JP4557158B2 - Manufacturing method of polyolefin resin-coated steel pipe with excellent surface appearance - Google Patents
Manufacturing method of polyolefin resin-coated steel pipe with excellent surface appearance Download PDFInfo
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- JP4557158B2 JP4557158B2 JP2005064051A JP2005064051A JP4557158B2 JP 4557158 B2 JP4557158 B2 JP 4557158B2 JP 2005064051 A JP2005064051 A JP 2005064051A JP 2005064051 A JP2005064051 A JP 2005064051A JP 4557158 B2 JP4557158 B2 JP 4557158B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 55
- 239000010959 steel Substances 0.000 title claims description 55
- 229920005672 polyolefin resin Polymers 0.000 title claims description 47
- 238000004519 manufacturing process Methods 0.000 title claims description 9
- 229920005989 resin Polymers 0.000 claims description 54
- 239000011347 resin Substances 0.000 claims description 54
- 238000001816 cooling Methods 0.000 claims description 52
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 49
- 238000000576 coating method Methods 0.000 claims description 27
- 239000011248 coating agent Substances 0.000 claims description 26
- 238000002844 melting Methods 0.000 claims description 21
- 230000008018 melting Effects 0.000 claims description 21
- 238000004804 winding Methods 0.000 claims description 4
- 238000000034 method Methods 0.000 description 15
- -1 polypropylene Polymers 0.000 description 8
- 239000010410 layer Substances 0.000 description 7
- 238000005507 spraying Methods 0.000 description 6
- 239000004743 Polypropylene Substances 0.000 description 5
- 239000012790 adhesive layer Substances 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 229920001155 polypropylene Polymers 0.000 description 5
- 239000000843 powder Substances 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 4
- 239000004698 Polyethylene Substances 0.000 description 3
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical compound [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 238000007765 extrusion coating Methods 0.000 description 3
- 229920006015 heat resistant resin Polymers 0.000 description 3
- 230000006698 induction Effects 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 229920001083 polybutene Polymers 0.000 description 3
- 229920000573 polyethylene Polymers 0.000 description 3
- 229920000306 polymethylpentene Polymers 0.000 description 3
- 239000011116 polymethylpentene Substances 0.000 description 3
- 239000007921 spray Substances 0.000 description 3
- 239000000498 cooling water Substances 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 229920001903 high density polyethylene Polymers 0.000 description 2
- 239000004700 high-density polyethylene Substances 0.000 description 2
- 229920013716 polyethylene resin Polymers 0.000 description 2
- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 239000004593 Epoxy Substances 0.000 description 1
- CERQOIWHTDAKMF-UHFFFAOYSA-N Methacrylic acid Chemical compound CC(=C)C(O)=O CERQOIWHTDAKMF-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- OFOBLEOULBTSOW-UHFFFAOYSA-N Propanedioic acid Natural products OC(=O)CC(O)=O OFOBLEOULBTSOW-UHFFFAOYSA-N 0.000 description 1
- 150000008065 acid anhydrides Chemical class 0.000 description 1
- 238000010306 acid treatment Methods 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 150000001735 carboxylic acids Chemical class 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005238 degreasing Methods 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- 238000007373 indentation Methods 0.000 description 1
- 229920000554 ionomer Polymers 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 238000010409 ironing Methods 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 229920000092 linear low density polyethylene Polymers 0.000 description 1
- 239000004707 linear low-density polyethylene Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 229920001684 low density polyethylene Polymers 0.000 description 1
- 239000004702 low-density polyethylene Substances 0.000 description 1
- VZCYOOQTPOCHFL-UPHRSURJSA-N maleic acid Chemical compound OC(=O)\C=C/C(O)=O VZCYOOQTPOCHFL-UPHRSURJSA-N 0.000 description 1
- 239000011976 maleic acid Substances 0.000 description 1
- 229920001179 medium density polyethylene Polymers 0.000 description 1
- 239000004701 medium-density polyethylene Substances 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 229920005629 polypropylene homopolymer Polymers 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 238000009958 sewing Methods 0.000 description 1
- VZCYOOQTPOCHFL-UHFFFAOYSA-N trans-butenedioic acid Natural products OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 description 1
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- Lining Or Joining Of Plastics Or The Like (AREA)
Description
本発明はポリオレフィン樹脂被覆鋼管の製造方法に関するものである。より詳しくは、ポリオレフィン樹脂被覆表面に凹凸などの外観不良の発生がない、表面外観に優れたポリオレフィン樹脂被覆鋼管の製造方法に関する。 The present invention relates to a method for producing a polyolefin resin-coated steel pipe. More specifically, the present invention relates to a method for producing a polyolefin resin-coated steel pipe having an excellent surface appearance and having no appearance defects such as irregularities on the surface of the polyolefin resin coating.
ポリオレフィン樹脂被覆鋼管の製造方法としては、鋼管の回転方向に対し斜めに配置された搬送ロール（スキューロール）により、加熱した鋼管を回転させつつ管長方向に前進させながら、鋼管の外面に溶融状態のポリオレフィン樹脂シートを連続的に螺旋状に巻き付けて、被覆する方法が知られている。 As a method for producing a polyolefin resin-coated steel pipe, a transport roll (skew roll) disposed obliquely with respect to the rotation direction of the steel pipe is advanced in the pipe length direction while rotating the heated steel pipe, while being melted on the outer surface of the steel pipe. A method is known in which a polyolefin resin sheet is continuously wound in a spiral shape and coated.
近年、長期の防食性能を重視する考えから、ポリオレフィン樹脂被覆の下地プライマーとして、従来の液状プライマーから粉体プライマーを使用する場合が増えてきている。その際には、鋼管の予熱温度を、被覆するポリオレフィン樹脂の融点をはるかに超えた、２００℃以上の高温にすることが必要となる場合があり、より高温に対応した被覆技術が望まれている。 In recent years, from the viewpoint of emphasizing long-term anticorrosion performance, the use of a powder primer from a conventional liquid primer as an undercoat primer for polyolefin resin coating is increasing. In that case, it may be necessary to set the preheating temperature of the steel pipe to a high temperature of 200 ° C. or more, far exceeding the melting point of the polyolefin resin to be coated, and a coating technique corresponding to a higher temperature is desired. Yes.
このように、高温の予熱温度の場合であっても、樹脂被覆後、搬送ロールによる被覆樹脂のつぶれを防止する目的から、樹脂を急速に冷却する必要がある。冷却方法として、通常は円周方向に配置されたノズルから噴出された水流により冷却する方法が一般的であるが、冷却後の樹脂表面に不規則な凹凸模様が形成され、外観上問題となる場合があった。 Thus, even in the case of a high preheating temperature, it is necessary to rapidly cool the resin after the resin coating in order to prevent the coating resin from being crushed by the transport roll. As a cooling method, a method of cooling by a water flow ejected from a nozzle arranged in a circumferential direction is generally used, but an irregular uneven pattern is formed on the resin surface after cooling, which causes a problem in appearance. There was a case.
この解決手段として、樹脂被覆直後に耐熱樹脂シートで被覆鋼管を覆い、この状態で外面から水冷を行う方法が開示されている（特許文献１参照）。 As a solution to this problem, a method is disclosed in which a coated steel pipe is covered with a heat-resistant resin sheet immediately after resin coating, and water cooling is performed from the outer surface in this state (see Patent Document 1).
また、溶融したポリオレフィン帯状体を被覆した後、被覆表面に水の微粒子を噴霧しながら、圧縮空気を吹きつけて被覆表面に付着した水滴を吹き飛ばす方法も開示されている（特許文献２参照）。 In addition, a method is also disclosed in which, after coating a melted polyolefin strip, spraying compressed air and blowing water droplets adhering to the coating surface while spraying fine water particles on the coating surface (see Patent Document 2).
しかしながら、樹脂被覆直後に耐熱樹脂シートで覆う方法では耐熱樹脂シートの巻き付け工程が必要なため、被覆スピードが速い場合には適しておらず、また、連続生産には不向きである。 However, the method of covering with a heat-resistant resin sheet immediately after resin coating requires a step of winding the heat-resistant resin sheet, and thus is not suitable when the coating speed is high, and is not suitable for continuous production.
また、水の微粒子を噴霧しながら圧縮空気を吹き付ける方法では、水の粒子を吹き付けたのち、圧縮空気で完全に水滴を吹き飛ばす事は困難であった。さらに、水の粒子により冷却しただけでは、特に高温の鋼管予熱を必要とする場合は、冷却能力が不十分であり、その後の圧縮空気による冷却では、表面が復熱、再溶融し、再度水冷した際に凹凸が発生するなど、充分に凹凸の課題を防止することは困難であった。 Further, in the method of spraying compressed air while spraying fine water particles, it is difficult to completely blow off water droplets with compressed air after spraying water particles. In addition, cooling with water particles alone does not provide sufficient cooling capacity, particularly when high-temperature steel pipe preheating is required, and subsequent cooling with compressed air causes the surface to reheat, remelt, It was difficult to sufficiently prevent the unevenness problem, such as unevenness being generated.
従って、高温の予熱温度に対応した凹凸発生防止方法として、良好なものはこれまでなかったのが実態であった。 Therefore, in reality, there has been no good method for preventing the occurrence of unevenness corresponding to a high preheating temperature.
本発明の目的は、防食性能に優れた粉体プライマーに要求される、高温の鋼管予熱を行なった場合においても、冷却後の樹脂表面の凹凸発生を防止することが可能な表面外観に優れたポリオレフィン樹脂被覆鋼管の製造方法を提供することにある。 The object of the present invention is to provide an excellent surface appearance that can prevent the occurrence of unevenness on the resin surface after cooling, even when preheating a high-temperature steel pipe, which is required for a powder primer having excellent anticorrosion performance. An object of the present invention is to provide a method for producing a polyolefin resin-coated steel pipe.
本発明者らは、鋭意検討を行った結果、冷却後の樹脂表面に凹凸の生成する原因が、溶融状態の樹脂に、局部的に付着した水滴により、樹脂が局部的に冷却・結晶化することにあることを見出した。そこで、樹脂表面をラミナー水冷し該樹脂表面全体を連続した水膜で覆って融点未満の温度まで冷却し、かつ一旦冷却した後、樹脂表面が融点以上に復熱しないようにさらに連続的に冷却することで、樹脂表面の凹凸発生が顕著に軽減され、表面外観に優れたポリオレフィン樹脂被覆鋼管が製造できることを見出し、本発明を完成させるに至った。 As a result of intensive studies, the present inventors have found that the resin is locally cooled and crystallized due to the water droplets locally attached to the molten resin due to the formation of irregularities on the resin surface after cooling. I found out that there was. Therefore, the resin surface is cooled by laminar water, the entire resin surface is covered with a continuous water film, cooled to a temperature below the melting point, and once cooled, further continuously cooled so that the resin surface does not reheat above the melting point. As a result, it was found that the occurrence of unevenness on the resin surface was remarkably reduced and a polyolefin resin-coated steel pipe excellent in surface appearance could be produced, and the present invention was completed.
すなわち、本発明は、回転している鋼管表面に、溶融状態にあるシート状ポリオレフィン樹脂を螺旋状に巻き付けながら被覆してなるポリオレフィン樹脂被覆鋼管の製造方法において、該樹脂被覆後の冷却工程で、樹脂表面をラミナー水冷し該樹脂表面全体を連続した水膜で覆って該樹脂の融点未満の温度まで冷却し、さらに前記ラミナー水冷後も、樹脂表面温度を融点以上に上昇させることなく冷却を継続するとともに、前記ラミナー水冷が円筒ノズルを配置し、かつ前記円筒ノズルから気泡を含まないように層流の水流を吐出して行うことを特徴とする表面外観に優れたポリオレフィン樹脂被覆鋼管の製造方法に関するものである。 That is, the present invention is a method for producing a polyolefin resin-coated steel pipe formed by coating a rotating steel pipe surface while spirally winding a sheet-like polyolefin resin in a molten state, in the cooling step after the resin coating, The resin surface is cooled with laminar water, and the entire resin surface is covered with a continuous water film to cool to a temperature below the melting point of the resin. Further, after the laminar water cooling, cooling is continued without increasing the resin surface temperature above the melting point. And the laminar water cooling is performed by disposing a cylindrical nozzle and discharging a laminar water flow so as not to include bubbles from the cylindrical nozzle. It is about.
本発明により、鋼管の外面に溶融状態のポリオレフィン樹脂シートを連続的に螺旋状に巻付けていくポリオレフィン樹脂被覆方法において、被覆表面に凹凸のない表面外観の優れたポリオレフィン樹脂被覆鋼管を得ることができる。 According to the present invention, in a polyolefin resin coating method in which a molten polyolefin resin sheet is continuously spirally wound around the outer surface of a steel pipe, a polyolefin resin-coated steel pipe having an excellent surface appearance with no unevenness on the coated surface can be obtained. it can.
本発明で用いられる鋼管の種類や寸法は特に制限されないが、例えば、電縫管、スパイラル鋼管、ＵＯＥ鋼管、メッキ管が挙げられる。 Although the kind and dimension of the steel pipe used by this invention are not restrict | limited in particular, For example, an electric sewing pipe, a spiral steel pipe, a UOE steel pipe, and a plated pipe are mentioned.
まず、必要により、鋼管外面にアルカリ脱脂・酸性処理またはブラスト処理などの除錆処理を施し、表面を清浄化する。次に優れた防食性を付与するために、鋼管の表面にクロメート処理、燐酸塩処理等の下地処理をほどこしてもよい。さらにその上層に、ポリオレフィン樹脂との接着性を高めるために、エポキシ樹脂等のプライマー層を設けても良い。プライマー層形成前のプライマーの形態としては、粉体プライマー、液状プライマー等があげられる。 First, if necessary, the outer surface of the steel pipe is subjected to rust removal treatment such as alkali degreasing / acid treatment or blast treatment to clean the surface. Next, in order to impart excellent corrosion resistance, the surface of the steel pipe may be subjected to a ground treatment such as chromate treatment or phosphate treatment. Further, a primer layer such as an epoxy resin may be provided on the upper layer in order to enhance the adhesion with the polyolefin resin. Examples of the form of the primer before forming the primer layer include a powder primer and a liquid primer.
プライマー層を形成させる場合には、通常、鋼管を１００℃〜２５０℃程度の温度に加熱する。鋼管の加熱方式としては、高周波誘導加熱、遠赤外加熱、ガス直火加熱などの方法が挙げられる。プライマー層の形成方法としてはスプレー塗装、ロール塗布、刷毛塗り、しごき塗布などの方法が用いられる。 When forming the primer layer, the steel pipe is usually heated to a temperature of about 100 ° C to 250 ° C. Examples of the heating method for the steel pipe include high-frequency induction heating, far-infrared heating, and gas direct-fire heating. As a method for forming the primer layer, methods such as spray coating, roll coating, brush coating, and ironing are used.
本発明の鋼管はポリオレフィン樹脂を被覆するものであるが、ポリオレフィン樹脂は一般に接着性が弱いため接着層を設けることが好ましい。接着層として好ましいものは変性ポリオレフィン樹脂やアイオノマー樹脂などである。変性ポリオレフィン樹脂としては、ポリオレフィン樹脂層に用いられるポリオレフィン樹脂をマレイン酸、アクリル酸、メタクリル酸などの不飽和カルボン酸もしくはその酸無水物で変性したものなどを用いることができる。接着層の厚みは０．１〜２ｍｍ程度、好ましくは０．３〜１．０ｍｍ程度が適当である。 Although the steel pipe of the present invention covers a polyolefin resin, it is preferable to provide an adhesive layer because the polyolefin resin generally has poor adhesion. Preferred examples of the adhesive layer include modified polyolefin resins and ionomer resins. As the modified polyolefin resin, a polyolefin resin used for the polyolefin resin layer may be modified with an unsaturated carboxylic acid such as maleic acid, acrylic acid or methacrylic acid or an acid anhydride thereof. The thickness of the adhesive layer is about 0.1 to 2 mm, preferably about 0.3 to 1.0 mm.
ポリオレフィン樹脂被覆に用いられるポリオレフィン樹脂としては、低密度ポリエチレン、中密度ポリエチレン、高密度ポリエチレン、直鎖状低密度ポリエチレン、ホモポリプロピレン、ランダムポリプロピレン、ブロックポリプロピレン、ポリブテン、ポリメチルペンテンなどの公知のポリオレフィン樹脂を用いることができる。ポリオレフィン樹脂の融点は、特に制限されないが、ポリエチレンの場合１０２〜１３７℃程度、通常押出被覆で使用する範囲は１１０〜１２５℃程度、ポリプロピレンの場合１３０〜１７０℃程度、通常押出被覆で使用する範囲は１４０〜１６５℃程度、ポリブテンの場合１１５〜１３５℃程度、通常押出被覆で使用する範囲は１２０〜１３０℃程度、ポリメチルペンテンの場合２２０〜２４０℃程度である。このポリオレフィン樹脂被覆の厚みは１〜５ｍｍ程度、通常１．５〜３．５ｍｍ程度である。 Known polyolefin resins such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, homopolypropylene, random polypropylene, block polypropylene, polybutene, polymethylpentene, etc. Can be used. The melting point of the polyolefin resin is not particularly limited, but in the case of polyethylene, it is about 102 to 137 ° C., and the range usually used for extrusion coating is about 110 to 125 ° C., in the case of polypropylene, about 130 to 170 ° C., the range usually used for extrusion coating. Is about 140 to 165 ° C, in the case of polybutene is about 115 to 135 ° C, and the range normally used for extrusion coating is about 120 to 130 ° C, and in the case of polymethylpentene is about 220 to 240 ° C. The thickness of the polyolefin resin coating is about 1 to 5 mm, usually about 1.5 to 3.5 mm.
本発明の方法においては、ポリオレフィン樹脂を加熱溶融してシート状に押出す。ポリオレフィン樹脂の溶融温度は融点より１０〜１６０℃程度高く、好ましくはポリエチレン、ポリブテンの場合６０〜１４０℃程度、ポリプロピレンの場合５０〜１１０℃程度高くする。ポリメチルペンテンの場合は４０〜７０℃程度高くする。シート状に押出すダイは公知のものでよく、Ｔダイ等を利用できる。シートの幅は特に制限されないが３５０〜５５０ｍｍ程度である。 In the method of the present invention, a polyolefin resin is heated and melted and extruded into a sheet shape. The melting temperature of the polyolefin resin is about 10 to 160 ° C. higher than the melting point, preferably about 60 to 140 ° C. for polyethylene and polybutene, and about 50 to 110 ° C. for polypropylene. In the case of polymethylpentene, the temperature is increased by about 40 to 70 ° C. The die to be extruded into a sheet shape may be a known one, and a T die or the like can be used. The width of the sheet is not particularly limited, but is about 350 to 550 mm.
接着層を設ける場合には、これをポリオレフィン樹脂に先立って鋼管に被覆してもよいが、ポリオレフィン樹脂を共押出しするのが簡便である。 When the adhesive layer is provided, the steel pipe may be coated prior to the polyolefin resin, but it is easy to co-extrude the polyolefin resin.
ダイから押出された溶融状態のポリオレフィン樹脂シートを必要により下地処理が施された鋼管の表面に螺旋状に巻回していく。 A polyolefin resin sheet in a molten state extruded from a die is spirally wound around the surface of a steel pipe that has been subjected to a base treatment if necessary.
その際の鋼管の温度は、ポリオレフィン樹脂がポリエチレン樹脂の場合、樹脂の融点より０〜１３０℃程度高い温度であり、ポリプロピレン樹脂の場合、０〜１００℃程度高い温度である。 In this case, the temperature of the steel pipe is about 0 to 130 ° C. higher than the melting point of the resin when the polyolefin resin is polyethylene resin, and about 0 to 100 ° C. when the polyolefin resin is polypropylene resin.
そこで、次いでこのポリオレフィン樹脂被覆鋼管を冷却するが、本発明ではまずラミナー水冷し、その際に形成される水膜で樹脂表面全体を覆って冷却を行うところに特徴がある。
ラミナー水冷（ラミナー冷却）とは、ミスト冷却やスプレー冷却とは異なり、棒状に吐出する水流による冷却のことである。この吐出された水流が樹脂表面に接触して水膜を形成する。
本発明では樹脂表面全体を連続した水膜で覆って該樹脂の融点未満の温度まで冷却することがとくに重要である。
樹脂表面の円周方向の全周にわたって、すき間（水膜で覆われていない部分）が生じることがないよう連続した水膜で覆うことにより、樹脂の局部的な冷却、結晶化を抑制し、樹脂表面の凹凸発生を回避することが可能となる。樹脂表面の一部に水膜で覆われていない部分が生じると、その部分に凹凸模様が形成されやすくなる。
通常、樹脂被覆鋼管を水冷する際には、該鋼管を回転させ、かつ前進させながら冷却する。本発明においては、ラミナー水冷を開始してから、樹脂表面温度が該樹脂の融点未満の温度に下がるまでの間、とぎれることのない水膜で覆われた状態を維持できるように冷却できればよい。
Then, this polyolefin resin-coated steel pipe is then cooled. In the present invention, laminar water cooling is first performed, and the entire resin surface is covered with a water film formed at that time to perform cooling.
Laminar water cooling (laminar cooling), unlike mist cooling or spray cooling, is cooling by a water flow discharged in a rod shape. This discharged water flow contacts the resin surface to form a water film.
In the present invention, it is particularly important that the entire resin surface is covered with a continuous water film and cooled to a temperature below the melting point of the resin.
By covering with a continuous water film so that there is no gap (portion not covered with a water film) over the entire circumference in the circumferential direction of the resin surface, local cooling and crystallization of the resin are suppressed, It is possible to avoid the occurrence of unevenness on the resin surface. When a portion that is not covered with a water film is formed on a part of the resin surface, a concavo-convex pattern is easily formed on the portion.
Usually, when water-cooling a resin-coated steel pipe, the steel pipe is cooled while being rotated and advanced. In the present invention, it is only necessary to be able to maintain the state of being covered with an uninterrupted water film from the start of laminar water cooling until the resin surface temperature falls below the melting point of the resin.
このラミナー冷却には、通常円筒ノズルから気泡を含まないように層流の水流を吐出して行う。円筒ノズル（開口形状は円状が好ましい。）は個別に設ける他、円状の管の内側に吐出口（開口形状は円状が好ましい。）を略等間隔に設けたものであってもよい。この管を螺旋状に形成することもできる。吐出口の間隔を狭め、かつ吐出口と樹脂表面との間隔を狭めて、水膜が途切れないようにすることが重要である。
鋼管の下面側の樹脂表面においても、水膜が途切れることなく付着した状態を維持するためには、下面側にも円筒ノズルを配置するとともに、樹脂被覆鋼管の外径、回転速度、送り速度等に応じて円筒ノズルの数及び間隔、吐出口と樹脂表面の間隔、冷却水量、吐出圧等を適宜、設定すればよい。
この点で、円筒ノズルの吐出口間の間隔は鋼管外径、冷却水量等により異なるが、管周方向に２００〜７００ｍｍ程度、好ましくは３００〜５００ｍｍ程度、吐出口とポリオレフィン樹脂表面との間隔は５０〜４００ｍｍ程度、好ましくは５０〜２００ｍｍ程度とするのがよい。これによって、円筒ノズルから吐出される水が樹脂表面に均一に接触して水膜を形成し、均一な冷却を行うことができる。円筒ノズルの数は通常、円周方向に８〜１２個程度になる。
This laminar cooling is usually performed by discharging a laminar water flow from a cylindrical nozzle so as not to include bubbles. The cylindrical nozzles (opening shape is preferably circular) may be provided separately, or discharge ports (opening shape is preferably circular) may be provided inside the circular tube at substantially equal intervals. . The tube can also be formed in a spiral shape. It is important to narrow the interval between the discharge ports and the interval between the discharge port and the resin surface so that the water film is not interrupted.
In order to keep the water film attached without interruption even on the resin surface on the lower surface side of the steel pipe, a cylindrical nozzle is also arranged on the lower surface side, and the outer diameter, rotation speed, feed speed, etc. of the resin-coated steel pipe The number and interval of the cylindrical nozzles, the interval between the discharge port and the resin surface, the cooling water amount, the discharge pressure, and the like may be set as appropriate.
In this respect, although the interval between the discharge ports of the cylindrical nozzle varies depending on the outer diameter of the steel pipe, the amount of cooling water, etc., the interval between the discharge port and the polyolefin resin surface is about 200 to 700 mm, preferably about 300 to 500 mm in the pipe circumferential direction. The thickness is about 50 to 400 mm, preferably about 50 to 200 mm. As a result, water discharged from the cylindrical nozzle uniformly contacts the resin surface to form a water film, and uniform cooling can be performed. The number of cylindrical nozzles is usually about 8 to 12 in the circumferential direction.
吐出する水の温度は、特別の目的がなければ、使用水そのままでよく、常温〜５０℃程度である。 If there is no special purpose, the temperature of the water to be discharged may be used as it is, and is about room temperature to about 50 ° C.
ラミナー冷却による水冷はポリオレフィン樹脂表面温度が該樹脂の融点未満、好ましくは軟化点以下になるまで行う。このために、水膜が少なくとも１５秒間、好ましくは１５〜６０秒間供給され続けるだけの水膜が形成される領域を確保することが好ましい。 Water cooling by laminar cooling is performed until the surface temperature of the polyolefin resin is lower than the melting point of the resin, preferably below the softening point. For this reason, it is preferable to secure a region where a water film is formed so that the water film is continuously supplied for at least 15 seconds, preferably 15 to 60 seconds.
表面の冷却速度は樹脂被覆後、最初の搬送ロールに樹脂表面が接触するまでの間に、樹脂表面の温度が確実に融点未満に下がる冷却速度であることが必須であるが、通常１０〜１００℃/ｓｅｃの範囲となる。 It is essential that the cooling rate of the surface is a cooling rate at which the temperature of the resin surface surely falls below the melting point before the resin surface comes into contact with the first transport roll after resin coating, but usually 10 to 100. It is in the range of ° C / sec.
また、一旦ラミナー冷却を行った後、水冷を中止するとすぐに鋼管のもつ熱が樹脂表面に伝わり樹脂表面が融点以上に復熱する。この場合、再び水冷すると前記の冷却方法によらなければ凹凸が発生する。したがって、ラミナー冷却により樹脂温度を融点未満に下げたあとは、引き続き公知の冷却方法により、後に冷却を中止しても融点まで復熱しなくなるまで冷却を継続する。通常は、鋼管温度が環境温度に下がるまで冷却を継続するのがよい。 Further, once the laminar cooling is performed, the water of the steel pipe is transferred to the resin surface as soon as the water cooling is stopped, and the resin surface is reheated to the melting point or higher. In this case, when water cooling is performed again, unevenness occurs unless the cooling method is used. Therefore, after the resin temperature is lowered below the melting point by laminar cooling, the cooling is continued by a known cooling method until the heat is not restored to the melting point even if the cooling is stopped later. Normally, cooling should be continued until the steel pipe temperature falls to the ambient temperature.
この公知の冷却方法としては、通常はノズルからの水流であり、これは表面の復熱を防止しうる方法であれば、方式やノズル配置等に制約はない。スプレー冷却による水冷でもよい。また鋼管の温度がその後に冷却を中止しても樹脂の融点以上に復熱しなくなる温度以下に下がった後は、空気等による放冷であっても問題はない。 This known cooling method is usually a water flow from the nozzle, and there is no restriction on the method and nozzle arrangement as long as it is a method capable of preventing the surface reheating. Water cooling by spray cooling may be used. Further, there is no problem even if the steel pipe is cooled by air or the like after the temperature of the steel pipe has dropped below the temperature at which it does not reheat above the melting point of the resin even if cooling is stopped.
［実施例１〜６、比較例１〜３］
ＪＩＳＧ−３４５７によるＳＴＰＹ４０、管長１２ｍ、外径９１４．４ｍｍ、管厚９ｍｍのＵＯＥ鋼管を使用し、その鋼管の外表面をグリットブラスト処理により清浄度をＳａ２．５以上とした。スキューロール上を回転させながら、搬送し、まず転写ロールを用いて、クロメート処理液を該鋼管表面に塗布した。塗布後、塗布面が次のスキューロールと接触するまでに、第１インダクションヒーターにより、鋼管温度を１００℃に昇温し、焼付けてクロメート層を形成した。次に、２３０℃まで鋼管温度を第２インダクションヒーターにより昇温し、エポキシ粉体塗料（密度１．４９、粒径２５０μｍ以下）を静電粉体塗装機により膜厚３５０〜４００μｍとなるように外面に塗装した。
[Examples 1-6, Comparative Examples 1-3]
A UOE steel pipe having STPY 40 according to JISG-3457, pipe length of 12 m, outer diameter of 914.4 mm, and pipe thickness of 9 mm was used, and the outer surface of the steel pipe was made to have a cleanness of Sa 2.5 or more by grit blasting. It was conveyed while rotating on the skew roll, and first, the chromate treatment liquid was applied to the surface of the steel pipe using a transfer roll. After coating, the steel pipe temperature was raised to 100 ° C. by a first induction heater until the coated surface contacted the next skew roll, and baked to form a chromate layer. Next, the steel pipe temperature is raised to 230 ° C. by the second induction heater, and the epoxy powder coating (density 1.49, particle size 250 μm or less) is made to have a film thickness of 350 to 400 μm by the electrostatic powder coating machine. Painted on the outside.
この鋼管に、図１に示すようにしてポリオレフィン樹脂を被覆した。ポリオレフィン樹脂と変性ポリオレフィン樹脂がそれぞれの押出機からＴダイを通して帯状に共押出しされ、図面右方に回転しながら進行している鋼管に螺旋状に巻付けられていく。変性ポリエチレン樹脂接着層には厚み０．２〜０．５ｍｍの無水マレイン酸変性ポリエチレン（融点１２１℃、ＭＦＲ１．０）を用い、ポリエチレン樹脂層には厚み３．０ｍｍの高密度ポリエチレン（密度０．９４３、融点１２４℃、ＭＦＲ０．２４）を用いた。こうしてポリオレフィン樹脂が被覆された鋼管のポリオレフィン樹脂被覆の表面温度は２２０〜２３０℃であった。 This steel pipe was coated with a polyolefin resin as shown in FIG. A polyolefin resin and a modified polyolefin resin are coextruded in a strip shape from each extruder through a T-die, and are spirally wound around a steel pipe that is advancing while rotating to the right in the drawing. Maleic anhydride-modified polyethylene (melting point 121 ° C., MFR 1.0) having a thickness of 0.2 to 0.5 mm is used for the modified polyethylene resin adhesive layer, and high-density polyethylene (density 0. 943, melting point 124 ° C., MFR 0.24). The surface temperature of the polyolefin resin coating of the steel pipe thus coated with the polyolefin resin was 220 to 230 ° C.
次に、この鋼管を、図１に示すように、円筒ノズルを円状に配置したその内側を通過させてラミナー水冷を行った。ノズルの吐出口間の間隔は管長方向に１００ｍｍ間隔で１〜３列とし、円周方向には略等間隔で４〜１０個配置した。そして吐出口と樹脂表面との間隔は２００ｍｍであった。
各実施例で用いたノズルの数は表１に示した。尚、帯状溶融樹脂シートの巻付位置（サポートロールの中心）とノズル（複数列の場合は最前列）との間の距離は約２５０ｃｍである。
Next, as shown in FIG. 1, this steel pipe was passed through the inside of which a cylindrical nozzle was arranged in a circular shape to perform laminar water cooling. The intervals between the discharge ports of the nozzles were 1 to 3 rows at 100 mm intervals in the tube length direction, and 4 to 10 nozzles were arranged at substantially equal intervals in the circumferential direction. The distance between the discharge port and the resin surface was 200 mm.
The number of nozzles used in each example is shown in Table 1. In addition, the distance between the winding position of the belt-shaped molten resin sheet (center of the support roll) and the nozzle (the front row in the case of a plurality of rows) is about 250 cm.
ラミナー水冷後は表１に記載の通りスプレー冷却又は空冷を行った。 After laminar water cooling, spray cooling or air cooling was performed as shown in Table 1.
こうして得られたポリオレフィン樹脂被覆鋼管の外観評価を次のようにして行った。 The appearance evaluation of the polyolefin resin-coated steel pipe thus obtained was performed as follows.
外観の評価
ポリオレフィン樹脂を被覆し、冷却した後の被覆樹脂表面外観を目視で確認し、凹凸の有無をしらべた。凹凸（微細なものも含む。）があるものは×、ないものは○として評価した。また、冷却が間に合わず、ロールによる圧痕による凹凸が発生したものについても×とした。
Appearance Evaluation After coating with a polyolefin resin and cooling, the appearance of the surface of the coating resin was visually confirmed to check for irregularities. Evaluation was made as x when there was unevenness (including fine ones) and ○ when there was no unevenness. Moreover, it was set as x also about what the unevenness | corrugation by the indentation by a roll generate | occur | produced in time for cooling.
上記の実験条件及び結果をまとめて表１に示す。 The above experimental conditions and results are summarized in Table 1.
本発明の製造方法で得られたポリオレフィン樹脂被覆鋼管は、ガス管、水道管、ラインパイプ、鋼管杭など防食鋼管に使用される。 The polyolefin resin-coated steel pipe obtained by the production method of the present invention is used for anticorrosion steel pipes such as gas pipes, water pipes, line pipes and steel pipe piles.
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| JPH03197020A (en) * | 1989-12-26 | 1991-08-28 | Mitsubishi Materials Corp | Device for cooling resin-coated pipe |
| JPH0911306A (en) * | 1995-06-29 | 1997-01-14 | Sumitomo Metal Ind Ltd | Manufacture of plastic-coated steel pipe |
| JPH11291398A (en) * | 1998-04-09 | 1999-10-26 | Nippon Steel Corp | Manufacture of polyolefin-coated steel pipe and manufacturing device |
| JP2004160532A (en) * | 2002-11-15 | 2004-06-10 | Nippon Steel Corp | Hot-rolled steel strip cooling control method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS50108587A (en) * | 1974-02-04 | 1975-08-27 | ||
| JPS61206428U (en) * | 1985-06-18 | 1986-12-26 | ||
| JPH03197020A (en) * | 1989-12-26 | 1991-08-28 | Mitsubishi Materials Corp | Device for cooling resin-coated pipe |
| JPH0911306A (en) * | 1995-06-29 | 1997-01-14 | Sumitomo Metal Ind Ltd | Manufacture of plastic-coated steel pipe |
| JPH11291398A (en) * | 1998-04-09 | 1999-10-26 | Nippon Steel Corp | Manufacture of polyolefin-coated steel pipe and manufacturing device |
| JP2004160532A (en) * | 2002-11-15 | 2004-06-10 | Nippon Steel Corp | Hot-rolled steel strip cooling control method |
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