Step-closing pressing of medium density fiberboard¶Part 2. Influences on panel performance and layer characteristics

Abstract

The previous paper in this series discussed the stepclosure pressing schedule to change the density pro®le of lab-made MDF panels. The purpose of this research was to investigate the effect of the step-closure schedule on the end-product performance, especially on the layer thickness swell and its relationship with layer density. The results of this work showed that step-closure schedules resulted in improved internal bond strength of the tested specimens. The step closing schedule signi®cantly increased the core density and decreased the face density, resulting in lower bending properties. The results showed that greater core density did not result in higher internal bond strength. The more unsteady phase in a mat resulted in the poorer quality of the bond formation. The layer thickness swell after three water exposure times is significantly and positively related to layer density in all panels studied. The correlation coef®cient between the actual layer thickness swell and layer density increased with increasing water exposure time. The greater thickness swell in the surface layers of MDF suggests that efforts to improve dimensional stability of MDF should be focused on stabilizing the high-density surface layers. Schrittweises Pressen von mitteldichten Faserplatten (MDF) Teil 2. Einfluû auf das Verhalten der Platten und der einzelnen SchichtenIm vorhergehenden Artikel wurde das schrittweise Pressen vorgestellt, womit das Dichtepro®l von Labor-MDF-Platten vera Èndert werden kann. In dieser Arbeit wird der Ein¯uû auf die Eigenschaften der fertigen Platten untersucht, insbesondere auf die Dickenquellung der einzelnen Schichten und deren Beziehung zur Dichte der Schichten. Die Ergebnisse zeigen, daû durch dieses Verfahren eine verbesserte Querzugfestigkeit der gepru Èften Proben erreicht wurde. Die Dichte der Kernschicht stieg signi®kant, die der Deckschicht verringerte sich, was niedrigere Biegefestigkeiten zur Folge hatte. Die ho Èhere Kerndichte fu Èhrte nicht zu ho Èherer Querzugfestigkeit. Die unstabilere Phase in der Matte ist verantwortlich fu Èr eine schwa Èchere Ausbildung der Bindungen. Die Dickenquellung der einzelnen Schichten nach verschiedenen Wa Èsserungszeiten ist bei allen Platten signi®kat und positiv korreliert mit der Dichte der Schichten. Der Korrelationskoef®zient zwischen tatsa Èchlicher Dickenquellung und Dichte der Schichten stieg mit zunehmender Dauer der Wa Èsserung an. Wegen der erho Èhten Dickenquellung der Deckschichten bei MDF sollten ku Ènftige Bemu Èhungen zum Verbessern der Dimensionsstabilita Èt sich darauf konzentrieren, die hochverdichteten Deckschichten zu stabilisieren.

Strain Measurements within Fiber Boards. Part I: Inhomogeneous Strain Distribution within Medium Density Fiberboards (MDF) Loaded Perpendicularly to the Plane of the Board

“…In the medium density or high density fiberboard (MDF/HDF) production, several coupled physical and chemical phenomena influence the entire production process and the final product. Numerous investigations have been performed to describe the correlation between the mechanical properties of fiberboards with adhesive application [ 1 , 2 , 3 , 4 ], matt forming [ 5 ], pressing [ 6 , 7 , 8 ], heat transfer [ 6 , 8 ] and adhesive curing [ 9 ].…”

Experimental Investigation of Vertical Density Profile of Medium Density Fiberboard in Hot Press

“…Medium density fiberboard's strength, hardness, and other important properties are determined by its vertical density profile, which is one of the most important factors that is determined in laboratory tests of MDF performance. This factor is the combination of the results of many process parameters [14]. During hot pressing, the internal condition of the sheets, temperature, and moisture content continuously change with time [15].…”

Analyzing Process Related, In-Plane Mechanical Variation of High Density Fiber Boards (HDF) Across the Feed Direction

“…In medium density or high density fiberboard (MDF/HDF) production processes, coupled physical, mechanical, and chemical phenomena influence the entire process and the final product. Numerous investigations have been performed to describe the correlation between mechanical properties of fiberboards and resin content (Maxwell et al 1984;Waters 1990;Roffael et al 2003;Roffael et al 2005), mat forming (Wang et al 2001), pressing (Park et al 1999;Carvalho et al 2001;Cao et al 2007), heat transfer (Park et al 1999;Cao et al 2007), and resin curing (Heinemann 2004;Walther 2006). To analyze board properties, the selection and preparation of specimens have to follow a precise procedure, regulated in EN 326-2.…”