Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2802~30
- 1 - O.Z. 0050/37634
Contact charging by means of a rotary disk atom;zer
The present invention relates to an apparatus
for safely apply;ng electr;cally charged drops by means
of a rotary disk atomizer or another su;table spraying
system.
Crop treatment agents are generally applied by
producing drops of from 100 to 600 ~m and then depos;ting
these drops under the influence of the k;net;c energy
imparted to the drops in the atomizing apparatus, and
gravity. The drops are preferably deposited on the sur-
faces directly facing the atomiz;ng apparatus.
For reasons of cost-effectiveness, it is neces-
sary to minimize the amount of liquid applied per unit
area. There are limits to the extent to ~hich the amount
of liquid can be reduced since on the one hand there is
a minimum number of drops which has to be applied per
unit area of crop surface in order to maintain the effec-
tiveness of a crop protection agent, and on the other
hand a reduction in the drop diameter increases the losses
due to drift and evaporation.
~ ence, it has long been attempted to improve the
deposition of droplets by the use of electric forces,
as in the case of electrostatic po~der coating. This
technique is expected to have the follo~ing advantages
over the procedure conventionally employed today:
- The effects of electric forces decisively imProve the
uniformity of drop distribution, for example in a crop;
deposition takes place not only on the surfaces adjacent
to and facing the atomizing apparatus but also on surfaces
further away and even on surfaces facing away from the
sprayer.
- Since the effects of electric forces improve the deposi-
tion of, in particular, small drops, it is possible
to apply finer drops and at the same t;me reduce the
losses due to drift and evaporation; this perm;ts a
substantial reduction in the amount of l;quid used per
un;t area and, because of the controlled appl;cation,
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permits a reduction in environmental pollution. In
the case of specific indications, it may be possible
to save active ingredient (cf. E. Moser and K. Schmidt,
"~esseren Pflanzenschutz mit elektrostatischer Aufladung",
DLG-Mitteilungen 8/1982).
In contrast to electrostatic powder coating in
paint shops, the spraying and atomizing process in agri-
culture has to be carried out under changing sPraying and
atomizing conditions which are not always optimum. This
is because the earth leakage resistance of the leaf to be
coated changes w;th the water content of the plants and of
the soil, the effect of the electric field in the environ-
ment of the spraying and atomizing equipment varies ~ith
the geometry of the plants, and the conductivity of the
liquid to be sprayed and atomized varies with the active
ingredients used.
The drops can be charged by different methods.
Possible methods are charging before drop production
(contact charging), charging during drop production
tinduction charging) and charging after drop production
(corona charging). Extensive investigations in practice
have shown that a substant;al improvement in drop deposi-
t;on ;s achieved by, preferably, contact charging. One
of the main reasons for the difficulties encountereJ in
using contact charging for spraying or atomizing conduc-
tive liquids is that, at an appropriately high voltage
and electrical capacitance~ the electrical energy stored
in the spraying system and in the tank can be so high
that it is dangerous for people to come into contact with
parts under voltage.
To date, the following methods have been adopted
in order to overcome these difficulties:
- The conductive liquid to be sprayed and atomized is
under high voltage; to avo;d safety problems, the
electrical capacitance of the entire system and hence
the capacity of the tank are kept small. The advantage
of the apparatus is the simple, safe construction; the
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disadvantage ls the restriction of the tank size.
- An intermediate tank is installed between an earthed
storage tank of large capac;ty and a storage tank which
has a smaller capac;ty and is charged via high voltage~
Liquid is transported batchwise from the earthed storage
tank into the charged storage tank via this intermediate
tank in such a way that the intermediate tank is brought
in each case to the potential of the storage tank con-
nected to it. The advantage of the method is that the re-
striction in tank size is dispensed with; the disadvantageis the very considerable expense and space requirement
for the installation of the ;ntermediate tank system.
- A long connecting l;ne of non-conductive material is
installed between the earthed storage tank and the
nozzle under high voltage; the high voltage applied
to the nozzle decreases between the latter and the
storage tank over the liquid column acting as a resis-
tance. ~he advantage is that the apparatus is compact
and also suitable for subsequent installation in exist-
ing equipment; the disadvantages are that use is re-
stricted to liqu;ds of low conductivity, the pressure
loss is high, and there is a tendency to blockage.
- The liquid to be sprayed or to be atomized is contained
in a system electrically insulated toward the outside,
and can be charged by means of a high-voltage system
integrated in the tank. This system can be used in
commercial agriculture; its disadvantage is the expense
incurred in the ;nsulat;on of the ent;re liqu;d system.
It is an object of the present ;nvent;on to retain
the contact charging method, wh;ch ;s recogn;zed as be;ng
particularly su;table, and des;gn a s;mple apparatus for
safely spraying or atom;z;ng electrostat;cally charged
droplets, the amount of l;quid available in the tank being
sufficiently large to permit economical use on agricultural
machinery or other spraying equiPment of large capacity.
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According to the present invention there is
provided an apparatus for applying a liquid in the form of
electrically charged drops via a spraying system from a
storage tank, the storage tank and all means for conveying
the liquid being uncharged, comprising:
a) means for conveying the liquid in the form of
droplets or as an intermittent jet over a distance
of from 3 to 30 through the air onto a target
surface,
b) means for applying a high voltage of from 10 to
150 to said target surface,
c) means for charging the liquid on said target
surface and throwing it off
d) said target surface being provided with a housing
so that electrical forces are prevented from
affecting people or adjacent parts of the
apparatus.
According to the present invention there is also
provided an apparatus for applying a liquid in the form of
electrically charged drops via a spraying system from a
storage tank, the storage tank and all means for conveying
the liquid being uncharged, comprising:
a) means for conveying the liquid in the form of
droplets or as an intermittent jet, through a
nozzle, over a distance of from 3 to 30 through
the air onto a rotating disk,
b) means for applying a high voltage of from 10 to
150 to said rotating disk,
c) means for charging the liquid on said rotating
disk and throwing it off,
d) said rotary disk being provided with a housing so
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f ~
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as to prevent electric forces from affecting
people or adjacent parts of the apparatus.
According to the present inven-tion there is also
provided a method for applying a liquid in the form of
electrically charged drops via a spraying system from a
storage tank, the storage tank and all means for conveying
the liquid being uncharged, wherein
a) the liquid is conveyed in the form of droplets or
as in intermittent jet over a distance of from 3
to 30 through the air onto a rotating disk,
b) high voltage of from 10 to 150 is applied to the
rotating disk,
c) the liquid is charged on the rotating disk and is
thrown off, and
d) said rotary disk atomizer is provided with a
housing so that electrical forces are prevented
from affecting people or adjacent parts of the
equipment.
With the novel apparatus, and using the contact
charging method recognized as being particularly suitable,
it is possible for liquid drops to be electrically charged
and to be safely sprayed or atomized from a tank by means of
a spraying or atomizing system without there being any
restrictions in respect of the size of the tank, without
space being required, or expense incurred, for an
intermediate tank, and without operation being confined to
certain narrow conductivity ranges of the liquid to be
sprayed.
The system has a particularly simple design, is
ready for operation in any position, has a low energy
consumption, does not become blocked and can be installed
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subsequently in conventional spraying and atomi~ing
equipment.
The novel apparatus is preferably used for
applying crop protection agents. Additional advantages of
using the apparatus according to the invention on
agricultural machines are:
a) :no restriction of use with regard to the width or
height of spraying due to the apparatus,
b) no restriction due to the apparatus in connection
with particularly dense plant growth as the
particles are transported by a combination of
gravitational force and electrical force, and
c) no deposition of drops on the person carrying out
the
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- 5 - O.Z. 0050/37634
application when this is effected with hand-held
apparatuses.
The novel apparatus can also be used for coating
paper webs and film webs, metallic articles, and articles
whose discharge capacity is sufficient for conventional
electrostatic coating.
The invention is ;llustrated below ~ith reference
to the drawing.
In Figure 1, the structure of the apparatus is
shown schematically.
The liquid 2 is conveyed from the earthed storage
tank 1 via a valve 4 to a nozzle 5 by means o~ a pump
3. Either by intermittent ol~eration of the valve 4 or
by suitable choice of the nozzle 5, the liquid is sprayed
in the form of individual drops or in the form of short
liquid threads from the nozzle 5 over a distance 6 of from
3 to 30, preferably from 5 to 20, cm through the air onto
a rotating disk 7 or ;s conveyed onto another suitable
target surface. The rotating disk 7 is driven by means
of a motor 8 and charged electrically by a high-voltage
generator 9. The air gap 6 serves to insulate the earthed
liquid system, consisting of storage tank 1, pump 3, valve
4 and noz~le 5, from the charged atomizing system, con-
sisting of rotating disk 7, motor 8 and high-voltage
generator 9. It is particularly advantageous if the
high-voltage generator 9 is integrated in the housing
11 for holding the rotating disk 7, and charging of the
droplets is matched to the optimum spraying conditions
by varying the high voltage.
The geometry of the air gap depends on the level
of the high voltage applied. For the range fr~m 50 to
iO0 kV, which is recognized as being particularly effective,
an air gap 6 of from 5 to ~0 cm is suitable. Th~ ability
of the system to function is ensured ~hen the liquid 2
fed does not form a conductive connection between nozzle
5 and rotating disk 7 when in the form of a cohesive jet.
The system conveying high voltage is enclosed
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by a housing 11 which can provide both protection from
spray and protection from contact. ~ecause of the low
electrical capacitance of the charged system, special
safety measures against accidental contact with voltage-
S carrying parts are not required if the maximum currentwhich the high voltage generator 9 is capable of delivering
in short-circuit operation does not exceed a certain
limiting value.
Drawing.
