Aperture Regulation
Mechanical aperture adjustment mechanisms deform the flexible upper lip of a paper machine headbox slice to regulate the cross-direction basis weight profile of the exiting stock jet. Positioned at the exit discharge of the headbox, slice lip profiling modifies the height of the rectangular orifice across individual cross-machine zones through precise mechanical or thermal actuators. Local changes to the slice opening alter the volumetric discharge rate of low-consistency furnish delivered onto the moving forming fabric, correcting for grammage variations detected across the web.
The mechanical profiling system acts directly on the high-velocity free liquid jet, with its operational influence ending once the furnish consolidates on the drainage table.
Mechanical Actuation
The slice lip consists of a precision-ground, flexible stainless steel beam spanning the full width of the paper machine. Micro-adjusting spindles are spaced at intervals between seventy millimetres and one hundred and fifty millimetres across the lip, each connected to a stepper motor or a thermally expanding heating rod. Automated quality control scanners positioned at the dry end of the paper machine read cross-direction basis weight continuously, transmitting correction signals back to the slice actuator arrays.
When the scanner detects a localized light band in the sheet, the corresponding actuator retracts, bowing the flexible lip upward to allow more furnish volume through that specific segment of the opening. Adjusting the lip alters local lateral pressure fields, producing complex cross-flows inside the nozzle that can distort jet landing angles and misalign surface fibres.
Profile Uniformity
Accurate slice lip control eliminates basis weight variations that cause thickness variations, uneven drying rates and reel winding defects. Packaging converters require uniform cross-direction basis weight to guarantee consistent scoring performance, flat carton conversion and predictable structural strength. Uncontrolled slice profile shifts generate calender roll pinching, resulting in localized blackening or sheet mottling on coated cartonboards.
Modern paper machines often combine this mechanical slice control with dilution headbox technology, using the mechanical lip for coarse profile shaping while dilution injection handles fine consistency corrections without creating hydraulic turbulence. Slice lip profiling remains a fundamental mechanical adjustment for securing dimensional consistency across paper and packaging production webs.
