Name:Fundamentals Of Wet Pressing
Description:Phase 1 Compression begins in this phase. Air flows out of both sheet and press fabric until the sheet is saturated with water. No hydraulic pressure is built up in the sheet during this phase and little change in dryness of the sheet occurs. Phase 2 The sheet is saturated and the buildup of hydraulic pressure in the sheet causes movement of the water from the paper into the press fabric. If the press fabric also reaches saturation, water moves out of the press fabric. Phase 2 continues up to mid-nip, where the pressure reaches maximum. It is believed for most cases that the hydraulic pressure reaches a maximum prior to mid-nip. Phase 3 The nip expands until the hydraulic pressure in the paper is zero. This is believed to correspond to the point of maximum paper dryness in the nip. Phase 4 Both the paper and press fabric expand and the paper becomes unsaturated. There is a possibility that water can return to the paper by one or a combination of mechanisms e.g. capillary absorption, vacuum in the sheet, or film splitting. The possibility of water reentering the sheet in phase 4 is recognized as a limitation to idealized water removal. Various mechanisms for rewetting are postulated, including capillary absorption, mechanical absorption, and film splitting. It is known that additional rewetting occurs following the nip unless the sheet and press fabrics are separated immediately. Most modem press designs provide for this separation. Often, the press fabric wraps the roll away from the sheet, while the sheet adheres to the hard smooth roll in a single felted press. Lead-out rolls are generally positioned so the sheet is located midway between top and bottom press fabrics on double-felted presses. Most other models start with this premise, and attempt to refine it.

Name:Feltperm
Description:The sheet water content leaving the press section is the best indication of the press efficiency. It is estimated that a 1% increase in sheet dryness leaving the press section can lead to 3 - 5% increase in production rate or a comparable reduction in energy use during drying. Sensors are available to measure sheet moisture at the press section, but grab samples remain the most commonly used method to determine press moistures. Tradeline distortion is an indication of the distortion of the base weave of a fabric. A small amount of distortion will have no affect on the fabric performance, but a tradeline that is off by more than 1 foot per 100 inches of width can change the permeability characteristics of the fabric. Distortion of this magnitude can influence the water removal, rate of filling, fabric and sheet moisture profiles, and the fabric stability. Dewatering flow rates can be a very important measure of the press performance. The flow rates should be measured for each of the press Uhle boxes, and saveall pans on the press nips. This is most commonly done with weirs and the flow rates can be determined from tables available in standard engineering references. With all of this information a press water balance can be done and the performance of the press can be tracked as clothing ages. TAPPI also has a detailed procedure ( TIS 0404-22 ) for an economic evaluation of the press section. There are about 20 variables that go into these calculations and yield results based on cost savings. The primary variables include the production rate, sheet dryness, cost of machine downtime, press clothing cost, clothing installation costs, fabric cleaning costs, maintenance costs, water costs, cost of lost production, energy costs for press drives, vacuum pump drives, water pumps, and heat input into the sheet to lower the water viscosity. Savings can be in dryer section steam, increased production, or quality improvements.