PROCESS DESCRIPTION
The diagram below reflects the basic Daproma manufacturing process utilizing agricultural fibers.
Consumption data for a plant with Capacity 430 m3/day 19 mm thickness (81 million sq.ft/year 3/4" thickness):
Per m3 board with density 680 kg/m3
| Straw B.D. | 810 kgs |
| MDI resin | 21 kgs |
| Release agent | approx. USD 3,50 |
| Electricity | 250 kWh |
| Water consumption | 70 m3/day |
Recommended building size: 30 x 275 mtr
Quality of product will comply with international standard.
Raw Material Handling
It is assumed that straw is not
available the whole year. Further it is assumed that the
straw is baled. Both round and square bales can be used.
Fibre Preparation
The bales are loaded onto an infeed
conveyor, which feeds them to the bale breaker. The bale
breaker opens the bales and reduces straw length to
approximately 1-5 inches. From the balebreaker the
material is transported to a live bottom bin. Moisture is
added to get up to 20-50 percent moisture content in the
straw. From this bin the material is fed through a
separator which separate out the grain, sand etc., and
then into a high efficiency hammer mill, where the straw
will be shortened to approximately 1/4 - 1/2 inch as well
as opened up to slim fibers. From the hammer mill the
material is transported to another bin from where the
fiber is fed over a roller screen where the accepted
fiber will be taken out and fed directly to the dryer
while the larger fibers are going into a Refiner for
further processing and than being fed to the dryer.
Drying
An indirectly heated tub bundle
dryer heated with hot oil is used for safety reasons,
being the least vulnerable to fire hazards, and easy to
operate. Its heat economy is very good, its dimensions
are comparatively small and it has an excellent
insulation against heat losses to the exterior.
Screening
From the dryer a screw conveyor to
the screen transports the material. This conveyor has a
flap, which is automatically activated in case of fire,
to discharge the material to the ground. Core and surface
materials are transported to their respective dry
material bins. From the bottom of the screen the dust is
conveyed to the dust silo. Oversize material and some of
the core material are transported to a refiner for
further grinding and then back to the screen.
Resin Blending
From the dry material bins, core
and surface materials are fed via weigh scales to their
respective resin blenders. Signals from the weigh scales
control the resin dosing units. The resin is sprayed into
the blenders by low pressure, high-speed atomizers,
creating a resin mist in the blenders. This method gives
an extremely even resin distribution, which in turn
guarantees the lowest possible resin consumption.
Mat Forming
The mat is formed in three
different forming stations. The first unit forms the
bottom surface layer; the second unit forms the core and
the third the top surface layer of the mat. The mats are
formed on aluminum cauls, which are moving continuously
through the forming line. After the forming, the mat goes
to the prepress for height reduction. After the prepress
a weigh scale checks and records the weight of each mat
before it enters the hot press. Before the forming the
cauls are sprayed with a release agent. Also after prepress the
mat is sprayed with release agent.
Hot Pressing
In the hydraulic hot press the mats
are pressed simultaneously. The caul plates with their
mats are stacked in an elevating loading rack in front of
the press and then simultaneously charged into the press.
After the pressing they are discharged into a
corresponding unloading rack behind the press, while the
following cauls with mats are charged into the press.
The press platens are heated by hot oil. Pressing time, pressure and temperature are automatically controlled according to a program, preset with regard to the actual type of board. From the unloading rack the cauls with their pressed boards are discharged one by one. Caul plates and boards are separated. The cauls return, and the boards are transferred onto to the cooling wheel and then stacked. Before the cooling devise the panel is sprayed with water on both sides to compensate for moisture losses in the surface during the pressing and also to speed up the cooling of the surface.
Subsequent Treatment
Before the boards are taken to the
combined sawing and sanding line, it is imperative that
they are properly stacked until they have cooled, the
resin has cured and the moisture has equalized. Then the
boards are sawn to the required size and sanded to the
final accurate thickness and smoothness.
Energy
A thermo oil heater is supplying
heat to the dryer and the hot press. The thermo oil
heater normally operates on sander dust and uses natural
gas/fuel oil for back-up and also for starting the
heater. For operation of the machinery, electric power is
supplied from an external source to a switch board center
from where it is distributed to the various parts of the
plant.
Quality Control
To maintain a high and even board
quality, a regular and thorough check-up of the process
is necessary. For that purpose, laboratory equipment is
supplied, allowing at various stages of the process,
required testing of the physical properties of materials,
including quality tests of the finished product.