JPH02241602A - Production of pipe with two fins on outside surface - Google Patents

Abstract

PURPOSE:To economically produce the high-quality pipe with two fins by inserting an inside surface regulating tool into a circular shock pipe of the bore smaller than the diameter of a roll caliber, inserting the stock pipe into the caliber and bulging a part of the pipe wall into the gap between the roll flanges. CONSTITUTION:Two pieces of caliber rolls 10a, 10b are disposed to face each other by aligning the caliber center to a pass line so as to form a gap G between the flanges 11a and 11b thereof. The stock pipe which is circular in section and has the bore smaller than the diameter d0 of the caliber is inserted therein with the inside surface regulating tool 30 and is then inserted into the caliber to decrease the thickness thereof. A part of the pipe 21 decreased in the thickness is bulged into the gap G between the flanges 11a and 11b of the rolls 10a and 10b. The fins extending in the axial direction are formed in the two positions symmetrical in the circumferential direction. The large fin height is assured in this way by one pass and the formation of overlaps and inside surface piping defects is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a tube with two fins on the outer circumferential surface, in which a tube having two fins parallel to the tube axis is manufactured by roll processing.

[Conventional technology]

This type of externally finned tube used as a heat transfer tube in a heat exchanger is often manufactured by extrusion or drawing using a ring die.However, these methods have low efficiency. The method of drawing using , reducing manufacturing efficiency.

In this case, processing using rolls can be considered.

As a method for manufacturing a tube with external fins using rolls, a method disclosed in Japanese Patent Application Laid-Open No. 142715/1984 is known. In this method, as shown in FIG. 5, three or more rolls 3', 3', etc. are provided around the pass line of the pipe to be processed with a predetermined gap, and the pipe is covered with these rolls. Reduction processing of the processed pipe 1 is performed. The fins 5 are formed in the gaps between adjacent rolls due to the roll reduction.

[Problems to be Solved by the Invention] However, in this method, there is virtually no change in the wall thickness of the tube to be processed 1 before and after processing, and the fins 5 are pinched toward the outer surface of the tube as shown in the figure. Even if a grooved roll is used, folds 6' will occur in the fin 5, and as a result, a large inner sink 6 will inevitably occur on the inner surface of the tube of the fin 5. If folds 6' or large internal sinks 6 occur on the inner surface of the tube, when used as a heat transfer tube by passing water inside,
Water scale may accumulate in this area, inhibiting heat transfer and causing corrosion. Also, in this method, role 3
Since the corresponding part of the shoulder 3'' and the top of the fin 5 are subjected to bending, the wall becomes locally thin, resulting in a decrease in strength.More importantly, with this method, the inner surface near the fin of a tube with two outer fins is crushed. cannot be manufactured because of the

The present invention provides a method for manufacturing a tube with two outer fins that can be manufactured efficiently by roll processing without causing problems such as excessive bending or shrinkage on the inner surface. The purpose is to provide.

[Means for solving the problem] If the causes of folding and large internal sinks in the conventional method are as described above, rolling a blank pipe with a circular cross section using a combination of grooved rolls and an internal regulating tool, and rolling It is believed that folding and large internal sinks can be prevented by allowing a portion of the pipe wall, which is reduced by the process, to bulge out into the gap between the flange surfaces of the grooved roll.

However, according to the research conducted by the present inventors, when two grooved rolls are used, sufficient centripetal force is not applied to the base of the fin forming part of the tube during processing, resulting in large internal sinks. Admitted. For this reason, the present inventors have proceeded with the practical application of fin tube manufacturing in the direction of increasing the number of grooved rolls,
For example, Japanese Patent Application No. 6:3-186487 proposes a method for manufacturing a finned tube of 40 mm and two outer surfaces.

According to this method, a centripetal force is applied to the base of the fin of the tube being processed, so that internal sinking is prevented. However, the fin height that can be formed by one rolling is low, and in order to manufacture a tube with a large fin height, it is necessary to increase the number of rolling steps or add drawing with a ring die after rolling, which increases the number of steps. There was a problem with the increase in

On the other hand, in the process of repeating this type of rolling experiment, the present inventors have confirmed that 20-ru is substantially more advantageous than 40-ru in securing the fin height. In the process of further experiments, we discovered that even with 20-millimeters, depending on the rolling conditions, problematic folds and excessive internal sinkage may occur.
I found out that there is no such thing. The condition for suppressing internal sinking at 20 mm is that the inner diameter of the raw pipe is smaller than the diameter of the groove formed between the two groove rolls. By rolling the raw tube under these conditions, a tube with two external fins having a large fin height can be efficiently manufactured in one bath without folding or excessive internal sinkage.

The present invention has been made based on the above findings, and consists of two grooved rolls that are arranged facing each other with their grooved centers aligned with the pass line so that a gap is formed between their flange surfaces.
, a blank pipe with a circular cross section having an inner diameter smaller than the diameter of the hole mold is inserted into the hole mold with an inner surface regulating tool inserted therein to reduce its wall thickness, and a part of the reduced pipe wall is removed from the hole. Symmetry in the opening direction 2 by bulging into the gap between roll flanges
The gist of the present invention is a method for manufacturing a tube with two fins on the outer surface, which is characterized by forming fins extending in the axial direction in the lateral position.

FIG. 1 is a schematic diagram showing a typical example of the rolling state of a tube in the manufacturing method of the present invention.

Two grooved rolls 1 facing each other with a pass line in between
0a and 10b are flange surfaces 1 parallel to the rotation center on both sides.
1a and 1lb, with perfectly circular cavalry portions 12a and 12b between them.

The centers of rotation of the grooved rolls 10a, 10b are parallel to each other on a plane perpendicular to the pass line, and are located at equal distances from the pass line. Therefore, the hole type 11-
The hole shape formed between the cavalry portions 12a and 42b of the grooves 10a and 10b is a right circle, and its center coincides with the pass line. Furthermore, a gap G is provided between the flange surfaces 11a and 11b of the grooved rolls 10a and 10t for bulging out the fins.

The blank pipe 20 having a circular cross section shown in FIG.
When the raw pipe 20 is rolled between the cavities 12a and 12b of 0a and 10h and the inner surface regulating tool 30, the wall thickness r$T of the raw pipe 20 is reduced, and a part of the reduced pipe thickness is applied to the flanges on both sides. It bulges out between surfaces 11a and llb. As a result, in the rolled tube, fin portions 22 that are continuous in the tube axis direction are symmetrically formed at two positions in the circumferential direction of the main tube portion 21. If the diameter d of the inner diameter of the blank pipe 20 is made smaller than the diameter d of the groove between the groove rolls 10a and 10b, folding and inner sinking occurring on the inner surface of the fin portion 22 can be significantly suppressed. Ru. Also, if rolled at 20-mill, it will be 4.
The height of the fin portion 22, that is, the fin height h, is greater than when rolling with a 0-roll.

In FIGS. 1 and 2, the outer diameter of the raw pipe 20 is represented by D6, the diameter of the inner surface regulating tool 30 is represented by dL, and the wall thickness of the pipe after rolling is represented by t. The diameter d0 of the hole is not an initial setting value (it is a dimension under the reaction force during rolling, and this dimension almost corresponds to the outer diameter of the main pipe portion 21 of the pipe after rolling.Similarly) In addition, the diameter di of the inner surface regulating tool 30 approximately matches the inner diameter of the tube after rolling.

The grooved rolls 10a, 10b may be arranged in one stage or in multiple stages in one bus. The number of passes is basically one pass, but if the material is difficult to process or the fin height is to be increased, multiple passes may be performed, and it is also possible to add drawing using a ring die after rolling. be.

The grooved rolls xoa, iob may also be driven or non-driven. In the case of non-drive, it is necessary to apply pipe feeding force from the outside like drawing.

[For production]

According to the manufacturing method of the present invention, as described above, the height h of the fin portion 22 is larger than that in the case of 40-L because of the 20-L. The reason is as follows.

20-R, the roll shoulder 14a indicated by the arrow in FIG.
The line of load action at 14b acts in the tangential direction of the outer peripheral surface of the tube. As a result, it is difficult to apply a sufficient centripetal force to the base of the fin 22, and the inner surface of the fin 22 tends to fold or sink. Since the line faces the inner surface, it is advantageous in terms of bending and inner surface sinkage.The fin portion 22 is produced by the metal flow in the circumferential direction as the raw tube 20 is rolled. In the case of 20-L, the direction of the load action line is along the direction of metal flow, so
Formation of the fins 22 is promoted. On the other hand, in the case of 40 mm, the line of load action faces the inner surface, and the load that suppresses the inner surface sink becomes a hindrance in terms of inducing metal flow.

Next, rolling conditions in the manufacturing method of the present invention will be described in detail.

In the manufacturing method of the present invention, in order to apply thinning processing to the raw pipe 20, the wall thickness T of the raw pipe 20, the diameter d0 of the hole, and the diameter d of the inner surface regulating tool 30 are set under the following equation (1). Needless to say, it is necessary to satisfy the following.

Figure 3 shows the thinning rate ΔT and the fin height h expressed by the following equation (2).
The inner diameter reduction rate ΔD is expressed by the following equation (3).

FIG.

According to the same figure, for any inner diameter reduction ratio ΔD1,
It can be seen that as the thickness reduction rate T increases, the fin height h increases. Furthermore, at the same thickness reduction rate ΔT, the larger the inner diameter reduction rate, the greater the fin height h.

Therefore, in order to manufacture a tube with two outer fins with a large fin height h using the manufacturing method of the present invention, it is desirable that both the wall thinning rate ΔT and the inner diameter reduction rate ΔDi be large, and 8T≧15%.
, ΔD, ≧5 is a preferable range.

Further, FIG. 3 shows the fin height in the case of the 40-L method (ΔD=8%) proposed earlier by the applicant in Japanese Patent Application No. 186487/1987. In the 40-rule method, in order to secure a fin height height of 3.5 degrees, T is required to exceed a thickness reduction rate of 40%. On the other hand, in the case of the manufacturing method of the present invention, 40
If T is added to the castle wall rate exceeding %, the inner diameter reduction rate △D1
Even with 8%, a fin height of approximately 1 va is secured, and the inner diameter reduction rate ΔD.

When T is 15%, a filtration rate T of only 10% results in a fin height approximately comparable to the fin height Il (3,5M+) in the case of the 40-L method.

In the manufacturing method of the present invention, the inner diameter Di of the raw pipe 20 is smaller than the diameter d0 of the hole, that is, p<
It is important that d, and DI ≧d.

If the raw pipe 20 is thin, bending occurs, and large inner sinkage occurs regardless of the wall thickness.

That is, the diameter d of the inner diameter regulating tool 30 is the hole diameter d.

necessarily smaller than For this reason, when the inner diameter of the raw pipe 20 becomes larger than the diameter d0 of the hole, the difference in diameter between the diameter d of the inner surface regulating tool 30 and the inner diameter Di of the raw pipe 20 becomes excessive. As a result, the area where the raw pipe 20 is rolled from the outer surface side is long in a state where the inner surface of the raw pipe 20 is not in contact with the outer surface of the inner surface regulating tool 30, and this causes folding and excessive inner surface sinkage. , Lji <do, then
This area is shortened and folds do not occur, nor do large inner surfaces that would cause problems.

Regarding internal sinkage, in ice-walled tubes for power generation boilers, which are the main use of externally finned tubes, a sink depth of up to O12 is permissible at the product level, so if the tube is used as a product after rolling, It is sufficient to suppress the burr depth to 0.2- or less. When drawing with a ring die after roll rolling, the sink depth should be set to 0.0, depending on the degree of drawing.
If it is set to 5w or less, the sink depth after drawing is corrected to 0.2s or less.

In addition, from the viewpoint of inserting the inner surface regulating tool 30 into the raw pipe 20, it is desirable for d to satisfy d≦0.95D from the viewpoint of insertion work.

Regarding the inner surface sink, the depth thereof is determined by the thinning rate ΔT,
The inventors' research has revealed that this is related to the inner diameter reduction rate ΔD.

FIG. 4 is a graph illustrating this relationship between the champions. As can be seen from the figure, in order to suppress the inner sink, the fin height h
Contrary to the case where the thickness reduction rate ΔT and the inner diameter reduction rate ΔD
It is desirable that both of , be smaller. However, even if the sink depth is reduced, the fin height h can be maintained sufficiently.For example,
At 8T-30%, ΔD, -15%, the fin height h is approximately 61
11[ll], but even under this condition, the sink depth is suppressed to 0.5 knots or less.

Further, when ΔDi=8%, a fin height h of approximately 5 m is secured at ΔT-35%, and the sink depth is suppressed to 0.2 pitch or less. When the sink depth is suppressed to 0.5 m or less and the fin height h is taken into account, the thickness reduction rate T and the inner diameter reduction rate ΔD are as follows.
It is desirable to manage within the range surrounded by A-D in FIG. 4.

In addition, A is (8T-15%, ΔDi5%), B is (ΔT
= 15%, ΔDi-18%), c is (8T-30%, Δ
D+-15%), D is (ΔT=47%, ΔD1-5%)
represents each point.

〔Example〕

The present invention will be explained in detail below.

Six types of raw pipes (D, =
46 Peng, D+=26m), (D,=48 Kaku, Dt=2
6wfIl), (D, =50+aa, DI
-26m), (D, =5011Il, Dt
-28M), (D.

-52++s, Di -28M), (D, = 58mn
,D.

= 40o) with two types of grooved rolls (d, = 38peng, 40
) and two types of internal regulation tools (d+ = 22m, 24 fermentation)
Eleven types of external double-finned tubes were manufactured by rolling at 20 millimeters. The flange surface gap G was 8 or 7 in all cases. Fin height of manufactured fin tube 1
1. The sink depth P is shown in Table 1 as 1 to 11.

For Seeds 1 to 9 that satisfy D,<d, a fin height h of more than 3- is ensured in one bass, and the sink depth 2 is suppressed to less than one fin. In particular, the sink depth is 0.5 m for Sho 1 to 4.6, which satisfy the hunting conditions surrounded by A-D in Figure 4.
The fin height h is suppressed to l11 or less, and a fin height h of 3.5 wa or more is secured.

In addition, the case where 40-roll rolling was carried out under substantially the same conditions as in Law 6 is shown in Figure 12, and the sink height h is 3.5.
It is m. On the other hand, for the 20-ex 6, the sink depth slightly increases from 0.1 m to 0.37 m, but the fin height increases from 3.5 m to 6.6 m to 3.1 exa.
is also increasing.

〔Effect of the invention〕

The method of manufacturing a tube with two external fins according to the present invention ensures a large fin height in one bath, and also suppresses the occurrence of bending and internal sinking. Therefore, the method of the present invention economically produces a high-quality pipe with two external fins, and is highly effective in reducing manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the rolling situation in the manufacturing method of the present invention,
FIG. 2 is an explanatory diagram of the raw pipe, FIGS. 3 and 4 are graphs showing the degree of influence of variation factors of fin height and sink depth, and FIG. 5 is an explanatory diagram of the conventional method. In the figure, IO: hole-shaped roll, 20: blank pipe, 30: inner surface regulation tool. Figure ΔT (%) Figure ΔT (%)

Claims (1)

[Claims] One or two groove rolls are arranged facing each other with their groove centers aligned with the pass line so that a gap is formed between their flange surfaces, and an element with a circular cross section having an inner diameter smaller than the diameter of the groove is formed. Circumferential symmetry 2 is achieved by inserting the pipe into the hole mold with the inner surface regulating tool inserted therein to reduce its wall thickness, and causing a part of the reduced pipe wall to bulge into the gap between the roll flanges. 1. A method for manufacturing a tube with two outer fins, characterized in that fins extending in the axial direction are formed at certain positions.