CN110394972B

CN110394972B - Device for manufacturing biaxial orientation PVC pipe elbow and method for manufacturing elbow

Info

Publication number: CN110394972B
Application number: CN201910723347.1A
Authority: CN
Inventors: 许德祥
Original assignee: Zhejiang Rongde Management Co Ltd
Current assignee: Zhejiang Rongde Management Co., Ltd
Priority date: 2019-08-07
Filing date: 2019-08-07
Publication date: 2020-08-21
Anticipated expiration: 2039-08-07
Also published as: CN110394972A

Abstract

The invention discloses a device for producing a biaxial orientation PVC pipe elbow and a method for manufacturing the elbow, wherein the device comprises a kit consisting of a first blank pipe expansion die, a second blank pipe expansion die, an elbow forming die, a die tail plug cover and a die head plug cover; the first blank pipe expanding die and the second blank pipe expanding die can be connected to one end of the elbow forming die and are used for manufacturing the blank pipes into the biaxial orientation PVC pipes; the elbow forming die is used for converting the prepared biaxial orientation PVC pipe into a biaxial orientation PVC bent pipe; the mould tail plug cover and the mould head plug cover are used for limiting each part of the elbow forming mould and preventing the elbow forming mould from moving; in the invention, the blank pipe expanding die and the elbow forming die are connected together, so that the whole production process is continuously carried out, the blank pipe in a high elastic state can immediately enter the elbow forming die to be bent and formed after the blank pipe is subjected to bidirectional stretching by the blank pipe expanding die, and the production efficiency is higher without pause in the middle.

Description

Device for manufacturing biaxial orientation PVC pipe elbow and method for manufacturing elbow

Technical Field

The invention relates to the field of plastic pipe fitting processing, in particular to processing and manufacturing of a biaxial orientation PVC pipe elbow.

Background

Biaxially oriented PVC pipe (also known as PVC-O pipe) is the most recent form of PVC pipe that has evolved and is manufactured by a special orientation process. The biaxially oriented PVC pipe has the advantages that the molecular arrangement structure of the material is changed by biaxially stretching the material, namely, the PVC-U pipe produced by the extrusion method is axially stretched and radially stretched, so that PVC long-chain molecules in the pipe are regularly arranged in two stretching directions, and the pipe has high strength, high impact resistance and excellent fatigue resistance.

At present, although the processing technology of the PVC-O straight pipe is mature, the processing technology of the PVC-O bent pipe is very complex, the processing reliability is poor, the rejection rate is high, and the use popularization rate of the PVC-O pipe elbow (namely the biaxial orientation PVC pipe elbow) is low. Therefore, in the existing PVC-O pipe water supply net, the turning part is usually connected by adopting the steel-plastic composite elbow, but the steel-plastic composite elbow has certain defects, such as high price, short service life (generally less than 20 years) and the like.

The main reasons for the complex processing technology of the PVC-O bent pipe are as follows: when the PVC-O straight pipe is bent, the PVC-O straight pipe needs to be heated to a thermoplastic state firstly and then can be bent, and the PVC-O straight pipe is obtained by heating a PVC-U straight pipe (namely a blank pipe) to the thermoplastic state and then performing radial expansion and axial stretching through ventilation, so that when the PVC-O straight pipe is heated again during bending, the pipe is easy to de-orient and retract, and particularly when the heating temperature is closer to the temperature (about 90 ℃) required by the thermoplastic state, the phenomenon of de-orientation retraction is more serious. Therefore, the existing PVC-O bent pipe processing technology is very complex, the quality is difficult to control in the processing process, the rejection rate is high, and the PVC-O bent pipe is difficult to widely popularize and use.

Because the PVC-O pipe has excellent performances such as high strength, high impact resistance and excellent fatigue resistance, the bend connection is not carried out by adopting a PVC-O pipe elbow in the PVC-O water supply network pipe, but the steel-plastic composite elbow is used for replacing the PVC-O pipe elbow, and the method is really nothing to do.

Therefore, the inventor believes that it is necessary to design a tool set to simplify the manufacturing process of biaxially oriented PVC piping elbows, to make the manufacturing process more reliable, and to produce more than one specification of biaxially oriented PVC piping elbows.

Disclosure of Invention

The invention aims to solve the technical problem of providing a device for producing a biaxial orientation PVC pipe elbow and a method for producing the PVC pipe elbow by using the device, so that the production process of the biaxial orientation PVC pipe elbow can be simplified and is more reliable, and the device has two functions and can produce the biaxial orientation PVC pipe elbows with two specifications.

The technical scheme adopted by the invention for solving the technical problems is as follows: the device for manufacturing the biaxial orientation PVC pipe elbow comprises a kit consisting of a first blank pipe expansion die, a second blank pipe expansion die, an elbow forming die, a die tail plug cover and a die head plug cover;

the first blank pipe expansion die is used for being connected to one end of the elbow forming die and comprises a first guide section, a first sealing section, a first expansion section and a first diameter section which are sequentially connected into a whole; the first guide section is a cylinder and is used for guiding a blank pipe to be expanded; the first sealing section is also a cylinder, the outer diameter of the first sealing section is slightly larger than that of the first guide section, and the first sealing section is in smooth transition connection with the first guide section through a conical surface; the first expansion section is a cone, the small-caliber end of the first expansion section is connected with the first sealing section, and the large-caliber end of the first expansion section is connected with the first diameter section; the first diameter section is a cylinder, and the outer diameter of the first diameter section is larger than that of the first sealing section;

the second blank pipe expansion die is also used for being connected to one end of the elbow forming die and comprises a second guide section, a second sealing section, a second expansion section and a second sizing section which are sequentially connected into a whole; the second guide section has the same structure as the first guide section and is also used for guiding the blank pipe to be expanded; the structure of the second sealing section is consistent with that of the first sealing section, and the second sealing section is also in smooth transition connection with the second guide section through a conical surface; the second expansion section is a cone, the small-caliber end of the second expansion section is connected with the second sealing section, and the large-caliber end of the second expansion section is connected with the second sizing section; the second sizing section is a cylinder, and the outer diameter of the second sizing section is larger than that of the second sealing section and is also larger than that of the first sizing section;

the elbow forming die comprises an inner die body, an intermediate die body and an outer die body; the inner layer die body is of a hollow bent pipe-shaped structure and is formed by combining a first half die and a second half die which can be separated from each other, and the outer diameter of the inner layer die body is consistent with that of the first diameter section; the middle layer die body is also of a hollow bent pipe-shaped structure and is formed by combining a third half die and a fourth half die which can be separated from each other, the inner diameter of the middle layer die body is larger than the outer diameter of the inner layer die body, and the outer diameter of the middle layer die body is consistent with the outer diameter of the second sizing section; the outer layer die body is also of a hollow bent pipe structure and is formed by combining a fifth half die and a sixth half die which can be separated from each other, and the inner diameter of the outer layer die body is larger than the outer diameter of the middle layer die body;

the mould tail part plug cover is used for covering one end of the elbow forming mould which is not connected with the first blank pipe expansion mould or the second blank pipe expansion mould, and comprises a bottom plate, a first platform body, a second platform body and a third platform body which are connected into a whole; the bottom plate is disc-shaped; the first platform body is positioned on one side of the bottom plate, a first groove is formed in the middle of one side, away from the bottom plate, of the first platform body, a first annular raised ring is arranged on the periphery of the first groove, and the first annular raised ring can be inserted into a gap between the outer layer die body and the middle layer die body in an interference fit manner; the second table body is arranged in the first groove, a second groove is formed in the middle of one side, away from the first table body, of the second table body, a second annular raised ring is arranged on the periphery of the second groove, and the second annular raised ring can be inserted into a gap between the middle layer mold body and the inner layer mold body in an interference fit manner; the third platform body is arranged in the second groove, is of a cylindrical structure and can be inserted into the inner cavity of the inner layer die body in an interference fit manner;

the die head plug cover is used for covering one end of the elbow forming die connected with the first blank pipe expansion die and comprises a hollow disc and a hollow ring which are connected into a whole; the diameter of the round hole in the middle of the hollow disc is between the inner diameter and the outer diameter of the middle layer die body; the hollow circular ring is connected to one side of the hollow circular plate and is coaxial with the hollow circular plate, and the hollow circular ring can be inserted into a gap between the outer layer die body and the middle layer die body in an interference fit mode.

Furthermore, the first half die is provided with a first positioning groove, the second half die is provided with a first positioning column, and the first half die and the second half die are positioned through the matching of the first positioning groove and the first positioning column; the third half die is provided with a second positioning groove, the fourth half die is provided with a second positioning column, and the third half die and the fourth half die are positioned through the matching of the second positioning groove and the second positioning column; the fifth half die is provided with a first lug plate, the sixth half die is provided with a second lug plate, and the fifth half die and the sixth half die are fixed through the connection of the first lug plate and the second lug plate.

Furthermore, the plug cover at the tail part of the mould is provided with at least two first air holes, at least two second air holes and a third air hole; the first air hole penetrates through the first platform body and the bottom plate from the first annular raised ring; the second air hole penetrates through the second platform body, the first platform body and the bottom plate from the second annular raised ring; the third air hole penetrates through the third platform body, the second platform body, the first platform body and the bottom plate at the same time.

Furthermore, the plug cover at the head part of the mould is provided with at least two fourth air holes; the fourth air hole penetrates through the hollow disc and the hollow circular ring at the same time.

Further, the first parison tube expansion mold is provided with a first through hole axially penetrating through the first parison tube expansion mold; the second blank pipe expanding die is provided with a second through hole which axially penetrates through the second blank pipe expanding die.

Further, the first parison tube expansion die further comprises a first threaded ring, the first threaded ring is connected to one end, away from the first expansion section, of the first diameter section, and external threads are arranged on the outer wall of the first threaded ring; an internal thread is arranged at one end of the inner layer die body connected with the first parison tube expansion die; the external thread of the first thread ring and the internal thread of the first parison tube expansion mould can be in thread fit to realize connection;

the second parison tube expansion die further comprises a second threaded ring, the second threaded ring is connected to one end, far away from the second expansion section, of the second sizing section, and external threads are arranged on the outer wall of the second threaded ring; an internal thread is arranged at one end of the middle layer die body connected with the second parison tube expansion die; the external thread of the second thread ring and the internal thread of the second parison tube expansion mould can be in thread fit to realize connection.

In addition, the invention also provides a method for manufacturing the PVC pipe elbow by using the device, and the method can manufacture two PVC pipe elbows with different sizes;

the method comprises the following steps:

s1, assembling an elbow forming die: sleeving the middle layer die body outside the inner layer die body, and sleeving the outer layer die body outside the inner layer die body;

when the first half die is in butt joint with the second half die, the first locating groove is matched with the first locating column to realize locating, when the third half die is in butt joint with the fourth half die, the second locating groove is matched with the second locating column to realize locating, and when the fifth half die is in butt joint with the sixth half die, the fifth half die is fixed with the sixth half die through connection of the first lug plate and the second lug plate;

s2, plugging a plug cover at the tail part of the mould into one end of the elbow forming mould, which is not connected with the first blank pipe expanding mould or the second blank pipe expanding mould;

when the tail plug cover of the mold is plugged, the first annular bulge ring is inserted into a gap between the outer layer mold body and the middle layer mold body in an interference fit manner, and the second annular bulge ring is inserted into a gap between the middle layer mold body and the inner layer mold body in an interference fit manner;

then, if the inner diameter is equal to the outer diameter of the inner layer die body and the outer diameter is equal to the inner diameter of the middle layer die body, the PVC pipe elbow is manufactured according to the following steps:

s311, connecting the first blank pipe expansion die to one end, far away from a die tail plug cover, of the elbow forming die, and simultaneously plugging a die head plug cover into one end, connected with the first blank pipe expansion die, of the elbow forming die;

when the first parison tube expansion die is connected, the external threads of the first threaded ring are matched with the internal threads of the inner die body to realize connection; when the plug cover is plugged into the head part of the mold, the hollow circular ring is inserted into a gap between the outer layer mold body and the middle layer mold body in an interference fit manner;

s312, heating the blank pipe to a high-elasticity state, guiding the blank pipe into a first blank pipe expansion die from a first guide section, and enabling the blank pipe to pass through a first sealing section under the action of traction force and then pass through a first expansion section and a first diameter section in sequence to be expanded into a biaxial orientation PVC pipe;

s313, under the action of traction force, enabling the expanded biaxial orientation PVC pipe to continuously move forwards and enter a gap between the inner layer die body and the middle layer die body, and bending the pipe to form a biaxial orientation PVC bent pipe;

s314, cooling and shaping the biaxially oriented PVC pipe after the pipe is bent and shaped;

s315, after shaping, disassembling the elbow forming die, and simultaneously removing the first parison tube expansion die, the die tail plug cover and the die head plug cover; then taking out the biaxial orientation PVC elbow, cutting off redundant parts at two ends of the biaxial orientation PVC elbow to prepare a biaxial orientation PVC pipe elbow;

if the inner diameter of the PVC pipe elbow is equal to the outer diameter of the middle-layer die body and the outer diameter of the PVC pipe elbow is equal to the inner diameter of the outer-layer die body, the method comprises the following steps:

s321, connecting the second blank pipe expansion die to one end, far away from a die tail plug, of the elbow forming die; when the second parison tube expansion mould is connected, the external threads of the second threaded ring are matched with the internal threads of the middle layer mould body to realize connection;

s322, heating the blank pipe to a high-elasticity state, guiding the blank pipe into a second blank pipe expansion die from a second guide section, and enabling the blank pipe to pass through a second sealing section under the action of traction force and then pass through a second expansion section and a second sizing section in sequence to expand the blank pipe into a biaxial orientation PVC pipe;

s323, under the action of traction force, enabling the expanded biaxial orientation PVC pipe to continuously move forwards and enter a gap between the middle layer die body and the outer layer die body, and bending the pipe to form a biaxial orientation PVC bent pipe;

s324, after the biaxially oriented PVC pipe is bent and formed, cooling and shaping the pipe;

s325, after shaping, disassembling the elbow forming die, and simultaneously removing the second parison tube expansion die and the die tail plug cover; and then taking out the biaxial orientation PVC elbow, and cutting off redundant parts at two ends of the biaxial orientation PVC elbow to prepare the biaxial orientation PVC elbow.

Further, in the step S313, hot air with a temperature higher than 90 ℃ is introduced into the elbow forming mold through the first air hole and the third air hole, and air is extracted from the second air hole;

in step S323, hot air at a temperature higher than 90 ℃ is introduced into the elbow forming mold through the second air hole, and air is extracted from the first air hole.

Further, in step S313 or step S323, the elbow forming mold is placed in the heat insulation box.

In the present invention: (1) when a small-sized PVC pipe elbow needs to be manufactured, firstly, an elbow forming die and a die tail plug are combined according to the steps of S1 and S2, then, a first blank pipe expansion die and a die head plug are combined with the elbow forming die according to the step of S311, then, the operation is carried out according to the steps from S312 to S315, in the operation process, a blank pipe in a high-elasticity state is guided by a first guide section and then sleeved on a first sealing section, then, under the action of traction force, radial and axial stretching (mainly radial) is gradually realized through the first expansion section, then, the blank pipe enters a first diameter section, the blank pipe is converted into a biaxial orientation PVC pipe, then, the traction force can continuously promote the pipe to move forwards, after the pipe enters the elbow forming die, the die body can continuously move forwards along a gap between an inner layer die body and an intermediate layer die body, and because the pipe is still in the high-elasticity state, the pipe can be bent along with the direction change of the gap in the moving process, and then obtaining the biaxial orientation PVC elbow, cooling and shaping the elbow, then removing the mould, taking out the elbow, and cutting and processing the elbow to obtain the biaxial orientation PVC elbow. (2) When a large-size PVC pipe elbow needs to be manufactured, an elbow forming die and a die tail plug are combined according to the steps of S1 and S2, then a second blank pipe expansion die and the elbow forming die are combined according to the step of S321, then the operation is carried out according to the steps of S322 to S325, in the operation process, a blank pipe in a high-elasticity state is guided by a second guide section and then sleeved on a second sealing section, then radial and axial stretching (mainly radial) is gradually realized through the second expansion section under the action of traction force, then the blank pipe enters a second sizing section, the blank pipe is converted into a biaxial orientation PVC pipe, then the traction force can continuously promote the pipe to move forwards, after the pipe enters the elbow forming die, the pipe can continuously move forwards along a gap between an intermediate layer die body and an outer layer die body, and the pipe is still in the high-elasticity state, so that the pipe can be bent along with the turning of the gap in the moving process, and then obtaining the biaxial orientation PVC elbow, cooling and shaping the elbow, then removing the mould, taking out the elbow, and cutting and processing the elbow to obtain the biaxial orientation PVC elbow.

The invention has the following beneficial effects:

a) the diameters of the prepared biaxial orientation PVC pipe elbows are different through the steps (1) or (2), so that the device has two functions and good practicability and economy, namely, one device can be used for producing two biaxial orientation PVC pipe elbows with different specifications, the device can be correspondingly assembled according to the size specification during production, the device is very practical, and the production cost of an enterprise is saved by one device and two devices;

b) the blank pipe expanding die and the elbow forming die are connected together, so that the whole production process is continuously carried out, and the blank pipe in a high elastic state immediately enters the elbow forming die to be bent and formed after being subjected to bidirectional stretching by the blank pipe expanding die; namely, the process of converting the PVC-U billet into the PVC-O elbow is continuous without pause, so that the production efficiency is high, and the production process is simple and reliable.

Drawings

FIG. 1 is a schematic representation of the components of the apparatus for making biaxially oriented PVC piping elbow of example 1;

FIG. 2 is a view from A-A of FIG. 1;

FIG. 3 is a schematic view of FIG. 2 after separation;

FIG. 4 is a perspective view of the closure of the mold tail of FIG. 1;

FIG. 5 is a perspective view of the mold head closure of FIG. 1;

FIG. 6 is an assembled view of the apparatus of example 1 when a PVC piping elbow is manufactured by the method of example 2;

FIG. 7 shows a biaxially oriented PVC piping elbow made by the process of example 2;

FIG. 8 is an assembled view of the apparatus of example 1 when a PVC piping elbow is manufactured by the method of example 3;

figure 9 shows a biaxially oriented PVC piping elbow made by the process of example 3.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.

Example 1:

as shown in fig. 1, the present embodiment provides an apparatus for manufacturing biaxially oriented PVC pipe elbow, which comprises a set consisting of a first parison tube expansion mold 1, a second parison tube expansion mold 2, an elbow forming mold 3, a mold tail plug 4 and a mold head plug 5.

The first parison tube expansion mold 1 is used for being connected to one end of the elbow forming mold 3 (see fig. 6), and comprises a first guide section 11, a first sealing section 12, a first expansion section 13 and a first diameter section 14 which are sequentially connected into a whole; the first guide section 11 is a cylinder and is used for guiding a blank pipe to be expanded; the first sealing section 12 is also a cylinder, the outer diameter of the first sealing section is slightly larger than that of the first guide section 11, and the first sealing section 12 is connected with the first guide section 11 through a conical surface in a smooth transition manner; the first expanding section 13 is a cone, the diameter of the small-caliber end of the first expanding section is equal to that of the first sealing section 12 and is connected with the first sealing section 12, and the diameter of the large-caliber end of the first expanding section is equal to that of the first diameter section 14 and is connected with the first diameter section 14; the first diameter section 14 is a cylinder, and the outer diameter of the first diameter section 14 is larger than that of the first sealing section 12.

The second parison tube expansion mold 2 is also used for being connected to one end of the elbow forming mold 3 (see fig. 8), and comprises a second guide section 21, a second sealing section 22, a second expansion section 23 and a second sizing section 24 which are sequentially connected into a whole; the second guide section 21 has the same structure as the first guide section 11 and is also used for guiding the blank pipe to be expanded; the structure of the second sealing section 22 is consistent with that of the first sealing section 12, and the second sealing section 22 and the second guide section 21 are also connected in a smooth transition way through a conical surface; the second expanding section 23 is a cone, the diameter of the small-caliber end of the second expanding section is equal to that of the second sealing section 22 and is connected with the second sealing section 22, and the diameter of the large-caliber end of the second expanding section is equal to that of the second sizing section 24 and is connected with the second sizing section 24; the second sizing section 24 is a cylinder, and the outer diameter of the second sizing section 24 is larger than the outer diameter of the second sealing section 22 and is also larger than the outer diameter of the first sizing section 14.

The elbow forming die 3 comprises an inner die body 31, an intermediate die body 32 and an outer die body 33; the inner mold body 31 is a hollow elbow-shaped structure, and is formed by combining a first mold half 311 and a second mold half 312 which can be separated from each other (see fig. 2 and 3), and the outer diameter of the inner mold body 31 is consistent with the outer diameter of the first diameter section 14 (see fig. 6); the intermediate layer mold body 32 is also a hollow elbow-shaped structure, and is formed by combining a third mold half 321 and a fourth mold half 322 which can be separated from each other (see fig. 2 and 3), and the inner diameter of the intermediate layer mold body 32 is larger than the outer diameter of the inner layer mold body 31, and the outer diameter is consistent with the outer diameter of the second sizing section 24 (see fig. 8); the outer mold body 33 is also a hollow elbow structure, which is formed by combining a fifth mold half 331 and a sixth mold half 332 (see fig. 2 and 3) that can be separated from each other, and the inner diameter of the outer mold body 33 is larger than the outer diameter of the intermediate mold body 32.

The mold tail plug 4 is used for covering one end of the elbow forming mold 3 which is not connected with the first blank pipe expanding mold 1 or the second blank pipe expanding mold 2 (see fig. 6 or fig. 8), and comprises a bottom plate 41, a first platform body 42, a second platform body 43 and a third platform body 44 (see fig. 1 and fig. 4) which are connected into a whole; the bottom plate 41 is disc-shaped; the first table body 42 is positioned on one side of the bottom plate 41, a first groove 421 is arranged in the middle of one side of the first table body 42, which is away from the bottom plate 41, a first annular raised ring 422 is arranged around the first groove 421, and the first annular raised ring 422 can be inserted into a gap between the outer layer mold body 33 and the middle layer mold body 32 in an interference fit manner; the second platform body 43 is arranged in the first groove 421, a second groove 431 is arranged in the middle of one side, away from the first platform body 42, of the second platform body 43, a second annular raised ring 432 is arranged around the second groove 431, and the second annular raised ring 432 can be inserted into a gap between the middle layer die body 32 and the inner layer die body 31 in an interference fit manner; the third block 44 is disposed in the second groove 431, and the third block 44 is of a cylindrical structure and can be inserted into the inner cavity of the inner mold 31 in an interference fit manner.

The die head plug cover 5 is used for covering one end (see fig. 6) of the elbow forming die 3 connected with the first blank pipe expanding die 1, and comprises a hollow disc 51 and a hollow ring 52 (see fig. 1 and 5) which are connected into a whole; the diameter of a round hole in the middle of the hollow disc 51 is slightly smaller than the outer diameter of the middle layer die body 32; the hollow circular ring 52 is connected to one side of the hollow circular plate 51 and is coaxial with the hollow circular plate 51, the inner diameter of the hollow circular ring 52 is consistent with the diameter of the circular hole in the middle of the hollow circular plate 51 (i.e., slightly smaller than the outer diameter of the intermediate layer die body 32), and the outer diameter of the hollow circular ring 52 is slightly larger than the inner diameter of the outer layer die body 33, so that the hollow circular ring 52 can be inserted into the gap between the outer layer die body 33 and the intermediate layer die body 32 in an interference fit manner (see fig. 6).

With respect to the elbow molding die 3, it is preferable that:

referring to fig. 3, the first mold half 311 is provided with a first positioning groove 311a, the second mold half 312 is provided with a first positioning column 312a, and the first mold half 311 and the second mold half 312 are positioned by the cooperation of the first positioning groove 311a and the first positioning column 312 a; the third mold half 321 is provided with a second positioning groove 321a, the fourth mold half 322 is provided with a second positioning column 322a, and the third mold half 321 and the fourth mold half 322 are positioned by matching the second positioning groove 321a with the second positioning column 322 a; the fifth mold half 331 is provided with a first lug plate 331a, the sixth mold half 332 is provided with a second lug plate 332a, the fifth mold half 331 and the sixth mold half 332 are fixed by the connection of the first lug plate 331a and the second lug plate 332a, wherein the connection of the first lug plate 331a and the second lug plate 332a is realized by passing a bolt through a hole of the corresponding lug plate and then locking the bolt with a nut.

When the inner mold body 31 is assembled, the first positioning groove 311a of the first mold half 311 is aligned with the first positioning post 312a of the second mold half 312, and then the two mold halves are closed without locking; when the middle layer mold body 32 is assembled, the second positioning groove 321a of the third mold half 321 is aligned with the second positioning column 322a of the fourth mold half 322, and then the two mold halves are closed, and locking is not needed; when the outer mold body 33 is assembled, the fifth mold half 331 and the sixth mold half 332 are closed, and then the corresponding first lug plate 331a and the corresponding second lug plate 332a are connected by bolts and nuts; of course, if the positioning of the fifth mold half 331 and the sixth mold half 332 is to be facilitated, positioning posts and positioning grooves similar to those described above can also be provided on the fifth mold half 331 and the sixth mold half 332.

In the above design, the reason why the two mold halves of the inner layer mold 31 and the middle layer mold 32 are not locked is that: if two half molds are locked, the locking structure is inevitably involved, for example, the lug plate which is the same as the outer layer mold body 33 is arranged on the outer wall of the half mold, and the locking structure cannot be arranged in order to ensure the smoothness of the outer wall because the outer walls of the inner layer mold body 31 and the middle layer mold body 32 are used for molding the bent pipe.

Accordingly, the mold tail plug 4 and the mold head plug 5 are designed to limit outward movement of each mold half, specifically, because the two mold halves of the inner mold body 31 and the intermediate mold body 32 are not locked: since the two

mold halves

331, 332 of the outer mold body 33 are locked, when the two annular protruding rings 422, 432 of the mold end plug 4 are respectively inserted into the gap between the corresponding mold bodies in an interference fit manner (see fig. 6), the annular protruding rings 422, 432 can play a role in limiting the separation of the first mold half 311 and the second mold half 312 and limiting the separation of the third mold half 321 and the fourth mold half 322; similarly, the mold head plug 5 can limit the separation of the third mold half 321 and the fourth mold half 322 when the hollow ring 52 is inserted into the gap between the intermediate mold body 32 and the outer mold body 33.

In addition, the first parison tube expansion mold 1 further comprises a first threaded ring 15, the first threaded ring 15 is connected to one end of the first diameter section 14, which is far away from the first expansion section 13, and the outer wall of the first threaded ring 15 is provided with external threads; an internal thread is arranged at one end of the inner layer die body 31 connected with the first blank pipe expansion die 1, and the external thread of the first thread ring 15 is in threaded fit with the internal thread of the first blank pipe expansion die 1 to realize connection; meanwhile, an inner ear plate 313 (see fig. 1, 2 and 6) may be further designed on the inner wall of the first parison expansion mold 1 near the internal thread, the inner ear plate 313 is simultaneously distributed on the first mold half 311 and the second mold half 312, and the inner ear plates 313 on the two

mold halves

311, 312 are connected by bolts and nuts to achieve locking.

Similarly, the second parison tube expansion mold 2 further comprises a second threaded ring 25, the second threaded ring 25 is connected to one end of the second sizing section 24, which is far away from the second expansion section 23, and the outer wall of the second threaded ring 25 is provided with external threads; an internal thread is arranged at one end of the middle layer die body 32 connected with the second parison tube expansion die 2; the external thread of the second threaded ring 25 and the internal thread of the second parison tube expansion mold 2 can be in threaded fit to realize connection; meanwhile, a ring of convex ring 27 can be arranged on the end surface of the outer layer second sizing section 24 of the second threaded ring 25, and a ring of annular groove 323 is arranged on the corresponding end surface of the middle layer die body 32 (the annular groove 323 is formed by splicing the third die half 321 and the fourth die half 322), the annular groove 323 and the convex ring 27 are consistent in size and can be matched with each other just (see fig. 1), so that when the second parison tube expansion die 2 is screwed on the middle layer die body 32, the convex ring 27 can be clamped into the annular groove 314, and the purpose of limiting the separation of the third die half 321 and the fourth die half 322 is achieved.

Because the pipe is ensured to be continuously in the high-elastic state in the bending process of the pipe, the elbow forming die 3 is required to be ensured to be continuously in the high-temperature state, so that heat can be transferred to the pipe to continuously keep the pipe in the high-elastic state; based on the invention, the following design is carried out:

referring to fig. 1 and 4, at least two first air holes 45, at least two second air holes 46 and a third air hole 47 are arranged on the mold tail plug cover 4; the first air hole 45 penetrates through the first table body 42 and the bottom plate 41 from the first annular raised ring 422; the second air hole 46 penetrates through the second platform body 43, the first platform body 42 and the bottom plate 41 from the second annular raised ring 432; the third air hole 47 penetrates the third stage 44, the second stage 43, the first stage 42, and the bottom plate 41 at the same time.

When the pipe is bent, high-temperature hot air can be introduced into the elbow forming die 3 from the corresponding air holes, so that the elbow forming die 3 is heated or insulated, and the aim of continuously keeping the pipe in a high elastic state is fulfilled.

Of course, on the basis of the above technical solution, it is also necessary to ensure that the hot air entering the elbow forming mold 3 has fluidity, so as to avoid the occurrence of air flow siltation, and the present invention is further designed as follows: referring to fig. 1 and 5, at least two fourth air holes 53 are formed in the mold head plug 5, and the fourth air holes 53 simultaneously penetrate through the hollow circular disc 51 and the hollow circular ring 52; meanwhile, the first parison stretching mold 1 is further provided with a first through hole 16 axially penetrating therethrough, and the second parison stretching mold 2 is further provided with a second through hole 26 axially penetrating therethrough.

The fourth air hole 53, the first through hole 16 and the second through hole 26 can discharge hot air in the elbow forming mold 3, so as to ensure that the hot air flows, and avoid the situation that the hot air is accumulated in the elbow forming mold 3 and is gradually cooled and cannot be discharged.

It should be further noted that: generally, the size of the gap between the middle layer die body 32 and the inner layer die body 31 is between 2mm and 10mm, and the size of the gap between the outer layer die body 33 and the middle layer die body 32 is also between 2mm and 10 mm; the first parison tube expansion mold 1 and the second parison tube expansion mold 2 are made of a metal material, the elbow forming mold 3 is a casting and is also made of a metal material, and the mold tail plug 4 and the mold head plug 5 are made of high-temperature-resistant rubber.

The following two embodiments provide methods for manufacturing a PVC piping elbow using the apparatus of embodiment 1, namely a method for manufacturing a small-sized PVC piping elbow (embodiment 1) and a method for manufacturing a large-sized PVC piping elbow (embodiment 2), specifically as follows:

example 2:

the method of the embodiment comprises the following steps:

s1, assembling the elbow forming die 3: the intermediate layer mold body 32 is sleeved outside the inner layer mold body 31, and the outer layer mold body 33 is sleeved outside the inner layer mold body 32;

when the first half mold 311 is butted with the second half mold 312, the first positioning groove 311a is matched with the first positioning column 312a to realize positioning, and the first half mold 311 and the second half mold 312 do not need to be locked after the positioning and the butting; when the third half mold 321 and the fourth half mold 322 are butted, the positioning is realized through the matching of the second positioning groove 321a and the second positioning column 322a, and the third half mold 321 and the fourth half mold 322 do not need to be locked after the positioning and the butting; when the fifth mold half 331 and the sixth mold half 332 are mated, the first ear plate 331a and the second ear plate 332a are connected to realize locking of the two;

s2, plugging the mold tail plug cover 4 into one end of the elbow forming mold 3, which is not connected with the first blank pipe expanding mold 1 or the second blank pipe expanding mold 2;

when the plug cover 4 at the tail part of the mold is plugged, the first annular convex ring 422 is inserted into the gap between the outer mold body 33 and the middle mold body 32 in an interference fit manner, and the second annular convex ring 432 is inserted into the gap between the middle mold body 32 and the inner mold body 31 in an interference fit manner;

thereafter, referring to fig. 6, the process continues as follows:

s311, connecting the first blank pipe expansion die 1 to one end, far away from the die tail plug cover 4, of the elbow forming die 3, and meanwhile plugging the die head plug cover 5 into one end, connected with the first blank pipe expansion die 1, of the elbow forming die 3;

when the first parison tube expansion mold 1 is connected, the first half mold 311 and the second half mold 312 are locked by the inner ear plate 313, and then the connection is realized by matching the external thread of the first threaded ring 15 with the internal thread of the inner mold body 31; when the plug cover 5 is plugged into the head part of the mould, the hollow circular ring 52 is inserted into the gap between the outer layer mould body 33 and the middle layer mould body 32 in an interference fit manner;

s312, heating the blank pipe to a high-elasticity state, guiding the blank pipe into a first blank pipe expansion die 1 through a first guide section 11, and enabling the blank pipe to pass through a first sealing section 12 under the action of traction force and then pass through a first expansion section 13 and a first diameter section 14 in sequence to enable the blank pipe to be expanded into a biaxial orientation PVC pipe;

s313, under the action of traction force, enabling the expanded biaxial orientation PVC pipe to continuously move forwards and enter a gap between the inner layer die body 31 and the middle layer die body 32, and bending the pipe to form a biaxial orientation PVC bent pipe;

s315, after shaping, disassembling the elbow forming die 3, and simultaneously removing the first parison tube expansion die 1, the die tail plug cover 4 and the die head plug cover 5; then the biaxially oriented PVC elbow is taken out and the excess portions at both ends are cut off to make a biaxially oriented PVC pipe elbow as shown in fig. 7.

In step S313, hot air with a temperature higher than 90 ℃ may be introduced into the bend forming mold 3 through the first air holes 45 and the third air holes 47, and air may be extracted from the second air holes 46. Wherein, the hot air entering the elbow forming die 3 from the first air hole 45 and the third air hole 47 can heat or insulate the elbow forming die 3 from the two sides of the pipe, thereby achieving the purpose of keeping the pipe in a high elastic state continuously; the purpose of drawing air outwardly from the second air hole 46 is: negative pressure is formed between the inner die body 31 and the middle die body 32, and the negative pressure can generate suction force to promote the pipe to move forwards.

Example 3:

the method of the embodiment comprises the following steps:

thereafter, referring to fig. 8, the process continues as follows:

s321, connecting the second parison tube expansion mold 2 to one end, far away from the mold tail plug cover 4, of the elbow forming mold 3; when the second parison tube expansion mold 2 is connected, the external threads of the second threaded ring 25 are matched with the internal threads of the intermediate layer mold body 32 to realize connection, and the convex ring 27 on the end surface of the second sizing section 24 can be clamped into the annular groove 323 on the end surface of the intermediate layer mold body 32 after connection, so that the third half mold 321 and the fourth half mold 322 are limited to be separated;

s322, heating the blank pipe to a high elastic state, guiding the blank pipe into a second blank pipe expansion die 2 through a second guide section 21, and enabling the blank pipe to pass through a second sealing section 22 under the action of traction force and then pass through a second expansion section 23 and a second sizing section 24 in sequence to enable the blank pipe to be expanded into a biaxial orientation PVC pipe;

s323, under the action of traction force, enabling the expanded biaxial orientation PVC pipe to continuously move forwards and enter a gap between the middle layer die body 32 and the outer layer die body 33, and bending the pipe to form a biaxial orientation PVC bent pipe;

s325, after shaping, disassembling the elbow forming die 3, and simultaneously removing the second parison tube expansion die 2 and the die tail plug cover 4; then the biaxially oriented PVC elbow is taken out and the excess portions at both ends are cut off to make a biaxially oriented PVC pipe elbow as shown in fig. 9.

In step S323, hot air with a temperature higher than 90 ℃ may be introduced into the elbow forming mold 3 through the second air hole 46, and air is extracted from the first air hole 45; similarly to the embodiment 1, the hot air entering the elbow forming mold 3 through the second air hole 46 can heat or insulate the elbow forming mold 3, thereby achieving the purpose of continuously keeping the pipe in a high elastic state; the first air hole 45 is pumped outwards to form negative pressure between the middle mold body 32 and the outer mold body 33, so as to promote the forward movement of the pipe.

In the

embodiments

2 and 3, when the step S313 or the step S323 is performed, the elbow forming die 3 may be placed in an incubator to further insulate the elbow forming die 3.

As can be seen from the above examples 2 and 3, the biaxially oriented PVC pipe bend obtained in example 2 has an inner diameter equal to the outer diameter of the inner layer mold body 31 and an outer diameter equal to the inner diameter of the intermediate layer mold body 32, and the biaxially oriented PVC pipe bend obtained in example 3 has an inner diameter equal to the outer diameter of the intermediate layer mold body 32 and an outer diameter equal to the inner diameter of the outer layer mold body 33. Therefore, the device of the embodiment 1 can manufacture two biaxial orientation PVC pipe elbows with different specifications, has a dual-purpose function and has good practicability and economy; when the device of the embodiment 1 is designed, an enterprise determines the sizes of all parts of the device according to the size of an elbow to be manufactured, then designs a drawing, and sends the drawing to a production department to process the device; later, when making biax orientation PVC pipe elbow, according to the preparation demand (be small-size elbow or jumbo size elbow) carry out corresponding equipment to the device can, unusual practicality, and one can also save manufacturing cost for the enterprise.

In addition, because the blank pipe expanding die 1/2 and the elbow forming die 3 are connected together, the whole production process is continuously carried out, and the blank pipe in the high elastic state immediately enters the elbow forming die 3 for bending forming after being subjected to the bidirectional stretching of the blank pipe expanding die 1/2; namely, the process of converting the PVC-U billet into the PVC-O elbow is continuous without pause, so that the production efficiency is high, and the production process is simple and reliable.

To be noted: the blank pipe referred to herein is a PVC-U pipe; in examples 2 and 3, the pulling force for moving the blank pipe is provided by a pulling machine arranged at the tail end of the blank pipe.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The device for manufacturing the biaxial orientation PVC pipe elbow is characterized by comprising a kit consisting of a first blank pipe expansion die (1), a second blank pipe expansion die (2), an elbow forming die (3), a die tail plug cover (4) and a die head plug cover (5);

the first blank pipe expansion die (1) is used for being connected to one end of the elbow forming die (3) and comprises a first guide section (11), a first sealing section (12), a first expansion section (13) and a first diameter section (14) which are sequentially connected into a whole; the first guide section (11) is a cylinder and is used for guiding a blank pipe to be expanded; the first sealing section (12) is also a cylinder, the outer diameter of the first sealing section is slightly larger than that of the first guide section (11), and the first sealing section (12) is connected with the first guide section (11) through a conical surface in a smooth transition manner; the first expansion section (13) is a cone, the small-caliber end of the first expansion section is connected with the first sealing section (12), and the large-caliber end of the first expansion section is connected with the first diameter section (14); the first diameter section (14) is a cylinder, and the outer diameter of the first diameter section (14) is larger than that of the first sealing section (12);

the second blank pipe expansion die (2) is also used for being connected to one end of the elbow forming die (3) and comprises a second guide section (21), a second sealing section (22), a second expansion section (23) and a second sizing section (24) which are sequentially connected into a whole; the second guide section (21) is consistent with the first guide section (11) in structure and is also used for guiding the blank pipe to be expanded; the structure of the second sealing section (22) is consistent with that of the first sealing section (12), and the second sealing section (22) is connected with the second guide section (21) in a smooth transition way through a conical surface; the second expansion section (23) is a cone, the small-caliber end of the second expansion section is connected with the second sealing section (22), and the large-caliber end of the second expansion section is connected with the second sizing section (24); the second sizing section (24) is a cylinder, and the outer diameter of the second sizing section (24) is larger than that of the second sealing section (22) and is also larger than that of the first sizing section (14);

the elbow forming die (3) comprises an inner die body (31), an intermediate die body (32) and an outer die body (33); the inner die body (31) is of a hollow bent pipe-shaped structure and is formed by combining a first half die (311) and a second half die (312) which can be separated from each other, and the outer diameter of the inner die body (31) is consistent with that of the first diameter section (14); the middle layer die body (32) is also of a hollow bent pipe-shaped structure and is formed by combining a third half die (321) and a fourth half die (322) which can be separated from each other, the inner diameter of the middle layer die body (32) is larger than the outer diameter of the inner layer die body (31), and the outer diameter is consistent with the outer diameter of the second sizing section (24); the outer layer die body (33) is also of a hollow bent pipe-shaped structure and is formed by combining a fifth half die (331) and a sixth half die (332) which can be separated from each other, and the inner diameter of the outer layer die body (33) is larger than the outer diameter of the middle layer die body (32);

the mould tail plug cover (4) is used for covering one end, which is not connected with the first blank pipe expansion mould (1) or the second blank pipe expansion mould (2), of the elbow forming mould (3), and comprises a bottom plate (41), a first platform body (42), a second platform body (43) and a third platform body (44) which are connected into a whole; the bottom plate (41) is disc-shaped; the first table body (42) is positioned on one side of the bottom plate (41), a first groove (421) is formed in the middle of one side, away from the bottom plate (41), of the first table body (42), a first annular raised ring (422) is arranged on the periphery of the first groove (421), and the first annular raised ring (422) can be inserted into a gap between the outer layer die body (33) and the middle layer die body (32) in an interference fit manner; the second table body (43) is arranged in the first groove (421), a second groove (431) is arranged in the middle of one side, away from the first table body (42), of the second table body (43), a second annular raised ring (432) is arranged on the periphery of the second groove (431), and the second annular raised ring (432) can be inserted into a gap between the middle layer mold body (32) and the inner layer mold body (31) in an interference fit manner; the third platform body (44) is arranged in the second groove (431), and the third platform body (44) is of a cylindrical structure and can be inserted into the inner cavity of the inner die body (31) in an interference fit manner;

the die head plug cover (5) is used for covering one end of the elbow forming die (3) connected with the first blank pipe expansion die (1), and comprises a hollow disc (51) and a hollow ring (52) which are connected into a whole; the diameter of the round hole in the middle of the hollow disc (51) is between the inner diameter and the outer diameter of the middle layer die body (32); the hollow circular ring (52) is connected to one side of the hollow circular plate (51) and is coaxial with the hollow circular plate (51), and the hollow circular ring (52) can be inserted into a gap between the outer layer die body (33) and the middle layer die body (32) in an interference fit manner;

wherein the mould tail plug cover (4) is provided with at least two first air holes (45), at least two second air holes (46) and a third air hole (47); the first air hole (45) penetrates through the first table body (42) and the bottom plate (41) from the first annular raised ring (422); the second air hole (46) penetrates through the second platform body (43), the first platform body (42) and the bottom plate (41) from the second annular raised ring (432); the third air hole (47) simultaneously penetrates through the third platform body (44), the second platform body (43), the first platform body (42) and the bottom plate (41); the mould head plug cover (5) is provided with at least two fourth air holes (53); the fourth air hole (53) penetrates through the hollow disc (51) and the hollow circular ring (52) simultaneously; the first blank pipe expanding die (1) is provided with a first through hole (16) which axially penetrates through the first blank pipe expanding die; the second blank pipe expanding die (2) is provided with a second through hole (26) which axially penetrates through the second blank pipe expanding die.

2. The apparatus for making biaxially oriented PVC piping elbows according to claim 1, wherein the first mold half (311) is provided with a first positioning groove (311a), the second mold half (312) is provided with a first positioning post (312a), and the first mold half (311) and the second mold half (312) are positioned by the cooperation of the first positioning groove (311a) and the first positioning post (312 a); the third half die (321) is provided with a second positioning groove (321a), the fourth half die (322) is provided with a second positioning column (322a), and the third half die (321) and the fourth half die (322) are positioned by matching the second positioning groove (321a) with the second positioning column (322 a); the fifth half die (331) is provided with a first lug plate (331a), the sixth half die (332) is provided with a second lug plate (332a), and the fifth half die (331) and the sixth half die (332) are fixed through connection of the first lug plate (331a) and the second lug plate (332 a).

3. The apparatus for making biaxially oriented PVC piping elbows according to claim 2, wherein the first parison expansion die (1) further comprises a first threaded ring (15), the first threaded ring (15) being attached to the end of the first gauge section (14) remote from the first expansion section (13), the outer wall of the first threaded ring (15) being provided with external threads; an internal thread is arranged at one end of the inner layer die body (31) connected with the first parison tube expansion die (1); the external thread of the first thread ring (15) and the internal thread of the first parison tube expansion mould (1) can be in thread fit to realize connection;

the second blank pipe expansion die (2) further comprises a second threaded ring (25), the second threaded ring (25) is connected to one end, away from the second expansion section (23), of the second sizing section (24), and external threads are arranged on the outer wall of the second threaded ring (25); an internal thread is arranged at one end of the middle layer die body (32) connected with the second parison tube expansion die (2); the external thread of the second thread ring (25) and the internal thread of the second blank pipe expansion die (2) can be matched in a thread mode to realize connection.

4. A method of making biaxially oriented PVC piping elbows by using the apparatus of claim 3, wherein the method is capable of making two different sizes of biaxially oriented PVC piping elbows;

the method comprises the following steps:

s1, assembling an elbow forming die (3): sleeving the middle layer die body (32) outside the inner layer die body (31) and sleeving the outer layer die body (33) outside the inner layer die body (32);

when the first half die (311) is butted with the second half die (312), the first positioning groove (311a) is matched with the first positioning column (312a) to realize positioning, when the third half die (321) is butted with the fourth half die (322), the second positioning groove (321a) is matched with the second positioning column (322a) to realize positioning, and when the fifth half die (331) is butted with the sixth half die (332), the fifth half die and the sixth half die are fixed through the connection of the first lug plate (331a) and the second lug plate (332 a);

s2, plugging a die tail plug cover (4) into one end of the elbow forming die (3), which is not connected with the first blank pipe expansion die (1) or the second blank pipe expansion die (2);

when the plug cover (4) at the tail part of the mold is plugged, the first annular raised ring (422) is inserted into a gap between the outer mold body (33) and the middle mold body (32) in an interference fit manner, and the second annular raised ring (432) is inserted into a gap between the middle mold body (32) and the inner mold body (31) in an interference fit manner;

then, if the PVC pipe elbow with the inner diameter equal to the outer diameter of the inner layer die body (31) and the outer diameter equal to the inner diameter of the middle layer die body (32) is manufactured, the following steps are carried out:

s311, connecting the first blank pipe expansion die (1) to one end, far away from a die tail plug cover (4), of the elbow forming die (3), and meanwhile plugging a die head plug cover (5) into one end, connected with the first blank pipe expansion die (1), of the elbow forming die (3);

when the first parison tube expansion die (1) is connected, the external threads of the first threaded ring (15) are matched with the internal threads of the inner die body (31) to realize connection; when the plug cover (5) is plugged into the head part of the mold, the hollow circular ring (52) is inserted into a gap between the outer layer mold body (33) and the middle layer mold body (32) in an interference fit manner;

s312, heating the blank pipe to a high-elasticity state, guiding the blank pipe into a first blank pipe expansion die (1) through a first guide section (11), and enabling the blank pipe to pass through a first sealing section (12) under the action of traction force and then pass through a first expansion section (13) and a first diameter section (14) in sequence to be expanded into a biaxial orientation PVC pipe;

s313, under the action of traction force, enabling the expanded biaxial orientation PVC pipe to continuously move forwards and enter a gap between the inner layer die body (31) and the middle layer die body (32) to form a biaxial orientation PVC bent pipe after bending;

s315, after shaping, disassembling the elbow forming die (3), and simultaneously removing the first parison tube expansion die (1), the die tail plug cover (4) and the die head plug cover (5); then taking out the biaxial orientation PVC elbow, cutting off redundant parts at two ends of the biaxial orientation PVC elbow to prepare a biaxial orientation PVC pipe elbow;

if the PVC pipe elbow with the inner diameter equal to the outer diameter of the middle layer die body (32) and the outer diameter equal to the inner diameter of the outer layer die body (33) is manufactured, the method comprises the following steps:

s321, connecting the second blank pipe expansion die (2) to one end, far away from the die tail plug cover (4), of the elbow forming die (3); when the second parison tube expansion mould (2) is connected, the external threads of the second threaded ring (25) are matched with the internal threads of the middle layer mould body (32) to realize connection;

s322, heating the blank pipe to a high elastic state, then leading the blank pipe into a second blank pipe expansion die (2) through a second guide section (21), leading the blank pipe to pass through a second sealing section (22) under the action of traction force, and then sequentially passing through a second expansion section (23) and a second sizing section (24) to expand the blank pipe into a biaxial orientation PVC pipe;

s323, under the action of traction force, enabling the expanded biaxial orientation PVC pipe to continuously move forward and enter a gap between the middle layer die body (32) and the outer layer die body (33) to form a biaxial orientation PVC bent pipe after bending;

s325, after shaping, disassembling the elbow forming die (3), and simultaneously removing the second blank pipe expanding die (2) and the die tail plug cover (4); and then taking out the biaxial orientation PVC elbow, and cutting off redundant parts at two ends of the biaxial orientation PVC elbow to prepare the biaxial orientation PVC elbow.

5. The method of making biaxially oriented PVC piping elbows according to claim 4, wherein during step S313, hot gas at a temperature greater than 90 ℃ is introduced into the elbow forming mold (3) through the first air vent (45) and the third air vent (47), while air is extracted from the second air vent (46);

in the step S323, hot air with a temperature higher than 90 ℃ is introduced into the elbow forming mold (3) through the second air hole (46), and air is extracted from the first air hole (45).

6. The method of claim 5, wherein the elbow forming mold (3) is in an incubator during step S313 or step S323.