US1165958A - Heating system for constant-temperature baths. - Google Patents

Description

T. B. FREAS.

HEATING SYSTEM FOR CONSTANT TEMPERATURE BATH S.

APPLICATION FILED MAR. I7. 1913.

1,165,958. Patented Dec. 28, 1915.

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HEATING SYSTEM FOR CONSTANT TEMPERATURE BATHS. I

APPLICATLON FILED MAR. 11. 1913.

1,165,958. Patented Dec. 28, 1915.

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HEATING SYSTEM FOR consum TEMPERATUREBATHS.

APPLICATION FILED MAR. 71 1913. 1,165,958. Patented Dec. 28, 1915.

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T. B; FREAS.

HEATING SYSTEM FOR CONSTANT TEMPERATURE BATHS.

' APPLICATION FILED MAR. 11. 1913.

1,165,958; Patented Dec. 28, 1915.

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THOMAS B. FREAS, OF NEW YORK, N. Y., ASSIGNOR T0 V. WEBER & COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.-

HEATING- SYSTEM FOR CONSTANT-TEMPERATURE BATES.

Specification of Letters Patent.

Patented Dec. 28, 1915.

Application filed March 17, 1913. Serial No. 754,717.

To all 10710 222, it may concern Be it known that I, THOMAS B. FREAs, a citizen of the United States of America, and a resident of the borough of Manhattan, city, county, and State of New York, have invented certain new and useful Improve ments in Heating Systems for (onstant- Temperature Baths, of which the following isa specification.

This invention relates to heating systems for coiistant-temperature baths of the type designed for use as chemical laboratory ovens, bacteriological incubators andother similar or analogous apparatus where such device finds application and the object of the invention is to provide means for maintaining the temperature accurately at any desired degree of neat irrespective of the changes of room temperature.

This invention is furthermore designed as an improvement upon the type of apparatus heretofore patented by me in U. S. Letters Patent No. 1,024.565. dated April 30, 1912.

In the following-l have described, in connection with the accompanying drawings, a

structure illustrating the application of the principles of my invention, the features thereof'being more particularly pointed out hereinafter in the claims.

In the drawings Figure 1 is a front elevation of one form of constant-temperature bath illustrating the practice of the principles of my invention. Fig. 2 is a side elevation of the structure shown in Fig. 1, the

support being omitted. Fig. 3 is a central vertical sectional view of the same, certain parts being shown in elevation. Fig. 4 is a detail view of the lower part of the thermostatic control. Fig. 5 is an isometric perspective view, on a somewhat enlarged scale,

of the automatic switch mechanism and control devices in connection therewith and Fig. 6 is a diagrammatic view of the electrical connections and wiring system.

Similar numerals. of reference indicate similar parts throughout'the several views.

In the form selected to illustratethe invention, as shown in the drawings,- the casing comprises an outer box 10 and an inner box I 11, the latter forming a receiving chamber 12 wherein the objects to be acted upon are to be placed. Adjustable she1ves13, 13 are pro vided to divide the space in chamber 12 as desired. The material employed for the walls of the boxesshould preferably be of an after.

acid proof, fireproof and heat and electrically insulating character such as that which is known in the trade as asbestos wood or transite. The space between the walls of the boxes is preferably filled with a suitable heat insulating material 14, such as cellular asbestos. The walls of the outer box are shown as extended upwardly to form, in connection with the top 10 and the floor 16, a chamber 15 for the reception of the automatic switch mechanism and associated parts hereinafter described. The top 10 and floor 16 are preferably of the same material as the walls.

17 is a door in the front of the casing, preferably having inwardly tapered edges adapted to form a tight joint with correspondingly tapered edges in the door frame.

' The edges of the door 17 and the door frame are each preferably made of metal cast in integral pieces respectively, each thus formthe side walls of the casing, closed by spring plugs 19", 19".

The front and rear walls of the door are preferably of nonheat conducting material,

' ing a unitary structure. The outer edges of of the observation openings 19, so that the door presents no heat conducting surface adjacent the chamber 12 and the metal parts of the door and door frame are substantially insulated from said chamber 12. It will be observed that the inner box 11 is provided with flanges 11 which abut the inner metallic edges of the door and door frame and cit-1;- tend some distance beyond said edges permitting no metal heat conducting part to come into proximity to the chamber The space between the front and rear walls of the door is preferably filled'with a nonheat conducting material such as cellular asbestos. I

22 is a shelf of insulating material. the function of which will-be explained herein- 23 is a. motor ear outer wall of the casing, lts armature suitably supported on the shaft 24 extending inwardly to the inside of the casing through a protecting sleeve 25. A centrifugal blower 26 is secured to the inner end of armature 24, and is adapted to draw the air at the top of chamber 12 through the opening 27 of the blower housing 27 and to force it through a downward extension 28 of the blower housing and out at 29 into the lower part of the chamber 12 below the shelf 22 and through and over the heating elements 32 and 33, which latter may be of any suitable form; as shown, 32 is the primary heating element and 33 is the secondary heating element, each comprising a coil of wire of suitable resistance supported on a frame 34, preferably of asbestos wood, in such manner as to permit free circulation of air around the same. At the outer end of sleeve 25 there is a disk provided with apertures 30 which may be opened or closed by turning a similarly apertured disk or cover 31 so as to establish communication between the outer air and the chamber 12 at the will of the operator in order that he may draw, by means of the blower 26, any desired quantity of fresh air into said chamber.

In the absence of the forced circulation of air the upper part of chamber 12- tends, through convection air currents, to become overheated and in the absence of insulating shelf 22, the lower part of chamber 12 tends, through the radiation of heat from the heating elements, to become overheated. The purpose of this forced circulation of air therefore within the chamber, is to provide a uniform distribution of the heated air within said chamber. The function of insulating shelf 22 is to prevent the heat radiating from the elements 32 and 33 from disturbing this uniformity of heat produced by the forced circulation. v

35 is a lamp supported within chamber 12.

36 is an attachment cap for connecting the electric mains.

37 is an opening through cover 10 for the purpose hereinafter described.

38, 38 are ventilating tubes leading from a the chamber 12 through cover 10 to the eX- terior and throughwhich thermometers may be suspended.

Referring now to Figs. 3 and 5, reference numeral 39 indicates a bed plate secured to floor 16 and carrying lugs 40, 40, bearings 40, 40 and standards 41, 41 and 42, 42

preferably cast therewith. Standards 42, 42 are provided with ways 43 for guiding the vertically adjustable scale face 44. Scale face 44 carries an interiorly screw threaded lug or block 45, through which passes a threaded rod 46 rotatably mounted against vertical movement in standard 42.

The top of rod 46 is provided with a slot so that, by means of a screw driver inserted through opening 37 the rod may be rotated the bed plate.

to cause lug or block 45 and its attached scale face 44, to travel vertically. 43 is tactor point 51 and a pointer 52 adapted to indicate on the temperature scale 53 on scale face44. (See Fig. 1). The divisions of scale 53 may represent an arbitrary calibration or may represent a standard calibration in degrees of temperature. 55 is a flexible conductor mounted on lever 47 and provided with a contactor 56 adapted to contact with an adjustable contactor 57 on conducting standard 58, suitable electrical insulation 59 being interposed between conductor 55 and lever 47. Lever 47 rests upon a-lifting arm 60 and is kept down taut on said arm by spring 61. .Lifting arm 60 is pivoted on rod 62 supported in lugs 40 on 63 is a female threaded block engaging male threaded rod 64 mounted to rotate in bearings 40 and 40 on bed plate and secured against longitudinal movenient by means of a collar 65. Block 63 carries a depending finger 66 which travels in a slot 67 in the bed plate 39 to prevent the block 63 from turning. A link 68 connects the block 63 and the lifting arm 60 as shown. The free end of the rod 64 projects through the front wall of the casing and through the scale face 44 as shown and is provided with an operating knob 69 so that the rod 64 may be rotated from without by the operator. Lever 48 is secured at one end to anarm 7O on a rocker plate 70 but is insulated therefrom by means of suitable insulation 71. Rocker arm 70 is pivoted at 50, 50 to standards 41, 41. At 72 lever 48 is ofiset so that the free end of the lever may extend through slot 54 in scale face 44 above the free end of lever 47. Lever 48 carries a contactor 73 adapted to contact with contactor 51 on lever 47 Rocker plate 70: is provided with an oflset lug 7O having a concave shaped bearing (not shown) on its under side adapted to engage the upper end of a pin 74 rigidlycarried by plate or bar 75. The lug 7 0 is offset with relation to the center of rotation of lever 48 about pivots 50, so that any vertical movement of pin 74 will cause lever 48 to rock and cause contactor 73 to move vertically a distance, which distance compared with the vertical movement of pin 74, is according to the ratio of the distances of contactor 73 and pin 74 from the center of rotation 50. The plate or bar 75 is so adjusted, by the means hereinafter described, that pin 74 will engage the concave shaped bearing in lug 7 0 when the temperature of thermostatic tubes 76 cor.- responds to the temperature at which the device has been set as indicated by the pointers 52 on scale 53. The thermostatic device comprises in part the thermostatic tubes 76,

, 76, made of a materialadapted to expand and contract in response to variations in temperature, preferably of thin brass and perforated. The tubes 76 are preferably perforated to provide for a freer circulation of air in order to cause a quicker response to changes in temperature. The material of which tubes 76 are made is such that the highest coefficient of expansion may be obtained consistent with strength and permanency of form under varying conditions of temperature. Brass has been found to give good results. The upper ends of tubes 76 are rigidly fastened to bar 75 and the lower ends of tubes 7 6 are connected with bar 77 by means of adjusting screws 78, 78. By means of these adjusting screws 78, 78, bar 75 carried by tubes 7 6, 76 may be vertically adjusted and thereby through pin 74, lug and lever arm 48, adjust contactor 73 so that it may come within range of scale 53, the finer adjustment being made by the vertical movement of the scale face 44 as hereinbefore described. 79 indicates a rod made of material whose coeliicient of expansion is practically nil. I have found invar (an alloy of 36% nickel, 74% steel) to be a satisfactory material for the purpose. Rod 79 at its lower end is attached to bar. 77 and at its upper end is rigidly attached to the bed plate 39 at 80. As shown the connection of rod 79 to bar 77 is adjustable for the same reason heretofore given in connection with adjustable screws 78, 78.

' The electrical connections are shown diagrammatically in Fig. 6. 85 and 86'indicate the mains, preferably provided with fuses 87 87. Motor 23 is connected across the mains and controlled by a switch 88. Lamp 35 is connected across the mains and controlled by a two-way switch 89 so that the lamp 35 maybe connected on the one hand, through contacts 82 and 83, directly across the mains or, on the other hand, may be connected across the mains through contacts 82 and 84, wire 94, conductor 91, contactors 51 and7 3, lever 48 and conductor 93. WVire 86 is connected to heating elements 32 and 33 through switch 90. Primary heating element 32 is connected by means of conductor 91 to lever arm 47 which latter is divided electrically into two parts by insulator 81. From lever arm 47 the path of the current is through contactors 51 and 73, lever arm 48 and conductor 93 to main '85. Secondary heating element 33 is connected by means of conductor 92, conducting standard 58, contactors 57 and 56 and wire 97 to conductor 91 and thence by the path hereinbefore described in connection with primary heating element (lontactors 51 and 73 are protected, on breaking the circuit, by condenser 95 and contactors 56 and 57 are are similarly protected by condenser 96. \Vhen contactors 56 and 57 are closed, and the additional load of heating element is on contactors 51 and 73, these latter con- .tactors, on the breaking of the circuit, are

protected by condenser 96 in addition to condenser 95.

In the operation of the apparatus described, the operator after closing switch 90, by means of operating knob 69 sets the pointers at the desired temperature as indicated on the scale 53. Assuming that all parts are properly adjusted, if the temperature in the receiving chamber 12, and thus the temperature of the thermostatic tubes 76, 76, is below that of the indicated setting, contactor 73 will rest on contactor 51, thereby completing the electrical connection through primary heating element 32. The heat given off from element 32 circulating through chamber 12, freely by convection currents or forcibly by the forced draft of the blower 26, will raise the temperature of the thermostatic tubes 76, 76, which tubes will expand and, because of the non-expansion of rod 79, will cause bar to rise and hence raise lever arm 48 and, on sufficient expansion of thermostatic tubes 76, 76, will break the current through contactors 73 and 51 and thus cut out heating element 32. Then, on the loss of a small quantity of the heat in chamber 12, the temperature of the thermostatic tubes 76, 76, will be lowered and a movement of a lever 48 opposite to that last described above will occur and the contactor 73 will again rest on contactor 51, thus throwing heating element 32 in again. Thus it will be seen that the heat of the chamber12, which is continuously being lost by conduction through the walls, even though these latter be of the best possible insulation, will be intermittently replaced by means of heating elements 32 operating as hereinbefore described. The capacity of heating element 32, for the more or less low temperatures, should be as low as possible consistent with the amount 'of heat required, because, for accurate regulation, the quantity of heat thrown in intermittently should have a low ratio to the quantity of heat lost continuously through the walls, otherwise a comparatively large quantity of intermittent heat thrown in would cause a comparatively large fluctuation of the temperature of chamber 12. Now when it is desired to operate at higher temperatures, additional heat direct connection with conductor 91 and thus parallel with heating element 32. This heating element 33 is thereafter controlled in a manner similar to that described in connection with heating element 32.

Lamp 35 may be connected directly across the mains as described, whenever it'is desired to obtain illumination in chamber 12 continuously, the operator of course not per mitting the heat furnished by the lamp to overheat the chamber as might occur with use at low'temperatures. In order to use the lamp for observation where there is danger of its heat overheating the chamber, it is connected across the mains by means of wire 94 as described and thus the thermostatic control will not permit overheating in the chamber. In addition, the lamp connected in this latter manner, furnishes the the operator to set the temperature of the chamber 12 at any desired predetermined point as indicated to him by pointers 52 on scale 53, is a very important point in thermostatic construction.

It is obvious. that additional heating elements similar to element 33 may be provided withoutdeparting from the spirit of the invention, it being understood that the contactors 56 and 57 may be adjusted to suit any required inflow of heat to assist the primary heating element.

It should be further observed that the motor 23 and its attached blower 26 are to be operated only at those times when the operator desires the greatest uniformity of temperature in chamber 12 which it is possible to obtain. When less uniformity of temperature is desired the motor may remain idle and the insulating plate 22 may be removed, thus permitting the convection currents of air and the radiated heat from the heating elements to create whatever uniformity of temperature it may.

Insulating plate 22 should fit tightly against the rear and side walls of receiving chamber 12, a space being left between the front edge of plate 22 and the door 17 to provide an exit for the air which has been blown into the space beneath plate 22 by blower 26. By this means the air in the 'receiving chamber is kept in constant circulation adjacent the walls of the chamber, the

air being drawn in by blower 26 from the top of the chamber, passed down along the rear wall, over the heating elements and up in a forced draft adjacent the door and thence to the top of'the chamber and again around through the blower as described.

Inasmuch as the door is the part of the apparatus which suffers the greatest loss of heat, it is a very desirable feature to cause the air which has just been passed over the heating elements to be brought immediately to the coolest portion of the bath to'counteract in some degree this unavoidable nonuniformity.

I do not restrict myself to any of thedetails of construction, arrangement of parts or composition of material as shown or described further than the scope of the appended claims demands.

What I claim and desire to secure by Letters Patent is:

1. In apparatus of the class described, a receiving chamber, a thermostat controlled by the temperature of said chamber, a support, a lever arm having one end pivoted to said support, means for actuating said lever arm controlled by said thermostat, a contactor on the other end of said lever arm from said pivotal point and distant from said thermostat, a second lever arm having one end pivoted to said support concentrically with the pivoted end of said first mentioned lever arm, a contactor on said second lever arm in the path of the contactor on the first mentioned lever arm and an electric heating element in circuit with said contactors.

2. In apparatus of the class described, a receiving chamber, a thermostat controlled by the temperature of said chamber, apin adapted to be moved by said thermostat, a

rocker plate in the path of movement of said pin, a lever arm carried by said rocker plate, a contactor on said lever arm at a point distant from said pin, a second contactor in the path of said first named contactor and an electric heating element in circuit with said contactors.

3. In apparatus of the class described, a receiving chamber, a pair of leverv arms, means controlled by the temperature of said receiving chamber for automatically controlling the movement of one of said lever arms, a support to which each of said lever arms is concentrically pivoted with reference to the other, a contactor carried by each of'said lever arms adapted to make contact with each other and a heating element in direct circuit with said contactors.

4:. In apparatus of the class described, a

pair of vertically movable contactors, a primary heating element in circuit with said tactors but controlled by the movement of one of said pair of contactors, a connection from said insulated contactor to that one of the pair of contactors controlling its movement, a contactor in the path of movement of said insulated contactor and a connection from said secondary heating element to said last named contactor.

5. In apparatus of the class described, a pair of vertically movable contactors adjacent each other, the movement of one of said contactors being automatically controlled and the movement of the other positively controlled, a secondary contactor electrically 15 adjacent said positively controlled conta'ctor and moving therewith, a contactor in the path of said secondary contactor, a primary heating element in circuit with said pair of contactors and a secondary heating element adapted to be brought into parallel with said primary heating element when said secondary contactors are in contact.

6. In apparatus of the class described, an air circulation system comprising a main chamber, a blower near the top of said chamber an air passage from said blower to the bottom of said chamber, a secondary air chamber at the bottom of said main chamber into which said air passage from the blower discharges, heat insulating means between said secondary chamber and main chamber, a discharge opening from said secondary chamber into said main chamber at a point opposite the exit from the air passage from the blower and a heating element in said secondary chamber.

In testimony whereof I have signed this specification in the presence of two subscribing witnesses.

THOMAS B. FREAS.

Witnesses:

SEABU'RY C. MASTICK, H. G. LEABD.

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