[0001] This invention relates to an apparatus for separation of impurities from a fiber
material at the manufacture of fibreboard according to the dry method. Heavy particles
such as shives, splinters, glue lumps, sand, scrap etc. are separated at different
occasions in the process.
[0002] At the manufacutre of fibreboard according to the dry method at first the raw material,
in the form of wood chips, is defibered so that the fibers are exposed. This fiber
material is thereafter treated with glue, dried, formed to a fiber mat, compressed
and pressed in a hot press. It is essential at this process that impurities and other
undesirable heavy particles are removed from the fiber material prior to the forming
and pressing process. To sort out such impurities in an economic way is a large problem
in the fiber and chip industry. In the course of time great resources have been invested
in the development of so-called scrap traps and air separators for this purpose. The
result thereof has been apparatuses of increasing complexity and with ever more sophisticated
and expensive equipment for their control.
[0003] The present invention offers a solution for the aforesaid problems. It relates to
a separation apparatus of simple design, which efficiently removes heavy impurities
from the fiber material.
[0004] The characterizing features of the invention are apparent from the attached claims.
[0005] The invention is described in greater detail in the following, with reference to
the accompanying figure showing an apparatus according to the invention.
[0006] According to the embodiment shown, the apparatus comprises a vertical cylindric chamber
10, to which an inlet 11 for the fiber material is connected. The inlet 11 consists
of a pipe, which extends inward to the centre of the lower portion of the chamber
10. The inlet is directed upward, and in front of its mouth a plane horisontal retardation
member 12 is located, which is intended to stop the vertical speed of the ingoing
fiber flow and deflect the fiber flow laterally. The upper side can be plane or possibly
upward tapering.
[0007] At the top of the chamber 10 an outlet 13 for accepted fibers, and in the bottom
of the chamber an outlet 14 for separated heavy particles (reject) are located. This
reject outlet 14 can be provided with a sluice means 15, for example in the form of
two tight dampers. In the bottom of the chamber 10, between the reject outlet 14 and
fiber inlet 11, ducts 16 are provided for the supply of a continuous and uniformly
distributed base flow of gas, for example air. These ducts 16 are connected to an
air distribution space 17, which distributes the air symmetrically into the chamber
10 through an adjustable slot 18 extending all about the entire circumference of the
chamber 10.
[0008] The fiber material to be screened is supplied through the inlet pipe 11 in the form
of an airborne fiber flow with a flow rate of 15-45 m/s. The fiber flow meets the
retardation member 12, which stops the vertical speed of the fiber flow and deflects
and distributes the fiber flow outward. The upwardly directed continuous base flow
of air then catches up the fiber material, and a stable, substantially highly uniform
and even flow is obtained quickly, which implies the possibility of a restricted height
of the chamber 10. Acceptable fibers are carried by the base flow, while heavy particles
with a higher fall rate drop down to the bottom of the chamber. This reject is discharged
via the dampers of the sluice means 15.
[0009] The acceptable fibers are moved upward by the upward air flow. By adjusting the air
flow by means of a by-pass shunt 19 with an air damper 20 controlled by a scanning
device 21 for the pressure drop between the chamber 10 and outlet 13, the separation
process and fiber transport can be controlled in a simple and efficient way. The circular
shape of the chamber 10 yields an air flow distributed across the cross-section. The
slot 18 of the air distribution space 17 causes the ingoing air to be directly distributed
across the entire cross-section. This in its turn prevents a strong local turbulence,
and the risk of separated particles being sucked along is at a minimum.
[0010] The separation apparatus is particularly suitable for use in a process for making
fibreboard, where air transports the fiber material from defibration via gluing and
drying to forming. Heavy particles such as undefibered material and lumped glue, resin
and latex particles etc. must be removed in some way. The present invention renders
it possible to separate these impurities rapidly and efficiently. The separation process
can be easily controlled, and the apparatus can be located in a suitable place, preferably
between drying and forming, in existent installations as well as in new ones. The
accepted fibers are continued to be transported from the outlet 13 of the chamber
10, for example to a fiber bin or a forming arrangement.
[0011] The separation process is very sensitive to variations in temperature and air humidity
and, therefore, an automatic control of the air flow rate is essential and in many
cases a prerequisite for a successful result. This problem has been solved by the
apparatus described above. The air flow to the base flow, thus, is controlled in that
a minor air flow is shunted the chamber 10 through the duct 19 where the flow is adjusted
by means of the damper 20. This damper is controlled by the scanning device 21 for
the difference pressure between the chamber 10 and the outlet 13. The adjustable slot
18 yields a low air rate with the possibility of local adjustment of the air flow
for a uniform distribution about the entire circumference. As transport air for the
fibers to the fiber inlet 11 and as a base flow preferably air is used, the largest
part of which is taken from the vacuum boxes of the forming arrangement, i.e. the
transport air which is separated at the forming of a fiber mat on an air-pervious
support.
[0012] A separate fan preferably is provided for the transport of air/fibers to the chamber
10. The separation apparatus thereby can be located in any optional place between
the fiber drier and the forming arrangement.
[0013] The invention, of course, is not restricted to the he scope of the invention idea.
1. An apparatus for separating heavy particles from an airborne flow of fiber material
at the manufacture of fibreboard according to the dry method, comprising a vertical
cylindric chamber (10) with an inlet (11) for ingoing fiber material and separate
outlets (13 and, respectively, 14) for fibers and heavy particles in the top and,
respectively, in the bottom of the chamber (10) and at least one duct (16) being connected
to the bottom of the chamber (10) for the supply of a continuous base flow of air
upward through the chamber at such a rate, that it can carry the fibers but not the
heavy particles, characterized in that the inlet (11) for the fiber material is directed upward and centrally located
in the lower portion of the chamber (10) above the supply duct (16) for the base flow,
that a plane horisontal retardation member (12) is provided in connection to the inlet
(11) for the fiber material so as to stop the vertical speed of the ingoing fiber
flow and to deflect and distribute the fiber flow outward.
2. An apparatus as defined in claim 1, characterized in that the duct (16) for the supply of the base flow of air is connected to an air
distribution space (17) at the chamber bottom, which space communicates with the chamber
through an adjustable slot (18) extending all about.
3. An apparatus as defined in anyone of the claims 1-2, characterized in that a sluice means (15) is connected in the bottom of the chamber (10) for the
discharge of the separated heavy particles.
4. An appratus as defined in anyone of the claims 1-3, characterized in that it comprises a device for controlling the air flow to the base flow, comprising
a channel (19) with a damper (20) for controlled by-pass shunting of a minor part
of said air flow past the chamber (10).
5. An apparatus as defined in anyone of the claims 1-4, characterized in that a separate fan is provided to supply the air/fiber flow to the fiber inlet
(11) in the chamber (10).
6. An apparatus as defined in anyone of the claims 1-5, characterized in that it is located in a fiber transport duct between a fiber drier and an arrangement
for forming the fibreboard.
