Round-to-square core rod for hot expansion of steel pipe
By designing a mandrel for hot expansion of steel pipes that transforms round pipes into square ones, and using a hot expansion process to process round pipes into seamless square pipes in one go, the problems of large equipment investment and edge hardening risk are solved, and efficient and low-cost production of large-size seamless square pipes is achieved.
Patent Information
- Application Number
- CN202520190728.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-07
- Publication Date
- 2026-02-10
- Estimated Expiration
- 2035-02-07
AI Technical Summary
Existing seamless square tube manufacturing methods suffer from problems such as large equipment investment, high production costs, and easy occurrence of edge hardening and cracks, especially the difficulty in achieving the desired result through the hot expansion process of transforming round tubes into square tubes.
A mandrel for hot expansion of steel pipes that transforms from round to square was designed, including a guide section, a diameter-changing section, a round-to-square transformation section, a shaping section, and a straightening section. The round pipe is processed into a seamless square pipe in one step through a hot expansion process. The hot deformation internal forming method avoids the hardening and cracking risks of cold working.
It enables the production of seamless square tubes with large outer diameters and thick walls, reduces production costs, avoids additional heat treatment, and can be produced on existing equipment, thus having broad application prospects.
Smart Images
Figure CN223888819U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model belongs to the field of seamless square tube processing equipment, and particularly relates to a core rod for hot expansion of a round-to-square steel pipe. BACKGROUND
[0002] A seamless square tube is a square tube with a hollow cross section and no joints on the periphery, and is usually made of carbon structural steel or low-alloy structural steel. The seamless square tube is widely used in various fields due to its high strength, light weight, corrosion resistance, high temperature resistance and other excellent properties, such as structural components such as beams, columns and frames in the field of construction, transmission shafts and supports in the field of mechanical manufacturing, body frames and chassis in the field of automobiles, and structural components such as transformer housings in the field of electric power, and the skeleton, bulkhead and deck of the ship body in the field of shipbuilding.
[0003] The existing manufacturing methods for seamless square tubes include hot rolling, cold rolling (drawing) and extrusion. However, the hot rolling method is only suitable for producing medium and small diameter, thin-walled seamless square tubes, and the investment in hot rolling equipment is huge. Although the cold rolling (drawing) method has high precision, it has the disadvantages of small outer diameter and thin wall thickness of the produced square tube, and environmental pollution in the production process. Therefore, the current common manufacturing method for seamless square tubes is the extrusion method, which can produce large-diameter, thick-walled seamless square tubes and has the advantages of high production flexibility and various product specifications.
[0004] The medium-frequency hot expansion process is a common method for producing large-diameter seamless steel pipes, which has the characteristics of flexible production mode and easy organization of production, and is suitable for multi-variety, multi-specification and batch production. However, it is mainly used for the manufacturing method of seamless round pipes, and there is little research on the hot expansion process from round to square. Although the above-mentioned extrusion method can also process round pipes into seamless square tubes through extrusion in the round-to-square mode, the seamless square tubes are prone to hardening at the corners due to cold forming, which has the risk of cracking and requires additional normalizing heat treatment to eliminate internal stress, which increases the production cost. At present, there is no domestic manufacturer using the hot expansion process to produce seamless square tubes, mainly because the design of the core rod for hot expansion of seamless square tubes has high technical difficulty. UTILITY MODEL CONTENTS
[0005] In order to solve the above-mentioned problems of the prior art, the utility model provides a core rod for hot expansion of a round-to-square steel pipe, which enables the seamless square tube to be produced by hot expansion from a round pipe at one time, breaks through the existing processing technology, and realizes another manufacturing method of the seamless square tube.
[0006] The disclosed core rod for hot expansion of a round-to-square steel pipe comprises, from front to back, a guide section, a diameter-changing section, a round-to-square changing section, a shape-fixing section and a straightening section, and each adjacent section is integrally connected.
[0007] The guiding section is cylindrical, the diameter-changing section is frustum-shaped, the surface of the round-to-square section is a gradually changing curved surface transitioning from round to square, the shaping section is square column-shaped, and the straightening section is square column-shaped or frustum-shaped.
[0008] Preferably, the length L1 of the guide section is 100-500mm, and the diameter d1 of the guide section is 10-100mm smaller than the inner diameter of the raw material tube. This guide section can guide the raw material tube to be stably advanced to the diameter-changing section.
[0009] Further, the length L2 of the variable diameter section is (d2 - d1) / (2 × tgα), where d2 is the maximum diameter of the variable diameter section, d1 is the diameter of the guide section (1), and α is the angle between the inclined surface of the variable diameter section and the axis, where α is 6 to 13°.
[0010] The maximum diameter d2 of the variable diameter section is (A+B)×2 / π-2×S-k1, where A and B are the two outer side lengths of the seamless square tube (hot expanded square tube) section of the product, and S is the wall thickness of the seamless square tube (hot expanded square tube). The compensation value k1 for the change from round to square is -10~+100mm. Of course, the minimum diameter of the variable diameter section is the same as the diameter d1 of the guide section.
[0011] The variable diameter section can increase the diameter of the raw material round tube to produce plastic deformation. The variable diameter section of the above specifications can make the transformation process smooth and make the circumference of the enlarged round tube slightly smaller than the cross-sectional circumference of the required seamless square tube, which facilitates the next step of the deformation transformation from round to square.
[0012] Preferably, the length L3 of the circular-to-square transition section is 50–900 mm;
[0013] The connecting end face of the circular-to-square transition section near the diameter transition section is a circular surface, and the diameter d3 of the circular surface is equal to the maximum diameter d2 of the diameter transition section.
[0014] The connecting end face of the circular-to-square section near the fixed section is a rectangular surface. The two side lengths of the rectangular surface are a3 and b3, respectively. a3 = A - 2 × S - k2, b3 = B - 2 × S - k2, and the temperature compensation value k2 is 0 to 5 mm.
[0015] The circular-to-square transition section of this specification can reasonably guide the plastic transformation of the expanded circular tube from a circular annular section to a square annular section. The transformation resistance is reasonable and smooth, and it is not easy to generate extrusion marks inside the square tube.
[0016] Preferably, the length L4 of the shaping section is 50-500mm, and the two side lengths a4 and b4 of the cross section of the shaping section are equal to the two side lengths a3 and b3 of the rectangular surface of the circular-to-square transformation section, respectively.
[0017] The outer radius of the shaping section is r4 = RS, where R is the outer radius of the seamless square tube (thermally expanded square tube) of the product; the shaping section mainly serves to shape the square tube and maintain its plastic deformation.
[0018] Furthermore, the length L5 of the straightening section is 1000-3000 mm, and the two side lengths a50 and b50 of the connecting end face of the straightening section are equal to the two side lengths a4 and b4 of the cross section of the shaping section, respectively.
[0019] The lengths of the two sides of the other end face of the straightening section are a51 and b51, where a51 = a50 - k3 and b51 = b50 - k3. The demolding compensation value k3 is 0 to 8 mm. The straightening section (5) plays the role of straightening and guiding the square tube. When k3 is 0, the straightening section is a square column. When 0 < k3 ≤ 8 mm, the straightening section is a truncated pyramid with a certain taper. When the hot-expanded square tube (seamless square tube) is separated from the mandrel, the resistance gradually decreases, which facilitates the demolding of the product.
[0020] The outer radius r5 of the straightening section is equal to the outer radius r4 of the shaping section.
[0021] Preferably, the core rod has a hollow structure, which makes it lightweight, has low manufacturing cost, and also facilitates heat dissipation.
[0022] Through the above technical solutions, this utility model has at least the following beneficial effects:
[0023] The mandrel for hot expansion of round-to-square steel pipes described in this application, through precise redesign of the mandrel's structure and specifications, enables the one-time hot expansion of round pipes into seamless square pipes on a hot expansion machine. This breakthrough overcomes existing processing technologies and realizes an alternative manufacturing method for seamless square pipes. Because hot expansion employs a hot deformation internal forming processing method, the metal deformation resistance is low, enabling the production of seamless square pipes with large outer diameters and thick walls. It can overcome the dimensional limits of cold working and hot rolling. Compared to the currently widely used extrusion method, there is no work hardening phenomenon at the corners of the seamless square pipe, nor is there a risk of corner cracks due to internal stress. Therefore, no additional normalizing heat treatment is required. Furthermore, the production of seamless square pipes can be carried out by replacing the existing equipment (hydraulic propulsion pipe expander) with this mandrel, greatly reducing capital investment. This makes the mandrel for hot expansion of round-to-square steel pipes have excellent prospects for widespread application. Attached Figure Description
[0024] The technical solutions in the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of this utility model in a schematic manner. Therefore, they only show the components related to this utility model.
[0025] Figure 1 This is a schematic diagram of the overall structure of a mandrel for hot expansion of a round-to-square steel pipe as described in an embodiment of this application;
[0026] Figure 2 This is a cross-sectional view of a mandrel for hot expansion of a round-to-square steel pipe as described in an embodiment of this application. Detailed Implementation
[0027] In the description of this application, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships are only for illustrative purposes and should not be construed as limiting this patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.
[0028] In the description of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.
[0029] Example 1
[0030] In this embodiment, to meet market demand, the required seamless square tube specifications are (A) 600mm × (B) 600mm × (S) 30mm, with an outer corner radius R = 80mm. The specifications of the raw material round tube used are as follows:
[0031] According to the technical solution of this application, a mandrel for hot expansion of round-to-square steel pipes suitable for producing products of the above specifications is provided, with reference to... Figure 1 and Figure 2It consists of, from front to back, a guide section 1, a diameter-changing section 2, a round-to-square section 3, a shaping section 4, and a straightening section 5, with each adjacent section integrally connected to the others. The guide section 1 is cylindrical, the diameter-changing section 2 is frustum-shaped, the surface of the round-to-square section 3 is a gradually changing curved surface transitioning from round to square, the shaping section 4 is square columnar, the straightening section 5 is frustum-shaped, and the entire mandrel is a hollow structure.
[0032] According to the technical solution of this application, the specific specifications of the mandrel for hot expansion of the round-to-square steel pipe are as follows:
[0033] L1=300mm, d1=400mm, k1=30mm, d2=(600+600)×2 / π-2×30-30=674mm, α=9°, L2=(674-400) / (2×tg(9×π / 180))=865mm, L3=260mm, d3=d2=674mm, k2=4mm, a3=600-2×30-4=536mm, b3=60 0-2×30-4=536mm, L4 is 260mm, a4=a3=536mm, b4=b3=536mm, r4=80-30=50mm, L5=2000mm, a50 =a4=536mm, b50=b4=536mm, k3=3mm, a51=536-3=533mm, b51=536-3=533mm, r5=r4=50mm.
[0034] Example 2
[0035] In this embodiment, as per customer requirements, the seamless square tube to be manufactured has the following specifications: (A) 300mm × (B) 300mm × (S) 8mm, with an outer corner radius R = 20mm. The specifications of the raw material round tube used are as follows: According to the technical solution of this application, a mandrel for hot expansion of round-to-square steel pipes suitable for producing products of the above specifications is provided, with reference to... Figure 1 and Figure 2 It consists of, from front to back, a guide section 1, a diameter-changing section 2, a round-to-square section 3, a shaping section 4, and a straightening section 5, with each adjacent section integrally connected to the others; the guide section 1 is cylindrical, the diameter-changing section 2 is frustum-shaped, the surface of the round-to-square section 3 is a gradually changing curved surface transitioning from round to square, the shaping section 4 is square column-shaped, and the straightening section 5 is square column-shaped (k3 is 0), and the entire mandrel has a hollow structure.
[0036] According to the technical solution of this application, the specific specifications of the mandrel for hot expansion of the round-to-square steel pipe are as follows:
[0037] L1=320mm, d1=220mm, k1=30mm, d2=(300+300)×2 / π-2×8-15=350mm, α=11°, L2=(350-220) / (2×tg(11×π / 180))=334mm, L3=200mm, d3=d2=350mm, k2=2mm, a3=300-2×8-2=282mm, b3= 300-2×8-2=282mm, L4 is 200mm, a4=a3=282mm, b4=b3=282mm, r4=20-8=12mm, L5=2000mm, a5 0=a4=282mm, b50=b4=282mm, k3=0, a51=282-0=282mm, b51=282-0=282mm, r5=r4=12mm.
[0038] Example 3
[0039] In this embodiment, as per customer requirements, the seamless square tube to be manufactured has the following specifications: (A) 500mm × (B) 300mm × (S) 16mm, with an outer corner radius R = 40mm. The specifications of the raw material round tube used are as follows:
[0040] According to the technical solution of this application, a mandrel for hot expansion of round-to-square steel pipes suitable for producing products of the above specifications is provided, with reference to... Figure 1 and Figure 2 It comprises, from front to back, a guide section 1, a diameter-changing section 2, a round-to-square section 3, a shaping section 4, and a straightening section 5, with each adjacent section integrally connected to the others; the guide section 1 is cylindrical, the diameter-changing section 2 is frustum-shaped, the surface of the round-to-square section 3 is a gradually changing curved surface transitioning from round to square, the shaping section 4 is square column-shaped, and the straightening section 5 is frustum-shaped, and the entire mandrel has a hollow structure.
[0041] According to the technical solution of this application, the specific specifications of the mandrel for hot expansion of the round-to-square steel pipe are as follows:
[0042] L1=320mm, d1=240mm, k1=20mm, d2=(500+300)×2 / π-2×16-20=457mm, α=10°, L2=(457-240) / (2×tg(10×π / 180))=615mm, L3=220mm, d3=d2=457mm, k2=3mm, a3=500-2×16-3=465mm, b3=3 00 - 2 × 16 - 3 = 265 mm, L4 is 220 mm, a4 = a3 = 465 mm, b4 = b3 = 265 mm, r4 = 40 - 16 = 24 mm, L5 = 2000 mm, a50 = a4 = 465 mm, b50 = b4 = 265 mm, k3 = 2 mm, a51 = 465 - 2 = 463 mm, b51 = 265 - 2 = 263 mm, r5 = r4 = 24 mm.
[0043] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Based on the present utility model and the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present utility model. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.
[0044] The hot-expanded square tube (seamless square tube) products manufactured by the mandrels of the above embodiments on existing hydraulic propulsion tube expanders can be formed by hot expansion of raw material round tubes in one go. This breaks through the existing processing technology and realizes another manufacturing method for seamless square tubes. Because the processing method of hot deformation internal forming is adopted, the metal deformation resistance is small, and seamless square tubes with large outer diameter and large wall thickness can be produced. It can break through the specification limits of cold working and hot rolling processing. Moreover, compared with the extrusion method currently widely used, there is no work hardening phenomenon at the corners of the seamless square tube, and there is no risk of corner cracks due to internal stress. Therefore, no additional normalizing heat treatment is required. Furthermore, the production of seamless square tubes can be carried out by replacing the mandrel with existing equipment, which greatly reduces the capital investment. This makes the hot expansion mandrel for round-to-square steel pipes have excellent prospects for promotion and application.
Claims
1. A mandrel for hot expansion of a steel pipe that transforms from round to square, characterized in that: The mandrel, from front to back, includes a guide section (1), a variable diameter section (2), a round-to-square variable section (3), a shaping section (4), and a straightening section (5), with each adjacent section integrally connected to the other. The guide section (1) is cylindrical, the variable diameter section (2) is frustum-shaped, the surface of the round-to-square section (3) is a gradually changing curved surface transitioning from round to square, the shaping section (4) is square column-shaped, and the straightening section (5) is square column-shaped or frustum-shaped.
2. The mandrel for hot expansion of a round-to-square steel pipe according to claim 1, characterized in that: The length L1 of the guide section (1) is 100-500 mm, and the diameter d1 of the guide section (1) is 10-100 mm smaller than the inner diameter of the raw material tube.
3. The mandrel for hot expansion of a round-to-square steel pipe according to claim 2, characterized in that: The length L2 of the variable diameter section (2) is (d2 - d1) / (2 × tgα), where d2 is the maximum diameter of the variable diameter section (2), d1 is the diameter of the guide section (1), and α is the angle between the inclined surface of the variable diameter section (2) and the axis, where α is 6 to 13°. The maximum diameter d2 of the variable diameter section (2) is (A+B)×2 / π-2×S-k1, where A and B are the two outer side lengths of the seamless square tube section of the product, S is the wall thickness of the seamless square tube of the product, the round-to-square compensation value k1 is -10~+100mm, and the minimum diameter of the variable diameter section (2) is the same as the diameter d1 of the guide section (1).
4. The mandrel for hot expansion of a round-to-square steel pipe according to claim 3, characterized in that: The length L3 of the circular-to-square transition section (3) is 50-900 mm; The connecting end face of the circular-to-square variable section (3) near the variable diameter section (2) is a circular surface, and the diameter d3 of the circular surface is equal to the maximum diameter d2 of the variable diameter section (2); The connecting end face of the circular-to-square section (3) near the fixed section (4) is a rectangular surface. The two side lengths of the rectangular surface are a3 and b3, respectively. a3 = A - 2 × S - k2, b3 = B - 2 × S - k2, and the temperature compensation value k2 is 0 to 5 mm.
5. A mandrel for hot expansion of a round-to-square steel pipe according to claim 4, characterized in that: The length L4 of the shaping section (4) is 50-500mm, and the two side lengths a4 and b4 of the cross section of the shaping section (4) are equal to the two side lengths a3 and b3 of the rectangular surface of the circular-to-square transformation section (3); The outer radius of the shaping section (4) is r4 = RS, where R is the outer radius of the seamless square tube of the product.
6. A mandrel for hot expansion of a round-to-square steel pipe according to claim 5, characterized in that: The length L5 of the straightening section (5) is 1000-3000 mm, and the lengths a50 and b50 of the two sides of the connecting end face of the straightening section (5) are equal to the lengths a4 and b4 of the two sides of the cross section of the shaping section (4); The lengths of the two sides of the other end face of the straightening section (5) are a51 and b51, where a51 = a50 - k3 and b51 = b50 - k3, and the demolding compensation value k3 is 0 to 8 mm. The outer radius r5 of the straightening section (5) is equal to the outer radius r4 of the shaping section (4).
7. A mandrel for hot expansion of a round-to-square steel pipe according to any one of claims 1-6, characterized in that: The core rod has a hollow structure.