Moisture is a very important parameter
in the manufacture of MDF, moisture content determines the
overall strength and durability of the board and surface appearance/quality
of the board is governed by moisture distribution. Blows (localized
de-lamination) are attributable, in part, to excessive steam
build up during the hot press process; core separation can
result in some instances. Moisture content of the furnish
needs to be optimized in order to save on fuel costs.
Incoming wood species such as pine, poplar and fir, is debarked,
chipped, and screened, prior to washing and entering the Digester.
Resin, wax, and in some cases urea water, is added to the
softened fiber which is flash dried whilst being conveyed
pneumatically to a fiber bin. Fiber passes through a grader,
and is laid out into a mat which is consolidated at the Forming
Pre-Press. The mat finally enters the hot press, where it
is converted into a panel through the application of high
pressure and temperature.
Moisture measurements are typically made on the incoming green
wood chips, on the refined fiber, and on the Pre Formed mat.
Owing to different manufacturing processes, installation locations
will differ between plants; the gauge is mountable over a
conveyor, over or side on to the mat, approximately 8”
above the product. It is also sited looking into a fiber bin
or the under- side of a gravity chute through a viewing window.
It is advisable to hook the air purge window up to a compressed
air line, in order to prevent resin and dust from settling
on the viewing window.