KR102489825B1 - Method for manufacturing a seamless integrated air manifold - Google Patents

Abstract

The present invention relates to a method for manufacturing a seamlessly integrated air manifold, which can increase the lifespan of an air manifold, comprising: a drawing and cutting process; a first forming process; a drilling process; a distribution port processing process; a distribution port connection process; a pickling process; and a surface processing process.

Description

Method for manufacturing a seamless integrated air manifold {Method for manufacturing a seamless integrated air manifold}

The present invention relates to a method for manufacturing a seamless integral air manifold. More specifically, the first round molding, the second round molding, the first extrusion molding, and the second extrusion molding are performed using a spinning roller having a trapezoidal cross section in which one side is formed to have a larger diameter than the other side. It relates to a method for manufacturing a seamless integral air manifold, characterized in that it is possible to increase the lifespan of a cylinder by molding through a process and maximizing corrosion resistance and wear resistance through a solid solution process and a surface coating process.

It is widely applied to sewage, process industries, etc. Although the market size is about 50 billion dollars a year, valves are one of the items with high trade imbalance with Japan and advanced countries in Korea. Supply is low. In other words, the domestic valve industry is an industry that needs a leap in technological competitiveness.

The valve is basically composed of a part that controls the fluid and a body that keeps these control parts structurally safe. Therefore, the purpose of using the valve is the primary purpose of fluid control (flow rate, pressure, flow rate), fluid direction conversion, transportation and blocking, and the secondary purpose of making it structurally strong and free from defects so that it can be operated smoothly under various conditions. Valve strength can be cited as the purpose.

A manifold valve is an installation that gathers a charge valve, a main valve, and a control valve in one place. The manifold valve can reduce the leakage of the air stored in the pressure container, and is mainly used to drive the generator, main engine starter, and control valves in the ship in combination with the air storage container.

An air manifold is a manifold having a passage serving as a pipe inside and having a plurality of device connection ports outside, and is used to guide intake or exhaust of each cylinder in a multi-cylinder engine.

When the valve of the manifold is rapidly opened, a severe shock occurs due to a rapid increase in pressure, so there is a need for a method for manufacturing an integrated air manifold that does not cause damage even under high pressure.

Prior art literature: KR Registration Patent Publication No. 10-0960268 (2010.06.04. Notice)

The present invention has been made to solve the above problems, and the spinning molding process is subdivided into first round molding, second round molding, first extrusion molding, and second extrusion molding, and one side is more than the other side. The precision can be improved by using spinning rollers that are now formed larger and have trapezoidal cross sections, and by using the solid solution process and surface coating process, it is a seamless and integrated air mani that can maximize the wear resistance and corrosion resistance of the cylinder. Its purpose is to provide a fold manufacturing method.

In order to achieve the above object, a method for manufacturing a seamless integrated air manifold according to the present invention includes a drawing and cutting process of manufacturing a pipe having a predetermined diameter and thickness through a drawing process and then cutting the pipe into a predetermined length; A first forming step of forming a neck portion and an inlet portion of a pressure resistant cylinder by hot spinning one end of the pipe manufactured in the drawing and cutting step; A drilling process of forming a plurality of through holes in a portion to be connected to a distribution port in a formed pipe; A distribution hole processing step of forming one end of the same curvature as the curvature of the pipe to be connected; a distribution hole connection step of connecting a distribution hole to a plurality of through holes formed in the drilling process; An acid washing step of cleaning the outer and inner surfaces of the molded pipe using an acidic solution to which an oxidation inhibitor is added; and a surface processing step of smoothly processing the surface of the molded pipe using a processing tool including a CNC lathe.

In addition, the distribution port connection process is to perform welding in a keyhole TIG (Keyhole TIG) method; And the butt-to-butt method, the gap is maintained at 0.5 mm or less, and the torch for performing the welding process has a diameter of 4.5 mm or more.

In addition, the heat treatment process includes performing the solid solution heat treatment process and the bright heat treatment process at the same time.

According to the present invention, it is possible to subdivide the hot spinning molding process step and process it using a spinning roller having a trapezoidal cross section to improve precision, and to maximize wear resistance and corrosion resistance to increase the lifespan of the air manifold. there is.

1 is a plan view of an air manifold manufactured by a seamless integral air manifold manufacturing method according to a preferred embodiment of the present invention.
2 is a perspective view of an air manifold manufactured by a seamless integral air manifold manufacturing method according to a preferred embodiment of the present invention.
3 is a view showing a process sequence of a method for manufacturing a seamless integral air manifold according to a preferred embodiment of the present invention;
Figure 4 is a view showing the sequence of the coating process.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to components of each drawing, it should be noted that the same components have the same numerals as much as possible even if they are displayed on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description will be omitted. In addition, although preferred embodiments of the present invention will be described below, the technical idea of the present invention is not limited or limited thereto and can be modified and implemented in various ways by those skilled in the art.

1 is a plan view of an air manifold manufactured by a seamless integrated air manifold manufacturing method according to a preferred embodiment of the present invention, and FIG. 2 is a plan view of an air manifold manufactured by a seamless integrated air manifold manufacturing method according to a preferred embodiment of the present invention. A perspective view of an air manifold, FIG. 3 is a view showing the process sequence of a method for manufacturing a seamless integrated air manifold according to a preferred embodiment of the present invention, and FIG. 4 is a view showing the sequence of a coating process.

Referring to FIG. 3, a method for manufacturing a seamless integral air manifold according to a preferred embodiment of the present invention includes a drawing and cutting process (S100), a first forming process (S200), a second forming process (S300), and drilling. Process (S400), distribution hole processing process (S500), distribution hole connection process (S600), pickling process (S700), heat treatment process (S800), screw tap processing process (S900), surface processing process (S1000), surface It is made including a coating process (S1100).

Hereinafter, components of a method for manufacturing a seamless integrated air manifold according to a preferred embodiment of the present invention will be described in detail.

In the drawing and cutting process (S100), a pipe having a target diameter and thickness of the body of the air manifold to be manufactured is manufactured by a drawing process, and then the manufactured pipe is cut into a predetermined length in consideration of the longitudinal dimension of the pressure-resistant cylinder to be manufactured. do.

The material used in the present invention is duplex stainless steel, which is a two-phase stainless steel composed of austenite and ferranite. Unlike general stainless steel, duplex stainless steel has excellent strength and corrosion resistance, so it can be used in high pressure and seawater atmospheres such as offshore plants or chemical oil refineries. Can be used as a pipe or valve in

Duplex stainless steels show the properties of austenitic stainless steels and ferritic stainless steels together, but tend to have properties closer to those between ferritic stainless steels because the base structure is in the ferritic phase.

The cut pipe is formed into the shape of a pressure-resistant cylinder through a first forming process (S200) and a second forming process (S300). Hereinafter, the first forming step (S200) and the second forming step (S300) will be described in detail.

Referring to FIG. 3, the first forming process (S200) includes a first fixing step, a first heating step, a first hot spinning forming step, a first cooling step, and a first cutting step. .

In the first fixing step, one end of the pipe manufactured in the drawing and cutting process (S100) is inserted into the pipe holder coupled to the rotating body, and the pipe is fixed using a wrench.

In the first heating step, while the pipe holder into which the pipe is inserted rotates using a rotating body coupled to the pipe holder, the other end of the exposed pipe coupled to the pipe holder is locally heated from the lower side of the pipe using a gas burner. and check the temperature of the heated part while heating.

In the first hot spinning forming step, when the temperature of the heating part of the heated pipe reaches the target temperature of 1200 ° C, the end of the pipe is contacted and pressed from the outer surface of the pipe toward the center using a spinning roller to form the pipe. do.

Referring to FIG. 12, the first hot spinning forming step includes a first round molding process, a second round molding process, a first extrusion molding process, and a second extrusion molding process.

The first round forming process is a rounding process in which the outer surface of the edge of the open end of a pipe heated to a target temperature of 1200 ° C is pressed toward the center of the pipe using a spinning roller to reduce the open area of the end. Do it.

The second round forming process closes one end of the pipe by reducing the area of the open end through sequential molding in which the end of the heated pipe is pressed using a spinning roller, and forms a neck of the pressure-resistant cylinder. In the second round molding, one side of the pipe is processed into a conical shape and the end is completely sealed.

In the first extrusion process, the closed end of the pipe is pressurized using the end of the spinning roller to form the inlet of the pressure-resistant cylinder.

In the second extrusion process, the length of the inlet part is increased by pressing the surface of the spinning roller from the inlet part of the internal pressure cylinder formed in the first extrusion molding in the direction of the neck part.

The spinning roller used in the hot spinning forming process has one side larger in diameter than the other side and has a trapezoidal cross section. The spinning roller also rotates along with it.

In the first extrusion molding process, the pipe is processed using the edge end of the large diameter surface of the spinning roller, and in the second extrusion molding, the pipe is processed using the surface located between the large diameter surface and the other surface of the spinning roller.

In the first cooling step, the heating part of the pipe formed through the first hot spinning forming step is rapidly cooled with cooling water.

The second forming process (S300) includes a second fixing step, a second heating step, a second hot spinning forming step, a second cooling step, and a second cutting step.

In the second fixing step, the end of the part molded in the first molding step (S200) is inserted into the pipe holder coupled to the rotating body and fixed.

In the second heating step, while the pipe holder into which the pipe is inserted rotates using a rotating body coupled to the pipe holder, the opposite end of the pipe formed in the first forming step, which is exposed and coupled to the pipe holder, is locally heated. and check the temperature of the heated part.

In the second hot spinning forming step, when the heated pipe reaches the target temperature of 1200° C., the end of the pipe is formed by contacting and pressing the end of the pipe from the outer surface of the pipe toward the center using a spinning roller.

The second forming process includes a second fixing step, a second heating step, a second hot spinning forming step, a second cooling step, and a second cutting step.

In the second fixing step, one end of the pipe manufactured in the drawing and cutting process is inserted into the pipe holder coupled to the rotating body, and the pipe is fixed using a wrench.

In the second heating step, while the pipe holder into which the pipe is inserted rotates using a rotating body coupled to the pipe holder, the other end of the exposed pipe coupled to the pipe holder is locally heated, and the temperature of the heated portion is checked. do.

In the second hot spinning forming step, when the temperature of the heating part of the heated pipe reaches the target temperature of 1200 ° C, the end of the pipe is contacted and pressed from the outer surface of the pipe toward the center using a spinning roller to form the pipe. do.

The second hot spinning forming step includes first round forming, second round forming, first extrusion molding, and second extrusion molding.

In the first round forming, round processing is performed to reduce the open area of the end by pressing the edge of the open end of the pipe heated to a target temperature of 1200 ° C using a spinning roller.

The secondary round molding reduces the area of the open end through sequential molding that presses the end of the heated pipe using a spinning roller, closes one end of the pipe, and forms a neck of the pressure-resistant cylinder. In the second round molding, one side of the pipe is processed into a conical shape and the end is completely sealed.

In the primary extrusion molding, the closed end of the pipe is pressed using the end of the spinning roller to form the inlet of the air manifold.

In the secondary extrusion molding, the surface of the spinning roller is used to pressurize the inlet of the air manifold formed in the primary extrusion in the direction of the neck to elongate the inlet.

A plurality of distribution ports are connected to the outer surface of the air manifold to distribute gas.

In the drilling process (S400), a through hole is formed on the surface of the air manifold formed through the first molding process and the second molding process at a portion where the distribution port is to be connected.

In the distribution hole processing step (S500), one end of the distribution hole to be connected to the air manifold is formed to have the same curvature as the pipe.

In the distribution hole connection process (S600), the distribution hole processed through the distribution hole processing step (S500) is connected to the through hole of the air manifold formed in the drilling process by using a joining method including welding.

More specifically, the air manifold manufactured by the present invention is an air manifold that can withstand high pressure, and forming a through hole on the outer surface of the air manifold to connect the distribution port is common due to the curvature formed on the outer surface of the cylinder. In the case of using the welding method, the life span of the air manifold is reduced due to reduced pressure resistance, and there is a concern that destruction may occur at the welding portion.

In the distribution port connection process (S600), welding is performed in a keyhole TIG method to solve this problem.

This keyhole TIG welding method can solve the instability of the molten pool, and the open keyhole shape allows arc gas to be discharged through the root of the welding part, and is less affected by convection behavior in the molten pool than other arc welding processes.

The welding process is a butt-to-butt method, and the gap is maintained at 0.5 mm or less, and the torch for the welding process has a diameter of 4.5 mm or more to increase the stability of the arc with high current.

When starting welding, the arc generator for arc start is insulated with high voltage so that sparks are generated only between the electrode and the base material, and when the torch is cooled by water cooling, the cooling performance is excellent. and cool it down

In the pickling process (S700), the manufactured air manifold is immersed in an acidic solution to clean the outer and inner surfaces of the molded pipe.

As a method of activating the surface, activation through heating in active hydrogen, removal of the passivation film by heating in a vacuum atmosphere, heating in an active gas containing fluorine, or a method of incorporating chlorine gas into nitric gas can be used. However, these methods require a lot of processing time, are highly likely to generate harmful substances, and may cause problems such as reduced corrosion resistance due to damage to cylinder materials.

Therefore, in the present invention, the oxide scale or carbon impurities are removed through the pickling process (S700) and the passivation film for the solid solution process is activated.

In addition, stainless steel is composed of an Fe-Cr alloy, and when molding is performed by applying heat, Fe-based oxide and Cr-based oxide may be formed on the surface of the stainless steel.

Oxide scale formed on stainless steel is dense and strongly bonded to stainless steel, so it is not easy to remove it.

When the chromium deficiency becomes thin, the concentration of chromium at the interface is lowered, so that the dissolution by the pickling solution can easily occur, so the pickling performance is improved.

More specifically, the pickling process includes a mechanical pretreatment step, a surface treatment step, a degreasing step, a pickling step, a water washing step, a high-pressure washing step, a drying step, and an inspection step.

If the metal oxide is not completely removed through the pickling process, the beautiful surface unique to stainless steel cannot be obtained and the corrosion resistance is not good. Therefore, the metal oxide must be removed. In the case of using only chemical pickling, which is commonly used to remove such dense oxides, it takes a lot of time to remove oxides, which is not good in terms of productivity.

Therefore, in the present invention, mechanical pretreatment is performed before the pickling process to remove a part of the oxide scale or generate cracks in the scale layer so that the oxide compound can easily penetrate into the base material.

In the mechanical pretreatment, pretreatment may be performed by spraying abrasive particles, and the abrasive may cause cracks in the thick oxide scale on the surface of the pressure-resistant cylinder, and may remove some scale by loosening the oxide scale.

When the pretreatment is performed by spraying abrasive particles, the scale removal effect is greater than other pretreatment methods, and the scale removal time is shortened, thereby improving the production line and reducing the use of strong acid.

In the mechanical pretreatment and surface treatment, a stainless brush or a stainless brush equipped with a power source may be used to remove a part of the oxide scale or generate cracks in the scale layer and remove foreign substances on the surface.

Oil and foreign substances on the surface of the air manifold may be oxidized during the pickling process and remain on the surface, thereby reducing pickling efficiency and contaminating the solution.

Degreasing is performed to remove oil and foreign substances on the surface of the air manifold. If the surface is cleanly cleaned by degreasing, pickling efficiency can be increased.

In degreasing, an organic solvent is applied to the surface of the air manifold with a spray or brush, and after 30 minutes to 2 hours at room temperature, the degreasing solution on the surface of the air manifold is washed using a high-pressure sprayer.

In the pickling step, pickling chemicals including hydrogen fluoride (HF) and nitric acid (HNO3) are applied to the surface of the air manifold using a diaphragm pump, or the air manifold itself is immersed in the chemicals and pickling is carried out at room temperature for 2 to 6 hours. carried out during

In the water washing step, the pickled air manifold is immersed in a water bath and maintained until the pH concentration of the surface of the air manifold reaches 2 to 3.

In the high-pressure washing step, high-pressure washing is repeatedly performed using purified water with a high-pressure sprayer until the pH concentration of the surface of the air manifold reaches 6 to 8.

After high-pressure washing, a drying step of drying naturally or by blowing air is performed.

In the inspection step, ferroxyl is sprayed on the air manifold surface to determine whether or not iron oxide remains on the air manifold surface, and after 10 to 15 seconds, the color of the sprayed area is determined, and the pH of the air manifold surface is measured using a litmus reagent. Measure the concentration.

In the pickling process, the factors affecting the pickling speed include temperature, acid concentration, dissolved metal ion amount, pickling time, fluidity, and the like.

In the heat treatment step (S800), the solution heat treatment and the bright heat treatment are performed simultaneously. In addition, in the conventional bright heat treatment, a technology of heat treatment by adjusting the furnace to an inert atmosphere through a vacuum furnace or a salt zone or by packaging the product with cast iron chips, stainless bags, foils, special carbon containers, etc. was used. Such conventional bright heat treatment has a problem in that expensive investment is required, which becomes a factor in cost increase.

In the conventional solution heat treatment, pickling and blasting operations were repeated due to the generation of an oxide film by the solution heat treatment, resulting in deterioration of gloss and appearance quality. And there was a problem that the cost due to environmental pollution was excessively consumed.

The present invention is characterized in that it is possible to maintain the gloss before heat treatment by performing bright heat treatment, and does not require separate pickling treatment and sandblasting after heat treatment.

In the screw tap processing step (S900), a thread is formed on the inner surface of the inlet of the manufactured air manifold.

In the surface processing step (S1000), the surface of the molded air manifold is smoothly processed by performing surface processing including polishing, perning, finishing, honing, and grinding using a processing tool including a CNC lathe.

After the surface processing step (S1000), a surface coating step (S1100) is performed to improve corrosion resistance and durability.

When coating is performed in a conventional manner during the surface coating process, heavy metal ions including chromium + hexavalent ions and plating wastewater containing harmful substances are released, which has a very serious impact on the human body and the ecosystem, resulting in environmental damage compared to superior performance. will have a lot of impact

In the surface coating process (S1100) of the present invention, corrosion resistance and durability can be improved while minimizing environmental impact by using an environmentally friendly coating solution that does not contain chromium + hexavalent ions and does not discharge plating wastewater.

More specifically, the surface coating process includes a coating solution preparation step (S1110), a first coating step (S1120), a first drying step (S1130), a second coating step (S1140), and a second drying step (S1150). It is done.

In the coating solution preparation step (S1110), after filtering only the particles of 20㎛ or less in order to form a uniform film from the raw materials of the coating solution including zinc powder, aluminum powder, and resin powder, they are put into a stirrer and stirred to obtain environmentally friendly inorganic Sn-Al. Prepare a coating solution.

In the first coating step (S1120), the air manifold is put into the coating basket, immersed in the coating liquid, and then rotated at a low speed using a centrifuge to remove the filtrate.

In the primary drying step (S1130), the coating liquid applied to the outer and inner surfaces of the cylinder on which the primary coating is completed is dried.

Drying is not simply drying the coating liquid, but a process of forming a polymer on the film formed by the coating liquid and the adhered portion of the cylinder made of stainless steel, and drying at a temperature of 150 to 200 ° C for 1 hour to 1 hour and 30 minutes.

In the secondary coating step (S1140), the coating liquid is applied by spraying the coating liquid onto the outer and inner surfaces of the cylinder after the primary coating and primary drying have been completed in an air spray method.

In the secondary drying step (S1150), the coating liquid applied to the outer and inner surfaces of the cylinder on which the secondary coating is completed is dried.

If the coating is applied only once, the surface is not smooth due to the presence of contact marks and traces of the filtrate flow, and the appearance is poor in aesthetics. The thickness is also excellent, and corrosion resistance can be further improved.

Conventionally, in order to manufacture an air manifold, a body pipe, a pipe cap, and a coupling port are manufactured, respectively, and each component is welded and combined.

When the body pipe and pipe cap, which are conventional manufacturing methods, are individually manufactured and then combined by welding, the corrosion and pressure resistance of the welded part deteriorates, resulting in a shortened lifespan when used under high pressure conditions. This problem is solved. In order to do this, the present invention manufactures an integral air manifold without welding seams through a hot spinning process, rather than welding after manufacturing the body pipe and pipe cap respectively, and after manufacturing the air manifold, through a surface coating process , It is possible to manufacture an air manifold that does not leak at all and has excellent corrosion resistance and wear resistance.

The above description is merely an example of the technical idea of the present invention, and those skilled in the art can make various modifications, changes, and substitutions without departing from the essential characteristics of the present invention. will be. Therefore, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments and the accompanying drawings. . The protection scope of the present invention should be construed according to the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

S100 - Drawing and cutting process S200 - 1st molding process
S300 - Second molding process S400 - Drilling process
S500 - Distribution port processing process S600 - Distribution port connection process
S700 - Pickling process S800 - Solid solution process
S900 - Thread tap processing process S1000 - Surface processing process
S1100 - Surface coating process

Claims (3)

A drawing and cutting process of manufacturing a pipe having a predetermined diameter and thickness through a drawing process and then cutting the pipe into a predetermined length;
A first forming step of forming a neck portion and an inlet portion of a pressure resistant cylinder by hot spinning one end of the pipe manufactured in the drawing and cutting step;
A drilling process of forming a plurality of through holes in a portion to be connected to a distribution port in a formed pipe;
A distribution hole processing step of forming one end of the same curvature as the curvature of the pipe to be connected;
a distribution hole connection step of connecting a distribution hole to a plurality of through holes formed in the drilling process;
An acid washing step of cleaning the outer and inner surfaces of the molded pipe using an acidic solution to which an oxidation inhibitor is added; and
A surface processing process that smoothly processes the surface of a molded pipe using processing tools including a CNC lathe
including,
Distribution port connection process
Performing welding by a keyhole TIG method; and
It is a butt-to-butt method, and the gap is maintained at 0.5 mm or less, and the torch for performing the welding process is 4.5 mm or more in diameter.
Including,
in the heat treatment process
Simultaneously performing the solution heat treatment process and the bright heat treatment process
contains
The pickling process
A mechanical pretreatment step capable of generating cracks in the oxide scale by spraying abrasive particles;
A surface treatment step of removing some of the oxide scale using a stainless brush equipped with a power source, generating cracks in the scale layer, and removing foreign substances on the surface;
A degreasing step of applying an organic solvent to the surface of the air manifold with a spray or brush, and washing the degreasing solution on the surface of the air manifold using a high-pressure sprayer after 30 minutes to 2 hours at room temperature;
A pickling step in which pickling chemicals containing hydrogen fluoride and nitric acid are applied to the surface of the air manifold or the air manifold itself is immersed in the chemicals and carried out at room temperature for 2 to 6 hours;
A water washing step in which the pickled air manifold is immersed in a water bath and maintained until the pH concentration of the surface of the air manifold reaches 2 to 3;
A high-pressure washing step of repeatedly performing high-pressure washing several times using purified water until the ph concentration of the surface of the air manifold reaches 6 to 8 with a high-pressure sprayer;
A drying step of drying naturally or by blowing air;
In order to determine the presence or absence of iron oxide residue on the surface of the air manifold, ferroxyl is sprayed on the surface of the air manifold, and after 10 to 15 seconds, the color of the sprayed area is determined, and the pH concentration of the surface of the air manifold is measured using a litmus reagent. inspection step
to include;
The material is composed of two-phase stainless steel composed of austenite and ferranite; and
The first forming process is
A first fixing step of inserting one end of the pipe manufactured in the drawing and cutting process into the pipe holder coupled to the rotating body and fixing the pipe using a wrench;
While the pipe holder into which the pipe is inserted rotates using a rotating body coupled to the pipe holder, the other end of the pipe coupled to the pipe holder and exposed is locally heated from the lower part of the pipe using a gas burner, and heated while being heated. The first heating step of checking the temperature of the part,
When the temperature of the heating part of the heated pipe reaches the target temperature of 1200 ° C, the first hot spinning forming step of forming the pipe is performed by contacting and pressing the end of the pipe from the outer surface to the center of the pipe using a spinning roller. ,
A first cooling step of rapidly cooling the heating part of the pipe formed through the first hot spinning forming step with cooling water
including,
The first hot spinning forming step is
1st round molding that performs round processing to reduce the open area of the end by pressing the outer surface of the edge of the open end of the pipe heated to the target temperature of 1200 ° C using a spinning roller toward the center of the pipe. process,
A second round forming process of closing one end of the pipe by reducing the area of the open end through sequential molding of pressing the end of the heated pipe using a spinning roller and forming the neck of the pressure-resistant cylinder;
A first extrusion molding process in which the closed end of the pipe is pressurized using the end of the spinning roller to form the inlet of the pressure-resistant cylinder;
A second extrusion molding step of extending the length of the inlet by applying pressure from the inlet to the neck of the internal pressure cylinder formed in the first extrusion using the surface of the spinning roller;
Including,
The spinning roller used in the first hot spinning forming step has one side larger in diameter than the other side and has a trapezoidal cross section. As the pipe rotates, the spinning roller also rotates.
Including, seamless integral air manifold manufacturing method. delete delete

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