Method and device for hot-dip plating of metal protection layer on inner wall of metal pipe

Abstract

The invention provides a method and device for hot-dip plating of a metal protection layer on the inner wall of a metal pipe, and belongs to the technical field of hot-dip plating of metals.The method comprises the steps that metal of the metal protection layer is placed in the metal pipe through hot dipping, and vortex current capable of maintaining the plating metal to be in a liquid state is generated on the inner wall of the metal pipe; the vortex current can generate thrust at the same time to drive redundant metal in the liquid metal protection layer to flow out from the steel pipe; the vortex current is formed by two groups of alternating magnetic fields which are arranged on the outer wall of the metal tube and are perpendicular to each other. According to the invention, two groups of alternating magnetic fields perpendicular to each other are arranged to form vortex current on the hot-dip metal protection layer on the inner wall of the metal pipe, and the vortex current acts on the coating metal, maintains the coating metal in a liquid state and drives redundant metal in the metal protection layer to flow out of the steel pipe, so that the uniformity of the hot-dip metal protection layer on the inner wall of the metal pipe is realized; the thickness of the metal protection layer is accurately controlled; without arrangement of a scraper and compressed gas which can penetrate into the metal tube, operation is convenient, and efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of hot-dip metal plating, and more specifically to a method and a device for hot-dip plating a metal protective layer on the inner wall of a metal pipe. Background Art

[0002] In order to protect steel products from environmental erosion, metal plating is often used on the surface of steel products. The commonly used metal is zinc. The zinc-plated layer with metallic zinc as a sacrificial anode is used to protect the steel products. However, the galvanized layer must have a certain thickness and lifespan to effectively protect the steel products. Galvanizing mainly includes electrogalvanizing and hot-dip galvanizing. Compared with electrogalvanizing, hot-dip galvanizing can provide a coating of 10 to 60 microns, which is not only much thicker than general electrogalvanizing, but also greatly increases the lifespan. Therefore, hot-dip galvanizing has long been a widely used anti-corrosion method for steel products. However, hot-dip galvanizing has the problem of uneven flow of liquid zinc. For example, after the hot-dip galvanizing process of 1 to 2 minutes is completed, the surface of the galvanized layer will be uneven and flat due to uneven flow, and then the steel products cannot be effectively protected, resulting in a low service life. It is often necessary to wipe off the redundant metallic zinc and zinc solution slag in addition to zinc and steel metal compounds.

[0003] In order to ensure uniform thickness of the galvanized layer after hot-dip galvanizing, controllable coating, and effectively remove redundant residue, scrapers, compressed air, and high-pressure steam are generally used to blow off the liquid zinc accumulated on the surface of steel products. This method can cope with the treatment of flat products and the outer wall of steel pipes, but for the inner wall of seamless steel pipes, since the length of seamless steel pipes can reach 6 meters and the diameter is generally 20-400 mm, it is very inconvenient to treat the inner wall by scrapers or gas, which is not only difficult to ensure the uniformity of the coating, but also may cause residues to accumulate at one end of the seamless steel pipe.

[0004] Two types of electromagnetic zinc plating technologies have been developed in the prior art, such as the Chinese invention patent with publication number CN 104233153 A, which discloses an electromagnetic zinc plating method for hot-dip galvanizing of steel wires and steel pipes. However, this technology uses the flow of hot zinc itself plus the magnetic field to generate the Lorentz force, but the efficiency is extremely low because the flow rate of liquid zinc is too slow; or it uses the Lorentz force of the magnetic field on the energized zinc layer, which requires the installation of metal electrodes, which not only consumes electricity and materials, but is also difficult to implement; therefore, neither can be applied to the inner wall of seamless steel pipes. Another example is the Chinese invention patent with publication number CN 116752065 A, which discloses an electromagnetic wiping device for the coating of hot-dip galvanized steel pipes. This technology uses three-phase AC induction electric push for wiping, similar to a three-phase motor. Although electrodes are no longer needed, since the liquid zinc is a whole piece, it is completely different from the squirrel cage bars in the motor rotor. When the external magnetic field rotates / translates, it cannot effectively generate the corresponding Lorentz thrust, so it is difficult to apply to the inner wall of the steel pipe. Summary of the invention

[0005] The purpose of the present invention is to solve the above-mentioned technical problems and provide a method for hot-dip plating a metal protective layer on the inner wall of a metal tube. When the method does not require the use of a scraper and compressed gas to process the hot-dip plating of the metal protective layer on the inner wall of the metal tube, it is difficult to ensure the uniformity of the coating; another purpose of the present invention is to provide a device for hot-dip plating a metal protective layer on the inner wall of a metal tube.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for hot-dip coating of a metal protective layer on the inner wall of a metal tube, wherein the metal of the metal protective layer is placed in the metal tube by hot dipping, and an eddy current is generated on the inner wall of the metal tube to maintain the coated metal in a liquid state, and the eddy current can also generate thrust to drive the redundant metal in the liquid metal protective layer to flow out of the steel tube; the eddy current is formed by two sets of mutually perpendicular alternating magnetic fields arranged on the outer wall of the metal tube.

[0008] The present invention forms eddy currents in the hot-dip metal protective layer on the inner wall of a metal tube by setting two sets of mutually perpendicular alternating magnetic fields. The eddy currents act on the coated metal, generating heat to keep the coated metal in a liquid state on the one hand, and generating thrust to drive redundant metal in the liquid metal protective layer to flow out of the steel tube on the other hand, thereby improving the uniformity of the hot-dip metal protective layer on the inner wall of the metal tube. The thickness of the metal protective layer can be precisely controlled by adjusting the alternating current.

[0009] Furthermore, the alternating magnetic field includes a first alternating magnetic field and a second alternating magnetic field, the first alternating magnetic field generates an eddy current along the circumferential direction of the metal tube in the metal tube; the second alternating magnetic field generates a Lorentz thrust along the axial direction of the metal tube in the metal tube; the Lorentz force downward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field is greater than the Lorentz force upward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field.

[0010] Furthermore, the phases of the driving currents required by the first alternating magnetic field and the second alternating magnetic field are adjustable.

[0011] Furthermore, the metal tube is a steel tube, a copper tube, a titanium tube or an aluminum tube, and the purpose of plating metal on the surface of the metal tube is to protect the metal tube from corrosion by sacrificing the plated metal according to the electrochemical principle.

[0012] Preferably, the metal pipe is a seamless steel pipe.

[0013] Furthermore, the metal of the metal protective layer placed in the metal tube is in a molten liquid state; and the metal tube is in a solid state.

[0014] Furthermore, the metal plated by the hot-dip metal coating is zinc, chromium, copper or iron. Zinc, chromium, copper or iron can be used as common coating metals, and their metal activity should generally be higher than that of the metal tube.

[0015] The present invention provides a device for hot-dip plating a metal protective layer on the inner wall of a metal tube, comprising a first electromagnet and a second electromagnet which can be arranged outside the metal tube, wherein the first electromagnet is a solenoid sleeved on the outer wall of the metal tube; the first alternating magnetic field generates an eddy current along the circumferential direction of the metal tube in the metal tube; the second electromagnet is arranged on the peripheral side of the outer wall of the metal tube; the second alternating magnetic field generates a Lorentz thrust along the axial direction of the metal tube in the metal tube; the Lorentz force downward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field is greater than the Lorentz force upward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field.

[0016] Furthermore, the second electromagnet is composed of an energized coil wound around an iron core, and the second electromagnet and the first electromagnet are arranged at intervals along the length direction of the metal tube.

[0017] Furthermore, the second electromagnet and the first electromagnet are respectively connected to a power supply that provides alternating current of the same frequency, and the power supply maintains a 90-degree phase difference and can be adjusted.

[0018] Furthermore, the second electromagnets are evenly distributed along the outer circumference of the metal tube.

[0019] Furthermore, the magnetic field strength at the lower portion of the second electromagnet is greater than the magnetic field strength at the upper portion.

[0020] Furthermore, the axial angle between the second electromagnet core and the metal tube is any angle between 0 and 90 degrees.

[0021] Preferably, the axial angle between the second electromagnet core and the metal tube is less than 90 degrees.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) The present invention forms eddy currents in the hot-dip metal protective layer on the inner wall of the metal tube by setting two sets of mutually perpendicular alternating magnetic fields. The eddy currents act on the coated metal, generating heat to keep the coated metal in a liquid state on the one hand; on the other hand, they drive the redundant metal in the liquid metal protective layer to flow out of the steel tube, thereby improving the uniformity of the hot-dip metal protective layer on the inner wall of the metal tube. The thickness of the metal protective layer can be precisely controlled by adjusting the alternating current.

[0024] (2) The present invention does not need to set up scrapers and compressed gas that can penetrate into the metal pipe. Only two groups of electromagnets that can generate the above-mentioned eddy current are set outside the metal pipe to achieve hot-dip metal protective layer on the inner wall of the metal pipe. The operation is convenient and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a side schematic diagram of the electromagnetic field distribution in each electromagnet along the axial direction of the metal tube and the stress condition of the metal protective layer.

[0026] Figure 2 It is the distribution diagram of the second electromagnet along the radial direction of the metal tube.

[0027] In the figure, A represents the second electromagnet; B represents the first electromagnet; F represents the downward Lorentz force exerted on the metal protective layer by the electromagnet; f represents the upward Lorentz force exerted on the metal protective layer by the electromagnet; the dot in the circle and the cross in the circle represent the electron exit and entry directions respectively, and X and Z in the coordinates represent the radial and circumferential directions of the metal tube respectively, and are perpendicular to each other. X and Z can represent the cross section of the metal tube, and Y represents the axial direction of the metal tube, which is parallel to the tube wall of the metal tube. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0029] Example 1

[0030] The present embodiment provides a method for hot-dip coating of a metal protective layer on the inner wall of a metal tube, wherein the metal of the metal protective layer is placed in the metal tube by hot dipping, and an eddy current is generated on the inner wall of the metal tube to maintain the coated metal in a liquid state. The eddy current can also generate thrust to drive the redundant metal in the liquid metal protective layer to flow out of the steel tube; the eddy current is formed by two sets of mutually perpendicular alternating magnetic fields arranged on the outer wall of the metal tube.

[0031] As an optional solution, the alternating magnetic field includes a first alternating magnetic field and a second alternating magnetic field, wherein the first alternating magnetic field generates an eddy current along the circumferential direction of the metal tube in the metal tube; the second alternating magnetic field generates a Lorentz thrust along the axial direction of the metal tube in the metal tube; the Lorentz force exerted downward along the inner wall of the metal tube on the metal protective layer in the second alternating magnetic field is greater than the Lorentz force exerted upward along the inner wall of the metal tube on the metal protective layer in the second alternating magnetic field. Preferably, the driving current phases required for the first alternating magnetic field and the second alternating magnetic field are adjustable.

[0032] Preferably, the metal tube can be a steel tube, a copper tube, a titanium tube or an aluminum tube; in this embodiment, a seamless steel tube is preferred. The metal plated by the hot-dip metal is a metal such as zinc, chromium, copper or iron. In this embodiment, zinc is preferred. Preferably, the metal protective layer placed in the metal tube is in a molten liquid state; the metal tube is in a solid state, which is actually also a requirement for the hot-dip metal protective layer on the inner wall of the metal tube.

[0033] Example 2

[0034] In order to provide a device for implementing the above method, the present embodiment provides a device for hot-dip plating a metal protective layer on the inner wall of a metal tube, comprising a first electromagnet and a second electromagnet that can be arranged on the outside of the metal tube, wherein the first electromagnet is a solenoid sleeved on the outer wall of the metal tube; the first alternating magnetic field generates an eddy current along the circumferential direction of the metal tube in the metal tube; the second electromagnet is arranged on the peripheral side of the outer wall of the metal tube; the second alternating magnetic field generates a Lorentz thrust along the axial direction of the metal tube in the metal tube; the Lorentz force downward along the inner wall of the metal tube is applied to the metal protective layer in the second alternating magnetic field, which is greater than the Lorentz force upward along the inner wall of the metal tube is applied to the metal protective layer in the second alternating magnetic field.

[0035] As an optional solution, the second electromagnet is composed of an energized coil wound around an iron core, and the second electromagnet and the first electromagnet are spaced apart along the length direction of the metal tube.

[0036] As an optional solution, the second electromagnet and the first electromagnet are respectively connected to a power supply that provides alternating current of the same frequency, and the power supply maintains a phase difference of 90 degrees and can be adjusted.

[0037] Preferably, the second electromagnets are evenly distributed along the outer circumference of the metal tube.

[0038] Example 3

[0039] As a more specific implementation, Figure 1 and Figure 2, choose the metal tube as seamless steel tube, with a diameter of 200 mm, a wall thickness of 10 mm, a tube length of 6 meters, and a magnetic permeability of 300. In fact, you can also choose various types of steel tubes with a diameter of 20-400 mm and a wall thickness of 3-15 mm. The metal of the metal protective layer is zinc, referred to as the galvanized layer.

[0040] The seamless steel pipe is placed in a zinc pool, and the melted metal protective layer flows into the metal pipe. When the hot dip is completed, one end of the steel pipe is pulled out of the zinc pool, and two electromagnets, the second electromagnet (represented by A electromagnet) and the first electromagnet (represented by B electromagnet) are installed on the seamless steel pipe to generate two types of magnetic lines of force respectively. The magnetic lines of force generated by the B electromagnet composed of the energized coil (such as the thin curved line with arrows drawn inside the steel pipe wall) are basically parallel to the steel pipe wall ( Figure 1 The Y direction of the coordinate is the axial direction of the steel pipe). When the alternating current passes through the magnet B, according to the Maxwell equation about the electric field curl and the magnetic field change rate, that is, Faraday electromagnetic induction, as shown in equation (1), an eddy current along the circumferential direction (Z) of the steel pipe will be generated in the steel pipe metal and the galvanized layer (gray area). Note that the metal current is composed of free electrons, so the dotted circle and the cross circle in the figure represent the direction of the electron flow corresponding to the current magnetic field increase.

[0041]

[0042] Among them, FB is the magnetic flux, EV is the induced electromotive force, and AD is the eddy current.

[0043] at the same time, Figure 1 The A electromagnet in the figure is composed of an energized coil wound around an iron core. Preferably, the A electromagnet is made of ferrite in the shape of a teacup handle, with a length of 100 mm, a thickness of 15 mm at the lower end, and 30-40 mm at the upper end; the B electromagnet is composed of a solenoid wound around the outer wall of a steel pipe. The two electromagnets will cover a 200 mm long pipe and can move along the length of the steel pipe (when the steel pipe is pulled out of the zinc pool at a 10-15 degree angle to the ground). Since the magnetic lines of force of the A electromagnet are concentrated on the lower iron core (ferrite), they will pass through the pipe wall approximately along the pipe diameter, perpendicular to the pipe wall (X direction), enter the galvanized layer inside the pipe, and act on the eddy current generated by the B electromagnet. Therefore, the galvanized layer, which is the carrier of the eddy current generated by the B electromagnet, will be subjected to the Lorentz force F, causing the liquid zinc to be pushed downward. And according to Figure 1 It is shown that the size of the upper core is 2~3 times that of the lower core, the magnetic field is weakened by 4~10 times, and the magnetic lines of force are far from being along the tube diameter. The upward Lorentz force f generated is correspondingly weakened by 4~10 times, which is significantly lower than F. (That is, F / f = the ratio of the upper and lower end areas).

[0044] In order to ensure that F is always pointing downward along the pipe axis, electromagnet A must also be driven by an alternating current of the same frequency, that is, the power supply of electromagnet A and the power supply of electromagnet B maintain a 90-degree phase difference, so that they are consistent with the eddy current. At the same time, the second eddy current generated by the magnetic field emitted by electromagnet A, under the action of the magnetic field emitted by electromagnet B, only causes the Lorentz force along the pipe diameter direction (X), and will not affect the movement of the galvanized layer along the pipe axis under the action of F. Finally, under the joint action of electromagnets A and B, the eddy current of the steel pipe wall heats the galvanized layer, and in addition to the part of zinc that has formed a compound with steel, the excess metal zinc can be pushed downward. If the steel pipe is moved upward at the same time, the excess zinc can be discharged from the pipe mouth.

[0045] In addition to the driving power supply of electromagnet A and electromagnet B must maintain the same frequency, the phase difference and power between the two are adjustable, which is also a necessary condition to ensure that the appropriate F is used to remove the excess metal zinc layer. As an optional solution, the power supply is a dual-output power supply with adjustable frequency (10-50 KHz), phase difference (0-180 degrees), and power (0.5~5 kilowatts). In order to adapt to steel pipes with different outer diameters, the A magnets distributed on the circumference can be moved radially using mechanical devices, and the A electromagnet can be set to multiple, such as 8 electromagnets arranged along the circumference of the pipe wall. Figure 2 As shown in the figure, the power of electromagnet A and electromagnet B is adjustable, which can also ensure that they have similar shield penetration effects when used on different steel or pipe materials.

[0046] When the steel or pipe has a relative magnetic permeability μ, the magnetic field B2 inside the pipe will be shielded to some extent and will be smaller than the magnetic field B1 outside the pipe.

[0047] For ordinary carbon steel, when the frequency of driving the electromagnet increases from 0 to 10 5 At Hz (100 kHz), μ drops from about 300 to 100. Therefore, for different inner and outer radii (Rin, Rout) of steel pipes, the shielding effect on the magnetic field is about several to dozens of times. The power of the two sets of electromagnets needs to be adjusted accordingly. Based on this, it can be deduced from this formula that as long as the thickness of the pipe wall is less than 10~20% of the radius, the magnetic field shielding multiple will be limited to a certain range, and it has little to do with the length of the steel pipe.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the solution. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents based on the understanding of the present solution without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for hot-dip coating of a metal protective layer on the inner wall of a metal pipe, characterized in that: The metal of the metal protective layer is placed in a metal tube by hot dipping, and an eddy current is generated on the inner wall of the metal tube to maintain the coated metal in a liquid state. The eddy current can also generate thrust to drive the redundant metal in the liquid metal protective layer to flow out of the steel tube; the eddy current is formed by two sets of mutually perpendicular alternating magnetic fields arranged on the outer wall of the metal tube.

2. The method for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 1, characterized in that: The alternating magnetic field includes a first alternating magnetic field and a second alternating magnetic field, wherein the first alternating magnetic field generates an eddy current along the circumferential direction of the metal tube in the metal tube; the second alternating magnetic field generates a Lorentz force along the axial direction of the metal tube in the metal tube; the Lorentz force downward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field is greater than the Lorentz force upward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field.

3. The method for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 2, characterized in that: The driving current phases required by the first alternating magnetic field and the second alternating magnetic field are adjustable.

4. The method for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 1, characterized in that: The metal pipe is a steel pipe, a copper pipe, a titanium pipe or an aluminum pipe.

5. The method for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 1, characterized in that: The metal of the metal protective layer placed in the metal tube is in a molten liquid state; the metal tube is in a solid state.

6. The method for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 1, characterized in that: The metal plated in the hot-dip metallization is zinc, chromium, copper or iron.

7. A device for hot-dip coating of a metal protective layer on the inner wall of a metal pipe, characterized in that: It comprises a first electromagnet and a second electromagnet which can be arranged outside a metal tube, wherein the first electromagnet is a solenoid sleeved on the outer wall of the metal tube; the first alternating magnetic field generates an eddy current along the circumferential direction of the metal tube in the metal tube; the second electromagnet is arranged on the peripheral side of the outer wall of the metal tube; the second alternating magnetic field generates a Lorentz force along the axial direction of the metal tube in the metal tube; the Lorentz force downward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field is greater than the Lorentz force upward along the inner wall of the metal tube received by the metal protective layer in the second alternating magnetic field.

8. The device for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 7, characterized in that: The second electromagnet is composed of an energized coil wound around an iron core, and the second electromagnet and the first electromagnet are spaced apart along the length direction of the metal tube.

9. The device for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 7, characterized in that: The second electromagnet and the first electromagnet are respectively connected to a power supply providing alternating current of the same frequency, and the power supply maintains a 90-degree phase difference and can be adjusted.

10. The device for hot-dip coating of a metal protective layer on the inner wall of a metal pipe according to claim 7, characterized in that: The magnetic field strength at the lower portion of the second electromagnet is greater than the magnetic field strength at the upper portion.

Images