Reference Manual

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Chapter 15
Stock Preparation
Stock preparation is the start of the papermaking
process and is the controlling factor over final
paper quality and how well the paper machine
runs. To be more specific, this process prepares
the fibers for the paper machine. In order for this
to occur, the fibers must be blended and the
consistency⎯or the percentage of fibers in the
water⎯controlled. Any contaminants must be
removed from the slurry and fibers mechanically
abraded or refined so they will bond well in the
papermaking process to form a clean sheet.
The stock flows through the various preparation
steps where additives including sizing agents,
fillers, starch, retention and drainage agents, and
dyes are added to the fiber furnish. The stock is
then further diluted to the final consistency so the
slurry can be pumped to the headbox and on to
the paper machine wire.
The stock preparation system can be broken down
into two main areas:
1. Thick stock system (figure 15-1): The initial
part of the stock prep system where fibers are
screened, refined, and blended to prepare the
slurry for each grade of paper to be made. This
process has a consistency of 3% to 5% solids.
2. Thin stock system: This system cleans,
screens, and dilutes to papermaking consistency.
This process has a consistency of 0.4% to 1.0%
solids.
Thick Stock Process
This process begins with in-coming bales of
purchased pulp, secondary fiber that might be
found in the high density storage chests, or fibers
from the pulp mill. The pulp is broken down and
Figure 15-1. Thick Stock System
Drawing is from TAPPI’s Making Pulp and
Paper Series and is used with permission.