Coating apparatus – Projection or spray type – Coating moving mass of solid particulate work
Reexamination Certificate
1999-12-22
2002-06-25
Crispino, Richard (Department: 1734)
Coating apparatus
Projection or spray type
Coating moving mass of solid particulate work
C118S313000, C156S578000
Reexamination Certificate
active
06409834
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a so-called gluing or resin-blending machine, ie a machine used in plants producing wood fibre panels by a dry method (in particular medium density fibreboard or MDF panels), the machine in this case blending wood fibres with a thermosetting liquid glue.
BACKGROUND OF THE INVENTION
As is well known to the expert of the art, MDF panels are produced by two types of plant, known respectively as a blow-line plant and a resin-blending or traditional plant.
The essential characteristics of a blow-line plant, shown schematically in
FIG. 1
, will now be described. This shows a grinder
10
which is fed with wood and steam (this feed being indicated by the arrow
12
) to reduce the wood to fibres. The fibres produced in this manner leave the grinder
10
through a blow-up valve
14
mixed with steam (relative humidity 100%) and are conveyed via a line
16
to a dryer
18
. A liquid glue is injected through the blow-up valve
14
(as indicated in
FIG. 1
by the arrow
20
) at a pressure of about 6-8 bar, so that a mixture of wood fibres and glue is fed to the dryer
18
. Hot gas
26
and air
28
at ambient temperature are also fed to the dryer
18
via a fan
22
and a line
24
, to dry the fibres. For this purpose the temperature within the dryer
18
can be varied from 120 to 250° C. The fibres dried in this manner are conveyed via a line
30
to a bank of cyclones
32
in which the dry fibre is separated from the steam and gas (formaldehyde) which develop during drying, the steam and gas being discharged to atmosphere, as indicated by the arrow
34
.
The fibres leaving the cyclones
32
, and having a moisture content varying from 2 to 10%, are fed via a mechanical conveyor
36
to a continuously operating so-called bunker weigher
38
where they are weighed out. The fibres leaving the bunker weigher
38
are conveyed to a pneumatic separator
40
the purpose of which is to remove the “impurities” present in the fibre (glue lumps and coarse fibres). At the exit from the separator
40
the fibres are fed by pneumatic conveying
42
to a cyclone
44
feeding a forming machine
48
via a metering belt
46
.
This type of plant produces good-quality panels, ie free from glue lumps which would limit their subsequent use (for example making them unsuitable for painting or for “cladding”, ie covering with decorative paper glued to the panel). The mechanical characteristics of these panels fall within the relative regulations. However glue consumption is high (between 120 and 180 kg per m
3
of finished panel) because of the fact that the glue is injected at the blow-up valve
14
. In this respect, the glue passes, together with the fibres, through the dryer
18
(which operates at high temperature), to hence undergo prepolymerization which reduces its effectiveness.
Even more penalizing for this method is the presence of formaldehyde (contained in the glue) in the gas discharged to atmosphere at
34
after leaving the drying cyclones
32
. This means that scrubbers have to be used for this gas together with treatment devices for the resultant water, with consequent considerable plant and operating costs.
A traditional or resin-blending plant is shown schematically in
FIG. 2
in which elements similar or identical to those of
FIG. 1
are indicated by the same reference numeral plus
100
. A grinder is again provided, fed with wood and steam as indicated by the arrow
112
. The fibres obtained from the grinder
112
, and mixed with the steam (relative humidity 100%), are conveyed through a blow-up valve
114
and along a line
116
to a dryer
118
similar to the dryer
18
of FIG.
1
. Hot gas
126
and air
128
at ambient temperature are also fed to the dryer via a fan
122
and a line
124
to dry the fibres. The dried fibres are then conveyed via a line
130
to a bank of cyclones
132
in which the dry fibre is separated from the steam which develops during drying, this being discharged to atmosphere, as indicated by the arrow
134
.
The fibres leaving the cyclones
132
, and having a moisture content varying from 2 to 10%, are fed via a mechanical conveyor
136
to a bunker weigher
138
where they are weighed out, to be then conveyed to a gluing machine (also known as a resin-blending machine)
120
. This gluing machine is essentially a horizontally positioned cylindrical chamber inside which there is a mixing member
223
consisting basically of a coaxial rotating shaft provided with radial paddles. Liquid glue is injected through nozzles into the chamber (as schematically indicated by the arrow
121
), it being the task of the mixing member
223
to uniformly distribute the glue throughout the fibre mass. After passing through the entire gluing machine, the fibres are conveyed into a pneumatic separator
140
to separate the “impurities” present in the fibre. The fibre is then fed by pneumatic conveying
142
to a cyclone
144
feeding a forming machine
148
via a metering belt
146
.
Compared with the preceding, this type of plant has the advantage of low glue consumption and low formaldehyde emission to the atmosphere. However the gluing machine
120
does not distribute the glue with sufficient uniformity throughout the fibre mass, so that this type of plant produces poor-quality panels with the formation of lumps and stains which drastically limit the use of the product obtained. In particular the panels produced cannot be painted or clad. Moreover because of the poor glue distribution, these panels do not present mechanical and engineering characteristics which remain constant with time and are uniform throughout the panel.
Italian patent 1274565, in the name of the present applicant, describes a gluing machine for wood fibre panel production by a dry process, which if used in a traditional plant enables the aforedescribed drawbacks to be overcome. This gluing machine comprises a horizontally positioned hollow cylindrical body, at one end of which there is provided an entry aperture for feeding an air stream which conveys the wood fibre mass within which the liquid glue is to be distributed, at the other end of the cylindrical body there being provided an exit aperture for outflow of the air stream conveying the glue-impregnated fibres. Sprayer means are also provided to spray with glue the fibre mass fed to the gluing machine. Means are also provided to maintain the fibres in proximity to the inner wall of the cylindrical body for a predetermined length as they flow through it. Said sprayer means are positioned coaxially along said length throughout which the fibres are maintained in proximity to the inner surface of the cylindrical body. The means for maintaining the fibres in proximity to said inner wall comprise a pipe having a downstream-facing open end which opens into the cylindrical body in the vicinity of the sprayer means, this pipe extending coaxially in the upstream direction from said end at least for a certain length before leaving the cylindrical body, an air stream being fed into the other end of this pipe.
This gluing machine can comprise a mixing member (for example a motorized shaft provided with paddles) arranged downstream of the position in which the fibres are struck by the jets of glue.
If used in a resin-blending plant in place of traditional gluing machines, the aforedescribed gluing machine enables wood fibre panels to be obtained of substantially better quality than those obtainable with traditional plants provided with a gluing machine. It has however the drawback that the lateral inner wall of the cylindrical body of the gluing machine is very easily fouled because the glue-impregnated fibres tend to adhere to it. This means that frequent plant shut-downs are required for cleaning said inner wall, with consequent serious repercussions on production costs.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the invention is therefore to provide a gluing machine which while enabling optimum quality wood fibre panels (ie suitable for painting or cladding) to be obtained from the relative plant with
C.M.P. Costruzioni Meccaniche Pomponesco S.p.A.
Crispino Richard
Steinberg & Raskin, P.C.
Tadesse Yewebdar T
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