JPH0243323A - Electrical heat treatment of bend part of u-bend pipe - Google Patents

Abstract

PURPOSE:To improve the follow-up accuracy of right and left energizing clamps and to obviate the generation of a residual stress after a heat treatment by moving the spacing between the energizing clamps according to the fluctuation in pitch arising from the expansion and shrinkage at the time of the heat treatment. CONSTITUTION:Both parallel pipe parts 1-2 of a U-bend pipe 1 are fixed and directly energized by the opening/closing type energizing clamps 20-1, 20-2. The spacing of the energizing clamps 20-1, 20-2 is forcibly widened according to the change in the pitch when the bend part 1-1 is heated and is thereby expanded or deformed. The bend part is then heated to the prescribed heat treatment temp. The bend part 1-1 begins to shrink when the bend part 1-1 is forcibly cooled. The spacing between the energizing clamps 20-1, 20-2 is conversely forcibly narrowed at this time. The change in the pitch of the bend part 1-1 is allowed with good accuracy in this way, by which the shape defects by the heat treatment are completely eliminated.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method of heat-treating a bend part (curved pipe part) of a beam-bend pipe by allowing the pitch of the bend part to change so as not to cause deformation when the bend part (curved pipe part) is subjected to heat treatment such as annealing by direct current application after forming.

[Conventional technology]

Generally, when a steel pipe used for a heat exchanger or the like is bent into a U shape, it is subjected to heat treatment such as annealing to remove residual stress at the bend. Fig. 4 is an explanatory diagram showing a conventional general heat treatment method for a bend section. In other words, the heating during the heat treatment of the bend' part (1-1) of the U-bend pipe (1) after forming shown in Figure (A) is the same as that of the U-bend pipe (1) as shown in Figure (B). Both of the parallel tube parts (1-2) are fixed with fixing clamps (energizing chucks) (2) and heated by direct energization.If the bend part (1-1) is heated in this way, the heat The curvature of the bend part (1-1) changes as it heats up due to expansion, causing deformation in the vicinity of the fixed clamp (2) (Figure B). 2) is cooled while being fixed with the fixing clamp (2),
This deformation is restrained, and residual stress is generated again in the bend portion (1-1). Due to this residual stress, the fixed clamp (2) may be released after cooling, or the distance P between the parallel tube sections (1-2) of the bent tube (1), that is, the pitch may be reduced, and the parallel tube sections (1-2) may be reduced.
2) are no longer parallel (Figure C). As a method for preventing deformation of the bent pipe due to such residual stress, a method has been proposed in which one of the current-carrying chucks is made movable to allow the pitch change of the bend portion due to heating and cooling (Japanese Patent Laid-Open No. 54116306). Public bulletin). As shown in Fig. 5, this method involves fixing the parallel pipe section (1-2) near the bend section (1-1) with a current-carrying clamp (2-1).
It is supported by a movable energizing clamp (2-2) and directly energized and heated, and the bend part (i-
This is a method in which a pitch change of i> is allowed by the movement of the movable energizing clamp (2-2). That is, in this method, the movable current-carrying clamp (2-2) freely moves outward as the bend portion (1-1) expands while the temperature is raised to a predetermined heat treatment temperature, and the parallel tube portion (1-2) )
The distance P between the bends (i-i) increases during cooling.
With the contraction of the movable current-carrying clamp (2-2), the movable current-carrying clamp (2-2) freely moves inward, and the distance P between the parallel tube parts (1-2) decreases and returns to the original pitch. However, in this method, the energizing cable (movable line) (5) between the movable energizing clamp (2-2) and the electrode (4) fixed on the support base (3), and the parallel tube part (1-2 ) The contact portion between the parallel tube portion (1-2) and a flat roller (not shown) having a rotation axis perpendicular to the axial direction of the movable current-carrying clamp (2-2) prevents free movement of the movable current-carrying clamp (2-2). There was a problem in that it did not accurately follow pitch fluctuations. This problem was particularly noticeable in thin-walled and small-diameter materials. (Problems to be Solved by the Invention) This invention is intended to solve the above-mentioned conventional problem, that is, the tracking accuracy problem of the method in which one of the energizing clamps is made movable to follow pitch fluctuations when the temperature rises or falls. By forcibly moving the left and right current-carrying clamps according to the amount of pitch variation, the tracking accuracy of the current-carrying clamps can be improved, and the generation of residual stress after heat treatment can be completely eliminated. This is an attempt to propose a method.

[Means to solve the problem]

This invention has a structure in which the clamp interval can be freely opened and closed when the tube is clamped, and the current-carrying clamp is opened and closed according to the amount of pitch variation during heating and cooling. Both parallel tube parts of the U-bend pipe are clamped using a current-carrying clamp device equipped with a pair of opening/closing current-carrying clamps, and the linear expansion coefficient of the U-bend pipe material is adjusted to The present invention provides a method for energizing heat treatment of a bend portion, which widens the pitch according to the amount of pitch variation determined by the heat treatment temperature, and allows pitch changes in the bend portion due to heating and cooling.

[For production]

Figure 1 is an explanatory diagram showing the heat treatment method for glue-bent pipes of the present invention. C) shows the state during heating of the bend part, FIG. When performing heat treatment on the bend portion (1-1) of the tube (1), an opening/closing method is used to move both parallel tube portions (1-2) of the U-bend tube (1) left and right as shown in Figure (B). Energizing clamp (20-1) (20
-2) and directly energize. The bend part (1-1) is heated by direct energization, and while the temperature rises to a predetermined heat treatment temperature, the bend part (1-1) expands and tries to deform. The opening/closing energizing clamps (20-1) (20-2
> Increase the distance between. At this time, the open/close type energizing clamp (20-1) (20-2
) is determined by the following formula based on the linear expansion coefficient of the U-bend pipe (1) and the heat treatment temperature. ΔP=PXαxt (1
)ΔP: Pitch variation amount P: Pitch before heat treatment α: Coefficient of thermal expansion t: Heat treatment temperature Here, the heat treatment temperature is determined by the heat treatment temperature required for the U-bend pipe (1) or the temperature sensor at the bend portion ( i
−i> is determined by measuring the temperature. In this invention, the left and right opening/closing energizing clamps (20-1) (20-2)
) is forcibly expanded and heated to the prescribed heat treatment temperature (Figure C
). The broken line in the figure shows the state before heating. After that, when the temperature is raised to a predetermined heat treatment temperature, the bend portion (1
-1) Forced cooling. With this cooling, the bend part (1-
1) begins to contract, and at this time, the interval between the open/close type energizing clamps (20-1) and (20-2) is forcibly narrowed (Figure D). At this time, open/close type energizing clamp (20-1)
The amount of movement (20-2) is also controlled according to the pitch variation amount ΔP determined by the equation (1). The broken line in the figure indicates the state during heating. Figure 2 shows an example of the interval pattern of the open/close type energizing clamps (20-1) (20-2) with respect to the temperature change of the bend part (1-1), and the pattern of the clamp interval is not particularly limited. However, either ■ or ■ can be adopted. ■ is an energizing clamp (20-1) (20-1) that opens and closes by the pitch variation △P before heating the bend part.
0-2) is a pattern in which the spacing is widened, a constant spacing is maintained during heating and cooling, and then returned to the original spacing after heating and cooling, while ■ is a pattern that opens and closes as the temperature rises at the bend. The interval between the energizing clamps (20-1) (20-2) is gradually opened, and when the predetermined heat treatment temperature is reached, the interval is maintained, and during the cooling process, the opening/closing type energizing clamps (20-1) (2
This is a pattern in which the interval between 0 and 2> is gradually narrowed. Among these, open/close type energizing clamp (20-1) (20
-2> is preferably controlled according to the heat treatment temperature. As a current-carrying clamp device for carrying out this invention, as shown in FIG.
11> A pair of left and right lower clamp molds (12) installed above, and a pair of left and right upper clamp molds (14) arranged on an upper pedestal (13) to face the lower clamp molds (12). Equipped with current-carrying clamps, left and right lower clamp types (1
2) is fixed on a movable base (16) that is slidably attached to the same frame (11), and this movable base (16) is screwed to a rotating screw shaft (17) with left and right reverse threads, and the rotating screw The left and right movable bases (16) can be moved toward and away from each other by rotating the shaft (17). The upper clamp mold (14), which is disposed opposite to the lower clamp mold (12), is attached to a movable base (21) slidably attached to the upper frame (13) so that it can be raised and lowered by a vertical cylinder (22). The stand (21) is screwed onto a rotating screw shaft (24) with left and right reverse threads, and the left and right movable stands (21) can be moved toward and away from each other by rotation of the rotating screw shaft (24). The rotation mechanism of each rotary screw shaft (17) (24) of the lower clamp type (12) and the upper clamp type (14) is a rotation transmission shaft (27) driven by a pulse motor (25) via a carrier (26), for example. ) and each rotating screw shaft (17) (24) via a gear (28) can be used. The opening/closing control of the clamp is performed by the sequencer (3) according to the heat treatment temperature of the bend portion measured by the temperature sensor (30).
1), the amount of movement of the clamp is determined, and the rotation of the pulse motor (25) is controlled based on this value. The rotational speed of the servo motor is inputted to a sequencer (31) via a pulse generator (32). By the way, when the heat treatment of the bend part is completed, the upper clamp mold (14) is raised by the vertical cylinder (22) to open and close the clamp of the U-bend pipe, and then the clamp is placed opposite the bend part of the LJ bend pipe. cooling header (not shown)
It cools down by injecting more refrigerant.

【Example】

Example 1 U-bend pipe (material: JIS-3
O8304) was heat treated by the method of the present invention. In the heat treatment, the bend portion was heated to 1080°C, then forced air cooled to 200°C, and left to cool after opening the clamp. The results are shown in Table 1. The calculated △P at this time is 36
It was 4 mm x 17 x 10-6 = 6.7 mm. In Table 1, test No. 7 is based on a method in which the energizing clamp on one side follows the pitch variation. As is clear from Table 1, in the example of the present invention in which the opening and closing of the clamp is controlled to a value that is close to the calculated △P, the pitch is the same as the heat treatment pitch even after cooling, and the method of the present invention reduces the expansion and contraction of the bend part. It can be seen that the accompanying pitch change can be sufficiently tolerated. Margin Example 2: Outer diameter 15.9w+m, wall thickness 0.8mm, pitch 368m
m thin wall small diameter U bend pipe (material JIS-3US 30
Table 2 shows the results of heat treating 4) under the same conditions as in Example 1. In this example, △P on the scale is 368mm x 17xl
O-s = 6.7 mm. As is clear from Table 2, even in the case of thin-walled, small-diameter glue-bent pipes, the pitch after cooling is the same as the pitch before heat treatment.
It can be seen that the method of the present invention can sufficiently tolerate changes in the bend portion due to heating and cooling. Margin below

【Effect of the invention】

As explained above, the method of this invention controls the gap by forcibly moving the left and right energizing clamps according to the change in pitch caused by expansion and contraction during heat treatment, so that the change in pitch at the bend can be sufficiently controlled. It can be tolerated with high accuracy, and shape defects due to heat treatment can be completely eliminated. Therefore, according to the method of the present invention, there is no need to perform residual stress removal treatment or pitch correction again after heat treatment, and it is highly effective in improving productivity and reducing costs of U-bend pipes.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the heat treatment method for glue-bent pipes of the present invention. Fig. (A) shows the glue-bend pipe before heating, Fig. C> shows the state during heating of the bend part, figure (D> shows the state after cooling the bend part, and figure ( ) shows the bent pipe after heating and cooling. Figure 2 shows the temperature change of the bend part made in the same heat treatment method. FIG. 3 is a diagram showing an example of a clamp spacing control pattern, where FIG. 3A shows a heating/cooling pattern and FIG. 3B shows a clamp spacing pattern. FIG. Fig. 4 is a schematic diagram showing an example. Fig. 4 is an explanatory diagram showing a conventional general heat treatment method for a glu-bend part, in which Fig. (A) shows the state of the glu-bend pipe before heating, and Fig. (B) shows the state during heating of the bend part. , and (C) respectively show the U-bend pipe after heating. Fig. 5 is a schematic perspective view showing an energization heating device in which one of the energization clamps is movable.

Claims (1)

[Claims] In the method of heat-treating the bent portion of the U-bend pipe by energization directly after forming, both parallel pipe portions of the U-bend pipe are clamped and heated using a current-carrying clamp device equipped with a pair of open/close type energizing clamps that can be separated from each other. Before or during heating, the interval between the opening and closing type energizing clamps is widened in accordance with the amount of pitch variation determined by the linear expansion coefficient of the U-bend pipe material and the heat treatment temperature, so as to allow pitch changes in the bend portion due to heating and cooling. A method for energizing heat treatment of a bend portion of a U-bend pipe.