From Kaipola groundwood to thermomechanical pulp

The raw material of Kaipola's first newsprint machines was groundwood and chemical pulp. 12 Roberts grinding machines made by Tampella were ordered for the plant. Groundwood production began in April 1954, but the quality did not come up to expectations in the early years. The work was heavy, as the logs were brought in by floating. Storing the logs in water was an advantage in groundwood manufacture. Each machine has its own loader and the logs were loaded by hand onto the grinding machines. In factory parlance, a job in the groundwood plant was taken under sufferance, while jobs on paper machines were coveted. Loading of logs was automated at the turn of the 1970s.

Kaipola groundwood plant in the 1960sThe log reception and cutting section was updated halfway through the 1960s. Kiramo, the log winch, was removed and replaced with a bundle gantry. In 1967, the standard length of groundwood logs was changed, so large quantities of offcuts, noggins, collected in the cutting section. In the past, the noggins had been sold for firewood, but now the quantities were so large that a way of utilising them had to be found.

Development work of refined mechanical pulp

Cold mechanical pulping plants had already been tried in Canada and Sweden in the 1960s. Refined mechanical pulp is obtained by grinding wood chips between grinding plates. United's Jylhävaara machine shop had started developing a groundwood pulper, and in 1969 a small test pulper was installed in the Kaipola groundwood plant. The equipment was tested and developed further. In the early 1970s, the mechanical pulping process was augmented by heat treatment, the wood chips were pre-treated with steam before pulping.

Kaipola mechanical pulping plantIn development of thermomechanical pulp, the Kaipola factories were pioneers. The work was directed by the works manager, Per-Erik Ohls. The aim of the development work was to replace the costly chemical pulp with cheaper mechanical pulp. The result was a light-coloured mass, which was better in strength than ordinary wood pulp. The thermomechanical pulping plant started up at the turn of the year 1975.

The development work continued, and thermomechanical pulp was tried out in various paper types on all four large papermaking machines. When the proportion of chemical pulp was reduced, the print qualities of the paper improved. In May 1975, 45 gsm lightweight print paper was manufactured for the first time in the world totally without cellulose. Kaipola’s successful development of refined mechanical pulp was a factor in the decision of United not to build further chemical pulp mills. In 1981, Jämsänkoski obtained its own mechanical pulping plant, which produced raw material for the new PK 5 papermaking machine. Kaipola moved wholly over to using refined mechanical pulp when the old groundwood plant closed down in 1988.
From Kaipola groundwood to thermomechanical pulp
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