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This invention relates generally to hot plates and more particularly to
industrial hot plates for use in highly corrosive environments including
operations involving the use of active chemical agents of both high
acidity and high alkalinity.
The prior art is replete with hot plates of the type disclosed. The more
recent ones utilize ceramic materials for the heated working surface or
top and, as such, these ceramic tops are very resistant to chemical
reaction with virtually all of the various chemicals that may be employed
as well as being capable of withstanding high temperatures. One such
ceramic top made is commercially available from the Corning Glass Works in
Corning, New York and can be purchased complete with a ribbon heating
element, backing plate and mounting clips fully assembled less electrical
power connectors and controls.
But even the most advanced designed hot plates, whether they employ the
commercially available Corning Glass Works ceramic hot plate or other
unknown but suitable substitutes, have failed to meet the specifications
demanded in certain industries simply because the various base structures
to which these ceramic tops are affixed are manufactured from materials
which subsequently fail due to the corrosive chemicals employed. Then too,
in many instances failure of the hot plate can be directly attributed to
an inadequately protected electrical supply lines to the heating element,
especially in those instances where the base structures stand on wet or
liquid covered surfaces.
In the present invention, these undesirable characteristics are alleviated
by providing a hot plate that is completely protected from any hostile
environment. According to the invention, there is provided a hot plate
comprising in combination a top portion having a heated working surface, a
heating element operably disposed is the top portion below the working
surface and having electrical terminals, circuit means for supplying
electrical energy from a power source to the terminals, a base portion for
operably supporting the top portion in thermal isolation therefrom, and
means including epoxy foam for encapsulating the heating element and the
circuit means to confine substantially all of the heat generated to the
working surface.
It is therefore a primary purpose and objective of the invention to provide
an improved hot plate.
It is another object of the invention to provide a hot plate of the type
described that can be operated in a highly corrosive environment.
It is still another object of the invention to provide a hot plate of the
type described that utilizes foam type materials to prevent chemicals of
both high acidity and high alkalinity from reacting with the electrical
components thereof.
It is yet another object of the invention to provide a hot plate of the
type described that is provided with a non-corrosive base portion adapted
to foam encapsulate the electrical components assembled therein.
Another object of the invention is to provide a hot plate of the type
described that utilizes a foam type material to seal the electrical
heating element from toxic and corrosive chemical substances.
These features, objects and other advantages of the invention are more
fully brought out in the following specifications, reference being had to
the drawing wherein:
FIG. 1 is a perspective view showing a hot plate constructed in accordance
with the present invention;
FIG. 2 is an enlarged, partial cross-sectional view taken along the line
2--2 of FIG. 1; and
FIG. 3 is a partial, cross-sectional view taken along the line 3--3 of FIG.
2.
Referring now to the drawing, shown there in FIG. 1 is a hot plate 10
constructed in accordance with the invention. The hot plate 10 includes a
base portion 12 upon which is operatively mounted a heated frame portion
14.
The base portion 12 may be formed by, for example, injection moulding using
a suitable plastic material preferrably from a class known as
fluorocarbons. As best seen in FIGS. 1 and 3, the base portion 12 includes
a top wall 16, side walls 18a, 18b as well as the respective opposite
walls thereto, not shown, and a bottom wall 20. Each of the side walls
18a, 18b, and 18c is provided with a recess 22, reference FIG. 3, to
receive the bottom wall 20 during assembly. The top wall 16 and depending
side walls define an internal wiring compartment 17.
Mounted on the side wall 18b is a coupling member 24 having an internal
threaded region 26 of predetermined length for receiving a conventional
compression fitting 28. The coupling 24 may be integrally molded with the
base portion 12, if desired. Passing through the side wall 18b and in
concentric alignment with the threaded region 26 is an opening 30 of
suitable diameter to permit the passage of electrical conductors 32 and
34. For the conductors 32 and 34, it is preferred that wire coated with a
fluorocarbon material be used. A plastic tube 36 which may be of the
shrink tubing type and preferably made of fluorocarbon materials is also
provided to carry the conductors 32 and 34 between a source of power, not
shown and the base portion 12.
Disposed within the coupling member 24 and surrounding the tubing 36 is a
tapered ring insert 38 which, upon properly mounting the fitting 28 into
the coupling 24 causes the insert 38 to be compressed against the tubing
36 and the conductors 32 and 34. When installed in this manner the
conductors 32 and 34 and the tubing 36 are securely fastened to the base
portion 12 at the coupling 24. In addition, a very effective seal is
provided to prevent all chemicals from coming into contact with the
conductors 32 and 34 since the tubing 36 terminates inside the base
portion 12 as shown in FIG. 2.
The heated frame portion 14 includes a ceramic body 40 having a top deck
defining an upper external planar working surface 42, a pair of mounting
clips 44 and 46, a ribbon heater element 48, a backing plate 50 and a heat
resistant foam layer 52 disposed between the backing plate 50 and the
heating element 48. A fibrous pad or layer 49 separates the heating
element from the epoxy foam layer 52.
The ceramic body 40 is provided with turned-down edges 54 along the
periphery of the working surface 42 and defining a peripherally continuous
depending wall. The deck and depending peripheral wall of the ceramic body
40 define a heater compartment 41. The mounting clips 44 and 46, as best
seen in FIG. 2, have two spaced apart, up-turned brackets 56 and 58 welded
together as depicted by a reference numeral 60 and are formed to fit
snugly on the edges 54. Threaded openings 62 are provided in the clips 44
and 46 to receive conventional fasteners 64 for assembling, to be
described. The backing plate 50, reference FIGS. 2 and 3, is also provided
with openings 66 to receive the conductors 32 and 34.
It should be pointed out that openings 68 are also provided in the top wall
16 for receiving the fasteners 64 and that similar openings 70 in the top
wall 16 are provided for the electrical conductors 32 and 34 to pass
through from the base portion 12 to the frame portion 14. Spacers 72 and
74 of predetermined length and preferably made from fluorocarbon materials
are provided for the fasteners 64 and the conductors 32 and 34
respectively. It should be noted that the conductors 32 and 34 terminate
at respective opposite ends of the heating element 48, as shown in FIG. 2
by a numeral 76. As best seen in FIG. 3, each of the conductors 32 and 34
is carried in plastic tubing 78 and 80 respectively, between the frame
portion 14 and the base portion 12. The plastic tubing 78 and 80, which
may be similar to the tubing 36, terminates respectively within the foam
layers 52 in the frame portion 14 and within a foam layer 82 provided in
the space between the top wall 16, the sides 18 and the bottom wall 20.
As for the foam layers 52 and 82, a two component, fast setting, low
temperature curing epoxy foaming system of any type commercially available
may be used. Assuming the epoxy materials have been mixed as per
instructions, and the ribbon heater element 48 has had the conductors 32
and 34 properly attached at the terminals 76 and has also been properly
positioned in the ceramic body 40, which may be done best with the ceramic
body 40 placed upside down, relative to that shown on the drawing, and on
a work surface, and each of the plastic tubing 78 and 80 has been slipped
on the conductors 32 and 34 respectively, then, with that done, a
predetermined amount of the epoxy material is spread over the ribbon
heater element 48. The conductors 32 and 34 along with the respective
plastic tubing 78 and 80 are now passed through openings 66 in the back
plate 50 and the back plate 50 positioned in place over the epoxy
materials, which ultimately becomes the foam layer 52. The mounting clips
44 and 46 may now be positioned in the down-turned edges 54 of the ceramic
body 40.
The frame portion 14 is now attached to the base portion 12 by way of the
threaded fasteners 64 which extend through the openings 68 in the top wall
16 from the bottom side as seen in the drawing and then through the
spacers 72 and ultimately into the threaded openings 62 of the mounting
clips 44 and 46.
Just prior to this, however, the conductors 32 and 34 together with the
plastic tubing 78 and 80 are passed through the spacers 74 and hence
through the two spaced apart openings 70. At a predetermined point below
the top wall 16 the plastic tubing 78 and 80 is terminated. From that
point on to the source of electrical power, if necessary, the conductors
32 and 34 are carried within the single plastic tubing 36, through the
opening 30, the coupling member 24, the tapered insert ring 38 and the
fitting 28.
With the conductors 32 and 34 positioned as pointed out above, and after
the fasteners 64 are securely tightened, another predetermined amount of
the mixed epoxy materials is applied over the conductors 32 and 34 and
within the region defined by the bottom surface of the top wall 16, the
inner surface of the side walls 18a, 18b and the walls, not shown,
opposite thereof, up to the lower part of the recess 22, when viewed in an
inverted position relative to that shown in the drawing.
At this point the bottom wall 20 is positioned within the recess 22 of the
side walls 18a, 18b, etc. over the mixture of epoxy materials which on
becoming cured has expanded to become the foam layer 82. If desired, the
bottom wall 20 may be permanently or removably attached to the base
portion 12 by suitable adhesives or other commonly known methods.
It should be noted that the heat resistant epoxy foam layer 52 serves to
prevent any chemically active agents from making contact with the heater
element 48. Similarly, the foam layers 52 and 82 prevent such similar
agents from coming into contact with the conductors 32 and 34 in the event
these agents were to eventually find a path between the spacers 74 and the
openings 66 and 70 respectively of the backing plate 50 and the top wall
16. As for that portion of the conductors 32 and 34 that is exterior of
the coupling 24, the tubing 36 provides the desired protection.
It should be stated that a ceramic hot plate, Model PC-35, made of
"Corningware", a registered trademark of the Corning Glass Works, Corning,
N.Y., and having suitable mounting clips, a ribbon heating element and a
back plate is available from the Corning Glass Works and can be used in
conjunction with the present invention as described above.
While I have herein shown and described my invention in what I have
conceived to be the most practical and preferred embodiment, it is
recognized that departures may be made therefrom within the scope of my
invention, which is not to be limited to the details disclosed herein but
is to be accorded the full scope of the claims so as to embrace any and
all equivalent devices and methods.
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