JPS6336930B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a coated steel pipe having a shark-skin pattern on its surface in order to prevent the plastic-coated steel pipe from slipping during transportation or from pulling out of the concrete lining, etc. that is placed on the plastic-coated steel pipe. Traditionally, steel pipes have been coated with external coatings based on bituminous materials such as asphalt or coal tar to prevent corrosion, but in recent years coatings have improved in terms of performance such as durability, heat resistance, and corrosion resistance, as well as improved work environment and productivity. Plastic-coated steel pipes have become widely used. However, since the surface of the coating layer of plastic-coated steel pipes is generally extremely smooth, when lifted and transported by cranes, hawk lifts, etc.
Covered steel pipes may slip at the contact points with wires, springs, and other hanging tools, causing cargo to shift or fall, and plastic-covered steel pipes may be used to protect the covering and add weight to pipes when buried underground. In the case where the lining is made of concrete, mortar, etc., there are problems such as slippage of the contact portion with the plastic coating layer, which may cause an accident in which the concrete or mortar lining is pulled out. In order to eliminate the slipperiness of the outer surface of the coating layer of such plastic-coated steel pipes, for example, JP-A No. 49-26823 uses pellet-based outer lining pipes, and JP-A No. 51-59975 uses heat-melted adhesive on the outer surface. Various proposals have been made, such as a method for processing plastic-coated steel pipes in which a coating agent is partially applied and hardened, and a method for manufacturing plastic-coated steel pipes with anti-slip surfaces on the outer surface of JP-A-52-71222. In both cases, pellets are formed on the outer surface of the plastic coating layer.
Special equipment and processes are required to newly apply the hot-melt adhesive, anti-slip agent, etc., which not only complicates the work but also increases manufacturing costs. In order to eliminate the above-mentioned drawbacks, the present invention provides an inexpensive and highly productive method of directly forming an anti-slip uneven pattern on the surface of a plastic coating, without applying a new anti-slip agent or the like to the surface of the coating layer. The purpose is to provide an excellent method. In the present invention, when continuously coating the outer surface of the tube with plastic by an extrusion method, the vicinity of the plastic extrusion port of the extruder is forcedly cooled to make the temperature in the vicinity lower than the temperature of the plastic to be extruded. The gist of this method is to form a shark-skin-like uneven pattern on the outer surface of the plastic, and by simply forcing the area near the plastic extrusion port of an extruder, an anti-slip pattern can be formed at the same time as the plastic coating. By adjusting the temperature difference between the surrounding temperature and the temperature of the extruded plastic, it is possible to freely adjust the height, pitch, etc. of the unevenness formed on the outer surface of the coated plastic. Specifically, the entire surface of the coating layer 1 of the plastic-coated steel pipe, in which the outer surface of the steel pipe is coated with plastic extruded from an ordinary round die extruder, is coated with shark skin (shark skin-like uneven skin) as shown in the cross-sectional view of Fig. 1. It is already known that an uneven pattern 2 called a surface) often appears with the unevenness arranged in parallel in the circumferential direction at right angles to the axis A-A of the original tube 3, but the inventors have investigated the cause of the occurrence of this shark skin. If it is possible to promote the formation of shark skin by artificially providing environmental conditions that facilitate the formation of shark skin during the plastic coating process, it is possible to apply special anti-slip agents to the coating surface as has already been proposed. The present invention was completed based on the idea that a plastic-coated steel pipe with an anti-slip effect could be obtained at low cost without requiring installation. It has already been found that the occurrence of shark skin is mainly caused by intermittent deterioration in the fluidity of plastic due to temperature changes that occur when extruding from the plastic extrusion port. As one of the methods to promote this, we conducted a test in which the lip part near the plastic extrusion port was cooled to below the temperature of the extruded plastic. , a certain amount of plastic in the area where the temperature has decreased in contact with the lip is intermittently extruded from the plastic extrusion port at regular intervals and breaks into the plastic layer, and fluidity is added to the plastic layer discharged from the extrusion port at regular intervals. It was confirmed that the so-called pulsating extrusion caused the formation of sharkskin-like irregularities with uniform height and pitch on the surface of the coating layer of the plastic-coated steel pipe. Figure 2 shows the height D and pitch P of the shark-skin-like unevenness of the coating layer of the coated steel pipe and the temperature difference when the lip section is cooled by varying the temperature difference between the plastic temperature in the die section and the lip section temperature. As can be seen in the figure, the relationship between the height D of the unevenness and the temperature difference between the plastic and the lip part, and the relationship between the pitch P and the temperature difference are shown by the characteristic curve D and the relationship between the pitch P and the temperature difference, respectively. It was also confirmed that there was a correlation shown by characteristic curve P. The method of the present invention will be explained in detail below. An example of a manufacturing apparatus for carrying out the method of the present invention is shown in FIGS. 3A and 3B. FIG. 3A is a vertical sectional side view of the upper half, and FIG. In the figure, the extruder 4 is a known one,
A die 6 is provided concentrically surrounding the original tube 5 at an appropriate interval, and a holder 7 is attached to the die 6.
and a pressing device (not shown) for extruding the plastic 8 from the plastic storage chamber 9 in the die 6 through the passage 10 to the outside from the plastic extrusion port 11, and for adjusting the gap of the plastic extrusion port 11. A ring-shaped lip portion 12 is removably attached to the front surface of the holder 7. 13
is a heater provided around the outer periphery of the holder 7 to heat the dice 6. In the embodiment, the cooling air blowing device 14 includes an annular tube 16 surrounding the raw tube 5 immediately after exiting the die outlet 15, and a large number of nozzle holes 17 formed in the lip portion 12 in the annular tube 16. The annular pipe 16 is connected to an air supply source (not shown), so that cooling air is blown onto the lip portion 12 for forced cooling. 18 is a thermocouple, and the plastic extrusion port 11
For example, one or more of them are inserted as appropriate into the lip part 12 nearby, and connected to the indicating device 20 by a lead wire 19, and the cooling air blowing device 14 turns on and off the cooling air blowing device 14 based on the temperature measurement result of the lip part. As a result, the temperature of the lip portion 12 is adjusted to a predetermined value. The device for forcibly cooling the vicinity of the plastic extrusion port may be, for example, provided with a cooling channel for circulating cooling water in the lip portion 12 and cooled by water, but is not particularly limited to the above embodiment as long as the lip portion can be effectively cooled. It's not something you do. To carry out the method of the present invention using the apparatus shown in FIG.
3 to heat the plastic 8 in the storage chamber 9 to the extrusion temperature, and then heat the plastic 8 in the lip part 12 and the storage chamber 9 to the desired height and pitch of the unevenness formed on the outer surface of the plastic-coated steel pipe. Cooling of the lip portion 12 is started by operating the cooling air blowing device 14 so that the temperature difference with the plastic reaches the target value. The temperature of the lip portion 12 is controlled by the heater 13.
Initially, the temperature is approximately the same as that of the plastic in the die due to the heating of the plastic, but it is gradually cooled by the blowing of cooling air and the temperature decreases. Since the jet of cooling air is turned on and off to maintain a predetermined temperature, when coating the raw tube 5 with plastic according to the conventional extrusion method, the fluidity of the extruded plastic, the extrusion force, etc. Due to this relationship, the plastic in the part where the temperature has decreased in contact with the lip part is extruded intermittently at regular intervals, resulting in so-called pulsating extrusion, resulting in a shark-skin-like uneven pattern having a predetermined height and pitch on the surface of the coating layer. is formed. Next, the effects of the method of the present invention will be explained with reference to Examples. Example: Steel pipes coated with polyethylene were made by using the method of the present invention to form shark-skin-like irregularities on the outer surface of raw pipes with an outer diameter of 20", and the same raw pipes were coated with polyethylene to have a smooth surface. Using a conventional coated steel pipe as a test steel pipe, the test steel pipe 21 was suspended from a crane hook 22 by a wire 23 as shown in FIG.
Table 1 shows the results of a sliding test on the wire during transportation with various values.

[Table] In Table 1, the slip start inclination angle means that when the inclination angle θ of the suspended test steel pipe 21 is gradually increased from 0° (horizontal), the test steel pipe 21 is This is the angle at which the slide started. As shown in Table 1, the inclination angle at which slipping starts for the test steel pipes (1 to 3) made by the method of the present invention is 20 to 30°, which is extremely large compared to 10° for the test steel pipes made by the conventional method.
If the slip starting angle of inclination is maintained at 20° or more, accidents due to slipping during actual transportation can be almost completely prevented. Example: The height of unevenness was increased by the method of the present invention on a raw tube with an outer diameter of 20″.
A polyethylene-coated steel pipe with a shark-skin-like uneven pattern of 0.9 mm and a pitch of 2 mm formed on its surface, and a conventional coated steel pipe with a smooth surface polyethylene coating applied to the same original pipe as a comparative example were used as test steel pipes. A concrete lining, which is commonly found on coated steel pipes for laying on the seabed, was applied to each pipe, and a push-out test was conducted on the concrete lining, and the results are shown in the diagram of FIG. Fig. 5 shows the push-out force of the concrete lining on the vertical axis and the displacement of the concrete lining on the horizontal axis, and the relationship between the push-out force and the displacement of the concrete lining in the example of the present invention is shown by the ○ mark and the characteristic curve R. , is a chart showing the same relationships in comparative examples with ● marks and characteristic curve S. As is clear from Figure 5, the comparative example is 6ton/m ²
Up to a certain level of push-out force, there is almost no movement of the concrete lining due to the adhesion between the concrete lining and the coating layer.
When a force exceeding 6 ton/m ² is applied, the adhesive force is broken, and when a force of 6 ton/m ² or less is applied, the concrete lining begins to move significantly, causing pull-out development. On the other hand, the example of the present invention has an excellent strength that hardly causes any movement up to a pull-out force of about 10 tons/ ^m2 , and it has been shown that there is no risk of the concrete lining being pulled out in actual use. It was done. As described above, the present invention provides an extremely simple method of applying forced cooling to the lip near the plastic extrusion port of an extruder, thereby efficiently creating a non-slip textured pattern on the outer surface of a plastic-coated steel pipe without increasing costs. It is extremely effective in preventing plastic-coated steel pipes from slipping during transportation or from pulling out external concrete linings.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing an anti-slip shark-skin pattern formed on the outer surface of a plastic-coated steel pipe;
The figure is a chart showing the relationship between the temperature difference between the lip part and the plastic and the height and pitch of the unevenness formed on the outer surface of the covered plastic. Figure 3A shows an example of an apparatus for carrying out the method of the present invention. A vertical cross-sectional side view of the upper half, Figure 3 (b) is a front view of the cross section of Figure 3 (a), Figure 4 is an explanatory diagram of a plastic-coated steel pipe suspended with a crane hook, and Figure 5 is a concrete FIG. 2 is a chart showing the relationship between the push-out force of the concrete lining and the amount of movement of the concrete lining in a plastic-coated steel pipe with a lining. FIG. 1: Covering layer, 2: Uneven pattern, 3, 5: Original tube,
4: Extruder, 6: Dice, 7: Holder, 8: Plastic, 9: Plastic storage chamber, 10: Passage, 11: Plastic extrusion port, 12: Lip part, 13: Heater, 14: Cooling air blower, 1
5: die outlet, 16: annular pipe, 17: nozzle hole, 18: thermocouple, 19: lead wire, 20: indicator device, 21: test steel pipe, 22: crane hook,
23: Wire.

Claims (1)

[Claims] 1. In a method for producing a plastic-coated steel pipe in which the outer surface of the steel pipe is coated with plastic continuously extruded by an extruder, the lip portion constituting the plastic extrusion port of the extruder is heated to a temperature lower than the temperature of the extruded plastic by a predetermined temperature. A method for manufacturing a plastic-coated steel pipe, which comprises pulsating extruding plastic by forced cooling and coating the outer surface of the steel pipe with the pulsatingly extruded plastic to form a plastic coating layer having an uneven pattern on the outer surface.