JPS5933445B2 - Manufacturing method of molten metal plated steel pipe - Google Patents

Description

[Detailed Description of the Invention] Conventionally, when continuously hot-dip metal plating something such as a thin plate or wire rod, since this kind of material is easy to bend,
After plating, it was possible to take it out while moving it upward.

Therefore, the problem of uneven plating thickness due to dripping of molten metal did not occur. However, when continuously hot-dipping steel pipes made from steel strips, it is difficult to bend the steel pipes, so the pipes have to be removed by running them horizontally, which causes the molten metal adhering to the steel pipes to move downwards. There was a problem that the plating layer at the bottom became thicker. In order to prevent this so-called sagging, there was a way to remove excess molten metal by blowing air immediately after taking it out to reduce the sagging of the molten metal, but since the surface of the steel pipe is smooth and the strength to hold the molten metal is weak, the sagging occurs. is likely to occur,
It has been considered difficult to apply thick plating layers. By the way, if the surface of the steel pipe is galvanized, for example,
Generally, the corrosion resistance of a zinc layer increases as the thickness of the zinc layer increases, so it has traditionally been an important concern to apply as thick a coating as possible to the surface of a steel pipe. However,
The present invention forms a large number of uneven portions with depths of several microns to several tens of microns and diameters of several microns to several hundred microns on the surface of a steel pipe, increasing the surface area to increase the holding power of the plated molten metal on the surface, and to improve the plating layer. It facilitates adhesion and forms a thick and strongly bonded plating layer on the steel pipe surface, which is highly corrosion resistant and optically non-reactive.
This makes it possible to provide steel pipes that always have a beautiful appearance. Hereinafter, one embodiment of the present invention will be explained in detail with reference to the drawings. (3- In the drawings, 1 is an uncoiler that supplies a strip steel coil, 3 is a shear end welder 1 for joining strips together, and 5 is a shear end welder 1 that stores the steel while joining the strips. The louvers 1 and 7 are cleaning devices that remove oil and moisture adhering to the surface of the steel pipe.

Reference numeral 9 denotes a shotplast device for forming irregularities on the surface of a steel strip, for example, in order to remove an oxide film.This shotplast device 9 is divided into three rooms, and the central room 15 is a blast room. Abrasive projection devices 17a, 17b, 17 are provided both above and below the passing steel strip.
c, 17'A, 17'B, and 17/c are provided respectively, so that abrasive can be projected onto both the upper and lower surfaces of the steel strip, and furthermore, the blast room 15 is provided with an inlet end and an outlet end. The abrasives projected from the abrasive projection devices 17a, 17c and 17'A, 17'c located in the blast room 15 are projected toward the inside of the blast room 15, and care is taken to prevent the abrasives from flying out. has been done.

In addition, the abrasive projection devices 17a, 17b, 17c and 17'A, 17/B, 17'c are equipped with a control device that adjusts the abrasive projection amount appropriately, and when the process starts or stops. During the transition period when the steel strip is accelerated or decelerated, the abrasive is adjusted so as not to overshoot or undershoot, and even when the steel strip is flowing at a constant velocity, it is adjusted depending on the material or surface condition of the steel strip. The amount of projection is adjusted appropriately. On the other hand, the two front and rear rooms 13 and 19 are the front and rear seal rooms, respectively, to prevent the projected abrasive from flying out of the device.
It is completely sealed with a special rubber curtain, and a surface cleaning device 2 is installed in the rear sealing room 19 to remove abrasives, scale, iron powder, etc. attached to the steel strip.
1 is provided.

Further, reference numerals 11a, 11b, 11c, and 11d are strip steel holding and guiding devices installed inside the shot blasting device 9 and near the outside of the strip entrance/exit, and holding and guiding the strip so that the strip receives the abrasive blast correctly. It is something to do. 23 is a forming machine that pulls the steel strip and forms the pulled steel strip into a tubular shape; 25 is a welding machine that continuously welds the joints of the steel strip formed into a tubular shape in the axial direction; and 27 is a temperature control machine. The equipment uses water to adjust the temperature of the steel pipe surface, adjust the temperature and temperature distribution of the welded part and its adjacent parts, which become hot during welding, and adjust the pickling speed of the steel pipe surface in the pickling equipment described later. , prevents the temperature of the pickling solution from becoming too high, and at the same time washes away iron powder and scales that adhere to the steel pipe surface during shot blasting, roll forming, or welding, and prevents stains and consumption of the pickling solution. It works to prevent.

Furthermore, 29 is an air blower provided near the outlet of the temperature control device 27 to remove moisture adhering to the surface of the steel pipe and prevent the pickling liquid from becoming diluted.

31 is a pickling device for removing the oxide film formed on the surface of the steel pipe due to the heat during welding, 33 is a water washing device for washing off the pickling liquid, and 35 is a flux liquid for applying oxidation prevention to the surface of the steel pipe. 37 is a drying preheating device; 39 is a molten metal plating device; 41 is a device for blowing air or an inert gas onto the surface of the steel pipe to wipe away excess molten metal adhering to the surface of the steel pipe to prevent dripping; 43 is a cooling device; 45 is a sizing device for setting the cross section of the steel pipe to standard dimensions by cold working; 47 is a straightening device for straightening the bend in the steel pipe; 49 is a surface treatment device; 51 is a cutting device. It is a device.

Next, the operation of the above configuration will be explained.

The steel strip supplied from the uncoiler 11 passes through a louver 5 and enters a cleaning device 7, where the surface is cleaned if it is contaminated with oil. The strip steel leaving the cleaning device 7 enters the shot blasting device 9 and is passed through the abrasive projection devices 17a, 17b, 17c and 17 in the blast room 15.
'A, 17'B, 17'c are subjected to abrasive projection according to the material of the steel strip, surface condition, and desired amount of plating, and the surface of the steel strip is exposed to a depth of several microns to several tens of microns and several microns to several microns. After a large number of uneven parts with a diameter of 100μ are uniformly formed,
After entering the rear sealing room 19, a surface cleaning device 21 removes abrasives, scale, iron powder, etc. attached to the surface of the steel strip. The steel strip with unevenness formed on its surface by the shot blasting device 9 is then transferred to the forming machine 23.
There, the steel pipe is cold-formed into a tubular shape, and the joints are continuously welded in the axial direction by a welding machine 25 to form a steel pipe. At this time, the welded area and its adjacent areas are covered with a strong oxide film due to the heat generated during welding, and this oxide film is thick at the weld bead where high temperatures occur and gradually becomes thinner as it moves away from the bead. ing. This steel pipe is then sent to a temperature control device 27 where it is temperature-controlled by water, and the cooling of the steel pipe surface is controlled, so that the temperature distribution on the steel pipe surface is such that the bead part with a thick oxide film is at a high temperature, and the bead part with a thick oxide film is at a high temperature. The temperature is set so that as the distance increases and the oxide film becomes thinner, the temperature becomes lower. The steel pipe whose surface has been temperature-controlled is sent to a pickling device 31 after moisture is removed by an air blow 29. The pickling speed in the pickling device 31 is determined by the temperature of the steel pipe surface, and the high-temperature oxidation The thicker parts of the oxide film are pickled at a faster rate, and the thinner parts of the oxide film where the temperature is lower are pickled at a slower rate. Therefore, the steel pipe surface is pickled within a certain period of time without over-pickling or under-pickling. The pickled steel pipe is washed with water by a water washing device 33, and sent to a flux device 35, where an anti-oxidation flux is applied to the surface. At this time, the surface area of the steel pipe is increased due to the unevenness formed on the surface of the steel pipe by shot blasting, so the flux thickly covers the surface of the steel pipe and does not last long even when exposed to high temperatures in the subsequent process. It can prevent oxidation of the steel pipe surface for hours. The steel pipe coated with flux is sent to a drying preheating device 37, where its surface is dried and preheated, and sent to a molten metal plating device 39, where plating molten metal adheres to its surface, and then transferred to the next blow-off device 4.
In step 1, excess molten metal that causes sagging is removed and then cooled. Note that during preheating in the dry preheating device 37, it is expected that internal strain in the steel pipe will be removed. At this time, the surface area is large due to the unevenness formed on the surface of the steel pipe, and the force to hold the adhered plating molten metal is large, so it is possible to form a pure metal plating layer that is thicker than the alloy layer. This plating layer is not only bonded to the surface of the steel pipe by the alloy layer, but also is a strong plating layer that is strongly bonded physically and mechanically. In other words, taking the case of hot-dip galvanizing as an example, the base material, that is, the surface layer of the steel pipe, is an alloy of iron and zinc, and a layer of pure zinc is formed on the alloy layer. In this case, the pure zinc layer becomes extremely thick. This means that
This makes it possible to obtain a thick plating layer within an extremely short period of time, improving production efficiency. Then, the plated steel pipe is cold-rolled in the sizing device 45 to make the cross-section of the standard size, but at this time, the plating layer, which is softer than the base metal, also undergoes plastic deformation and bites into the irregularities on the surface of the steel pipe. The bond becomes even stronger, and the mesh layer itself becomes a dense and solid structure.

In addition, the unevenness on the surface of the plating layer itself is smoothed out, resulting in a smooth, glossy, beautiful silver matte surface. After sizing, the steel pipe is sent to a straightening device 47 to correct any bends, etc., then sent to a surface treatment device 49 for treatment, and then cut to an appropriate length by a cutting device 51 to create a beautiful silver pear. A steel pipe with a thick and durable plating layer is completed. As described above, according to the above configuration, (1) The forming machine 23 pulls the steel strip without providing a special strip drive device in the shot blasting device 9 or the like.

Therefore, when the steel strip passes through the shot blasting device 9, etc., it is always under constant tension, and even though it moves at high speed, twisting, vibration, etc. do not occur. In particular, in this state, the abrasive blast is applied by the shot blasting device 9, so that the surface of the steel strip is uniformly uneven with many irregularities having a depth of several microns to several tens of microns and a diameter of several microns to several hundred microns. It can be formed without any problem. Note that the uneven portion of the present invention is obtained by projecting a large number of particles of shot blast, so as shown in FIG. is obtained.

That is, in FIG. 4, A and b are the recesses received by the first particle, and c is the recess A received by the first particle.
, b are the recesses that received the second particle. 1st
The surface of the concave portion is hardened by the particles of the second time, and the depth of the concave portion by the second particle is thought to be smaller, and as a result, as shown in FIG. 4, a substantially uniform concavo-convex portion is formed. (
2) When removing the oxide film generated on the surface of steel pipes during welding, in the conventional technique of mechanically removing it using a rotating brush or the like, the oxide film removal effect was uneven due to wear of the brush or the like.

However, in the present invention, before cooling the steel pipe surface which has become high temperature due to the heat generated during welding, the temperature control device 27 works to adjust the temperature of the steel pipe surface to a temperature distribution according to the thickness of the oxide film. By adjusting the pickling speed in the pickling device 31 according to the thickness of the oxide film, the pickling device 3
In step 1, the surface of the steel pipe can be pickled in just the right amount for a certain period of time during which the steel pipe passes through. (3) In the shot blasting device 9, abrasive is projected onto the steel strip surface to uniformly distribute irregularities with depths of several microns to several tens of microns and diameters of several microns to hundreds of microns, and the surface area By increasing (1
) In the flux device 35, since the flux liquid can be applied thickly to the surface of the steel pipe, oxidation of the surface can be prevented for a long time even if it is exposed to high temperatures in subsequent steps.

(4) In the molten metal plating process, a pure plating metal layer can be plated thicker than an alloy layer.

This plating layer is not only bonded to the steel pipe surface by the alloy layer, but also has a strong physical and mechanical bond. Because it follows the uneven surface, it exhibits an optically beautiful satin texture. Next, an example of a steel pipe made with the above configuration is shown below: shot blasting conditions, plating conditions, molten zinc bath temperature: 450°C.

As a result of the above treatment, as shown in the photograph of FIG. 5b, irregularities with a depth of about 20 μm were formed on the surface of the steel strip, and the average plating thickness of the manufactured steel pipe was 33 μm.

For comparison, if a steel pipe is produced under the same conditions without shot blasting from a cold-rolled steel plate with no rust, the resulting steel pipe will look like the one shown in the photograph in Figure 5a, with no plating adhesion. The thickness is approximately 15μ, and the amount of plating deposited is much smaller than that of the steel pipe according to the present invention, and the effects of the present invention are clearly recognized.

In addition, in the arrangement shown in FIG. 1, if the sizing device 45 is moved between the water washing device 33 and the flux device 35 and arranged as shown in FIG. 2, the unevenness on the surface of the plating layer can be left as is. It is possible to produce molten metal plated steel pipes with a surface texture suitable for painting.

Furthermore, in the arrangement shown in FIG. 2, in place of the surface treatment device 49, an exterior device 53 such as a device for painting ceramics, paint, or other appropriate materials, or a device for coating plastics, etc. may be arranged as shown in FIG. For example, it is also possible to manufacture a steel pipe with a rough plating layer coated with ceramics, paint, or other suitable material or with a plastic coating. Furthermore, instead of molten metal plating, the surface of the steel pipe may be plated with a suitable metal or coated with plastic. In addition, although the above embodiments of the present invention have been described in the case of manufacturing from a steel band such as a hot rolled steel plate, it is also possible to manufacture from a finished steel plate, a galvanized steel plate, etc., or a band steel that has been shot blasted in advance. , is the most effective in this case.

[Brief explanation of drawings]

FIGS. 1 to 3 are explanatory diagrams showing an example of the manufacturing process of the present invention, FIG. 4 is an explanatory diagram showing an example of uneven portions of a steel pipe in the manufacturing process of the present invention, and FIG. FIG. 5b is a cross-sectional explanatory photograph of the surface of a steel pipe according to an embodiment of the present invention, and FIG. 6 is an enlarged photograph of the surface of the same. The parts that appear white are the convex parts, and the parts that appear black are the recesses, which indicates the almost uniformly distributed plating state of the present invention. Explanation of symbols representing main parts of the drawings: 1... Uncoiler 1, 9... Shot blasting device, 11a, 11b, 1
1c, 11d...Strip steel holding guide device, 13...Front seal room, 15...Blast room, 17a, 1
7b, 17c, 17/A, l7'B, l7/C,...
Abrasive projection device, 19...rear seal room,
21... Surface cleaning device, 23... Forming machine, 25... Welding machine, 27... Temperature control device, 31... Pickling device, 37... Drying preheating device, 3
9... Molten metal plating device, 43... Cooling device, 5
1... Cutting device, 53... Exterior device.

Claims (1)

[Claims] 1. A method for manufacturing steel pipes continuously coated with hot-dip metal, including (a) continuously rolling steel strips from an ein coiler;
(b) shot blasting the steel strip; and (c) continuously cold-rolling the steel strip into a tubular shape. (d) continuously seam welding the joints of the steel strip formed into a tubular shape; and (e) cooling the welded steel pipe and forming a thick weld bead with an oxide film on the surface of the steel pipe. (f) removing the oxide film from the surface of the steel pipe; (f) removing the oxide film from the surface of the steel pipe; (g) pickling the surface of the steel pipe continuously; (h) applying a plastic coating to the surface of the steel pipe; and (i) cutting the steel pipe to a predetermined size. Method of manufacturing plated steel pipes.