US 3838600 A
An improved sheathed fever thermometer and method of preparing the same wherein the thermometer structure, fabricated from glass, is encapsulated within a contoured sheath. The sheath is provided with a tapered wall thickness which increases from the bulb end to the tip end, with the tip end having a gripping tab which enables the user to grasp the tab for achieving enhanced motion for shaking down the conventional mercury column.
Description (OCR text may contain errors)
[451 Oct. 1, 1974 15 SLEEVE FOR FEVER THERMOMETERS AND METHOD OF ATTACHING SAME  Inventors: Robert A. Ersek; Donald E. Wall,
both of Minneapolis, Minn.
 Assignee: Med General, Inc., Minneapolis,
Minn'  Filed: Aug. 16, 1972  Appl. No.: 281,131
 U.S. Cl. 73/373, 206/165  Int. Cl. G0lk 5/04  Field of Search 73/371, 374; 206/165  References Cited UNITED STATES PATENTS 1,363,259 12/1920 Mills 206/165 2,096,471 10/1937 73/373 2,435,588 2/1948 Hintsala 73/373 2,839,927 6/1958 Futterman 73/373 3,490,287 1/1970 Coben 73/371 3,528,292 9/1970 Maynard 73/374 Primary Examiner-Richard C. Queisser Assistant Examiner-Daniel M. Yasich [5 7] ABSTRACT An improved sheathed fever thermometer and method of preparing the same wherein the thermometer structure, fabricated from glass, is encapsulated within a contoured sheath. The sheath is provided with a tapered wall thickness which increases from the bulb end to the tip end, with the tip end having a gripping tab which enables the user to grasp the tab for achieving enhanced motion for shaking down the conventional mercury column.
between the mandrel and the sheath enhances the.
release of the individual mandrel fingers from the sheath structure. A vinyl plastisol has been found to be preferred for the sheath fabrication material.
4 Claims, 8 Drawing Figures SLEEVE FOR FEVER THERMOMETERS AND METHOD OF ATTACI-IING SAME BACKGROUND OF THE INVENTION The present invention relates generally to an improved sheathed fever thermometer, and more specifically to a fever thermometer having a protective sheath enveloping the entire structure, wherein the sheath is fabricated from a tough, durable transparent film of predetermined configuration. The encapsulating film has a wall thickness which tapers from the tip end to the bulb end so as to provide substantial protection over the cylindrical barrel of the structure, while reducing the thermal resistance across the film in the area of the bulb. A further feature of the structure of the present invention includes the provision of a gripping tab adjacent the free tip end of the thermometer structure.
In the past, various methods, techniques, and apparatus have been proposed for the establishment of a sheath or enclosure about a conventional fever thermometer. These fever thermometer structures normally include an elongated barrel, cylindrical in form, having a generally centrally located capillary tube or bore, with this tube or bore portion terminating at one end in a reservoir bulb. The reservoir bulb contains a substance which responds dimensionally to temperature variations, and accordingly will expand in the bore upon exposure of the bulb to increases in temperature. The tip end of the thermometer is sealed, with the bore being evacuated to permit movement of the temperature responsive substance in the bulb portion.
Since fever thermometers typically are fabricated from glass, they are easily broken or cracked, and when this occurs, they pose a potential hazard to the user. However, the use of a covering sheath, while solving certain of the mechanical problems, may be found to addadditional problems to the use of the device. For example, if a sheath is added which is made of heavy raw material, the optical, as well as thermal properties of the device may be adversely affected, with the mercury column becoming difficult to read because of the mismatch of indices of refraction, and with the response being impeded because of the added resistance to transmission of thermal energy. However, in connection with the aspects of the present invention, the optical properties are not adversely affected, and the sheath is provided with a thin wall structure adjacent the bulb end thereof in order to minimize the additional impedance to flow of thermal energy due to the interposition of the sheath thereon.
SUMMARY OF THE INVENTION The present invention overcomes these disadvan tages by the use of a sheath element over a conventional fever thermometer which provides substantial protection on the barrel portion of the thermometer, while providing minimal impedance to the transmission of thermal energy across the bulb zone. In addition, an upper tabular element is provided which enhances the shake-down characteristics of the unit. An additional feature of the present invention is the provision of a sheath which interposes little, if any, distortion of the mercury column of the fever thermometer, thereby enabling the user to read the column height, and accordingly the temperature reached with minimal distortion.
In preparing the improved sheath for thermometer encapsulation, and pursuant to the present invention, an optically clear polyvinyl chloride plastisol is employed, with a heated mandrel being employed for immersion in the plastisol. The retained plastisol is cured in an oven while remaining on the mandrel, with the mandrel being inverted so as to provide a tapered wall thickness which increases from the bulb end to the free tip end. Thereafter, the sheath is removed from the mandrel under the influence of vacuum, with water being employed between the mandrel and the plastisol surface to assist in expediting removal.
Therefore, it is a primary object of the present invention to provide an improved sheath for thermometers wherein the sheath is optically clear to assist in visual clarity, and wherein the portion of the sheath encapsulating the bulb end is thin in cross-section in order to assist in providing minimal impedance to transfer of thermal energy through the sheath well.
It is a further object of the present invention to provide an improved protective sheath for fever thermometers, wherein the sheath is mechanically durable, opti-v cally clear, and thermally conductive.
It is yet-a further object of the present invention to provide an improved method and technique for the preparation of sheath enclosures for fever thermometers, and wherein the sheaths are formed from a moltened plastisol, and wherein the curing of the plastisol occurs in a manner permitting the plastisol to flow modestly so as to provide a tapered wall thickness which increases from the bulb end to the tip end.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims, and accompanying drawings. I
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of an encapsulated thermometer, with the view showing the fever thermometer in plan view, and with the sheath being shown in section;
FIG. 2 is a vertical sectional view taken along the line and in the direction of the arrows 2-2 of FIG. 1;
FIG. 3 is a top plan view of the structure illustrated in FIG. 1, with a portion of the protective sheath being shown broken away;
FIG. 4 is a perspective view of a partially completed sheath element prepared for use on a fever thermometer and pursuant to the various aspects of the present invention;
FIG. 5 is a schematic illustration of certain of the techniques employed in preparing a sheath component for encapsulation purposes; I
FIG. 6 is a schematic illustration similar to FIG. 5, and illustrating some additional apparatus employed in certain operations of sheath preparation pursuant to the present invention;
FIG. 7 is a schematic illustration of still a further operation utilized in connection with the sheath prepara tion; and
FIG. 8 is a schematic illustration showing the sheath in expanded form in a vacuum fixture and arranged to receive a fever thermometer therewithin.
DESCRIPTION OF THE PREFERRED EMBODIMENT Pursuant to the preferred embodiment of the present a tip end portion 14 separated by a cylindrical barrel, as indicated at 15. As is conventional, the fever thermometer contains indicia indicative of the temperature reached by the indicating column of mercury which is retained in the bulb portion 13, for direct transmission through the capillary zone 16 formed concentrically therewithin.
The fever thermometer 11 is normally cylindrical in configuration, however the term cylindrical is being utilized in a comprehensive sense since the crosssection of the structure is somewhat triangular in form, particularly as illustrated in FIG. 2. With further attention being directed to FIG. 2, it will be observed that the sheath 12 is in contact with the outer surface of the fever thermometer 11 at three equi-arcuately spaced points therearound, with the sheath being spaced outwardly from the thermometer surface at the intermit tent points. It has been found that this spacing assists in clarity of the reading characteristics of the device, and the possible mismatching of indices of refraction do not seriously affect the readability of the encapsulated device.
The synthetic resin sheath is preferably fabricated from polyvinyl chloride plastisol, these materials being, of course, commercially available. Polyvinyl chloride plastisols are heat curable and, as such, form a cohesive integral sleeve. The nature of polyvinyl chloride plastisols is such that it is normally desirable to cure the sleeve prior to its making contact with the surface of the thermometer in order to avoid any over-heating of the fever thermometer device. For example, fever thermometers should not be subjected to temperatures above approximately 1 15 F. for any significant period of time inasmuch as they may be adversely affected by such exposure. Temperatures in the working range of the fever thermometers are, of course, normally utilized, such as, for example, temperatures up to 106 F.
Turning now to some additional features of the structure, and with particular attention being directed to FIGS. 1 and 3 of the drawings, the upper tip end of the sheath, such as is illustrated at 18 is in the form of a generally rectangularly formed tab. This tab 18 is formed by virtue of heat-sealing the sheath for a length extending beyond the tip end 14 of the fever thermometer 11, this tab forming a desirable function for the structure. A user, by gripping the tab 18, may more easily and readily shake-down the thermometer so as to permit re-use.
Turning now to the technique for preparing the sheath, and with particular reference to FIGS. 5-8 of the drawings, it will be appreciated that the sheath device is initially prepared on a suitable mandrel structure, cured to completion, and thereafter the mandrel is removed and the sheath is prepared for reception of the thermometer. The details of the preparation operation will be described hereinafter.
As is indicated in FIG. 5, mandrels 20 and 21 are mounted on a rotatable retaining member 22 which is mounted for axial rotation on shaft 23. The operation further includes a synthetic resin retaining receptacle 25, along with a heating chamber 26 disposed at from the receptacle 25. A charge of a heat curable synthetic resin is received within receptacle 25, such as is indicated at 27. In this stage of the operation, the individual mandrels, such as mandrel 21, is immersed in the receptacle 25 so as to become coated with synthetic resin to a desired extent, such as, for example, up to a level indicated at 28. The mandrel is heated in order to promote adherence of the plastisol onto the mandrel surface when dipped therewithin. For most purposes, a mandrel temperature of about 400 F. is preferred for dipping, this temperature achieving a uniform controllable thickness of sheath in the plastisol mixture employed.
While various polyvinyl chloride plastisols may be utilized, one which has been found particularly useful in connection with the preparation of sheaths for use in the present invention is identified as Vinacron VP-892871 and available from Loes Enterprises of Minneapolis, Minn. It will be appreciated that other plastisol coatings may be employed as well, however that polyvinyl chloride plastisol identified hereinabove is useful for the purpose of the present invention.
Turning now to FIG. 6 of the drawings, an additional operational stage is illustrated. In this figure, the mandrels are coated with the cured plastisol, having been removed from reciprocably movable heating chamber 26, and arranged to be received within the vacuum removal fixture 30, as illustrated in the bottom portion of FIG. 6. It will be appreciated that the individual sheaths may be subjected to initial removal operations while the devicesare being prepared for further treatment and exposure to the vacuum chamber 30. FIG. 6 is,
therefore, an intermediate stage of operation between those operations illustrated in FIGS. 5 and 7.
Turning now to FIG. 7, the cured sheath is being prepared for introduction in the vacuum fixture 30, wherein the vacuum generated by evacuation line 31, which is coupled to a vacuum source, expands the sheath about the circumference of the base mandrel. In this operation, a receiving flange or ring is shown at 32 for providing the locking seal which enables a vacuum to be drawn within the chamber 33 of vacuum fixture 30. This exposure to vacuum both removes the sheath from the mandrel and prepares the sheath for reception of the thermometer. It has been further found that the removal operation may be expedited if water is interposed between the inner sheath surface and the outer mandrel surface. The availability of water at this stage of the operation has been found to achieve a greater rate of separation between the sheath surface and the mandrel surface.
With attention now being directed to FIG. 8, the
/ mandrel is removed from the expanded sheath, which is illustrated at 35 in FIG. 8, and thermometer 36 is placed therewithin. The tip sealing operation is performed in a conventional fashion, with the sheath being preferably rendered of uniform diameter prior to sealing. As is apparent, the open top of the sleeve element is sealed upon itself in order to both close the sleeve, and form an ear tab element adjacent the tip end of the encapsulated fever thermometer.
It will be appreciated, therefore, that the operations for preparing the sheath include an initial heating of a mandrel to a suitable temperature, such as a temperature of 400 F. prior to immersion in the plastisol. Following this immersion, the plastisol is cured in oven enclosure 26, with the bulb end of the sheath being disposed above the tip end while curing, in order to achieve the tapered wall thickness from bulb end to tip end. Upon completion of cure, and rendering the polyvinyl material optically clear, the sheath is placed in sealed relationship to vacuum chamber 33 of vacuum fixture 30, and when vacuum is applied to the device, the sheath expands so as to permit removal of the mandrel fingers and ultimate insertion of the thermometer therewithin.
The details of the sheath are illustrated in FIG. 4 of the drawings, with a portion being cut away so as to illustrate the details of the sheath. For example, the taper extends from the tip end to the bulb end with a wall thickness of about 5-8 mils being desired in the bulb end, and with a wall thickness of between about 12 and 15 mils being useful in the barrel portion of the structure. The bulb end of the sheath is also necked down in order to reduce the tendency to retain air and thus form bubbles between the bulb surface and the wall of the sheath 12. The presence of air spaces in this area will, of course, impede the transfer of thermal energy and thus retard the rate of response of the fever thermometer while in use.
Water has been found to be a desirable material for assisting removal of the sheath from the mandrel surface. Water may be evacuated from the sheath, prior to insertion of the thermometer, at temperatures ranging from between about 94 F. and 96 F. This out-gasing of water may be accomplished without adversely affecting the characteristics of the finished sheath.
The polyvinyl chloride plastisol employed is one which, in addition to being optically clear, provides a Shore hardness in the range of between 70 and 90 durometers. A preferred reading is 80. which provides the durability required for the finished product.
In order to verify a complete cure of the plastisol, it will be noted that the plastisol remains milky colored or opaque until cured, and then is rendered clear. If the cure is continued beyond completion, the hardened polyvinyl chloride may become amber, and thus less desirable from a durability standpoint.
As has been indicated in FIG. 2, the sheath walls are spaced from the shank of the barrel of fever thermometer 11, thus providing a gap area therealong. This gap, in addition to providing enhanced optical properties, aids in mechanical properties of the device in rendering the structure more shatterproof, by providing a certain degree of resiliency. This zone also assists in the shock absorbing features of the device should it be dropped upon a hard surface such as a floor or the like.
2. We claim:
1. Sheathed fever thermometer means comprising:
a. a fever thermometer comprising a glass barrel having a tip end and a bulb end;
b. a protective sheath means encapsulating said fever thermometer and comprising a generally tubular plastic sheath with an integral closed base covering said bulb end and an outwardly extending sealed tab ear tip end covering said tip end providing a thermometer shake down capability; and
c. said plastic sheath means having a tapered crosssectional wall thickness increasing from said bulb end to said tip end, said wall thickness of the bulb end ranging from 5 to 8 mils.
2. The sheathed fever thermometer means as defined in claim 1 being particularly characterized in that said sealed tab ear forms a gripping ear at the tip end of said sheathed fever thermometer means.
3. The sheathed fever thermometer means as defined in claim 1 being particularly characterized in that said sheath has a normal inner peripheral dimension which exceeds the outer peripheral dimension of said fever thermometer to form a gap therebetween, said sheath being heat sealed upon itself to form a closed envelope and with an outwardly extending tab disposed adjacent said tip end.
4. The sheathed fever thermometer means as defined in claim 3 being particularly characterized in that said sheath means is formed of curved polyvinyl chloride.
v UNITED STATES PATENT OFFICE,
CERTIFICATE OF CORRECTION Patent No. r r P. Dated October 1, 1974- Inventor (s) Robert A. Ersek and Donald E. Wall It is certified that error appears in the"above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:
Column 6-, line '7, "in" (First ocourrence) should read the Line 12, the numeral "2." should be deleted Line 40, "curved" should read cured Signed and sealed this 17th day of Deoember 1974.
(SEAL) Attest: v I McCOY M. GIBSON JR. v c. MARSHALLCDANYN Y Arresting Officer Comnissione'r'pf Patents- F oRM PO-105O (10-69) uscoMM-uc' scan-pea V 9 GOVERIIIINT PRINT'NG crFICE 2 I," 3-33