High speed hot expansion process and device for steel tubes

Abstract

Steel pipe high-speed hot expansion process and device relate to the technical field of steel pipe processing, and the heating coil is divided into a preheating coil and a hot expansion heating coil by taking the starting expansion position of the steel pipe as a critical point, the preheating coil is distributed on the outer periphery of the steel pipe in a uniform interval wire winding mode, the hot expansion heating coil is distributed on the outer periphery of the steel pipe in a sparse-to-dense wire winding mode, and the wire winding interval of the preheating coil is smaller than the minimum wire winding interval of the hot expansion heating coil, so that the wire winding of the preheating coil is more dense, so that the preheating coil can heat the steel pipe to a sufficient starting expansion temperature during the advancing process and reach the starting expansion position, thereby improving the starting expansion temperature of the steel pipe without increasing energy consumption, thereby reducing the abrasion of the mandrel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel pipe processing, and particularly relates to a steel pipe high-speed hot expansion process and device. BACKGROUND

[0002] The steel pipe hot expansion process has been widely applied in the current industrial production and is used for realizing plastic deformation and size expansion of the steel pipe. The traditional steel pipe hot expansion process usually adopts an induction heating coil so that the surface of the steel pipe is affected by thermal energy, thereby achieving the heating effect.

[0003] Figure 1 The traditional steel pipe hot expansion process principle is shown, which has some problems in actual application. First, the distribution of the induction heating coil is relatively uniform, which leads to the dispersion of the heating energy, and the start expansion temperature cannot be comprehensively improved. As can be seen in the figure, the indicated start expansion temperature is only about 400 DEG C, and the medium-frequency induction heating zone formed by the distribution range of the entire coil is relatively long, which makes the heating energy more dispersed. Specifically, Figure 1 The start expansion position of the steel pipe is a critical point, the heating coil region formed after the critical point is a preheating zone, and the heating coil region formed before the critical point is a hot expansion zone. The coil needs to undergo a slow heating process for a long distance in the preheating zone to only reach a temperature of 400 DEG C, which is actually caused by the heat dispersion caused by the distribution form of the coil.

[0004] When the start expansion temperature of the steel pipe is insufficient, the expansion amount is relatively small, and the required expansion degree cannot be achieved, so the advancing speed of the steel pipe is usually slow, which leads to a long production cycle. In addition, the start expansion temperature of the steel pipe is not high enough, which causes the part to still be in a state with a certain hardness, which causes a large wear on the core mold during the advancing process, shortens the service life of the core mold, and when the core mold is worn, a certain degree of depression occurs at the start expansion part, as shown in FIG. 2, the front and rear ends of the depression have relatively sharp edges, which causes the inner wall surface of the steel pipe to be scratched, and the lubricating layer structure on the inner wall surface of the steel pipe is damaged. Figure 3

[0005] Some existing solutions directly increase the heating temperature of the coil to increase the start expansion temperature to a sufficient temperature, but this will face the following problems: on the one hand, the energy consumption is greatly increased, and on the other hand, the temperature of the steel pipe after the start expansion is too high, which causes the cooling speed of the steel pipe to be slow after the steel pipe leaves the hot expansion zone. At this time, the steel pipe is gradually separated from the core mold and loses the support, so that the surface of the steel pipe is easily deformed in the form of depression under the influence of high temperature, which affects the processing quality of the steel pipe. SUMMARY

[0006] ​The present application aims to provide a steel pipe high-speed hot expansion process to increase the starting expansion temperature of the steel pipe without increasing energy consumption, thereby reducing the wear of the mandrel.

[0007] To solve the above technical problems, the present application adopts the following technical solution: a steel pipe high-speed hot expansion process, which mainly divides the heating coil into a preheating coil and a hot expansion heating coil with the starting expansion position of the steel pipe as the critical point, makes the preheating coil be distributed on the outer periphery of the steel pipe in the form of uniformly spaced wire windings, makes the hot expansion heating coil be distributed on the outer periphery of the steel pipe in the form of wire windings that are sparser in front and denser in back, and makes the wire winding spacing of the preheating coil be smaller than the minimum wire winding spacing of the hot expansion heating coil, so that the wire windings of the preheating coil are more dense, thereby enabling the preheating coil to heat and warm up the steel pipe during the advancing process and reach a sufficient starting expansion temperature when reaching the starting expansion position.

[0008] Preferably, during the advancing process of the steel pipe, the temperature of the steel pipe when reaching the rear end of the preheating coil reaches 150℃, the temperature of the steel pipe when advancing from the rear end of the preheating coil to the starting expansion position reaches 500℃, and the temperature of the steel pipe when advancing from the starting expansion position to the front end of the hot expansion heating coil reaches 760℃. During the advancing process of the steel pipe, the temperature of the steel pipe when approaching and reaching the rear end of the preheating coil increases from 50℃ to 150℃.

[0009] Preferably, the preheating coil has 4 groups of turns; and the hot expansion heating coil has 4 groups of turns.

[0010] More preferably, each wire winding spacing of the preheating coil is 85mm, and the wire winding spacing of the hot expansion heating coil is 115mm, 110mm, and 97mm from front to back.

[0011] More preferably, the spacing between the hot expansion heating coil and the preheating coil is 92mm.

[0012] More preferably, the advancing speed of the steel pipe is 300-350mm / min.

[0013] In addition, the present application also provides a steel pipe high-speed hot expansion device, which comprises a hot expansion mandrel, a heating coil for distribution on the outer periphery of the steel pipe, and an advancing mechanism for advancing the steel pipe, the heating coil comprises a preheating coil and a hot expansion heating coil, the connection point of the preheating coil and the hot expansion heating coil corresponds to the starting expansion position of the steel pipe, the preheating coil is distributed on the outer periphery of the steel pipe in the form of uniformly spaced wire windings, the hot expansion heating coil is distributed on the outer periphery of the steel pipe in the form of wire windings that are sparser in front and denser in back, and the wire winding spacing of the preheating coil is smaller than the minimum wire winding spacing of the hot expansion heating coil. The device operates with the above-mentioned steel pipe high-speed hot expansion process.

[0014] Compared with the prior art, the present application realizes that the preheating area before the steel pipe is expanded has more concentrated heating energy by improving the layout of the induction heating coil, reduces the heat loss, and achieves the purpose of improving the steel pipe expansion temperature, so that the heating temperature of the heating coil does not need to be additionally increased; and since the steel pipe expansion temperature is improved, the wear of the mandrel at the expansion position is greatly reduced, which on the one hand improves the service life of the mandrel, and on the other hand avoids the mandrel scratching off the lubricating layer structure of the inner wall surface of the steel pipe after being damaged, ensuring the quality of the steel pipe hot expansion; moreover, since the preheating area before the steel pipe is expanded has more concentrated heating energy, the advancing speed of the steel pipe can be correspondingly accelerated, which can be increased by nearly 50% on the basis of the original hot expansion process advancing speed, which enables the process to realize greater capacity improvement on the basis of maintaining the original energy consumption, and can bring significant industrial benefits. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a schematic diagram of the existing steel pipe hot expansion process principle;

[0016] Figure 2 It is a schematic diagram of the heat radiation principle of the heating coil in the existing steel pipe hot expansion process;

[0017] Figure 3 It is a schematic diagram of the local structure of the damaged mandrel in the existing steel pipe hot expansion process;

[0018] Figure 4 It is a schematic diagram of the steel pipe hot expansion process principle of the present application;

[0019] Figure 5 It is a schematic diagram of the heat radiation principle of the heating coil in the steel pipe hot expansion process of the present application.

[0020] In the figure:

[0021] 1-steel pipe 2-preheating coil 3-hot expansion heating coil

[0022] 4-mandrel. DETAILED DESCRIPTION

[0023] In order to facilitate the understanding of those skilled in the art, the present application will be further described below in conjunction with the embodiments and the drawings, and the content mentioned in the embodiments is not a limitation of the present application.

[0024] It should be pointed out in advance that in the present application, unless otherwise explicitly specified and limited, the first feature is "before" or "after" the second feature, which can include direct contact of the first and second features, or indirect contact of the first and second features through another feature therebetween.

[0025] As Figure 4As shown, the steel tube high-speed hot expansion process divides the heating coil into a preheating coil 2 and a hot expansion heating coil 3 with the start-expanding position of the steel tube 1 as a critical point, the preheating coil 2 is distributed on the outer periphery of the steel tube 1 in a uniform interval wire winding manner, the hot expansion heating coil 3 is distributed on the outer periphery of the steel tube 1 in a sparse-to-dense wire winding manner, and the wire winding interval of the preheating coil 2 is smaller than the minimum wire winding interval of the hot expansion heating coil 3, so that the wire winding of the preheating coil 2 is more dense and the rear end thereof is closer to the start-expanding position, thereby enabling the preheating coil 2 to heat the steel tube 1 to a sufficient start-expanding temperature during the advancing process and when the steel tube 1 reaches the start-expanding position.

[0026] In the above process, the temperature of the steel tube 1 reaches 150°C when the steel tube 1 reaches the rear end of the preheating coil 2, the temperature of the steel tube 1 reaches 500°C when the steel tube 1 advances from the rear end of the preheating coil 2 to the start-expanding position, and the temperature of the steel tube 1 reaches 760°C when the steel tube 1 advances from the start-expanding position to the front end of the hot expansion heating coil 3 during the advancing process of the steel tube 1. Through the above process, the temperature of the steel tube 1 is raised in a very uniform and linear manner, which makes the heating process of the steel tube 1 very uniform and smooth, and the product quality of the expanded tube is also more stable. Figure 4 As can be seen, the temperature of the three temperature points is raised in a very uniform and linear manner, which makes the heating process of the steel tube 1 very uniform and smooth, and the product quality of the expanded tube is also more stable. In addition, during the advancing process of the steel tube 1, the temperature of the steel tube 1 is raised from 50°C to 150°C when the steel tube 1 approaches and reaches the rear end of the preheating coil 2, and those skilled in the art should know that the steel tube 1 will also be heated to a certain temperature when it is away from the coil, because the core mold 4 is always in the induction heating coil, the core mold 4 maintains a certain temperature and conducts heat to the steel tube 1, so that the steel tube 1 can also be heated to a certain extent when it is away from the induction heating coil, so it can reach about 50°C before approaching the preheating coil 2.

[0027] In order to achieve the above heating effect, the number of turns of the preheating coil 2 in the present embodiment is 4 groups; the number of turns of the hot expansion heating coil 3 is 4 groups. Compared with the existing steel tube hot expansion process, the number of turns of the preheating coil 2 in the present embodiment is significantly less than that of the preheating coil in the existing steel tube hot expansion process, and is closer and denser, which greatly reduces the dispersion of heat and greatly improves the utilization rate of heat energy, thereby also saving the material cost of the heating coil to a certain extent. It should be noted that those skilled in the art should know that the preheating coil 2 and the hot expansion heating coil 3 are actually the rear and front parts of the entire induction heating coil connected in series, the entire induction heating coil is arranged on the outer periphery of the steel tube 1, and the specific installation method is still the conventional method in the prior art. The application only improves the arrangement density of the heating coil, and the invention point is not on the installation of the heating coil. Those skilled in the art can make adaptive adjustments according to the site arrangement, so it is not described in detail.

[0028] In the embodiment, as a preferred scheme, the lead wire winding spacing of each winding of the preheating coil 2 is 85 mm, the lead wire winding spacing of the heat expansion heating coil 3 is 115 mm, 110 mm, and 97 mm from front to back, and the spacing between the heat expansion heating coil 3 and the preheating coil 2 is 92 mm. As can be seen from the existing heat expansion process, the conventional heat expansion coil is usually uniformly distributed around the outer periphery of the steel pipe in the form of a lead wire winding spacing of 115 mm. Therefore, compared with the prior art, the lead wire winding spacing of the preheating coil 2 in the embodiment is reduced by 30 mm, the spacing is greatly shortened, a more compact layout is achieved, heat energy is more concentrated in the preheating area, the heating temperature of the area can be more quickly improved, and therefore the advancing speed of the steel pipe 2 can be obviously improved. In the embodiment, the advancing speed of the steel pipe 2 can reach 350 mm / min, while in the conventional steel pipe heat expansion process, the advancing speed is only 240 mm / min. The advancing speed of the steel pipe 2 in the embodiment is increased by nearly 50%, and the improvement of the advancing speed of the steel pipe 2 means that the production efficiency is greatly improved, that is, more process procedures can be completed in the same time, which is obviously very helpful for the improvement of production capacity, especially on the basis of the same energy consumption, which is very helpful for the improvement of enterprise efficiency.

[0029] Those skilled in the art should know that, in the steel pipe heat expansion process production, the induction heating coil is a process of heating the material by using the eddy current loss generated when the changing magnetic field passes through the conductor. When alternating current passes through the induction heating coil, the current passing through the coil generates an alternating magnetic field. When the magnetic field passes through the steel pipe, the conductor (i.e. the steel pipe itself) inside the steel pipe will induce an induced current, and the induced current forms a circular current path inside the conductor. These current paths form eddy currents, and the existence of eddy currents causes the electrical energy inside the conductor to be converted into heat energy, so that the steel pipe is heated (see the existing steel pipe heat expansion process heating coil heat radiation principle diagram shown in Figure 2 So, as shown in Figure 5 In the embodiment, the lead wire winding spacing of the heating coil is reduced, the path of the eddy current is more compact, that is, more current passes through the steel pipe, and the compact path causes the current to be concentrated in the central area of the steel pipe, so that more concentrated heat is generated, and the heat loss around the steel pipe is reduced.

[0030] The device on which the high-speed thermal expansion process of the steel pipe is based specifically includes a thermal expansion mandrel 4, heating coils distributed around the outer periphery of the steel pipe 1, and a propulsion mechanism for pushing the steel pipe 1. Since the propulsion mechanism can be an existing conventional propulsion mechanism, how to specifically push the steel pipe 1 is not the focus of this invention, so the propulsion mechanism is not limited. The process of high-speed thermal expansion of steel pipe is as follows: After arranging the heating coils in the manner provided in this embodiment, the heating coils are energized, and then the steel pipe 1 is pushed in. The steel pipe 1 first enters the heating range of the preheating coil 2, and the temperature gradually increases until the steel pipe 1 is pushed to the starting expansion position of the contact mandrel 4. At this time, the steel pipe 1 has reached a sufficiently high starting expansion temperature, so that it can expand its diameter by further pushing under the contact action of the mandrel 4. Then, it enters the heating range of the thermal expansion heating coil 3 through the starting expansion position. The steel pipe 1 gradually expands its diameter to the required size. During this process, the steel pipe 1 is continuously and uniformly heated until the diameter expansion is completed and it leaves the heating range of the thermal expansion heating coil 3. At this time, it is still supported by the mandrel 4 and maintains the pushing speed. After the steel pipe 1 gradually cools down, it disengages from the mandrel 4.

[0031] It should also be noted that in this embodiment, the suitable starting temperature for the selected steel pipe 1 is 500°C. This is the optimal starting temperature determined by the type and material characteristics of the steel pipe itself. When dealing with steel pipes of different types and material characteristics, the suitable starting temperature will be different, but those skilled in the art only need to adjust the power of the heating coil accordingly.

[0032] The advantages of the high-speed hot expansion process for steel pipes provided by the above-described embodiments are as follows: By improving the layout of the induction heating coils, the preheating area before the expansion of steel pipe 1 achieves more concentrated heating energy, reduces heat loss, and achieves the goal of increasing the expansion temperature of steel pipe 1, thus eliminating the need to additionally increase the heating temperature of the heating coils; due to the more compact arrangement of the heating coils, the heating rate of steel pipe 1 is more uniform, through... Figure 4 As can be seen from the temperature change curve shown at the bottom, the heating rate of the steel pipe 1 in this embodiment exhibits a smoother and more uniform linear increase. The uniform increase in heating rate can also help avoid stress concentration and deformation problems caused by the difference in thermal expansion of the steel pipe.

[0033] Furthermore, because the expansion temperature of steel pipe 1 is increased, the wear on mandrel 4 at the expansion initiation position is significantly reduced. This not only extends the service life of the mandrel but also prevents damage to the mandrel 4 from scraping away the lubricating layer structure on the inner wall of steel pipe 1, thus ensuring the quality of the hot expansion of steel pipe 1. Those skilled in the art know that the lubricating layer structure on the inner wall of a steel pipe is generally composed of various lubricants, such as grease or a mixture of lubricants. This structural layer can fill the tiny gaps between steel pipe 1 and mandrel 4, forming a lubricating film, thereby reducing friction and wear between the steel pipe 1 and mandrel 4, and promoting a smooth hot expansion process. When the expansion starting point of the mandrel 4 is subjected to impact wear from the insufficiently heated steel pipe 1, forming sharp, concave edges, these sharp edges will inevitably damage the integrity of the lubricating film, leading to decreased lubrication and increased friction. The direct contact between the inner wall of the steel pipe and the mandrel intensifies friction, increasing energy loss and reducing expansion efficiency. Furthermore, it causes wear, scratches, and dents on the inner wall of the tube, reducing the processing quality of the steel pipe. Simultaneously, the decreased lubrication due to wear may necessitate more frequent replacement or repair of the mandrel, increasing production and maintenance costs. Therefore, this invention, by increasing the expansion starting temperature of the steel pipe 1, effectively reduces impact wear on the expansion starting point of the mandrel 4, preventing easy damage to this point. This effectively avoids the aforementioned problems, reduces waste, and extends the service life of the mandrel 4.

[0034] In addition, because the preheating zone before expansion of steel pipe 1 has more concentrated heating energy, the advancing speed of steel pipe 1 can be increased accordingly. This increased advancing speed is due to several factors: First, under high temperatures, the plasticity of the steel pipe increases. When the steel pipe reaches a sufficiently high expansion temperature, its expansion rate increases, thus increasing the advancing speed. Second, under high temperatures, the surface tension of the steel pipe decreases. This reduced surface tension decreases the resistance experienced by the steel pipe during thermal expansion, further increasing the advancing speed. Third, when the temperature is sufficiently high, the internal stress of the steel pipe also decreases, which also promotes the advancement of the steel pipe. Therefore, by providing more concentrated heating energy in the preheating zone before expansion, the advancing speed of the steel pipe can be significantly increased. Since this setting only changes the layout of the induction heating coil and does not require changing the power of the induction heating coil to increase the heating temperature, this process significantly increases the advancing speed of the steel pipe while maintaining the original energy consumption. This naturally leads to a greater increase in production capacity and brings significant industrial benefits, especially the advantage of shortening the production cycle, which allows for faster fulfillment of delivery requirements for urgent orders or customers under high pressure. Furthermore, at a more detailed level, the faster advance speed can even reduce interference from external factors and decrease variables in the production process, thereby improving product consistency and stability. It is evident that the high-speed thermal expansion process for steel pipes provided by this invention can achieve very significant and practical technical effects.

[0035] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified. The above embodiments are preferred implementations of this invention. In addition, this invention can be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this invention.

Claims

1. A high-speed hot expansion process for steel pipes, characterized by: The heating coil is divided into a preheating coil (2) and a thermal expansion heating coil (3) with the expansion position of the steel pipe (1) as the critical point. The preheating coil (2) is distributed on the outer periphery of the steel pipe (1) with evenly spaced wire windings. The thermal expansion heating coil (3) is distributed on the outer periphery of the steel pipe (1) with sparser wire windings in the front and denser wire windings in the back. The wire winding spacing of the preheating coil (2) is smaller than the minimum wire winding spacing of the thermal expansion heating coil (3) so that the wire windings of the preheating coil (2) are more compact. This makes the preheating area before the expansion of the steel pipe (1) have more concentrated heating energy, thereby increasing the expansion temperature of the steel pipe. This allows the preheating coil (2) to heat the steel pipe (1) during the advancement process and reach the expansion temperature when it reaches the expansion position.

2. The high-speed hot expansion process for steel pipes according to claim 1, characterized in that: During the advancement of the steel pipe (1), the temperature of the steel pipe (1) reaches 150°C when it reaches the rear end of the preheating coil (2), the temperature of the steel pipe (1) reaches 500°C when it is advanced from the rear end of the preheating coil (2) to the expansion position, and the temperature of the steel pipe (1) reaches 760°C when it is advanced from the expansion position to the front end of the thermal expansion heating coil (3).

3. The high-speed hot expansion process for steel pipes according to claim 2, characterized in that: During the advancement of the steel pipe (1), the temperature of the steel pipe (1) increases from 50°C to 150°C as it approaches and reaches the rear end of the preheating coil (2).

4. The high-speed hot expansion process for steel pipes according to claim 3, characterized in that: The preheating coil (2) has 4 turns; the thermal expansion heating coil (3) has 4 turns.

5. The high-speed hot expansion process for steel pipes according to claim 4, characterized in that: The spacing between each wire winding of the preheating coil (2) is 85mm.

6. The high-speed hot expansion process for steel pipes according to claim 5, characterized in that: The wire winding spacing of the thermal expansion heating coil (3) is 115mm, 110mm and 97mm from front to back.

7. The high-speed hot expansion process for steel pipes according to claim 6, characterized in that: The distance between the heat expansion heating coil (3) and the preheating coil (2) is 92mm.

8. The high-speed hot expansion process for steel pipes according to claim 3, characterized in that: The steel pipe is pushed at a speed of 300-350 mm / min.

9. A high-speed thermal expansion device for steel pipes, comprising a thermal expansion mandrel (4), heating coils distributed around the outer periphery of a steel pipe (1), and a propulsion mechanism for advancing the steel pipe (1), characterized in that: The heating coil includes a preheating coil (2) and a thermal expansion heating coil (3). The connection point of the preheating coil (2) and the thermal expansion heating coil (3) corresponds to the starting position of the expansion of the steel pipe (1). The preheating coil (2) is distributed on the outer periphery of the steel pipe (1) in a uniformly spaced wire winding manner. The thermal expansion heating coil (3) is distributed on the outer periphery of the steel pipe (1) in a sparse-to-dense wire winding manner. The wire winding spacing of the preheating coil (2) is smaller than the minimum wire winding spacing of the thermal expansion heating coil (3). The high-speed thermal expansion process of the steel pipe is operated using any one of claims 1-8.

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