Pulp consistency
What does the term mean?
In papermaking, pulp consistency usually refers to a dry-material fraction in a fibre-water mixture, commonly expressed as mass percent. It differs from physical density, which relates mass to volume. The precise definition used by the mill must be established.
Relevance to process measurement
Clarify which solids the reference result includes. Measuring fibres alone differs from determining total solids including mineral fillers. The sensor result and laboratory analysis must use the same scope.
What should be agreed for consistency measurement?
Specify the constituents included and the laboratory reference method. A hypothetical total-solids fraction of 3% corresponds to 6 g of dry residue from a 200 g sample. Without further analysis, this does not reveal how much is fibre or filler.
Check whether that ratio changes between grades or recipes. Fibre distribution, sampling and the corresponding process reading must align for a useful comparison. A measurement curve applies to the product composition for which it was checked.
Distinguish between fibre content and total solids
When evaluating stock consistency, it must be established whether the operational reference value comprises fibres only or also includes other solids. Two fibre-water mixtures with the same total solids content may have different proportions of fibres and mineral fillers. A shared percentage figure therefore does not imply that both mixtures have the same composition in every respect. This distinction must be included in the description of the measurement task, in the laboratory instructions and in the designation of the displayed quantity.
When changing product types, comparative samples should reflect the actual compositions present. Select the sampling method so that the fibre distribution in the product under investigation remains representative. Note the corresponding process time and the laboratory method used. A discrepancy between the process value and the laboratory result may also arise if solids become unevenly distributed between sampling and analysis. This possibility should be checked before making any changes to the measurement curve.
For an application-specific assessment, the intended stock density range, the fibre types and fluctuating filler contents are helpful. Please also specify whether total solids or a more narrowly defined parameter is required. A conversion to physical density requires additional information and must not be derived solely from the term ‘stock density’.