A method for producing polytetrafluoroethylene multicolor blank

Abstract

The invention discloses a method for making a multi-color polytetrafluoroethylene blank, comprising the following steps: S1. setting the number of colors of polytetrafluoroethylene materials to N, and pressing each color of polytetrafluoroethylene materials into a single-color polytetrafluoroethylene blank; S2. sequentially loading the N single-color polytetrafluoroethylene blanks into a first extruder according to the color sequence of the cable insulator; S3. the first extruder sequentially extrudes the N single-color polytetrafluoroethylene blanks into single-color polytetrafluoroethylene blank strips; S4. roughening the contact surfaces on both sides of the N single-color polytetrafluoroethylene blank strips; S5. sequentially introducing the N single-color polytetrafluoroethylene blank strips into a polytetrafluoroethylene blank tube of an automatic receiving device to form a multi-color polytetrafluoroethylene blank strip assembly. The invention is easy to make, can achieve large-scale and high-efficiency production; the multi-color polytetrafluoroethylene blank strip assembly is not easy to mix colors, does not need to be cut, is not easy to deform, and is easy to be subsequently extruded by a plunger to form a multi-color cable insulator.

Description

Technical Field

[0001] The invention relates to a cable insulator blank processing method, in particular to a polytetrafluoroethylene multi-color blank manufacturing method. Background Art

[0002] Polytetrafluoroethylene (PTFE) is used to manufacture communication cable insulators. The wire is soft and has a temperature resistance range of -40℃ to 300℃, with good high temperature resistance.

[0003] Polytetrafluoroethylene, commonly known as the "king of plastics", is a high molecular polymer made by polymerizing tetrafluoroethylene as a monomer; it is white waxy and translucent, has no real melting point, and its melting temperature is generally between 260℃ and 340℃. At 327℃, the mechanical strength suddenly disappears, the melt is in a jelly state, and the fluidity is extremely poor, making it impossible to achieve hot melt extrusion. Above 450℃, it slowly decomposes and directly turns into gas. Because the molten state of polytetrafluoroethylene hardly flows, multi-color polytetrafluoroethylene cable insulators cannot use the mature multi-machine co-extrusion process. It can only be produced by first making multi-color polytetrafluoroethylene blanks, and then using the plunger extrusion process to produce multi-color polytetrafluoroethylene cable insulators.

[0004] In the prior art, there are two processes for making polytetrafluoroethylene multi-color blanks:

[0005] The first process is to use a separator to separate the PTFE pressing cavity into multiple independent spaces, and then fill each independent space with PTFE powder of different colors according to the color arrangement of the multi-color PTFE cable insulators, remove the separator, and then extrude the required multi-color blanks. The disadvantages of this process are: difficulty in filling, difficulty in removing the separator, easy mixing of colors, etc., making it difficult to achieve large-scale and high-efficiency production.

[0006] The second process is to first press out a single-color PTFE blank, then use a knife to cut the single-color PTFE blank into single-color blank strips of suitable shapes, and then piece together single-color blank strips of various colors into a multi-color PTFE blank strip assembly. The disadvantages of this process are: the PTFE blank is easy to break during cutting, and cutting causes PTFE fiberization and deformation, which affects the subsequent plunger extrusion molding. Especially when there are many colors, it is difficult to achieve effective cutting. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for producing a polytetrafluoroethylene multi-color blank based on the deficiencies in the prior art. The method is very easy to produce a single-color polytetrafluoroethylene blank and a multi-color polytetrafluoroethylene blank strip assembly, and can achieve large-scale and high-efficiency production. The multi-color polytetrafluoroethylene blank strip assembly is not easy to mix colors, does not need to cut the single-color polytetrafluoroethylene blank strips, is not easy to deform, and is easy to be subsequently plunger-extruded to form a multi-color cable insulator.

[0008] In order to solve the above technical problems, the technical solution of the present invention is: a method for making a multi-color polytetrafluoroethylene blank, comprising the following steps:

[0009] S1. Set the number of colors of polytetrafluoroethylene materials to N, N ≥ 2, N is an integer; each color of polytetrafluoroethylene material is pressed into a single-color polytetrafluoroethylene blank, a total of N single-color polytetrafluoroethylene blanks;

[0010] S2. According to the color order of the cable insulator, N kinds of monochromatic polytetrafluoroethylene preforms are sequentially loaded into the first extruder;

[0011] S3. The first extruder extrudes N kinds of monochromatic polytetrafluoroethylene preforms sequentially into monochromatic polytetrafluoroethylene billets;

[0012] S4. roughening the contact surfaces on both sides of N types of single-color polytetrafluoroethylene blank strips;

[0013] S5. Introduce N kinds of single-color polytetrafluoroethylene blank strips into the polytetrafluoroethylene blank tube of the automatic receiving device in sequence to form a multi-color polytetrafluoroethylene blank strip assembly. In the multi-color polytetrafluoroethylene blank strip assembly, the contact surfaces of any adjacent single-color polytetrafluoroethylene blank strips are relative.

[0014] Preferably, the method for making the multi-color polytetrafluoroethylene blank further comprises the steps of:

[0015] S6. The polytetrafluoroethylene blank tube having a multi-color polytetrafluoroethylene blank strip assembly is loaded into the second extruder, and the multi-color polytetrafluoroethylene blank strip assembly is simultaneously pushed out from the polytetrafluoroethylene blank tube to the pre-pressing device of the second extruder, and the pre-pressing device of the second extruder presses the multi-color polytetrafluoroethylene blank strip assembly into a multi-color polytetrafluoroethylene blank strip integrated body;

[0016] S7. The multi-color polytetrafluoroethylene billet strip integration body is plunger extruded into a multi-color cable insulation in the second extruder.

[0017] Preferably, in step S1, the monochromatic polytetrafluoroethylene preform is in the shape of a rod with a length of 600 mm to 900 mm, and contains a set content of lubricating oil.

[0018] Preferably, in step S3, a first extrusion die is installed in the first extruder, and the first extrusion die has a cavity with a fan-shaped ring-shaped cross section. After the single-color polytetrafluoroethylene blank passes through the first extrusion die, it is extruded into a single-color polytetrafluoroethylene blank strip, and the cross section of the single-color polytetrafluoroethylene blank strip is fan-shaped.

[0019] Preferably, a scraping jig is provided at the die opening of the first extrusion die, and the scraping jig roughens the contact surfaces on both sides of the single-color polytetrafluoroethylene blank strip respectively, so that the contact surfaces on both sides of the single-color polytetrafluoroethylene blank strip change from smooth surfaces to rough surfaces.

[0020] Preferably, the polytetrafluoroethylene blank tube is a circular polytetrafluoroethylene blank tube, the inner wall of the polytetrafluoroethylene blank tube is divided into N inner wall surfaces, each inner wall surface is respectively provided with a receiving groove, and each receiving groove is respectively introduced into a single-color polytetrafluoroethylene blank strip; the cross-sectional shape of the multi-color polytetrafluoroethylene blank strip assembly composed of N single-color polytetrafluoroethylene blank strips is annular.

[0021] Preferably, the length of the polytetrafluoroethylene blank tube is 500mm-1500mm, and the diameter is 50mm-200mm; and detachable covers are respectively installed at both ends of the polytetrafluoroethylene blank tube.

[0022] Preferably, the automatic receiving device also includes a cutting device, which is arranged at the feed end of the polytetrafluoroethylene blank tube. The monochrome polytetrafluoroethylene blank strip is introduced into the accommodating groove inside the polytetrafluoroethylene blank tube from the feed end of the polytetrafluoroethylene blank tube. When the monochrome polytetrafluoroethylene blank strip contacts the tail of the polytetrafluoroethylene blank tube, the cutting device cuts off the monochrome polytetrafluoroethylene blank strip.

[0023] Preferably, the automatic receiving device further comprises a rotating device, the polytetrafluoroethylene blank tube is mounted on the rotating device, and the working steps of the rotating device are as follows:

[0024] 1) The rotating device drives the polytetrafluoroethylene blank tube to rotate to the initial position, so that the first receiving groove of the polytetrafluoroethylene blank tube is aligned with the first extrusion die outlet of the first extruder;

[0025] 2) A first single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the first containing groove in the polytetrafluoroethylene billet tube, and cut off by a cutting device;

[0026] 3) The rotating device drives the polytetrafluoroethylene blank tube to rotate a set angle so that the second receiving groove of the polytetrafluoroethylene blank tube is aligned with the outlet of the first extrusion die of the first extruder;

[0027] 4) The second single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the second containing groove in the polytetrafluoroethylene billet tube, and cut off by the cutting device;

[0028] 5) The method of step 3) to step 4) is analogous until the N-th single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the N-th containing groove in the polytetrafluoroethylene billet tube, and cut off by the cutting device.

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention is easy to produce a single-color polytetrafluoroethylene preform. The conventional polytetrafluoroethylene production process can be used to press polytetrafluoroethylene materials, such as powders, granules, etc., into single-color polytetrafluoroethylene preforms. The polytetrafluoroethylene preforms of each color of the present invention are individually pressed and formed. The process of individual pressing and forming is relatively simple, and large-scale and high-efficiency production can be achieved. The present invention does not need to press polytetrafluoroethylene materials of multiple colors together into preforms, which is relatively complicated.

[0031] (2) Since the monochromatic polytetrafluoroethylene blank strip of the present invention is formed by extrusion of a monochromatic polytetrafluoroethylene blank, after N types of monochromatic polytetrafluoroethylene blank strips are formed into a multicolor polytetrafluoroethylene blank strip assembly, there will be no problem of color mixing between the monochromatic polytetrafluoroethylene blanks;

[0032] (3) Since the contact surfaces on both sides of the N types of single-color polytetrafluoroethylene blank strips are roughened respectively in the present invention, after the multi-color polytetrafluoroethylene blank strip assembly is pressed into a multi-color polytetrafluoroethylene blank strip integrated body in the second extruder, the contact surfaces between adjacent single-color polytetrafluoroethylene blank strips can be tightly connected together;

[0033] (4) Since the present invention is provided with a polytetrafluoroethylene blank tube, the extruded single-color polytetrafluoroethylene blank strips are directly introduced into the polytetrafluoroethylene blank tube in sequence to form a multi-color polytetrafluoroethylene blank strip assembly, and the assembly process is highly efficient and can achieve mass production; and the multi-color polytetrafluoroethylene blank strip assembly with the polytetrafluoroethylene blank tube is easy to carry, so that it can be pushed into the subsequent extruder and plunger extruded to form a multi-color cable insulator;

[0034] (5) Compared with the conventional technology, the present invention does not need to cut the single-color polytetrafluoroethylene blank strip; the single-color polytetrafluoroethylene blank strip after extrusion molding is not easy to deform, and the assembled multi-color polytetrafluoroethylene blank strip assembly is also not easy to deform and mix colors, which makes it easy to subsequently use a plunger to extrude and mold a multi-color cable insulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1This is a molding flow chart of a preferred embodiment of the present invention.

[0036] Figure 2 It is a side view of the polytetrafluoroethylene stock tube in the preferred embodiment.

[0037] Figure 3 It is a schematic diagram of the structure of the end portion of the polytetrafluoroethylene blank tube in a preferred embodiment.

[0038] Figure 4 A diagram showing the state of loading four single-color polytetrafluoroethylene blank strips into the polytetrafluoroethylene blank tube in the preferred embodiment. Implementation

[0039] The structural principle and working principle of the present invention are further described in detail below with reference to the accompanying drawings.

[0040] like Figure 1 As shown, this embodiment is a method for making a multi-color polytetrafluoroethylene blank, comprising the following steps:

[0041] S1. See Figure 1 (a) The number of colors of polytetrafluoroethylene materials is set to 4, and each color of polytetrafluoroethylene material is pressed into a single-color polytetrafluoroethylene blank, for a total of 4 single-color polytetrafluoroethylene blanks; the 4 single-color polytetrafluoroethylene blanks are all in the shape of rods with a length of 600 mm to 900 mm, and the single-color polytetrafluoroethylene blanks contain a set amount of lubricating oil.

[0042] S2. According to the color sequence of the cable insulator, four kinds of single-color polytetrafluoroethylene preforms are sequentially loaded into the first extruder; for example: the cross-sectional colors of the cable insulator include the first color, the second color, the third color and the third color along the clockwise direction, then the order of loading the four kinds of single-color polytetrafluoroethylene preforms into the first extruder is: 1) loading the single-color polytetrafluoroethylene preform of the first color, 2) loading the single-color polytetrafluoroethylene preform of the second color, 3) loading the single-color polytetrafluoroethylene preform of the third color, 4) loading the single-color polytetrafluoroethylene preform of the fourth color.

[0043] S3. See Figure 1 (b) A first extruder sequentially extrude four kinds of single-color polytetrafluoroethylene blanks into single-color polytetrafluoroethylene blank strips; in this step, a first extrusion die is installed in the first extruder, and the first extrusion die has a cavity with a fan-shaped ring-shaped cross section. After the single-color polytetrafluoroethylene blank passes through the first extrusion die, it is extruded into a single-color polytetrafluoroethylene blank strip, and the cross section of the single-color polytetrafluoroethylene blank strip is fan-shaped.

[0044] S4. Roughen the contact surfaces on both sides of the four types of single-color polytetrafluoroethylene blank strips respectively; a scraping jig is provided at the mold mouth of the first extrusion mold, and the scraping jig roughens the contact surfaces on both sides of the single-color polytetrafluoroethylene blank strips respectively, and the contact surfaces on both sides of the single-color polytetrafluoroethylene blank strips change from smooth surfaces to rough surfaces.

[0045] S5. See Figure 1 (c) Four kinds of single-color polytetrafluoroethylene blank strips are introduced into the polytetrafluoroethylene blank tube of the automatic receiving device in sequence to form a multi-color polytetrafluoroethylene blank strip assembly. In the multi-color polytetrafluoroethylene blank strip assembly, the contact surfaces of any adjacent single-color polytetrafluoroethylene blank strips are relative to each other.

[0046] S6. See Figure 1 (d) Loading a polytetrafluoroethylene billet tube having a multi-color polytetrafluoroethylene billet strip assembly into a second extruder, and simultaneously pushing the multi-color polytetrafluoroethylene billet strip assembly out of the polytetrafluoroethylene billet tube to a pre-pressing device of the second extruder, wherein the pre-pressing device of the second extruder presses the multi-color polytetrafluoroethylene billet strip assembly into a multi-color polytetrafluoroethylene billet strip integrated body.

[0047] S7. See Figure 1 (e) The multi-color polytetrafluoroethylene billet strip integrated body is plunger-extruded in a second extruder to form a multi-color cable insulator, and the multi-color cable insulator is coated on the outside of the cable (not shown in the figure).

[0048] In the multi-color polytetrafluoroethylene blank strip assembly or the multi-color polytetrafluoroethylene blank strip integration of the present invention, the color of each polytetrafluoroethylene blank strip can be different or have repeated colors, for example, Figure 4 In the invention, four monochrome polytetrafluoroethylene blank strips 1, 2, 3, and 4 are included, but the four monochrome polytetrafluoroethylene blank strips are divided into two pairs, and the colors of each pair of monochrome polytetrafluoroethylene blank strips are consistent, that is, the colors of monochrome polytetrafluoroethylene blank strip 1 and monochrome polytetrafluoroethylene blank strip 3 are consistent, and the colors of monochrome polytetrafluoroethylene blank strip 2 and monochrome polytetrafluoroethylene blank strip 4 are consistent.

[0049] like Figure 2 , Figure 3 and Figure 4As shown, the polytetrafluoroethylene blank tube 100 is a circular polytetrafluoroethylene blank tube, and the inner wall of the polytetrafluoroethylene blank tube 100 is divided into four inner wall surfaces, each inner wall surface is respectively provided with a receiving groove 101, and each receiving groove 101 is respectively introduced with a single-color polytetrafluoroethylene blank strip 1, 2, 3, 4; the cross-sectional shape of the multi-color polytetrafluoroethylene blank strip assembly composed of the four single-color polytetrafluoroethylene blank strips is annular. Preferably, the length of the polytetrafluoroethylene blank tube 100 is 500mm-1500mm, and the diameter is 50mm-200mm; removable covers 102 are respectively installed at both ends of the polytetrafluoroethylene blank tube 100, so that the single-color polytetrafluoroethylene blank strip can be prevented from slipping out of the polytetrafluoroethylene blank tube 100 during transportation; and when the subsequent plunger extrusion molding multi-color cable insulator process is required, it is only necessary to open the cover 102 to push the multi-color polytetrafluoroethylene blank strip assembly into the second extruder

[0050] As a preferred embodiment of the present invention, the automatic receiving device also includes a cutting device, which is arranged at the feed end of the polytetrafluoroethylene blank tube. The monochrome polytetrafluoroethylene blank strip is introduced into the accommodating groove inside the polytetrafluoroethylene blank tube from the feed end of the polytetrafluoroethylene blank tube. When the monochrome polytetrafluoroethylene blank strip contacts the tail of the polytetrafluoroethylene blank tube, the cutting device cuts off the monochrome polytetrafluoroethylene blank strip. By setting the cutting device, the monochrome polytetrafluoroethylene blank strip can be automatically cut off to improve the degree of automation and production efficiency.

[0051] As a preferred embodiment of the present invention, the automatic receiving device further comprises a rotating device, the polytetrafluoroethylene blank tube is mounted on the rotating device, and the working steps of the rotating device are as follows:

[0052] 1) The rotating device drives the polytetrafluoroethylene blank tube to rotate to the initial position, so that the first receiving groove of the polytetrafluoroethylene blank tube is aligned with the first extrusion die outlet of the first extruder;

[0053] 2) A first single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the first containing groove in the polytetrafluoroethylene billet tube, and cut off by a cutting device;

[0054] 3) The rotating device drives the polytetrafluoroethylene blank tube to rotate a set angle so that the second receiving groove of the polytetrafluoroethylene blank tube is aligned with the outlet of the first extrusion die of the first extruder;

[0055] 4) The second single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the second containing groove in the polytetrafluoroethylene billet tube, and cut off by the cutting device;

[0056] 5) The method from step 3) to step 4) is analogous until the fourth single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the fourth receiving groove in the polytetrafluoroethylene billet tube, and cut off by the cutting device.

[0057] By providing a rotating device, the single-color polytetrafluoroethylene billet strips extruded from the first extruder can be introduced into the corresponding containing grooves in the polytetrafluoroethylene billet tube in sequence.

[0058] It should be noted that the number of polytetrafluoroethylene materials of the present invention is not limited to 4, and may also be 2, 3, 5 or more colors of polytetrafluoroethylene materials. The manufacturing method of the present invention is very easy to manufacture single-color polytetrafluoroethylene blanks and multi-color polytetrafluoroethylene blank strip assemblies, and can achieve large-scale and high-efficiency production; the multi-color polytetrafluoroethylene blank strip assemblies are not easy to mix colors, do not need to cut single-color polytetrafluoroethylene blank strips, are not easy to deform, and are easy to be subsequently plunger-extruded to form multi-color cable insulators.

[0059] The above description is only a preferred embodiment of the present invention. Any slight modification, equivalent changes and modifications made to the above embodiments according to the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for producing a multi-color polytetrafluoroethylene blank, characterized in that: The method comprises the following steps: S1. Set the number of colors of polytetrafluoroethylene materials to N, N ≥ 2, N is an integer; each color of polytetrafluoroethylene material is pressed into a single-color polytetrafluoroethylene blank, a total of N single-color polytetrafluoroethylene blanks; S2. According to the color order of the cable insulator, N kinds of monochromatic polytetrafluoroethylene preforms are sequentially loaded into the first extruder; S3. The first extruder extrudes N kinds of monochromatic polytetrafluoroethylene preforms sequentially into monochromatic polytetrafluoroethylene billets; S4. roughening the contact surfaces on both sides of N types of single-color polytetrafluoroethylene blank strips; S5. Introduce N kinds of single-color polytetrafluoroethylene blank strips into the polytetrafluoroethylene blank tube of the automatic receiving device in sequence to form a multi-color polytetrafluoroethylene blank strip assembly. In the multi-color polytetrafluoroethylene blank strip assembly, the contact surfaces of any adjacent single-color polytetrafluoroethylene blank strips are relative.

2. The method for making a multi-color polytetrafluoroethylene blank according to claim 1, characterized in that: Also includes the steps: S6. The polytetrafluoroethylene blank tube having a multi-color polytetrafluoroethylene blank strip assembly is loaded into the second extruder, and the multi-color polytetrafluoroethylene blank strip assembly is simultaneously pushed out from the polytetrafluoroethylene blank tube to the pre-pressing device of the second extruder, and the pre-pressing device of the second extruder presses the multi-color polytetrafluoroethylene blank strip assembly into a multi-color polytetrafluoroethylene blank strip integrated body; S7. The multi-color polytetrafluoroethylene billet strip integration body is plunger extruded into a multi-color cable insulation in the second extruder.

3. The method for making the multi-color polytetrafluoroethylene blank according to claim 1, characterized in that: In step S1, the monochromatic polytetrafluoroethylene blank is in the shape of a rod with a length of 600 mm to 900 mm, and contains a set content of lubricating oil.

4. The method for making a multi-color polytetrafluoroethylene blank according to claim 1, characterized in that: In step S3, a first extrusion die is installed in the first extruder, and the first extrusion die has a cavity with a fan-shaped cross-section. After the single-color polytetrafluoroethylene blank passes through the first extrusion die, it is extruded into a single-color polytetrafluoroethylene billet strip, and the cross-section of the single-color polytetrafluoroethylene billet strip is fan-shaped.

5. The method for making a multi-color polytetrafluoroethylene blank according to claim 4, characterized in that: A scraping jig is provided at the die opening of the first extrusion die, and the scraping jig roughens the contact surfaces on both sides of the single-color polytetrafluoroethylene blank strip respectively, so that the contact surfaces on both sides of the single-color polytetrafluoroethylene blank strip change from smooth surfaces to rough surfaces.

6. The method for making a multi-color polytetrafluoroethylene blank according to claim 1, characterized in that: The polytetrafluoroethylene blank tube is a circular polytetrafluoroethylene blank tube, the inner wall of which is divided into N inner wall surfaces, each inner wall surface is provided with a receiving groove, and a single-color polytetrafluoroethylene blank strip is introduced into each receiving groove; the cross-sectional shape of the multi-color polytetrafluoroethylene blank strip assembly composed of N single-color polytetrafluoroethylene blank strips is annular.

7. The method for making a multi-color polytetrafluoroethylene blank according to claim 6, characterized in that: The length of the polytetrafluoroethylene blank tube is 500mm-1500mm, and the diameter is 50mm-200mm; and detachable covers are respectively installed at both ends of the polytetrafluoroethylene blank tube.

8. The method for making a multi-color polytetrafluoroethylene blank according to claim 6, characterized in that: The automatic receiving device also includes a cutting device, which is arranged at the feeding end of the polytetrafluoroethylene blank tube. The single-color polytetrafluoroethylene blank strip is introduced into the containing groove inside the polytetrafluoroethylene blank tube from the feeding end of the polytetrafluoroethylene blank tube. When the single-color polytetrafluoroethylene blank strip contacts the tail of the polytetrafluoroethylene blank tube, the cutting device cuts off the single-color polytetrafluoroethylene blank strip.

9. The method for making a multi-color polytetrafluoroethylene blank according to claim 8, characterized in that: The automatic receiving device also includes a rotating device, on which the polytetrafluoroethylene blank tube is installed. The working steps of the rotating device are as follows: 1) The rotating device drives the polytetrafluoroethylene blank tube to rotate to the initial position, so that the first receiving groove of the polytetrafluoroethylene blank tube is aligned with the first extrusion die outlet of the first extruder; 2) A first single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the first containing groove in the polytetrafluoroethylene billet tube, and cut off by a cutting device; 3) The rotating device drives the polytetrafluoroethylene blank tube to rotate a set angle so that the second receiving groove of the polytetrafluoroethylene blank tube is aligned with the outlet of the first extrusion die of the first extruder; 4) The second single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the second containing groove in the polytetrafluoroethylene billet tube, and cut off by the cutting device; 5) The method of step 3) to step 4) is analogous until the N-th single-color polytetrafluoroethylene billet strip is extruded from the outlet of the first extrusion die, introduced into the N-th containing groove in the polytetrafluoroethylene billet tube, and cut off by the cutting device.

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