Resin spotting in medium density fibreboard.

Abstract

This project investigated the problem of resin spotting in Medium Density Fibreboard, (MDF). It tried to determine the cause and also ways to eliminate the problem preferably from the source. The object was to identify the process conditions which lead to a buildup in the blowline/dryer tube, identify the source of material leading to resin spot downgrade in the panel and determine strategies to prevent the buildup of this material in the blow line or in the dryer tube. The measurements taken included monitoring of buildup on the blowtube and dryer walls, analysis of the resin jet, comparing the penetration distance with predictions, and investigating the fibre flow inside the blowtube at the point of resin injection. Also the mixing mechanism of the resin and the fibre was varied and any change in the amount of resin spotting occurring was monitored. Finally, a simple modelling experiment was performed on a possible method of separating the resin spot material from the fibre stream from within the dryer. From this investigation it appears that the cause of resin spots in MDF is from the buildup of resinous material that occurs in mainly the dryer. After a certain period of building up, this material will detach itself from the wall and cause a particularly bad period of resin spotting. This is supported by the fact that calculations done on the rate of resin spot production from dryer buildup match the actual resin spot production rate encountered. The conditions that lead to heavy buildup is mainly based on the amount of resin being injected into the fibre stream, ie a high resin content product produces a larger amount of buildup than a low resin content product and hence more resin spotting in general. However it is possible that there are other unidentified factors that also have an affect on resin spotting. From our study of the resin mixing mechanism and the experiments that were carried out it is evident that the resin mixing mechanism has no affect on the amount of resin spotting. It was also noted that the unsteady flow of fibre appears to have no affect on resin spotting (from work done at other plants). There appears to be no direct simple production strategy that could easily be implemented to prevent the buildup in the dryer of resin spot material other than what is been done at present (namely the china man's hat on the dryer end of the blowtube and the weekly steaming and cleaning of the dryer). It is the author's opinion that at present the best strategy for reducing resin spotting significantly in Medium Density Fibreboard is to employ a separator to remove the resin spot material from the fibre stream after the dryer. Separators have already been designed and are in use in other plants around the world and seem to have proved successful there. To this end it is recommended that the design of the existing dropout box could be improved to facilitate the separation of the resin spot material from the fibre stream.