the lack of sufficient radial support force on the top metal, the metal at the end of the blank will have a violent inward turning tendency along the chamfered surface of the extrusion punch 2, such as... Figure 5 The simulation results at k=0.9 show that the metal end exhibits obvious inward curling and folding, resulting in streamline breakage and structural defects in the inner cavity of the tube mold.

[0033] When ≥1.1, the upsetting section 101 of the upsetting punch 1 is significantly larger than the extrusion section 201 of the extrusion punch 2. This means that during the upsetting process in the first station, a sufficient volume of metal is pre-stacking on the upper part of the socket forming area 501 and the straight section guide area 502 of the forming cavity 5, forming a thick "metal source". Figure 5The simulation results at k=1.5 show that when the extrusion punch 2 moves downward, the thick metal layer provides sufficient resistance to curling, allowing the end metal to be completely constrained in the annular gap between the extrusion punch 2 and the inner wall of the die 3, flowing smoothly upward. The metal flow lines remain intact and continuous, and no more inward folding defects are generated. Therefore, k≥1.1 is the minimum critical value to ensure smooth metal flow and suppress inward curling defects. This proportional relationship constitutes the coordinated metal flow channel described in this invention.

[0034] The die 3 is provided with an ejection mechanism, which includes an ejector rod 6 and a drive device (such as a hydraulic cylinder or a pneumatic cylinder). The bottom end of the ejector rod 6 is fixedly connected to the output end of the drive device. The bottom of the die 3 is provided with an ejection hole, which is coaxially arranged with the molding cavity 5. The inner diameter of the ejection hole is smaller than the inner diameter of the molding cavity 5. The ejector rod 6 passes through the bottom ejection hole, and the top end of the ejector rod 6 contacts the bottom surface of the pad block 4.

[0035] When the reverse extrusion molding process is completed, after the extrusion punch 2 exits the molding cavity 5 of the die 3, the ejection mechanism is activated to eject the formed tube mold along with the pad block 4 from the bottom of the die 3 upwards, so that the part can be taken out and enter the next process.

[0036] By sequentially configuring the forming cavity inside the die from top to bottom along the axial direction as a socket forming area, a straight section guiding area, and a spigot forming area, the inner surface structure of the socket forming area is the same as the outer surface structure of the socket end of the pipe mold, and the outer surface structure of the upsetting punch is the same as the inner surface structure of the socket end of the pipe mold. The bottom of the spigot forming area is detachably connected to a pad whose shape is adapted to the inner flange. The socket end, spigot end, and inner flange of the pipe mold can be formed in one step during the upsetting process using the upsetting punch, and the straight pipe of the pipe mold can be formed in the reverse extrusion process using the extrusion punch. This eliminates the need for welding the socket end, spigot end, and inner flange of the pipe mold as in the prior art, achieving one-time forming of the socket end, spigot end, and inner flange of the pipe mold. This significantly shortens the production cycle while ensuring the forming quality of the pipe mold.

[0037] Example 2 This embodiment provides a method for forming pipe molds for centrifugally cast ductile iron pipes, utilizing a pipe mold forming device for centrifugally cast ductile iron pipes as described in Embodiment 1. Figure 6 As shown, it includes the following steps; Step S1: Billet preparation and heating First, high-purity, uniformly structured, high-quality alloy steel ingots or bars are selected as raw materials. Based on the volume and weight of the target tube mold, a band saw is used for precise cutting to obtain cylindrical blanks with flat end faces and dimensions that meet the requirements.

[0038] The cylindrical billet after cutting is fed into a medium-frequency induction heating furnace or a ring heating furnace for heating. The heating process requires strict control of the heating rate and holding time to ensure that the temperature of the core and surface of the billet is uniform and consistent, so as to avoid internal thermal stress cracking caused by excessive temperature difference.

[0039] In this embodiment, the billet is heated to the initial forging temperature range (e.g., 1100°C to 1200°C for a specific alloy steel). After heating, the billet should exhibit a uniform orange-yellow or bright yellow color, without overheating or underheating. If necessary, an infrared thermometer can be used to randomly check the surface temperature of the billet after it exits the furnace to ensure that its temperature meets the requirements for plastic forming.

[0040] Step S2: Upsetting and Pre-forming The heated billet is transferred to the upsetting station by a robotic arm or automatic conveyor. At this station, the die assembly has been pre-installed and a pad for forming the inner flange is placed at the bottom of the forming cavity.

[0041] Before upsetting, a layer of high-temperature glass lubricant is evenly sprayed onto the upper, lower, and side surfaces of the billet using a spraying device. This lubricant melts into a glassy film at high temperatures, effectively reducing the coefficient of friction between the billet and the mold, preventing material from sticking to the mold, and reducing the formation of oxide scale on the billet surface.

[0042] Subsequently, the moving crossbeam of the press drives the upsetting punch downwards, and the bottom end face of the upsetting punch contacts the top of the billet. At this time, the press speed is low to ensure smooth contact and avoid impact.

[0043] When the press speed is increased to the set value, the blank expands radially under the downward pressure of the punch, and its outer surface gradually fits into the socket forming area of ​​the die to form the conical socket shape of the tube mold.

[0044] As the punch continues to descend, the metal at the bottom of the blank is forced to flow downwards, gradually filling and completely filling the inner flange cavity of the bottom pad. This process ensures that the flange structure is precisely pre-formed during the upsetting stage.

[0045] After the upsetting punch descends to the preset end of its stroke, it is held under pressure for a short time to relieve internal stress in the metal. Then, the movable crossbeam drives the upsetting punch to return rapidly, preparing it for the next stage. At this point, a metal blank with a pre-formed socket profile and a complete inner flange at the bottom is formed inside the die cavity.

[0046] Step S3: Reverse extrusion molding After the upsetting punch returns, the die changing mechanism (such as a rotary die changing table or a transverse transfer mechanism) is activated to precisely move the extrusion punch and align it to the center position directly above the die.

[0047] After the extrusion punch is locked in the working position, the press moving beam moves down again, driving the extrusion punch into the die cavity.

[0048] During the downward movement of the extrusion punch, the guide cone at the bottom of the extrusion punch first contacts the center of the top of the upsetting billet. Due to the geometric constraint of a≥1.1b, the top of the billet has a sufficiently thick metal layer at this point. The radial pressure generated by the downward movement of the extrusion punch is effectively absorbed and balanced by this thick metal layer, preventing the end metal from turning inward toward the central axis of the punch (i.e., effectively suppressing the "inward folding" defect in traditional processes).

[0049] The metal flows smoothly upward in a laminar flow state along the annular gap between the straight guide section of the extrusion punch and die.

[0050] As the extrusion punch descends to the set end of its stroke, the straight section of the die body (deep hole section), the final outline of the socket end, and the inner flange structure of the spigot end are all formed simultaneously in one go.

[0051] After forming is completed, the extrusion punch returns under the drive of the movable crossbeam and exits the die cavity.

[0052] Step S4: Demolding and subsequent processing After all the forming processes are completed, the ejection mechanism at the bottom of the die is activated. The ejector rod moves upward, pushing the bottom end of the forming die and smoothly ejecting it from the inner cavity of the die and the bottom pad.

[0053] After demolding, the tube forgings need to undergo subsequent processing (heat treatment and finishing) to eliminate residual stress and achieve the final performance.

[0054] This method employs a continuous process route of "material feeding → heating → upsetting pre-forming → reverse extrusion final forming → demolding and subsequent processing". By precisely controlling the billet temperature, lubrication conditions, and punch stroke, the seamless integral forming of the flared end, straight body, and inner flange structure can be completed simultaneously in a single mold system.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pipe mold forming die for centrifugal casting of ductile iron pipes, characterized in that, The device includes an upsetting punch, an extrusion punch, and a die. The die has a forming cavity inside, which consists of a socket forming area, a straight section guide area, and a spigot forming area from top to bottom. The inner surface structure of the socket forming area is adapted to the outer surface structure of the socket end of the pipe mold, and the outer surface structure of the upsetting punch is adapted to the inner surface structure of the socket end of the pipe mold. The socket forming area and the upsetting punch form the socket end of the pipe mold in the upsetting process. The bottom of the spigot forming area is detachably connected to a gasket whose outline is adapted to the inner flange. The spigot forming area and the gasket form the spigot end of the pipe mold and the inner flange in the upsetting process. The straight section guide area and the extrusion punch form the straight pipe of the pipe mold in the reverse extrusion process.

2. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 1, characterized in that, The straight section guide area is located below the socket forming area and is smoothly connected to the bottom of the socket forming area. The inner diameter of the straight section guide area is the same as the outer diameter of the straight pipe of the pipe mold.

3. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 1, characterized in that, The insertion forming area is located at the bottom of the forming cavity, and the inner diameter of the insertion forming area is the same as the inner diameter of the straight section guide area.

4. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 1, characterized in that, The pad is a cylindrical structure, with the outer diameter of the pad being the same as the inner diameter of the socket forming area. The upper surface of the pad has an inner flange cavity at its center that matches the outline shape of the inner flange.

5. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 1, characterized in that, The upsetting punch has an inverted frustum shape, and the taper of the upsetting punch is adapted to the taper of the die forming area. Furthermore, the maximum outer diameter of the upsetting punch is smaller than the maximum inner diameter of the die forming area.

6. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 1, characterized in that, The upsetting punch consists of an upsetting section and a forming section along its axial direction from bottom to top. The upsetting section is a cylindrical structure with a flat bottom surface. The outer wall contour of the forming section is the same as the inner wall contour of the mold socket end.

7. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 6, characterized in that, The extrusion punch consists of an extrusion section, a transition section, and a straight rod section along its axial direction from bottom to top. The extrusion section has an inverted frustum-shaped structure, the transition section has a cylindrical structure, and the diameter of the transition section is smaller than the inner diameter of the straight section guide area of ​​the forming cavity. The bottom end of the straight rod section is connected to the top surface of the transition section, and the top end of the straight rod section is connected to the movable crossbeam of the extruder.

8. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 7, characterized in that, The upsetting section of the upsetting punch and the extrusion section of the extrusion punch satisfy the length condition a = kb, where a is the length of the upsetting section, b is the length of the extrusion section, k is the filling guarantee coefficient, and k ≥ 1.

1.

9. The pipe mold forming die for centrifugal casting of ductile iron pipes as described in claim 1, characterized in that, An ejection mechanism is provided below the die cavity. The ejection mechanism includes an ejector rod and a drive device. The bottom end of the ejector rod is fixedly connected to the output end of the drive device. An ejection hole is provided at the bottom of the die cavity. The ejection hole is coaxially arranged with the molding cavity, and the inner diameter of the ejection hole is smaller than the inner diameter of the molding cavity. The ejector rod passes through the bottom ejection hole, and the top end of the ejector rod contacts the bottom surface of the pad block.

10. A method for forming a pipe mold for centrifugal casting ductile iron pipes, utilizing a pipe mold forming die for centrifugal casting ductile iron pipes as described in any one of claims 1-9, characterized in that, Includes the following steps: Step 1: Sawing to obtain a cylindrical billet, heating the billet to ensure that the core and surface temperatures of the billet are uniform and reach the initial forging temperature; Step 2: Place the pad at the bottom of the forming cavity, place the heated blank inside the forming cavity, spray lubricant evenly on the upper and lower end faces of the blank, and the upsetting punch moves down to upset the blank, forming the socket end, spigot end and inner flange of the tube mold. After upsetting is completed, the upsetting punch returns. Step 3: Replace the extrusion punch and position it in the working position. The extrusion punch moves down to perform reverse extrusion on the upset billet. After extrusion reaches the set stroke, it stops to form a straight tube of the tube die. After extrusion is completed, the extrusion punch returns. Step 4: Eject the formed tube mold along with the spacer block from the cavity mold, remove the spacer block, and perform heat treatment and finishing on the formed tube mold.

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