Equipment Description:Refining
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In Refining pulp suspensions are subjected to a mechanical treatment designed to cut and control the fibre length of the pulp and to alter the smooth wall structure of the fibres in such a way as to create fibrils or small hair like extensions. This serves to make for easier inter fibre bonding when forming a paper web and generally increases the final strength of the paper sheet. The is done using a Refiner. This machine forces the pulp suspension between two stainless steel rotating plates with specially etched ridged patterns on their surfaces. The narrowness of the gap, the consistency of the stock, the type of refiner plate pattern and the speed of rotation are all control parameters used to produce the desired effects on the fibre. |
Knifage is the term used to describe the cutting effect of the refining process on the pulp. Fibrillation is the term used to describe the effect of refining on a pulp fibre Freeness is the term used to describe the ability of a pulp to drain or lose its water and the amount of refining is directly related to the freeness of a particular pulp. |
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Most refining processes are carried out on a pulp suspension of around 3% to 4% consistency. Some Medium (6%) and High (10%) consistency refining is practiced in order to achieve specific effects, but generally the energy efficiency of these processes is poor. Refiners themselves come in a variety of designs and utilise large amounts of energy. Generally they will have one fixed plate and the second plate is rotated at a fixed distance in front of it. Stock is introduced between the plates and forced to make its way between the ridges etched into the faces of the plates before exiting at the rim. Variations on this theme would be both plates revolving in different directions, the stock introduced and exiting at different places and the multitude of patterns on the plate faces. Generally the gap between the plates is the major process control of the refining process and this is achieved by an external physical measurement or by the load on the motor driving the plates. |
Refining was also mentioned in the following Fact Sheets (13):
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