JP2002254127A - Method for manufacturing reducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a method for forming a reducer by die-forming capable of reducing die costs, improving a material yield, and curtailing manufacturing man-hours. SOLUTION: In the method for manufacturing the reducer characterized by the feature that a die 2 is inserted from the end surface of tube stock 1 having uniform internal and external diameters composed of carbon steel or alloy steel or a portion to be formed into a reducer large diameter tube portion of the tube stock 1 preliminarily formed to the configuration of the reducer, and the die is pressed and formed into a desired reducer configuration, when a reducer having 1.4 or more of the D/d rate between the internal dia.(D) of the reducer large dia. tube portion and the internal dia.(d) of the reducer small dia. tube portion is formed, the portion to be formed into the reducer large dia. tube portion of the tube stock is partially heated up to 55 deg.C or more to be formed by the above method in the light of preventing cracks and buckling generated on the small dia. tube portion at the time of forming. Accordingly, a desired configuration of reducer can efficiently be formed directly from the tube stock using only inner die by improving the forming method via die forging using the traditional outer and inner dies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a large-diameter pipe portion which is provided as a casing of a ball valve, a pipe joint of a pipeline, or a pipe joint having a different diameter at a portion having a variable diameter such as a pressure vessel. The present invention relates to a method for manufacturing a reducer including a small-diameter tube.

[0002]

2. Description of the Related Art Reducers are frequently used as joints between pipes having different diameters at different diameter branches such as pressure vessels and pipelines. In some ball valves, a half of the casing is called a reducer, and the casing of one ball valve is formed by welding or flange-connecting the large-diameter pipe portions of these two reducers to face each other.

Conventionally, in manufacturing these reducers having various dimensions and shapes, various manufacturing methods have been proposed in consideration of quality, productivity, or cost. Examples of the main production method include, in the case of a thin wall, a forming process using a spatula from a disk, a spinning process from a pipe, and a press process (die forging) using inner and outer (upper and lower) dies. In addition, when the above-described processing method is not appropriate, a manufacturing method has been adopted in which a material is formed by hot free forging, rolling mill rolling, casting, or the like, and final forming is performed by machining.

However, each of the above-mentioned conventional manufacturing methods has advantages and disadvantages. In other words, reducers formed by plastic working have less variation in strength compared to cast products, and stable quality can be obtained. There is a limit to the thickness that can be made, and it cannot be applied to thick ones.
Further, the molding method using the inner and outer molds has a disadvantage that the mold cost is increased. The forming method by hot free forging has a high adaptability to the size, but has a problem that the forming accuracy is not good, so that the material yield is low and the machining cost is high. The casting method is inexpensive to manufacture and relatively easy to manufacture, but has the disadvantage that the quality is more variable than forged products.

[0005] A number of improved patents have been filed to solve the above manufacturing problems. The main ones are described in JP-A-49-95865, which discloses a mold having a large-diameter tube side and a small-diameter tube side corresponding to a large-diameter tube portion and a small-diameter tube portion of a reducer to be molded. A method for forging and molding a reducer in which a reducer having a large ratio between the large-diameter tube side and the small-diameter tube side can be molded in one step by inserting a material tube into the tube and simultaneously squeezing the other while expanding one of the material tubes. Is disclosed. (See Fig. 4)

Japanese Patent Application Laid-Open No. Sho 62-100109 discloses that a reducer is formed by applying a forming roll to the inside and outside of a reducer material and moving the reducer material relative to the forming roll while rotating the reducer material relative to each other. By doing so, a continuous and smooth reducer is obtained,
A reducer molding method capable of reducing the number of manufacturing steps is disclosed.

Japanese Patent Application Laid-Open No. 53-79761 discloses that a reducer material is cast in advance by centrifugal casting, and this reducer material is formed into a desired reducer shape by die forging using an outer die and an inner die (core metal). By doing so, there is disclosed a manufacturing method in which the number of internal defects is small, the variation in product quality is small, and the material yield is improved.

[0008] Japanese Patent Application Laid-Open No. 9-1657 discloses that
The end of the raw tube formed into the small-diameter tube of the reducer is heated to near the melting temperature at which the diameter can be reduced, and then the heated end is forcibly inserted into the reduced-diameter portion of the mold to reduce the diameter, A method for forming a resin reducer for forming a small-diameter tube is disclosed.

[0009]

SUMMARY OF THE INVENTION The present invention mainly deals with a reducer for a ball valve, which is an object of the conventional forming method in the die forming (forging), that is, the die cost is reduced and the material yield is improved. It is another object of the present invention to establish a method of molding a reducer by molding that can further reduce the number of manufacturing steps.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and a first manufacturing method of the present invention is to provide a raw material pipe made of carbon steel or alloy steel and having a uniform inner and outer diameter. Alternatively, a die is inserted from an end face of a portion formed into a reducer large-diameter tube portion of a raw tube preformed in a reducer shape, and pressure-molded into a desired reducer shape. The second production method of the present invention heats a portion formed into a reducer large-diameter tube portion of a raw tube made of carbon steel or alloy steel and having a uniform inner and outer diameter or a raw tube preformed in a reducer shape, It is characterized in that a mold is inserted from the end face of the heating portion and pressure is formed into a desired reducer shape. A third manufacturing method of the present invention is characterized in that, in the second manufacturing method, the heating temperature of the raw tube is limited to 550 ° C. or higher. And the fourth manufacturing method of the present invention comprises:
In the size and shape of the reducer manufactured by the second or third manufacturing method, the inner diameter of the reducer large-diameter tube is limited to at least 1.4 times the inner diameter of the reducer small-diameter tube.

(Function) First, the material of the raw tube used in the present invention is limited to carbon steel or alloy steel such as low alloy steel, medium alloy steel, high alloy steel, etc. This is because it is considered difficult to apply the present invention as it is to non-ferrous metals and non-metals, since plastic working characteristics such as hot deformation resistance of non-metal such as plastic are different from those of carbon steel or alloy steel.

In the present invention, a commercially available seamless pipe or plate-wound welded pipe is generally used as the raw pipe, and it is desirable to form the pipe by one pressing. However, a reducer having a remarkably large step-down, that is, a large-diameter pipe section is required. In the case of a reducer in which the ratio of the inner diameter of the small-diameter pipe portion is extremely large, cracks may occur if molded at once, or buckling may occur in the small-diameter pipe portion when performing soaking. May be applied. In any case, according to the method of the present invention, a seamless pipe or a welded pipe can be used, and the finish cutting after forming is small, so that the material yield can be improved.

Further, according to the present invention, it is possible to perform hot or cold molding using only the inner mold without the need for the outer mold, so that the die cost can be reduced. FIG. 1 shows a molding method according to the present invention. By molding by pressing an inner die into a base tube, the wall thickness of the large-diameter tube side is reduced and the overall length is also reduced. The degree of the reduction depends on the ratio D / d of the inner diameter (D) of the large-diameter pipe and the inner diameter (d) of the small-diameter pipe of the reducer and the magnitude of the friction between the mold and the material. Therefore, the wall thickness and length of the tube must be determined in anticipation of this reduction.

When the method of the present invention is carried out with the temperature of the raw tube uniform, there is a limit to the shape that can be formed. That is, when the inner diameter (d) of the small diameter pipe of the reducer is to be expanded to the inner diameter (D) of the large diameter pipe, particularly when the temperature exceeds the limit of the uniform elongation characteristic of the material, the local wall thickness is significantly reduced or reduced. Causes cracks. However, even if the elongation characteristics of the material are improved by uniform heating, when the uniform heat processing is performed on a reducer having a shape in which D / d exceeds a critical value, buckling occurs in the small diameter pipe portion during the processing. The critical D / d is 1.2
~ 1.4. Therefore, when molding a reducer having a shape exceeding this critical ratio, the present invention heats a portion of the reducer that is formed into a large-diameter tube,
The part formed in the small-diameter tube part of the reducer is kept at a low temperature by suppressing the temperature rise, and is heated at the boundary by using the temperature gradient generated by itself to correspond to the transition of the shape. A reducer having a smooth shape can be continuously obtained from the diameter tube portion toward the small diameter tube portion.

The heating temperature of the raw tube is limited in claim 3. The reason for the limitation is that the mechanical properties of the steel at a high temperature shown in FIG. 5 include hot workability (hot deformation resistance). Focusing on the closely related values of tensile strength, hardness and elongation, the tensile strength and hardness tend to decrease gradually at 300 ° C. or higher, and the elongation increases conversely to 50% at around 550 ° C. The heating temperature of the raw tube was limited to 550 ° C. or higher because the temperature reached the temperature and the temperature increased significantly on the high temperature side.

The reason for limiting D / d to 1.4 or more in claim 4 is that, as described above, buckling occurs in the small-diameter pipe portion when the present invention is carried out by cold or uniform heating. Since the critical ratio of D / d is 1.2 to 1.4,
When molding a reducer having a D / d of 1.4 or more,
From the viewpoints of crack prevention and buckling prevention, a molding method using partial heating must be adopted, and due to the design structure of the ball valve, there is a D between the D and d of the casing (reducer) incorporated therein. ≧ {2d} 1.4d is limited on the basis that the relationship must be maintained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG. First, JIS. A tube made by bending and welding a steel plate of SM490 (inner diameter 375 mm, outer diameter 42
5 mm, length 780 mm), and about half of the length (the part to be formed into a large-diameter tube of the reducer) is about 1
The mixture was heated to 000 ° C. and the other half was placed outside the furnace to avoid heating. After heating, as shown in FIG.
Inserting the inner mold 2 from the end face of a, from the state of (a) to (b)
And press-formed with a 1000 ton press. After pressure molding, measure the dimensions at each position shown in FIG.
From the comparison between the measurement results and the completed shape of the reducer shown in FIG. 3, the cutting allowance shown in Table 1 was obtained. Shaving allowance is up to 8m
With m, there was little shaving allowance and a reducer with good machining accuracy was obtained.

[0018]

[Table 1]

In this embodiment, the inner mold 2 is placed on the press plate 3, and the raw tube 1 is placed on the inner die 2 with the heating portion 1a facing down. Inner die 2 from mounting end face
Is inserted, and the pressure forming is performed. The raw tube 1 is placed on the press plate 3 with the heating portion 1a facing upward, and the inner mold 2 is placed on the raw tube 1 and inserted. Another embodiment in which the pressure molding is performed is also possible.

[0020]

As described above, according to the present invention,
By improving the conventional molding method by die forging using an outer mold and an inner mold, it is possible to accurately mold a reducer of a desired shape directly from a pipe (base tube) using only the inner mold, so that mold costs can be reduced. In addition, the material yield can be improved, and the number of manufacturing steps can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a reducer molding method of the present invention.

FIG. 2 is a view showing a dimension measurement position after molding in an example of the present invention.

FIG. 3 is a diagram showing a completed shape of a reducer in the embodiment.

FIG. 4 is a view showing a conventional method of forming a reducer by die forging.

FIG. 5 is a view showing mechanical properties of steel at a high temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw pipe 1a Heated part of raw pipe 1b Temperature transition part of raw pipe 1c Non-heated part of raw pipe 2 Inner die 3 Press plate 4 Upper anvil 5 Outer die

Claims (4)

[Claims] 1. A mold is inserted from an end face of a part formed into a reducer large-diameter tube part of a raw pipe made of carbon steel or alloy steel and having a uniform inner and outer diameter or a preformed reducer raw pipe. For producing a reducer having a reduced shape. 2. Heating a portion formed into a tube having a uniform inner and outer diameter of carbon steel or alloy steel or a reducer large-diameter tube portion of a preformed reducer tube, and an end face of the heated portion. Characterized in that a mold is inserted from the mold and pressure is formed into a desired reducer shape. 3. The method for manufacturing a reducer according to claim 2, wherein the heating temperature of the raw tube is 550 ° C. or higher. 4. The method of manufacturing a reducer according to claim 2, wherein the reducer is formed into a reducer shape in which the inner diameter of the large-diameter reducer is at least 1.4 times the inner diameter of the small-diameter reducer.