Fluidized solids particle discharge device

The described apparatus is designed to be inserted into a fluidized solids temperature calibration bath to eliminate dusting, particle impingement and test instrument temperature environmental problems.

FIELD OF THE INVENTION 
This invention relates to fluidized solids temperature calibration baths, 
in general, and to a particle discharge device which permits the accurate 
and safe use of such equipment, in particular. 
BACKGROUND OF THE INVENTION 
As is well known and understood by those skilled in the art, temperature 
calibration baths using heat treating salts, or oils, as the calibration 
medium are being replaced, in many instances, by baths using fluidized 
solids. As will be appreciated, this use of fluidized solids, such as 
aluminum oxide, as the calibration medium, served to reduce the 
possibility of explosion or fire hazard, which were sometime experienced 
when salts or oils were used. In these regards, the bath was primarily 
used for thermometer calibration work, and safer to use because the medium 
is chemically inert, and the danger from spitting, splashing, or spilling 
type accidents is reduced. 
Experience has shown, however, that there exist a series of problems with 
these fluidized solids temperature calibration baths which both limit 
their accuracy and their usefulness. Characteristic of such baths is that 
air flows up through the bottom of the fluidized bed, and fluidizes the 
solid particles, usually of 100-180 mesh size, with the air then exiting 
the bath through the top of an open reservoir. With the bath temperature 
being maintained and controlled by immersion heaters, it has been found 
that the exiting air carries the aluminum oxide, or other particles along 
with it ("dusting"), to be deposited on nearby surfaces. Such "dusting" 
effect presents a potential health hazard for operating personnel, the 
potential for damage to the test instruments being calibrated, and the 
possibility of having an adverse effect on the calibration accuracy. 
Secondly, as the temperature of the bath might run relatively high, e.g., 
to 1500.degree. F., the exiting air may cause damage to the parts of the 
instrument located outside the bath--for example, to the heads, to 
electrical connectors, to dial faces, etc., as well as causing 
inaccuracies in calibrated readings. With certain temperature sensitive 
instruments to be calibrated, furthermore, difficulties were encountered 
in immersing the instrument to the proper depth in the fluidized bath 
necessary to obtain an accurate indication of bath temperature, for to do 
so, led to the undesirable intrusion of the fluidized particles into vital 
parts of the instrument and/or an overheating of vulnerable parts. 
Temperature sensitive switches, in this regard, were particularly affected 
by the fluidized particles getting into their working parts. Thus, while, 
in general, overcoming many of the disadvantages associated with salt and 
oil type calibration baths, the fluidized solids calibration baths have 
shown to pose a potential health hazard to temperature calibration bath 
operators that are exposed to breathing airborne particles during the 
calibration process, and have an adverse effect on the calibration of 
temperature measuring test instruments by subjecting them to excessive 
case temperatures. 
SUMMARY OF THE INVENTION 
As will become clear hereinafter, a fluidized solids particle discharge 
device embodying the invention was constructed of a bucket-like structure, 
consisting of an upper and lower ring, a removable nonmetallic base plate 
(made of Transite or equivalent hard thermal insulating material, for 
example), and walls made up of an inner and outer sheet cylinder separated 
by an annular space through which a cooling fluid, such as air, is caused 
to flow. With the sensor part of the temperature measuring test instrument 
extending through the nonmetallic base plate into the fluidized bed, and 
with the instrument case and/or vulnerable parts housed within the 
bucket-like structure, the apparatus of the invention was found to 
substantially eliminate all "dusting" and particle impingement on the 
temperature measuring test instrument, by effecting a mechanical seal 
between the fluidized solids particle discharge device and the temperature 
calibration bath, and by using the thermal insulating material as a 
barrier between the fluidized solids bed and the temperature instruments. 
Besides its use as a mechanical barrier, the thermal insulating material 
was also found effective in reducing the amount of heat undesirably 
transmitted from the fluidized solids bed to the temperature instrument 
being calibrated, which, in turn, was found further reduced by the 
circulating cooling air which lowered the wall temperature of the 
apparatus of the invention.

DETAILED DESCRIPTION OF THE DRAWING 
Referring now to the drawing, the fluidized solids particle discharge 
device 10 is generally in the form of a bucket-like structure having an 
upper ring 12 and a lower ring 14. A removable nonmetallic base plate 16 
is also included, constructed of Transite or equivalent hard thermal 
insulating material, with inner and outer walls 18, 20, constructed to 
form a sheet metal cylinder. These walls 18, 20 are separated by an 
annular space 22, through which a cooling fluid, usually air, is caused to 
flow--for example, by compressed air introduced into the annular space 
through a stainless steel tube 24 which, in turn, exits through a second 
stainless steel tube 26 and muffler cap (not shown). When the two 
stainless steel tubes 24, 26, are separated by a vertical divider plate 
(not shown, but extending vertically down in the annular space 22 between 
the walls 18, 20), compressed air entering through the inlet tube 24 is 
forced to circulate around the walls of the space 22, to exit through the 
second tube 26 and muffler cap, which serves to reduce any noise which 
might emanate from the exiting air. A pair of standpipes 28, 30 extend 
through the top ring 12, to permit air to circulate upwards from the 
fluidized bed, and outwardly therefrom, but are selected of narrow 
cross-section and of a reversed bend and shape so as to prevent measurable 
carry-over of fluidized particles into the exiting air. An adapter 32 is 
used to secure a thermometer, or other heat sensitive device, the probe 
end of which extends through the underlying aperture 34 into the fluidized 
solid calibration medium. A second aperture 36 is provided, through which 
a thermometer extends into the fluidized bed, to serve as a "standard" 
against which comparisons and/or calibrations are being measured. 
In use, the upper ring 12 serves to cap the annular space 22 and to provide 
a flange which rests on top of the bath 42 (FIG. 3) or on the top edge of 
the bath reservoir 40, thereby holding the fluidized solids particle 
discharge device 10 in place when in use. An insulating gasket material 44 
(Kaowool or equivalent) is situate between the upper ring 12 and the bath 
or reservoir top, to prevent air and solid particles from escaping 
therefrom. The lower ring 14, on the other hand, similarly serves to cap 
the annular space 22, and also to provide a flange which holds the 
removable base plate 16. With a second gasket 46 (FIG. 2) used between the 
base plate 16 and the top of the lower ring 14 so as to seal that joint, 
it will be apparent that these gaskets 44 and 46 additionally serve to 
provide thermal insulation so as to aid in cooling the upper ring 12 and 
base plate 16. 
Those skilled in the art will appreciate that the base plate 16 is drilled 
to permit insertion of variously shaped temperature standards and 
temperature sensing devices which it is desired to calibrate. Such 
drillings may be counterbored or otherwise shaped, where possible, so as 
to seal against air and particles escaping around the inserted 
instruments. Kaowool or equivalent soft blanket type insulation materials 
may be used as a packing around the insertion holes, where necessary, to 
insure this. The thickness of the base plate 16 can additionally be varied 
to provide the correct immersion depth of the probe or sensor 48 of the 
device to be calibrated, with such depth into the fluidized solids 50 
being also controllable somewhat by varying the thickness of the upper or 
lower ring gaskets. As indicated in FIG. 3 cooling air is introduced 
through tube 24, and after flowing through the annular space 22, exits 
through tube 26. A pair of beakers 60, 62 are employed to collect any 
particle carry-over which is able to transmit through the standpipes 28, 
30. Air flowing through the fluidized solids 52 permits a heating of the 
solids by immersion heaters (not shown), but the particles are prevented 
from entry into the structure 10 due to the lower ring 14 and base plate 
16 serving as mechanical barriers. In such manner, both the "standard" 
thermometer 64 and test instrument 66 have their heads, connections, and 
critical parts protected from the grit particles. Additionally, the 
insulating plate 16 and the cooled walls of the reservoir serve to 
maintain the temperature in the bucketlike structure substantially lower 
than that in the fluidized bed, which can be as high as 1500.degree. F. 
for certain kinds of temperature tests. 
In one construction of the invention, the following dimensions could be 
employed: 
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A 2 inch radius F 9 inches 
B 2 inches G 13 3/4 inches 
C 2 1/2 inches H 1/2 inch 
D 3 5/16 inches I 11 1/8 inches 
E 3 3/16 inches J 10 5/8 inches 
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with an annular space 22 of 1/8 inch gap and wall thicknesses 18, 20, of 
1/16 inch each. 
Various advantages and features followed from the use of the fluidized 
solids particle discharge device of the invention. For example, the device 
prevents particles from escaping the bath, thereby protecting personnel 
and equipment in the calibration room from possible harm which might 
result from the introduction of particulates into the ambient air. 
Additionally, the apparatus prevents particles and heated air from 
impinging on vulnerable parts of the temperature sensitive devices being 
calibrated in the bath. Furthermore, both these features are accomplished 
without any need for additional energy, or space, and requires little or 
no maintenance because no moving parts are employed. Furthermore, the 
device of the invention shields the heat sensitive devices from the hot 
walls of the bath reservoir and surrounds them with relatively cool 
air--which, together with the feature of preventing hot air and hot 
particle impingement on the heat sensitive test instrument, protects them 
from damage or from inaccuracy during calibration, thus providing a 
suitable temperature environment for the calibration work to proceed. When 
considered with the ability of the device to control immersion depth so as 
to make possible the ability to immerse the temperature sensitive portion 
in the solid sufficiently to obtain proper measurements of bath 
temperature, it will be seen that the invention permits the accurate and 
safe use of current and future fluidized solids temperature calibration 
equipment. Also, the circulating medium protects the user from burning 
himself on the hot reservoir walls, while the standpipes, besides limiting 
the escape of the fluidized particles, permits sufficient circulation of 
air to maintain the bed and keep it from collapsing. 
While there has been described what is considered to be a preferred 
embodiment of the present invention, it will be readily apparent to those 
skilled in the art that modifications may be made without departing from 
the scope of the teachings herein of providing a separate device designed 
for insertion into a fluidized solids bath to eliminate dusting, particle 
impingement and environment problems. For example, whereas the invention 
has been described in the specific context of test instrument calibration, 
it will be evident that its usefulness extends to other applications of 
fluidized baths, as where instrumentation, equipments and other apparatus 
are to be subjected to heat treating, etc., in which only a portion of the 
arrangement is immersed within the bath, while external portions may be 
adversely affected by particle impingement. For at least such reason, 
therefore, resort should be had to the claims appended hereto for a 
correct understanding of this invention.