The biggest folding boxboard producer in Europe, Metsä Board, started up a new extrusion coating line in Husum mill, Sweden, in April 2017. Having implemented the 38 million investment, the mill can now produce 100 000 tons per year of PE coated board for food and food service packages.

Extron-Mecanor supplied extrusion coating line

The new extrusion coating line was supplied by Raumaster Paper and Extron-Mecanor who have previously supplied coating lines e.g. to Stora Enso Imatra mill in Finland. Extron-Mecanor supplied all the technology required for PE coating between unwinder and winder starting from pre-treatment unit (corona treatment) to two-sided PE coating and, finally, to post-treatment (electric corona treatment).

Extron-Mecanor’s scope of supply included raw material storage silos and material transfer system, extrusion wagons and laminator. Raumaster complemented the delivery by supplying technology for web run, unwinder, winder and system for controlling rolls of the coated board.

To secure a significant turn-a-key delivery, Extron-Mecanor created a project organization having the functions of sales, purchasing, project management, engineering, production, logistics, testing and commissioning and training working seamlessly and efficiently.

PE extrusion coating line

Plastic coating of board requires not only a reliable raw material storage and transfer system but also a precisely operating gravimetric dosing system to extruders. The extruders (3 x Ex-160) were installed on two separate wagons that are perpendicular to the coating line. Two-sided coating requires two wagons that are moved to the line for coating and returned when off-line. One of the wagons has two extruders while another has only one. The maximum capacity of polyethylene production is 3300 kilos per hour.

Before coating, the board is pre-treated with a flame corona. The purpose of the treatment is to secure a firm adhesion between board surface and polyethylene. After the treatment, the board web of 3450 mm width is run through a laminator where coating takes place at the speed of 600 m per minute.

Coating line automation

Electrification and automation of the coating line was an essential part of the delivery. Engineering alone took thousands of working hours resulting in a PLC-based automation network of tens of Profinet communication servers, variable frequency drives and over 1000 I/O connection points. Four local operation panels and a control room provide with a user interface for controlling and monitoring the coating line.

Both operators and process are protected by hundreds of process alarms which are based on numerous on-line process measurements received from sensors. The measurements are also essential for on-line feedback controls, such as gravimetric dosing and temperature control of extrusion, which aim to maximize production and quality while minimizing downtime and process interruptions.

Turn-a-key delivery

Extron-Mecanor committed to the project delivery also in terms of providing operator and customer training during the project and supporting the start-up and testing of the new coating line. Owing to the good customer relationship and communication, Extron-Mecanor was very pleased to have the opportunity to deliver the new PE coating line technology to Metsä Board.

Translated and shortened from a Finnish story published in the magazine MuoviPlast (3/2017). MuoviPlast 3/2017. The original article in Finnish..