Note: Descriptions are shown in the official language in which they were submitted.
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GAS-VENTING ARRANGEMENT
FIELD OF THE INVENTION
[0001] The present invention relates to a gas-venting arrangement
in a paint-toning machine which comprises one or more containers for storing
colour paste or the like, and a dispensing device connected to each container
for dispensing the colour paste from the colour paste container, the
dispensing
device comprising an at least substantially vertical-shafted dispensing pump
connected through a suction pipe to the inside of the colour paste container
and through a dispensing pipe to a dispensing nozzle and comprising a
dispensing cylinder and inside it a reciprocating replacement element,
whereby the dispensing is controlled by a suction valve arranged in the
suction
pipe and a dispensing valve arranged in the dispensing pipe.
[0002] Paint-toning machines as described above are known from
US patent publications 4,708,269; 5,445,195 and 5,938,080, for instance.
[0003] In dispensing colour paste, a pump 8 based on admission
and outward, i.e. dispensing, strokes, as shown in Figure 1 of the attached
drawing, is used in general. Such a pump usually has a valve with a sliding
slide valve 3 having a small inner volume. In some cases, different poppet
valve modifications are also used as the valves. Toning machines usually
have several paste containers 1 and they are located as close together as
possible so that the assembly would not require too much space. The most
common construction method is to locate the valve 3 substantially close to the
bottom surface of the container 1 and the pump 8 immediately above it. The
plunger 4 of the pump then moves upward during an admission stroke and
downward towards the valve during an outward, or dispensing, stroke. The
arrangement provides the shortest possible suction pipe 2 length and the
highest possible hydrostatic pressure caused by the height of the natural
liquid
level of the colour agent to facilitate the entry of the slow-moving colour
paste
to fill the pump 8 during an admission stroke.
[0004] The above-mentioned construction method has been in use
in manually-operated toning machines during more than 40 years. A
corresponding construction has also passed down to the automatic toning
machines, and it has been very common in them during more than 25 years. A
serious disadvantage in the construction is the imprecision of the smallest
doses, the reason for which has not been understood up till now. On the other
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hand, the devices have been relatively inexpensive and thus a great precision
has not been expected of them.
[0005] A practical study of the matter has been very difficult
because of the difficult behaviour of colour agents. To prevent imprecision,
the
usual method has been to make the valve as small in volume as possible. The
imprecision problem in small doses in particular has this way been only
passably solved.
[0006] Manufacturers of toning systems have, however, wanted to
be able to dispense smaller and smaller doses precisely. This would provide a
possibility to develop stronger colour pastes than before and make the
dispensing faster. At the same time, it would be possible to develop lighter
tones than before and to tone them precisely in even smaller canisters. This
would, as a whole, also provide a considerable advantage in that the filling
interval of machines would become longer and less transport and storage
space would be needed.
BRIEF DESCRIPTION OF THE INVENTION
[0007] It has been discovered according to the invention that the
above-mentioned precision problem related to dispensing small doses in
particular can be solved by means of a gas-venting arrangement, which is
characterized in that the lower end of a displacement element in the lower
extreme position of the dispensing movement of the element with respect to
earth gravity is either level with the upper edge of a dispensing pipe opening
into a dispensing cylinder or past it, and that the mutual height positions of
the
suction and dispensing pipes and the lower end of the displacement element
in said extreme position are such that they together form a substantially
horizontal flow path or a flow path ascending in the direction of the
dispensing
flow.
[0008] In the present pasta dispensing devices according to Figure
1, the dispensing errors have been detected to originate from the structure of
the conduit between the suction valve 3, the dispensing pump 8 and the
dispensing valve 3. This structure easily accumulates gas bubbles 7 and, due
to the compressibility of gas, causes significant errors in dispensing. Gas
bubbles 7 accumulate especially to the bottom surface of the lower end of the
displacement element 4 of the dispensing pump already when the machine is
taken into use and also when paste is sucked by means of this displacement
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element, these gas bubbles cannot exit said space in a conventional suction
pump construction. When these gas bubbles expand during the suction phase
and compress during the dispensing phase by effect of the displacement
element, an error is caused in the amount of paste moved by the displacement
element, and, naturally, the smaller the dispensing amount, the bigger the
relative error.
[0009] When using the dispensing pump construction of the
invention, all gas bubbles on the bottom surface of the lower end of the
displacement element when the machine is taken into use will immediately at
the end of the first dispensing phase move on towards the dispensing valve
and thus do not decrease the dispensing precision during the next suction
phase. Similarly, all gas bubbles which along with the paste being dispensed
end up on the bottom surface of the lower end of the displacement element
through the suction valve can move on towards the dispensing valve and do
not remain to decrease the dispensing precision of the dispensing pump.
BRIEF DESCRIPTION OF THE FIGURES
[0010] In the following, the gas-venting arrangement of the
invention is described in greater detail with reference to the attached
drawing,
in which
Figure 1 shows a schematic diagram illustrating dispensing in a
paint-toning machine of prior art,
Figure 2 shows a schematic diagram illustrating dispensing in a
paint-toning machine of the invention during an admission stroke,
Figure 3 shows a schematic diagram illustrating dispensing in a
paint-toning machine of the invention during the end of a dispensing stroke,
and
Figure 4 shows a variation of the paint-toning machine of Figure 3.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Figures 2 and 3 of the attached drawing show a schematic
diagram of the structure and operating principle of a paint-toning machine of
the invention. Figure 2 especially shows the general structure of the machine
with respect to colour paste dispensing in particular. Basically, the machine
comprises one or more containers 11 for colour paste or another liquid to be
dispensed. Dispensing means are connected to each container 11, the main
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components of which are a suction valve 12, a dispensing pump 20 and a
dispensing valve 16.
[0012] The dispensing pump 20 is a displacement pump having a
substantially vertical shaft. This means that at least basically, the movement
of
the displacement element of the pump is in the direction of earth gravity or
in a
direction which only differs from it to some extent. This dispensing pump 20
comprises a dispensing cylinder 21 and inside it, a reciprocating displacement
element 14, which in the following will be referred to as a plunger regardless
of
whether it is moved by a plunger rod or a bellows-type unit.
[0013] The dispensing pump 20 is connected to the container 11
through a suction pipe 13 which is connected to the bottom part of the
container 11, most preferably to its bottom. A suction valve 12 is arranged to
this suction pipe 13 for controlling the direction of travel of the paste
during
dispensing. The direction of travel of the colour paste during dispensing is
marked by arrow A. Figure 2 shows a dispensing situation in which paste is
being sucked into the dispensing pump 20 from the container 11. The suction
valve 12 is then open and paste can flow from the paste container 11 to the
dispensing pump 20. When moving the plunger 14 in the direction of arrow B
in Figure 2, the paste moves from the container 11 and fills the cylinder 21
to
the extent that the plunger 14 is lifted.
[0014] According to the invention, the essential in the situation of
Figure 2 is that the top edge of the suction pipe 13 starting from the suction
valve 12 is either level with or lower than the bottom surface of the lower
end
of the plunger 14 in all dispensing positions of the plunger 14. Gas bubbles
19
in the sucked paste can then move from the suction valve 12 and suction pipe
13 to the suction pump 20.
[0015] Figure 3 shows the paint-toning machine of Figure 2 in a
situation in which the dispensing plunger 14 is in its lowest extreme
position,
i.e. the position it reaches at the end of the dispensing phase. In this
situation,
the suction valve in the suction pipe 13 is closed and the dispensing valve 16
in the dispensing pipe 17 starting from the dispensing pump 20 is open to
allow the liquid being dispensed to flow through the dispensing pipe 17 to the
dispensing nozzle 18.
[0016] It is essential for the invention, as also shown in Figure 3,
that in this situation in which the dispensing plunger is at its lowest
dispensing
position, the bottom surface of the lower end of the dispensing plunger 14 is
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either level with or lower than the top edge 15 of the dispensing~pipe 17. The
gas bubbles 19 can then move on from the dispensing pump 20 in the
direction of the dispensing nozzle 18. Thus, the gas bubbles do not remain in
the dispensing pump, which would significantly decrease the dispensing
5 precision.
[0017] In the embodiment of the invention according to Figures 2
and 3, it has been possible to leave out entirely a separate vertical channel
collecting gas bubbles between the pump and valve. The described
arrangement of the invention guarantees that at the very end of the
dispensing, the liquid being dispensed flows a short distance to the side
and/or
up with respect to gravity. This essential change in the flow direction of the
colour paste in the immediate proximity to the plunger 14 makes the gas
bubbles 19 bound to the colour paste flow along with the colour paste being
dispensed away from the pump 20. With a suitable timing of the suction and
dispensing valve 12 and 16 operation, it is possible to make these
continuously forming and accumulating gas bubbles 19 move away from the
pump 20 through the nozzle 18. Making this operation automatic and
continuous during dispensing, it efficiently prevents the accumulation of gas
bubbles inside the pump 20, in the valves 12 and 16 or in the dispensing pipe
17 and nozzle 18. Said arrangement makes it possible to eliminate the
imprecision of small-dose dispensing occurring in earlier corresponding paint-
toning machines.
[0018] The outflow of gas bubbles described above can further be
improved by an arrangement of Figure 4, in which the machine of Figures 2
and 3 is slightly tilted in such a manner that the dispensing nozzle side end
of
the machine is lifted slightly upward. By means of this arrangement, the
exiting
of gas bubbles can be further intensified. In this arrangement, the movement
of the gas bubbles resembles the behaviour of the bubble in a builder's level
and is a very efficient way of removing the generated gas bubbles. In
practical
experiments, the arrangements of the invention have provided a substantial
improvement in dispensing precision. At the same time, it has been possible to
keep the space utilisation of fihe remaining construction of the machine
excellent. Thus, the construction method of the invention makes it possible to
significantly improve dispensing precision especially with small doses and in
principle with nearly no additional costs, when the dispensing pump and the
channels connected to it are implemented according to the invention.
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[0019] The paint-toning machine of the invention and its operation
are above described by means of two exemplary embodiments only, and it is
to be understood that several modifications can be made to it without
departing from the scope of protection defined by the attached claims.
