How sonic ZD measurements can optimise the paper machine

In-plane sonic measurements have been used for many years to determine fibre orientation and more recently to predict some traditional paper properties like ring crush, SCT and burst. Due to the complexity of the measurement, zd sonic stiffness measurements have not been introduced as a main stream measurement within the paper industry. Despite this, the measurement is a valuable adjunct to the usual paper laboratory testing. Because of the zd sonic test's strong relationship with bonding in the paper sheet it can be used to sensitively reflect paper machine treatments or processes that develop or hinder paper property development. The measurement is useful in identifying issues with and optimising paper machine processes like forming, pressing, starch, calendering and draw settings. This paper describes how the measurement has been used to gather information on the paper machine regarding process effects on paper performance. In many cases the technique delivers insights into paper performance that are not available from traditional testing.