Design of blow line resin injector for MDF production

Abstract: This master’s thesis work was carried out at autumn 2006 on Metso
Panelboard in Sundsvall (Sweden). Metso Panelboard is one of the leading
suppliers of engineering know-how, technology and after-market services for
the production of medium density fibreboards (MDF). The objective for this
thesis is to design a way of adding the resin into the blow line such that
the resin (glue) consumption is reduced.

The resin stands for 30 % of the total cost of a MDF board. By keeping the
resin consumption down i.e. the mixing as efficient as possible, the total
cost of the boards can hence be significantly reduced. The resin binds the
fibres in the MDF board together and gives the board its strength. One way
to improve the board strength is to increase the number of connections from
fibre to fibre, with is achieved by better blending and resin distribution.
The resin injector is positioned on the blow line where fibre and steam are
flowing from the refiner to the dryer. After a litterature survey of the
research and the theories about resin consumption, four main issues was
identifyed. These are resin drop size, blow line turbulence, fibre
penetration and pre-curing. This led to the design guidelines atomisation,
adjustment, placing, angles of the injectors and maintenance.

Because of the lack of information and reports regarding this subject the
design could not be connected directly to resin consumption. Compared to
today’s design, the design proposed in this thesis is a more mechanical
advanced and probably more reliable design with a self-cleaning function.
This concept was chosen based on the idea to use one self-controlling resin
injector. The injector controls the pressure difference with the plunger
that adjusts the column to get the right area of the annular gap.
Controlling the pressure difference gives a possibillity to minimise the
drop size regardless of the flow rate. The plunger will also clean the
orifice between resin recipe changes or when the resin flow stops. The
plunger will further protect the internal of the injector from fibres in
the blow line, when there is no flow through the injector. To ensure the
function, flow calculation and computational fluid dynamic (CFD)
simulations were performed. Complete drawings were produced for the design
so that a prototype can be manufactured and tested in the future.