US2114396A - Heating pad - Google Patents

Description

L R A F c M L R D A P G N I T A E H Filed Dec. 18, 1956 FIG. I.

i Patented Apr. 19;

UNITED STATES PATENr oi-"Flea Ronald Lyman McFarlan, Marblehead Neck, and

v John A. C. Bowleo, Boston, Mass.

Application December 18, 1938, Serial No. 116,514

11 Claims.

hospitals.

Among the several objects of the invention may be noted the provision of a heating pad of the class described which includes an electric or other heating element for supplying heat pad, and a heat storing or thermophoric compoenergy to the sition for delivering up said heat energy as supplied to the pad, over a protracted period of time;

the provision of a heating pad of the class described which is provided with means automatically regulating the temperature to be achieved by the pad; the provision of a heating pad of the class described which is substantially hermeticah 1y sealed, and which is capable of extended use and re-use over long periods of time without a y substantial deterioration; the provision, in a heating pad of the ciass described, of a new ther mophoric composition of matter, which is adapted to deliver up heat stored therein (such as latent heat of fusion) over a greatly protracted period of time, which composition of matter undergoes a reversible reaction on the introduction and withdrawal of heat thereto and therefrom,

without substantially changing any compositional characteristics over repeated reversals; and the provision of a heating pad, and a thermophorlc composition ofmatter for use therein, which are economical in construction and operation.

Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the el'emerits and combinations of elements, features of construction and composition, and arrangements of parts, which will be exemplified in the structures and products hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing; in which is illustrated one of various possible embodiments of the invention, n

Fig. 1 is a plan view of a heating 'ing the present invention;

pad embodysubstantially substantially Fig. 4 is an enlarged cross section taken substantially along line 4-4 of Fig. 1; Fig. 5 is a cross section taken along line 5-5 of Fig. 4.

Similar reference characters in and, substantially dicate correspending parts throughout the several views of the drawing.

Referring now more particularly to Fig. l, numeral 8 indicates a rubber or like flexible, plastic materiai bag or sack, which is shown as of gerrerally rectangular shape. The'shape of the tag i. is of no importance, however. At one end thereof, the bag 9 is formed as a neck or cyiindrical outlet portion t. In the finished pad, the preferred form of the outiet 3 is a solid cylindrical member which embeds a pair of electrical com nesting prongs 5 which are adapted to be inserted into the customary form of electric outlet. However, it is contemplated that the prongs 5 may be replaced by other connecting means, such as suitable socket elements, so that electrical connections may be made to the pad by fitting in a plug rather than by plugging the device itself into a socket.

inside the bag i there is provided an electrical heating device indicated generally by numeral 1. In the preferred embodiment of the invention, the device I comprises an electrical resistance heating coil 9 embedded in a flexible rubberor like matrix H. The constructionof this device 'I may well be of the type shown in DeLaney et al. Patent 2,018,512, dated October 22, 1935. Included in the device i is a thermostat I3, likewise embedded in the matrix II. The construction of the thermostat 53, which is likewise shown in the aforementioned DeLaney et al. patent, is indicated for convenience in Figures 4 and 5. It comprises a box I! having a cover i1, Mounted in one end of the box IS in such manner as to project into the central hollow portion of the box l5'i's a bimetallic blade IS. The resistance heating coil 9 is connected to one end of the blade I! by a connection indicated by numeral 2|. The other end of the blade I! carries a mov able contact 23, which cooperates with a fixed contact 25 mounted in the box II, which is in turn connected, exteriorlycf the box 15, with another portion of the resistance heating coil 8.

. The resistance heating coil 9 has .its opposite ends connected to the two prongs 5, with the thermostat I; in series therewith. The leads of the resistance heating coil 8, indicated by numeral 28 in Fig. 1, are embedded in a neck 21 of rubber or like material which serves structurally to interconnect the device! and the plug portion 3 of the outer bag i. In the preferred embodiment of the invention, the neck 21 connects to the solid portion oi the plug 3 in such manner as to leave an annular trough or or fused together in such manner as to form a homogeneous, hermetically sealed unit. The final sealing is not ordinarily done, however, until after a certain thermophoric composition to be described, has been placed in the bag.

From Figures 1 and 2, it will be noted that the heating device I hangs rather loosely in the bag I, by means of the neck 21, in such manner as to provide a relatively large free space 3| therein. The free space 3| is filled, in the finished article, with a thermophoric composition. A preferred thermophoric composition is as follows:

Percent by weight Manganous chloride tetrahydrate (MnClz.4HzO) 3.45 Sodium acetate trihydrate (NaC2H3Oz.3I-I2O) 96.55

An alternative thermophoric composition, likewise found to be satisfactory, is as follows:

Percent Manganous chloride tetrahydrate (MnChAHzO) 3.3 Sodium acetate trihydrate (NaC2H3Oa3I-InO) 9 Glycerine 3.0

Still another satisfactory thermophoric composition is as follows:

1 Percent Manganous chloride tetrahydrate (MnClzAHzO) 3.3 Sodium acetate trihydrate (NaCzH30z.3HzO) 94.0 Ethylene glycol (CI-IzOHEHzOH) 2.7

If difierent temperatures of operation are desired, the proportions in the above compositions may be varied without disturbing the desired action of the compositions.

In general, the space 3| isbompletely filled with one of the thermophoric compositions above described, or any other suitable thermophoric composition, and the bag then finally hermetically sealed.

The operation of the heating pad as thus described is as follows:

The pad is connected by the prongs 5 to a source of electric current, whereupon the heating device 1 commences to deliver heat, and the electrically generated heat is stored by the conversion of the sodium acetate in the thermophoric composition from its crystalline form to its liquid form. The thermostat l3 shuts ofl the electric current after the crystalline mixture has been substantially converted into liquid form. Normally, the thermostat II should be set to open the circuit upon the attainment of a temperature not greatly in excess of 75 C. in the pad, because temperatures in excess of this value are sometimes destructive to the thermophoric compositions above specified.

of changing from the tetrahydrate to the dihydrate form at a temperature of the order of 58 C., which is approximately the same temperature at which sodium acetate loses its water of crystallization. When the melted mixture is cooling, and giving off heat, the change from manganous chloride dihydrate to manganous chloride tetrahydrate removes water from the melt, thus tending to prevent supersaturation of the melt and consequent failure of the sodium acetate to recrystallize.

The annular trough 29 hereinbefore mentioned likewise aids inpreventing supersaturation and failure of recrystallization, because it is so formed as to contain a certain amount of the thermophoric composition which, through being removed a greater distance from the heating unit I, usually does not melt during the controlled time interval for the melting of the rest of the thermophoric composition. When cooling commences, the presence of a small amount of solid thermophoric composition in the annular trough 29 serves to seed the crystallization of the liquid portion of the thermophoric composition, and thus tends to inhibit the formation of supersaturated solutions. Obviously, for this purpose, the trough 29 may be replaced by any other suitable recess, within the scope of the invention.

In preparing the thermophoric composition, care should be exercised not to expose it to the air for too long a time, such as more than six hours, because there is a tendency for the man- "ganous chloride to form manganese hydroxide upon extended exposure to the air.

In operation, the pad should be allowed to come to room temperature before reheating.

Depending upon the size of the pad,.the time required for heating it is from the order of ten to the order of fifteen minutes, and the time during which the pad will stay hot will vary from the order of ten to the order of twenty hours. The pad automatically maintains a temperature in the region of 58 C. for the thermophoric mixtures above given. This temperature can be varied somewhat by varying the proportions of the constituents in the thermophoric composition. The figure of ten to twenty hours (during which the pad will stay hot) has been experimentally ascertained and found to hold true for an eight hundred gram quantity of the thermophoric composition.

While in the foregoingdescription details have been given for the mechanical structure of a preferred embodiment of the invention, it will readily be seen that the mechanical form of the invention may be widely varied without departing from the spirit of the invention.

Nor is the above description to be considered as limiting the invention to the particular thermophoric composition described, as manyother suitable compositions may be satisfactorily used in the general combination, either to achieve different temperatures, during the prolonged cooling period, or for other reasons. However, it is to be noted that the thermophoric compositions herein described, which are believed to be novel with the present invention, are particularly advantageous for use in connection with the heating pad of the present invention/because of their characteristics hereinbefore given, and because they are capable of sustaining a temperature that so nearly approximates the desired temperature for a heating pad of the general character here concerned.

An incidental advantage of the heating shown in the present invention is that it can be heated by means other than the electric current. For example, the pad shown in Fig. 1, in the event of non-availability of electric current, may be heated simply by dropping'it into a pan of boiling water for a suflicient length of time to bring substantially all of the thermophoric mixture to a liquid condition (this can readily be ascertained by feeling the bag and noting its relative rigidity as the heating progresses). Thereafter, the bag can be removed from the hot water and it will 'give off heat over a protracted period of time in much the same manner as if it had been heated electrically,

By making pads of associated elements of rubber, a flexibility is provided which is distinctly advantageous in pads of this type, since it permits the pad to conform to the part of the body with which it is placed in contact. However, such flexibility is sometimes not necessary, and in that event, it is within the scope of the present invention to make the pad out of metal, fiber, or any other suitable container material.

The thermophoric compositions herein set forth are separately claimed in our copending application Serial No. 173,220, filed November 6, 1937.

In view of the above, it will be seen that the I several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above constructions and compositions without departing from the scope of the inven tion, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim: 1. In a heating pad, 9. container, a thermophoric composition within said container, and electrical resistance means within the container for supplying heat to said thermophoric composition, said container comprising a bag made of a flexible material.

2. In a heating pad, a container, a thermophoric composition within said container, and means within the container for supplying heat to said thermophoric composition, said container comprising a bag made of a flexible material, said heating means comprising an electrical resistance heating unit embedded in a flexible a thermostat in the container in series with said electrical resistance heating element, said thermostat being adapted to disconnect the element from a source of electricity when the temperature of the pad reaches a predetermined value.

5. In a heating pad, a container, a thermophoric composition within said container, and means within the container for supplying heat to said thermophoric composition, said container having an interior recess at a point relatively remote from the heating means, the said recess being adapted to contain a portion of said thermophoric composition and substantially maintain it against melting while the remainder of the thermophoric composition is melting under the heating influence of said heating means.

6. In a heating pad, a container, a thermophoric composition within said container, means within the container for supplying heat to said thermophoric composition, said means comprising an electrical resistance heating element, and a thermostat in the container in series with said electrical resistance heating element, said thermostat being adapted to disconnect the element from a source of electricity when the temperature of the pad reaches a predetermined value, said container having an interior recess at a point relatively remote from the heating means, the said recess being adapted to contain a portion of said thermophoric composition and substantially maintain it against melting while the remainder of the thermophoric composition is melting under the heating influence of said heating means.

7. A heating pad as set forth in claim 5, in which the container comprises a rubber sack.

8. A heating pad as set forth in claim 6, in which the container comprises a rubber sack.

9. In a heating pad, a container, a thermophoric composition within said container, and means within the container for supplying heat to said thermophoric composition, said thermophoric composition comprising a mixture of sodium acetate trihydrate and manganous chloride tetrahydrate.

10. In a heating pad, a container, a thermophoric composition within said container, and means within the container for supplying heat to said thermophoric composition, said thermophoric composition comprising a mixture of sodium acetate trihydrate and manganous chloride tetrahydrate, the sodium acetate trihydrate constituting more than the order of 90% of the mixture.

11. In a heating pad, a container, 2, thermophoric composition within said container, and means within the container for supplying heat to said thermophoric composition, said thermophoric composition comprising a mixture of sodium acetate trihydrate and manganous chlo-- ride tetrahydrate, together with a small proportion of a liquid selected from the class composed of glycerine and ethylene glycol.

RONALD LYMAN MCFARLAN. JOHN A. C. BOWLES.

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