JPH02106341A - Manufacture of steel material with plastic coating - Google Patents

Abstract

PURPOSE:To make it applicable onto a steel material having a complicated shape by fusion bonding adhesive plastic powder to preheated steel material, and then scattering mixture powder having a different melt index to form an irregular uneven part on the surface of the corrosion protective plastic layer. CONSTITUTION:When adhesive plastic powder, corrosion protective plastic mixture powder are scattered to be fusion-bonded on a preheated steel material 1, a plastic layer is formed on the surface of the material 1. Accordingly, a corrosion protective plastic layer 4 is easily formed on the surface irrespective of the shape of the steel material. The mixture powder is composed of plastic powder containing different melt index (M.I). Thus, when the mixture powder is fusion-bonded, the powder having larger M.I. is melted and fusion-bonded to the periphery of the powder having smaller M.I., while the powder having smaller M.I. is not sufficiently melted to the center, or even if it is melted, it does not flow out. The powder having smaller M.I. is swelled in a raised state on the surface of the coating layer to form an irregular uneven part on the surface of the coating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a plastic-coated steel material mainly laid on the bottom of a river or a harbor.

(Prior Art) Steel pipes for piping laid on the bottom of rivers, ports, etc. are required to have corrosion resistance, so steel pipes coated with a plastic layer such as polyethylene are used. Such coated steel pipes are usually lined with concrete or mortar on the outer peripheral surface of the coating layer for the purpose of stable installation on the bottom of the water. For this reason, irregularities are formed on the outer peripheral surface of the coating layer to strengthen the adhesion of concrete and the like.

As a method for manufacturing such a plastic cladding tube with an uneven surface, as disclosed in Japanese Patent Application Laid-open No. 62-267132, heated and molten plastic is extruded from a gou that encapsulates a steel tube, and this is applied to the steel tube. Covered, 60~
There is a method in which after cooling to 150'C, a roughening process is applied by pressing a quality roll, and then cooling is performed to completely solidify the coating layer.

(Problems to be Solved by the Invention) However, in the above method, the manufacturing process becomes complicated because a process for forming the concave surface must be provided in the middle of the process of lining the plastic layer. Another problem is that it cannot be applied to irregularly shaped pipes such as curved pipes and T-shaped pipes.

The present invention has been made in view of such problems, and provides a method for manufacturing plastic-coated steel materials having surface irregularities that do not require surface treatment and can be applied to steel materials with complex shapes such as irregularly shaped pipes. With the goal.

(Means for Solving the Problems) The method for manufacturing plastic-coated steel materials of the present invention, which has been made to achieve the above object, involves spraying adhesive plastic powder onto a preheated steel material and fusing it, and then reducing the melt index. The structure of the invention is to scatter and fuse mixed powders of different anticorrosive plastics to form irregular irregularities on the surface of the anticorrosive plastic layer in which the plastic powder particles with the smaller melt index are raised. It is something.

(Function) According to the manufacturing method of the present invention, a mixed powder of adhesive plastic powder and anti-corrosion plastic is sprinkled on preheated steel material.
Since the plastic layer is formed on the surface of the steel material simply by fusing, the anti-corrosion plastic layer can be easily formed on the surface of the steel material regardless of its shape.

In addition, the mixed powder has a melt index (hereinafter referred to as M,
It is abbreviated as I. ), when the mixed powder is fused, the M
, 1. The larger one is M, 1. While it melts and fuses around small objects, M,! Powder particles with a small value of 33 M or 1.0 do not fully melt to the center, or even if they do, they do not flow out, and the powder particles with a small size of 33 M or 1.0 bulge out on the surface of the coating layer. , irregular irregularities are formed on the surface of the coating layer.

(Example) Next, an example of the present invention will be described based on the drawings. 1st
The figure shows a cross-sectional view of a polyethylene-coated steel pipe according to an embodiment, and the surface is irregularly uneven with an adhesive plastic layer 5 made of an epoxy primer layer 2 and an adhesive polyethylene layer 3 on the outer peripheral surface of the steel pipe 1. Corrosion-preventing polyethylene layers 4 are laminated. Hereinafter, each coating layer 2.3.4 will be explained together with its formation process with reference to FIG.

The steel pipe 1 is subjected to John blasting or sandblasting as a pretreatment to remove the oxide film and rust on the surface. The degree of surface finishing by blasting is preferably Sa 2.5 or higher according to the Swedish standard SIS.

The steel pipe 1 is normally fed in the axial direction while being rotated, but before feeding, the entire length or a necessary portion of the steel pipe 1 is first preheated by the preheater 11. The preheating temperature of the steel pipe 1 is 200 to 290°C (preferably 250 to 270°C) on the surface of the steel pipe.
) is better. If it is less than 200°C, there is insufficient heat to melt and fuse the various synthetic resin powders described below, while if it exceeds 290°C, the epoxy primer layer may be thermally decomposed, which is not preferable. In addition, the preheating temperature is 2
If the temperature is as low as about 00°C, the amount of heat may be replenished by performing intermediate heating after dispersing the epoxy synthetic resin powder for forming the primer.

The intermediate heating temperature is also optimally set to 250 to 270°C as described above.

After the steel pipe 1 is preheated, epoxy synthetic resin powder 12 for forming a brimer is sprinkled on its surface and melted and fused by the heat retained in the steel pipe 1 to form a film with a thickness of 50 to 200 tII11.
A primer layer 2 of about 100 mL is formed. The epoxy synthetic resin used to form the powder is preferably one to which a phenolic curing agent having a high decomposition temperature is added in consideration of high temperature application. The average particle size of the epoxy synthetic resin powder is 100
~150 μm is preferable. If the diameter is less than 100 μm, the powder tends to scatter and workability is difficult, while if it exceeds 150 μm, the fluidity during melting is poor and it is difficult to form a smooth surface. As a means for spraying and applying powder, it is appropriate to use an electrostatic powder coating device because the powder particle size is relatively small. In FIG. 2, 15 indicates a powder jetting nozzle of the same device.

Next, adhesive polyethylene powder 13 is sprinkled on the steel pipe 1 coated with the epoxy primer layer in a molten state, and is melted and fused by the heat retained in the steel pipe, resulting in a film thickness of 100 to 500 μm.
An adhesive polyethylene layer 3 having a thickness of about m (usually 150 to 250 μm) is formed. As the adhesive polyethylene, one modified with a carboxyl acid anhydride can be exemplified, and the optimal number of functional groups is one per polyethylene molecule. As for mechanical properties, gate, 1. -4 to 6, a tensile strength at break of 200 kg/d, a tensile elongation of 850%, and a density of 0.925 g/- is optimal. powder particle size,
Suitable examples of the dispersing means are the same as those for the epoxy synthetic resin powder.

The adhesive polyethylene layer 3 also has adhesion (fusion) properties to the steel pipe 1, but the adhesiveness and adhesion of the epoxy primer layer 2 to the steel pipe 1 are extremely good. It has better adhesion to the primer layer 2 than to the steel pipe 1. Therefore, it is preferable that the adhesive plastic layer 5 has a two-layer structure consisting of an epoxy primer layer 2 and an adhesive polyethylene layer 3. Note that the epoxy primer layer 2 and the adhesive polyethylene layer 3 are not parts directly exposed to the outside, but act exclusively as adhesive media for the anticorrosive polyethylene layer 4, which will be described later, so they are less expensive than the anticorrosive polyethylene layer 4. An extremely thin layer is sufficient.

Next, anti-corrosion polyethylene powder 14 is sprinkled on the steel pipe 1 coated with the adhesive polyethylene layer 3 in a molten state, and the polyethylene powder 14 is melted and
Fusion bonding layer thickness of about 1.5M (preferably 2.5mm)
The above anticorrosive polyethylene layer 4 is formed. As anti-corrosion polyethylene, the adhesive polyethylene mentioned above is natural polyethylene (normal non-polar polyethylene,
It is supplied to the market at low cost. ) can be used because it fuses well with polyethylene. As the anticorrosion polyethylene powder 14, M, 1. A mixed powder of different polyethylene powders is used. M, 1. It is preferable to provide a difference of 2 or more. M in mixed powder, 1. As a combination of polyethylene powders with different values, low density polyethylene (LD-PE) powder and high density polyethylene (HD-PE)
PE) powder or vapor phase polyethylene (LLD/P
E, low density polyethylene obtained by gas phase polymerization reaction) and LD-PH can be exemplified.

Incidentally, polyethylene M, which has rigidity and impact resistance applicable to steel pipe coating, 1. is l(D-PE is 0°03
~1.0, LD-PE is 0.4-4, LLD-P
E is about 3 to 6. Among the above combinations, LLD
- A good combination of PE and LD-PR. LLD-P
This is because E has excellent ESCR (stress crack resistance) and fluidity, and easily fuses with LD/PE. The amount of polyethylene powder with small Ll in the mixed powder is 20 to 5
0-t% is suitable. If it is less than 20%, there will be less unevenness,
This is because if it exceeds 50%, the fusion properties will be impaired.

Since polyethylene deteriorates due to ultraviolet rays and loses its weather resistance, anti-corrosion polyethylene powder is made by adding carbon black (C, B,) to polyethylene powder (both high and low M, 1). It is preferable to use a mixture of about 3 wt%. In addition, antioxidants, colorants,
Additives commonly used in the plastics industry, such as ultraviolet absorbers, can be added as appropriate to the extent that they do not impair the physical properties and moldability of polyethylene. Incidentally, when adding and mixing C and B, it is preferable to use an olefin dispersant (addition amount 1 to 3 wt%) in combination and mix for about 3 to 5 minutes with a water-cooled super mixer.

The polyethylene powder particle size of the anticorrosive polyethylene powder (including those to which C, B, dispersants, antioxidants, etc. are added and mixed as necessary) is such that the layer thickness of the anticorrosive polyethylene layer is large; In addition, in order to form moderate unevenness, the average particle size is 3.
It is preferable to use one with a diameter of 00 to 400 μm. As for the dispersion means, since the particle size of the powder is large and it is easy to spread, not only an electrostatic powder coating device but also a free fall dispersion method (eg, trough method) is sufficiently practical.

The steel pipe 1 coated with the anti-corrosion polyethylene layer 4 is sent to a post-heating device 16, where M,!
, sufficiently melts polyethylene powder with high .

The heating temperature is preferably 200 to 270°C, and the heating time is M.
I.

Keep it to a level that does not cause significant deformation of items with low temperatures. L
In the case of a combination of LD-PE and LD-PR,
Approximately 240°C x 10 minutes to 200°C x 20 minutes is sufficient.

Even with this degree of heating, if anti-corrosion polyethylene powder of 300 to 400 μm is used, the
Irregularities of μIll to IM are formed. As the heating means, induction heating, far-infrared heater, etc. can be used.

Thereafter, each coating layer is cooled and solidified by the cooling device 17. For cooling, since overcuring is likely to occur with rapid cooling using only water cooling, it is desirable to use air cooling in combination, and it is preferable to cool the material to 150 to 180° C. by air cooling before water cooling.

The steel material coated with the anticorrosive polyethylene layer is not limited to the steel pipes described above, but may also be steel materials with complicated shapes such as sheet piles and curved pipes. Further, the covering portion may be not only the entire length of the steel material but also a partial portion thereof.

Further, the adhesive plastic layer does not necessarily include an epoxy primer layer, and may be formed only from adhesive polyethylene powder. Further, the anti-corrosion plastic layer is not limited to polyethylene as in the embodiments, but may be formed using other plastic powders.

(Effects of the Invention) As explained above, according to the method for manufacturing plastic-coated steel materials of the present invention, the plastic layer is coated by dispersing and fusing the plastic powder as desired, so that the steel material to be coated is coated with the plastic layer. It can be applied regardless of the shape. In addition, anti-corrosion plastic powder is M, 1. Since it is composed of a mixed powder of different plastic powders, it is possible to create a difference in the melting state. The surface of the coating layer has an uneven surface with raised small plastic powder particles.
It can be formed simultaneously with the plastic powder melting process, offering extremely high productivity.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of a polyethylene-coated steel pipe according to an example, and FIG. 2 is an explanatory diagram of lining procedures. 1... Steel material, 4... Anticorrosion polyethylene layer, 5...
・Plastic layer for adhesion.

Claims (1)

[Claims] (1) After spraying adhesive plastic powder on the preheated steel material and fusing it, a mixed powder of anti-corrosion plastics with different melt indexes is spread and fusing, and the surface of the anti-corrosion plastic layer has a small melt index. A method for manufacturing a plastic-coated steel material, characterized in that the plastic powder particles on one side form raised irregular irregularities.