Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/20—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of indefinite length
  • B29C44/32—Incorporating or moulding on preformed parts, e.g. linings, inserts or reinforcements
  • B29C44/322—Incorporating or moulding on preformed parts, e.g. linings, inserts or reinforcements the preformed parts being elongated inserts, e.g. cables
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/09—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/15—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor incorporating preformed parts or layers, e.g. extrusion moulding around inserts
  • B29C48/151—Coating hollow articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2705/00—Use of metals, their alloys or their compounds, for preformed parts, e.g. for inserts
  • B29K2705/08—Transition metals
  • B29K2705/12—Iron
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2009/00—Layered products
  • B29L2009/003—Layered products comprising a metal layer
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2023/00—Tubular articles
  • B29L2023/22—Tubes or pipes, i.e. rigid

Definitions

• the present invention relates to a method for coating a steel pipe by extrusion, in which method the steel pipe is pretreated and the pretreated steel pipe is led through an extrusion tool, wherein it is coated with an adhesive layer and at least with a relatively thick thermoplastic layer, after which the coated pipe is coo ⁇ led.
• the coating of a steel pipe occurs normally in such a way that the steel pipe is mainly immediately after the pretreatment, comprising e.g. warming-up, blasting, heating and a potential epoxy coating, led into an extrusion tool at as high a tempera ⁇ ture as possible so that the activity on the epoxy layer does not decrease before the adhesive layer and the thermoplastic layer or layers are applied. It is namely generally believed that the adhesive capacity on an ap ⁇ plied epoxy layer considerably decreases after it has hardened. For achieving as good an adhesion as possible, attempts are therefore made to lead the epoxy-coated steel pipe as rapidly as possible into the extrusion tool.
• the cooling of the plastic namely takes place relatively slowly, because of which the first supporting point of the pipe after the extrusion tool must be located at an extremely long distance therefrom, which may make e.g. the cente ⁇ ring of the steel pipe difficult. Since the cooling of coated steel pipes mainly takes place from the outer side, the applied plastic mass solidifies first on the outermost layer, from which the solidification slowly advances radially inward. The first supporting point of a coated pipe must therefore be located within such a distance from the extrusion tool, in which the cooling process has advanced through all plastic layers, whereby these obtain a sufficient bearing capacity.
• the object of the present invention is to eliminate these problems especially when thick plastic layers are applied to steel pipes by extrusion during a single stage. This is achieved by means of a method characterized in that the pretreated steel pipe is led into the extrusion tool at a temperature below the solidification point of the extruded plastic material and that the coated steel pipe is heated after cooling by induction heating for ac ⁇ hieving an effective adhesion between the steel pipe and the coating.
• the plastic mass to be extruded on the steel pipe normal ⁇ ly has a temperature of ca. 200°C, whereas the temperatu- re of the pretreated steel pipe entering the extrusion tool is ⁇ 100°C.
• the total quantity of heat to be transported away from the coated pipe is thereby considerably lower than in connection with previously known processes.
• the extruded layers therefore quickly reach a sufficient bearing capacity for supporting the weight of the pipe.
• the adhesion of the extruded layers to the steel pipe is not yet completely satisfactory, but this is facilitated according to the invention in an effective manner, i.e. the steel pipe is next heated by induction heating.
• the electromagnetic waves enter directly through the extruded plastic layers into the steel pipe without heating of the plastic layers. Since the steel pipe is heated, heat is conducted to the adjacent plastic layers, which are thereby heated to a plastic state.
• the invention is next described in more detail with reference to the accompanying drawing, which shows a basic scheme of a production line according to this invention.
• the steel pipe 1 to be coated is pretreated on a pre- treatment station 2, on which the steel pipe 1 is first heated in such a way that possible moisture is removed, after which the outer shell of the steel pipe is blasted for obtaining a clean and new steel surface.
• the blasted steel pipe l can be led directly into an extrusion tool 3 at a tempe ⁇ rature, which is essentially below the melting point of plastic masses that are intended to be applied to the steel pipe in the extrusion tool 3.
• the blasted steel pipe 1 is heated to ca.
• an adhesive medium 4 as a relatively thin layer as well as at least a relatively thick layer of thermoplast 5 are applied to the steel pipe l.
• the solidification process starts immediately, which results in that all extruded layers solidify relatively quickly and require a considerably shorter cooling bath 6 after the extrusion than in con ⁇ nection with conventional methods.
• the first support point of the extruded pipe 1 can thus be located quite near the extrusion tool 3. In this way, the extruded layers quickly reach a solidified state, and a pipe with good centering is obtained, but the adhesion to the steel pipe l or the epoxy surface is relatively low.
• a suitable temperature for the steel pipe 1 entering the extrusion tool 3 has proven to be ⁇ 100 ⁇ C.
• the extruded thermoplastic layer can be a foamy insulating layer and/or a compact protective layer.
• the inventive method has proven especially suitable.
• Another suitable embodiment is a steel pipe coated with an adhesive layer, a relatively thick foam layer and a thinner compact protective cove ⁇ ring.
• the process can either be interrupted after the pretreatment stage and steel pipe 1 can be transfer ⁇ red to a waiting storage, or the distance between the pretreatment station 2 and the extruder 3 must be adjus ⁇ ted long enough.
• the steel pipe In connection with the final induction heating, the steel pipe should preferably reach a surface temperature of ca. 160-180°C, which is approximately the same as the melting point of the adhesive layer.

Landscapes

• Extrusion Moulding Of Plastics Or The Like (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=26158498

Family Applications (1)

Country Status (5)

Cited By (2)

Families Citing this family (1)

Citations (5)

• 1989
  • 1989-02-10 FI FI890646A patent/FI84449C/fi not_active IP Right Cessation
• 1990
  • 1990-08-10 WO PCT/FI1990/000193 patent/WO1992002353A1/en active IP Right Grant
  • 1990-08-10 EP EP90912059A patent/EP0542740B1/en not_active Expired - Lifetime
  • 1990-08-10 DK DK90912059.4T patent/DK0542740T3/da active
  • 1990-08-10 DE DE69025201T patent/DE69025201T2/de not_active Expired - Lifetime

Patent Citations (6)

Also Published As

Similar Documents

Legal Events