JPH0576379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The disclosed technology belongs to the technical field of manufacturing piping such as wear-resistant double pipes that tightly connect an outer pipe and an inner pipe.

<Summary of the gist> The invention of this application is, for example, in order to improve the wear resistance of piping used for slurry transportation, pneumatic transportation, etc. Continuous circumferential annular heating in the axial direction of the outer tube by moving the blank tube such as a double tube in the axial direction relative to the circumferential annular heating means of the outer tube and the cooling means around the heating part. This invention relates to a method for reducing the diameter of a tube in which the outer tube and the inner tube are tightly connected by cooling the periphery of the heating part in a temporally staggered manner. When performing ring-shaped heating and cooling of the surrounding area, the expansion diameter of the heating area is restricted by cooling the area around the heating area, and the heating area is made to yield so that the diameter of the heating area becomes smaller than the initial diameter after cooling. This invention relates to a direction in which the diameter of the tube is reduced, so that it is possible to obtain a double tube that is fitted with a fitting margin in a strongly tightened state.

<Prior art> As is well known, piping is widely used in various industrial fields to transport fluids. In pipes for transporting slurry mixed with liquid, or pipes for transporting powder particles such as dust and silica sand, there is a problem in that the inner surface of the pipe is easily worn out over time due to operation.

Therefore, cheap steel pipes such as gas pipes are usually used for this type of piping, and when they wear out, they can be replaced with new pipes or welded backing plates to the worn parts. There is.

Of course, especially for piping applications where wear resistance is required, pipes made of materials with excellent wear resistance, such as high chromium cast iron, may be used.

Generally, the wear resistance of steel materials has a good correlation with hardness, and materials with excellent wear resistance are uniformly extremely hard.

For example, it is often used as a wear-resistant material.
27Cr cast iron has a Shore hardness of 81 or higher.

<Problems to be Solved by the Invention> However, as the hardness increases, the toughness of steel materials tends to decrease, and pipes made of wear-resistant materials such as the above-mentioned high chromium cast iron are subject to impact forces. It has the disadvantage of being easily damaged.

In addition, since high-hardness wear-resistant materials have extremely poor weldability and workability, they have the drawback that, for example, it is almost impossible to attach flanges to pipe bodies by welding for joints. Even when the flange is integrally formed with the pipe body, it is difficult to perform finishing and drilling afterwards, and repair welding is also difficult.

In addition, it also has the disadvantage of high manufacturing costs.

For this reason, so-called clad steel pipes, in which the main body of the steel pipe is lined with a wear-resistant material, have come into use.

The type clad steel pipe is usually manufactured by centrifugal casting method or
The lined pipe is made by a welding method or the like, and is metallurgically joined to the pipe body.

Since the inner surface of the clad steel pipe is covered with the wear-resistant material of the lining pipe, it has a much higher wear resistance than ordinary single-layer steel pipes made of materials that do not take wear resistance into account. It has excellent characteristics.

Further, since the tube body does not need to be made of wear-resistant material, it is possible to use a material that has sufficient toughness and has good weldability and workability.

Therefore, unlike a pipe made only of wear-resistant material, it has sufficient impact resistance, and it is also possible to form a separate flange and attach it by welding or drilling holes.

However, with clad steel pipes, tensile stress remains in the lined pipe regardless of the manufacturing method, so
It has the disadvantage that it tends to crack during operation.

Moreover, once a crack occurs, since the lining pipe and the pipe main body are metallurgically joined, the crack easily propagates to the pipe main body, and there is also a disadvantage that it is easy to cause a through crack.

Therefore, we developed a double-layered tube consisting of an outer tube with sufficient toughness for practical use and an inner tube with excellent wear resistance. Therefore, it is desired to develop a self-stressing double pipe in which the inner pipe is placed in a compressive stress state.

This is because such self-consolidated double pipes have the same advantages as clad steel pipes, and moreover, the above-mentioned disadvantages of clad steel pipes are eliminated.

By the way, the conventional manufacturing techniques for self-tightening double pipes include firstly the shrink fitting method, secondly the pipe expanding method, and thirdly the so-called heat expanding method developed earlier by the applicant. Each of these methods has disadvantages as methods for manufacturing abrasive self-containing double pipes.

First, the first method requires strict machining accuracy for the inner diameter of the outer tube and the outer diameter of the inner tube, but in the case of a double tube with a wear-resistant inner surface, the inner tube has poor machinability and wear resistance. Since it is a material, it is extremely difficult to perform the required processing.

In addition, this method generally makes it extremely difficult to fit long tubes.

In addition, in both the second and third methods, the inner tube is expanded plastically, but in this case, the strength (yield point) of the inner tube is very high, and the inner tube has a higher strength than a corrosion-resistant double tube. Since the pipe becomes somewhat thick, an extremely high pressure for expansion is required, which is not practical.

In particular, in the second method, the strength (yield point) of the outer tube
In the case of double-walled pipes, where the strength (yield point) of the inner pipe is higher than that of the inner pipe, even if the inner pipe is expanded plastically, a gap will be created between the inner and outer pipes due to elastic return.

As described above, although there is a potentially strong need for a wear-resistant double pipe, the prior art has not been able to provide a wear-resistant double pipe that satisfies the requirements.

<Object of the Invention> The object of the invention of this application is to solve the problems of double-pipe manufacturing based on the above-mentioned prior art, and to solve the problem of double-pipe manufacturing based on the above-mentioned prior art. By simultaneously applying heating and cooling to the surrounding area, for example, continuously while moving relative to each other in the axial direction, the diameter of the outer tube is reduced and the inner tube is tightened so that the outer tube rattles. Therefore, it is an object of the present invention to provide a method for reducing the diameter of a pipe that can be applied to the production of excellent double-walled pipes that are useful in the fields of piping technology used in various industries.

<Means/effects for solving the problem> In order to solve the above-mentioned problem, the structure of the invention of this application, which is based on the scope of the above-mentioned patent claims, is to solve the above-mentioned problem by relatively loosely inserting the inner tube and the outer tube. When reducing the diameter of the outer tube of the blank tube by using a material with high wear resistance for the inner tube of the blank tube (loose insertion of the outer tube into the tube, the inner tube into the outer tube, or both tubes), Ring-shaped heating is applied to the outer tube, and the annular heating means in the circumferential direction and the base tube are moved relative to each other in the axial direction. By providing cooling means at the front and rear, the thermal expansion of the heating section is restrained by the low-temperature area around the heating section, suppressing the expansion diameter and yielding the heating section, so that the heating section can be cooled and shrunk at an early stage. A technical measure was taken to make the diameter smaller than the diameter.

<Basic Background of the Invention> Generally, the pipe diameter is changed by subjecting the pipe to a heat treatment in which the pipe is heated locally in an annular shape and the surrounding area is cooled.

This phenomenon is due to thermo-elasto-plastic behavior.

In other words, when a local part of the tube is heated, the heated part tends to expand in diameter due to thermal expansion, but at this time, if the area around the heated part is forcibly cooled, the expanded diameter is restrained by the cooled part, and the yield stress is reduced at high temperatures. Coupled with the fact that the temperature is lower, the heated portion easily undergoes plastic deformation, and the amount of expansion becomes significantly smaller than that during free expansion.

Then, during subsequent cooling, the tube undergoes thermal contraction relatively freely, so the tube diameter of the portion that has undergone this thermal history becomes smaller than the initial diameter.

By performing this heat treatment in the circumferential direction of the tube and also continuously in the longitudinal direction, the tube diameter can be uniformly reduced in the length direction, and it is also possible to reduce the tube diameter partially in the longitudinal direction. It is also possible to locally reduce the tube diameter by applying

Figure 5 shows a simulation of the basic phenomenon in which the diameter of a pipe is reduced by the annular thermal reduction method (a method of reducing the diameter of the pipe by applying annular heating and cooling to the pipe described above) using thermoelastic-plastic numerical analysis. This figure shows the learned state, and in this case, the analysis model is a mild steel pipe (outer diameter 165.2
mmφ x wall thickness 5.5 mm), and the analysis conditions were to provide a continuous thermal history in the longitudinal direction of the tube, in which the tube was locally and annularly heated up to 800°C rapidly and then cooled. .

In Figure 5, the amount of plastic strain that occurs in response to a given thermal history (left vertical axis) and the corresponding amount of transient change in pipe diameter (both values at the center of the plate thickness) are shown. is shown on the right vertical axis, and the longitudinal coordinate of the tube is shown on the horizontal axis.

When heated, the expansion diameter is small and a large compressive plastic strain occurs in the circumferential direction, and when cooled, tensile plastic strain occurs, but the amount is smaller than when heated, and therefore, It can be seen that after cooling, the compressive plastic strain of the tube remains and the tube diameter decreases.

The amount of plastic strain generated by changing the shape of the heat source (heating gradient, cooling gradient, maximum heating temperature, etc.) changes, and the amount of change in pipe diameter changes. It can also be seen that the amount of change in pipe diameter can be controlled by providing thermal history.

<Example> Next, an example of the invention of this application will be described below with reference to the drawings.

The illustrated embodiment is a mode of manufacturing a wear-resistant double pipe such as a slurry transport pipe, and the outer pipe 1 is made of a high toughness material such as low carbon steel with a carbon content of about 0.25%, and The inner tube 2 is made of wear-resistant material such as high carbon steel with a carbon content of approximately 0.55%, and the inner tube 2 is hardened by quenching and is inserted loosely and double-sided as shown in Fig. 1. Set the tube as tube 3.

Then, the double tube blank tube 3 is set to move at a predetermined speed in the axial direction as shown by the arrow, and furthermore, as shown in FIG. For example, a high-frequency induction heating device 4 is set, and cooling devices 5, 5 of a ring-shaped shower device, such as tap water, are set in front and back in the axial direction close to the high-frequency induction heating device 4 at a predetermined distance apart. However, by moving the double tube blank tube 3 in the direction of the arrow, the heating device 4 and the cooling devices 5, 5 are moved relative to the double tube blank tube 3.

Therefore, when the double tube blank tube 3 is moved at a predetermined speed in the direction of the arrow, the heating device 4 applies an expansion effect due to heating to the outer tube cooling by the cooling devices 5, 5 before and after the heating device 4, but this process In this case, as schematically shown in Fig. 2, if both ends of the heating part are free ends with respect to the cooling part, the diameter will freely expand and protrude in the radial direction, as shown in Fig. 2. In reality, since both ends of the heating part are restrained by the cooling part, the heating part has a bending moment in the radial direction toward the center with respect to the longitudinal direction, as shown in Fig. 4. The F acts on the material, the temperature increases, and the yield point decreases, resulting in yielding, and as a result, a ring-shaped plastically deformed portion with a curved axial cross section is formed.

Then, as the double tube blank tube 3 moves relatively in the direction of the arrow, the portion heated and plastically deformed by the heating device 4 passes through the heated portion and passes through the cooling device 5,
When the outer tube 1 is cooled by the inner tube 5, the diameter of the outer tube 1 is reduced to a large extent as shown in FIG.

Since this action acts on all circumferential portions of the outer tube 1, by continuously moving the double tube element tube 3 relative to each other in the axial direction, all portions of the outer tube 1 are reduced in diameter. , a binding spring state appears in the full-duplex pipe blank 3, and as a result, a large self-tightening double-pipe is formed.

The above-mentioned tightening process is performed regardless of the wall thickness of the inner tube 2, and since it is formed in the full double tube blank tube 3 regardless of the axial length, it is further This process has almost no relation to the accuracy of the joint surface of the inner tube 2, and is extremely effective for manufacturing wear-resistant double tubes where the inner tube 2 has a large wall thickness and is a long tube. It is.

It should be noted that the embodiments of the invention of this application are of course not limited to the above-mentioned embodiments, and may include manufacturing a corrosion-resistant double-walled pipe in which the inner pipe is made of ceramics, that is, using a corrosion-resistant material for the inner pipe. Various aspects can be adopted, such as the following.

Moreover, it is applicable not only to straight pipes but also to curved pipes such as bent pipes.

Note that the invention of this application differs from the circumferential diameter increasing/reducing means which uses a linear heating means or a cooling means in the moving direction, and the expansion diameter of the heated annular portion is caused by the adjacent cooling portion. restrained,
The diameter of the heating part is reduced by reducing the diameter after cooling, so that, for example, the outer tube is tightened to the inner tube when manufacturing a double tube, and the self-tightening mechanism is completely different. .

Further, the diameter reduction process can be applied not only once but repeatedly.

This process may be performed only once, but by repeating it not only once but twice or more, the amount of diameter reduction can be increased.

Next, an example based on the above-mentioned example will be shown below.

Figure 6 shows the amount of outside diameter change (cumulative) of the outer tube 1 for each ring thermal diameter reduction process and the fitting of the inner and outer tubes 1 and 2 of the double tube base tube 3 in double tube manufacturing by the ring thermal diameter reduction method. This is an example showing the generation status of mating surface pressure (horizontal axis: number of ring heat reduction treatments (RHS); vertical axis: mating surface pressure, amount of diameter reduction). Material: STPG
−38, shape: outer tube 90A/Sch40, inner tube 80A/
Sch40) is shown.

In this case, the clearance (diameter difference) between the inner and outer tubes 1 and 2 is 1.5 mm, and it can be seen that the two are brought into contact after four treatments, and after the fifth treatment, they are fitted.

Here, the initial clearance is sufficient to overlap the two, and in practical terms, for example, 1 to 5 mm.
That's about it.

Further, the amount of diameter reduction per one treatment can be arbitrarily determined depending on the implementation conditions, but in reality, it is, for example, about 0.5% of the diameter of the outer tube.

As can be seen from the data of the experimental example, the amount of diameter reduction of the outer tube 1 increases as the number of treatments increases until both the inner and outer tubes 1 and 2 come into contact, and after they come into contact, a fitting surface pressure is generated. There is.

Furthermore, since the fitting surface pressure increases as the number of treatments increases, it can be seen that the fitting surface pressure can be changed by controlling the number of treatments.

<Effects of the Invention> As described above, the invention of this application basically aims at integrating the inner and outer tubes by fitting the inner and outer tubes together by reducing the diameter of the outer tube when manufacturing a wear-resistant double tube.

For this reason, in the case of manufacturing a wear-resistant double tube by expanding the diameter of the inner tube, the fitting force between the inner and outer tubes decreases after the tube expansion force is removed due to the difference in elastic return, and in some cases, the inner and outer tubes may However, after treatment, the diameter of the inner and outer tubes can be reduced without separating, which makes the inner tube stronger than the outer tube, making it extremely accurate for a self-contained double tube. It has the advantage of being able to obtain a product with a high pressure, and also does not require the enormous pressure required for pipe expansion, resulting in low power costs during production and can be produced at low cost.

Also, unlike conventional shrink fitting methods, the accuracy of the joint surface between the outer tube and inner tube is not required to be as great.
Therefore, an excellent effect is achieved in that long tubes and the like can be manufactured relatively freely.

In addition, even in cases where the inner tube is wear-resistant and the outer tube is highly tough, the diameter can be reduced without any restrictions on design freedom, and therefore the selection of materials for the outer and inner tubes is easy. It has the effect of being free.

[Brief explanation of the drawing]

The drawings are schematic explanatory diagrams of one embodiment of the invention of this application, and FIG. 1 is a partial cross-sectional side view when the outer tube and inner tube are stacked relative to each other, and FIG. 2 is a partial cross-sectional view of the presser bending moment imparting mechanism by heating. Figure 3 is a cross-sectional view of the diameter reduction mechanism through the presser bending moment due to cooling, Figure 4 is a schematic perspective view of applying presser bending moment, and Figure 5 is a simulation of the basic phenomenon of the ring thermal diameter reduction method. FIG. 6 is a graph of an experimental example of ring thermal diameter reduction. 3... tube, 1... outer tube, 4... heating (means),
5... Cooling (means), F... Presser bending moment.

Claims (1)

[Scope of Claims] 1. Annular heating 4 in the circumferential direction and cooling 5 in the surrounding area are simultaneously applied to the tube 1, and the thermal expansion of the heated part is restrained by cooling on both sides to suppress the expansion diameter. A tube 1 characterized in that the heated part contracts upon cooling so that the diameter of that part becomes smaller than the initial diameter.
Diameter reduction method. 2 Annular heating 4 in the circumferential direction and cooling 5 around the circumference are simultaneously applied to the tube 1, the thermal expansion of the heated part is restrained by cooling on both sides to suppress the expansion diameter, and the heated part contracts by cooling. Then, the tube 1 and the heating means 4 are moved relative to each other in the axial direction so that the diameter of the tube 1 after cooling becomes the initial diameter over the entire moving length of the tube. A method for reducing the diameter of a tube 1, characterized by making the tube smaller.