Earlier this century, pulp and paper mills were often inoperative for part of the year, providing ample time for maintenance, modifications, and rebuilds. For example, parts of the world commonly shut down mills for six to eight weeks a year for vacation time and major holidays, and many pulp mills were built to operate only eight months a year. Mills around the northern region of the Baltic Sea operated for even shorter periods, often only four months annually, due to the frozen waters. This changed, however, as icebreakers developed ways for keeping the waters open all year and transport systems improved, leaving less time to perform maintenance.

As technology surrounding the paper industry gradually improved, less time was available for maintenance. In 1968, the bronze wire of a newsprint machine lasted about 10 days, yet still provided an opportunity for about eight hours of maintenance work every 10 days. However, maintenance employees were already beginning to complain about the lack of time for their work.

In addition, the increased speed of paper machines imposed a further maintenance challenge, with paper machine speeds increasing 1.5 times over newsprint machines between 1945 and 1970. Tissue machine speeds had also more than doubled. Then, as now, many people held the opinion that it was impossible to continue operating with little or no time for maintenance.

Today, due to even further improvements, mills cannot afford even the luxury of the maintenance time available in 1968. In the 1970s and 1980s, paper machine wires were replaced with higher- quality material, increasing longevity from 10 days to anywhere from 90 to 180 days. Furthermore, felts and other machine clothing also began lasting longer.

With few exceptions, the available time for production is now 365 days or 8,760 hours a year. Today, there is limited maintenance time available during changes of felts, wires, and other machine clothing, so it is only natural that downtime due to maintenance takes a larger portion of total downtime. However, some opportunity for maintenance still exists during roll changes, which can take four to six hours on many paper machines.

On a recent visit to a steel plant with a group of engineers from pulp and paper mills, I promised them that the plant, which was the most profitable steel plant in the world for 1996, could change two big rolls in 25 minutes. These rolls were in the cold rolling line where steel plates are rolled down to about a 2mm thickness. During the visit, the line was shut down until both rolls were changed, taking only 23 minutes.

Comments from the pulp and paper engineers included, "Of course, they can do the roll changes in such a short time, because the equipment is designed to allow that."

So, why don't we design paper machines in such a way that a pair of rolls can be changed in 15 minutes? This will probably happen eventually, leaving even less time for maintenance.