KR20020013704A - Manufacturing method of inner surface resin lining pipe - Google Patents

Abstract

PURPOSE: To manufacture a thick inner surface resin lining pipe at a low cost by lining a metal pipe with a resin pipe not almost having heating diameter expanding properties like an ordinary polyethylene pipe. CONSTITUTION: The resin pipe to be applied to the inner surface of the metal pipe is cooled to be temporarily contracted in its diameter and, in this state, the resin pipe is inserted into the metal pipe to facilitate insertion work. Thereafter, the inserted resin pipe returns to the normal temperature or it is preheated and the outer surface of the resin pipe comes into contact with the inner surface of the metal pipe. In this state, the metal pipe is heated to temperature not lower than the fusing temperature of the resin pipe, and the resin pipe is fused to the inner surface of the metal pipe to form an inner surface lining layer.

Description

MANUFACTURING METHOD OF INNER SURFACE RESIN LINING PIPE

The present invention relates to a method for producing an inner resin lining tube used for water and sewage.

Internally, resin-lined steel pipes have been used for various pipes including water and sewage, taking advantage of its corrosion resistance, non-exhaustability, and durability. Among them, polyethylene lining steel pipes have the above-mentioned characteristics remarkably, and have attracted more attention because hardly any environmental problems occur.

However, the market share of polyethylene-lined steel pipes is lower than that of vinyl chloride-lined steel pipes. The main reason is the manufacturing method and cost.

The main manufacturing method of the vinyl chloride lining steel pipe is the expansion method using a vinyl chloride expansion tube. That is, the vinyl chloride expansion tube (heating function) which gives the heating expansion property by shape memory (the function which freezes the state which first reduced diameter as it is, and restores it to the diameter state near the original diameter by heating). The expansion rate of about 20 to 50%) is inserted into the steel pipe, and the vinyl chloride expanded tube is expanded to be heated and lined on the inner surface of the steel pipe. It is very easy to give the vinyl chloride tube about 20 to 50% of the heating expandability because it can be carried out by heat treatment and mechanical processing.

On the other hand, in the case of a polyethylene tube, when trying to impart a heat expandability equivalent to that of a vinyl chloride expansion tube, it is necessary to perform crosslinking or modification treatment of the resin, and in addition, heat treatment and mechanical processing are required in theory. It is possible, but lacks economic feasibility, and the difficulty of manufacturing resin pipes also increases. For this reason, the production of polyethylene-lined steel pipes is not currently employed in the production of polyethylene-lined steel pipes. Polyethylene-lined steel pipes are used in a so-called powder fusion method in which pulverized polyethylene powder is fed into a heated steel pipe and dissolved by heat to form a film. Is being manufactured. In this method, however, the powder is used, so the material cost is high, which is quite expensive compared to the vinyl chloride tube produced by the extrusion method from the pellets. Further, in the powder fusion method, thickening is not technically easy, and in the present state, it is substantially about 0.5 mm, and there is a tendency to give an unstable impression compared to 1 mm or more of vinyl chloride. In addition, the amount of expensive powder resin is increased by the amount of thickened film, resulting in a further increase in cost.

The present invention has been made in view of these phenomena, and it is preferable to lining a resin pipe that does not impart the heating expandability as a normal polyethylene tube, or a resin tube having a small heating expansion even if given to a metal tube such as a steel pipe. It is an object of the present invention to provide a method for enabling the production of a thick film inner surface resin lining tube at low cost.

In the present invention, in order to easily insert a resin tube having no heating expansion or small resin tube into a metal tube such as a steel tube, and to reliably adhere and line the inner surface of the metal tube, the resin tube is cooled and temporarily reduced in such a state. The resin tube is attached to the inner surface of the metal tube by inserting into the metal tube and then heating the metal tube. Thus, when the resin tube was inserted into the metal tube, the resin tube was cooled and temporarily reduced in diameter. Therefore, even if the original outer diameter was a resin tube approximately equal to the inner diameter of the metal tube, the resin tube was easily inserted into the metal tube. The resin tube can be brought into close contact with the inner surface of the metal tube by returning to the normal temperature and returning to the original outer diameter, or preheating or heating as necessary to restore or enlarge the outer diameter of the resin tube. In this state, the metal tube can be heated to be bonded to the metal tube inner surface by heating the resin tube outer surface. In this way, an inexpensive resin tube can be easily lined on the inner surface of the metal tube, and the resin lining of the desired thickness can be formed by setting the thickness of the resin tube as desired, and the inner surface resin lining tube of the thick film is made with low cost. It can manufacture.

Embodiment of the Invention

As described above, the manufacturing method of the inner surface resin lining tube according to the present invention inserts into the metal tube a resin tube which has been cooled and temporarily reduced when resin lining the inner surface of the metal tube, and then heats the metal tube to the inner surface of the metal tube. It is characterized by adhering the branch pipe.

The metal pipe used for this invention is a steel pipe normally, but the metal pipe of other materials may be sufficient. In addition, the resin tube used in the present invention is not particularly limited, but in view of anticorrosiveness, non-release property, durability, and environmental problems, a resin tube made of polyolefin (polyethylene, polypropylene, polybutene, or the like or a mixture thereof) This is preferred. In this case, the physical properties of the polyolefin are not limited, but considering the ease of insertion into the metal tube, one having a high rigidity (more than medium density in terms of polyethylene) is preferable.

The resin pipe used for this invention may or may not be equipped with the heating expandability by shape memory, and the magnitude | size of the heating expandability is also arbitrary. The use of a resin tube having a heating expandability allows the outer diameter of the resin tube to be inserted to be made smaller as the heating expandability is increased, thereby making it easier to insert into a metal tube, while costly to manufacture. Therefore, depending on the material, it may not be an advantage. For example, in polyethylene pipes, in order to give 20 to 50% of the heating expandability, crosslinking and modification of the resin are required, so that the cost is extremely high, and it is not advantageous, but about 1 to 5%. The heat expandability can be given by heat treatment and mechanical processing such that the die is passed through the die in the heated state, reduced in diameter, immediately cooled and solidified, and the cost is not increased. Therefore, it is desirable to provide about 1 to 5% of the heating expandability.

The outer diameter of the resin tube used in the present invention is selected as follows. In other words, in the case of using a resin tube having no heating expandability, the outer diameter between the resins is that the outer surface of the resin tube is in contact with the inner surface of the metal tube when the resin tube is cooled and inserted into the metal tube and returned to normal temperature or when it is preheated. Select to be in a state. When a resin tube having a heating expandability is used, the outer diameter of the resin tube is selected so that the outer surface of the resin tube is in contact with the inner surface of the metal tube when the resin tube is cooled, inserted into the metal tube, and heated and expanded. Here, the "state in which the outer surface of the resin tube is in contact with the inner surface of the metal tube" includes not only a state in which the outer surface of the resin tube is pressurized with a suitable contact pressure to the inner surface of the metal tube, but also a state in which the outer surface of the resin tube is substantially in contact with the inner surface of the metal tube. Therefore, when using a resin tube having no heating expandability and not preheating, the outer diameter of the resin tube is approximately equal to or larger than the inner diameter of the metal tube. In the case of using a resin tube that does not have a heating expandability and preheating, the outer diameter of the resin tube can be selected to be smaller than the outer diameter of the resin tube in the case of not preheating, so that the insertion work can be performed by that amount. It becomes easy. In addition, in the case of using a resin tube having a heating expandability, the outer diameter thereof can be selected as small as the amount of the heating expansion ratio as compared with the case of using a resin tube having no heating expandability, so that the insertion work can be performed by that amount. It becomes easy. As described later, it is preferable to interpose an adhesive layer between the outer surface of the resin tube and the inner surface of the metal tube. When the adhesive layer is interposed therebetween, the outer diameter of the resin tube is brought into contact with the inner surface of the metal tube through the adhesive layer. Good to choose.

Since the resin tube is attached to the inner surface of the metal tube after insertion into the metal tube to form a resin lining layer, the thickness of the resin tube may be set equal to the desired thickness of the resin lining layer to be formed on the inner surface of the metal tube. In other words, by setting the thickness of the resin tube to be equal to the desired thickness of the resin lining layer to be formed, and inserting the resin tube into the metal tube and adhering, the resin lining layer having a desired thickness can be easily formed. A thick polyethylene lining layer is also easily formed.

Formation of the resin tube is important for easily inserting the resin tube into the metal tube. In other words, if there is dispersion or bending of the outer diameter, it causes difficulty in insertion. Therefore, it is preferable to suppress the outer diameter of the resin tube to within ± 50 µm and to have almost no bending. Such a resin tube can be easily manufactured by recent technological progress.

When inserting a resin pipe into a metal pipe, the resin pipe is cooled beforehand and reduced in diameter. This makes it possible to create a suitable gap between the inner surface of the metal tube and facilitate the insertion of the resin tube into the metal tube. In this case, the lower the cooling temperature of the resin tube is, the larger the shaft weight is, thereby making it easier to insert into the metal tube, while the cost required for cooling increases. Therefore, the cooling temperature of the resin tube is determined in consideration of these, and the value thereof is preferably about -20 to -40 ° C. When a resin tube whose outer diameter at room temperature is equal to the inner diameter of the metal tube is cooled to -20 ° C, about 1% of the shaft diameter is generated in the polyethylene tube. For this reason, a resin tube having an outer diameter of 100 mm produces a shaft diameter of about 1 mm, and a gap of about 1 mm can be secured between the metal tubes, thereby making it easier to insert the resin tube into the metal tube. In addition, cooling at about -20 to -40 ° C can be performed using a relatively inexpensive liquid (dry ice + methanol liquid or ethanol liquid) or using a freezer or a freezer, and thus can be performed at low cost.

What kind of method may be used for the cooling method of a resin pipe, Specifically, the method of immersing in low temperature liquid, the method of cooling using a freezer or a freezer, etc. are mentioned. As an example of a low temperature liquid, dry ice + methanol liquid or ethanol liquid, liquid nitrogen, or liquid air can be illustrated. Since dry ice + methanol liquid may lower | hang temperature to about -80 degreeC, since it is enough to cool a resin pipe about -20-40 degreeC as mentioned above, since a cost is comparatively low, it is preferable. On the other hand, in the case of using liquid nitrogen, the temperature can be lowered to about -196 ° C, so that the axial diameter of the resin tube can be increased, and even if there is some dispersion in the shape, it can be inserted. Only, for example, it becomes below the general embrittlement temperature (−80 ° C.) of polyethylene, so care must be taken not to damage the insert.

In the method of inserting the cooled resin tube into the metal tube, either the method of pushing the resin tube into the metal tube and inserting it, the method of pulling the resin tube into the metal tube, or both may be used in combination. Pulling the resin tube and inserting it into the metal tube has an advantage that the shaft diameter is caused by the tensile force acting on the resin tube, thereby making it easier to insert. However, it is necessary to insert quickly when it is reduced in diameter by cooling anyway.

After the resin tube is inserted into the metal tube, the outer surface of the resin tube is bonded to the inner surface of the metal tube by heating the metal tube. Although this adhesive force may be produced by fusion of the resin tube itself, it is preferable to interpose the adhesive layer which adheres well to both between a resin tube and a metal tube, and to use the adhesion by the adhesive layer. As the adhesive layer used herein, a thermoplastic resin having a lower melting point than that of the resin tube is suitable. Specifically, when a polyolefin tube is used as the resin tube, carboxylic acid-modified polyolefin, EVA, EAA, and the like can be exemplified. Although the thickness of an adhesive bond layer is 10-100 micrometers enough, it does not have the trouble which becomes thicker than this according to circumstances, such as when performing two-layer extrusion mentioned later.

For interposing the adhesive layer between the resin tube and the metal tube, the adhesive layer may be formed on the outer surface of the resin tube in advance, or the adhesive layer may be formed on the inner surface of the metal tube, and the former is preferable in view of workability. As a method of forming the adhesive layer on the outer surface of the resin tube in advance, a method of forming the adhesive layer at the same time as the production of the resin tube by two-layer extrusion, a method of winding the adhesive sheet in the form of a spiral shape on the outer surface of the resin tube, a liquefied adhesive To spray the outer surface of the resin tube. Among these methods, the method of forming an adhesive layer at the same time as the production of a resin tube by two-layer extrusion is suitable for inexpensive mass production, the adhesive layer can be formed uniformly on the outer circumference, and the adhesive at the time of insertion into a metal tube It is preferable to dry the layer in a wet state. On the other hand, as a method of forming an adhesive layer on the inner surface of a metal tube, the method of attaching an adhesive sheet to the inner surface of a metal tube is mentioned. In the case of using a polyethylene tube as the resin tube, it is effective to pretreat the corona surface or the like beforehand depending on the adhesive.

After the resin tube is inserted into the metal tube, the metal tube is heated to heat and melt the outer surface of the resin tube or the adhesive layer to adhere to the inner surface of the metal tube. Even if there are some gaps between the inner surface of the metal tube and the outer surface of the resin tube or the adhesive layer during the heating operation, when the heating is started, the resin tube also starts to expand due to the heat of the metal tube, and tends to be in close contact with the outer surface of the resin tube or the adhesive agent. Heating of the layer is possible. However, for good heat transfer from the metal tube to the resin tube outer surface or the adhesive layer, it is preferable that the outer surface of the resin tube is in contact with the metal tube inner surface directly or through the adhesive layer. Therefore, after the resin tube is cooled and inserted into the metal tube, it is allowed to stand for a suitable time in that state before the heating of the metal tube is started. As a result, the resin tube is returned to room temperature in the metal tube and expanded in diameter. When the original resin tube outer diameter is equal to or larger than the metal tube inner diameter, the resin tube is brought into contact with the inner surface of the metal tube. Thereafter, heating operation of the metal tube is started. In addition, when the resin tube is cooled and inserted into the metal tube, the surface of the resin tube may condense. In that case, it is preferable to put a drying step prior to heating so that there is no drying of the steam.

In the case where the outer diameter is used as the resin tube smaller than the inner diameter of the metal tube or the like, even if the resin tube inserted into the metal tube returns to room temperature, a gap may occur between the inner surface of the metal tube and the inner side. In that case, the resin tube is preheated before the metal tube is heated, and the resin tube is expanded to contact the inner surface of the metal tube directly or through an adhesive layer. The preheating temperature must, of course, be below the melting point of the adhesive. The preheating may heat up only the resin tube by sending hot air into the resin tube. The preheating may be performed for each steel tube by placing the whole in a furnace, or the metal tube may be heated in the same manner as the main heating of the metal tube described later, and the heat transfer from the metal tube may be performed. You may heat up a resin tube by this. Even in this case, the thermal expansion rate of the resin tube is not only 10 times that of the metal tube, and therefore, even if the temperature is raised to the same temperature, the amount of expansion of the resin tube greatly exceeds that of the metal tube, and the resin tube can be brought into contact with the inner surface of the metal tube. Moreover, when using what has a heating expandability as a resin pipe, even if the resin pipe inserted in the metal pipe returns to normal temperature, the clearance gap exists with the inner surface of a metal pipe. Therefore, before heating the metal tube, the resin tube is heated to express the heating expandability of the resin tube, and the inner surface of the metal tube is brought into contact directly or through an adhesive layer. Naturally, the heating temperature is higher than the temperature at which the heating expandability can be expressed and lower than the melting point of the adhesive. In this heating, only the resin tube may be heated or heated for each steel tube, for example, by sending hot air into the resin tube.

As described above, the resin tube is brought into contact with the inner surface of the metal tube directly or through an adhesive layer, and then the metal tube is heated, and the metal tube is heated below the melting point of the resin tube or the adhesive layer. As a result, the outer surface of the resin tube or the adhesive layer melts, and the resin tube adheres to the inner surface of the metal tube. Here, when an adhesive bond layer is not used, a resin pipe is heated above melting | fusing point by heating of a metal pipe, and a resin pipe may melt not only the outer layer which contacted a metal pipe but an inner layer. However, the polyethylene for extrusion generally used as a resin tube has poor melt fluidity, and there is no problem especially unless deformation occurs. Another advantage is that the residual stress is reduced by melting the inner and outer layers once.

The heating of the metal tube may be performed by heating and heating the entire metal tube at the same time by using an electric furnace or the like. The total heating is changed to heat the small section in the longitudinal direction of the metal tube, and the heating part is directed from one end of the metal tube to the other end. Or it is preferable to carry out by the moving heating which moves to an axial direction from a center part to both ends. When such moving heating is performed, the fusion site of the resin pipe and the metal pipe sequentially moves in the axial direction, and the fusion site advances while the air bubbles between the resin pipe and the metal pipe are extruded. For this reason, it is possible to minimize the incorporation of air bubbles into the tubes of the resin tube and the metal tube, and the adhesion of the resin tube to the metal tube is possible.

High frequency induction heating is optimal as a means for carrying out the heating heating of the metal tube. In other words, by using high frequency induction heating, an induction coil for securing a desired heating width is disposed on the outer circumference of the metal tube and energized so that the inner metal tube portion can be heated to a desired temperature in a folk manner, and the induction coil is heated in a metal tube. By moving in a relatively axial direction with respect to the heating portion can be moved. In addition, the heating means is not limited to high frequency induction heating, and in consideration of the shape, quantity, and economics of the article, gas heating, electric furnace heating caused by moving inside the electric furnace, or a combination thereof may be used.

After the metal tube is heated and the resin tube is bonded to the metal tube inner surface, the metal tube may be cooled by cooling or water cooling.

(Example)

Example 1

Resin tube: high density polyethylene tube

Dimension: outer diameter 42.0mm, inner diameter 34.2mm, thickness 3.9mm, length 500mm

Metal pipe: Steel pipe (SGP40A)

Dimension: outer diameter 48.6mm, inner diameter 41.7mm, thickness 3.5mm, length 500mm

Adhesive: maleic anhydride modified polyethylene tape

Dimension: thickness 50㎛, width 25mm

The above material was prepared.

First, the inner surface of the steel pipe was blasted, and a modified polyethylene tape was temporarily fixed in the direction of the steel pipe axis on the inner surface pole.

Next, the polyethylene tube was immersed in the liquid nitrogen bath (-196 ° C) for 3 minutes, reduced in diameter, and quickly inserted into the steel tube. The outer diameter of the polyethylene tube at the time of shaft diameter was about 41.0 mm.

Next, the steel pipe into which the polyethylene tube was inserted was inductively heated by an induction coil having a heating width of 30 mm, and moved at a rate of 220 mm / min from one end to a heating temperature of 150 ° C. After cooling, the resultant was cut and subjected to appearance observation and peeling test to obtain the following results.

Appearance: Glossy inside, no swelling, wrinkles, scratches.

Adhesive force: As a result of the 10 mm width peeling test, 20 kg or more was shown and it was sufficient value.

Example 2

Resin tube: high density polyethylene tube

Dimension: outer diameter 41.5mm, inner diameter 38.0mm, thickness 2.0mm, length 500mm

However, the outer layer is 100㎛ EAA resin coating layer

Metal pipe: Steel pipe (SGP40A)

Dimension: outer diameter 48.6mm, inner diameter 41.7mm, thickness 3.5mm, length 500mm

The above material was prepared.

First, the inner surface of the steel pipe was blasted.

Next, the polyethylene tube was immersed in a dry ice + methanol bath (-79 ° C) for 3 minutes, reduced in diameter, and quickly inserted into a steel pipe. The outer diameter of the polyethylene tube at the time of shaft diameter was about 41.0 mm.

Next, the steel pipe into which the polyethylene pipe was inserted was induction heated by an induction coil having a heating width of 20 mm, and the preheating of the polyethylene pipe was performed at a heating temperature of 90 ° C. at a speed of 110 mm / min from one end. By this preheating, it was confirmed that the steel pipe and the polyethylene which had a slight gap were in close contact with each other.

Next, induction heating was carried out by an induction coil having a heating width of 30 mm before the temperature was cooled, and the heating was performed at a heating temperature of 120 ° C. at a speed of 220 mm / min from one end.

It cut | disconnected after cooling, and the external observation and the peeling test were done, and the following result was obtained.

Appearance: Glossy inside, no swelling, wrinkles, scratches.

Adhesive force: As a result of the 10 mm width peeling test, 20 kg or more was shown and it was sufficient value.

As described above, the present invention provides a resin tube in which the resin tube to be lined on the inner surface of the metal tube is cooled and reduced in advance, inserted into the metal tube in such a state, and then the resin tube is brought into contact with the inner surface of the metal tube by heating the metal tube. Can be easily inserted into the metal tube, and the metal tube can be favorably adhered to the metal tube by heating the metal tube, and the inner resin lined tube having the resin lining having a desired thickness can be produced at low cost.

If the resin tube inserted into the metal tube is preheated prior to heating the metal tube, the resin tube can be brought into contact with the inner surface of the metal tube by thermal expansion by preheating. In other words, the outer diameter of the resin tube is not preheated. It can be selected smaller than in the case where it is not, so that the effect can be more easily inserted into the metal tube.

In addition, when the resin pipe is inserted into the metal pipe, a resin pipe having a heating expandability by shape memory can be used, so that the resin pipe can be heated and expanded after insertion into the metal pipe. In addition, it is possible to use a smaller one, and therefore, the effect that the insertion into the metal tube can be made easier.

Moreover, if the adhesive pipe layer of lower melting | fusing point than a resin pipe | tube is interposed between the said metal pipe | tube and the resin pipe | tube inserted in it, the metal pipe and a resin pipe | tube can be mutually bonded by melting the adhesive bond layer by heating of a metal pipe | tube, Compared to the case where the resin tube is melted and bonded to the metal tube, the heating operation can be lowered and the bonding operation can be performed, and more firm adhesion can be obtained.

In the case where the adhesive layer is used, the outer surface of the resin tube to be inserted into the metal tube is covered with an adhesive layer having a lower melting point than that of the resin tube. Since an adhesive bond layer can be interposed between branch papers, and an adhesive bond layer may be arrange | positioned on the outer surface of a resin pipe, the effect which can arrange | position an adhesive bond layer on the outer surface of a resin pipe can be acquired uniformly and easily.

When the heating of this metal tube for bonding a resin tube to a metal tube is performed by the heating heating which heats the small section of the metal tube in the axial direction, and moves the heating part from one end to the other end or from the center part to both ends, it heats. The fusion is performed while the fusion region by the metal pipe proceeds in the axial direction of the metal pipe, thereby fusion is performed while the air bubbles between the resin pipe and the metal pipe are extruded, and the adhesion between the resin pipe and the metal pipe hardly rolls up is ensured. You can get the effect.

By using a polyolefin tube such as a polyethylene tube as the resin tube used in the present invention, it is possible to obtain an effect that the polyolefin lining tube of a thick film having excellent anticorrosiveness, non-exhaustability, durability and no environmental problems can be produced at low cost. do.

Claims (7)

When the resin lining is applied to the inner surface of the metal tube, a resin tube previously cooled and temporarily reduced in diameter is inserted into the metal tube, and then the resin tube is bonded to the inner surface of the metal tube by heating the metal tube. Manufacturing method. The method of manufacturing the inner resin lining tube according to claim 1, wherein the resin tube inserted into the metal tube is preheated prior to the heating of the metal tube. The inner resin lining tube manufacturing method according to claim 1 or 2, wherein a resin tube having a heating expandability by shape memory is used as the resin tube inserted into the metal tube. The inner resin lining tube manufacturing method according to any one of claims 1 to 3, wherein an adhesive layer having a lower melting point than a resin tube is interposed between the metal tube and the resin tube. The inner surface resin lining tube manufacturing method according to any one of claims 1 to 4, wherein an outer surface of the resin tube inserted into the metal tube is covered with an adhesive layer having a lower melting point than that of the resin tube. The transfer heating according to any one of claims 1 to 5, wherein the heating of the metal tube is performed by heating a small section in the axial direction of the metal tube to move the heating portion from one end of the metal tube to the other end or from the center portion to both ends. Process for producing an inner surface resin lining tube, characterized in that performed by. The inner resin lining tube manufacturing method according to any one of claims 1 to 6, wherein a polyolefin tube is used as the resin tube inserted into the metal tube.