From Paper-mill to Pressroom

by William Bond Wheelwright

The result, obviously, will be a variation in finish over the whole width of the paper instead of over a portion. Moreover, too much drying makes the paper fuzzy and likely to become wavy, besides weakening the fibers.

Another result of uneven pressing is to make the paper thinner where the pressing is hardest. Such a defect is quite obvious in a pile of paper, as the top will not be as level as it would be in paper that is uniform in thickness throughout.

Assuming that the paper is perfect as it leaves the driers there is still a chance that one or more of the calender rolls may get out of true, especially when starting a run after they have been idle long enough to get cold. Under such conditions they often heat up and expand unevenly so that the pressure is harder in some sections than in others. The result is a thin streak in the paper. Whether the thinness be caused by poor pressing or calendering, it can easily be detected in a roll of paper, as the thin streak makes a soft spot in the roll which can quickly be located by tapping the roll all the way across. A muffled rather than a ringing sound discloses soft places.

This defect, if bad, may cause considerable trouble on a web press, as no amount of manipulation will make the paper draw evenly as it runs into the press if the edge of the roll is slack.

Occasionally, segregated areas in paper are found to vary in finish, and when these do not run in continuous streaks they may often be caused by the felts which carry the paper through the press rolls having become clogged up in spots so that the water can not pass out evenly from the paper through the felt. This must be guarded against by occasionally stopping the machine and washing the felts, or changing them, as the occasion dictates.

Such damp spots in the paper crush in the calendering and make blackened areas in the paper. Uneven drying may also have been occasioned by slackness of the drier felt which holds the paper against the driers. In sheeting the cheaper grades of book paper it is customary to cut off from a number of rolls simultaneously, which often accounts for a variation in finish or bulk in sheets from the same case.

Of course, when any of these symptoms appear it is the duty of the men on the machines to correct them, and in the continuous course of paper-making it is inevitable that felts become filled up and require washing or changing, or that the variations of consistency in the stuff should call for some form of regulation. Stuff which runs too moist on the wire will often “crush” under the couch roll, producing a curdled appearance. Stuff run with insufficient water will not form evenly. The skilful machine-tender avoids these extremes.

Trade Customs.—In recognition of the many variable elements in paper-making, trade customs have been established, such as allowances for a normal variation in the weight of paper above or below the nominal ream-weight, and reasonable allowance should be made for normal variations in other characteristics.

Eternal vigilance and alert judgment are certainly required for setting high standards in the manufacture of paper. It is a matter of common observation that mills using practically the same raw materials vary widely in their reputation for uniformity and excellence of product. The reason for this is to be found in the human element.

Calender Defects.—A number of difficulties may arise from much less excusable causes than those mentioned. For example, the paper sometimes may run slack through the calenders, with the result that it wrinkles and cuts in diagonal jags called “calender cuts.”