US2785269A

US2785269A - Steam superheating apparatus

Info

Publication number: US2785269A
Application number: US533061A
Authority: US
Inventors: Don S Strader
Original assignee: PANTEX Manufacturing CORP
Current assignee: PANTEX Manufacturing CORP
Priority date: 1955-09-08
Filing date: 1955-09-08
Publication date: 1957-03-12
Anticipated expiration: 1974-03-12

Description

March 12, 1957 D. s. STRADER 2,735,269

STEAM SUPERHEJATING APPARATUS Filed Sept. 8, 1955 2 Shets-Sheet 1 zyfi/zzar J70 (1 4 25 644567 3 MM MM;

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March 12, 1957 D. s. STRADER 2,785,269

STEAM SUPERHEATING APPARATUS Filed Sept. 8, 1955 2 Sheets-Sheet 2 IWW J7 J7 Wade) United States Patent STEAM SUPERHEATIN G APPARATUS Don S. Strader, East Greenwich, R. I., assignor to Pantex Manufacturing Corporation, Central Falls, R. L, a corporation of Delaware Application September 8, 1955, Serial No. 533,061

6 Claims. (Cl. 21938) This invention relates to steam superheating apparatus and more particularly it relates to a superheater which may be portable and is specifically adapted for spray painting.

In the art of spray painting, it is known that certain advantages are to be had if superheated steam rather than compressed air is used to atomize the paint. Not the least of these advantages is a substantial saving in paint. The present invention is concerned with apparatus to superheat steam for this type of operation. It should be understood, however, that the apparatus according to the present invention is also suitable for various other applications, and indeed, many such applications will no doubt occur to those skilled in the art.

In designing apparatus of the above-mentioned character, various problems are encountered which are peculiar to the environmental conditions associated with spray painting. More specifically, since the apparatus will presumably be located in a paint atmosphere, it is essential that it be made explosion proof, and that the temperature of its various exposed surfaces not be permitted to exceed a predetermined limit based on the combustibility of this type of atmosphere.

It is an object of the present invention, therefore, to provide an efficient steam superheating apparatus of explosion proof construction.

It is another object of the present invention to provide steam superheating apparatus of relatively simple design and which is therefore economical to manufacture.

,It is a further object of the present invention to provide portable steam superheating apparatus which meets the requirements generally associated with a conbustible atmosphere environment.

It is a still further object of the present invention to provide a thermal over limit switch of novel construction for use with apparatus of the above-mentioned character.

In brief, the apparatus of the present invention comprises a housing having an inlet to admit steam to the interior of the housing and an outlet to supply superheated steam to a utilization device, such as a paint spray gun. Disposed within the housing are electrical heating elements whose energization is controlled by a thermostatic control unit responsive to the temperature of the superheated steam at the steam outlet. By means of this control unit, under normal operating conditions, the temperature of the superheated steam is maintained very nearly at a predetermined value as is required for optimum results with the spray gun. In addition to the control of the energization by the heating elements afforded by the thermostatic control unit aforementioned,

there is also provided an over limit switch promptly to deenergize the heating elements in the event that the temperature of the housing approaches a predetermined critical value as prescribed by the combustible character of the atmosphere wherein the apparatus is to be employed. As will be explained in more detail subsequently hereto, this latter switch prevents an unsafe condition "ice from arising in the event that the thermostatic control unit is unable to function normally due to a lack of steam in the apparatus as, for example, when the steam supply is temporarily cut off. The novel limit switch itself is comprised of a pair of stationary contact elements and a pair of interconnected movable contact elements arranged to bridge the gap between the stationary elements thereby completing an electrical circuit. The stationary elements are carried by a mounting block of insulating material which in turn is fastened to the outer wall of the superheater housing substantially intermediate its ends, and the movable elements are held in a position of surface-to-surface engagement with the fixed elements by the combination of a spring, a fusible element electrically insulated therefrom, and a heat transfer strip projecting from the housing and having a flange portion which bears against one end of the fusible element. Should the temperature of the housing exceed a predetermined value, the fusible element is arranged to melt from the heat of the housing conducted through the transfer strip so that no longer is there present a force acting to compress the spring and thereby maintain the movable contact elements in engagement with the stationary elements. As a result, the movable elements fall by gravity out of engagement with the stationary contact elements, and the energizing circuit for the heating elements is broken to prevent a hazardous condition from arising.

To further limit the temperature of the housing in the event that the over limit switch is actuated, there is provided a coil of tubing around the housing through which the supply steam is passed in a counterflow manner before it enters the housing. While preheating the steam, this tubing serves not only to maintain a lower operating temperature during normal operation but also to dissipate heat from the housing sufficiently rapidly to prevent its being overheated by latent heat from the heating elements once they have been deenergized by the over limit switch.

The novel features of this invention, together with further objects and advantages thereof, will become more readily apparent when considered in connection with the accompanying drawings in which:

Fig. l is a front elevation with portions cut away of the steam superheater apparatus according to the present invention;

Fig. 2 is a sectional view on a greatly enlarged scale taken on line 22 of Fig. 1;

Fig. 3 is a similarly enlarged sectional view taken on line 33 of Fig. 1;

Fig. 4 is a sectional view similar to that of Fig. 3 except that the over limit switch is shown in an actuated condition; and

Fig. 5 is a wiring diagram for the apparatus according to the present invention.

Referring now to the drawings and more particularly to Fig. 1, it will be observed that the steam superheating apparatus of the present invention comprises in essence a cylindrical housing or tube 12 providing an internal heating chamber having an inlet 14 to admit steam to the chamber and an outlet 16 for the superheated steam. As shown, the housing is preferably formed of a length of steel pipe with a reducer 18 at its outlet end and a coupling 20 at its other end wherein an outlet 22 is provided to drain oft" condensate through a trap 23. Surrounding the housing for the greater part of its length is a coil of tubing 24, preferably of highly heat conductive material, such as copper, having one if its ends connected to inlet 14 and other of its ends provided with a fitting 26 for connection with a length of pipe 23 through which wet steam, from a suitable supply (not shown), at any desired temperature is supplied to the apparatus.

For paint spraying this temperature is in the neighborhood of 270 to 300 F. A pair of heating elements 30, such as Calrods, are disposed within the housing, and as shown, these heating elements extend for substantially its full length. An electrical connection to the heating elements is made at the base end of the housing through a suitable pressure tight connector 32 of-explosion proof construction and a length of conduit 34 connected thereto.

Connected to the opposite end of the housing, or more specifically to the outlet in of the reducer i8, is a T fitting 36 through which the superheated steam is discharged and which also serves to connect outlet 16 to a pressure gauge 33 through a length of tubing 40. Another T 42 is connected to the discharge end of T 36 to provide a mounting for and connection to a thermostatic control unit 4-4, whose sensing element 44 extends into the aligned regions of both Ts, as shown in dotted outline. Control unit 44 in turn includes an electrical switch to control the energization of the heating elements and for like purpose, there is provided in the energization circuit of the heating elements, a manually operable main switch 46 enclosed by a suitable explosion proof junction box 46' which is attached to the casing 48 enclosing the assembly including the housing 12, the coil of tubing 24 therearound, and the high limit switch 50 about to be described.

With reference more particularly to Figs. 2, 3 and 4, as well as Fig. 1, it will be observed that there is attached to the housing 12, between'two adjacent coils of the tubing 24 which are spaced for the purpose, an over limit switch indicated generally by the numeral 50. The switch includes a ceramic mounting block 52 for a pair of stationary contact elements 54. Mounting block 52 is attached to the cylindrical housing 12 by means of a pair of machine bolts 56 whose heads are welded directly to the outer surface of the housing, and as shown, the portion of mounting block 52 adjacent the housing is concave so that its fits snugly against the same where it is held by nuts 53 threaded onto bolts 56. Contact elements 54- are welded individually to base arms 66 which are attached to portions of the mounting block 52 by means of machine screws 62. The latter are threaded into the base arms and also serve as electrical terminals.

To bridge the gap, in effect, between contact elements 54, and thereby close the switch S9, there are provided a pair of movable contact elements 64 for surface-tosurface engagement with elements 54 carried by a single support or base arm 66 extending between the elements r ed as shown. Base arm 66 is adapted for movement toward and away from stationary contacts 54, and for this purpose 'it is provided with a pair of slot shaped recesses- 67 in its upper and lower edges substantially intermediate its ends. Cooperating with the portions of the arm 66 defining these slots is a guide member 68 of substantially U-shaped configuration whose individual legs fit in the slots and thereby constrain arm 66 to move linearly. The forward travel of arm 66 in the direction of contact elements 54 is limited by a pair of tabs 70 formed at the ends of the legs of guide member 63; and the rearward travel away from elements 54 is limited by a compression spring 72 which is laterally fixed between arm 66 and the web portion of guide member 68 by cylindrical projections or nubs on both the arm 66 and on an insulating washer '74. Washer 74 is maintained adjacent the outer surface of the web portion of member 63 by means of the nub 75 thereon which projects through the member 68, a hole therein being provided for this purpose.

Completing the over limit switch is a fusible element '76 formed as a washer of slightly larger diameter than washer 74 and having a centrally located cylindrical projection or nub '76 adapted to fit in a hole 73 formed in a heat transfer strip 78.

temperature in a combustible atmosphere.

Heat transfer strip 73 is preferably formed of copper or some other good conductor of heat and is welded to the outside of the housing so that its temperature will accurately reflect the housing temperature. As shown, a depending flange portion 78" of strip 73 wherein hole '78 is located bears against fusible element 76 which in turn bears against washer 74 thereby to fix one end of spring 72 axially. By means of the spring, arm 66 is urged towards contact elements 54 holding elements 64 in engagement therewith.

It should be apparent, at this point, that

elements

54 and 64 form in effect a single-pole single-throw switch which is normally held closed by the fusible plug and which upon being actuated by fusing of the plug as a result of the housing reaching an excessive temperature serves to deenergize the heating elements. Fig. 5 illustrates in more detail the electrical system adapted to accomplish this result. With reference to Fig. 5, it will be observed that the heating elements 30 are supplied with power from a suitable line source 80 of, for example, or 220 volts which is connected to the line terminals of main switch iti. One of the load terminals, which may be a neutral terminal, of the main switch is then connected directly to one of the terminals of the heating elements, whereas the other load terminal is connectel to a terminal of the other heating element through the switch associated with the temperature control unit 44 and through the over limit switch 50. The remaining terminals of the heating elements are connected to one another so that, as will be apparent to those skilled in the art, the heating elements are efiectively placed in series. As will likewise be apparent to those skilled in the art, however, heating elements 30 may be arranged in parallel, if desired, the choice of connection employed depending primarily on the voltage rating of the heating elements as it relates to the value of the line voltage which is most readily obtainable.

In operation, wet steam, whose temperature is in the neighborhood of from 270 to 300 F., is introduced into the interior of the housing through pipe section 28 and through the coil of tubing 24 so that by the time the steam reaches the housing it is substantially dry due to its being heated all along the length of tubing by heat from the wall of the housing. The steam thus admitted to the housing is then superheated by the heating elements to a temperature of approximately 425 as is most desirable for paint spraying, the exact temperature of the steam depending upon the setting of the thermostatic control unit which in turn controls the energization of the heating elements. As is apparent, gauge 38 serves to indicate the pressure of the superheated steam, whereas the stem section of T 42 permits connection of the apparatus to some utilization device, such as a paint spray gun for which superheated steam is required.

In the event that the steam supply for the apparatus should be temporarily out off, halting flow through the superheater, and most of the steam within the housing used up just subsequent to the thermostatic control unit calling for heat so that heating elements 30 are energized, it follows that the sensing element 44' associated with thermostatic control unit 44 will not function normally to deenergize the heating elements at some later time, since no steam will be flowing past it. That is to say, because of the'cessation of steam flow the thermostatic control 44 becomes ineffective and the heating ele ments would remain energized but for the provision of over limit switch 50. Without steam to carry away the heat, the walls of the housing and also the walls of the cover would be quickly overheated to a temperature which would exceed what is generally regarded as a safe Before such hazardous condition can occur, over limit switch S0 functions to deenergize the heating elements and to maintain them deenergized until manually reset. Specifically, when the temperature of the outside of the housing averages reaches a predetermined value less than the safe limit aforementioned, fusible element 76 is melted by the heat of the housing applied through heat transfer strip 78, and as a result, the whole assembly, including movable contact elements 64 and guide member 68, is caused to fall away by gravity, as shown in Fig. 4. Accordingly, contact between

elements

54 and 64 will be broken notwithstanding the fact that the fusible element forms no part whatever of the electrical circuit of the switch.

Even with the heating elements thus deenergized, the same may have such a relatively large amount of latent heat as to cause a very substantial increase in the temperature of the housing, such an increase sometimes being known as an overrun or overshoot. The invention operates in two ways to keep any overrun within safe limits, i. e., below the critical unsafe temperature for the particular atmosphere in which the unit is being used. First, the counterflow introduction of the wet steam at relatively low temperature, say 270 F., through the heat-conducting jacket of copper tubing surrounding the superheating chamber makes for a normal operating temperature within the casing 48 much lower than would occur if the tubing were eliminated and the wet steam introduced directly to the inlet 14 from the outside. Thus should the steam supply fail and the limit switch 50 operate to break the heating circuit, there is a much greater margin of safety available in the form of permissible temperature rise, wholly apart from the second limiting effect resulting from the novel arrangement. Second, overheating under these conditions is further prevented by the rapid dissipation of the heat from the heating elements over the large area of the highly heat-conductive copper tubing as well as by the absorption of heat in the form of latent heat of vaporization of water particles in the wet steam vaporized within the tubing. Any tendency for hot spots to appear is also substantially eliminated because of the more even and rapid heat distribution afforded by the coiled heat-conductive tubing.

Although the invention has been described and illustrated with reference to a preferred embodiment, various modifications of this embodiment, which are within the spirit and scope of the invention, will no doubt occur to those skilled in the art. Therefore, the invention should not be deemed to be limited to the precise embodiment having been described in detail by way of illustration, but should be deemed to be limited only by the scope of the appended claims.

What is claimed is:

1. Steam superheating apparatus comprising: a housing having an inlet to admit steam and an outlet to discharge superheated steam; heating elements disposed within said housing to superheat steam admitted to the interior of the housing through said inlet; means to con trol the energization of said heating elements in accordance with the temperature of the superheated steam discharged from said outlet thereby to maintain the temperature of the superheated steam very nearly at a predetermined operating temperature value; thermally actuated control means associated with said housing and sensitive to the temperature thereof to deenergize said heating elements when the temperature of said housing exceeds a predetermined over limit value; and heat conductive means surrounding at least the major portion of said housing and in thermal engagement therewith to dissipate heat from said housing sufficiently rapidly to prevent the same from being overheated by latent heat from said heating elements when deenergized by said second-named means.

2. Steam superheating apparatus comprising: a housing having an inlet to admit steam and an outlet to discharge superheated steam, electric heating elements disposed within said housing to superheat the steam admitted through said inlet; means to control the energization of said heating element in accordance with the temperature of the superheated steam discharged from said outlet thereby to maintain the temperature of the superheated steam very nearly at a predetermined operating temperature value; an electrical switch for deenergizing said heating elements, said switch having at least one pair of normally closed contact elements and a fusible element in thermal contact with said housing adapted to cause said contact elements to open when the temperature of said housing exceeds a predetermined over limit value; and heat conductive means surrounding at least the major portion of said housing and in thermal engagement therewith to dissipate heat from said housing suificiently rapidly to prevent the same from being over heated by latent heat from said heating elements when deenergized by said switch.

3. For use in electrically energized fluid heating apparatus having a housing providing a heating chamber, a high temperature limit switch adapted to be placed in thermal engagement with said housing and controlling the electrical heating circuit of said apparatus, said switch comprising at least one stationary contact element, a freely movable contact element for snrface-to-surface engagement with said stationary element in a substantially vertical plane, a compression spring urging said movable ele' ment towards said stationary element to maintain the elements in a normally closed condition, said movable element being unsupported except by said spring, a heat transfer strip having one of its ends adapted to be in contact with said housing when said switch is in operative position, and a fusible element disposed between the other end of said strip and the end of said spring remote from said movable element, said fusible element being adapted to melt when the temperature of said housing exceeds a predetermined over limit value thereby releasing the pressure of the spring on said movable element and permitting the same to fall out of engagement with said stationary contact element.

4. Steam superheating apparatus comprising: a housing having an inlet to admit steam and an outlet to discharge superheated steam; electric heating elements disposed within said housing to superheat the steam admitted through said inlet; means to control the energization of said heating elements in accordance with the temperature of the superheated steam discharged from said outlet thereby to maintain the temperature of the superheated steam very nearly at a predetermined operating temperature value; means to deenergize said heating elements when the temperature of said housing exceeds a predetermined over limit value; and a length of tubing coiled around said housing for the greater part of its length and having one of its ends connected to said inlet and its other end adapted to be connected to a source of wet steam, said tubing in combination with said housing serving to preheat the steam admitted through said inlet when the supereating apparatus is operating normally, and to dissipate heat from said housing sufficiently rapidly to prevent the same from being overheated by latent heat from said heating elements when deenergized by said secondnamed means.

5. Steam superheating apparatus comprising: a housing having an inlet to admit steam and an outlet to discharge superheated steam; electric heating elements disposed within said housing to superheat the steam admitted through said inlet; means to control the energization of said heating elements in accordance with the temperature of the superheated steam discharged from said outlet thereby to maintain the superheated steam temperature very nearly at a predetermined operating temperature value; an electrical switch for deenergizing said heating elements, positioned adjacent the outer surface of said housing substantially intermediate its ends, said switch having a fusible element thermally connected to said housing and arranged to melt when the temperature of said housing exceeds a predetermined over limit value, and at least one pair of relatively movable contact elements 1 7 maintained in a normally closed condition'by said fusibleelement only iwhen'the same is in a solid state; and a length'of'tubing coiled around said'housing 'for the greaterpart of its length and having one of its ,ends connected to said inlet and its other end adapted to betconnected to -a source of wet steam, said tubing in combination with said housing serving to preheat steam admitted through said inlet when the superheating apparatus is operating normally, and to dissipate heat from said housing sufficiently rapidly to Prevent the same from being overheated'by latent heat from said heating elements when deenergized by said switch.

6. Steam superheating apparatus comprising: a housing having an inlet to admit steam and an outlet to distemperature value; an electrical switch positioned adjacent the outer surface of said housing substantially intermediate its ends for deenergizing said heating elements, said switch-having at least one stationary contact element, :a movable contact element for surfaceTtO-Surface engage ment with said stationary element in a substantially vertical .plane, a compression spring urging said movable element towards said stationary element to :maintain :the

elements in a normally closed condition, :a heat transfer strip having one of its ends in contact with saidhousing,

and-a fusible elernentidi-sposed between the other end :of

said strip and oneend-of said spring,said fusible element being adaptedto melt when the temperature of said housing exceeds a predetermined over limit value thereby releasingsaidspring and permitting said movable contact element to fall out of engagement with said stationary contact-element; andra length of tubing'coiled around said housing forthe greater .part of its length and having one of its ends connected to said inlet, said tubing in combination with said-housing serving to preheat steam admit- .ted through said inlet when the superheating apparatus is operating normally, .and to dissipate heat from said rousing sufficiently rapidly to prevent the same from being overheated .by latent heat from saidheating elements when deenergized by said switch.

References Cited in the file of this patent UNITED STATES PATENTS 1,439,340 St. Clair Dec. 19, 1922 1,657,144 Armstrong Jan. 24, 1928 2,000,277 Durkee May 7, 1935 2,223,359 Eisinga Dec. 3, 1940 2,412,737 Kercher Dec. 17, 1946 2,688,069 Combest Aug. 31, '1954