[0001] This invention relates to an arrangement for feeding a mat of disintegrated lignocellulose-containing
fiber material into a press comprising continuously driven lower and, respectively,
upper press belts for the manufacture of board, such as particle board, fiberboard
etc.
[0002] The manufacture of board based on lignocellulose according to the dry method is carried
out in known manner by disintegrating the lignocellulose-containing raw material to
a suitable form, drying and glueing it, form it to a material mat which is pre-pressed
and transported to a hot press, which can be a discontinous or continuous press where
the material mat is compressed and the glue by the influence of heat hardens and gives
the resulting board the strength required.
[0003] Board types manufactured in principle in this way are particle board, fiberboard
and other board.
[0004] Medium Density Fiberboard (MDF) and similar fiberboard with varying density are board
types, which in recent years have been used to a rapidly increasing extent, and which
are based on lignocellulose-containing raw material defibered to fibers. The material
mat thus obtained is almost exclusively a so-called single-layer board, i.e. it has
a substantially homogenous structure with uniform fiber distribution, and the mat
has a considerable thickness after forming, but also after pre-pressing and at the
transport into the hot press.
[0005] Particle board at present is built up mostly as three-layer board, i.e. it comprises
a central layer with coarse chips and two surface layers with fine chips. As these
surface layers are made separately, the possibility is used to choose different moisture
content and glue content in the layers, The fiber mat at the use of chips is not as
thick as at MDF.
[0006] At the introduction of a material mat of the said or similar kind into the inlet
of a continuous press, the material mat is exposed to heat from the hot upper steel
belt in the hot press, and at the inlet to the press nip it is subjected to a reduction
in thickness, which implies a.o. that air included in the material mat rapidly must
be evacuated out of the material mat.
[0007] The material mat, thus, is not exposed symmetrically to the hot steel belts, because
the lower surface of the mat is protected by its conveyor all the way to the take-off
occasion. Arrangements to protect the upper surface of the mat against radiation heat
from the hot upper steel belt are known, but have practical disadvantages, such as
the risk of accumulation of chips/fibers, which can fall down on the mat and cause
second quality board etc. The undesired heating of the surface layer of the mat. results
in the drying-out of the surface layer whereby also the glue dries out and is inactivated.
The surface layer, therefore, is given an unsatisfactory hardness and strength. The
surface layer thus obtained often is called pre-hardening layer, because the glue
there is hardened and/or dried up before sufficient surface pressure effecting good
contact between fibers or particles has been produced in the press nip. In order to
compensate for the pre-hardening layer, the board must be manufactured with excess
size, which must be ground off. Unsymmetrical heating implies greater grinding allowances.
[0008] At board manufacture in a continuous press, in order to obtain a desired high surface
density, the material web should be compressed rapidly to a thickness immediately
above its final thickness. The ingoing material mat has a considerably greater thickness,
at times up to ten times the final thickness. It is, therefore, understood that a
great amount of air must be evacuated out of the material mat. This should take place,
thus, as rapidly as possible, but is restricted by the fact that the overpressure
thus built up in the material mat must not become so high, that the material mat is
disrupted. This appears mostly in the form of transverse stripes in the finished board.
These surface cracks often can pass unnoticed through the production, and first when
the board is to be painted at the customer it is observed,that the surface cracks
have caused variations in the surface density, resulting in varying paint absorption
and thereby varying glaze. This inevitably gives rise to reclamations.
[0009] The design and control of the conveyor delivering the material mat into the press
nip, therefore, is of great importance for minimizing the aforesaid shortcomings.
[0010] Known designs of feed conveyors have disadvantages in these respects and, moreover,
are not guided safely for preventing collision with the hot lower steel belt.
[0011] The method and arrangement according to the present invention imply minimization
of the said problems and at the same time offer additional advantages. The mat, for
example, can be guided into the press nip so that the air evacuation out of the material
mat. takes place in the most lenient manner at the same time as the nose of the feed
conveyor cannot collide with the steel belt and pre-hardening can be affected.
[0012] The characterizing features of the invention become apparant from the attached claims.
[0013] A feed arrangement according to the invention can be designed so that the nose portion
is movable and rolls against a roll surface, the geometry of which mirrors the geometry
in the press nip, whereby the nose follows the geometry of the lower press belt in
the inlet and, thus, always is at a certain distance from the lower steel belt. The
equipment can be pre-programmed so that adjustment of the nose position can be carried
out automatically by means of rack and pinion drive, for example to a suitable pre-programmed
nose position when the board thickness is changed or in that a continuous measuring
of the thickness of the material mat immediately before the press provides corresponding
information, which then is processed in the control equipment and provides a suitable
nose position.
[0014] The invention is described in greater detail in the following, with reference to
the accompanying drawings showing only one embodiment of the invention.
- Fig. 1
- shows the movable structure for the conveyor and the lower press nip and roll surface.
- Fig. 2
- shows the nose portion of the movable structure and the press nip.
- Fig. 3
- shows a detail of the nose portion with the lower press nip.
- Fig. 4
- shows an imagined embodiment of the conveyor.
[0015] The inlet gap in the continuous hot press shown in the Figures is designed in known
manner to comprise front guide rollers and heating plates, which are formed with a
large guide radius R of the same magnitude as the radius of the guide rollers. The
heating plates thereafter transform to a substantially horizontal portion. Depending
on the thickness of the board to be produced, the inlet opening
b is adjusted so that the press operation is optimized.
[0016] The material mat in all Figures is thought to move from left to right.
[0017] The movable structure 1 shown in Fig. 1 rests on rolls 2 and 3 and is movable in
a substantially horizontal direction by a mechanism 4. The nose 5 of the structure
is located at a certain distance above the lower steel belt 6 of the press nip. The
roll surface 7 is designed so that the distance between the nose 5 and steel belt
6 is maintained almost constant when the stucture is moved by the mechanism 4. The
form of the roll surface 7 mirrors the geometry of the lower steel belt 6, geared
with regard to the distances between roll 2 and roll 3 and, respectively, roll 2 and
nose 5, and the distances between the centre for radius R and the radius of the roll
surface 7 in horizontal direction, and the distances between roll 2 and roll 3 and,
respectively, roll 2 and nose 5 in vertical direction.
[0018] Fig. 2 shows the location of the material mat 8 in the press nip with the lower steel
belt 6 and upper steel belt 9. The height of the material mat is
m, and the nose 5 has been placed on height
c below the inlet opening with the measure
b. The guide radius is R, and its angle with the nose 5 is
v.
[0019] Fig. 3 shows the geometry about the nose 5 with nose radius
r, the distance
a between the nose 5 and steel belt 6, and the height
h of the nose 5 above the nearest point 10 on the steel belt 6. The geometry is now
fully determined and can relatively simply be drafted. So is, for example,

.
[0020] Fig. 4 shows a preferred embodiment of the invention, where the mechanism 4 for moving
the structure 1 comprises a rack and pinion drive, where the rack is mounted on the
fixed stand 11, in which drive roll 12, rear end roll 13 and fixed gliding plane 14
with link 15 are mounted. In the link 15 the pivoting gliding plane 16 is attached.
At its free end it rests on the movable structure 1. The endless conveying belt 17
is guided over the nose 5, passes on its return a guide roll 18 and a drawing roll
19, which is operated by cylinders 20. The parts 18-20 are mounted on the movable
structure 1. By means of this design, the structure 1 can be moved without changing
the length of the belt 17 and without changing the speed of the belt, i.e. also of
the material mat 8.
[0021] The arrangement also comprises a control system (not shown) with associated suitable
measuring equipment. Hereby information on actual production parameters, such as nominal
board thickness, selected thickness
b in the press nip, thickness of the material mat to the hot press (either as measured
value or as programmed experience value stored in the control system for every nominal
thickness) etc. is obtained. According to the invention, furthermore, the distance
c has been pre-programmed for all nominal thicknesses, in a certain relation to the
actual thickness of the material mat and with regard to previous experience and calculations
of optimum position with regard to most lenient air evacuation and pre-hardening.
By means of this information and with the knowledge of the geometry according to above,
a suitable position of the structure 1 is calculated automatically, whereafter the
result controls the operation 4.
[0022] Tne arrangement can be varied within the scope of the invention idea and is not restricted
to the embodiment shown.
1. An arrangement for feeding a mat of disintegrated lignocellulose-containing material
into a press with continuously driven lower and, respectively, upper press belts (6,9)
for the manufacture of board, comprising a conveyor with a movable nose portion (5)
extending into the nip between the press belts (6.9), characterized in that a mechanism (4) is provided for moving the nose portion (5) along a fixed roll
surface (7), the geometry of which corresponds to the geometry in the press nip, so
that the distance of the nose portion (5) to the lower press belt (6) substantially
is maintained constant at the movement of the nose portion (5).
2. An arrangement as defined in claim 1, characterized in that a control system is provided for adjusting the position of the nose portion
(5), depending on the thickness of the material mat or board.
3. An arrangement as defined in claim 2, characterized in that a thickness measuring gauge for measuring the material mat before the press
is coupled to the control system.