A wet end survey and online charge control optimized runnability of a board machine and cut costs of chemicals.
Mayr-Melnhof Karton is a major manufacturer of coated board made out of recycled fiber. The cardboard is produced in seven facilities in Europe and mainly used for folding cartons for food applications. The Deisswil mill in Switzerland run three board machines. Machine KM6 produced approximately 200.000 tons per year of speciality greaseproof board. At KM6 the challenge was to counteract increased chemical consumption, quality problems and poor runnability. To begin with, laboratory measurements were made to determine the zeta potential and the cationic demand of the raw materials applied in the top layer using the Mütek lab devices SZP and Mütek PCD. The results revealed fluctuating charge levels in the used raw materials such as mixed recovered paper and board. To examine the top layer circuit in greater detail, a wet end survey was conducted at five measurement positions from the machine chest to the headbox (white water) and before and after chemical addition. The wet end survey indicated that the particularly expensive grease barrier product mistakenly worked as an anionic trash collector and a poor adsorption of the resin/ alum. Against this background, charges were stabilized at a lower level with a short-chained, highly-charged cationic polymer before the introduction of other functional additives.
After three weeks of intensive laboratory work, Deisswil switched to online charge measurement with the PCT-20 Charge Analyzer in combination with a TSS-70 Filtration Sampler after the dosing system for the cationic fixative was installed. Closed-loop fixative control was introduced with the fixing agent being directly added to the machine chest. Online fixative control at KM6 lead to: