Stock preparation is the heart of papermaking, where fibers, water, and chemistry are tuned for stability, quality, and efficiency. In this guide on Top 10 Stock Preparation Practices for Paper Mills, you will learn practical methods that work on the mill floor and scale to high speed machines. We keep explanations simple, but we also add details that help engineers and operators act. Topics include fiber refining, dewatering, mixing, screening, and charge balance. The aim is to reduce variation, save energy, and improve sheet properties. Use these practices as a checklist to strengthen control, solve defects, and make every ton more profitable without risking runnability.
#1 Homogeneous furnish mixing and stable dosing
Uniform mixing in machine chest and blend chests prevents basis weight and formation swings that begin upstream. Target adequate chest turnover, low dead zones, and gentle agitation that avoids fiber damage or entrained air. Use ratio control on pulper, broke, and virgin streams so gram per square meter changes do not disturb fiber blend. Install mass flow meters and consistency transmitters to maintain setpoints during headbox flow moves. Validate polymer and dye dilution with static mixers, then locate addition points where turbulence is high. Audit sampling points monthly to confirm blend homogeneity and correct analyzer drift.
#2 Efficient screening and cleaning for pulp cleanliness
Coarse and fine pressure screens remove stickies, shives, and plastics that cause sheet defects and wire picks. Set screen feed consistency and differential pressure within supplier windows to minimize energy while protecting capacity. High density cleaners take out sand and metal fines that accelerate refiner plate wear and pump seal failure. Balance bypass flows so accepts quality stays high without starving stock. Trend reject rates, motor load, and pulsation to detect basket plugging early. Plan basket rotation and rebuilds by run hours and particle counts rather than calendar time alone for predictable quality.
#3 Controlled refining that targets fiber development, not power
Refining increases bonding by fibrillation, but excess cutting raises fines and drainage loss. Define sheet property targets such as tensile, SCT, and porosity, then link them to specific edge load and specific energy. Use plate patterns matched to furnish type and install online freeness and drainage sensors to close the loop. Operate with stable dilution water temperature and conductivity to avoid viscosity swings. Track refiner gap, plate wear, and no load power daily. Adopt staged refining with primary and secondary units to reach strength with lower specific energy and lower variability.
#4 Chest hygiene, level control, and consistency stability
Thick and thin stock chests must run clean, vented, and free of stratification to stop slugs that upset the headbox. Use radar or bubbler level transmitters with proper stilling to prevent oscillation. Install high accuracy consistency sensors and apply ratio or cascade control from machine speed so basis weight stays constant. Keep chest turnover within recommended hours to limit bacterial growth and odor. Trim agitator speed to maintain suspension without vortexing. Schedule periodic vessel cleaning and verify spray ball coverage. Calibrate transmitters with grab samples at two points to avoid linearity errors.
#5 White water balance and fiber recovery that saves cost
A tight white water loop reduces fresh water use and improves retention. Map all inflows and outflows to maintain consistent solids and conductivity, then adjust silo controls to buffer short term swings. Use save-alls, disc filters, or dissolved air flotation to return fines and fillers to the system with minimal shear. Avoid air entrainment by submerging returns and eliminating free falls. Monitor anionic trash and cationic demand so chemistry remains effective as closure increases. Track recovery yield in kilograms per ton to expose losses and justify maintenance on seals, filters, and piping.
#6 Charge balance and retention program tuned in stock prep
An effective retention system starts upstream with good charge control. Measure streaming current or zeta potential to understand system demand and place fixatives where contact time is long. Dilute polymers to the correct concentration and age them for full activation before injection. Sequence additions so fixatives act first, then microparticles or starch, and finally the main polymer. Verify shear exposure with residence time audits across pumps and valves. Trend first pass retention against basis weight and machine speed to spot drift. Keep salt and hardness stable to avoid surprises in adsorption and floc structure.
#7 Dewatering and thickening for energy and quality gains
Thickeners, screw presses, and disc filters raise pulp consistency for efficient refining and mixing. Set target outlet consistency that supports stable stock flows without slugging. Maintain seal sprays, filtrate clarity, and vacuum levels to prevent carryover. Use condition based maintenance on screens and felts by tracking differential pressure and filtrate turbidity. Stabilize temperature across dewatering stages to maintain viscosity and refiner load. Return filtrate to the correct loop to protect chemistry balance. Benchmark specific energy per percentage point of dryness increase to guide upgrades and to prioritize capital projects.
#8 Clean broke handling that protects fiber quality
Broke is valuable fiber that must be repulped without adding dirt, wax, or excessive fines. Keep broke storage covered, drained, and segregated by grade to prevent contamination. Control addition rate to the system with ratio control so strength and drainage do not swing. Use deflakers and coarse screens after repulping to remove flakes that cause holes. Monitor stickies load and apply detackifiers when needed. Measure ash and brightness to keep balance with virgin streams. Track the percentage of broke in the furnish and cap it by grade to maintain runnability and product specifications.
#9 Process water quality, air control, and microbiology
Stable stock starts with clean water and low air. Measure dissolved and entrained air, then fix suction leaks and add deaeration where needed to protect pumps, sensors, and headbox flow. Hold conductivity, pH, and alkalinity in defined windows so chemistry works the same shift to shift. Apply biocide programs that rotate actives and use shock dosing to prevent resistance. Keep temperatures steady to avoid viscosity swings. Audit dead legs and low velocity lines that harbor slime. Trend plate counts and ATP for early warning, and verify effectiveness with post treatment grab samples.
#10 Measurement discipline, automation, and practical analytics
Good stock preparation runs on facts. Calibrate consistency, flow, pressure, and conductivity transmitters on a schedule and record as found and as left results. Use soft sensors to estimate freeness or drainage when lab data are sparse, but validate with regular lab checks. Build simple dashboards that show stability: variability of consistency, refiner load, differential pressure, and retention. Layer alarms with sensible deadbands so operators act on real change. Review grade change and startup data to capture best settings. Run small trials, keep clear logs, and turn successful settings into standard work instructions.