[0001] Known apparatus e.g. for making paint, comprises a vessel for receiving liquid and
other material to be mixed and a rotary agitator for immersion into the contents of
the vessel. The other materials may comprise opacifiers, pigments and the like, and
are often added in successive increments. The size of an increment is determined by
the state of the liquid to which the increment is added, and the desire to avoid clots
and lumps in the mixture. In general, it is better to add successive small increments
than fewer larger increments.
[0002] European Patent No. 0000827 describes apparatus of the mentioned kind in which the
agitator is vertically moved in the vessel under the control of means responsive to
the noise level emitted by the contents of the vessel during agitation. Effectively,
the addition of a powder increment, although having a blanketing effect, causes increased
turbulence and hence more noise and this noise is sensed and a resulting signal causes
the agitator to be raised so as to be nearer the surface of the liquid. In this position
the agitator has a greater effect on mixing and dispersing of the powder (assumed
to be located towards the surface of the liquid) and consequently the speed and efficiency
of the dispersion is improved.
[0003] The apparatus is maae in various sizes, for example a nominal 500 litre, 2500 litre
and so on vessel capacity. If a large vessel is used for a small batch for example
a 400 litre batch in a 2500 litre vessel as is sometimes necessary because of the
unavailahility of smaller apparatus, pool of liquid is shallow and the scope for raising
and lowering of the agitator is quite limited because the agitator must be immersed
in the solvent. The apparatus of said European Patent is then of only limited value
or even is not useful.
[0004] The object of the invention is to provide improvements.
[0005] In accordance with the invention, mixing apparatus comprising a vessel for receiving
liquid and other materials to be mixed, a rotary agitator for immersion into the contents
of the vessel, and means responsive to the noise level emitted by the contents of
the vessel during agitation, is characterised in that the said means responsive to
the noise level are used to vary the effectiveness of the agitator other than by height
adjustment.
[0006] Hence the adjustment based on noise level is used effectively in situations where
the apparatus of said EP is useless, although the present invention is in fact useful
in other situations also, that is to say, as a substitute for the apparatus of said
EP.
[0007] Various possibilities for carrying out the invention will now be discussed with reference
to the accompanying drawing wherein the sole figure is a schematic view of apparatus
for making paint. In the drawing a pot 10 is charged with powder and solvents which
are mixed and dispersed by rotor 12 driven by shaft 14. The shaft can be raised and
lowered by ram 16 and the shaft is rotated by a motor in the head 18. Microphone 20
senses noise which is used by appropriate circuitry to vary the mixing conditions
from time to time.
[0008] According to a feature of the invention, the agitator is to be rotated by a variable
speed drive (known per se) and the noise responsive means varies the speed of rotation
of the agitator. An increase in turbulence as a result of a powder increment will
lead to an increase in rotation speed, and vice versa, but with upper and lower threshold
limits between which no variation takes place, in order to avoid unnecessary "hunting".
[0009] One example of a known variable speed drive is in BP1051692 where a variable volume
pump is used in a hydraulic transmission. In applying the present invention to a drive
of the kind described in said BP, the noise signal from microphone 20 will be used
to control the swash plate angle of the variable volume pump which drives the motor
in head 18.
[0010] According to another feature of the invention, the rotary agitator is provided with
blades of variable pitch, and the pitch is adjusted by the noise responsive means.
The effect will be similar to that attained by agitator speed variation, in that an
increase in pitch will increase the agitation of the liquid for better mixing, and
a reduction in pitch, that is movement towards a fully "feathered" position will have
the opposite effect, and threshold limits avoid hunting.
[0011] For example, the blades of the agitator 12 may be pivoted on a hub at the bottom
of the agitator shaft 14 for movement between the feathered and effective positions,
and be spring urged to one or other. A loose collar or tubular shaft surrounding the
drive shaft 14 may be axially displaced by an actuator in head 18 operated by the
noise control system so as to cam the blades against the spring to the opposite position.
[0012] According to another feature of the invention, the agitator is provided with blades
which are adjustable between positions more and less closely akin to radial positions.
Effectively the overall diameter of the agitator is varied by such adjustment, and
hence a decrease in noise due to powder addition will result in an increase in agitator
diameter and vice versa, with thresholds for the same reasons as would be the case
if either of the alternative features were utilised.
[0013] This possibility may be utilised by again having inner and outer shafts 14 with one
driving (rotating) the agitator blades 12 and the second moved relatively to the first,
such as by an epicyclic gear set via a noise sensing system to cam the blades to different
angles, between the radial and the tangential to the shafts, so that the blades sweep
through different diameter circles according to the angular position of the blades
to the shafts. At maximum diameter the mixing effect is greatest, akin to maximum
pitch displacement from the feathered position, likewise akin to maximum speed of
the drive shaft 14, or to maximum effective height of the agitator in the pot in the
various respective other possibilities mentioned.
[0014] However, it is possible to utilise all of these features in combination, or ones
of these features in combination.
[0015] It is also possible to utilise any of these features or combination of these features,
in combination with the vertical adjustment feature.
1. Mixing apparatus comprising a vessel for receiving liquid and other materials to
be mixed, a rotary agitator for immersion into the contents of the vessel, and means
responsive to the noise level emitted by the contents of the vessel during agitation,
is characterised in that the said means responsive to the noise level are used to
vary the effectiveness of the agitator other than by height adjustment.
2. Mixing apparatus as claimed in Claim 1 characterised in that the agitator is rotated
by a variable speed drive (known per se) and the noise responsive means varies the
speed of rotation of the agitator.
3. Mixing apparatus as claimed in Claim 1 characterised in that the rotary agitator
is provided with blades of variable pitch arranged to be adjusted by the noise responsive
means.
4. Mixing apparatus as claimed in Claim 1 characterised in that the agitator is provided
with blades which are adjustable between positions more and less closely akin to radial
positions under the control of the noise sensor.
