Continuous annealing furnace for plastic pipes and its annealing process

Abstract

The present invention discloses a continuous annealing furnace for plastic pipes and an annealing process thereof, comprising a furnace body, a hot air circulation heating device, and a continuous pipe conveying device. The furnace body is fixed to the ground via a steel support frame, and the hot air circulation heating devices are symmetrically arranged at opposite positions on both sides of the furnace body. The hot air circulation heating devices can extract the space within the furnace body, heat it, and then re-enter the furnace body. The continuous pipe conveying device is arranged within the furnace body and can realize the loading, continuous annealing, and unloading of pipes. The continuous annealing process proposed by the present invention has a high degree of automation, good heating uniformity during the annealing process, and can accurately control the annealing time, thereby ensuring the mechanical properties of each pipe and improving the quality of the product.

Description

Technical Field

[0001] The invention relates to the technical field of plastic pipe annealing, and in particular to a plastic pipe continuous annealing furnace and an annealing process thereof. Background Art

[0002] Random copolymer polypropylene offers advantages such as thermal insulation, energy conservation, environmental friendliness, and excellent heat resistance, oxygen stability, and hygienic properties. Due to its excellent physical and mechanical properties, molding and processing capabilities, as well as its good chemical stability, heat resistance, and creep resistance, it has been widely used in the industrial sector in recent years, particularly in indoor and outdoor hot and cold water pipes. PPR pipes have very high requirements for the comprehensive performance of the resin, requiring excellent rigidity, heat resistance, chemical resistance, creep resistance, and certain impact resistance. However, their high low-temperature brittleness and susceptibility to stress-induced cracking have hampered the production, storage, transportation, installation, and use of PPR pipes.

[0003] To more effectively improve and enhance the overall performance of PPR pipes and expand their applications, toughening and modification methods such as blending, filling, and annealing are currently being widely used. Blending involves dispersing elastomers or trace amounts of nanoparticles in a microparticle-like form within the PPR base material to enhance the plastic's toughness. This method has been extensively researched and has shown significant results. Commonly used elastomers for blending and modification of PPR include ethylene-octene copolymer (POE), high-density polyethylene (PE-HD), and styrene-based thermoplastic elastomers (SBS). Filling modification involves the addition of fillers during the plastic molding process, which not only improves and enhances the performance of plastic products but also reduces production costs. Commonly used fillers include CaCO₃, SiO₂, TiO₂, talc, mica, kaolin, montmorillonite, and glass fiber. However, both blending and filling modification methods present significant challenges, including uneven distribution of the secondary phase, particle agglomeration, and poor compatibility with the matrix. Annealing is environmentally friendly, safe and efficient. Proper annealing treatment can solve the problems of fast cooling rate and incomplete crystal development during polymer processing and molding, effectively improve the crystallization process of the polymer, reduce the residual stress in the matrix, and thus improve the comprehensive mechanical properties of the material.

[0004] Chinese invention patent application number 201510911629.6 discloses a process for producing stress-relieved random copolymer polypropylene pipes. The process involves placing the formed PP-R pipes in an oven, adjusting the temperature from room temperature to 40-60°C over a specified period of time, maintaining it at 40-60°C for 3-7 minutes, then increasing it from 40-60°C to 70-95°C over a specified period of time, maintaining it at 70-95°C for 3-7 minutes, then increasing it from 70-95°C to 104-110°C over a specified period of time, maintaining it at 104-110°C for 0.7-1.5 hours. The pipes then naturally cool to 30-40°C over 0.7-1.5 hours, then the oven is removed from the oven and allowed to cool to room temperature. However, this annealing process is a secondary step, requiring the entire vehicle to be placed in the annealing chamber for heat treatment. Furthermore, the annealing process is complex and time-consuming.

[0005] Chinese invention patent number: 201510562833.1, discloses a PPR pipe annealing process, including five heating and cooling treatments. The first and second heating treatment temperatures are controlled below 100°C, and the heating treatment time is controlled to about 2 hours to prevent pipe deformation caused by excessively high temperatures and prolonged times; the third and fourth heating treatment temperatures are controlled below 125°C, and the heating treatment time is controlled to about 1 hour to eliminate or reduce the internal stress generated by PPR molecular crystallization during the pipe production process; the fifth heating treatment temperature is controlled below 100°C, and the heating treatment time is controlled to about 0.5 hours to prevent or reduce the secondary internal stress generated during the annealing process and reduce the shrinkage, bending and deformation of the pipe caused by excessive temperature differences. Although this solution can solve the problems of low-temperature brittle cracking that are prone to existing PPR pipes, it has more process steps similar to the above solution, long processing time and low production efficiency.

[0006] Invention patent number: 201621356674.6, proposes a shelf for annealing plastic pipes. By setting a frame and a number of cages, the cages can be stacked in the frame, and then the plastic pipes are placed side by side on the surface of the cages. Each layer of cages can fix the plastic pipes while leaving enough space to avoid damage caused by mutual squeezing between the plastic pipes and deformation caused by stress during cooling; by setting positioning shafts and positioning slots, the frames can be stacked, so that the plastic pipes occupy a small area and have good stacking firmness. A large number of plastic pipes can be transported at one time, and a large number of plastic pipes can be annealed at one time; by setting forklift sockets and rollers, the shelf can be easily transported, and continuous annealing operations cannot be achieved. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a rationally designed continuous annealing furnace for plastic pipes and an annealing process thereof.

[0008] The technical solutions of the present invention are as follows:

[0009] The continuous annealing furnace for plastic pipes comprises a furnace body, a hot air circulation heating device and a continuous pipe conveying device; the furnace body is fixed on the ground by a steel support frame, and the hot air circulation heating device is symmetrically arranged at relative positions on both sides of the furnace body. The hot air circulation heating device can extract the space in the furnace body, heat it and then re-send it into the furnace body; the continuous pipe conveying device is arranged inside the furnace body, and the continuous pipe conveying device can realize the loading, continuous annealing and unloading of pipes.

[0010] Furthermore, the hot air circulation heating device includes a circulation fan, a circulation air duct and a heating tube assembly. One end of the circulation air duct is connected to the side of the furnace body, and the other end is connected to the top of the furnace body. The heating tube assembly is arranged inside the circulation air duct, and the circulation fan is arranged on the circulation air duct. The air inside the furnace body is heated by the circulation fan through the heating tube and then sent into the furnace body again from the top of the furnace body.

[0011] Furthermore, the circulating fan includes a motor, a transmission assembly, a main shaft assembly and fan blades, the fan blades are connected to the main shaft assembly, one end of the transmission assembly is connected to the main shaft assembly, and the other end is connected to the motor; the circulating air duct includes an air inlet section, a heating section and an air outlet section, the fan blades are arranged at the air inlet section, and the heating tube assembly is arranged at the heating section; the heating tube assembly includes several heating tubes, the heating tubes are U-shaped tubes, and are horizontally arranged in the cavity of the heating section.

[0012] Furthermore, the top surface and four side surfaces of the furnace body are closed, and an opening is provided on the bottom surface of the furnace body.

[0013] Furthermore, the continuous pipe conveying device includes a pipe loading mechanism, a pipe horizontal conveying mechanism, a pipe unloading mechanism and a driving mechanism. The pipe loading mechanism is an inverted L-shaped structure, which can convey the plastic pipe at the bottom to the top of the furnace body along the side of the furnace body. The horizontal pipe conveying mechanism is arranged between the pipe loading mechanism and the pipe unloading mechanism, which can enable the pipe to be continuously S-shaped conveyed inside the furnace body to realize continuous annealing operation; the pipe unloading mechanism is an inverted L-shaped structure, which can deliver the plastic pipe passing through the horizontal pipe conveying mechanism from the bottom of the furnace body to the side of the furnace body.

[0014] Furthermore, the pipe unloading mechanism has the same structure as the pipe loading mechanism, both of which include a conveying support frame, a first driving shaft is provided on one side of the conveying support frame, a group of sprockets are provided on the first driving shaft along its axial direction, a support shaft is provided on the other side of the conveying support frame, a group of sprockets are provided on the support shaft along its axial direction, the conveying support frame is provided with a first driven shaft at a lower position on one side of the support shaft, a group of sprockets are provided on the first driven shaft along its axial direction, the same first transmission chain is wound around the sprockets corresponding to the first driving shaft, the support shaft and the first driven shaft, and gear rods are provided at equal intervals on the first transmission chain.

[0015] Furthermore, two support shafts are provided on one side of the conveying support frame, and the support shaft includes an upper support shaft and a lower support shaft arranged below the upper support shaft; bearing assemblies are respectively provided at both ends of the first driving shaft, the upper support shaft, the lower support shaft and the first driven shaft, and are supported on the furnace body through the bearing assemblies; one end of the first conveying chain is provided on the sprocket of the first driving shaft, and the other end is arranged around the upper ends of the sprockets of the upper support shaft and the lower support shaft and then wound around the sprocket of the first driven shaft, thereby forming an L-shaped conveying loop; the gear rod is tilted on the first conveying chain, and the angle between the gear rod and the first conveying chain is an acute angle, which is convenient for positioning the pipe and ensuring that the plastic pipe fittings are loaded and unloaded under the action of the first conveying chain.

[0016] The transmission mechanism is a pair of transmission mechanisms, each of which is connected to the transmission mechanism, and the transmission mechanism has a pair of transmission mechanisms, each of which is connected to the transmission mechanism, and the transmission mechanism has a pair of transmission mechanisms, each of which is connected to the transmission mechanism, and the transmission mechanism has a pair of transmission mechanisms.

[0017] Furthermore, the driving mechanism includes a driving motor, a driving sprocket, a tensioning sprocket and a driving chain. The driving motor is arranged on the outer wall of the furnace body. The driving sprockets are respectively arranged on the output shaft of the driving motor, the first driving shaft of the pipe feeding mechanism, the second driving shaft of the pipe horizontal conveying mechanism, and one end of the first driving shaft of the pipe unloading mechanism. The tensioning sprocket is arranged on the furnace body, and the driving chain is wound around the driving sprocket and the tensioning sprocket, so that the driving motor drives the pipe feeding mechanism, the pipe horizontal conveying mechanism, and the pipe unloading mechanism to work simultaneously.

[0018] A continuous annealing process for plastic pipes, comprising the following steps:

[0019] 1) Annealing furnace circulation heating: A hot air circulation heating device is installed on the annealing furnace. The air in the annealing furnace is extracted from the side of the annealing furnace and heated. The heated air is then sent into the annealing furnace from the top of the annealing furnace to achieve hot air circulation heating;

[0020] 2) Loading of annealing furnace: Plastic pipes are lifted to the top of the annealing furnace in sequence from the bottom of one side of the annealing furnace through the pipe loading mechanism;

[0021] 3) Annealing in the annealing furnace: After the plastic pipe reaches the top of the annealing furnace, it enters the top layer. Under the action of the pipe feeding mechanism, the plastic pipe is horizontally transported to the other side of the annealing furnace and then falls to one side of the next layer. Under the action of the pipe horizontal conveying mechanism, the plastic pipe is horizontally transported to the other side of the layer and then falls to the next layer. This continues in the S-layer route until the plastic pipe reaches the bottom layer.

[0022] 4) Annealing furnace unloading: After the plastic pipe reaches the bottom layer, the pipe unloading mechanism will transport the plastic pipe to one side of the annealing furnace for unloading;

[0023] 5) Complete the annealing furnace process.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1) By arranging hot air circulation heating devices symmetrically on both sides of the annealing furnace, the air at the bottom of the annealing furnace can be heated by electric heating and then transported from the top of the annealing furnace to the inside of the annealing furnace, which can achieve the effect of circulating hot air heating, ensure the flow of air in the annealing furnace and the uniformity of heating inside the annealing furnace, and improve the annealing effect; in addition, the hot air circulation heating device is arranged on the outside of the annealing furnace, which improves the space utilization rate inside the furnace and provides a basis for the layout of the conveying system in the annealing furnace.

[0026] 2) By arranging a tube loading mechanism, a tube horizontal conveying mechanism and a tube unloading mechanism inside the annealing furnace, the automatic annealing process of the tube can be realized. In addition, under the action of the tube horizontal conveying mechanism, the tube can run inside the annealing furnace according to a continuous S-layer route, which effectively guarantees the annealing time and further improves the annealing effect.

[0027] 3) The continuous annealing process proposed in the present invention has a high degree of automation, good heat uniformity during the annealing process, and the annealing time can be precisely controlled, thereby ensuring the mechanical properties of each pipe and improving the quality of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the installation structure of the hot air circulation heating device of the present invention;

[0029] Figure 2 This is a schematic structural diagram of the hot air circulation heating device of the present invention;

[0030] Figure 3 This is a schematic diagram of the internal structure of the hot air circulation heating device of the present invention;

[0031] Figure 4 This is a schematic diagram of the installation structure of the pipe continuous conveying device of the present invention;

[0032] Figure 5 This is a schematic diagram of the overall structure of the pipe continuous conveying device of the present invention;

[0033] Figure 6 This is a schematic structural diagram of the pipe feeding mechanism of the present invention;

[0034] Figure 7 It is a structural schematic diagram of the horizontal pipe conveying mechanism of the present invention;

[0035] Figure 8 This is a schematic structural diagram of the pipe blanking mechanism of the present invention;

[0036] Figure 9 This is a schematic diagram of the gear lever installation structure of the present invention;

[0037] In the figure: 1 - furnace body; 2 - continuous pipe conveying device; 21 - pipe feeding mechanism; 2101 - first driving shaft; 2102 - upper support shaft; 2103 - lower support shaft; 2104 - first conveyor chain; 2105 - first driven shaft; 2106 - gear lever; 22 - pipe unloading mechanism; 23 - horizontal pipe conveying mechanism; 2301 - second driving shaft; 2302 - second driven shaft; 2303 - second conveyor chain; 24 - conveyor support frame; 25 - Longitudinal support frame; 26-transverse support frame; 27-bearing assembly; 28-sprocket; 29-material stop frame; 31-drive motor; 32-drive sprocket; 33-tensioning sprocket; 34-drive chain; 3-drive mechanism; 4-hot air circulation heating device; 401-motor; 402-air inlet section; 403-heating section; 404-air outlet section; 405-transmission assembly; 406-spindle assembly; 407-fan blades; 408-heating tube; 5-steel support frame. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings.

[0039] like Figure 1-9 As shown, a continuous annealing furnace for plastic pipes includes a furnace body 1, a hot air circulation heating device 4 and a continuous pipe conveying device 2.

[0040] The furnace body 1 is fixed on the ground by a steel support frame 5. The hot air circulation heating device 4 is symmetrically arranged at relative positions on both sides of the furnace body 1. The hot air circulation heating device 4 can extract the space in the furnace body 1, heat it, and then send it back into the furnace body; the pipe continuous conveying device 2 is arranged inside the furnace body 1. The pipe continuous conveying device 2 can realize the loading, continuous annealing and unloading of pipes.

[0041] Specifically, the hot air circulation heating device 4 includes a circulation fan, a circulation air duct and a heating tube assembly. One end of the circulation air duct is connected to the side of the furnace body 1, and the other end is connected to the top of the furnace body 1. The heating tube assembly is arranged inside the circulation air duct, and the circulation fan is arranged on the circulation air duct. The air inside the furnace body 1 is heated by the circulation fan through the heating tube and then sent into the furnace body again from the top of the furnace body.

[0042] Specifically, the circulating fan includes a motor 401 , a transmission assembly 405 , a main shaft assembly 406 and fan blades 407 . The fan blades 407 are connected to the main shaft assembly 406 . One end of the transmission assembly 405 is connected to the main shaft assembly 406 , and the other end is connected to the motor 401 .

[0043] Specifically, the circulating air duct includes an air inlet section 402 , a heating section 403 and an air outlet section 404 . The fan blades 407 are arranged at the air inlet section 402 , and the heating tube assembly is arranged at the heating section 403 .

[0044] Specifically, the heating tube assembly includes a plurality of heating tubes 408 , which are U-shaped tubes and are horizontally arranged in the cavity of the heating section 403 .

[0045] Specifically, the top surface and four side surfaces of the furnace body 1 are closed, and the bottom surface of the furnace body 1 is provided with openings (the openings are provided at positions corresponding to the tube feeding mechanism 21 and the tube unloading mechanism 22 ).

[0046] The continuous pipe conveying device 2 of the annealing furnace (plastic pipe continuous annealing furnace pipe transmission assembly) includes a pipe feeding mechanism 21, a pipe horizontal conveying mechanism 23, a pipe unloading mechanism 22 and a driving mechanism 3. The pipe feeding mechanism 21 is an inverted L-shaped structure, which can convey the plastic pipe at the bottom to the top of the furnace body 1 along the side of the furnace body 1. The pipe horizontal conveying mechanism 23 is arranged between the pipe feeding mechanism 21 and the pipe unloading mechanism 22, which can enable the pipe to be continuously S-shaped conveyed inside the furnace body 1 to realize continuous annealing operation; the pipe unloading mechanism 22 is an inverted L-shaped structure, which can convey the plastic pipe passing through the pipe horizontal conveying mechanism 23 from the bottom of the furnace body 1 to the side of the furnace body 1.

[0047] Specifically, the pipe unloading mechanism 22 has the same structure as the pipe loading mechanism 21, and both include a conveying support frame 24. A first driving shaft 2101 is provided on one side of the conveying support frame 24, and a group of sprockets 28 are provided on the first driving shaft 2101 along its axial direction. A support shaft is provided on the other side of the conveying support frame 24, and a group of sprockets 28 are provided on the support shaft along its axial direction. The conveying support frame 24 is provided with a first driven shaft 2105 at a lower position on one side of the support shaft, and a group of sprockets 28 are provided on the first driven shaft 2105 along its axial direction. The same first transmission chain 2104 is wound around the sprockets 28 corresponding to the first driving shaft, the support shaft and the first driven shaft, and gear rods 2106 are arranged at equal intervals on the first transmission chain 2104.

[0048] Specifically, two support shafts are provided on one side of the conveying support frame 24 (since the conveying chain runs in a closed loop, both the upper and lower sides of the conveying chain need support to ensure smooth operation). The support shafts include an upper support shaft 2102 and a lower support shaft 2103 provided below the upper support shaft 2102.

[0049] Specifically, bearing assemblies 27 are respectively provided at both ends of the first driving shaft 2101 , the upper supporting shaft 2102 , the lower supporting shaft 2103 and the first driven shaft 2105 , and are supported on the furnace body 1 through the bearing assemblies 27 .

[0050] Specifically, one end of the first conveying chain 2104 is set on the sprocket 28 of the first driving shaft 2101, and the other end is set around the upper ends of the sprockets 28 of the upper support shaft 2102 and the lower support shaft 2103 and then wound around the sprocket 28 of the first driven shaft 2105, thereby forming an L-shaped conveying loop.

[0051] Specifically, the shift rod 2106 is tiltedly arranged on the first conveyor chain 2104 , and the angle between the shift rod 2106 and the first conveyor chain 2104 is an acute angle, which facilitates the positioning of the pipe and ensures that the plastic pipe fittings are loaded and unloaded under the action of the first conveyor chain 2104 .

[0052] The horizontal pipe conveying mechanism 23 includes a conveying support frame 24, and a second driving shaft 2301 is provided on one side of the conveying support frame 24, and a second driven shaft 2302 is provided on the other side. A group of sprockets 28 are correspondingly provided on the second driving shaft 2301 and the second driven shaft 2302 along the axial direction. A second conveying chain 2303 is wound between the second driving shaft 2301 and the second driven shaft 2302, and gear rods 2106 are arranged at equal intervals on the second conveying chain 2303.

[0053] Specifically, bearing assemblies 27 are respectively provided at both ends of the second driving shaft 2301 and the second driven shaft 2302 , and are supported on the furnace body 1 by the bearing assemblies 27 .

[0054] Specifically, the conveying support frame 24 includes a longitudinal support frame 25 and a transverse support frame 26. A group of the longitudinal support frames 25 are arranged at intervals and in parallel, and a group of the transverse support frames 26 are arranged at intervals and in parallel, and vertically penetrate the longitudinal support frame 25, and the two ends of the transverse support frame 26 are respectively supported on the furnace body 1.

[0055] Specifically, the furnace body 1 is provided with material blocking racks 29 (in a continuous C-shaped structure) on both sides of the pipe loading mechanism 21, the pipe unloading mechanism 22 and the pipe horizontal conveying mechanism 23, respectively, to ensure that the pipes can enter the pipe horizontal conveying mechanism 23 from the pipe loading mechanism 21, the pipes can be continuously conveyed in an S-shape in the pipe horizontal conveying mechanism 23, and the pipes can enter the pipe unloading mechanism 22 from the pipe horizontal conveying mechanism 23.

[0056] The driving mechanism 3 includes a driving motor 31, a driving sprocket 32, a tensioning sprocket 33 and a driving chain 34. The driving motor 31 is arranged on the outer wall of the furnace body 1. The driving sprocket 32 is respectively arranged on the output shaft of the driving motor, the first driving shaft of the pipe feeding mechanism, the second driving shaft of the pipe horizontal conveying mechanism, and one end of the first driving shaft of the pipe unloading mechanism. The tensioning sprocket 33 is arranged on the furnace body 1. The driving chain 34 is wound around the driving sprocket 32 and the tensioning sprocket 33, so that the pipe feeding mechanism 21, the pipe horizontal conveying mechanism 23, and the pipe unloading mechanism 22 are driven to work simultaneously by the driving motor 31. The present invention only uses one motor to realize the operation of the pipe feeding mechanism, the pipe horizontal conveying mechanism and the pipe unloading mechanism.

[0057] A continuous annealing process for plastic pipes, the specific steps are as follows:

[0058] 1) Annealing furnace circulation heating: A hot air circulation heating device is installed on the annealing furnace. The air in the annealing furnace is extracted from the side of the annealing furnace and heated. The heated air is then sent into the annealing furnace from the top (the temperature inside the annealing furnace is controlled at 90 degrees Celsius) to achieve hot air circulation heating. The hot air circulation heating device is symmetrically arranged on both sides of the annealing furnace body and adopts an electric heating blast heating method.

[0059] 2) Loading of annealing furnace: Plastic pipes are lifted to the top of the annealing furnace in sequence from the bottom of one side of the annealing furnace through the pipe loading mechanism; the pipe loading mechanism adopts a set of inverted L-shaped conveyor belts arranged along the axial direction of the plastic pipe.

[0060] 3) Annealing in the annealing furnace: After the plastic pipe reaches the top of the annealing furnace, it enters the top layer. Under the action of the pipe feeding mechanism, the plastic pipe is horizontally transported to the other side of the annealing furnace and then falls to one side of the next layer. Under the action of the pipe horizontal conveying mechanism, the plastic pipe is horizontally transported to the other side of the layer and then falls to the next layer, following the above-mentioned continuous S-layer route until the plastic pipe reaches the bottom layer; the pipe horizontal conveying mechanism adopts a set of straight-line conveyor belts arranged in the vertical direction.

[0061] 4) Annealing furnace unloading: After the plastic pipe reaches the bottom layer, the pipe unloading mechanism will transport the plastic pipe to one side of the annealing furnace for unloading. The pipe unloading mechanism adopts a set of inverted L-shaped conveyor belts arranged along the axial direction of the plastic pipe, and the pipe unloading mechanism and the pipe loading mechanism are arranged in parallel on the same side of the annealing furnace.

[0062] 5) The time that the plastic pipe runs in the annealing furnace is controlled within 1-2 hours (by controlling the speed of the annealing furnace's pipe continuous conveying device, the specific time is 80 minutes) to complete the annealing furnace process.

[0063] The above embodiments are only preferred embodiments of the present invention and are not limitations on the technical solutions of the present invention. Any technical solution that can be implemented on the basis of the above embodiments without creative work should be deemed to fall within the scope of protection of the patent of the present invention.

Claims

1. Plastic pipe continuous annealing furnace, characterized by: The invention comprises a furnace body (1), a hot air circulation heating device (4) and a continuous pipe conveying device (2); the furnace body (1) is fixedly arranged on the ground by a steel support frame (5); the hot air circulation heating device (4) is symmetrically arranged at opposite positions on both sides of the furnace body (1); the hot air circulation heating device (4) can extract the space in the furnace body (1), heat it and then re-enter the furnace body; the continuous pipe conveying device (2) is arranged inside the furnace body (1); the continuous pipe conveying device (2) can realize the loading, continuous annealing and unloading of pipes; The hot air circulation heating device (4) comprises a circulation fan, a circulation duct and a heating tube assembly, one end of the circulation duct is connected to the side of the furnace body (1), and the other end is connected to the top of the furnace body (1), the heating tube assembly is arranged inside the circulation duct, and the circulation fan is arranged on the circulation duct. The circulation fan heats the air inside the furnace body (1) through the heating tube and then sends the air into the furnace body again from the top of the furnace body; The pipe continuous conveying device (2) comprises a pipe loading mechanism (21), a pipe horizontal conveying mechanism (23), a pipe unloading mechanism (22) and a driving mechanism (3); the pipe loading mechanism (21) is an inverted L-shaped structure, capable of conveying the plastic pipe at the bottom to the top of the furnace body (1) along the side of the furnace body (1); the pipe horizontal conveying mechanism (23) is arranged between the pipe loading mechanism (21) and the pipe unloading mechanism (22), capable of performing continuous S-shaped conveying of the pipe inside the furnace body (1), thereby realizing a continuous annealing operation; the pipe unloading mechanism (22) is an inverted L-shaped structure, capable of conveying the plastic pipe passing through the pipe horizontal conveying mechanism (23) from the bottom of the furnace body (1) to the side of the furnace body (1); The pipe unloading mechanism (22) has the same structure as the pipe loading mechanism (21), and both include a conveying support frame (24), a first driving shaft (2101) is provided on one side of the conveying support frame (24), and a group of sprockets (28) are provided on the first driving shaft (2101) along its axial direction, a support shaft is provided on the other side of the conveying support frame (24), and a group of sprockets (28) are provided on the support shaft along its axial direction, the conveying support frame (24) is provided with a first driven shaft (2105) at a lower position on one side of the support shaft, and a group of sprockets (28) are provided on the first driven shaft (2105) along its axial direction, the first driving shaft, the support shaft and the sprockets (28) corresponding to the first driven shaft are wound with the same first conveying chain (2104), and the first conveying chain (2104) is provided with gear bars (2106) at equal intervals; The pipe horizontal conveying mechanism (23) includes a conveying support frame (24), a second driving shaft (2301) is provided on one side of the conveying support frame (24), and a second driven shaft (2302) is provided on the other side, a group of sprockets (28) are provided on the second driving shaft (2301) and the second driven shaft (2302) along the axial direction, a second conveying chain (2303) is wound between the second driving shaft (2301) and the second driven shaft (2302), and shift rods (2106) are provided on the second conveying chain (2303) at equal intervals; bearing assemblies (27) are provided at both ends of the second driving shaft (2301) and the second driven shaft (2302), and are supported on the furnace body (1) through the bearing assemblies (27); the conveying support frame (24) The invention comprises a longitudinal support frame (25) and a transverse support frame (26), wherein a group of the longitudinal support frames (25) are spaced apart and arranged in parallel, and a group of the transverse support frames (26) are spaced apart and arranged in parallel and vertically penetrate the longitudinal support frames (25), and both ends of the transverse support frames (26) are respectively supported on the furnace body (1); inside the furnace body (1), material blocking frames (29) are respectively provided on both sides of the pipe feeding mechanism (21), the pipe unloading mechanism (22) and the pipe horizontal conveying mechanism (23), so as to ensure that the pipe can enter the pipe horizontal conveying mechanism (23) from the pipe feeding mechanism (21), the pipe can be continuously conveyed in an S-shape in the pipe horizontal conveying mechanism (23), and the pipe can enter the pipe unloading mechanism (22) from the pipe horizontal conveying mechanism (23).

2. The continuous annealing furnace for plastic pipes according to claim 1, characterized in that: The circulating fan comprises a motor (401), a transmission assembly (405), a main shaft assembly (406) and a fan blade (407), wherein the fan blade (407) is connected to the main shaft assembly (406), one end of the transmission assembly (405) is connected to the main shaft assembly (406), and the other end is connected to the motor (401); the circulating air duct comprises an air inlet section (402), a heating section (403) and an air outlet section (404), wherein the fan blade (407) is arranged at the air inlet section (402), and the heating tube assembly is arranged at the heating section (403); the heating tube assembly comprises a plurality of heating tubes (408), wherein the heating tubes are U-shaped tubes and are horizontally arranged in the cavity of the heating section (403).

3. The continuous annealing furnace for plastic pipes according to claim 1, characterized in that: The top surface and four side surfaces of the furnace body (1) are closed, and the bottom surface of the furnace body (1) is provided with an opening.

4. The continuous annealing furnace for plastic pipes according to claim 1, characterized in that: Two support shafts are provided on one side of the conveying support frame (24), and the support shafts include an upper support shaft (2102) and a lower support shaft (2103) provided below the upper support shaft (2102); bearing assemblies (27) are provided at both ends of the first driving shaft (2101), the upper support shaft (2102), the lower support shaft (2103) and the first driven shaft (2105), and are supported on the furnace body (1) through the bearing assemblies (27); one end of the first conveying chain (2104) is provided on the first driving shaft (2101), the upper support shaft (2102), the lower support shaft (2103) and the first driven shaft (2105); 1), and the other end is arranged around the upper end of the sprocket (28) of the upper support shaft (2102) and the lower support shaft (2103) and then around the sprocket (28) of the first driven shaft (2105), thereby forming an L-shaped conveying loop; the shift rod (2106) is tilted and arranged on the first conveying chain (2104), and the angle between the shift rod (2106) and the first conveying chain (2104) is an acute angle, which is convenient for positioning the pipe and ensuring that the plastic pipe fittings are loaded and unloaded under the action of the first conveying chain (2104).

5. The continuous annealing furnace for plastic pipes according to claim 1, characterized in that: The driving mechanism (3) includes a driving motor (31), a driving sprocket (32), a tensioning sprocket (33) and a driving chain (34). The driving motor (31) is arranged on the outer wall of the furnace body (1). The driving sprocket (32) is respectively arranged on one end of the output shaft of the driving motor, the first driving shaft of the pipe feeding mechanism, the second driving shaft of the pipe horizontal conveying mechanism, and the first driving shaft of the pipe unloading mechanism. The tensioning sprocket (33) is arranged on the furnace body 1. The driving chain (34) is wound around the driving sprocket (32) and the tensioning sprocket (33), so that the pipe feeding mechanism (21), the pipe horizontal conveying mechanism (23) and the pipe unloading mechanism (22) are driven to work simultaneously through the driving motor (31).

6. The continuous annealing process for plastic pipes according to any one of claims 1 to 5, characterized in that: The steps include: 1) Annealing furnace circulation heating: A hot air circulation heating device is installed on the annealing furnace. The air in the annealing furnace is extracted from the side of the annealing furnace and heated. The heated air is then sent into the annealing furnace from the top of the annealing furnace to achieve hot air circulation heating; 2) Loading of annealing furnace: Plastic pipes are lifted to the top of the annealing furnace in sequence from the bottom of one side of the annealing furnace through the pipe loading mechanism; 3) Annealing in the annealing furnace: After the plastic pipe reaches the top of the annealing furnace, it enters the top layer. Under the action of the pipe feeding mechanism, the plastic pipe is horizontally transported to the other side of the annealing furnace and then falls to one side of the next layer. Under the action of the pipe horizontal conveying mechanism, the plastic pipe is horizontally transported to the other side of the layer and then falls to the next layer, following the continuous S-layer route until the plastic pipe reaches the bottom layer; 4) Annealing furnace unloading: After the plastic pipe reaches the bottom layer, the pipe unloading mechanism will transport the plastic pipe to one side of the annealing furnace for unloading; 5) Complete the annealing furnace process.

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