Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ENCASED TEMPERATURE AND CRACK RESISTANT MAGNETIC STIRRING BAR
BACKGROUND OF THE INVENTION
In chemistry and biology laboratories, magnetic stirrers are often used for
mixing modest
amounts of liquids or mixtures of liquids and solid powders. A magnetic
stirrer employs
a rotating magnetic field placed beneath the vessel with the liquids or
mixtures of liquids
and solid powders to cause a stirring bar, which is immersed in the liquid or
the mixture
of liquids and solid powders, to spin very quickly, thus stirring the liquids
or mixtures.
The rotating magnetic field may be created either by a rotating permanent
magnet or
assembly of electromagnets.
Magnetic stirrers can be used for both open and hermetically closed vessels.
Specially,
when it is used in hermetically closed vessels, it is not necessary to use the
costly and
complicated rotary seals. More specially, this also avoids using lubricants
which could
contaminate the reaction vessel and the product. A magnetic stirring bar is a
magnet
that is encased in materials that won't react with the fluid it is immersed
in. U.S. Patent
No. 2,844,363 disclosed a coated magnet in plastic or covering it with glass
to make it
chemically inert and not contaminate or react with the reaction mixture they
are in.
Nowadays, many kinds of shaped magnetic stirring bars are invented for better
mixing
effects. No matter what shape is used, the most used magnetic stirring bars
are typically
coated in Teflon, or less often, in glass, as glass or Teflon does not
appreciably affect a
magnetic field and the chemical reactions. These coated stirring bars are
commonly used
in glass vessels at a relatively low temperature and at atmospheric pressure
or even in
vacuums.
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The highest used temperature for Teflon coated stirring bars is 270 C. Teflon
coated
magnetic stir bars used in most low temperature chemical testing can be
softened and
even molten at high temperatures and finally fall off from the magnetic rod.
Instead of a
Teflon coated one, a glass encased stirring bar can be used at higher
temperatures.
Although an encasing of glass can be used at high temperatures, the encased
glass can
easily break during the stirring, especially, when it is stirred vigorously.
The stirring bar
may jump and collide with the rigid walls of the reactor. This can break the
encasing
glass. Chemical reactions do not only occur at low temperatures and low
pressure, as
many reactions occur at high temperatures and at high pressure. As a result,
stainless steel
autoclaves which are equipped with complicated rotary seals are frequently
used for such
conditions. This makes the autoclave more expensive. If the use of a
complicated rotary
seal can be avoided, the cost of the autoclave may greatly be reduced. A high
pressure
reactor and a magnetic stirrer equipped with a stirring bar which is covered
by materials
that are temperature resistant and shatter proof is thus desirable and can
replace the more
expensive autoclave.
It is therefore the object of the present invention to provide a method for
preparing a
magnetic stir bar encased or covered with materials which are temperature
resistant and
are less fragile so as to be used in high temperature conditions. The
coverings are
chemically inert and do not contaminate or react with the reaction mixture
contained
therein.
It is a further object of the present invention to provide a cost-effective
autoclave for high
temperature and high pressure condition applications.
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BRIEF SUMMARY OF THE INVENTION
According to the present invention, methods are provided for preparing a
stirring bar
covered with materials that are shatter proof and afford better temperature
resistance.
The covering material is chemically inert, has no appreciable effect on the
magnetic field,
such as stainless steel, ceramic or other materials which could be used at
high
temperatures in order to offer fragility resistance. The use of the present
invention in a
high pressure and high temperature reactor can replace a complicated magnetic
rotary
equipped autoclave system.
DETAILS OF THE DESCRIPTION OF THE INVENTION
The present invention relates to the preparing of a magnetic stirring bar
covered with
materials which are temperature resistant and shatter proof so as to be used
in a rigid
autoclave reactor at high temperatures in a vigorously stirring environment.
The
invention relates to methods of manufacturing the magnetic stirring bars
without
significantly reducing their magnetic flux.
This invention relates to the use of a cost-effective autoclave for high
temperature and
high pressure reactions. Namely, this invention replaces the autoclave
equipped with a
complicated magnetic rotary system with a magnetic stirrer as described in the
present
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invention. The key issue of this invention is to have a temperature resistant
and fragility
resistant stirring bar.
Magnetic stirring bars are coated magnets used to stir liquids or mixtures of
liquids and
solid powders in a sealed container. The covering materials of the magnetic
stirring bar
include materials with temperature and crack resistance properties and are
chemically
inert when it is immersed in the fluid and/or mixture. The covering materials
include, but
are not limited to, stainless steel, ceramic, composite materials, other
metals, should have
no or less appreciable effect on magnetic fields and the chemical reactions.
The methods
to cover the magnetic bars are: machining, welding, threading, and electroless
plating, or
a combination of these methods.
DESCRIPTION OF THE DRAWINGS
Fig. 1-5 is an axial cross-sectional view of the stirring bar at each
construction stage.
Referring to the drawings in detail, in all figures, item 1 is the magnetic
metallic bar
which may be of any known or other suitable permanent magnet material. As the
material used to construct magnetic metallic bars are usually rather
vulnerable to many
reagents, the magnetic rod in the present invention is wholly enclosed in a
uniform
thickness tube 2 of a stainless steel or other material which is highly
resistant to most
reagents and resistant to high temperatures. 2 has no or less appreciable
effect on
magnetic fields. 5 are internal threads at the ends of tube 2 with a distance
of 8-10
threads and 6 is the plug with external threads with a distance of 10-12
threads. 7 is an
0-ring sealing gasket, such as graphite, which can withstand high
temperatures.
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According to the present invention, in Fig. 1, the uniform thickness of the
stainless steel
tube 2 is firstly sealed at one end 3 and the surface of this end is machined
into a shaped
arc. The tube 2 also can be manufactured from boaring a metallic rod so that
one end of
the tube is not boared through, therefore maintains one closed end.
According to the present invention the magnetic bar 1 is fitted into the one
end sealed
stainless steel tube 2, the external diameter of the magnetic rod and the
inner diameter of
the tube 2 is so dimensioned that the rod will fit in the tube with sufficient
tightness. The
tube 2 is of sufficient length for bar 1. The other end 4 is then sealed by
welding and it is
then machined to the desired shape of an arc. The shape at both ends is the
same in the
arc and the finished magnetic stirring bar is in symmetry.
A point of consideration and concern is that the high temperature of welding
may cause
the loss of the original magnetic flux of the rod. With the present invention,
the finished
stirring bars were then tested for petroleum vacuum residue upgrading in an
autoclave
operating at high temperatures and high pressure and no obvious loss of their
magnetic
flux was found.
In order to completely avoid the concern of loss of original magnetic flux of
the rod by
welding, a design using threads instead of welding is proposed and shown in
Fig.2. The
prior stage is the same as described therebefore. Only the second end
manufacturing
process is modified. The second end or threaded openings 5 of the tube 2 is
closed by
externally threaded plug 6 of the same stainless steel material. The second
end of the
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tube is internally threaded with the threads 5 having 8-10 threads. A male
plug 6 with
external threads having 10-12 threads is used for closing the second end. If
necessary, an
0-ring gasket 7 is used for ensuring the sealing. The plug 6 is thus threaded
into the
internal threads 5 and presses the 0-ring with sufficient force to the end of
rod 1. To
facilitate assembly of the plug, a hexagonal kerf 8 is provided in plug 6 to
receive a
hexagonal L key, and two flat kerfs 9 are provided on tube 2 to receive a
wrench. After
tightening the plug 6 as shown in Fig. 3, the second end is machined to the
same shape as
end 3 and makes both ends in symmetry. The shape of the finished stirring bar
is then the
same as Fig. 1.
Another design is that both tubular ends for the stirring bar can be designed
using threads
and plugs as shown in Fig. 4. The stirring bar can be used as is after
tightening as shown
in Fig. 5 or be machined to the shape as shown in Fig. 1.
Using electroless plating technology to coat the magnetic rod with composite
materials,
such as NiP, is proposed. As NiP has high temperature and fiction resistance,
it can be
used in a high temperature autoclave. Using a graphene coating technology can
also
achieve the desired effect of the present invention.
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