JPH0479728B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of manufacturing an elbow without buckling or uneven thickness of the tube wall and with a high material yield.

Normally, an elbow 1 as shown in Fig. 4 is used for bent parts of piping in various plants, etc.
This elbow is classified into types such as "45° elbow", "90° elbow", etc. based on the central angle [θ]. On the other hand, two types of large and small axial curvature radii [R] are defined for each outer diameter [D] of the elbow, and these are respectively called "long elbow" and "short elbow". In addition, the R/D of the long elbow is approximately 1.11 to 1.76, and the R/D of the short elbow is approximately 1.11 to 1.76.
D is about 0.74 to 1.0.

This invention is a long elbow and a short elbow with a center angle of 45°, and t/D (t is wall thickness).
The present invention relates to a method for manufacturing an elbow suitable for manufacturing thin-walled products with a thickness of 0.05 or less.

<Prior art and its problems> Generally, when manufacturing a 45° elbow, first the 90°
The method of forming an elbow and dividing it into two to obtain two products is said to be advantageous in terms of "yield" and "processing efficiency." Then, the t/D is about
The "mandrel forming method" is the most common method for forming thin-walled 90° elbows of 0.1 or less from straight pipe materials.

FIG. 5 shows an example of the mandrel forming method. In this method, the diameter gradually becomes larger toward the tip, and the radius of curvature of the axis near the tip is approximately the same as the radius of curvature R of the product elbow. A mandrel 2 of equal kissel shape is used. Then, for forming, straight raw tubes 3 cut in advance to a length that allows one 90° elbow to be collected are successively inserted into the mandrel 2 from the small diameter side, and these raw tubes 3 are placed in a feeding device (not shown). This is carried out by pushing the tube forward toward the tip of the mandrel, but the raw tube 3 that advances along the mandrel 2 is heated in a heating furnace 4 to reduce the deformation resistance, and is expanded and bent to fit the shape of the mandrel. As a result, a semi-finished product 5 having almost the same curvature as the elbow is obtained.

Since this mandrel forming method does not constrain the outer surface of the workpiece, it is difficult to secure a circular cut surface that spans the entire length of the semi-finished product 5 using only this method.
Therefore, subsequent "finish molding" is necessary.
Therefore, the cross section of the semi-finished product 5 is usually an ellipse with D _a = 1.05D _b to 1.10D _b as shown in Fig. 5.
It is shaped so that D _b is slightly smaller than the diameter D of the product elbow. And the finishing molding is
As shown in FIG. 6, a pair of upper and lower dies _6a , which form a die hole having the same shape as the outer shape of the product elbow,
_6b is used to press-form the semi-finished product 5 into a perfect circular cross-sectional shape with predetermined dimensions.

FIG. 7a shows the finished molded product 7 obtained through the process described above, and this finished molded product 7 is cut at the positions of broken lines 8 _a , 8 _b , and 8 _c to form a semifinished product with a 45° elbow. _9a and _9b , and then the scale generated during heating is removed and, if necessary, heat treatment is performed to form the 45° elbow 10 shown in FIG. 7b.

This mandrel forming method is a forming method with high production efficiency because it is a processing method in which a large number of straight blank tubes 3 are inserted in series into a long mandrel 2 and extruded one after another as shown in Fig. 5. However, on the other hand, it had the following problems. That is, (a) scratches are likely to occur on the inner surface of the semi-finished product 5 due to sliding with the large diameter portion of the tip of the mandrel 2.

(b) Axial compressive force is applied to the raw pipe 3 due to pipe expansion,
When t/D is extremely small, "wrinkles" 11 as shown in FIG. 8 occur in the raw tube 3 and the preceding material 3' near the heating start point.

In addition, it is necessary to apply a lubricant to the inner surface of the raw pipe 3 to prevent the inner surface scratches mentioned in (a) above, but this requires a considerable amount of man-hours and also requires a large amount of effort to maintain the smoothness of the mandrel surface. I needed to be careful.
Furthermore, when using materials such as stainless steel that are prone to scratches, it is often necessary to perform a polishing process on the inner surface of the elbow, resulting in a reduction in production efficiency, which cannot be ignored.

In addition, the limit t/D that can be formed without producing the "wrinkles" 11 pointed out in (b) above tends to decrease as D increases, and stainless steel is larger than carbon steel (for example, D = 114.3mm, carbon steel is 0.025 for both long elbow and short elbow, stainless steel is 0.035, and D =
For 60.5mm, carbon steel is 0.045 and stainless steel is 0.06). Therefore, the application of the mandrel forming method to small-diameter, thin-walled pipes, particularly stainless steel pipes, has been subject to significant limitations.

However, the "hydraulic bulge forming method" is known as a method for forming thin-walled elbows that cannot be formed using the mandrel forming method from a straight pipe material. FIG. 9 shows the method disclosed in Japanese Patent Application Laid-open No. 19114/1983 as an example.
As shown in Figure a, first, the straight raw pipe 3 is sandwiched between the upper mold 12 and the holding molds 13, 13', and both ends of the raw pipe are held by pistons 14, 14'. Oil is injected from 15 to fill the inside of the tube and apply internal pressure. Note that the reference numeral 16 indicates an air vent hole. Following this operation, the lower mold 17 is raised by a device not shown, and at the same time the pistons 14, 14' start moving forward, and as shown in FIG. 9b, the upper and lower molds come into close contact and the bending process is performed. Complete.

The reason why internal pressure is applied during forming is to prevent bending of the pipe wall and poor roundness due to bending, but even so, the radius of curvature of the elbow is small and the t ₀ /D ₀ (t ₀ is wall thickness, D ₀ is outer diameter)
It is extremely difficult to avoid buckling and poor roundness when the diameter is small. Therefore, when such a problem occurs, finish forming is performed by increasing the internal pressure when the bending is completed to make the outer surface of the work fully fit into the upper and lower molds.

However, if the buckling is large, it cannot be completely corrected even by the above-mentioned finishing forming method. It was necessary to apply a special method of bending while adding. Of course, in this case, it is necessary to employ a complicated tube end sealing mechanism, which increases the molding cost considerably.

Moreover, since all of these hydraulic bulge forming methods attempt to obtain the curvature of the elbow by bending with a mold,
There was also the problem that it was inevitable that the dorsal side (b) was thicker than the dorsal side (c and d in Figure 4). In order to avoid this, it is possible to use a raw pipe with uneven thickness, but in this case, it is difficult to avoid increasing the manufacturing cost of the raw pipe.

Furthermore, since the axial force during forming must be transmitted effectively, the bending shape of the raw pipe is limited to that shown in Figure 9, and therefore the 45° bending shape that can be obtained from one raw pipe is limited. The number of elbows was only four at most as shown in FIG. 10, and the dissatisfaction with manufacturing efficiency and material yield could not be resolved.

<Means for Solving the Problems> The present invention solves the problems found in the conventional elbow manufacturing methods using the mandrel forming method and hydraulic bulge forming method as described above, and eliminates buckling and uneven thickness. This work was completed through research conducted by the present inventors in order to stably manufacture elbows of desired dimensions and shapes without causing any problems, and with sufficiently satisfactory working efficiency and material yield. During manufacturing, a straight blank tube with a smaller diameter than the product elbow is held by a forming die, and axial pressure and internal pressure are applied to the blank tube to form one tube wall in the center {X: see Figure 2 b}. in one direction perpendicular to the tube axis, and the tube walls Y and Z on the opposite sides of the center portion are expanded and raised in the opposite direction to the product elbow outer diameter to form an elbow. The dorsal side and abdomen of the elbow are molded into the shape of the dorsal side, and then similar expansion ridges are applied to the left and right tube ends adjacent to these ridges (if there are many molded elbows, this process is repeated sequentially). The invention is characterized in that the above object is achieved by forming a meandering tube in which the sides are alternately combined in the longitudinal direction and then cutting the tube into rings.

The contents will be explained in more detail below based on FIGS. 1 and 2.

First, an intermediate elbow product obtained by molding a straight blank pipe according to the method of the present invention has a plurality of elbow parts 18 whose dorsal sides and ventral sides are arranged alternately, as shown in FIG. Combined serpentine pipe 19
It is. Here, the outer diameter D and the radius of curvature R of the axial center of the meandering portion are each equal to those of the 45° elbow product.

In addition, in FIG. 1, there is a ring-shaped portion 20 indicated by a broken line between adjacent elbow portions 18, 18.
is the extra cutting length for cutting out and collecting the elbow after completion of molding, and the cutting is carried out at this ring-shaped part 2.
This is done at an intermediate position of 0. After cutting, heat treatment and tube end bevel processing are performed as necessary to produce the product elbow.

Furthermore, small bulges 21 are provided at both ends of the meandering pipe 19, which is an intermediate product of the elbow, and are connected to the ventral side of the elbow portion 18;
(Elbow part 1)
8) is also used to collect a normal elbow. If this bulge 21 does not exist and this part remains in the straight plain tube shape, a normal elbow will be collected from the expansion ridges located at both ends of the meandering tube. It should be easily understood from Figure 1 that it is not possible to extract the The outer diameter D ₀ at both ends of the meandering tube 19 is equal to the outer diameter of the blank tube, and the relationship between the outer diameter D of the meandering portion and D ₀ is expressed as D>D ₀ .

Such a meandering pipe 19 is manufactured from a straight blank pipe through a hydraulic bulge forming process as shown in FIG.

First, a straight raw pipe 3 with an outer diameter D ₀ , a wall thickness t ₀ , and a length l ₀
is set and held in a pair of upper and lower forming dies 22, 22', as shown in FIG. 2a.

The upper and lower molding dies 22, 22' are held in close contact with each other by a pressure device (not shown), and a broken line 23 in the figure indicates a mating surface between the two.
The upper and lower forming dies 22, 22' have a straight part 24 with an inner diameter D ₀ at both ends, an inner diameter D at the center, and an axial curvature radius R (D is the outer diameter of the product elbow, R
The die hole has a meandering part 25 with a radius of curvature of the axis of the product elbow), and the meandering part 25 is formed at one place on the shape forming die side and at two places sandwiching this on the lower forming die side. It is composed of a recess.

What is indicated by the reference numeral 26 is a piston that slides within the straight portion 24 of the die hole.
6 and 26 enter the die hole and come into close contact with both ends of the straight blank tube, respectively.

Following this, the working fluid is injected and filled into the blank tube 3 through the small holes 27 provided in the pistons 26, 26 which also serve as air vent holes. When the internal pressure of the tube 3 is increased by this hydraulic fluid and the pistons 26, 26 are moved forward from both ends, the tube 3 bulges outward as shown in FIG. 2b. The outer surface is brought into close contact with the inner wall of the meandering portion 25 of the die hole, and a primary molded product 28 is obtained.

Here, focusing on the deformation behavior of the raw pipe 3, when the outer diameter of the raw pipe 3 expands from D ₀ to D in the meandering part 25 due to internal pressure, the part inside the meandering part 25 tries to contract in the axial direction. , the friction between the die hole straight portion 24 and the raw pipe impedes this. When the shrinkage deformation is inhibited in this way, the meandering portion 2
The wall thickness of the raw pipe at the portion located within 5 is reduced, and depending on the material, there is a risk of breakage. Therefore, in order to prevent this, the axial pressure from the pistons 26, 26 must help move the material in the axial direction.

When the above primary molding process is completed, the hydraulic fluid in the obtained primary molded product 28 is discharged, and the piston 26,
26 is retracted and the upper and lower forming dies 2
2 and 22' are separated to complete the primary forming operation.

Next, as shown in FIG. 2c, the primary molded product 28 is set and held in new upper and lower molding dies 29, 29', and parts other than the molded part are subjected to hydraulic bulge processing. The molding dies 29 and 29' used at this time have die holes for forming new meandering portions at adjacent portions of the left and right tube ends of the meandering portion of the primary molded product 28, respectively. The method of applying axial pressure and internal pressure by the pistons 26, 26 is the same as in the primary forming operation, and the state after forming is shown in FIG. 2d.

This Fig. 2 shows the case where the meandering pipe 19 is formed by two hydraulic bulging processes, but even if the meandering part continues for a longer time, the meandering part can be gradually widened from the center to the left and right. The molding method is the same,
Stable molding can be performed simply by increasing the number of moldings.

By the way, as shown in FIG. 3, when forming the meandering pipe 19, it is possible to set the straight blank pipe 3 into the upper and lower forming dies 30, 30' from the beginning and form it all at once. is the back side of the elbow of the raw pipe 3, that is, the recesses 31, 31, . . . of the upper molding die 30 and the recess 3 of the lower molding die 30'.
1', 31', . . ., axial tension is generated, resulting in large thickness reduction, which is likely to cause breakage, so this method cannot be said to be a preferable method at all.

On the other hand, in the hydraulic bulging process according to the method of the present invention, thinning of the raw pipe occurs due to pipe expansion, but since the thinning in this case is almost uniform throughout the meandering part, the wall pressure is uniform. The elbow can be formed stably.

As mentioned above, one major feature of the method of the present invention is that the elbow shape is obtained by expanding the pipe using internal pressure, and as shown by arrows m and m' in FIG. The bending caused by conforming to the inner shape of 22, 22' is only applied to the thick cross section. Suwachi: Bending of the entire cross section of the pipe, which causes buckling and uneven thickness, does not work.

Further, the tube expansion ratio D/D ₀ (D ₀ : outer diameter of the raw tube, D: outer diameter of the elbow) in FIG. 12 is geometrically calculated using the following equation (1).

D/D ₀ =1/1-2(1-cosθ)R/D-g/Dsinθ
...(1) Here, θ is the center half angle of the elbow, R is the radius of curvature of the elbow axis, and g is the extra cutting length (ring-shaped part)
20 width.

Therefore, the smaller R/D is, the smaller D/D ₀ becomes. That is, the smaller R/D is, the smaller the amount of deformation in the circumferential direction is.

In the conventional manufacturing method by bending the entire pipe cross section, the amount of deformation applied to the elbow increases as R/D decreases, so it can be seen that the processing method according to the present invention has features not seen in the conventional method.

Next, try calculating the tube expansion ratio D/D ₀ using equation (1) above. First, assuming g/D to be 0.1, θ=22.5° (45°
elbow). In this case, the elbow standard R/
For the minimum value of D 0.74, D/D ₀ = 1.18, R/D
For the maximum value of 1.76, D/D ₀ =1.44.

On the other hand, according to the experiments of the present inventors, for example
For annealed SUS304 stainless steel material, D/D ₀ = 1.8,
And for carbon steel with a carbon content of 0.2% by weight, D/D ₀
It has become clear that it is possible to expand the tube up to = 1.5, so according to the molding method of the present invention, the total [R/
It is clear that molding with a value of D] is possible.

Furthermore, even if the material is poor in ductility and cannot withstand such tube expansion, smooth forming is possible by once interrupting the bulge process, performing intermediate annealing, and then performing the bulge process again.

In addition, in the method of this invention, the wall thickness t ₀ of the raw pipe 3 may be set approximately according to the following formula.

t ₀ =D/D ₀ ·t [However, D: outside diameter of the elbow, D ₀ : diameter of the raw pipe 22, t: wall thickness of the elbow].

Further, it goes without saying that the length l ₀ of the raw pipe needs to be set in consideration of the amount of axial shrinkage due to pipe expansion.

In the above explanation, a 45° elbow has been described, but as is clear from the above equation (1), D/D ₀ increases as the elbow center half angle θ increases. That is,
Machining is more difficult for a 90° elbow than for a 45° elbow, but the method of the present invention can of course be applied to a 90° elbow if the ductility of the raw pipe is extremely good or if intermediate annealing is added. .

Next, the present invention will be explained with reference to examples.

<Example> Outer diameter [D]: 89.1 mm, nominal wall thickness [t]: 4.2 mm,
Seventy 45° long elbows made of SUS S304 stainless steel with an axial center curvature radius [R] of 114.3 mm were fabricated by the method of the present invention incorporating a bulging process as shown in FIG.

In addition, as a straight pipe, the outer diameter [D ₀ ]: 68.2 mm,
Thickness [t ₀ ]: 4.6 mm, length [l ₀ ]: 740 mm 10
A book was prepared, and seven 45° elbows were taken from each piece as shown in Figure 1. This 45° elbow 1
The weight of each raw tube was 763g.

On the other hand, for comparison, in a process including the conventional hot mandrel forming method as shown in Figures 5 to 7, the outer diameter [D ₀ ]: 70.0 mm, the wall thickness [t ₀ ]: 4.5 mm,
Length [l ₀ ]: First, 90° elbows were formed from 35 straight blank tubes of 260 mm, and this was divided into two 45° elbows to produce 70 long elbows. At this time, 1 45° elbow The weight of each raw tube was 945 g.

Therefore, in terms of yield, it has been confirmed that the method of the present invention improves the yield by about 19% compared to the case where the conventional hot mandrel forming method is adopted.

Furthermore, since the method of the present invention completely prevented scratches on the inner surface of the elbow, it was confirmed that the number of man-hours required for the finishing process was reduced to about one-third compared to the comparative method.

<Summary of Effects> As explained above, according to the present invention, straight pipes made of various materials and sizes can be manufactured using high-quality materials without causing buckling or uneven wall thickness, or scratches on the inner surface. Industrially useful effects are brought about, such as making it possible to stably manufacture elbows with low yields.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a meandering pipe obtained by the method according to the present invention, and FIG. 2 is a schematic diagram illustrating the process of manufacturing the meandering pipe by the method according to the present invention. Figures 2a to 2d show each process, Figure 3 is a schematic diagram showing the situation when a meandering pipe is to be formed from a straight blank pipe at once, and Figure 4 is a A schematic diagram illustrating the shape of the product elbow, Figure 5 is a conceptual diagram illustrating the conventional hot mandrel forming method, and Figure 6 is the final forming process of the elbow semi-finished product obtained by the hot mandrel forming method. FIG. 7 is a schematic diagram showing the process of manufacturing a product elbow from the molded product obtained in the finishing molding process shown in FIG. 6, and FIG. 7a shows the finished molded product and Figure 7b shows a 46° elbow as a product, Figure 8 is a schematic diagram explaining how wrinkles occur during hot mandrel forming, and Figure 9 shows conventional hydraulic bulge forming. FIG. 9 is a schematic diagram showing an elbow forming process according to the method;
Figure a shows the start of bending by the hydraulic bulge forming method, and Figure 9 b shows the end of the same bending. Figure 10 is an explanatory diagram showing an example of a 45° elbow taken from a raw pipe. FIG. 11 is an explanatory diagram showing the state of deformation of the raw pipe in the method of the present invention, and FIG. 12 is an explanatory diagram regarding the amount of deformation of the raw pipe in the method of the present invention. In the drawings, 1...elbow, 2...mandrel, 3...straight blank pipe, 3'...preceding material of straight blank pipe,
4... Heating furnace, 5... Semi-finished product, 6a... Upper die, 6b... Lower die, 7... Finished molded product, 1
0...45° elbow, 11...Wrinkle, 12...Upper mold, 13...Press die, 14, 14'...Piston,
15... Oil inlet, 16... Air vent hole, 17...
...Lower mold, 18...Elbow part, 19...Meandering pipe,
20...Ring-shaped part, 21...Bulge, 2
2, 29, 30...Upper forming die, 22', 2
9', 30'...Lower forming die, 23...Matching surface of upper and lower dies, 24...Straight part, 25...
Meandering portion, 26...Piston, 27...Small hole, 28
...Primary molded product, 31...Concavity of upper molding die,
31'...Concavity of lower molding die.

Claims (1)

[Claims] 1 Hold a straight blank tube with a diameter smaller than the product elbow with a forming die, and apply axial pressure and internal pressure to the blank tube to move one tube wall X in the center in one direction perpendicular to the tube axis. In addition, the tube walls Y and Z on the opposite sides of the central part are expanded and raised in the opposite direction to the outside diameter of the product elbow to form the shape of the back side of the elbow, and then these raised A similar expansion ridge process was performed on the left and right tube ends adjacent to the section to form a meandering tube in which the dorsal and ventral sides of the elbow were alternately combined in the longitudinal direction, and then this was cut into rings. Features: Elbow manufacturing method.