Coil coating

Coil Coating , also coil coating or continuous coating metal band called, is a continuous process for unilateral or bilateral coating of steel - or aluminum - metal sheets . The resulting material is a composite of a metallic carrier material and an organic coating. Common coating materials are paints , plastic powders and foils . EN 13523-0 calls sheets that are provided with a coil coating as coil- coated metals .

In 2008, around 1,200 million m² of steel and 300 million m² of aluminum were coated in Europe. This corresponds to a paint consumption of around 200,000 tons per year.

Applications

Coil coating sheets made of steel and aluminum are mostly used in roof and facade construction, mostly for commercial buildings.

In some cases, electrical and household appliances such as washing machines, microwave ovens and refrigerators are also made from coil-coated sheets made of steel (a competing process for this application is subsequent powder coating ). Other applications are (office) furniture, enclosures for control cabinets, EDP devices and lights, slats for blinds, metal doors and gates, garages, garden sheds and sheds, (suspended) coffered ceilings, trailer bodies, caravans and caravans.

Cans for food (e.g. biscuit and tin cans) that are made from pre-printed and lacquered sheets are made of tinplate or aluminum.

Coating process

Sheet steel and aluminum are used almost exclusively for the coil coating process. After production, the up to 2.6 meter wide metal strips are rolled up and delivered to the coating plant. There they are unwound and alternately looped above and below over several rollers that serve as tape storage so that the beginning and end of the roll can be welded together without having to stop the rest of the process. First of all, the strips are freed from fats and oils that were applied to protect the surface after the metal strip production. This is done through an alkaline cleaning. The metal sheets are then chemically passivated by a pre-treatment .

Adhesion promoter (primer) and topcoat are applied using a roller process and baked at around 240 ° C. Then the paint can be protected by a liner. Finally, the endless metal belt is guided back via a band memory, and separated into a roll ( English coil ) winds.

The process is very efficient. The surface quality is more uniform and the layer thicknesses can be controlled more easily than with non-continuous coating methods. There is also hardly any paint loss due to spray mist, as is the case with classic wet painting in the spray process. Modern coil coating systems are operated at speeds of up to 200 meters per minute. The entire system structure can be over 100 meters long. Strip galvanizing and coil coating systems are often attached to steel production.

Function and properties

The primer improves adhesion and corrosion protection . The top coat determines the appearance of the sheet metal and can be produced in almost any color. The gloss level and structure of the top coat can also vary.

The internal coating of cans from tinplate to prevent tin detached from the plate, but may in turn do not contain soluble substances which pass into the food.

Coil-coating paints have to be extremely flexible, as the sheets are only deformed after they have been painted. In this way, the strips are rolled into trapezoidal sheet metal and facade elements without the paint cracking or peeling off. Printed and painted tinplate has also been formed into cans and other tin containers since 1930.

materials

The tape consists of

• Sheet steel (cold rolled)
  • raw or
  • Electro- galvanized or hot-dip galvanized using the Sendzimir process , zinc alloys such as zinc-nickel are also used
• Aluminum ( wrought alloys )
• rarely also stainless steel, zinc sheet, tin, brass, copper and other non-ferrous metals

Modern coil coating paints usually consist of polyester resins that are crosslinked with either melamine resins or isocyanates . Also, polyurethane , PVDF , epoxy and plastisols are used.

In addition to paints, plastic films and powders can also be applied.

literature

• Bernd Meuthen, Almuth-Sigrun Jandel: Coil Coating. Coil coating: processes, products and markets. Vieweg-Verlag, 2005, ISBN 3-528-03975-2 (hardcover).
• Artur Goldschmidt, Hans-Joachim Streitberger: BASF Handbook Painting Technology. 12th edition, Vincentz Verlag, 2002, ISBN 3-87870-324-4 .
• Stahl-Informations-Zentrum (Ed.): Characteristic features 093 - Organically coil-coated flat products made of steel . Edition 2006, ISSN  0175-2006 , ( PDF; 0.87; MB ).

Individual evidence

1. ^ Coil coatings: Statistics of the European Coil Coatings Association 1992–2008. In: paint and varnish. No. 2, 2009, p. 10.
2. ↑ Lars Courage, Architect, Archived copy . Archived from the original on June 22, 2013. Retrieved March 8, 2012.