Note: Descriptions are shown in the official language in which they were submitted.
- The present invention relates to stirring apparatus
which utilize a rragnetic stirring element in connection with
magnetic stirring apparatus, and more particularly to such a
stirring element haviny a vaned or finned structure.
Magnetic stirring apparatus is well-known in the
art. Briefly, such apparatus includes a ro~atably driven drive
magnet. A vessel containing a liquid tc) be mixed is placed
over this drive magnet and a magnetic stirring element dropped
into the vessel. The drive magnet and stirring element are
magnetically coupled through the container walls so that when
the drive magnet is rotated the magnetic stirring element in
the vessel is rotatably driven to stir and mix the liquid
contents of the vessel.
A magnetic stirring element is simply a bar or disc
magnet encased in an inert material such as plastic. ~ lements
of this general type are shown for exa~ple, in U.S~ Patent Nos.
2,951,689 granted on September 6, 1960 to Howard L. Asp et al;
2,518,758 granted on August 15, 1950 to George B. Cook; and
3,749,369 granted on July 31, 1973 to Kurt Landsberger. In
addition, magnetic stirring elements having some sort of
vaned structure are also known in the art and one such element
is illustrated in U.S. Patent No. 3,0~8,716 granted on May 7,
1963 to Frank Dudley Scott. The present invention is parti-
cularly concerned with a new and improved magnetic stirring
element having a vaned structure.
There are disadvantages to the vaned magnetic stirring
elements of the prior art. For example, the typical construction
is to have vanes or fins placed only on the top surface of the
element above the magnetic portion. This construction tends
to make vaned stirring elements of the prior art unstable
hecause of the relatively large moment arm created by the
magnet-to-vane distance. Also, the vaned element of the prior
axt must settle on the bottom of the vessel vane side up so
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`that some care must be used in puttiny the stirring el~ment
into the vessel. Also, with the vane posltion as shown in
- the prior art, the vanes are located at some distance above ~
the bottoTn of the vessel so that there is little or no mixing
along the bottom which makes it difficult to dissolve powder
or other solids which might settle to the bottom of the vessel.
In the present invention, a magnetic stirring element
is provided with a central disc portion having vanes both
upstanding and depending from the disc for better and more
efficient mixing. The magnet is intermediate the upper and
lower vanes so that there is a balancing of the magnet-to-vane
moment arms thereby making the magnetic stirring element of the
present invention relatively stable over a wide range of
rotational speeds. Moreover, the present invention contemplates
a variation in the shape and placement of the vanes to adapt
the stirring elements to any specific mixing function.
; In this latter respect, different applications may call
for differe~t stirring and/or mixing functions. For example,
in some biomedical applications such as cell growth in a liquid
culture, very gentle stirring is required with little or no
agitation or mixing. In certain chemical reactions requiring
the absorption of air or other gases, it is desirable to create
a deep vortex in the liquid. In other reactions or mixing
applications where aeration is undesirable, agitation without
vortex formation is needed. Rather than discussing the fluid
mechanics involved in agitation or mixing of a liquid, it would
be suf~icient for purposes of the present invention merely to
say that the rotation of the stirring element may produce
agitation with or without the formation of a vortex and the
formation of a vortex is not necessarily a measure of the
amount of agitation or mixing which is being accomplished.
The present invention may be characterized in one
aspect thereof by the provision of a stirring element used with
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~agnetic stirrers, the element havin~ at least three vanes both
upstanding and depending from a central disc, and a permanent
magnet disposed at least partly in said disc wherein said vanes
and disc are integrally molded of non-magnetic material about
said permanent magnet.
Broadly defined the present invention is a stirring
element for use with magnetic stirrers comprising: a central
disc portion adapted for rotation about a vertical axis; vane
me~bers upstanding and depending from the central disc portion;
the central disc portion and vane memhers being integrally
molded from a non-magnetic material; and a permanent magnet
disposed horizontally in the disc portion.
These and other features and advantages of the present
~ invention will become more apparent upon the consideration of
.. the following detailed description thereof when taken in
`~ connection with the accompanying drawings depicting the sameO
:,~ Figure 1 is a perspective view showing one embodiment
~; of the magnetic stirring element of the present invention;
Figure 2 is a top view of the embodiment shown in
Figure 1 partly broken away and in section, the bottom view
being identical;
Figure 3 is a side elevation view of the embodiment
shown in Figure 2;
Figure 4 is a schematic view of the magnetic mixing
apparatus employing the stirring element of the present
invention;
Figures 5-7 are views similar to Figure 2 only showing
stirrers having different vane configurations;
Figure 8 is a view similar to Figure 3 only showing
another embodiment of the invention;
Figure 9 is a fragmentary plan view showing a different
configuration for the ends of the vanes;
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Figure 10 is a perspective view of still another
emhodiment of the invention; a~d
Figure 11, located on the sheet of drawings containing
Figure 1, is a view showing the flow pattern produced by one
embodiment of the invention.
Referring to the drawings, Figure 1 shows the magnetic
stirring element of the present invention generally indicated
at 10. In the embodiments shown in Figure 1 the stirring
element includes an intermediate disc portion 12 with up-
10 standing and depending vane members 14, 16 respectively. Both
the upstanding and depending vane members are composed of two
sections (a) and (b) disposed at right angles to each other,
each section extending along the diameter of disc 12.
As shown in Figures 2 and 3, the stirring member
; contains a small bar magnet 18 located within the disc portion
and extending along the diameter thereof in the area of one of
the vane members. While any suitable material may be used for
the stirring element, a plastic material is preferred as this
`~ allows the bar magnet to be encapsulated within the material
- 20 of the stirring element, as by molding the stirring element --
around the bar magnet. The preferred plastic material is poly-
tetrafluoroethylene as this plastic, while difficult to mold,
is the most inert chemically and has a very low coefficient
of friction.
In use, as shown schematicallv in Figure 4, the stirring
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element 10 is placed ln a beaker or o-ther vessel 20 containing
the liquid to be rnixed. The beaker is located over a
conventional magnetic stirring apparatus consisting substantially
of a motor 22 which rotatably drives a magnet 24. The magnetic
coupling between magnet 24 and bar magnet 18 within the stirring
element causes -the stirring element to rotate about a vertical
axis as the drive magnet 24 is rotated by motor 22 so that the
vertical surfaces of the vanes push against the liquid. Arrows
26 indicate flow lines and show that the vaned design of the
stirring element of the present invention produces considerable
movement of liquid close to the bottom of the vessel wherein the
arrows indicate -tha-t the liquid is forced radially along the
bottom of the vessel and then deflected upwardly along the
sides. Since there is considerable liquid movement along the
bottom of the vessel, the mixing and dissolving of powders and
the like which settle to the bottom of the vessel is facilitated
by the stirring element of the present invention.
Furthermore, the vaned configura-tion of the stirring
element of the present invention makes available a relatively
large cross-sectional area for actually mixing fluids as
opposed to conventional magnetic mixing bars. In this respec-t,
Figure 3 shows the relatively large vertical area provided by
the upstanding and depending vane members 1~, 16 respec-tively
for "pushing" against the liquid as the stirring element
rotates. This is in contrast to the vertical area of a more
conventional element as shown for example in ~.S. Patent No.
2,951,689. Furthermore, when rotated 90 the embodimen-t shown
in Figure 3 presents the same vertical area for "pushing"
against the liquid whereas a similar rota-tion of the
aforementioned prior art elemen-t results in a greatly reduced
vertical area. Consequen-tly, a smaller vaned s-tirring element
j31~
of -the present invention can accomplish the same amount of
stirring as any larger straight cylinder7 bar or like
conventional magnetic stirring element.
The present design of having vanes upstanding and depending
from a cen-tral disc portion has the further advantage of
loca-ting bar magnet 18 substantially at the center of gravity
of the stirring element. This provides a more stable operation
of the stirring element in that even wi-th a relatively large
cross-sectional mixing area, -there is a relatively short
momen-t arm from the magnet to the top and -the bottom of the
s-tirring element. Accordingly, during operation, the stirring
element of the present inven-tion is less likely to "spin out",
that is, to become uncoupled from the drive magnet and stop.
The design also produces a vortex at relatively low mixing
speeds.
Having upstanding and depending vanes has a further
advantage in that there is no right or wrong side to the
stirring element. In this respec-t the stirring elemen-t 10 can
be simply dropped into the vessel and no care need be taken to
ensure that one side or the other comes to rest on the bottom of
the vessel.
While a preferred embodiment has been described with
reference to Figures 1-3, other vane configurations may be
used depending upon the par-ticular mixing application. While
two in-tersecting vane members disposed at righ-t angles and
extending along the diameter of the disc is preferred for most
applica-tions, a -three vane struc-ture (Figure 5) can also be
used. Here the vanes 28 extend radially outward from the cen-ter
of the disc. The stirring element may also have more than -two
intersecting vane members 30 extending across the diameter of
the disc as shown in Figure 6.
Also, while it is preferred that the vanes extend from
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the center to the periphery of the disc, the vanes of any
configuration may extend inwardly from -the periphery of` the
disc to terminate short of the center 32 of the disc as shown
in Figure 7.
Where the vessel containing the liquid to be mixed has a
convex bottom, a vaned stirring element as shown in Figure 8 may
be used wherein the upstanding and depending vanes have there
upper and lower edges 34, 36 respectively tapered inwardly from
the periphery to the center of the disc.
Figure 9 shows a further embodiment wherein the leading
and trailing edges 38, 40 respectively of the vanes are provided
with a curved contour as opposed to the straight sided vanes
shown for example in Figure 2.
A still further embodiment is shown in Figure 10. In this
embodiment the upstanding and depending vanes provided on the
end faces of central disc portion 40 take the form of wedges 42.
The riser or trailing face 44 of each wedge projects
substantially normal fr~m the plane of the disc. The inclined
surface 46 of each wedge tapers from the top edge of one
riser to the base of the following riser. Further, the top
edge of each riser is inclined upward from the center 48 of
the stirring element to the outer end poin-ts 50 of the top
edges, so that the center point 48 lies in a plane located
below the plane of end points 50. With the element ro-tating
clockwise as viewed in Figure 10, the inclined surfaces of
the wedges at the top of the element tend to push the liquid
upward in a direction normal to the plane of ro-tation much
like a screw or propeller. Meanwhile, the vertical end faces of
the wedges on the bot-tom of the element tend to move liquid
on the bottom of the vessel radially. Thus, the stirring
element shown in Figure 10 develops a primarily vertical as
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opposed to rotary agitation so as to reduce the possibility
of developing a vortex. Accordingly, this embodiment finds
most utility where agitation without vortex development is
required. The flow pattern produced by this embodiment is
illustrated in Figure 11.
Thus, it should be appreciated that the present invention
accomplishes its intended objects in providing a magnetic
stirring element having a relatively large cross-sectional area
available for mixing as opposed to conventional cylindrical
stirring bars of comparable size, which is more stable than
vaned stirring elements of the prior art and which provides a
vaned s-tructure which is symmetrical about a horizontal plane so
that the stirring element will operate effectively regardless of
which surface is up or down.
While various vane configurations have been shown by way
of example only, it should be appreciated tha-t the present
invention is not limited to the embodiments described and that
vanes of various o-ther cross-sections or profiles finding
utility in specific applications are within the scope of the
invention as claimed.
