JPH0462789B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cooling device for the inner surface of a metal tube when the outer surface of the metal tube is coated with a coating material such as polyethylene by an extrusion method or the like.

[Prior Art] Conventionally, in order to improve corrosion resistance, a method of coating a metal pipe such as a steel pipe with a synthetic resin such as polyethylene has been used. When applying, the adhesive is applied in advance and then the synthetic resin is applied. 2 in parallel
The parallel die method using two dies, or the two-layer die method in which adhesive and synthetic resin are applied from one die, etc., are used, and various dies such as T dies or round dies are used. ing. Generally, in order to continuously wrap the synthetic resin around the tube, the metal tube P itself is transported while being rotated in the circumferential direction by a turning roller 51 or the like, as shown in FIG.

However, when the metal tube is rotated by the turning roller as described above, the semi-solidified synthetic resin coating attached to the metal tube is pressed by the turning roller. Since large diameter steel pipes are generally joined by welding, a weld bead WB rises from the surface of the steel pipe P. And such welded steel pipe P
In this case, the pressing force by the turning roller 51 particularly acts on the raised weld bead WB portion. As a result, as shown in FIG. 10, the thickness tb of the synthetic resin coating 52 at the weld bead WB is smaller than the thickness ta at other locations. 53 is a primer layer made of epoxy resin or the like.

In addition, the standards for this type of coated steel pipe require that the minimum coating thickness be at least a specified thickness.
In anticipation of the film thickness reduction amount Δt (=Δta−Δtb), an extra thick film must be coated. the result,
The amount of synthetic resin used increases, resulting in a decrease in the basic unit. On the other hand, cooling of coated steel pipes has conventionally relied solely on cooling from the outside, and the cooling rate has been controlled. However, polyethylene resin and the like have low thermal conductivity, so even if the amount of cooling water is increased, a high cooling rate cannot be expected. As a result, in Figure 6
As shown by the F ₀ line, although the cooling effect is relatively sufficient at both ends of the tube, in the longitudinal center of the tube, the polyethylene crystals become coarser due to the insufficient cooling rate, especially on the inner surface of the coating. This leads to a decrease in the physical properties of the polyethylene and a decrease in the adhesion between the adhesive and the steel surface. The adhesion force is related to the cooling rate, as shown by the S line in FIG. The person is aware of this.

By the way, the present inventor previously published Japanese Patent Application Laid-Open No. 57-201571.
In the publication, as a solution to the above problems, the idea of cooling the inner surface of the steel pipe by injecting water was disclosed. but,
The publication does not teach any specific means of water injection. Further, no specific consideration has been given to the fact that the coated steel pipes flow through the line while being separated from each other.

[Problems to be Solved by the Invention] As described above, the conventional technology mainly relies on cooling only from the outer surface, so the cooling rate is insufficient, the adhesion of the film is low, and the adhesion is likely to be unstable. The amount of covering material used increases. In addition, even if there is a method that also uses cooling from the inner surface, the only disclosures in the publication state that the coated steel pipes are sequentially transferred along the line while changing the mutual distance, and that after coating a single steel pipe, Under the circumstances that the next steel pipe to be coated is brought to the coating position in a short period of time, it is extremely difficult to provide continuous internal cooling to each coated steel pipe over its entire length.

The present invention aims to solve such conventional problems.

"Means for Solving the Problems" The present invention provides a device for solving the above problems, and will be described with reference to the reference numerals in the drawings.The outer surface of the metal pipe P is coated with a synthetic resin coating material. A device for cooling the coating after coating is provided with cooling water and gas supply passages 11 and 12 along the line direction, and cooling water and gas supply passages 11 and 12 formed at a plurality of positions in the line direction in communication with these passages. A horizontal boom 5 having supply ports 10A and 10B and whose tip end is inserted into the metal pipe P close to the coating position; a head 7 that communicates with the channel 11 and discharges cooling water; a head 8 that is located at the tip of the horizontal boom 5 and on the upstream side of the line and communicates with the supply channel 12 and discharges gas; A plurality of support devices S2 and S3 are provided to support the horizontal boom 5 at a plurality of positions in the line direction, and the support body 16 of the support device rises to a position where it supports the horizontal boom 5 and descends to release the support. and a position that avoids the height range through which the metal tube P passes. It is characterized by being configured so that it communicates with the supply ports 10A and 10B, and the communication is cut off when it is lowered.

[Function] Figure 1 shows an outline of a production line for coated steel pipes made of polyethylene, etc. After the steel pipe P is carried into the line, it is shot blasted, heated by an induction heating machine 1, and then heated. After the primer is applied to the steel pipe P, polyethylene resin is extruded through a T-die 2 or the like and wrapped around the outer surface of the steel pipe P. After that, it is cooled while passing through the outer water cooling zone 3, and after leaving the water cooling zone 3, the transfer speed is The pipes are sped up, transported while being separated from the following steel pipes, are cooled by air in the process, and are finally kicked out of the line.

According to the present invention, in order to cool the inner surface of the steel pipe P at a position slightly downstream of the resin coating position and, as a result, rapidly cool the coating resin, the steel pipe P ₀ being coated is
A horizontal boom 5 is inserted therein together with a cooling water discharge head 7. It is possible to support this boom 5 at the rear end of the line, but since the distance from the covering position to the end of the line is usually about 70 m, it is practically impossible to support the boom at the rear end. Therefore, it is preferable to support it at a position as close to the covering position as possible. For this purpose, a support device is provided close to the coating location. However, if there is only one support device, the steel pipe cannot be transferred any further.
Therefore, in the present invention, a plurality of, for example, three supporting devices S1, S2, and S3 are provided. According to this, the support part of the support device S2 at the position where the steel pipe P should pass is lowered, moves away from the path of the steel pipe P to allow it to pass, and is supported by the other support devices S1 and/or S3. Boom 5 can still be supported.

On the other hand, in order to promote cooling from the inner surface of the steel pipe P slightly downstream of the covering position, it is necessary to supply cooling water along the boom 5 to the cooling water discharge head 7 attached to the tip. However, if the cooling water supply point is fixed, it will interfere with the coated steel pipe. Therefore, the cooling water is supplied from a plurality of positions, preferably attached to each support device as in the specific example described later, and each time the cooling water is supplied from a position that does not interfere with the passage of the steel pipe.

In addition, in the device of the present invention, support and non-support by the support device and the supply position of cooling water to the boom (in other words, the cooling water discharge head) are determined according to the position of the pipes after coating (including those under coating). If the selection is made automatically or manually, the steel pipe can be smoothly transferred to the end of the line.

[Specific Examples of the Invention] The present invention will be explained in detail below with further reference to the drawings.

Referring to FIGS. 1 to 4, the boom 5 has a tubular shape, for example, and as shown in FIG. It can be supported by S2 and S3. In order to support the tip of the boom 5, support rolls 6a to 6c are provided at the tip of the boom 5 to contact the lower inner surface of the steel pipe P and rotate freely. Further, at the tip of the boom 5, there is a cooling water discharge head 7 having an annular header 7a and a cooling water discharge nozzle 7b attached thereto facing diagonally downstream; An air ejection head 8 having an air ejection nozzle 8b facing diagonally downstream is attached to the air ejection head 8.

A pair of thrust receiver rings 9A and 9B are fixed to positions corresponding to each of the support devices S1 to S3 of the boom 5, and a receiver coupler 10, which constitutes the cooling water and gas supply ports of the present invention, respectively, is fixed thereto.
A and 10B are attached. The receiving couplings 10A, 10B and the annular headers 7a, 8a are connected by a cooling water pipe 11 and an air pipe 12.
On the other hand, the support device S includes a lifting cylinder 13 installed on the base and a base plate 1 attached to the tip of the rod.
4. An arcuate support 16 is provided on the base plate 14 to support the boom 5 via a support block 15. The base plate 14 also has a guide rod 17,
17 are fixed, and these are the guide tubes 1 installed on the base.
8, 18. This ensures smooth lifting and lowering of the lifting section. Furthermore, the base plate 14 has a fitting coupling 19 at its upper end that constitutes the cooling water and gas supply ports of the present invention, respectively.
Introductory short pipes 20A and 20B having pipes A and 19B are fixed, and a cooling water W conduit 21A and an air A conduit 2 are connected to these short pipes 20A and 20B.
1B is connected.

Now, when the rod of the lifting cylinder 13 extends from the lowering limit position (the imaginary line position in FIGS. 2 and 3), the support body 16 rises together with the base plate 14 to support the boom 5. At the same time, the fitting coupling rings 19A and 19B are connected to the receiving coupling ring 10.
A, 10B, the cooling water conduit 21A and the air conduit 21B communicate with each other for the first time,
Cooling water W and air A are supplied. Conversely, when the rod of the lifting cylinder 13 contracts and moves downward, the couplings come apart and the cooling water W
And the supply of air A is stopped. Also, when the support body 16 is lowered, the steel pipe P can freely pass through the support device section, as can be seen in FIG.

Next, with reference to FIG. 4, the relationship between tube movement and boom support will be explained.

The tubes that are successively introduced into the line are in contact with each other in the coating position, and this condition continues until they pass through the external cooling zone. Once that tube B leaves its outer cooling zone, the transport speed is increased and it begins to move away from the next tube A. In the case of X1 (Fig. c), as shown in Fig. e, it is supported by the third support device S3.
In addition, in figure e, an x mark indicates a non-supported state, and an ○ mark indicates a supported state. Then, as in the case of X2, tube B
When it reaches near the third support device S3, the support by the third support device S3 is stopped and the support by the second support device S3 is stopped.
Supported by 2. Furthermore, as in the case of X3,
The tube B passes through the third support device S3, and the second support device S
2, the support is switched to only by the third support device S3. After that, as in the case of X4, if the next pipe A also passes through the second support device S2, both the second and third support devices S2, S
3 supports the boom 5.

Note that the first support device S1 supports the tip of the boom 5 at the initial stage, and once the coating process begins, the support rolls 6a to 6c continue to support the steel pipe P using the inner surface as a seat. Not necessary.

Furthermore, since the pipe passing through the cooling water discharge head 7 is continuous as described above, cooling water is always being discharged.

By the way, as in the above example, the cooling discharge nozzle 7
b is directed toward the downstream side, and air is ejected from the air ejection nozzle 8b located upstream of it, allowing the discharged cooling water to flow only downstream, thereby cooling the steel pipe that has been heated to a temperature suitable for coating. can be prevented.

In the present invention, cooling is also performed from the inner surface of the tube, so as shown by the T line in Figure 5, the first turning roller
By the time R ₁ is reached, the coating is cooled to its curing temperature. In FIG. 5, the T ₀ line indicates the cooling rate by the conventional device, and T indicates the cooling rate by the device of the present invention. As a result, as shown by the F line in Figure 6, a high adhesion force is obtained over the entire length of the tube, and as shown by the Δt ₁ line in Figure 8, the difference in thickness between the bead and other parts is smaller than that of the conventional one. It is smaller than that shown by the Δt ₂ line, and the effect of reducing the amount of synthetic resin coating material used is large.

[Effects of the Invention] As described above, according to the present invention, since cooling is performed from the inner surface of the metal tube, rapid cooling of the coating is possible, improving the adhesion of the coating and reducing the amount of coating material used. It can definitely be achieved. Furthermore, continuous cooling and smooth transfer of metal tubes can be achieved even on long production lines.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a metal pipe coating line equipped with the device of the present invention, Fig. 2 is a front view of its main parts, Fig. 3 is a view taken along the - line, and Fig. 4 a to e show the positions of steel pipes. An explanatory diagram showing the relationship with the support mode by the support device,
Fig. 5 is a correlation diagram of an example of cooling rate of the present invention in comparison with a conventional example, Fig. 6 is an explanatory diagram of an example of improved adhesion, and Fig. 7 is a diagram of the relationship between cooling rate and adhesion. 8th
The figure is a relationship diagram showing an example of a reduction in the difference in film thickness between the bead and other parts, Figure 9 is a cross-sectional view of the support mode of a welded steel pipe, and Figure 10 is a cross-sectional view of the main part of the welded steel pipe for explaining the coating shape. It is a diagram. 2...T-die, 3...Outer cooling zone, 5...
Boom, 6a-6c...Support roll, 7...
Cooling water discharge header, 13... Lifting cylinder, 16
...Support, P, P ₀ ...Steel pipe, S1 to S3...
Support device, W...cooling water, A, B...steel pipes.

Claims (1)

[Scope of Claims] 1. A device for coating the outer surface of a metal pipe P with a synthetic resin coating material and then cooling it, which is provided with cooling water and gas supply channels 11 and 12 along the line direction, and a horizontal boom 5 having cooling water and gas supply ports 10A and 10B that are connected and formed at a plurality of positions in the line direction, and whose tip end is inserted into the metal pipe P close to the coating position; a head 7 located at the tip of the horizontal boom 5 and on the downstream side of the line and communicating with the supply channel 11 to discharge cooling water; A head 8 that communicates with the supply channel 12 and discharges gas, and a plurality of support devices S2 and S3 that support the horizontal boom 5 at a plurality of positions in the line direction, and the support body 16 of the support device is raised. It is configured to be able to move up and down freely between a position where it supports the horizontal boom 5 and a position where it is lowered to release the support and avoid the height range through which the metal pipe P passes, and when the support body 16 is raised, it is configured to be able to move up and down freely. Inner surface cooling of a coated metal tube, characterized in that the cooling water and gas supply ports 19A and 19B communicate with the cooling water and gas supply ports 10A and 10B, and the communication is cut off when descending. Device.