CN115750932A - Composite plastic-coated steel pipe and production method thereof - Google Patents

Abstract

The invention discloses a composite plastic-coated steel pipe and a production method thereof, belonging to the field of composite plastic-coated steel pipes. A composite plastic-coated steel pipe is prepared by coating a PFA film on a steel pipe, and the coating process comprises the following steps: s1, plasticizing PFA particles to enable PFA plastic to be in a flowing state to obtain a product A; s2, adding the die into the curing channel for heating, extruding the product A into the die through a high-pressure extruder while heating the die, continuously extruding the product A onto the outer surface of the steel pipe which axially moves at a constant speed, and integrally and continuously extruding and molding PFA plastic and the steel pipe to obtain a product B; and S3, performing stress relief treatment on the B product to obtain the composite plastic-coated steel pipe. The composite plastic-coated steel pipe provided by the invention has smooth surface, is not easy to accumulate dust, and has simple coating process and is more economic.

Description

Composite plastic-coated steel pipe and production method thereof

technical field

The invention relates to the field of composite plastic-coated steel pipes, more specifically, to a composite plastic-coated steel pipe and a production method thereof.

Background technique

In order to prevent the steel pipe from being corroded and damaged in the service environment, the steel pipe is generally covered with a plastic or paint to isolate the steel pipe surface from the external environment. The steel pipe covered with plastic is usually processed by die-casting or socketing, that is, a plastic pipe is die-cast on the outer surface of the steel pipe, or a plastic pipe is socketed on the outer surface of the steel pipe to form a plastic steel pipe. However, this type of production method is prone to produce air holes during production, which not only leads to poor connection stability between the plastic pipe and the steel pipe, and the plastic pipe is easier to separate from the steel pipe, but also affects the isolation effect of the plastic pipe on the steel pipe surface, resulting in the steel pipe. The service life is shorter. In addition, the thickness of the plastic sleeve on the plastic steel pipe produced by this kind of production method is relatively large, which not only has high material cost, but also has large thermal resistance and poor heat transfer effect when used as a heat exchange tube. Therefore, the existing plastic steel pipe production methods have the disadvantages of easily producing pores, poor connection stability between the plastic pipe and the steel pipe, poor isolation effect, short service life of the steel pipe, high material cost, large thermal resistance of the finished product, and poor quality of the finished product. The problem of poor heat transfer effect.

The publication number is CN105946194A, which discloses a production method of fluoroplastic steel pipe. The method is to centrifugally rotate the fluoroplastic powder through a centrifuge, and remove impurities in the fluoroplastic powder by centrifugal force; then plasticize the product A. , so that product A enters the plasticized flow state, then extrudes the fluoroplastic into the mold through a high-pressure extruder and continuously extrudes it on the outer surface of the steel pipe, and continuously extrudes the fluoroplastic and the steel pipe in one piece; finally put it in the curing channel for heating After stress removal treatment, the finished product is obtained. The invention can not only avoid the generation of air holes, improve the connection stability, improve the isolation effect, and prolong the service life of the steel pipe, but also has the advantages of low material cost, small thermal resistance of the finished product, good heat exchange effect of the finished product and high production efficiency. But still there is following defect in above-mentioned production method:

(1) The prepared pipe has a rough surface and is easy to accumulate dust.

(2) A layer of plastic is extruded outside the fluoroplastic steel pipe, and the cracks can be seen through magnification, which makes the isolation effect of the fluoroplastic steel pipe poor, and the service life is relatively short.

(3) Fluoroplastic powder needs to be centrifuged to remove impurities, which is time-consuming and labor-intensive.

(4) Fluoroplastic powder needs to be pretreated, and aviation kerosene with high cost must be added, which greatly increases the production cost of fluoroplastic steel pipes.

Contents of the invention

1. technical problem to be solved

In view of the problems existing in the prior art, the object of the present invention is to provide a composite plastic-coated steel pipe, and another object of the invention is to provide a preparation method for a composite plastic-coated steel pipe. The surface of the composite plastic-coated steel pipe provided by the present invention is smooth and does not It is easy to accumulate dust, and its coating process is simple and economical.

2. Technical solutions

In order to solve the above problems, the present invention adopts the following technical solutions.

A composite plastic-coated steel pipe made of steel pipe coated with PFA film, the specific coating process is as follows:

S1, carry out plasticizing treatment to PFA particle, make PFA plastic become flow state, obtain A product;

S2. Add the mold to the curing channel for heating. While heating the mold, extrude product A into the mold through a high-pressure extruder, so that product A is continuously extruded on the outer surface of the steel pipe moving axially at a uniform speed. PFA plastic and steel pipe are integrally extruded continuously to obtain product B;

S3. Perform stress relief treatment on product B to obtain a composite plastic-coated steel pipe.

The PFA membrane is at least one layer.

The specific coating process is the coating process of each layer of PFA membrane.

The mold is a conventional extrusion molding mold.

Further, the PFA film covering the steel pipe is double-layered, and the double-layer PFA film is stretched on the outer peripheral side of the steel pipe, and there is no air gap between the inner PFA film and the outer PFA film.

Further, the thickness of each layer of PFA film is 0.25mm-3mm.

Further, the one-piece continuous extrusion molding in the step S2 is to place the steel pipe in the mold, so that a cavity is formed between the mold and the outer surface of the steel pipe, and finally the product A is extruded into the cavity and integrally extruded with the steel pipe Forming, while the steel pipe moves at a constant speed in the mold, so that product A is continuously extruded on the outer surface of the steel pipe.

Further, the diameter of the steel pipe is 10mm-60mm, and the thickness of the steel pipe is 0.5mm-6mm.

Further, in the step S2, the high-pressure extruder applies an extrusion force of 20 MPa to the product A, and heats the product A to 65°C and extrudes it into the first mold; the axial moving speed of the steel pipe is 0.7 m/ point.

Further, the curing channel includes 4 channels connected in sequence with a length of 3 meters, and the heating temperatures of the 4 channels are 100°C, 200°C, 300°C and 400°C in sequence.

Further, the moving speed of product A in the curing channel is 0.7 m/min.

Further, the stress relief treatment is to pass into the cooling channel at a speed of 0.7 m/min for cooling; the cooling channel includes a 300°C cooling section, a 100°C air cooling section and a normal temperature water cooling section connected in sequence, and the length of the cooling section is 3 meters, the length of the air-cooled section is 7 meters, and the length of the water-cooled section is 2 meters.

A method for producing composite plastic-coated steel pipes, comprising the following steps:

S1, carry out plasticizing treatment to PFA particle, make PFA plastic become flow state, obtain A product;

S2. Add the first mold to the curing channel for heating. While heating the first mold, extrude product A into the first mold through a high-pressure extruder, so that product A is continuously extruded and moves axially at a constant speed For the outer surface of the steel pipe, the PFA plastic and the steel pipe are integrated and continuously extruded to obtain the B product;

S3, carry out stress-relief treatment to product B to obtain finished product C.

Plasticization refers to the whole process in which the plastic is heated in the barrel to reach a fluid state and has good plasticity.

Further, the one-piece continuous extrusion molding in the step S2 is to place the steel pipe in the first mold, so that a cavity is formed between the first mold and the outer surface of the steel pipe, and finally the product A is squeezed into the cavity and the steel pipe One-piece extrusion molding, while the steel pipe moves at a constant speed in the first mold, so that product A is continuously extruded on the outer surface of the steel pipe.

Further, the diameter of the steel pipe is 10 mm to 60 mm, the thickness of the steel pipe is 0.5 mm to 6 mm, and the cavity formed between the first mold and the outer surface of the steel pipe in the step S2 has a thickness of 0.25 mm to 3 mm.

Further, in the step S2, the high-pressure extruder applies an extrusion force of 20 MPa to the product A, and heats the product A to 65°C and extrudes it into the first mold; the axial moving speed of the steel pipe is 0.7 m/ point.

Further, in the step S3, the stress removal treatment is to pass into the cooling channel at a speed of 0.7 m/min for cooling; the cooling channel includes a cooling section at 300°C, an air cooling section at 100°C, and a water cooling section at normal temperature, The length of the cooling section is 3 meters, the length of the air cooling section is 7 meters, and the length of the water cooling section is 2 meters.

The curing channel in the step S2 includes four consecutively connected channels with a length of 3 meters, and the heating temperatures of the four channels are sequentially 100°C, 200°C, 300°C and 400°C; the movement of product A in the curing channel The speed is 0.7 m/min.

Further, a production method of composite plastic-coated steel pipes also includes step S4 and step S5;

S4. Place the finished product C obtained in the step S3 in the second mold, so that a cavity is formed between the second mold and the outer surface of the finished product C, and then add the second mold to the curing channel for heating. While the mold is heating, product A is extruded into the cavity and molded integrally with finished product C, while finished product C moves at a constant speed in the second mold, so that product A is continuously extruded on the outer surface of finished product C to obtain product D;

S5. Perform stress relief treatment on product D to obtain a composite plastic-coated steel pipe.

Further, in the step S4, the stress removal treatment is to pass into the cooling channel at a speed of 0.7 m/min for cooling; the cooling channel includes a cooling section at 300°C, an air cooling section at 100°C, and a water cooling section at normal temperature. The length of the cooling section is 3 meters, the length of the air cooling section is 7 meters, and the length of the water cooling section is 2 meters.

Further, the curing channel in the step S4 includes four consecutively connected channels with a length of 3 meters, and the heating temperatures of the four channels are 100°C, 200°C, 300°C and 400°C; The moving speed is 0.7 m/min.

Further, the cavity formed between the second mold and the outer surface of the finished product C in the step S4 has a thickness of 0.25 mm to 3 mm.

Further, the high-pressure extruder in the step S4 applies an extrusion force of 20 MPa to the product A, and heats the product A to 65°C and extrudes it into the second mold; the axial moving speed of the finished product C is 0.7 m/min.

Further, the thickness of the cavity formed between the second mold and the outer surface of the finished product C in the step S4 is different from the thickness of the cavity formed between the first mold and the outer surface of the steel pipe in the step S2.

Further, the first mold and the second mold are both conventional extrusion molding molds.

3. Beneficial effect

Compared with the prior art, the present invention has the advantages of:

(1) The present invention produces composite plastic-coated steel pipes by integral extrusion molding of PFA plastics and steel pipes. The plasticized PFA plastics have good fluidity, and the formed composite plastic-coated steel pipes have a smooth surface and are not easy to accumulate dust. Moreover, in When processing composite plastic-coated steel pipes, there is no need to remove impurities from PFA plastics, and it is not necessary to use aviation kerosene to pretreat PFA plastics to improve the fluidity of plastics and avoid the generation of pores. Further, it can also reduce compounding. Production steps and processing costs of plastic-coated steel pipes.

(2) The present invention makes up for the defect that cracks will appear in the single-layer film when the steel pipe undergoes thermal expansion and contraction due to temperature changes by coating the steel pipe with a double-layer film, resulting in short service life of the composite steel pipe; By covering the steel pipe with two layers of PFA plastic, and extruding and heating at the same time during the process of covering each layer of PFA plastic film, the PFA plastic and the steel pipe are integrally extruded, so that the molecular gap between the two layers of PFA film is very small, When the two layers of film are thermally expanded and cracks appear, they can fill up the cracks that appear, so as to improve the barrier performance of the composite layer outside the steel pipe, and further increase the difficulty of sewage and other contact with the outer surface of the steel pipe, thereby prolonging the life of the steel pipe. Service life, the service life of the composite plastic-coated steel pipe is higher than the service life of the fluorine-plastic steel pipe processed by a fluorine-plastic steel pipe production method described in the background technology.

Detailed ways

The present invention will be further described below in conjunction with the examples, but not as a basis for limiting the present invention.

Embodiment 1: A production method of a composite plastic-coated steel pipe, the composite plastic-coated steel pipe is made of a steel pipe coated with a single-layer PFA film, the thickness of the PFA film is 0.25mm, and the specific processing steps are as follows:

S1, carry out plasticizing treatment to PFA particle, make PFA plastic become flow state, obtain A product;

S2. Add the first mold to the curing channel for heating. While heating the first mold, extrude product A into the first mold through a high-pressure extruder, so that product A is continuously extruded and moves axially at a constant speed For the outer surface of the steel pipe, the PFA plastic and the steel pipe are integrated and continuously extruded to obtain the B product;

S3. Perform stress relief treatment on product B to obtain a composite plastic-coated steel pipe.

In the step S2, the cavity formed between the first mold and the outer surface of the steel pipe has a thickness of 0.25 mm.

The diameter of the steel pipe is 40mm, and the thickness of the steel pipe is 3mm.

In the integral continuous extrusion molding in the step S2, the steel pipe is placed in the first mold, so that a cavity is formed between the first mold and the outer surface of the steel pipe, and finally product A is extruded into the cavity to be integrally extruded with the steel pipe. Plastic molding, while the steel pipe moves at a constant speed in the first mold, so that product A is continuously extruded on the outer surface of the steel pipe.

In the step S2, the high-pressure extruder applies an extrusion force of 20 MPa to the product A, heats the product A to 65° C. and extrudes it into the first mold; the axial moving speed of the steel pipe is 0.7 m/min.

The curing channel includes 4 channels connected in sequence with a length of 3 meters, and the heating temperatures of the 4 channels are 100°C, 200°C, 300°C and 400°C in sequence; the moving speed of product A in the curing channel is 0.7 meters /point.

The stress relief treatment is to pass into the cooling channel at a speed of 0.7 m/min for cooling; the cooling channel includes a 300°C cooling section, a 100°C air cooling section and a normal temperature water cooling section connected in sequence, and the length of the cooling section is 3 meters , the length of the air-cooled section is 7 meters, and the length of the water-cooled section is 2 meters.

Embodiment 2: A production method of a composite plastic-coated steel pipe, the composite plastic-coated steel pipe is made of a steel pipe coated with a single-layer PFA film, the thickness of the PFA film is 0.28mm, and the specific processing steps are as follows:

S1, carry out plasticizing treatment to PFA particle, make PFA plastic become flow state, obtain A product;

S2. Add the first mold to the curing channel for heating. While heating the first mold, apply an extrusion force of 20MPa to product A through a high-pressure extruder, and heat product A to 65°C and extrude it into the first mold. In the mold, the product A is continuously extruded on the outer surface of the steel pipe moving axially at a uniform speed, and the PFA plastic and the steel pipe are integrated and continuously extruded to obtain the product B;

S3. Perform stress relief treatment on product B to obtain a composite plastic-coated steel pipe.

In the step S2, the cavity formed between the first mold and the outer surface of the steel pipe has a thickness of 0.28 mm.

The diameter of the steel pipe is 40mm, and the thickness of the steel pipe is 3mm.

In the integral continuous extrusion molding in the step S2, the steel pipe is placed in the first mold, so that a cavity is formed between the first mold and the outer surface of the steel pipe, and finally product A is extruded into the cavity to be integrally extruded with the steel pipe. Plastic molding, while the steel pipe moves at a constant speed in the first mold, so that product A is continuously extruded on the outer surface of the steel pipe.

In the step S2, the high-pressure extruder applies an extrusion force of 20 MPa to the product A, heats the product A to 65° C. and extrudes it into the first mold; the axial moving speed of the steel pipe is 0.7 m/min.

The curing channel includes 4 channels connected in sequence with a length of 3 meters, and the heating temperatures of the 4 channels are 100°C, 200°C, 300°C and 400°C in sequence; the moving speed of product A in the curing channel is 0.7 meters /point.

The stress relief treatment is to pass into the cooling channel at a speed of 0.7 m/min for cooling; the cooling channel includes a 300°C cooling section, a 100°C air cooling section and a normal temperature water cooling section connected in sequence, and the length of the cooling section is 3 meters , the length of the air-cooled section is 7 meters, and the length of the water-cooled section is 2 meters.

Embodiment 3: A production method of a composite plastic-coated steel pipe, the composite plastic-coated steel pipe is made of a steel pipe coated with double-layer PFA film, the thickness of the inner PFA film is 0.25mm, and the thickness of the outer PFA film is 0.28mm , the specific processing steps are as follows:

S1, carry out plasticizing treatment to PFA particle, make PFA plastic become flow state, obtain A product;

S2. Add the first mold to the curing channel for heating. While heating the first mold, apply an extrusion force of 20MPa to product A through a high-pressure extruder, and heat product A to 65°C and extrude it into the first mold. In the mold, the product A is continuously extruded on the outer surface of the steel pipe moving axially at a uniform speed, and the PFA plastic and the steel pipe are integrated and continuously extruded to obtain the product B;

S3, carry out stress-relief treatment to product B to obtain finished product C.

S4. Place the finished product C obtained in the step S3 in the second mold, so that a cavity is formed between the second mold and the outer surface of the finished product C, and then add the second mold to the curing channel for heating. While the mold is heating, product A is extruded into the cavity and molded integrally with finished product C, while finished product C moves at a constant speed in the second mold, so that product A is continuously extruded on the outer surface of finished product C to obtain product D;

S5. Perform stress relief treatment on product D to obtain a composite plastic-coated steel pipe.

The thickness of the cavity formed between the second mold and the outer surface of the finished product C in the step S4 is 0.28 mm, and the thickness of the cavity formed between the first mold and the outer surface of the steel pipe in the step S2 is 0.25 mm.

The diameter of the steel pipe is 40mm, and the thickness of the steel pipe is 3mm.

The curing channel includes 4 channels connected in sequence with a length of 3 meters, and the heating temperatures of the 4 channels are 100°C, 200°C, 300°C and 400°C in sequence; the moving speed of product A in the curing channel is 0.7 meters /point.

In the step S2, the high-pressure extruder applies an extrusion force of 20 MPa to the product A, heats the product A to 65° C. and extrudes it into the first mold; the axial moving speed of the steel pipe is 0.7 m/min.

In the integral continuous extrusion molding in the step S2, the steel pipe is placed in the first mold, so that a cavity is formed between the first mold and the outer surface of the steel pipe, and finally product A is extruded into the cavity to be integrally extruded with the steel pipe. Plastic molding, while the steel pipe moves at a constant speed in the first mold, so that product A is continuously extruded on the outer surface of the steel pipe.

The high-pressure extruder in the step S4 applies an extrusion force of 20 MPa to the product A, and heats the product A to 65°C and extrudes it into the second mold; the axial moving speed of the finished product C is 0.7 m/min .

The curing channel includes 4 channels connected in sequence with a length of 3 meters, and the heating temperatures of the 4 channels are 100°C, 200°C, 300°C and 400°C in sequence; the moving speed of product A in the curing channel is 0.7 meters /point.

The stress relief treatment is to pass into the cooling channel at a speed of 0.7 m/min for cooling; the cooling channel includes a 300°C cooling section, a 100°C air cooling section and a normal temperature water cooling section connected in sequence, and the length of the cooling section is 3 meters , the length of the air-cooled section is 7 meters, and the length of the water-cooled section is 2 meters.

Embodiment 4: A production method of a composite plastic-coated steel pipe, the composite plastic-coated steel pipe is made of a steel pipe coated with double-layer PFA film, the thickness of the inner layer of PFA film is 0.25mm, and the thickness of the outer layer of PFA film is 0.25mm , the specific processing steps are as follows:

S1, carry out plasticizing treatment to PFA particle, make PFA plastic become flow state, obtain A product;

S2. Add the first mold to the curing channel for heating. While heating the first mold, apply an extrusion force of 20MPa to product A through a high-pressure extruder, and heat product A to 65°C and extrude it into the first mold. In the mold, the product A is continuously extruded on the outer surface of the steel pipe moving axially at a uniform speed, and the PFA plastic and the steel pipe are integrated and continuously extruded to obtain the product B;

S3, carry out stress-relief treatment to product B to obtain finished product C.

S4. Place the finished product C obtained in the step S3 in the second mold, so that a cavity is formed between the second mold and the outer surface of the finished product C, and then add the second mold to the curing channel for heating. While the mold is heating, product A is extruded into the cavity and molded integrally with finished product C, while finished product C moves at a constant speed in the second mold, so that product A is continuously extruded on the outer surface of finished product C to obtain product D;

S5. Perform stress relief treatment on product D to obtain a composite plastic-coated steel pipe.

The thickness of the cavity formed between the second mold and the outer surface of the finished product C in the step S4 is 0.25 mm, and the thickness of the cavity formed between the first mold and the outer surface of the steel pipe in the step S2 is 0.25 mm.

The diameter of the steel pipe is 40mm, and the thickness of the steel pipe is 3mm.

The curing channel includes 4 channels connected in sequence with a length of 3 meters, and the heating temperatures of the 4 channels are 100°C, 200°C, 300°C and 400°C in sequence; the moving speed of product A in the curing channel is 0.7 meters /point.

In the integral continuous extrusion molding in the step S2, the steel pipe is placed in the first mold, so that a cavity is formed between the first mold and the outer surface of the steel pipe, and finally product A is extruded into the cavity to be integrally extruded with the steel pipe. Plastic molding, while the steel pipe moves at a constant speed in the first mold, so that product A is continuously extruded on the outer surface of the steel pipe.

In the step S2, the high-pressure extruder applies an extrusion force of 20 MPa to the product A, heats the product A to 65° C. and extrudes it into the first mold; the axial moving speed of the steel pipe is 0.7 m/min.

The high-pressure extruder in the step S4 applies an extrusion force of 20 MPa to the product A, and heats the product A to 65°C and extrudes it into the second mold; the axial moving speed of the finished product C is 0.7 m/min .

The stress relief treatment is to pass into the cooling channel at a speed of 0.7 m/min for cooling; the cooling channel includes a 300°C cooling section, a 100°C air cooling section and a normal temperature water cooling section connected in sequence, and the length of the cooling section is 3 meters , the length of the air-cooled section is 7 meters, and the length of the water-cooled section is 2 meters.

Claims (10)

1. A composite plastic-coated steel pipe is characterized in that: the steel pipe is coated with a PFA film, and the specific coating process is as follows:

s1, plasticizing PFA particles to enable PFA plastic to be in a flowing state to obtain a product A;

s2, adding the die into the curing channel for heating, extruding the product A into the die through a high-pressure extruder while heating the die, continuously extruding the product A onto the outer surface of the steel pipe axially moving at a constant speed, and integrally and continuously extruding and molding PFA plastic and the steel pipe to obtain a product B;

and S3, performing stress relief treatment on the B product to obtain the composite plastic-coated steel pipe.

2. A composite coated steel pipe as claimed in claim 1, wherein: the PFA film covering the steel pipe is double-layer, the double-layer PFA film is tensioned on the outer periphery of the steel pipe, and no air gap exists between the inner PFA film and the outer PFA film.

3. A composite coated steel tube as claimed in claim 1, wherein: the thickness of each PFA film is 0.25 mm-3 mm.

4. A production method of a composite plastic-coated steel pipe is characterized by comprising the following steps: the method comprises the following steps:

s1, plasticizing PFA particles to enable PFA plastic to be in a flowing state to obtain a product A;

s2, adding the first die into the curing channel for heating, extruding the product A into the first die through a high-pressure extruder while heating the first die, continuously extruding the product A onto the outer surface of the steel pipe axially moving at a constant speed, and integrally and continuously extruding and molding PFA plastic and the steel pipe to obtain a product B;

and S3, performing stress relief treatment on the product B to obtain a finished product C.

5. A method of manufacturing a composite coated steel tube as claimed in claim 4, wherein: and S2, placing the steel pipe in a first die to form a cavity between the first die and the outer surface of the steel pipe, extruding the product A into the cavity to be integrally extruded with the steel pipe, and simultaneously moving the steel pipe in the first die at a constant speed to continuously extrude the product A onto the outer surface of the steel pipe.

6. In the step S2, a high-pressure extruder applies 20MPa of extrusion force to the product A, heats the product A to 65 ℃ and extrudes the product A into a first die; the axial moving speed of the steel pipe is 0.7 m/min.

7. A method of manufacturing a composite coated steel pipe as claimed in claim 4, wherein: further comprising step S4 and step S5;

s4, placing the finished product C obtained in the step S3 in a second mold, enabling a cavity to be formed between the second mold and the outer surface of the finished product C, then adding the second mold into a curing channel for heating, extruding the product A into the cavity while heating the second mold, and integrally extruding and molding the product A and the finished product C, and enabling the finished product C to move in the second mold at a constant speed, so that the product A is continuously extruded and molded on the outer surface of the finished product C, and obtaining a product D;

and S5, performing stress relief treatment on the D product to obtain the composite plastic-coated steel pipe.

8. The method of claim 7, wherein the method comprises the steps of: the high-pressure extruder in the step S4 applies extrusion force of 20MPa to the product A, heats the product A to 65 ℃, and then extrudes the product A into a second die; the axial moving speed of the finished product C is 0.7 m/min.

9. A method of producing a composite coated steel tube as claimed in claim 4 or 7, wherein: removing stress, and introducing into a cooling channel at a speed of 0.7 m/min for cooling; the cooling channel comprises a 300 ℃ cooling section, a 100 ℃ air cooling section and a normal temperature water cooling section which are sequentially connected, wherein the cooling section is 3 meters in length, the air cooling section is 7 meters in length, and the water cooling section is 2 meters in length.

10. A method of producing a composite coated steel tube as claimed in claim 4 or 7, wherein: the curing channel comprises 4 channels which are sequentially connected and have the length of 3 meters, and the heating temperature of the 4 channels is 100 ℃, 200 ℃, 300 ℃ and 400 ℃ sequentially; the moving speed of the product A in the curing passage is 0.7 m/min.