US2022716A - Automatic furnace - Google Patents

Description

Dec. 3, 1935. H. A. GRINE El AL AUTOMATIC FURNACE Filed Feb. 20, 4 Sheets-Sheet l- INVENT RS MRRyABR/NE .fwnvJPszo l/an Aliza/x9? 5.6% ATTORNEY Dec. 3, 1935. GRINE ET AL 2,022,716

AUTOMATIC FURNACE Filed Feb. 20, 1933 4Sheets-Sheet 2 ATTORNEY Dec. 3, 1935. H.A. GRINE ET AL AUTOMATIC FURNACE Filed Feb. 20

, 1933 4 Sheets-Sheet 3 Dec. 3, 1935. H. A. GRINE 'ET AL AUTOMATI C FURNACE 4 Sheets-Sheet 4 Filed Feb. 20, 1933 ATTORNEY Patented Dec. 3, 1935 iIZ'TIEi-"F-"UNITED STATES .PA'reN OFFICE AUTOMATIC FURNACE Harry A. Grine, White Plains, N. 1., and John G.

Reid and Harry A. Wagner, Pottsville, Pa., assignors to The Philadelphia and Reading Coal and Iron Company, 'Philadelphia, Pa", a corporation of Pennsylvania 7 Application February 2 0, 1933, Serial N6.-657,538 1 1 enabling the attainment of improved domestic furnace operation ciency of combustion. An outstanding feature 'of the invention resides in novel provisions for. maintaining predetermined fuel and ash bed. -.i-

depths, in which connection the invention pro-1; tojthe top central portion of the combustion vides novel automatic means for controlling the removal of ashes whereby ash accumulations'are' prevented from exceeding a given amount in the. a combustion chamber and on the other handthe ash removal is effectively precluded from con- 'tinuing to an undesirable extent.

In current methods and apparatus for burning solid fuels, the distribution of fuel on the grate and the method of admitting air to the .fi're are such as to cause uneven distribution of air in the fuel bed and consequent uneven burning of the fuel, thus resulting in the passage of excess air through some portions of the fire, cansing excessively high rates of combustion in these sections and producing clinkering. Other portions may not have sufficient air for combustion of the fuel, resulting in unburned fuel passing minimizing the loss of eificie'ncy in burning of fuel common to present furnaces by reason of diluting gases from combustion with excess uncombined oxygen passing through the fuel bed.

In current types of furnaces in which it is common practice to intermittently charge a considerable amount of fuel, there is produced a wide variation in fuel bed depth and temperature, as well as a temperature on the upper surface of the fuel which is too low to ignite combustible gases evolved from the fresh coal and there is a considerable loss of efficiency due to the escape of these gases from the fuel. With our improved method of burning, the coal is constantly fed to the top central portion of the fuel bed as needed and the incoming coal is surrounded by an incandescent surface of burning coal at the top of the The inincluding increased effi:

on its supporting shaft for the purpose of giving fuel bed which ignites combustible gases evolved from the fuel bed and causes them to burn, par: ticularly when supplied with secondary air ad-" m-itted over the fuel bed. Maintaining the upper surface of the fire jsufliciently hot to ignite 5- fgafsesevolved in the fuel bed is further facilitated aby the fact that the coal is preheated in the lower :end of the magazine feed.

In'conjunction with the feeding of the-fuel' '10 chamber, whereby the top of the fuel bed in the combustion chamber assumes a conical shape, sloping downward from the coal feed pipe t the wall, there is provided in this improved apparatus a conical shaped rotatable grate with air passages on its surface, thus giving to the bottom of the fuel bed a conical form and assuring an even depth of fuel bed over the grate and *proper distribution and diifusion of the primary 'air in the fuel bed. This conical grate is of 2 smaller base diameter than that of the combustion chamber, allowing for passage of ash be-. tween it and the walls of the combustion cham-' her. The grate is further mounted eccentrically a slight crushing action on the ash, as the grate rotates, causing the ashes to come down more freely.

Also, in current domestic furnaces the shaking down and removal of ashes involves periodical manual attention. In this improved furnace motorized mechanical means for removal of ashes is provided andis automatically controlled by means of a thermostat placed in the bottom zone of the combustion chamber and operated by means of varying temperatures in this zone.

Other objects and advantages of the invention will become apparent from the ensuing description andclaims.

In the accompanying drawings:

Fig. 1 is a vertical longitudinal sectional view of apparatus constituting a preferred embodiment for the carrying out of our invention.

Fig. 2 is a vertical transverse section on line 2-2 of Fig. 1.

Fig. 3 is a detail view partly in vertical section, illustrating the thermostat and associated parts.

Fig. 4 is a detail horizontal sectional view, with parts broken away, showing more particularly the mo or.

" I Fig. 6 is a wiring diagram further illustrating said connections.

Figs. '7, 8, and 9 are views illustrating the oper-' ation of the time limit switch mechanism.

Fig. 10 is a vertical sectional detail view showing a modified form of grate. 1

. ed by a cylindrical shell I, which, in turn, is positioned within and spaced from a shell 3. The latter comprises a curved forward end portion 8' (Fig. 4) and parallel side portions 3". Extending across said side portions is a vertical plate or partition 9; A bottom plate in extends across the. space between said shell I and 8 and plate 9; the space between said shells and said plates 9 and I0 constituting a chamber surrounding the combustion chamber 6 and adapted to receive water or other fluid medium. The shells I, 8, may be supported on a base member I I of any suitable construction mounted upon the base plate l2.

In the bottom portion of the combustion chamber there is mounted a rotatable grate i3, the latter being shown as of conical formation and provided with perforations l4 for admitting air to the fuel bed. The grate may conveniently comprise a top section I3 and four lower segmental sections l3"; the top section being mounted on a. vertical shaft 15, and the lower sections having arms l6 pinned to the arms I! of a spider l 8. The latter has a central tubullar portion l8 journaled on the shaft l5, and supported on a pedestal base member is. Lugs I30 depending from the top section l3 of the grate extend into the spaces between adjacent arms ll of the spider whereby rotation of the latter causes rotation not only of the lower grate segments I 3", but also of the top segment l3. -An anti-friction thrust bearing unit 20 'may be interposed between said member i9 and portion l8 of spider l8 as shown. A screw 2| in the pedestal l9 engages a groove 22 in the shaft I5 for maintaining the latter in a definite vertical position with respect to said pedestal and thus to the furnace. The spider. arms ll have arcuate flanges I I at their ends. The grate is mounted eccentrically with respect to the combustion chamber, for a purpose which will hereinafter appear more specifically. This may be conveniently accomplished by so constructing the top grate section that the vertical axis through the apex thereof is slightly off-set with respect to the vertical axis of the shaft I 5, and by constructing the spider l8 so that the vertical axis through the intersection of the center lines of the arms i1 is similarly oif-set with respect to the vertical axis of said shaft. In short, the vertical axis of the spider l8 and of the cone shaped grate comprising the sections i3, I3", is off-set with respect to the vertical axis of shaft l5.

Secured to the flanges ll of the spider arms I1 is a ring 23 having a horizontal and circumferential flange 24 adapted to receive ashes from the combustion chamber. Said flange 24 overlies an inwardly extending circumferential flange 25 on the base member Ii. The ash ring flange 24 has formed on its underside a beveled annular gear 26 with which meshes a beveled pinion 27 on a shaft 28 driven by an electric motor 29. Secured to the base member II and projecting obliquely across the ash ring flange 24 is an ash deflecting arm 30 (Figs. 2 and {1), whereby, as

the ash ring rotates, the ashes thereon are scraped laterally oil! the flange 24 and thence passed downwardly into a well or casing H from which they are removed by an elevator 32. The base member ll may, as shown in Figures 2 and 5 4, be provided with a downwardly and laterally inclined portion 3| for facilitating the discharge of ashes into the receptacle 3i! Extending through the top plate I and thence downwardly into the combustion chamber is a 10 coal chute or magazine, which may comprise sections 33, 33'. Said chute may also include at its upper end an inclined hopper portion 34, communicating with a coal bin (not shown).

A water jacket is provided around the lower portion of the magazine 33 by a tube 35 and bottomring 36., Extending between the tube 35 and the shell I is a ring 31 forming a top plate I for the combustion chamber. The rings or plates 36, 31, magazine section 33, andshells I and 35 20 may conveniently be welded together; as may also the bottom ring I 0 and the shells I and 3. The sections 33, 33' of the coal chute may be bolted together as shown at 33.

It will be seen that by feeding the coal into 25 the top central portion of the combustionchamber 8, the upper surface of the fuel bed slopes downwardly from the magazine to the sides of the combustion chamber, thereby assuming a conical formation. Through the conical grate 30 i3 a conical form is also given to the bottom of the fuel bed. Thus, through the provision of said grate in conjunction with the overhead feeding of the coal to the chamber 6, there is assured a substantially uniform depth of fuel bed to- 35 gether with equalized distribution of air therethrough. As shown, the grate is of less diameter than the combustion chamber, thus allowing the ashes to pass downwardly between said grate and the combustion chamber. By virtue of the 40 eccentric mounting of said grate on the shaft IS the rotation of the grate imparts a slight crushing action to the ashes, causing them to move downwardly more freely. on to the ash ring flange 24. 4.5

If desired, the lugs I30 of the top section of the grate may be omitted so that said section will remain stationary during rotation of the lower sections I3 with the spider l3 and ash ring 23. so

The space at the top of the shell 8 may be covered by the dished plate 39 and the concave plate 40, the latter resting at one end on the top edge of the vertical plate 9 and at its edges on the top edges of the legs 8" of the shell 8. The plate 39 has a flange 39' fitting within the curved portion 8' of said shell. Said plates 9, 39, and 40, and shell 8 may be securedtogether in any suitable way, as by welding. Openings in the adjoining portions of the plates 39 and 40 provide for the 6:) passage of the magazine section 33. Plate 40 is further provided with openings communicating with outlet pipes 4|, 4|, for conducting steam from the water to the customary radiators or other heating units (not shown). a;

Mounted in openings in the shell I and in corresponding openings in the plate 9 are flue members 42 having passages 43 (Fig. l) therethrough for enabling the gases of combustion to flow from the combustion chamber 6 into the space to the 70 rear of said plate.

The rear end of the base member II is provided with an opening 44 therethrough for admitting air to the underside of the grate. This opening is in registry with an opening 45 in a 7 frame member 40 secured to said base member II and adapted to be closed by a door 41 secured to a shaft 48 rotatably mounted in suitable bearings. Said shaft extends through the side wall 3 of the casing and has attached thereto a handle 00' whereby the door 46 may be readily adjusted to regulate the draft of air passing through said openings. To facilitate the passage of air to the combustion chamber the end plate 0 of the furnace casing is provided with perforations 49. Openings 50 are also provided in the supporting standards 5| for the rear or heat absorbing portion of the furnace.

Positioned below the coal magazine and surrounding the top portion of the fuel bed is a secondary air ring 52 having perforations 03 whereby combustion of the combustible gas evolved from the bed of fuel is expedited. This ring is supported in any suitable way. An air supply pipe 56 extends upwardly from a point below the bottom plate I0 (Fig. 4) and thence through the water in the chamber formed between the shells 'I and 8, said pipe then projecting through the upper part of shell I into a coupling 6! communicating with the interior of the air ring 52. Air is thus continuously supplied to said ring and is preheated by the water surrounding the combustion chamber. The lower end of the pipe 56 below the plate I0 may terminate within thebase member I I and thus receive air from within said base member, or it may extend into the atmosphere at any other point. The rear or boiler portion of the furnace may be of any suitable type, the particular construction thereof being immaterial to the invention herein claimed.

It has been noted that the lower portion of the fuel magazine 33 is surrounded by a water jacket. The hot water therein heats the fuel preliminarily to the entry of the fuel into the combustion chamber, thereby assisting in maintaining the upper surface of the fire bed sufliciently hot to ignite the gases evolved. In addition to this, the water jacket aforesaid prevents the fuel in the magazine 33 from reaching so high a temperature as to burn in the magazine.

As combustion of the fuel in the combustion chamber proceeds, ashes will, of course, collect on the grate I3 and, as hereinbefore noted, will be removed from time to time by rotation of the grate I3 and ash ring 23 through the motor 29. We have provided for the control of said motor in response to temperature conditions at a predetermined point in the combustion chamber. More particularly, we provide a thermostat in a chamber or housing mounted in a wall of the combustion chamber for subjecting the thermostat to temperature changes in the bed of ash and fuel on the grate l3.

Through our thermostatic control provisions, including the location of the thermostat and the predetermined length and diameter of the fuel feed tube 33, substantially uniform depths of fuel bed and ash bed are maintained.

Preferably the top of said ash bed is maintained substantially on a level with the apex of the conical grate but the top of ash bed may be maintained at any desired level with relation to the grate.

For this purpose we provide a thermostat mounted in a housing 98 inserted in the front wall of the furnace, said housing extending through openings in the front end plate 4, the

shell 1, and the shell 8. A casing 99 within said housing surrounds the thermostat, the end wall I00 of which casing is engageable by the material in the lower part of the combustion chamber, as shown in Figure 1. The thermostat may be of any well-known type, that shown comprising a heat-responsive coiled element l-0I (Fig. 3) secured at one end to the interior of a shell or casing I02 within the casing 99 and at its other end to a rotatable shaft I03. Change of temperature in thebed of ash and fuel adjacent the plate I00 results inexpansion or contraction of the element IOI and in rotation of shaft I03 in one direction or the other. The parts are shown so located with respect to the grate I3 that the axis of the thermostat and of the chamber in which it is mounted are substantially on a level with the apex of the grate, but this relation may be varied if desired. A tubular extension I04 of casing I02 surrounds the shaft I03 and extends through end plate I05 -at the.front end of the casing 99, said extension I04 joining a casing I06 mounted on a bracket I01 projecting from the front wall of the furnace. The end plate I00 may be of any material capable of withstanding the temperatures in the fuel bed, and at the same time of the desired heat conductivity for transmitting the temperatures from the fuel bed into the thermostat housing. We have found the metal known to the trade by the name Ascaloy to be highly satisfactory in this connection, although any other suitable material may be employed in the plate I00.

The connections whereby the thermostat controls the motor 29 may be of any suitable or conventional type. In the embodiment shown there is provided in the casing I08 a so-called Mercoid" switch of well-known type and shown diagrammatically in Figure 5. This switch comprises a toothed wheel I08 secured to the thermostat shaft I03. A pair of spaced lugs I09, IIO are carried by said wheeland engage the teeth thereof. Joumaled on said shaft I03 is an arm Ill carrying at its upper end a chamber II2 containing mercury or other suitable conducting liquid H3. Said chamber II2 also contains a pair of spaced contacts I, II5. These contacts are suitably insulated from each other. When the arm III and chamber II2 are shifted by lug IIO into the position shown in full lines in Fig. 5, the contacts I I4, I I5 are bridged by the mercury II3, whereby a circuit is closed through the motor 29; and when, on the other hand, the arm I II and chamber 2 are moved by lug I09 into the dotted line position of Fig. 5, the mercury moves out of engagement with said contacts. More specifically, when due to accumulation of ashes in the lower part of the combustion chamber, the temperature in the thermostat casing is lowered to a certain point, the resulting contraction of the thermostat and rotation of the shaft I03 causes the rotation of wheel I00 and shifting of arm II! by lug IIO to bring the chamber II2 into the full line position shown in Figure 5, whereupon the motor circuit is closed. The motor 29 thus comes into operation and rotates the ash receiving ring 23 and grate I3. As noted previously herein, the eccentric mounting of the grate I3 imparts a crushing action to the ashes between said grate and the combustion chamber walls, whereby the passage of the ashes from the grate into the ash receiving ring is expedited. As the ring 23 rotates, the arm 30 deflects the ashes from the flange 24 of said ring and causes them to pass into the ash lifter well 3|. The withdrawal of ashes from the combustion chamber results in lowering of the coal above the ashes with corresponding increase of temperature adjacent the thermostat. Upon sumcient increase of said temperature, the shaft I03 is rotated sufficiently to cause lug I08 to move arm III and chamber II2 into the dotted line position of Figure with resultant disengagement of the mercury in said chamber from the contacts II4, I I5. If desired, this shifting of the chamber II 2 to remove the mercury from engagement with said contacts may be relied upon to break the motor circuit. In short, the contacts H4, H5 may be connected directly in the motor circuit, whereby the bridging of said contacts energizes the motor directly and the removal of the mercury from engagement with said contacts deenergizes said motor. We have, however, shown in conjunction with the motor control connections provisions for insuring that the motor 29 will not continue in operation beyond a predetermined time following the bridging of contacts I I4, II5. Thus the operation of the motor is limited to a definite period in case the thermostat coil IOI takes too long to restore switch arm III to the off position in response to increase of temperature in the lower part of the fuel bed. For this purpose we employ a safety control limit switch of standard type, designated I20 and comprising a relay I2I and relay motor I22. Since this unit is well known, its operation need not be discussed in detail except to note briefly that when the contacts I I4, I I5 are bridged by the mercury II3, a circuit is closed through coils I23 of relay I2l. by way of wire I24 connected to one pole of a suitable source of electrical energy and thence through contact II5, mercury II3, contact H4, wires I25-l29, relay coils I23, wire I30, wire I3I, and wire I32 to the opposite pole of said source. Relay I2I is thus energized and armature I33 thereof operated to close contacts I 34--I 35 in the usual manner (said armature being connected with contact I 35 by a rod I36, as is well understood). Contacts I31, I38 are normally closed and a circuit is thus established from wire I28 through wires I39, I40, contacts I31, I38, wires I40, I4I, I45, contacts I34, I35, wire I41, the relay motor I22, and thence through wires I48 and I3I to wire I32. Also current flows from wire I41 through the furnace motor 29 by way of. wires I49 and I50 and thence to wire I32. Thus both the relay motor I22 and the furnace motor 29 are placed in operation.

After a predetermined time, limited by the setting of the relay (for which purpose a pointer I5I is provided) the furnace motor and relay motor circuits are broken by the disengagement of contact I 31 from contact I38. To summarize the action of the limit switch relay mechanism upon said contacts, it may be noted that when the relay coils I23 are energized, the operation of armature I33 not only closes the contacts I 34, I35 as above pointed out, but also, through link I36, shifts a pawl I53 into engagement with one of the gears I54 of an epicyclic train driven by the relay motor and associated with the disk I55, loosely mounted on the shaft I56. The parts are now in the position shown in Fig. 7. Upon the engagement of pawl I53 with gear I54 the disk I55 is rotated through the actuation of the epicyclic train by the relay motor, and energy is stored in a spring (not shown) to which said disk is connected. Attached to said disk is a stop pin I51 which, at the end of the predetermined time aforesaid, engages and raises an arm I58, lifting bar I59 out of the path of spring element I60. The latter -now snaps back, and its upper on'set projection I8I engages and retracts the spring member I82 which carriescontact I31, thereby disengaging said contact from contact I38, as shown in Fig. 8. The furnace motor, as well as the relay motor, is thus now stopped 5 after a predetermined period of operation. The manner in which the relay motor acts upon the epicyclic gears and disk I55 and the manner in which the time when the pin I51 shall engage member I58 is predetermined are well understood in the art and description thereof is unnecessary to an understanding of our invention.

The furnace motor 29 may now remain inactive until after the relay motor armature I33 returns to its normal position. This occurs when the switch arm I II is moved to its "off" or dotted line position, breaking the circuit through contacts H4, H5, with consequent deenergization of relay coils I23. Armature I33 now returns to its normal position, under suitable spring action, pushing spring I60 rearwardly permitting bar I59 to drop back into its normal position and contact I 31 to return into engagement with contact I38 at the same time, contact I 34 is withdrawn from engagement with contact I35, con tact I34 being mounted on said spring element I60.

Also, the retraction of said armature disengages pawl I53 from gear I 54, whereupon disk I55 is returned to its normal position by its spring previously referred to. The relay mechanism is now again in its normal position (Fig. 9) ready to repeat the cycle aforesaid upon bridging of the contacts H4, H5.

It will be apparent that any suitable time nm-. it switch mechanism other than the conventional one here shown may be employed in connection with the thermostat and furnace motor. The time limit for which the mechanism is set is such that the motor circuit will be broken after a period which will enable the accumulated ashes to be removed from the fuel bed but before burning fuel is removed, and before burning fuel engages the grate.

If the thermostat should shift the switch arm 5 III into its off position while the relay motor is in operation but before stop pin I51 engages pawl I58, the relay coils I23 will be demagnetized, armature I52 and disk I returned to normal position, and contact I34 withdrawn from 50 engagement with contact I35; the circuit through the relay and furnace ni'glors being thus broken and the relay restored to normal.

A signal light I may be connected across the wires I25, I32 as shown, and may be located at any desired point for giving an indication that the mercoid switch is in its on position.

It may be noted that the operation of the switch arm I II may be regulated as desired by adjusting the lugs I09, IIO to appropriate positions on the n toothed wheel I08.

The ashes ejected from the ash ring 23 into the well or casing 3| are removed by the ash elevator 32 comprising a series of buckets I10 on an endless chain I1I. Said chain is driven by 65 a sprocket wheel I12 secured to the motor driven shaft 28. The elevator operates in a vertically extended casing I13 provided at its upper end with a suitable opening through which the ashes are discharged into any suitable receptacle. Since ash elevators of this type are known in the art, further description thereof is not essential.

The air ring 52 provides for distributing and diffusing oxygen to the combustible gases immediately above and in the center of the fire bed to assure their complete combustion. The air supplied to said ring is preheatedv by passing through the pipe 56 which, as has been noted,

extends through the shell 'I and downwardly through the space between said shell and the shell 8, finally extending through the bottom plate Ill. The space between the shells 6 and 8 being filled with hot water, it will be seen that the air which passes through the pipe 56 to the ring 52 is effectively heated. Preferably the air ring is provided with two rows of holes 53, one on the inside and the other on the outside of said ring, and at an angle corresponding to that at the top of the fuel bed. In other words, preferably the holes 53 are so arranged that an imaginary surface passed through the two rows thereof assumes an angle corresponding to that of the frusto-conical top portion of the fuel bed.

'The furnace herein described has been found particularly effective for burning prepared sizes of anthracite coal, especially those known to the trade as egg, stove, and chestnut. The invention, of course, is not restricted to the burning of any particular coal or size thereof.

In Figure 10 there is shown a modification of the invention wherein deflecting plates I extend between the arms ill of the spider i8 and are secured thereto. These deflecting plates, which are inclined at an angle corresponding to that of the conical grate, receive the small particles of ash which pass through the holes of the grate during the rotation of the latter and deflect said particles on to the ash ring flange 24. Also, the ash ring flange 24 is formed with upwardly inclined segmental portions 24 which extend between the spider arms i1 and are secured to said arms by bolts as shown. The inclined segmental portions 24' aforesaid also receive ash particles from the holes in the lower part of the grate, as well as from the plates I15. In this form of invention also the deflecting arm 30 has secured thereto and extending therefrom a piece of spring steel I16 for engagement with the segmental extensions 24 to remove ash therefrom. In this manner the ash which passes through the openings in the grate is effectively collected and passed to the well or boot of the ash removing elevator 32. It may be noted also that the bearing portion I'll of the top section of the grate has a downwardly flaring extension I18, thereby insuring that any ashes passing through the top grate section adjacent said bearing portion will be directed on to the plates I15 and thence to the segmental extensions 24' and the ash ring flange 24.

A door I19 of conventional type may be provided for opening or closing the interior of a shell or housing I80 extending through the wall 3 and the shells 1 and 8, whereby access may be gained, when desired, to the combustion chamber. Suitable heat insulating material I8! is provided, as shown, between the outer shell or casing and the inner sections of the furnace.

Coal may be automatically supplied to the magazine 33, 33', either by gravity from an overhead storage bin or by means of an automatically controlled elevator synchronized with the ash removal apparatus.

The terms and expressions which we have employed are used as terms of description and not of limitation, and we have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

We claim:

1. In a furnace, a combustion chamber, a grate for supporting a fuel bed in said chamber, means including said grate for removing ashes from said chamber, a motor for operating said ash removing means, a thermostat positioned to be responsive to temperature conditions in the combustion chamber, a power circuit for said motor including a switch controlled by said thermostat, a relay energized when said switch is in one position and de-energized when said switch is in another position, said relay closing said circuit through said motor when the relay is energized, and means controlled by said relay for breaking the circuit through the motor at the end of a predetermined time following the energization of said motor.

2. In a furnace, a combustion chamber, means positioned to be responsive to temperature conditions in a fuel bed in said chamber, a motor, means operable by said motor for removing ashes from said chamber, a pair of normally open contacts, means controlled by said heat responsive means for closing said contacts to establish a circuit through said motor, a pair of normally closed contacts in said circuit, and time-controlled means for opening the last mentioned contacts for breaking said circuit upon the lapse of a predetermined time while the first-mentioned contacts are closed.

3. In a furnace, a combustion chamber having an opening in a wall thereof, a plate of high-temperature-resistant heat-conductive metal in said opening and positioned to be contacted by burning fuel and ashes in said combustion chamber, a housing rearward of said plate, means for removing ashes from said chamber, and thermostatic means controlled by the temperature in said housing for controlling the operation of said ash removing means.

4. In a furnace, a combustion chamber, a grate for supporting fuel and ash beds in said chamber, said grate having its outer edge spaced from and forming an ash passage with a side wall of said chamber, means including said grate for removing ash from said chamber, a motor for causing operation of said ash removal means, a power circuit for supplying energy to said motor, a thermostat positioned in a side wall of said chamber and above said grate, contacts controlled by said thermostat for controlling the supplying of energy from said power circuit to said motor, said thermostat being adapted to cause opening and closing of said contacts in response to temperature conditions in said chamher, and time limit switch means for breaking said power circuit and deenergizing said motor after a predetermined time following closing of said contacts.

5. In a furnace, a combustion chamber, heat responsive means positioned to be contacted by an ash bed in said chamber when said ash bed exceeds a predetermined depth and to be contacted by a burning fuel bed in said chamber when said ash bed is less than a predetermined depth, means for supporting ash and fuel beds in said chamber, means including said ash and fuel bed supporting means for removing ash from said chamber, power driven means for causing operation of said ash removal means, a power circuit for supplying energy to said power driven means, and contacts for controlling the supplying of energy by said power circuit to said power driven means,

said heat responsive means being adapted to cause closing of said contacts when said ash bed exceeds a predetermined depth, and to cause opening of said contacts when said ash bed is less than a predetermined depth.

6. In a furnace, a combustion chamber, heat responsive means positioned to be contacted by an ash bed in said chamber when said ash bed exceeds a predetermined depth and to be contacted by a burning fuel bed in said chamber when said ash bed is less than a predetermined depth, means for supporting ash and fuel beds in said chamber, means including said ash and fuel bed supporting means for removing ash from said chamber, power driven means for causing operation of said ash removal means, a power circuit for supplying energy to said power driven means, and contacts for controlling the supplying of energy by said power circuit to said power driven means, said heat responsive means being adapted to cause closing of said contacts when said ash bed exceeds a predetermined depth, and

to cause opening of said contacts when said ash- 7. In a furnace, a combustion chamber, heat responsive means positioned to be contacted by an ash bed in said chamber when said ash bed exceeds a predetermined depth and to be contacted by a burning fuel bed in said chamber when said ash bed is less than a predetermined depth, means for supporting ash and fuel beds in said chamber, means including said ash and fuel bed supporting means for removing ash from said chamber, power driven means for causing operation of said ash removal means, a power circuit for supplying energy to said power driven means, and contacts for controlling the supplyi ing of energy by said power circuit to said powerf driven means, said heat responsive means being adapted to cause closing of said contacts when said ash bed exceeds a predetermined depth, and to cause opening of said n tacts when said ash bed is less than a predetermined 'depth, a relay controlled by said contacts, said relay being energized when said contacts are closed and deenergized when said contacts are open, and means controlled by said relay for breaking said power circuit at the end of a predetermined time even though said relay remains energized.

HARRY A. GRINE. JOHN G. REID. HARRY A. WAGNER.

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