Note: Descriptions are shown in the official language in which they were submitted.
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CENTRIFUGAL ATOMIZER HAVING A KNIFE-EDGED ROTATING CONE
Field of the Invention
This application pertains to centrifugal atomizers and more
particularly to centrifugal atomizers of the spinning disc type
used for dispersing liquid resin in wood chip blenders used in
the production of waferboard.
Background of the Invention
Liquid resin is used as a binder in the manufacture of
particle board, wafer board, oriented-strand board, and similar
wood products. These products are manufactured by coating wood
chips, flakes, strands, or the like (hereafter referred to as
"furnish") with resin binders, the coated furnish then being
aligned, compressed, and heated to form sheets of wood building
products. The integral strength of these products is based on
the uniform dispersement of the liquid binder throughout all the
surfaces of the furnish.
A substantial cost element in the manufacture of such wood
products is the cost of the resin binder used. Consequently, if
a reduction in the amount of resin required in the manufacturing
process is accomplished while maintaining the coating standards
for the furnish, the cost of manufacture is directly lowered.
In the prior art, resin binders have been applied by
numerous method including the use of pulverised dry resin,
spraying of liquid resin through nozzles, and the use of rotating -~
sprayers to create a resin mist. The dry resin method has the ;
drawback of being inefficient in use of the resin and therefor
most expensive. The nozzle-spraying method has the disadvantage
of producing a wide range of sizes of resin droplets.- ;~
Rotary sprayer were introduced to provide a con-
trollable spray of uniform-sized droplets. Canadian patent No.
1,160,038, issued January 10, 1984 to Beattie, discloses the use
of dual, spinning, slightly conical discs for spraying liquids ~
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within a nearly-horizontally-rotating, tubular furnish blender.
A circular tubular ring provided with a series of orifices feeds
the liquid resin against the spinning recessed face of a central
plate driven by a hydraulic motor. Centrifugal force causes the
liquid to flow outwardly over the plate to be held in a circum-
ferential reservoir located internally near the perimeter of the
disc. As the reservoir is fed with liquid, the liquid from the
reservoir is forced over restraining dams so that it flows
radially outward over the disc face. The liquid accumulates on
the circumferential edge of the disc until forced off as a spray
by the spinning action of the disc.
Beattie teaches that medium-sized droplets (50 to 200
microns in diameter) are preferred in that larger droplets are
wasteful of the liquid resin and smaller droplets do not travel
the distance required to meet the furnish as per the Beattie
design. Indeed, Beattie states that droplets that are too small
not only fail to travel far enough to meet the furnish, but also
coalesce en route. The Beattie patent therefore does not
consider the use of very small droplet size as a viable option.
Beattie also teaches that the sharpness of edge profile of the
disc is of minor importance (p. 9, lines 21-22). Prior art discs
have a radius of curvature of the disc edge on the oprder of 1/4
inch.
Beattie describes how the surfaces of the reservoir dams
are machined to final dimension after assembly to ensure
identical radii of the dam surfaces from the axis of rotation.
The dam surfaces control the distribution of the flow of liquid
from the reservoir to the disc face. Therefore, careful
alignment and machining is required to ensure a uniform spray
leaving the disc. Machining the components after assembly
increases the complexity and cost of manufacture of the centrifu-
gal atomizer.
Such prior art atomizers have a number of disad-
vantages. Resin droplets are created which, although small enough
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to be described as a mist, are unnecessarily large, causing
unnecessarily high consumption of resin. Such atomizers are ex-
pensive to manufacture in that machining of the rotary sprayer
head is done after assembly to exacting tolerances to achieve
uniform spraying. Also, since the liquid resin flows across the
face of the disc, dust covers may be required in certain
applications.
Summary of the Invention
To more efficiently use liquid resin as a binder in the
manufacture of particle board, wafer board, oriented-strand
board, and the like, an atomizer for producing a fog of atom-
ized liquid resin is provided which has a rotating cone where-
in said cone spins at high speeds and has a sharp, knife edge
around its outermost circumference and a plurality of apertures
around the circumference of its face. Liquid resin is supplied
to an annular chamber formed in the rear of the cone. The resin
is then propelled by the rotating motion of the cone through the
apertures around the circumference of the face of the cone, onto
the inside surfaces of the cone, and sprayed as an atomized fog
from the sharp edge of the cone in a plane defined by the sharp
edge of the cone. ~-
Brief Descri~tion of the Drawings
The attached drawings disclose a preferred embodiment of
the invention which should not be construed as limiting the~;~
spirit or scope of the invention in any way.
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Figure 1 is a perspective view of the invention. ~-~
Figure 2 is a cross-section taken along lines 2-2 of Figure -
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Figure 3 is a cross-section taken along lines 2-2 of Figure
1 showing the main housing in isolation.
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Figure 4 is a front elevation view of the main housing shown
in Figure 3.
Figure 5 is a rear elevation view of the main housing shown
in Figure 3.
Figure 6 is a front elevation view, partially cut away,
of the cone of the invention.
Figure 6A is a cross section taken along lines 6A-6A of
Figure 6.
Figure 7 is a front elevation view, partially cut away,
of the resin plate of the invention.
Figure 7A is a cross section taken along lines 7A-7A of
Figure 7.
Figure 8 is a partial cross section taken along lines 8-8
of Figure 5.
Detailed Description of the Preferred Embodiment
The centrifugal atomizer of the invention, designated
generally as 1, is designed for use in a blender as disclosed
in the Beattie reference above. It has been found that furnish
subjected to a resin fog for a short period of time during the
manufacturing of such wood-building products produces boards that
meet the required structural standards. Further, such a process
is more efficient with respect to resin consumption.
Referring to Figure 2, the atomizer consists essentially
of a main housing 3, a rotating cone 2, and resin plate 7 fixed
to the non-rotating housing 3. An electric two-pole motor 4,
which rotates at 15,000 r.p.m., is secured by clamp 14 and screw
15 drives cone 2 via drive shaft 10. Cone 2 is connected to drive
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shaft 10 by nut 20, washer 21 and cotter pin 22. A hardened
washer is also provided at 23.
Air line 12 provides cooling air to the motor 4. Magnetic
pick-up 8 interacts with metal inserts in the rotating cone 2 to
sense the rotation of the cone and to provide a signal repre
sentative of the cone's rotational speed via signal carrier 16.
Cover plate 18 provides access to magnetic pick-up 8. Heat sensor
17 also provides a signal via line 19 representative of the heat
of the atomizer. Resin feed line 9 connects to feed channel 5,
which is shown for purposes of illustration in figure 2 at a
different angular location than the actual position shown in
figures 4, 5 and 8.
Resin plate 7 is fixed to housing 3 by cap screws 26. An
O-ring is provided at 25 to prevent leakage of resin.
Figure 3 illustrates in cross section in further detail the
housing 3, with the cone, motor and resin plate removed. The
resin plate 7 fits over hub 33 to form the resin flow path. Cut-
outs 36 are milled in the body of the housing for weight
reduction. A bore 34, (not shown in Figure 2) is provided in the
housing communicating with cut-out 36 by channel 38 to provide
cooling air flow from the air line 12, through the motor cavity,
and out bore 34. A cap is provided for the outer end 39 of bore
34. Channels 42 and 44 are provided for sensor 8 and line 16
respectively.
Figures 6 and 6A illustrate the cone 2. It has a rear
opening 48 which fits over resin plate 7. Holes 30 are formed in
the face 45 of the cone and may form two complete continuous
circumferential rows as partially illustrated in Figure 6. The
holes are drilled in a slightly spiralling offset manner (i.e.
not parallel to the axis of rotation nor to each other) for
better resin flow. Edge 32 is a sharp knife edge. Conical
surface 31 preferably diverges from face 45 at an angle of about
37 degrees.
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Figure 7 and 7A show the resin plate, which is secured to
housing 3 through holes 47.
Figure 8 illustrates in better detail the resin feed channel
5. The end of channel 5 communicates with an angled bore 50 which
carries the resin into area 51 behind the resin plate.
In operation, cone 2 is rotated by motor 4 at high speed.
Liquid resin enters via resin feed-line 9 under pressure and
follows the path shown by arrows 11 through opening 13, through
opening 29 between resin plate 7 and housing 3, and into chamber
28 where the resin is aerated and propelled by a centrifugal
force through apertures 30, onto and along the cone inside
surface 31, and onto sharp edge 32. High centrifugal forces cause
the resin to leave the knife edge 32 as a fog lying in a plane
perpendicular to the axis of rotation of the cone.
As will be apparent to those skilled in the art in the light
of the foregoing disclosure, many alterations and modifications
are possible in the practice of this invention without departing
from the spirit or scope thereof. Accordingly, the scope of the
invention is to be construed in accordance with the substance
defined by the following claims.
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