Expression roll presses

Pressing. The press seetion removes water and affeets eonsolidation of the sheet. The wet-web is lifted from the wire and transferred to porous earrier felts before passing between a series of roll presses or press nips. As the wet-web is pressed, first air and then water is expressed from the web. The water is absorbed by eapillary aetion in the pores of the earrier felts. However as the web exits the roll press it is deeompressed and some of the expressed water is sueked baek into the web. The effeetive press time is no more than 5 milliseeonds. At the first nip roll the speed of flow of water from the wet-web is rate-limiting, while at the last nip roll the pressure that ean be applied without erushing the sheet is rate-limiting. Traditionally moisture is squeezed out until the mat is down to 50-60% water (50-40% dry solids). Thereafter physical dewatering ceases to be efficient. 

Roll press For roll press the relative change of volume of particulate as a function of stress can be expressed as follows... 

Conversion of fiberboard furnish to board begins with the felting operation. Fibers suspended in a liquid or gaseous fluid are deposited on a moving wire and concentrated into an interfelted mat by the removal of the suspending fluid. Application of pressure between rolls or platens in the cold-press operation further reduces interfiber void space and expresses the forming fluid. 

Runnability is often expressed as the number of paper web breaks per 100 rolls. Paper web breaks during press runs are very costly in terms of money and time. Thus, high-speed newsprint presses also require newsprint with good tensile properties. Although the tensions in newsprint presses are kept well below the average tensile strengths of the paper, breaks do occur. These are generally the result of some defect in the paper such as shives that are not removed from the mechanical pulp fraction of newsprint. 

Figure 10. Comparison between the theoretical prediction (-) and measurements of the film split location expressed in terms of a dimensionless channel width for the forward roll coating process. Reproduced from Coyle et al., copyright 1986 [40], Reprinted with the permission of Cambridge University Press.

What is the optimum roll speed for a compaction process What factors does the formulating scientist or process engineer need to consider to maximize compact quality and compaction throughput Johanson (29) attempted to answer these questions by predicting roll-limiting speeds for briqueting presses. He developed mathematical expressions considering even the gas and liquid effects as they can theoretically be... 

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