U.S. patent number 3,679,184 [Application Number 05/002,169] was granted by the patent office on 1972-07-25 for mixing devices.
Invention is credited to Lloyds Bank Limited, executor and trustee of the estate, Cecil Halliday Woodham, deceased.
United States Patent |
3,679,184 |
Woodham, deceased , et
al. |
July 25, 1972 |
MIXING DEVICES
Abstract
A device for mixing dental cements comprises a structure mounted
for rotation about a first axis, a motor for rotating the structure
about that axis, a receptacle for the substance to be mixed mounted
on the structure at a location spaced from the axis of rotation
thereof and rotatable relative to the structure about a second axis
inclined at an angle of less than 90.degree. to the first axis, a
transmission being provided to rotate the receptacle relative to
the structure as the structure rotates. The receptacle receives a
capsule comprising a main body having at least two compartments for
the substances to be mixed, the compartments being separated by a
dividing wall which is ruptured when required to permit the flow of
a substance from one compartment to the other. Said one compartment
also has an external rupturable wall so that the dividing wall may
be ruptured by passing a piercing instrument first through the
external wall and then through the dividing wall.
Inventors: |
Woodham, deceased; Cecil
Halliday (Kingswood, Surrey, EN), Lloyds Bank
Limited, executor and trustee of the estate (N/A) |
Family
ID: |
27447212 |
Appl.
No.: |
05/002,169 |
Filed: |
January 12, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Jan 14, 1969 [GB] |
|
|
2,137/69 |
Feb 17, 1969 [GB] |
|
|
8,573/69 |
Apr 3, 1969 [GB] |
|
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17,724/69 |
Sep 11, 1969 [GB] |
|
|
44,896/69 |
Oct 17, 1969 [GB] |
|
|
51,216/69 |
Nov 6, 1969 [GB] |
|
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54,515/69 |
|
Current U.S.
Class: |
366/219; 206/219;
241/284 |
Current CPC
Class: |
B01F
15/0205 (20130101); A61C 5/68 (20170201); B01F
9/0001 (20130101); B01F 9/0034 (20130101); B01F
9/10 (20130101); B01F 2009/0085 (20130101) |
Current International
Class: |
A61C
5/06 (20060101); A61C 5/00 (20060101); B01F
9/10 (20060101); B01F 15/02 (20060101); B01F
9/00 (20060101); B01f 009/02 () |
Field of
Search: |
;259/DIG.20,3,14,30,72,81R,89,54,57,58 ;233/25,26 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Scheel; Walter A.
Assistant Examiner: Coe; Philip R.
Claims
I claim:
1. A device for mixing together a plurality of substances
comprising a structure mounted for rotation about a first axis,
means for rotating said structure about said axis, a receptacle for
the substances mounted on said structure at a location spaced from
the axis of rotation thereof for rotation relative to said
structure about a second axis inclined at an angle of less than
90.degree. to said first axis, and a pulley system comprising a
pulley wheel rotating with said receptacle about said second axis,
a fixed further pulley wheel coaxial with said first axis, an
endless band encircling said pulley wheel and said fixed pulley
wheel whereby said receptacle is rotated relative to said structure
by said pulley system as said structure rotates.
2. A device according to claim 1 wherein one of said pulley wheels
is slightly eccentric.
3. A device according to claim 1 wherein said endless band passes
over idler pulley wheels rotatably mounted on the structure.
4. A device for mixing together a plurality of substances
comprising a structure mounted for rotation about a first axis,
means for rotating said structure about said axis, a receptacle for
the substances mounted on said structure at a location spaced from
the axis of rotation thereof for rotation relative to said
structure about a second axis inclined at an angle of less than
90.degree. to said first axis, a fixed track coaxial with said
first axis, a wheel rotating with said receptacle about said second
axis having its periphery frictionally engaging said track so that
said wheel and receptacle are rotated as said structure
rotates.
5. A device for mixing together a plurality of substances
comprising a structure mounted for rotation about a first axis,
means for rotating said structure about said axis, a receptacle for
the substances mounted on said structure at a location spaced from
the axis of rotation thereof for rotation relative to said
structure about a second axis inclined at an angle of less than
90.degree. to said first axis, a track on a member coaxial with the
first axis, a wheel rotating with said receptacle about said second
axis having its periphery frictionally engaging said track and
means to rotate said member relative to said structure.
6. A device according to claim 4 wherein said track is slightly
eccentric with respect to said first axis.
7. A device according to claim 1 wherein the receptacle comprises a
circular cross-section socket the outer surface of which is
rotatable in a bearing on said structure and wherein the lower end
of said socket is open so that the lower end of a capsule located
in said socket may protrude into the air, means being provided to
locate said capsule axially and rotationally in said socket.
Description
The invention relates to mixing devices and is particularly, but
not exclusively, applicable to devices for mixing together
substances to form cements and fillings for use in dental work.
It is known to form dental cements and amalgams by introducing the
materials into a chamber which is oscillated to mix the materials
together. This method depends on the materials being continually
thrown from side to side of the chamber by the oscillation. While
this method is suitable for forming amalgams of mercury and metal
powder and for mixing other materials which have little
adhesiveness, it is found that it is not particularly suitable for
materials which are adhesive and which tend to stick to the walls
of the chamber since, at practical speeds of oscillation, such
materials are not thrown across the chamber in the required manner
to effect thorough mixing. The present invention provides a mixing
device which is suitable for mixing such adhesive materials.
According to the invention a device for mixing together at least
two substances comprises a structure mounted for rotation about a
first axis, means for rotating the structure about that axis, a
receptacle for the substances mounted on the structure at a
location spaced from the axis of rotation thereof and adapted for
rotation relative to the structure about a second axis inclined at
an angle of less than 90.degree. to the first axis, means being
provided to rotate the receptacle relative to the structure as the
structure rotates.
A mixer constructed according to the present invention is
particularly suitable for mixing dental cements, but it may also be
used for mixing together other materials. For example by
constructing the mixer on a larger scale it is possible to mix
together calcium or potassium alginate with water to provide a
material suitable for taking dental impressions. Plasters and
artificial stones may also be mixed by this method.
The second axis is preferably in the same plane as the first axis
and is inclined at between 35.degree. and 45.degree. thereto. For
example it may be inclined at about 371/2.degree. to the first
axis.
The means for rotating the receptacle may comprise a driving
transmission operated by rotation of the structure whereby the
receptacle is rotated in synchronism with the structure.
The driving transmission may be a pulley system comprising an
endless band encircling a pulley wheel rotating with the receptacle
about said second axis and also encircling a fixed further pulley
wheel co-axial with said first axis. Alternatively the endless band
may encircle a further pulley wheel co-axial with said first axis,
means being provided to rotate said further pulley wheel relative
to the structure. The speed of rotation of the receptacle relative
to the structure may thus be adjusted by adjusting the speed of
rotation of the further pulley wheel.
At least one of said pulley wheels may be slightly eccentric so
that the rotational speed of the receptacle fluctuates as the
structure rotates.
The endless band may pass over idler pulley wheels rotatable
mounted on the structure.
In an alternative arrangement the driving transmission comprises a
wheel rotating with the receptacle about said second axis, the
periphery of which wheel frictionally engages a fixed track
co-axial with said first axis so that the wheel and receptacle are
rotated as the structure rotates. Alternatively the wheel may
engage a track on a member co-axial with the first axis, means
being provided to rotate said member relative to the structure. In
either arrangement the track may be slightly eccentric with respect
to said first axis.
In any of the above arrangements the receptacle is preferably
adapted to receive a capsule containing the materials to be
mixed.
The receptacle may comprise a circular cross-section socket the
outer surface of which is rotatable in a bearing on said structure.
The lower end of the socket may be open so that the lower end of a
capsule located in the socket may protrude into the air, means
being provided to locate the capsule axially and rotationally in
the socket.
Since the build up of a static electrical charge may effect the
quality of mixing certain parts of the device are preferably formed
from material of a kind which does not build up a static electrical
charge when subjected to friction. Similarly where certain parts of
the device are formed from metal those parts are preferably earthed
to dissipate any static electrical charge built up during operation
of the device.
One form of capsule for use in the device comprises a main body
having at least two compartments for the substances to be mixed,
the compartments being separated by a dividing wall adapted to be
ruptured when required to permit the flow of a substance from one
compartment to the other, said one compartment also having an
external rupturable wall so that the dividing wall may be ruptured
by passing a piercing instrument first through the external wall
and then through the dividing wall.
Said other compartment may be formed partially by a cup-shaped
element which is detachable from the main body of the capsule and
into which the substances pass when said dividing wall is ruptured.
For example the main body of the capsule may be generally tubular
and the rim of the cup-shaped element may be in tight frictional
engagement with the rim of the main body.
Preferably the internal surface of the bottom wall of the
cup-shaped element has a central projection.
Preferably the portion of said other compartment which is in said
main body of the capsule is of sufficient volume to accommodate the
whole of the substance in said compartment, whereby the capsule may
be filled by placing the substance in said portion and then
applying the cup-shaped element thereto.
The dimensions of the cup-shaped element are preferably such that
the whole of the exposed inner surface of the element is swept by
the substance during mixing.
The cup-shaped element may be formed from metal to facilitate the
earthing of any static charge built up during mixing.
In any of the forms of capsule referred to said one compartment may
comprise a thin metal container located in a cavity in the main
body of the capsule, the metal of the container being sufficiently
thin to be readily ruptured by a piercing instrument. For example
the container may be a sachet formed from metal foil.
Alternatively the container may be a canister, that wall of the
canister which constitutes the aforesaid rupturable dividing wall
being substantially conical to assist the flow of the material from
the canister when said wall has been ruptured.
The external surface of the capsule may be integrally formed with
projections to locate the capsule in the socket of the mixing
device.
For the reasons mentioned above at least a portion of the capsule
is preferably formed from material of a kind which does not build
up a static electrical charge when subjected to friction.
The following is a more detailed description of various embodiments
of the invention reference being made to the accompanying drawings
in which:
FIG. 1 is a vertical section through a mixing device;
FIG. 2 is a similar view through an alternative form of mixing
device;
FIG. 3 is a section along the line 3--3 of FIG. 2;
FIGS. 4 and 5 are vertical sections through further forms of mixing
device;
FIG. 6 is a cross-section through the socket of the apparatus of
FIG. 1 and for holding a mixing capsule;
FIGS. 7 and 8 are vertical sections through alternative forms of
capsule for use in the apparatus of FIG. 1;
FIG. 9 is a section through the lower cap part of the capsule shown
in FIGS. 7 and 8;
FIGS. 10 and 11 are vertical sections through alternative forms of
capsule;
FIGS. 12 and 13 show alternative forms of the metal canister used
in the capsule of FIG. 11;
FIGS. 14, 15, 16 and 17 are vertical sections through further forms
of capsule;
FIG. 18 is a horizontal section through the lower part of the
capsule shown in FIG. 17; and
FIG. 19 is a vertical section through a further form of
capsule.
The mixing device shown in FIG. 1 comprises a base plate 10 which
constitutes the upper wall of a casing for an electric motor (not
shown). The output shaft 11 of the electric motor passes through
the base plate 10, through a disc 12 mounted on the base plate and
through a fixed pulley wheel 13 secured to the disc 12. A rotatable
structure 14 is secured to the shaft 11 by a grub screw 15 located
in a threaded hole 16.
At one end of the structure 14 is a bearing portion 17 within which
is rotatable a tubular socket 18 which is of such a size as to
receive and locate a capsule for the materials to be mixed. The
axis of rotation of the socket 18 is inclined at an angle of about
371/2.degree. to the vertical.
A pulley wheel 19 is mounted on the lower end of the socket 18. An
endless band 20 passes around the pulley wheel 19 and the fixed
pulley wheel 13 and each stretch of the band between those two
pulley wheels passes across an idler wheel 21, two idler wheels
being freely rotatable on opposite sides of the structure 14. The
lower flange of the pulley wheel 19 is of greater diameter than the
upper flange to prevent the endless band balooning downwardly under
centrifugal force.
The idler pulleys preferably have shaped peripheries, in known
manner, to locate the stretch of the endless band passing over
them. Also since the pulley wheel 19 on the lower end of the socket
is of different diameter to the other pulley wheel 13 encircled by
the endless band it may be desirable to incline the shafts carrying
the idler wheels so that the peripheries of the wheels are
correctly aligned with the endless band. A further grub screw 22
within the threaded hole 16 acts as an adjustable counter-balancing
weight.
It will be seen that as the structure 14 is rotated by the electric
motor the socket 18 will also be rotated, about its axis, by the
pulley system.
To protect the rotating structure 14 and to prevent clothing, for
example, being caught in it, a disc 23 is mounted on the top of the
structure. The disc may be integrally moulded with the structure 14
or separately formed and screwed to it. The disc 23 rotates beneath
a circular aperture 24 in an inverted cup-shaped cover 25 the lower
periphery of which is a press fit on the disc 12.
In the simplest method of operation the materials to be mixed are
introduced into a capsule 26 which is then inserted in the socket
18. As mentioned earlier the device is particularly suitable for
the mixing of dental cements which are normally mixed from a powder
and a liquid, some times with the addition of a catalyst.
As the arm 14 is rotated it will be appreciated that the material
within the capsule will be thrown away from the axis of rotation by
centrifugal force so that it will gather in the part of the capsule
furthest from the axis of rotation. However as the capsule 26 is
itself rotating about its central axis, the material will move
towards the axis of rotation of the arm 14 by being carried around
to a certain extent by adhering to the walls of the capsule. At a
certain point however the centrifugal force due to rotation of the
arm 14 as a whole will overcome the adhesion of the material to the
walls of the capsule and will throw the material outwardly again to
the outermost side of the capsule. This process will be continually
repeated and results in rapid and thorough mixing of the liquid and
powder to form the cement.
Preferably the relative rates of rotation of the arm 14 and the
socket 18 are so selected that the material loses its adhesion to
the walls of the capsule only when the capsule has been rotated
through 180.degree. from the position shown in FIG. 1. Thus the
material will be constantly thrown radially outwards by centrifugal
force across the width of the capsule. It will be appreciated that
if the rate of rotation of the arm 14 is too great in relation to
the speed of rotation of the capsule the material will not be
carried round to any great extent by the rotation of the capsule
and will remain substantially at the outermost side of the capsule.
On the other hand if the rate of rotation of the capsule is too
great in relation to the rate of rotation of the arm 14 the
material will adhere to the walls of the capsule throughout its
complete rotation and will not be thrown across the container by
centrifugal force due to rotation of the arm 14.
Excessive centrifugal force may also have the effect of tending to
maintain the powder and liquid separate within the container the
device acting somewhat in the manner of a centrifugal
separator.
In the arrangement shown the axis of rotation of the socket 18 is
arranged at about 37 1/2 to the vertical but it will be appreciated
that the axis may be arranged at other angles. The smaller the
angle of the axis of rotation to the vertical the easier it is for
the materials to move across the container since the bottom wall of
the container will be less "steep."
As mentioned above the materials may be placed in the capsule 26
before it is placed in the socket 18. However it will be
appreciated that if the capsule is open-topped the materials may be
introduced into the capsule whilst it is in position in the socket,
or the socket 18 itself may have a closed bottom and may constitute
the capsule into which the materials are introduced. By using a
dispenser which rotates with the arm 14, the materials may also be
introduced into the capsule whilst the arm is rotating. The
dispenser (not shown) may comprise a feeding duct extending
radially outwards from the axis of rotation of the arm 14 to the
open upper end of the capsule. Predetermined quantities of the
materials are introduced into the duct from a measuring dispenser
on the axis of rotation of the arm 14 and are then thrown outwardly
along the duct by centrifugal force and ejected into the
capsule.
Alternatively and preferably, however, predetermined quantities of
the materials to be mixed may be provided in prepacked capsules
which are placed in the socket 18. Various forms of such capsules
will be described below.
In the particular example described the socket in which the capsule
is to be located may have a radius of nine thirty-seconds of an
inch and its axis may be at a radial distance of 2 11/16 of an inch
from the center of rotation of the rotating arm of the device. As
described above the capsule is rotated at such a speed in relation
to the rotation of the arm as a whole that the material in the
capsule is constantly thrown across the diameter of the capsule. It
is found that suitable speeds for the dimensions given may be of
the order of 2,000 r.p.m. for the arm and 1,250 r.p.m. for the
capsule relatively to the arm. Thus as the arm rotates through
360.degree. the capsule rotates through 225.degree. relatively to
the arm.
The rotating arm 14 carrying the capsule may be mounted beneath a
transparent domed cover (not shown) which provides protection but
which enables the capsule to be seen when mixing has been
completed. The shaft 11 on which the arm 14 rotates may project
upwardly through the domed cover and may be provided with a knob by
means of which the arm may be brought manually to a halt and
rotated to a position opposite a hatch in the dome so that the
capsule may be removed from the arm. The hatch may have the
operating switch of the motor associated with it in such a manner
that shutting of the hatch closes the switch. The arm cannot
therefore rotate until the hatch has been closed.
The switch controlling the motor may be a time switch to control
automatically the length of time during which mixing takes place.
At low temperatures the viscosity of the liquids used increases
making effective mixing less rapid. The time switch may therefore
be graduated on a temperature scale.
It is found that in a mixing device of the kind described there may
be a tendency for the ease and quality of mixing to deteriorate
under certain conditions. Although it is not known for certain, it
is believed that one reason for this might be the generation of
static electricity in the mixing device. It may therefore be
desirable to reduce or eliminate the generation and/or effect of
static electricity.
It is believed that static electricity can be generated in two
ways: It may be generated as a result of friction between the
moving parts of the mixer, and also by friction of the material
being mixed against the walls of the containing capsule as well as
friction between elements of the material itself.
In the arrangement shown in FIG. 1 the arm 14 might be formed from
plastics bearing material, such as molybdenum-disulphide filled
nylon, to provide a self-lubricating bearing for the sock 18 which
would be formed from metal. However rotation of the metal socket in
the bearing material may built up a charge of static electricity
which may be dangerous and may interfere with the ease and quality
of mixing.
It will be seen from FIG. 1 that the socket 18 is formed at its
upper end with a peripheral flange 27. To earth any static
electricity generated a metal spring (not shown) may be connected
by the clamping screw 15 to the shaft 11 and the opposite end of
the spring arranged to bear against the flange 27. Since the shaft
11 of the motor will be earthed the spring will earth the socket 18
as it rotates so dissipating any static electricity which is
generated. The arrangement of the spring may be such that
centrifugal force tends to urge the end of the spring into good
electrical contact with the flange 27 as the socket rotates.
The opposite end of the spring to the end which contacts the flange
27 may be deformed, the deformed part being received in a
depression in the upper surface of the arm 14 to prevent
displacement of the spring on the arm. However it will be
appreciated that there are many other ways in which the spring may
be mounted and connected to the shaft 11.
In some cases the shaft 11 itself may not be adequately earthed and
if this is the case then a further earthed spring may be mounted on
the motor casing at its lower end to bear against a projecting
extension of the motor shaft to ensure adequate earthing of the
shaft. This further spring may be a simple leaf spring bearing
against the end of the shaft or may be a spring loaded collar
encircling the extension of the shaft.
Static electricity may also be generated by rotation of the idler
wheels 21 and the metal shaft 28 on which they run is also
therefore preferably earthed. To achieve this the spring referred
to above may be integrally formed with arms which are bent down on
opposite sides of the arm 14 and have at their ends parts which
embrace the shaft 28 so as to earth that shaft.
Instead of the whole arm 14 being formed from a bearing material,
however, it is preferably formed from a suitable metal, such as an
aluminium alloy, and the socket 27 may then rotate in a bearing
nylon bush in the portion 17 of the arm. In this case it will be
appreciated that the spring referred to could simply be connected
to the body of the arm 14 itself and need not be connected directly
to the shaft 11. In this case the shaft 28 of the idler pulley will
then automatically be earthed.
Instead of the metal socket 27 rotating in a bearing nylon mesh in
the portion 17 of the arm 14, it may be coated on the outside with
a plastics bearing material, such as "Nylatron" and may be
rotatable in a steel bush in the portion 17.
In an alternative and preferred arrangement shown in FIG. 1,
however, the arm 14 is formed from a suitable metal such as an
aluminium alloy and is bushed with a steel bearing, the socket 18
in this case being formed from a bearing nylon such as "Nylatron
G.S.." In this case the static electricity due to friction in the
bearing is automatically earthed, but it is also desirable to earth
the capsule itself. In the arrangement shown in FIG. 1 this is
achieved by making the capsule 26, or at least the lower part 26a
in which the materials are actually mixed, from metal such as
stainless steel or aluminium. The lower metal end of the receptacle
bears against a metal projection 29 on a metal bracket 30 which is
secured to the metal arm 14. The capsule itself is thus always
connected to earth. The projection 29 is arranged to be the sole
support for the capsule, in the axial direction, so that
centrifugal force ensures good contact between the projection and
the capsule.
As mentioned earlier, static electricity generated in the capsule
itself may be generated by friction between the materials being
mixed and the interior walls of the capsule. It follows therefore
that the problem might also be reduced by using for the capsule a
material which does not tend to generate a static charge. For
example Bakelite may be a suitable material for this purpose. In
this case if little or no static charge is generated there may be
no necessity for the capsule itself to be connected to earth. A
similar type of material is also preferably used for the pulley
wheels 13 and 19 since static electricity may be generated by the
endless belt rubbing against the pulleys.
To reduce the likelihood of capsules building up a static charge
during storage and transport it is preferable for the capsules to
be stored in an earthed metal storage rack so that any static
charge built during storage and handling is dissipated before the
capsules are used.
If the capsule 26 or the cup part 26a are formed from aluminum it
may be anodized.
It will be seen that in the arrangement of FIG. 1 the part 26a of
the capsule in which the materials are actually mixed projects
below the pulley wheel 19 into the open air. This assists in
keeping the capsule and materials cool during mixing and reduces
conduction of heat to the mixing cup from the bearing for the
socket 18.
It will be appreciated that there are many different ways in which
the socket 18 may be arranged to rotate in synchronism with the arm
14.
For example the pulley system 13, 19, 20, 21 may be replaced by a
gear transmission or the socket may carry a star wheel which is
struck around by one or more fixed pins as the arm 14 rotates.
Alternatively the socket 18 may carry a gear wheel in mesh with a
fixed roothed rack encircling the device, or could be rotated by a
miniature electric motor mounted on the arm 14. The socket 18 may
also carry a friction wheel arranged to run on a fixed track as
shown in FIG. 2. In this case the bearing part 17 could be mounted
to pivot so that centrifugal force urges the friction wheel into
engagement with the fixed track.
In a further modified version of the arrangement shown in FIG. 1,
the pulley wheel 19 is mounted about halfway along the socket 18
instead of at the lower end as shown. In this case the portion 17
of the arm 14 will be suitably slotted to accommodate the pulley
and the positions of the pulley 13 and idler wheels 21 will require
to be repositioned accordingly. Such an arrangement will serve to
distribute the bearing lead more evenly along the length of the
bearing for the socket 18.
In the alternative arrangement shown in FIGS. 2 and 3 the rotating
structure 31 is slidable in a bearing member 32 secured to the
upper end of the motor shaft 33.
The structure 31 is formed at one end with a bearing part 34 in
which is rotatable a socket 35. A wheel 36 having a rubber tire 37
is secured to the lower end of the rotatable socket 35. The rubber
tire 37 bears against a conical surface 38 surrounding the shaft
33. The end of the structure 31 opposite to the socket 35 has a
threaded hole 39 which receives a grub screw 40 which acts as a
balance weight. The grub screw 40 is located in a position such
that centrifugal force biases the structure in a direction to urge
the periphery of the wheel 36 into engagement with the surface 38
so that the socket 35 is rotated as the structure 31 rotates. Since
this biassing of the structure 31 throws the assembly out of
balance, the balance is restored by an adjustable grub screw 41 in
a threaded hole 42 in the bearing member 32. As will be seen from
FIG. 3 the bearing member 32 is formed in two parts the lower of
which is formed with a groove to receive the structure 31 in a
slidable manner.
In the case of some materials to be mixed it may be desirable that
the speed of rotation of the capsule should be somewhat less than
can readily be achieved by suitably selecting the sizes of the
wheel 36 and conical surface 38 and FIG. 4 shows an arrangement by
which a slower speed of rotation of the capsule may be achieved for
a given speed of rotation of the structure.
In the arrangement of FIG. 4 the socket 43 for the capsule carries
a wheel 44 encircled by a rubber ring 45 which bears against a
conical surface 46 on a pulley wheel 47. The pulley wheel 47 is
rotatable on a tubular bush 48 through which the shaft 47 of the
motor 50 passes. A pulley wheel 51 is secured to the shaft 49 and
drives, via an endless band 52, a pulley wheel 53 mounted on a stub
shaft 54 parallel to and spaced from the shaft 49. The stub shaft
54 carries a further pulley wheel 55 which drives the pulley wheel
47 via and endless band 56.
It will be seen that due to this arrangement the pulley wheel 47 is
rotated in the same direction as the shaft 49 and structure 57, but
at a slower speed. This means that the socket 43 rotates at a
slower speed than it would if the track 46 were stationary as in
the arrangement shown in FIGS. 2 and 3.
In a modification of the arrangement of FIG. 4 the pulley wheel 44
does not bear on a conical track on the pulley wheel 46 but is
driven from an endless band encircling a further pulley wheel
rotatable with the pulley wheel 46. The endless band passes around
idler wheels corresponding, for example, to the idler wheels 21 in
the arrangement of FIG. 1.
FIG. 5 shows a modified device according to the invention. The
device comprises a casing 60 in which is mounted an electric motor
61. The shaft 62 of the electric motor passes through an aperture
63 in the upper wall of the casing. A rotor 64 is mounted on
splines 65 on the shaft 62 so that it is capable of limited degree
of up and down sliding movement on the shaft. The rotor comprises
diametrically opposed bearing parts 66 in each of which is
rotatable a socket 67 adapted ro receive a mixing capsule
containing a cement materials. The sockets rotate about axes
inclined to the vertical axis of the shaft 62.
Each socket 67 has mounted at its lower end a wheel 68 having a
rubber tire 69. The rubber tires 69 bear against a conical surface
70 integrally formed, or secured to, the upper wall of the casing
60 and surrounding the shaft 62. The arrangement is such that, as
in the arrangement of FIGS. 2 and 3, as the rotor 64 is rotated by
the motor 61 the sockets 67 are also rotated due to the engagement
of the tires 69 with the track 70. As described above this effects
thorough mixing of the materials. The arrangement now described,
however, has the advantage that two batches of cement may be mixed
simultaneously and the rotor is automatically balanced since it is
symmetrical.
In order that the tires 69 bear in frictional engagement against
the track 70 a helical compression spring 71 encircles the shaft 62
above the rotor 64 and is compressed between a washer 72 engaging a
fixed abutment 73 on the shaft and a washer 74 bears against the
upper surface of the rotor 64. The spring serves therefore to urge
the rotor downwardly into engagement with the surface 70. This
biassing arrangement could also be used in the arrangements of
FIGS. 2, 3 and 4 in which only a single socket is provided with a
wheel bearing against a track.
Although the arrangement described incorporates two diametrically
opposed sockets it will be appreciated that almost any number of
sockets may be provided in the rotor 64, the sockets being equally
spaced around the central axis of rotation of the rotor. For
example three sockets may be provided. In the case where a number
of sockets are provided the rotor 64 preferably mounted on the
splines 65 with sufficient play to enable the tires 69 to seat
themselves automatically on the conical surface 70.
Where two or more sockets are used a number of capsules can be
mixed in one operation. However if it is required to mix a number
of capsules less than the total number of sockets the free sockets
are preferably balanced by placing in them a blank of the same
weight as a capsule.
In a modified form of the arrangements described above, and indeed
in any arrangement where the sockets have wheels which run against
a fixed track, the rotor itself may be rigidly fixed to the motor
shaft and the track itself may be biassed upwardly by a spring to
engage the wheels carried by the sockets.
In all the above arrangements the rotor is in each case mounted
directly on the shaft of the electric motor. In some cases this may
not be desirable since it may not give a suitable layout to the
components of the device or because it may be necessary to gear the
drive to the shaft up or down. In this case it will be appreciated
that any suitable transmission may be provided to dive the shaft
carrying the rotor. For example the shaft carrying the rotor may be
driven through a pulley and endless belt transmission or through
toothed gearing.
In the arrangement of FIG. 4 the shaft 49 is directly driven by the
motor 50. It will be appreciated however that the drive could be
transmitted to the rotor by arranging for the motor 50 to drive the
shaft 54. This also applies to the modified version referred to in
which the wheel 44 does not bear on a conical track on the pulley
wheel 46 but is driven from an endless band encircling a further
pulley wheel rotatable with the pulley wheel 46.
In the case of some materials to be mixed it may be found that the
relative rotational speeds between the socket and the whole
rotatable structure are fairly critical to obtain satisfactory
mixing. This relationship may be made less critical by causing the
speed of rotation of the socket to fluctuate. In the arrangement
shown in FIG. 1 this may be achieved by arranging for the fixed
pulley 13 to be slightly eccentric with respect to the shaft 11.
The endless band 20 is resilient, being formed from rubber like
material, and thus as the arm 14 rotates the eccentricity of the
pulley wheel 13 causes fluctuations in the speed of rotation of the
socket 18. It will be appreciated that a similar effect might be
obtained by arranging for the pulley wheel 19 to be eccentric with
respect to the socket 18 or, indeed, both pulley wheels 13 and 19
could be eccentrically arranged. In any of these arrangements the
stretches of the endless band 20 passing over the idler wheels 21
may tend to move laterally as the rotor rotates. The idler wheels
21 are therefore preferably slidable on the shaft 28 on which they
are mounted to permit this side to side movement.
In the arrangements shown in FIGS. 2 and 4 the conical surfaces 38
and 46 may also be eccentric with respect to the shafts 33 and 49
respectively to give fluctuating speeds of rotation to the sockets
as described above with respect to the arrangement of FIG. 1.
In any of the arrangements described above it is preferable that
the motor driving the apparatus is such as to give an immediately
high rotational speed from rest. It is found that if the machine
gathers speed relatively slowly the mixing tends to be less
satisfactory than if rotational speed is reached rapidly.
It is not essential for the sockets for the capsules to rotate
continuously and the transmission in any of the above arrangements
may be such as to rotate the socket intermittently or to oscillate
it back and forth through 180.degree. as the arm which carries it
rotates. Similarly it is not essential for the arm itself to rotate
continuously but this also could provide centrifugal force by
simply oscillating back and forth.
The capsule for containing the materials to be mixed may be of
various forms and a number of examples will now be described with
reference to FIGS. 6 to 19.
Referring to FIGS. 6: the internal bore of the socket 18 of the
mixing device is preferably formed with three axially extending
semi-circular grooves 75 which extend partially down the socket
from the upper end thereof. Any capsule for use in the machine,
such as capsules of the kind shown in FIGS. 7 and 8, may be formed
with projections 76 which co-operate with the grooves 75. These
projections prevent the capsule rotating in the socket 18 and also,
since the grooves 75 do not extend completely through the socket
18, the projections can serve to locate the capsule axially in the
socket if the support arrangement 29, 30 on the device (see FIG. 1)
is omitted. Also since the capsule is located by the grooves it
need not be a particularly tight fit in the socket and this permits
air to circulate around the capsule for the purposes of mixing. It
will be appreciated that the projections 76 and grooves 75 may be
of many different forms and arrangements to locate the capsule in
the socket 18.
There will be described below capsules which contain both liquid
and powder in separate compartments the compartment containing the
liquid being ruptured to permit the materials to mix when required.
This is desirable when the materials need to be used in precisely
predetermined quantities. However if the relative quantities of the
materials are not so critical it is possible to use a capsule of
the kind shown in FIGS. 7 and 8 into which materials are measured
as required, from a dispenser. Alternatively this form of capsule
may be pre-packed with the powder only.
Each capsule may be formed from a suitable plastics and comprises a
main body portion 77 and a cap portion 78 on which the projections
76 are formed. The capsule shown in FIG. 7 has a domed main body
portion 77. In the case where the capsule is pre-packed with a
predetermined quantity of powder only, the capsule is inverted so
that the cap 78 is uppermost and is then tapped against a hard
surface so that powder is thrown out of the cap into the domed main
body portion 77. The cap 78 is then removed and from a dropper
bottle or other measuring dispenser the required amount of liquid
is deposited into the now empty cap. The cap is then replaced on
the main body portion taking care not to spill the contents of
either. The capsule is then ready to be placed in the device for
mixing.
The alternative form of capsule shown in FIG. 8 has a removable
stopper 79 so that liquid may be added by removing the stopper. A
tear-off enclosure such as adhesive paper may be used instead of
the stopper.
The advantage of having capsules which are pre-packed with powder
only is that the shelf life of the capsules is increased. The shelf
life of capsules, described below, containing both liquid and
powder may be limited by the tendency of liquid to be lost due to
evaporation through the walls of the capsule or by interaction with
the material of the capsule. Various other methods of reducing this
problem will be described below.
If the capsules are not to be pre-packed, the upper end of the body
portion may be open and funnel-shaped for ease of filling.
It will be seen from FIGS. 7 and 8 that the central portion of the
bottom wall 79 of each capsule is formed with a smooth dome 80 and
the junction between the peripheral wall 81 of the cap and the base
79 is smoothly curved. The reason for this is that it is found that
if the cap is formed with a flat floor there is a tendency, as the
capsule is rotated, for unmixed grains of material to remain in the
central area of the cap, thus spoiling the mix. This is more
noticeable in thick mixes than in mixes of materials of thinner
consistencies which are most easily removed. The higher central
portion of the base ensures that particles in the mix do not tend
to remain in the middle of the cap.
FIG. 10 shows a modified form of capsule which is pre-packed with
measured quantities of both liquid and powder. In the capsule of
FIG. 10 the upper part 77 is integrally formed with a compartment
82 for the liquid the compartment having a conically shaped lower
portion 83 and being closed at its lower end by a tin wall 84. The
junction between the peripheral wall of the part 77 and the thin
wall 84 is rounded as shown so that particles of material cannot be
trapped there during mixing. The upper part of the compartment is
closed by a further thin wall 85 which may, for example, be of thin
plastics bonded to the capsule or may be of aluminum foil. The
measured quantity of powder is located in the cap 78.
The liquid and powder are normally kept separate in the capsule but
when it is required to form a cement the walls 85 and 84 of the
capsule are ruptured for example by a tapered steel pin indicated
at 86. For example the capsule may be placed in a suitable press as
described below. When the walls 85 and 84 are ruptured the liquid
flows downwardly into the cap 78 and the capsule is placed in the
socket 18 on the mixing apparatus. The arm 14 of the apparatus is
then rotated and the liquid and powder are mixed in the manner
described above. It will be appreciated that the effect of
centrifugal force is to ensure that all the liquid id completely
ejected from the compartment 82 into the cap 78.
When mixing has been completed, the capsule is removed from the
device and the upper part 77 removed from the cap 78 and discarded.
The mixed cement may then readily be removed from the cap 78.
The dimensions of the cap 78 are so chosen in relation to the
quantities of material in the capsule that when the materials are
being mixed the mix sweeps over substantially the whole of the
exposed interior surface of the cap 78.
The surface of the mix, during mixing, is indicated by the dotted
line 87 and it will be seen that besides sweeping over the entire
internal surface of the cap 78 the mix also sweeps over the lower
end edge 88 of the upper part 77 thus when mixing has been
completed any unmixed particles will be confined to the interior of
the part 77, which is discarded and the mix in the cap 78 will not
be contaminated by such unmixed particles.
The lower edge of the part 77 is a tight fit in the upper edge of
the cap 78 so that particles cannot find their way between the two
parts of the capsule. In a modified arrangement, not shown, the
mating parts of the two portions of the capsule are tapered so as
to provide a tight wedging fit. Although the capsules are described
as being of circular cross-section, they may also be of any other
convenient cross-sectional shape, for example the interior
compartment may be of oval or other elongated cross-section. The
space 77a within the part 77 and below the wall 84 may be as large
or small as convenient without effecting the mixing action,
provided of course that it is of sufficient capacity, with the cap
78, initially to accommodate the charge of powder.
As mentioned above the two materials contained within the capsule
may be brought into contact with one another by rupturing the wall
84 by a metal spike. A convenient device for effecting this
comprises a hollow circular cross-section tube of a size to
accommodate the capsule. One end of the tube is closed and a metal
spike extends axially into the tube from the end wall. To operate
the device the capsule is introduced into the tube with the wall 85
facing towards the spike and the capsule and tube are then pressed
together so that the spike passes axially through both walls 85 and
84. The capsule is then withdrawn from the tube and placed in the
mixing device.
It is found that in some cases (for example when the liquid
contained in the capsule is phosphoric acid) polythene and similar
plastics from which the capsule may be conveniently formed may be
slightly permeable to the liquids contained in them. Such
permeability can shorten the shelf life of the capsule especially
under high temperature conditions. The capsule shown in FIG. 11 is
designed to overcome this problem. In this form of capsule the
liquid is contained within a canister 89 formed from thin aluminum
and located within the chamber 82. In this case the thin wall 84 is
not necessary although it may be present if required to give
further support to the canister 89. The canister 89 has walls of
about ten thousandths of an inch in thickness and the bottom wall
of the canister is conically shaped.
Since the aluminum canister 89 is impermeable to liquid there is no
tendency for the liquid to be lost by permeation and thus the shelf
life of the capsule is increased. When it is required to form a mix
the upper and lower walls of the canister 89 are pierced by a steel
pin in a similar manner to that described above in relation to the
capsule of FIG. 10.
It will be seen that in the capsules of FIGS. 10 and 11 the point
where the liquid emerges from the compartment 82 or canister 89 is
disposed below the surrounding upper wall of the chamber 77a. It is
found that if this is not done there is a tendency for droplets
emerging from the aperture formed by the pin 86 to be thrown
radially outwards in contact with the upper wall of the chamber 77a
(due to their surface tension) rather than being thrown into the
mix by centrifugal force. The arrangement shown in FIGS. 10 and 11
ensures that liquid emerging from the compartment or canister is
thrown outwardly by centrifugal force clear of the upper wall of
the chamber 77a and into the mix. Also due to the curving of the
upper wall of the chamber 77a there is little tendency for grains
of the powder material to adhere to the corners of the chamber 77a
and thus not become fully mixed.
The canister 89 may be formed in two parts and FIGS. 12 and 13 show
examples of methods of closing the canister. In FIG. 12 the
canister 89 has a bottom part 90 which has an enlarged diameter
upper portion 91 so as to form a shoulder 92. A soft metal
diaphragm 93 rests on the shoulder 92 between two washers 94 and
95. The upper end of the portion 91 is then folded inwardly (as
indicated in dotted lines at 96) to secure the washers and
diaphragm firmly against the shoulder 92 and thus seal the
canister. In the alternative arrangement shown in FIG. 13 the
canister is closed by a thin metal disc 97 having a peripheral
upstanding wall 98. The wall 98 may be welded to the surrounding
portion 91 or the two parts 91 and 98 may be secured together by
folding or rolling them inwardly or outwardly. It will be
appreciated that many other methods may be used for sealing the
canister.
As mentioned earlier capsules may be employed for mixing together
more than two materials. Where two or more different liquids are to
be used the upper part of the capsule may include two or more
canisters, each having a different liquid and placed one above the
other so that the canisters can all be pierced at the same time by
the pin 86. If more than one canister is used in this manner then
the canisters may be a loose fit in the compartment n the in 77 to
allow liquid from an upper canister to flow downwardly around a
lower canister. In this case the upper part of a lower canister may
be formed with a raised dome to prevent liquid from an upper
canister being trapped on top of the lower canister. It will be
seen that the canister will then be domed in a similar manner at
each end. An advantage of having the canister similarly shaped at
opposite ends is that it is then immaterial how the canister is
inserted in the compartment 82 and this facilitates assembly of the
capsule during manufacture. A projection formed on the lower
conical part of the canister or on the mating conical part of the
body portion 77 will prevent these two surfaces bedding together
and thus allow for the passage of the liquid around the lower
canister from an upper canister. Alternatively a washer with a
central hole and a serrated or star shaped edge placed below the
lowermost canister will serve this purpose. It will be appreciated
that there are many shapes of canister which will allow the free
passage of liquid between the canister and the surrounding wall and
will also prevent the lower canister sealing off the hole in the
body portion 77.
Alternatively the lower part of an upper canister may be conically
formed and may fit within a conical depression in the upper part of
the canister beneath it so that when the canisters have been
pierced the liquid from the upper canister runs downwardly through
the lower canister before passing into the chamber 77a.
FIG. 14 shows an alternative form of capsule where two liquids are
to be mixed with a third powdered material. As in the arrangements
described above the body portion 77 of the capsule is formed from
an easily pierceable material such as polythene and the compartment
82 accommodates one liquid. In this case the canister 89 contains a
second liquid and is spaced above the bottom wall 84 of the
compartment 82. It will be seen that the canister 89 then serves as
a stopper to contain the liquid in the compartment 82. The two
liquids may be released and delivered into the mixing cap 78 by
passing a single piercing instrument through the canister 89 and
the wall 84. It will be seen that in the arrangement of FIG. 14 the
upper thin wall 85 to the capsule has been dispensed with.
In the mixing apparatus described earlier the socket in which the
capsule is mounted is inclined at about 371/2.degree. to the
vertical. In the capsules shown in FIGS. 10, 11 and 14 the bottom
walls of the compartments for containing liquids are conical. It is
preferable for the conical angle to be such that when the capsule
is placed in the inclined socket 18 centrifugal force tends to
force the liquid down to the apex of the cone at all points around
the conical surface. it will be appreciated that if the conical
angle is too shallow there may be a tendency for liquid on parts of
the surface furthest away from the center of rotation of the arm 14
to be thrown upwardly. This may not be serious since it will only
happen around a small portion of the conical surface but it is
preferable to avoid this if possible.
As mentioned earlier the lower part of the capsule may be formed
from metal such as stainless steel or aluminum so that it may be
earthed to dissipate any static electricity generated. Thus in the
capsules described the lower cap part 78 of the capsule may be
formed from metal. Alternatively the whole capsule may be made from
a material which does not generate static electricity, such as
Bakelite (Registered Trade Mark).
FIG. 15 shows an alternative form of capsule somewhat similar to
that shown in FIG. 11 but in which the liquid is contained within a
sachet 90, of metal foil, mounted within a suitably shaped recess
91 in the upper part of the capsule portion 77. The sachet consists
of two circular discs welded or otherwise bonded together around
their periphery. A locating ring 92 is wedged in the recess 91 to
locate the sachet 90 in position and the ring 92 prevents the
sachet 90 being withdrawn from the capsule body as the pin which
has been used to puncture the sachet is withdrawn.
There are already known various forms of capsule for containing
cement-forming materials in predetermined quantities. Such capsules
have hitherto been used in mixing apparatus which simply oscillates
the capsule to effect mixing. However such a known form of capsule
may also be employed in a mixing apparatus according to the present
invention. One such capsule comprises an elongated body part domed
at one end and closed at the other end by a removable cap. The main
body part of the capsule contains the powder material and the cap
contains the liquid. The liquid is normally either contained in a
metal foil sachet, similar to the sachet 90 of FIG. 15, or is
retained within the cap by sealing discs and rings. The arrangement
is such that when the cap and main body portion of the capsule are
squeezed together the sealing disc or sachet is ruptured so that
the liquid passes into the main body of the capsule containing the
powder. Although such a capsule may be used in the mixing device
described earlier it is preferably modified by replacing the domed
end of the main portion of the capsule by a removable cap similar
to the cap 78 in the arrangements described above, and also by
forming the capsule with external projections to engage the
projections in the socket of the device.
The capsules described above are all suitable for use in the device
shown in FIG. 1. There will now be described certain further forms
of capsule which have features not found in the capsules described
above. Since the capsules to be described below are of different
shape and proportions to those so far described it will be
appreciated that the socket 18 of the device of FIG. 1 would
require to be suitable modified to accommodate them.
The capsule shown in FIG. 16 is formed from plastics material and
comprises a lower mixing chamber 93 of circular cross-section one
end of which is closed in liquid-tight manner by a piston 94. The
upper end of the chamber 93 is formed with an inwardly projecting
annular flange 95 encircling a central aperture 96. The chamber 93
contains the powder component for forming the cement. The lower end
97 of a hollow cover 98 is a tight fit in the aperture 96 and a
flange 99 on the cover 98 overlies the flange 95. The cavity in the
cover 98 contains the liquid component of the materials for forming
the cements.
The lower part of the cavity within the cover is conically formed
as indicated at 100 the lower apex of the cone leading to an outlet
aperture 101. The outlet aperture 101 and the upper end of the
cover are closed by thin walls 102 and 103 respectively. The walls
102 and 103 may be of thin plastics bonded to the remainder of the
cover or one of them may be formed during the moulding process.
Alternatively one or both of them may be formed from any rupturable
materials such as aluminum foil. As in the case of the capsules
previously described the liquid may be mixed with the powder by
rupturing the walls 102 and 103 by a steel pin 104 before the
capsule is placed in the mixing device.
When mixing has been completed the capsule is removed from the
apparatus and the cover 98 discarded. The mixing chamber 93 is then
placed over a suitably shaped spigot and pressed downwardly so that
the piston 94 is forced upwards to meet the flange 95. This brings
the mixed cement to the top of the chamber where it may be readily
removed.
Any unmixed particles of powder present in the chamber 93 after
mixing will be adhering to the walls of the chamber and thus will
be trapped below the flange 95 when the piston 94 is raised so that
these unmixed particles of powder will not contaminate the cement.
It will be appreciated however that if the depth of the chamber 93
is small enough the material will extend up the whole height of the
wall of the chamber when the material is thrown to its outermost
position in the inclined capsule during mixing. Thus as the chamber
rotates the materials will sweep over the whole of the internal
walls and thus there should not be any unmixed particles of powder
remaining. Thus in some instances the flange 94 may not be
necessary.
FIGS. 17 and 18 show an alternative form of capsule. The cover 105
of the capsule is similar to the cover 98 of FIG. 16 except that it
is formed with a peripheral skirt 106 which tightly embraces the
upper end of the lower mixing chamber 107. The mixing chamber 107
however differs from the chamber 93 in that the space within the
capsule is in the form of a transverse slot 108 (as best seen in
FIG. 18). This arrangement has the advantage that when the material
being mixed is disposed at one end of the slot 108, when the
capsule is in the mixing device, the side walls of the slot tend to
prevent the material losing adhesion until the slot has turned
through 180.degree.. This means that when using the capsule of
FIGS. 17 and 18 the relationship between the speeds of rotation of
the arm 14 and the capsule may not be so critical in order to
produce the ideal operation referred to in which the material are
carried round through 180.degree. rotation of the capsule before
adhesion is lost through centrifugal force and the materials are
thrown across the capsule.
There may also be less tendency for particles of powder to be
unmixed and therefore a flange corresponding to the flange 95 of
FIG. 16 may not be necessary. The capsule shown in FIGS. 17 and 18
is also particularly suitable for mixing dental amalgams of mercury
and metal alloy powder. Such an amalgam has very little
adhesiveness to the walls of a container and thus would not be
carried round by the walls of a circular receptacle. The amalgam
would however tend to be carried round through 180.degree. by the
transverse slot type of container shown in FIGS. 17 and 18.
The slot 108 is shown in FIG. 17 as having a flat bottom but it may
if required have a rounded bottom.
The capsules may be formed from any suitable plastics material but
in the case of that shown in FIG. 16 the piston part 94 may be
formed from a softer plastics material then the rest of the chamber
93 to insure a liquid-tight fit between the piston and the walls of
the chamber as well as facilitating movement of the piston 94
upwards to eject the cement. The piston 94 might also be formed
from rubber or polythene as may also the cover 98 or the cover
105.
Although the capsules are described as having liquid in the cover
and powder in the mixing chamber it will be appreciated that the
powder could be in the cover and the liquid in the chamber.
As mentioned earlier in some cases three or more materials may
require to be mixed to form a cement, for example, some cements are
formed from a powder a liquid and a catalyst. In this case the
cover may be formed with a number of compartments each containing
one of the materials to be mixed and the compartments all being
ruptured in a similar way to discharge the materials from them into
a single mixing chamber in the lower part of the capsule. The
capsule shown in FIGS. 17 and 18 is particularly suitable for such
an arrangement since the compartments in the cover may be spaced
apart in register with the elongated slot 108. When a number of
compartments for liquid or powder are provided in the cover the
underside of the cover is preferably provided with a projection
which registers with the upper end of the slot 108 so that the
outlets from the compartments are accurately located with respect
to the slot.
Referring to FIG. 19 the capsule shown in that Figure comprises a
lower mixing chamber 109 of circular cross-section.
The central portion of he bottom wall of the chamber 109 is domed
as in the capsules first described above. The capsule also
comprises an upper cover 110 which is formed from a resilient
plastics material such as polythene, the lower portion 119 being
formed from a more rigid plastics material. The cover 110 if formed
with a downwardly projecting peripheral skirt 111 which tightly
encircles the upper end of the chamber 109. The upper end of the
peripheral wall 112 of the mixing chamber is received within an
annular slot 113 within the under side of the cover 110.
The annular slot 113 is a close fit over the wall 112. The
thickness of the wall 112 may be slightly larger than the width of
the slot so that the resilient materials of the cover will be
stretched by the wall so that a tight fit is effected.
The cover 110 is formed with a circular cross-section cavity 114
the lower part of which is conically formed, the lower apex of the
cone leading to an outlet aperture 115 closed by a thin wall 116.
The under surface of the wall of the cover surrounding the aperture
115 is recessed as indicated at 117 for the purpose described with
reference to FIGS. 10 and 11.
A canister 118 formed from thin aluminum is located within the
cavity 114 and is shaped externally to correspond to the interior
shape of the cavity. The walls of the canister may be about ten
thousandths of an inch in thickness. The canister contains the
liquid component of the substances to be mixed and is closed at its
upper end by a thin aluminum cap (not shown) as described in the
earlier arrangements. A further cap of plastics material may also
be sealed over the closed upper end of the aluminum canister to
secure the canister within the cover. Alternatively the canister
could closed by a polythene plug covered by an impermeable skin
such as if often used over bottle stoppers. The canister and thin
wall 116 are ruptured by a steel pin in a similar manner to that
described with relation to the canisters described earlier.
Although the provision of an aluminum or other metal canister in
the arrangements described above may prevent loss of liquid by
evaporation certain liquids may attack the metal of the canister.
This problem may be reduced by anodising the metal of the canister
or by lining the inside of the canister by a plastics material
which is not attacked by the liquid. The canister will still then
prevent loss of liquid by permeation. Alternatively the liquid may
be contained within a container formed from a plastics which is not
attacked by the liquid the outer surface of the container being
coated with aluminum to prevent permeation through the walls of the
container.
* * * * *