The drainage rate during sheet forming is a critical issue in the operation and design of the wet-end of a papermachine. Previous attempts to correlate laboratory pulp drainage tests with pulp drainage on a papermachine have had limited success. Laboratory pulp drainage usually involved thick stock suspensions drained to form a high basis weight mat. In this study, a laboratory drainage tester has been developed to characterize the drainage of pulp slurries unde industrial porcess conditions. Typical ranges for operating parameters such as headbox consistency, basis weight, and average drainage velocity, were incorporated into the device design. Average drainage velocities were measured for several grades and former arrangements during pilot papermachien trials. Evaluation of these three paramters indicates the drainage process can occur quickly, usually in under a second, and data collection must occur instantaneously and at a high frequency.
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