Formation Testing as a Means of Monitoring Strength Uniformity

Abstract

In any attempt to predict the durability or runnability of paper in its end uses, a means must be sought that is capable of measuring minimum strengths. Through the use of double exposure interference holography, an analysis is made of the strain variation of newsprint webs under critical tensile loading conditions. The coefficient of variation of strain is compared with formation values, which ideally should be measures of mass distribution. The QNSM, MK Systems and STFI formation testing instruments were used for this purpose and it was found that, in the case of the latter instrument, the index of determination of strain variation could reach 0-81. An assessment of the thermal uniformity of paper webs during tensile straining is facilitated by a liquid crystal thermal analysis and it is found that paper exhibits a particularly uniform distribution of temperature suggesting a constant work field model. While the influence of web defects on strength uniformity is briefly examined in this work, reference is made to a more detailed study to be found in another contribution to this symposium.