Pinholes

1. Furnish considerations:
— it is easier to close up the sheet structure with slush pulps.
— use easy beating fibers that meet other specifications
— ensure that level of broke used is appropriate for the grade.
— in lighter weight grades, coarse, unrefined pulps give a mat that is too open to avoid pinholes.
— avoid pulps with excessive fines.
2. Stock preparation:
— use the highest practical refining consistency.
— strive for minimum cutting in refining.
— keep stock temperatures as low as possible at start of refining to maximize fiber swelling.
— gradually increase refining loads as it is essential to avoid heavy refining early in the process.
— maintain careful control of filler addition.
3. Air entrainment:
— minimize introduction of air into stock at any point in the approach system.
— use mechanical deaerators or defoamers to minimize air in the stock to the headbox.
— pay close attention to pH and total acidity, especially in neutral or alkaline systems.
4. Paper machine conditions:
— use the finest mesh forming fabric consistent with other operating conditions.
— check position of slice apron relative to centerline of breast roll.
— graduate vacuums on foils and suction boxes.
5. Press section:
— check first press for tendency toward crushing.
— do not overload first press.