An investigation of factors affecting steambox heating effectiveness.

Application: Mills can use the ideas in the paper to estimate whether or not a steambox will effectively heat a sheet and to determine whether or not a vacuum box will assist the heating process.

This is the third set of experiments conducted at the Institute of Paper Science and Technology (IPST) investigating steambox heating effectiveness. Earlier studies indicated that air permeability was a primary determinant of steam heating effectiveness. The intent of this set of experiments was to validate that conclusion, using the following hypothesis:

   Steam penetration into the sheet and correspondingly
   steam heating of the sheet is primarily governed by
   the air permeability of the sheet and furnish is not a
   factor. Furnish is only a factor in that different furnishes
   produce sheets of different permeabilities
   under the same fabrication processes.

This hypothesis is based on the concept that the sheet structure (pore shape, size, interconnectedness, fiber physical structure, etc.) is the primary factor governing steam penetration into the sheet. Permeability is an indirect characterization of the sheet structure. Sheet structure is affected by furnish, refining, pressing, and other sheet processing methods.

The experiment used four different fiber types (southern pine, virgin kraft, wet pulp; northern pine, virgin kraft, dry lap; chemithermomechanical pulp, dry lap; and bleached hardwood, dry lap). Hand sheets of three basis weights (80 g/[m.sup.2], 100 g/[m.sup.2], and 120 g/[m.sup.2]) and two refining levels were fabricated using standard procedures. The sheets were then subjected to an identical steaming process using the Steam Box Comparator apparatus [TAPPI J. 79(3): 269(1996)]. Temperature measurements taken during the testing were subsequently used to calculate the steam energy absorbed by the samples.

The main conclusion from the experimental work is that furnish and basis weight are not determinant factors in controlling the effectiveness of steam heating. Furnish and basis weight are only important in that changing furnish or basis weight can alter the permeability of the sheet. Thus, the experimental work supports the hypothesis developed for the experiment.

Patterson is senior research engineer at the Institute of Paper Science and Technology, 500 10th Street NW, Atlanta, GA, 30318; email [e-mail].