Equipment Description:Pressing Types & Arrangements
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The Press Section of the modern paper machine has seen a lot of technical development. One key reason for this is the high cost of energy. Drying the sheet of paper using steam heated dryers is a lot more expensive than using efficient presses. The primary function of the press section therefore is to remove as much water from the sheet as possible, consolidate the sheet and improve the surface smoothness. While the fibres are still wet they are flexible therefore many of the sheet properties can be determined as a result of the press section. Once the sheet is in the dryers a process called irreversible hornification takes place whereby the fibres lose much of their flexibility, permanently. The objective, therefore is to remove the water using the minimum amount of pressure in the nips of the press rolls. |
Press Fabrics: Felts used to carry the sheet through the presses. Nip Pressure: The loading between two rolls. Edge guides: These units control the run of the felt to make sure they run straight. Shoe Press: This is an extended nip press. Draw: This is the term used for the tension between each section of the machine. Roll hardness: This is the surface hardness of the press rolls. |
 Press Configurations |
In the Plain press the water is squeezed out of the sheet and into the felt. The suction press has a vacuum box in the nip sucking the water out of the sheet, through the felt and through the drilled hollow roll into the vacuum box. The grooved or blind drilled press is often found in the Main Press position. The water removal is relying on the felt, however, the blind drilled or grooved press allows more water to be carried out of the sheet because the grooves etc act as vessels to carry the water. The double felted plain press is also found in the main press position. Similarly, most of the mechanical water removal has been carried out in the primary press, therefore this unit depends on the water being squeezed out of the sheet and into the top and bottom felts. |
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