JP3240127B2 - Manufacturing method of refractory double-layer pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a fire-resistant double-layer pipe comprising an outer pipe formed by laminating non-combustible materials and an inner pipe made of synthetic resin, and in particular, to improve interlayer adhesion of the outer pipe and enhance impact resistance. The present invention relates to a method for producing a fire-resistant double-walled pipe.

[0002]

2. Description of the Related Art In recent years, fire-resistant double-layered pipes in which an inner pipe made of a synthetic resin and an outer pipe made of a noncombustible material are combined are widely used for drainage pipes and ventilation pipes of apartment houses and the like. As the inner pipe of the fire-resistant double-layer pipe, a pipe made of a synthetic resin such as PVC is used, and is excellent in chemical resistance, corrosion resistance, inner surface smoothness, workability, and the like. On the other hand, the disadvantage of poor fire resistance is covered by covering with an outer tube made of a non-combustible material. By enhancing the fire resistance in this way, even if a fire starts in one place of an apartment house, it is possible to prevent the fire from spreading to another room through a drain pipe or the like. A non-combustible material containing asbestos as a reinforcing fiber has been used for the outer tube of the fire-resistant double-layer tube. However, in recent years, reinforcement with organic and inorganic short fibers has been attempted as an alternative to asbestos due to depletion of asbestos and harm to the human body. In general, short fibers are reinforced and mixed randomly with a hydraulic inorganic material such as cement, so that they are randomly arranged in the outer tube.

[0003] On the other hand, it has been proposed to use long fibers and net-like fibers for reinforcing these incombustible outer tubes. For example, Japanese Patent Application Laid-Open No. 57-165226 discloses a method of applying a water-kneaded material of a hydraulic inorganic material to a cloth-like body, winding the outer surface of a tubular body (core tube) with the application surface inside, and forming an outer tube. At the time of production, a method is disclosed in which a water-kneaded material is applied leaving only the vicinity of the winding end side of the cloth-like body, wound around the outer periphery of the tubular body, and pressed from the outer periphery. As another example, Hikai Hira 4-
As disclosed in Japanese Patent No. 68277, a plurality of reinforcing long fibers (which may be in a net shape or a mat shape) are wound around a hydraulic inorganic material one or more times along the axial direction of the outer tube. Composite tubes having tubes have been proposed.

[0004]

The refractory double-layer pipe is constructed through various processes from the completion of the production of the factory to the construction site. First, in the production process, a hydraulic inorganic material is formed into a sheet (usually called a green sheet), and this sheet is wound around the outer peripheral surface of the core tube a plurality of times to produce a nonflammable outer tube. Then, after curing and curing, the core tube is pulled out. In this step, the end of the outer tube is easily broken, which is a major cause of occurrence of defective products and reduction of production efficiency. For this reason, there has been a demand for reinforcement to make the end of the outer tube difficult to break. In addition, in the handling of the product after completion of the product, a crack may be generated in the outer tube due to various external forces such as an impact due to transportation, a load of loading, and an impact in handling at a construction site. This crack in the outer tube not only significantly reduces the commercial value, but also degrades the most important fire resistance. In order to improve the impact resistance, Japanese Unexamined Patent Publication No. Sho 57-165226 and Japanese Utility Model Laid-Open Publication No.
In the technology described in Japanese Patent No. 277, a reinforcing method using reinforcing long fibers (including a net shape or a mat shape) has been proposed.
Reinforcement over the entire surface (all layers) raises the cost, and in addition, there is a problem that delamination is likely to occur due to poor interlayer adhesion at the portion where the net-like reinforcing fiber is inserted. Therefore, an object of the present invention is to prevent the end of the core tube from being damaged at the time of drawing out the core tube in the manufacturing process, to prevent the outer tube from cracking in various processes from the completion of the production to the completion of the product, and An object of the present invention is to provide a method for manufacturing a fire-resistant double-layer pipe capable of preventing peeling between pipe layers.

[0005]

According to the first aspect of the present invention, an outer tube formed by laminating a plurality of layers of non-combustible material, and an outer diameter slightly longer than the outer tube and smaller than the inner diameter of the outer tube. In a method for manufacturing a fire-resistant double-layer pipe comprising an inner pipe made of synthetic resin having the inner pipe inserted into the outer pipe, a first raw material liquid is formed by a papermaking method to form a green sheet. A second step of disposing reinforcing long fibers on the green sheet formed in the first step, and a plurality of green sheets on which the reinforcing long fibers are disposed in the core tube in the second step. A third stage of winding, a fourth stage of extracting the core tube from which the green sheet has been wound in the third stage after curing and curing to form an outer tube, and an outer tube formed in the fourth stage. A fifth step of inserting an inner tube made of synthetic resin, and forming the inner tube in the second step. 30 from both ends in the longitudinal direction of the outer tube that
A plurality of reinforcing fibers at predetermined lengths between the layers of the non-combustible material of
The object is achieved by arranging reinforcing long fibers at positions where they are inserted into a layer or a plurality of layers.

According to the second aspect of the present invention, an outer tube formed by laminating a plurality of layers of noncombustible material, and an inner tube made of a synthetic resin having an outer diameter slightly longer than the outer tube and smaller than the inner diameter of the outer tube. A method for producing a refractory double-layer pipe comprising inserting the inner pipe into the outer pipe, forming a green sheet by extracting a predetermined raw material liquid by a papermaking method; A second step of disposing the reinforcing long fibers on the green sheet formed in the step, and a third step of winding the green sheet on which the reinforcing long fibers are disposed in the second step a plurality of times around a core tube. A fourth step of extracting the core tube from which the green sheet has been wound in the third step after curing and curing, and forming an outer tube;
A fifth step of inserting an inner tube made of synthetic resin into the outer tube formed in the fourth step, and in the second step, from one end of the outer tube formed in the longitudinal direction to the other end thereof. At a position where a plurality of reinforcing long fibers are spirally inserted between one or more layers of the outer tube at a predetermined angle at a predetermined angle with respect to an end cross section of the outer tube and at a predetermined interval with a width of 30 to 100 mm. The above object is achieved by arranging reinforcing long fibers.

According to the third aspect of the present invention, an outer tube formed by laminating a plurality of layers of noncombustible material and an inner tube made of a synthetic resin having an outer diameter slightly longer than the outer tube and smaller than the inner diameter of the outer tube. A method for producing a refractory double-layer pipe comprising inserting the inner pipe into the outer pipe, forming a green sheet by extracting a predetermined raw material liquid by a papermaking method; A second step of disposing the reinforcing long fibers on the green sheet formed in the step, and a third step of winding the green sheet on which the reinforcing long fibers are disposed in the second step a plurality of times around a core tube. A fourth step of extracting the core tube from which the green sheet has been wound in the third step after curing and curing, and forming an outer tube;
A fifth step of inserting an inner tube made of synthetic resin into the outer tube formed in the fourth step; and in the second step, 30 to 100 mm from both ends of the formed outer tube in the longitudinal direction. In the length, a plurality of reinforcing filaments are inserted at predetermined intervals between the layers of the outer tube, one or more layers are inserted in the circumferential direction, and a portion where the reinforcing filaments are not inserted is 30 parts. ~ 100mm
The above object is achieved by disposing reinforcing long fibers at positions where a plurality of reinforcing long fibers are spirally inserted between one or more layers of the outer tube at predetermined intervals with a width of. .

[0008] In the invention described in claim 4, in the invention described in claim 1, 2, or 3, the reinforcing long fibers disposed on the green sheet in the second step are net-shaped. Thereby, the above-mentioned object is achieved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to FIGS. FIG.
It is a figure showing composition of a refractory two-layer pipe. This fire-resistant double-layer tube 1
No. 0 is constituted by covering the synthetic resin inner tube 20 with a nonflammable outer tube 30 which is slightly shorter than the inner tube. The outer diameter of the synthetic resin inner tube 20 is slightly smaller than the inner diameter of the noncombustible outer tube 30 so that the inner tube can be easily inserted into the outer tube. This synthetic resin inner tube 20
By providing a small gap between the inner tube and the non-combustible outer tube 30, the inner tube 20 made of synthetic resin which is generated when hot water or the like is drained is formed.
By absorbing the thermal expansion of the non-flammable outer tube 30. Here, first, a general method of manufacturing this refractory double-layer pipe will be described. The inner tube made of synthetic resin is
Use general-purpose products. On the other hand, the outer tube formed by laminating non-combustible materials is formed by a papermaking method (round net paper machine, flow-on paper machine, fourdrinier paper machine), an extrusion molding method, an injection molding method, or the like.

FIG. 2 shows an example of paper making by a flow-on paper making machine. The apparatus includes a bat 50 as a raw material liquid layer, an endless water-permeable belt (felt) 52 for conveying a formed green sheet 80, and a green sheet 80.
And a core tube supply device 84 for supplying the core tube. Then, as shown in FIG. 3, a thin green sheet 8 produced by the papermaking method
0 is wound and formed into a steel tube called a core tube 70,
Since the green sheet 80 is extremely thin,
The green sheets wound up a plurality of times are laminated (layered) and formed into a desired thickness of the outer tube. In the present embodiment,
Before winding the green sheet 80 around the core tube, by arranging a reinforcing long fiber or a reinforcing net on the green sheet 80, a layer of the outer tube in which a non-combustible material is laminated in a desired form at a desired position A reinforcing long fiber or a reinforcing net is inserted between them.

The reinforcing long fiber and the reinforcing net used here may be organic or inorganic. Organic fibers include those made of fibers such as vinylon, nylon, polyethylene, polypropylene, and polyvinyl alcohol, or urea resin, melanin resin, phenolic resin, resorcinol resin, epoxy resin, polyester resin, urethane resin, and polyamide. Resins made of synthetic resins such as resin, polyimide resin, vinyl acetate resin, vinyl chloride resin, polyvinyl resin, acrylic resin, and polyolefin resin can be used. A hot-melt adhesive used as a hot-melt adhesive can be processed into a linear shape and a net shape. Rubber, chloroprene rubber,
Nitrile rubber, SBR rubber, natural rubber, recycled rubber, butyl rubber, block rubber, silicone, polysulfide, chlorinated rubber, cellulose, and the like can be used. In the case of the hot melt adhesive type, a thin linear resin (hot melt adhesive) can be supplied onto the green sheet by selecting the caliber of the cartridge gun 110 of the hot melt applicator 100 shown in FIG. By selecting a supply method, it can be supplied linearly, spirally, in a pattern or the like, and the molten resin is cured at a low temperature (10 to 30 ° C.) of the green sheet, which is convenient. As the inorganic fibers, alkali-resistant glass fibers, carbon fibers, steel fibers, and the like can be used.

The situation in which an outer tube of a fire-resistant double-layer tube is obtained by the above-mentioned manufacturing method will be described with reference to FIG. 5 for Examples 1 to 5 and Comparative Examples 1 to 3 manufactured by other methods. (Example 1) The mixing of the raw materials of the inorganic material used for the non-combustible outer tube of Example 1 is as follows. Ordinary Portland cement 60% by weight Reinforcing fiber (pulp and synthetic fiber) 5% by weight Admixture (charcoal, scrap, etc.) 30% by weight Lightweight material (pearlite, etc.) 5% by weight Was used. Reinforcing long fiber: Alkali-resistant glass fiber with a diameter of 13.5 μm Reinforcing net: 100 mm wide net of alkali-resistant glass fiber with an aperture ratio of 73.3%

First, a slurry was prepared by adding water to the raw materials having the above composition, and the slurry was formed into a green sheet by a flow-on type paper machine shown in FIG. This green sheet has a thickness of 0.6
mm and a width of 2100 mm. The green sheet forming one outer tube is developed, and the location of the reinforcing long fibers on this sheet is as shown in FIG. The reason why this reinforcing long fiber is not arranged at the left end (A side) (at an interval of L shown in the figure) is to prevent the reinforcing long fiber from being inserted in the first or second winding. To do that. When this green sheet was wound into two cores on a steel pipe core tube having a diameter of 100 mm and a length of 2320 mm, reinforcing filaments having a length of 600 mm were placed at a pitch of 3 mm on an unwound green sheet at both ends of the winding width. 3
Zero (approximately 100 mm in width) was provided, subsequently wound up and laminated, and formed into a laminated thickness of 7.5 mm. In this example, the number of windings was 14. An outer tube was obtained in which a non-combustible material in which reinforcing long fibers were inserted in about two turns in the circumferential direction was laminated between two or three layers and three to four layers at both ends of the molded body at about 100 mm in the longitudinal direction. After the completion of molding, the core tube was subjected to normal steam curing (60 ° C. × 5 hours), and the core tube was pulled out. The completed outer tube was used as a specimen for other tests. The number of layers between the layers into which the reinforcing long fibers are inserted and the number of turns in the circumferential direction are not limited to the above, and can be appropriately selected as necessary.

(Example 2) The reinforcing long fibers of Example 1 were replaced with 1
An outer tube having a non-combustible material laminated thereon was obtained in the same manner as in Example 1 except that the reinforcing net had a width of 00 mm. After molding, normal steam curing was performed under the same conditions as in Example 1, and then the core tube was pulled out.

(Example 3) The blending of the raw materials, the used core tube, the papermaking method and the winding method are the same as those in Example 1, and the angle of the core tube with respect to the axis is about 70 degrees, that is, the angle with respect to the end face of the core tube. Twenty reinforcing fibers (about 100 mm in width) are arranged at a pitch of 3 mm at an angle of 20 degrees, and then the green sheet is wound and laminated, and the total length from the longitudinal end to the other end of the molded body To form a molded body having a laminated thickness of 7.5 mm, in which long fibers for reinforcement were spirally (spirally) arranged. The total number of windings was 14. After molding, normal steam curing was performed under the same conditions as in Example 1, and then the core tube was pulled out.
In the third embodiment, since the reinforcing long fibers are arranged in a spiral shape (spiral), the reinforcing long fibers are not arranged in a layered manner in the finished product.

(Embodiment 4) In Embodiment 4, Embodiment 3
The same procedure as in Example 3 was repeated, except that the reinforcing long fiber used in the above was changed to a reinforcing net having a width of 100 mm to obtain an outer tube laminated with a nonflammable material. After molding, normal steam curing was performed under the same conditions as in Example 1, and then the core tube was pulled out. In the fourth embodiment, as in the third embodiment, the reinforcing net is provided in a spiral shape (spiral shape).
Reinforcing nets are not arranged in layers.

Example 5 The same procedures as in Example 1 were repeated up to the mixing of the raw materials, the core pipe used, the papermaking method, the winding method, and the arrangement of the reinforcing filaments at both ends in the pipe length direction. In the meantime, 30 reinforcing long fibers at a pitch of 3 mm (about 100 m in width) are formed at an angle of about 20 degrees with respect to the reinforcing fibers.
m) is disposed, subsequently wound and laminated, and a 7.5 mm thick laminated body in which reinforcing long fibers are spirally (spirally) disposed in the circumferential direction at both ends of the molded body and in the middle thereof. Formed. The total number of windings was 14. After molding, normal steam curing was performed under the same conditions, and then the core tube was pulled out. In this embodiment, the spiral reinforcement is intermediate between the reinforcements at both ends of the outer tube. However, in a state where the first and second embodiments are combined, the insertion position (layer) is changed and both ends of the outer tube and the outer tube end are changed. It is also possible to reinforce both the spiral shape and the entire outer tube from the part to the other end. Also in Example 5, since the reinforcing long fibers are arranged in a spiral shape (spiral shape),
In the finished product, the reinforcing long fibers are not arranged in layers.

Example 6 The reinforcing long fiber of Example 5 was replaced with 1
Instead of a reinforcing net having a width of 00 mm, the same molding as in Example 5 was carried out to obtain a nonflammable layered outer tube. After molding, normal steam curing was performed under the same conditions as in Example 1, and then the core tube was pulled out. Also in the sixth embodiment, as in the fifth embodiment, the reinforcing nets are arranged in a spiral shape (spiral shape), so that the reinforcing nets are not arranged in an overlapping manner in the finished product.

(Comparative Example 1) The raw material blending, the core pipe used, the papermaking method and the winding method were the same as those in Example 1, and the laminated thickness was 7.5 m without using the reinforcing long fiber and the reinforcing net.
m was formed. The total number of windings was 14. After molding, normal steam curing was performed under the same conditions as in Example 1, and then the core tube was pulled out.

(Comparative Example 2) The composition of the raw materials, the core pipe used, the papermaking method and the winding method were the same as those in Example 1, and a reinforcing net having a length of about 3 m was used for each of from 2 to 3 layers to 12 to 13 layers. Between the layers, the entire length of the outer tube was inserted. The laminated thickness of the outer tube is 7.
The total number of winding was 14 times at 5 mm. After molding, normal steam curing was performed under the same conditions as in Example 1, and then the core tube was pulled out.

(Comparative Example 3) The raw material blending, the core tube used, the papermaking method and the winding method were the same as those in Example 1, and a reinforcing net having a width of about 1 m and a length of about 3 m was formed from a few layers to 12 to 13 layers. Between the layers up to the layers, the outer tube was inserted at the center in the length direction of the outer tube. The outer tube has a thickness of 7.5 mm and the total number of windings is 1
It was four times. After molding, normal steam curing was performed under the same conditions as in Example 1, and then the core tube was pulled out.

Using each of these specimens, a test was performed by the following test method, and comparisons of (1) to (4) were made. The results are shown in Table 1 of FIG. (1) Pullability (see FIG. 7) Iron tube 60 having an inner diameter 1 mm larger than the outer diameter of the core tube (length 100
mm, thickness 12 mm), pass the core tube (formed state) around which the outer tube is wound through the iron tube at 12 m / min, pull out the core tube, and observe the shape of the end portion of the outer tube and the drawn state at that time. I do. ◎: The end of the outer tube could be pulled out without chipping of 20 mm or more. ：: The end of the outer tube could be pulled out without chipping of 50 mm or more. Δ: The end of the outer tube could be pulled out without chipping of 100 mm or more. The end of the outer tube was chipped less than 50 mm, but was broken at the center. XX: Cannot be pulled out

(2) Impact resistance (see FIG. 8) The outer tube 30 is gently pressed in parallel with the sand surface on the sand 90 (air-dried state, depth 100 mm) in the sand box. 500 meters in height from a 500 g mass made from above
m (from the lower end of the weight to the upper surface of the specimen), drop it to the center of the specimen, and then drop it from a height of 450 mm, which is 50 mm lower than the previous height, and determine the state of breakage of the tube according to the following criteria. . The test specimens are 2 at the center and at the end of the outer tube (1 m and 50 cm from the end for 2 m of the outer tube length).
Standard. ：: Depressed, but no effect such as cracking or chipping around was observed. Δ: Cracking, chipping, etc. occurred around. ×: destroyed

(3) Adhesion between layers The outer tube is broken by a bending strength tester (center concentrated load with a span of 800 mm), and the state of adhesion of the cross section is determined according to the following criteria. Specimens shall be of two levels: the center and the end of the outer tube (1 m and 50 cm from the end for a total length of 2 m). : Completely in one sheet, with unknown layer も の: Visually visible hair-like line ×: Clearly recognized void between layers

(4) Comparison of cost (comparison in the state shown in FIG. 5) Comparison is made with the length of the reinforcing long fiber.

As a result of this comparison, first, in terms of (1) pullability, Examples 2, 5 and 6 are particularly good.
In Comparative Examples 1 and 3, the end of the outer tube was significantly crushed. (2) In the impact resistance, Examples 3 to 6 were good at both the end and the center. (3) In the interlayer adhesion, Examples 1 and 2 were particularly good. In the example using the net of Comparative Example 2, there was no problem in pull-out property and impact resistance, but there was a problem in this interlayer adhesion. (4) In terms of cost, Comparative Example 1 does not use a reinforcing fiber, so that the cost is naturally low.
Example 1 and Example 2 use a small amount of reinforcing fibers and are low in cost. It can be said that Examples 3 to 6 are also considerably lower in cost than Comparative Examples 2 and 3. Summarizing the above comparisons, Examples 1 to 6 all gave good results in each comparison.

[0027]

According to the invention described in each of the claims, the probability of the occurrence of pullout breakage in the reinforcing long fiber and the net reinforced at both ends is greatly improved. Further, even if the reinforcing long fibers and the net are not reinforced on the entire outer tube, the structure is resistant to impact, the reinforcing method is simple, and economical. Since the reinforcing long fibers and the net do not cover the entire outer tube, poor delamination can also be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a fire-resistant double-layer pipe according to the present embodiment.

FIG. 2 is a diagram showing an example of papermaking by a flow-on papermaking machine.

FIG. 3 is a diagram illustrating a state in which a green sheet is wound around a core tube.

FIG. 4 is a view showing the appearance of a hot melt applicator.

FIG. 5 is a diagram showing the state of sheets used in Examples 1 to 5 and Comparative Examples 1 to 3.

FIG. 6 is a table showing comparison results.

FIG. 7 is a diagram for explaining a pull-out test situation.

FIG. 8 is a diagram illustrating a test situation of impact resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fire-resistant double-layer pipe 20 Synthetic resin inner pipe 30 Nonflammable outer pipe 60 Fixed iron pipe 70 Core pipe 80 Green sheet 90 Sand 95 Weight

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-52-108417 (JP, A) JP-A-4-68277 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B28B 21/00-23/22

Claims (4)

(57) [Claims] 1. An outer tube formed by laminating a plurality of layers of noncombustible material, and an inner tube made of a synthetic resin having an outer diameter slightly longer than the outer tube and smaller than the inner diameter of the outer tube. In a method for manufacturing a refractory double-layer pipe in which an inner pipe is inserted into the outer pipe, a first step of forming a green sheet by extracting a predetermined raw material liquid by a papermaking method, and a green formed in the first step A second step of disposing the reinforcing long fibers on the sheet, a third step of winding the green sheet on which the reinforcing long fibers are disposed in the second step a plurality of times around a core tube, A fourth step of extracting the core tube from which the green sheet has been wound in the step after curing and curing to form an outer tube, and inserting a synthetic resin inner tube into the outer tube formed in the fourth step. In the second step, 30 to 1 from both ends in the longitudinal direction of the outer tube formed. A plurality of reinforcing filaments are arranged at a predetermined interval between the layers of the non-combustible material of the outer tube at a length of 00 mm, and the reinforcing filaments are arranged at positions where one or more layers are inserted in the circumferential direction. A method for manufacturing a refractory double-layer pipe, comprising: 2. An outer tube formed by laminating a plurality of layers of non-combustible material, and an inner tube made of a synthetic resin having an outer diameter slightly longer than the outer tube and smaller than the inner diameter of the outer tube. In a method for manufacturing a refractory double-layer pipe in which an inner pipe is inserted into the outer pipe, a first step of forming a green sheet by extracting a predetermined raw material liquid by a papermaking method, and a green formed in the first step A second step of disposing the reinforcing long fibers on the sheet, a third step of winding the green sheet on which the reinforcing long fibers are disposed in the second step a plurality of times around a core tube, A fourth step of extracting the core tube from which the green sheet has been wound in the step after curing and curing to form an outer tube, and inserting a synthetic resin inner tube into the outer tube formed in the fourth step. The second stage, from one end to the other end in the longitudinal direction of the outer tube formed, With a predetermined angle to the end section of the outer tube,
The reinforcing long fibers are arranged at positions where a plurality of reinforcing long fibers are spirally inserted between one or more layers of the outer tube at predetermined intervals with a width of 30 to 100 mm. A method of manufacturing a fire-resistant double-layer tube. 3. An outer tube formed by laminating a plurality of layers of non-combustible material, and an inner tube made of a synthetic resin having an outer diameter slightly longer than the outer tube and smaller than the inner diameter of the outer tube. In a method for manufacturing a refractory double-layer pipe in which an inner pipe is inserted into the outer pipe, a first step of forming a green sheet by extracting a predetermined raw material liquid by a papermaking method, and a green formed in the first step A second step of disposing the reinforcing long fibers on the sheet, a third step of winding the green sheet on which the reinforcing long fibers are disposed in the second step a plurality of times around a core tube, A fourth step of extracting the core tube from which the green sheet has been wound in the step after curing and curing to form an outer tube, and inserting a synthetic resin inner tube into the outer tube formed in the fourth step. In the second step, 30 to 10 from both ends in the longitudinal direction of the outer tube formed. At a length of 0 mm, a plurality of reinforcing long fibers are inserted at predetermined intervals between the layers of the outer tube, and are inserted in one or more layers in the circumferential direction, and at a portion where the reinforcing long fibers are not inserted. A plurality of reinforcing filaments are arranged at positions where a plurality of reinforcing filaments are spirally inserted between one or more layers of the outer tube at predetermined intervals with a width of 30 to 100 mm. Method for producing a fire-resistant double-walled pipe. 4. The refractory double-layer pipe according to claim 1, wherein the reinforcing long fibers disposed on the green sheet in the second step are in a net shape. Production method.