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Most modern hospitals, other health care facilities and even doctors'
offices have done away with the traditional mercury-filled glass
thermometers and have replaced them with electronic units which employ a
heat-responsive probe containing a sensing element in the form of a
thermocouple that functions to produce a visual display, usually in
digital form, of the patient's temperature. These devices either use a
self-contained rechargeable power supply or an external power supply
available in the areas where the thermometer is used.
The thermometer itself is an expensive piece of electronic equipment which,
for obvious reasons must be reused over and over again. Moreover, the
design and construction of these units is such that they cannot be
sterilized easily between uses. The sterilization temperatures and
environment are such that the electronic components could easily become
damaged or at least cease to function as intended. Scaling out all
moisture becomes a problem as does the elimination of all joints, pockets
and other sites on the exterior of the case where contaminants could
collect. In any event, the electronic thermometer manufacturers have
chosen to cover the probe with a sterile disposable single-use cap rather
than attempt to design and construct a sterilizable thermometer.
Unfortunately, these caps leave much to be desired in that they materially
lessen the effectiveness of the thermometer for its intended purpose,
namely, that of quickly and accurately providing a reading of the
patient's temperature.
The problems associated with the prior art caps, while complex, all
basically involve efficient heat transfer to the thermocouple of the
probe. In fact, the heat transfer is so poor through the prior art caps
that rather than wait the approximately two minutes or so it takes for the
thermometer to actually reach the temperature inside the patient's mouth,
a reading is taken well in advance of this final reaching and extrapolated
electronically to the end point along a predetermined temperature curve.
Saying this more simply, if, for example the actual temperature of the
probe in twenty seconds was 88.degree. F., the indicated temperature might
be 102.5.degree. F. because previously determined time temperature curves
showed this relationship to exist. Obviously, there are certain
inaccuracies inherent in such a system, yet, if one waits until the
temperature of the probe actually reaches the temperature inside the
patient's mouth, so much time will have elapsed that use of the electronic
thermometer has nothing of significance to offer over the conventional
mercury-filled glass ones.
Seemingly, therefore, the answer lies in more efficient heat transfer from
the patient's mouth to the thermocouple in the probe. Metal caps or
metal-tipped plastic caps offer an obvious answer; however, a full metal
cap is far too expensive to be practical as is the combination metal and
plastic one which, while less expensive to make, involves a costly
assembly operation. Manufacturing costs of less than a cent apiece must be
realized if the product is to reach the consumer at a realistic price of
around a nickel because there remain expensive sterilization and sterile
packaging operations to be performed in addition to the normal marketing
expenses.
Another possible solution is to design some type of inexpensive all plastic
cap having heat transfer capabilities close to that of a metal cap or a
metal-tipped plastic one. So far, while this has been the approach most
manufacturers have taken, it has proven to be singularly unsuccessful.
There are several reasons for this, most of which have to do with the
design of the caps and the methods by which they are molded. Regardless of
the cause, the result has been that the tip of the cap which covers the
thermocouple has ended up being quite thick. At least this is true of the
rigid molded plastic caps which are the only kind in widespread use for
this purpose, the thinnest being of the order of 0.01 inches thick. Heat
transfer through a molded plastic wall of such a dimension is very slow to
say the least. Add to this the problem that a good deal of the heat is
conducted to insensitive areas of the probe through walls of the cap
remote from the thermocouple in contact therewith and one gets some
appreciation of the problem.
It has now been found in accordance with the teaching of the instant
invention that these and other shortcomings of the prior art disposable
probe caps can in large measure be overcome by the simple, yet unobvious,
expedient of molding a cap with a highly localized area in the tip which
is of the order of 0.001 inches thick and surrounding same with a series
of three or more angularly-spaced inwardly projecting ribs that radiate
therefrom and cooperate to maintain at least that area of the cap that is
placed within the patient's mouth in minimal contact with the probe except
where the thin area contacts the thermocouple. The slots in the core of
the mold that produce the ribs perform the exceedingly important function
during the molding operation of channeling the plastic molding material
migrating along the core from the four equiangularly-spaced gates at the
hose thereof into the tip section so as to produce the thin area essential
for fast and efficient heat transfer to the thermocouple of the probe. The
novel technique by which four balanced streams of plastic molding material
simultaneously enter the base of the mold, flow around the core and join
together as they migrate therealong toward the tip section is also
believed to be unique and comprises the only way known to applicant for
reliably producing the thin area in the tip while, at the same time,
maintaining an equal pressure around the mold core so as to not tilt it
within the mold cavity and produce sidewalls of unequal thickness and,
perhaps, even create holes where the core touches the mold.
It is, therefore, the principal object of the present invention to provide
a novel and improved disposable molded plastic cap for covering the heat
sensitive probe of electronic thermometers.
A second objective of the within described invention is to provide a unique
method of molding the cap which comprises simultaneous introducing four
balanced streams of molding material into the mold cavity at
equiangularly-spaced points around the base of the core.
Another object is to provide a device of the type aforementioned which is
thinner in the critical area covering the thermocouple of the probe by a
several fold factor over that of the best that the prior art has yet
produced in a rigid cap.
Still another objective is the provision of a novel method of forming the
cap which enables a localized thin area in the tip of the cap to be
produced and reproduced reliably even in a multi-cavity mold.
An additional object is to provide the tip of the cap with rib-like
projections which are so designed and located relative to one another that
they cooperate to maintain the probe centered therebetween and in minimal
heat exchange relation except for that highly localized thin area covering
the thermocouple where fast efficient heat transfer is most needed.
Further objects are to provide a cap for electronic thermometers which is
simple to make, inexpensive, uniform, reliable, easy to sterilize,
compact, lightweight, tasteless, non-toxic, and a unit that is readily
adaptable for use with any of the commercially available thermometers with
only minor modification.
Other objects will be in part apparent and in part pointed out specifically
hereinafter in connection with the description of the drawings that
follows, and in which:
FIG. 1 is a diagram illustrating the accepted prior art method for molding
long thin plastic caps of the type forming the subject matter hereof which
calls for the plastic molding material to enter the mold cavity at the tip
of the core;
FIG. 2 is a diagram like FIG. 1 illustrating a second prior art molding
method wherein the molding material is introduced into the mold cavity in
a single stream at the base of the core;
FIG. 3 is still another diagram like that of FIGS. 1 and 2 showing what
occurs when one introduces two streams of material into the mold cavity at
the base of the core but at diametrically disposed points on opposite
sides thereof and without channeling material into the tip area;
FIG. 4 is a perspective view to a reduced scale showing the molded cap as
it leaves the mold prior to its being trimmed;
FIG. 5 is a perspective view similar to FIG. 4 and to the same scale
showing the cap trimmed and ready for use, the thermometer probe having
been indicated in phantom lines;
FIG. 6 is a diametrical section to the same scale as FIGS. 1-3 showing the
molded plastic cap in the present invention in its untrimmed form as it
leaves the mold after having been molded in accordance with the unique
molding method that also forms the subject matter hereof;
FIG. 7 is a horizontal section through the base of the mold and insert
therefor showing the manifolding into the mold cavity;
FIG. 8 is a plan view looking down on top of the untrimmed cap of FIG. 6;
FIG. 9 is still a further enlarged fragmentary diametrical section showing
the right half of the mold and core thereof together with the whole tip of
the cap, portions of the latter having been broken away; and,
FIG. 10 is a fragmentary section even further enlarged taken along line
10--10 of FIG. 9 showing one of the ribs in cross section.
Referring next to the drawings for a detailed description of the present
invention and, initially, to FIG. 1 for this purpose, the latter
represents the traditional method of injection molding elongate thin
walled caps. The plastic material is forced under high pressure into the
mold at the portion thereof where the closed end or tip T will be formed
as indicated by the letter g which stands for "gate." As the plastic
enters the mold cavity c defined between the hollowed-out main body of the
mold m and the core or insert i, it will flow down alongside the latter
until it reaches the base of the mold b. The plastic material will thus
have filled cavity c and produced the desired tapered cap closed at one
end.
Such a method is old in the art and widely employed for elongate thin
walled caps and spouts such as those that are used on dispensers for
liquid adhesives and the like. Unfortunately, they produce a cap which is
highly unsatisfactory because it is the thickest adjacent gate g which is
directly above the "thermistor of the thermometer probe" where it should
be the thinnest. By introducing the material into the tip area of the
mold, provision must be made for a sufficient volume to enter so that it
will migrate all the way to the base b and this results in the mold cavity
c being quite wide adjacent gate g as shown.
One effort to overcome this problem has been illustrated in FIG. 2, again
labeled "PRIOR ART" to which reference will now be made. Here the gate g
into the mold cavity c has been moved to the base b of the mold from the
tip thereof. By so doing, the space separating the tip of the insert i
from the top of the mold m can be made somewhat narrower thus resulting in
a thinner tip section T in the finished workpiece. The reason this becomes
possible is, of course, that the portion of the mold cavity c at the tip
of the insert need no longer be oversized to accommodate the material
entering through a gate in this position, but instead, the greater volume
needs to be near the base b of the mold where the gate has been relocated.
Unfortunately, the arrangement of FIG. 2 while solving one problem has
created certain others that are equally serious if not more so.
The most significant of these problems is the deflection of the core or
insert i as the molding material impinges thereagainst. As illustrated, in
FIG. 2, the top of the insert has moved to the left under the influence of
the sidewise pressure exerted on the right side thereof as the molding
material enters single gate g. This molding material will, obviously, fill
the cavity c on the side adjacent the gate g before it migrates around to
the opposite side thus creating this very substantial deflection force.
The net result is to produce a workpiece having a non-uniform cross
sectional wall thickness which becomes progressively worse from the open
lower end o upward toward the tip T. In fact, this deflection can, and
often does, become so gross that the core or insert i actually comes into
contact with the wall of the mold m thus producing a hole in the
workpiece.
The last of the prior art illustrations is that forming the subject matter
of FIG. 3 to which reference will now be made. In FIG. 3, two gates,
g.sub.1 and g.sub.2 have been placed in the base of the mold m with the
purpose in mind of introducing material at diametrically opposed points on
opposite sides of the core or insert c so as to minimize the unequal
loading of the latter. As such, the scheme of FIG. 3 constitutes an
attempt to solve the problems inherent in the molding technique of FIG. 2.
While some improvement is possible, certain problems still remain
unsolved.
If, for instance, the same amount of material at the same pressure does not
enter both gates g.sub.1 and g.sub.2 at precisely the same instant, an
unbalanced condition will exist that tends to deflect the core the same
way as the core in FIG. 2 albeit to a lesser degree due to a smaller
differential. Secondly, there is nothing to prevent the core from
deflecting in a direction at right angles to the plane of the two gates,
i.e., toward or away from the viewer looking at FIG. 3.
Even more important than these, however, is the common problem present in
both the prior art molding methods shown in FIGS. 2 and 3 and that is the
necessity for leaving a certain minimum gap in the mold cavity in critical
area T to insure that the plastic material will enter and fill same
completely. It appears that a minimum gap in the order of 0.01 inches is
required to insure that area T will be completely filled under ordinary
injection molding techniques while using conventional materials.
Unfortunately, this is still far too thick for best results.
Still another proposed solution to the problem should be mentioned briefly
even though it has not been illustrated and that is the use of an elastic
balloon-like membrane of some type that is stretched over the tip of the
thermometer probe and releasably secured to the base thereof. As far as
the thickness of the membrane in the area of the heat sensor or thermistor
is concerned, no injection molded part can be made nearly as thin. There
are problems, however, and they are quite serious ones. To begin with, it
becomes very difficult for the nurse or other user to install such a
membrane over the probe without contaminating it as it must, under most
circumstances, be handled a good deal in performing this operation.
Secondly, the "wet noodle-like" consistency of the membrane is such that
it does not admit readily to automatic packaging and sterilization.
Finally, the very nature of the article renders it susceptible to pin hole
imperfections which open up when stretched over the probe and thus provide
an avenue for bacterial contamination and the like. While it is possible
to test for these and other anomalies, to do so is far too expensive for a
single-time use disposable item of this character which must, to be
competitive, sell to the hospital for a few cents at most.
The remaining figures of the drawing to which reference will now be made
are directed to the novel disposable thermometer cap which has been
broadly referred to by numeral 12 and to the unique method of making same.
As was the case with the prior art methods illustrated in FIGS. 2 and 3,
the cap of the instant invention is molded by injecting the molding
material at the base of the mold, however, here is where the similarity
ends. For a proper understanding of the molding method, reference will be
made initially to FIG. 7 of the drawings where the main mold M has been
partially illustrated along with the manifolding by means of which the
molding material is introduced into the base of the mold cavity C through
four equiangularly-disposed gates G.sub.1, G.sub.2, G.sub.3 and G.sub.4.
The molding material is forced under pressure into the main passage "X"
where it is divided into two streams each carrying half of the total flow
of main passage X. These two streams are-conducted in opposite directions
through branch passages "Y", the cross sections of which are uniform and
sized as previously noted to carry half the flow. Located equidistant from
the junction "Q" of these branch passages Y with main passage X are two
pasages "P" that interconnect said branches Y with two other passages Z.
In other words, the passages P are so located relative to junction Q that
the molding material flowing within branches Y will simultaneously enter
passages Z through passages P. Passages P are preferably located
diametrically opposite one another using the axis of the mold insert "I"
as a center.
Passage P enter passages Z intermediate the ends thereof as shown so that
the flow of molding material in the latter passages will enter the mold
cavity C simultaneously through equiangularly-spaced gates G.sub.1,
G.sub.2, G.sub.3 and G.sub.4. Once again, the passages Z are so sized that
they will each carry half the flow of molding material flowing through
passages Y. From the foregoing, it is obvious that the manifold in the
main die has as its purpose the dividing of the total flow of molding
material entering the die into four equal streams which enter the mold
cavity C simultaneously at four equiangularly-spaced locations (G.sub.1
-G.sub.4) at the base thereof. By manifolding the mold M in this way, the
molding material fills the cavity C by flowing around the core I thereof
and applying a balanced fluid pressure thereagainst which maintans it
precisely centered, a condition which is difficult if not virtually
impossible to attain with either of the prior art "bottom-fed" injection
molding methods of either FIGS. 2 or 3.
Next, with reference to FIGS. 4, 6 and 8 of the drawings, it will be seen
that the cap 12 emerges from the mold M with the congealed streams 14
representing the manifolding within the mold still attached thereto. It
(14), of course, represents excess material which is trimmed away from the
cap 12 and reused in the conventional manner. Such surplusage, therefore,
has no functional significance and, for this reason, can be disregarded
for purposes of the present invention.
In FIG. 9, it will be seen that the core or insert I of the mold assembly
has indentations 16 at angularly-spaced points around the base thereof
that produce projections 18 which releasably lock beneath an annular rib
or the like (not shown) at the base of the thermometer probe 20 (phantom
lines in FIG. 5). Snap caps of one type or another are notoriously old in
the art as a means for covering necked and spouted containers and no
novelty is predicated upon this feature. Furthermore, the projections
shown are intended as being merely representative of one type of
releasable closure, others being interlocking continuous annular ribs,
threads, etc.
Referring next to both FIGS. 6 and 9 and particularly to the right half of
FIG. 9 where the mold and core are shown, it will be seen that the gap 22
between the tip 24 of the insert I and the adjacent wall 26 of the mold
body is considerably thinner than the thickness of the frustoconical wall
28. Preferably, the area 30 at the extreme tip of the cap 12 which will
ultimately overlie and contact the thermistor (not shown) of the
thermometer probe 20 is of the order of 0.001 inches thick or less to
insure rapid heat transfer therethrough.
Now, in accordance with the teaching of the prior art bottom-fed injection
molding methods including that of FIG. 3, it is not possible to reliably
form tip section 30 with a wall thickness much less than say about 0.01
inches, 0.008 being about as thin as has yet been attained. The reason for
this is that if gap 22 is less than 0.01 inches or so, the molding
material cannot be forced into the tip area with sufficient pressure to
fill same completely thus resulting in holes and other imperfections which
cannot be tolerated in a sterile cap for a thermometer probe.
It has now been discovered in accordance with the teaching of the instant
invention that these and other shortcomings of the prior art borttom-fed
injection molding methods can, in large measure at least, be overcome by
the simple, yet unobvious, expedient of merely grooving the core or insert
as shown at 32 adjacent the tip area 30 and leading into the latter so as
to channel sufficient molding material therein to completely, repeatedly
and reliably fill gap 22. As the four streams entering the base of the
mold cavity through gates G.sub.1 -G.sub.4 merge and rise therein,
channels 32 in the core feed it into the narrow gap 22 in the tip area 30
so as to produce a closed end having a wall thickness in the order of
0.001 inches thick which is thinner by a severalfold factor than that
which has been realized by any other injection molding technique so far as
applicant is aware.
Finally, with reference to FIGS. 6, 9 and 10, it will be noted that the
channeling of the insert or core I results in inwardly projecting ribs 38
being produced on the inside of the cap radiating in more or less
equiangularly-spaced relation from the thin section 30 thereof. Obviously,
molding material could be channeled into narrow gap 22 by grooving the
wall of the main mold M bordering the cavity C instead of the insert I;
however, to do so has certain disadvantages. To begin with, the ribs 38
would be on the outside of the cap and provide a somewhat rough and
abrasive surface that could be uncomfortable to place in the mouth. Be
that as it may, the main reason for preferring that the ribs 38 be on the
inside of the cap is that they perform certain very useful functions when
so located.
First, these ribs cooperate with one another, or at least can be made to do
so, such that they engage and maintain the thermometer probe centered
within the interior of the cap. This becomes important because it is
highly undesirable to have the cap in heat conductive contact with areas
of the probe other than that containing the heat sensor or thermistor. In
other words, if the heat from the patient's mouth is by passed by the cap
to those areas of the probe having no heat sensing capability, the
efficiency of the whole unit suffers.
This brings us to the final point most clearly revealed in FIGS. 9 and 10
where it will be seen that all of the ribs 38 have a generally triangular
transverse cross section such that they terminate in a sharp ridge 40. By
appropriately shaping the tip of the probe as indicated by phantom lines
on the left side of FIG. 9, it not only becomes possible to center the
latter within the cap but also to maintain multiple point contact
therewith. As such, the heat losses through the cap to insensitive areas
of the probe are even further minimized. Other than these points where the
thermistor rests up snug against the thin section 30 and the ribs make
point contact with the probe, the only other area of contact should be at
the base when the snap connection is made because this portion of the
assembly will usually lie outside the patient's mouth anyway.
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