US2214421A - Heating furnace - Google Patents

Description

s. KNEAss, JR 2,214,421

HEATING FURNACE Filed Feb. 27, 1959 3 Sheets-Sheet 1 zo) Sept. l0, 1940.

S. KNEASS. JR

HEATING FURNACE Sept. l0, 1940.

3 Sheets-Sheet 2 led Feb. 27, 1939 7 mw] o2.

Sept-10, 1940. s. KNEAss, JR 2,214,421

HEATING FURNACE Filed Feb. 27, 1959 3 Sheets-Sheet 3 192 of'ney Patented Sept. 10, 1940 UNITED STATES APATENT OFFICE HEATING FURNACE Application February 27, 1939, Serial No. 258,601

l, 6 Claims.

This invention relates to heating furnaces, and more particularly to continuous furnaces for heating metal billets and to a method of operating such furnaces.

In the usual continuous billet heating furnace,

5 the billets are charged at the rear end of the furnace on a level with the hearth, and they are pushed down the skids to the discharge end in a continuous solid line. Fuel is introduced at the front or discharge end of the furnace, and the hot gaseous products of combustion pass rearwardly over the tops of the billets to the chimney flue at the charging end. Only the top surfaces of the billets are exposed to the hot gases, and the heat transfer is largely by radiation. This heat transfer is Ieflicient and rapid while the gases are incandescent, but it becomes much less effective as their temperature decreases. It is customary to build this type of furnace with such a length that the gases are discharged to the chimney at av temperature of at least 1200 degrees Fahrenheit. The increased furnace length required to reduce the temperature of the gases below this point is usually not justifiable on eco-` nomic grounds. y

In order to increase the efliciency and capacity of such furnaces it has been proposed to install recuperators arranged to transfer heat from the waste gases to the combustion air. These recui perators are bulky, expensive, and sub-ject to frequent repairs. Furthermore, the use of `preheated air increases the combustion temperature, and the temperaturer of the gases may become so high (particularly with high intensity fuels such as coke oven gas) as to melt the oxide coating on the billets and form a slag which adheres to` the brick hearth of the furnace. In addition, the heating of the billets may take place so rapidly that their top surfaces are at a much higher temperature than their bottom surfaces, causing difficulties in the subsequent rolling of the billets into commercial shapes.

It is accordingly one object of the invention to overcome these diiculties and to provide an improved method and apparatus whereby the capacity and efficiency of a continuous billet heating furnace may be increased considerably without the use of recuperators.

It is a further object of the invention to provide an improved method and apparatus whereby the transfer of heat to the billets in a continuous billet 4heating furnace may be greatly increased without materially lengthening the furnace.

It is a further object of the invention to provide 'u an improved method and apparatus for charging billets to a continuous billet heating furnace whereby the temperature of the outwardly flowing gaseous products of combustion may bereduced to a comparatively low value by the transfer of heat to the incoming billets.

It is a further obje-ct of the invention to provide an improved method and apparatus for heating billets continuously by the combustion of fuel such that the transfer of heat to the bi1- lets will take place so efliciently as to reduce the temperature of the gaseous products of combustion to a low value in a comparatively small space.

kIt is a further object of the invention to provide an improved method and apparatus whereby metal billets may be heated rapidly and with great uniformity throughout their cross section.

With these and other objects in view, as will f be apparent to those skilled in the art, the invention resides in the combination of parts and the steps o-f the process set forth in the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention and in which like reference numerals indicate like parts:

Fig. 1 is a longitudinal section through a continuous billet heating furnace, the section being taken on the line I-I of Fig. 6;

Fig. 2 is a fragmentary view similar to Fig. 1 showing a different phase of the charging cycle;

Fig. 3 is a fragmentary view similar to Fig. 1 showing a still further phase of the charging cycle; n

Fig. 4 is a diagram of certain electrical controls;

Fig. 5 is a section on the line 5-5 of Fig. 1;

. Fig. 6 is a section on the line 6 6 of Fig. 5; and

Fig. '7 is a fragmentary View similar to Fig. 3, showing aslight modification.

The embodiment illustrated comprises a furnace I0 arranged for the continuous heating of elongated metal bars or billets B and provided with the usual hearth I I along which the billets are moved broadside toward the left as viewed in Fig. 1. This hearth may be of any well-known construction, and it will be understood that the billets may rest on the brickwork itself or on elevated rails or skid pipes as desired. Above the hearth there is provided a horizontal passage or chamber I2 through which the hot gaseous products of combustion flow toward the right as viewed in Fig. l. The discharge end of the furnace may be lof the usual construction, with the customary discharge knuckle I3, and a suitable 55 burner l3nt adapted to supply fuel and air for combustion purposes.

The billets on the hearth I I are in lateral contact with each other, with only their upper surfaces exposed, and the transfer of heat from the hot gases to the billets takes place largely by radiation. Such radiant heating is effective so long as the gases are at a high temperature, but since the rate of heat transfer varies approximately as the 4th power of the temperature difference the heating effect will decrease rapidly as the gases approach the charging end of the furnace. Consequently an extremely long furnace would be required to reduce the temperature of the gases to a desired value if radiant heating alone were utilized. In order to recover a large part of the heat remaining in the gases without lengthening the furnace excessively or utilizing a recuperator I provide means whereby the escaping gases are brought into intimate Contact with the incoming billets in such a way as to transfer heat thereto largely by convection. This is preferably brought about by arranging the billets in a series of superimposed horizontal layers separated by spacers, the billets in each layer being spaced apart laterally, and causing the gases to pass through the resulting stack of billets, preferably in a downward direction. The stack may be maintained at a substantially constant height by adding layers of cold billets to the bottom and transferring layers of heated billets from the top of the stack to the furnace hearth.

Referring now to Fig. 1, it will be seen that a vertical passage or flue I4 is provided which leads the gases downwardly from the end of the horizontal passage I2. The lower end of the passage I4 may be connected to a suitable induced draft fan I 4a, ejector, or other draft-producing apparatus. Within this passage I4 there is positioned a stack of billets B arranged in superimposed horizontal layers, the layers being separated by spacer bars S. The billets extend in a direction transverse to the gas passage I2, whereas the spacers extend in a direction approximately parallel with said passage. The billets in each layer are spaced apart to allow the gases to iiow downwardly between themt There are twospacer bars S for each layer of billets, and the two lowermost spacer bars serve to support the weight of the entire stack, the ends of these bars resting on the upper ends of dogs I5 arranged in pairs on opposite sides of the passage I 4. These dogs I5 are pivotally supported at their lower ends on hinge pins I6, so that they may swing inwardly or outwardly with respect to the passage I4. As shown in Fig. 6, the dogs are of inverted U-shape, and openings I8 are provided in the walls of the passage I4 to receive them.

The incoming billets are added to the bottom of the stack, preferably one layer at a time, and for this purpose there is shown a car 20 comprising a pair of spaced parallel I-beams 2| connected by transverse members 22. This car is adapted to enter the passage I4 through an opening 24 (Fig. 6) in one wall thereof, and to be positioned directly beneath the stack of billets and between the dogs I5. In order to support the car while itis in this position rollers 25 are mounted on the inner sides of the dogs. When outside the passage the car rests on rollers 26. It will be understood that with the car 26 in its outer position two spacer bars S will be placed thereon at the proper distance apart and a layer of billets B will be placed on the spacer bars. Thereupon the loaded car will be pushed inwardly through the opening 24 on to the rollers 25, as shown in Fig. 1.

Means is provided to lift the loaded car 20 upwardlyl from the rollers 25 and to elevate the entire stack of billets until the two lowermost spacer bars Si, which have been resting on the car, are in position topbe -supported, by the upper ends of the dogs I5, Forthis purposeI provide a pair of spaced parallel beams. 28 which extend through -the openings I8 and beneath the car 2U. As shown in'Fig. 6 the dogs I5 straddle these beams. The end portions of the beams 28 rest on vertical screws 29 each of which is threaded through a worm :gear 30 (Fig. l) arranged to be rotated by means of a worm 3|. There are four of these worms and they are all driven simultaneously by an electric motor 33 (Fig. 5) through the medium of shafting 34 and bevel gears 35. It will be understood that by operating the motor 33, the worms 3I and worm gears 30 can be rotated, raising the screws 29 and beams 28, and thus elevating the-car 26 with the two spacer b-ars and the layer of billets thereon. During this upward movement the layer of billets -will engage the two spacer bars which rest vo-n the dogs I5, as shown in Fig. 2, and as the movement continues the entire stack of billets will be raised until the topmost layer is level with the hearth II, whereupon the motor 33 will be stopped, As the two lowermost spacer bars pass upwardly they will engage cam surfaces 36 on the inner sides of the dogs I5 and force the upper ends of the dogs apart, and `when these spacer bars pass beyond the surfaces 36 the dogs will return by gravity to their former positions as shown inFig. 3. Subsequently the motor 33 will be reversed, lowering the beams 28 and the car 20 until it rests upon the rollers 25, the dogs I5 serving tosupport the billet stack with the new layer added to the bottom thereof.

The topmost layer of billets is pushed from the billet stack on to the hearth I I, and for this purpose I have shown a pair of reciprocable pusher bars 31 resting on rollers 38 and arranged topass through openings 39 in the furnace wall. As shown in Fig. 4,' each bar 31 is provided'with a rack 4I which meshes with a pinion 42. The two pinions 42 arel mounted o-n a common horizontal shaft 43l driven by an electric motor 44.

By suitably controlling the motor 44, the bars 31 can be advanced into the furnace to push the topmost layer of billets on to the hearth I I, and afterwards if desired the pusher bars can be advanced intermittently to cause one billet at a time to fall over the discharge knuckle I3 of the furnace. When the pusher bars have reached the limit of their stroke they will be withdrawn to allow the stack of billets to be raised, so that the next layer can be pushed off.

Before this next billet layer can be pushed on ,f

to the hearth, however, the two spacer bars at the top of the stack should be removed. This maybe brought about by means of the pusher bars 31. In the preferred construction illustrated a latch 46 is pivotally mounted on the side of each s Contact 6U.

latches will engage the inner ends of the spacer bars and withdraw them through the openings 39 on to suitable gravity conveyors 48 which may lead to a position such that the spacer bars can be conveniently placed on the car 29. To avoid undue complexity in the' drawings only a portion of these conveyors has been shown.

Referring now to Fig. 4, I have there illustrated in diagrammatic form certain electrical circuits intended tofacilitate the operation of the apparatus. The motor 33, which actuates the elevating screws 29, is conected to a suitable electrical supply 55 through a reversing switch which includes a group of three normally open contacts I and a group of three normally open contacts 52. The contacts 5I serve to energize the motor 33 for downward movement of the screws, and the contacts 52 serve to energize the motor for upward movement of the screws. The contacts 5l are controlled by a coil 54, which also controls a normally closed contact 55 and a normally open contact 56. The contacts 52 are controlled by a coil 58, which also controls a normally closed contact 59 and a normally open The coils 54 and 58 are arranged to be energized by a suitable electrical supply 62 under the control of two push buttons 55 and 64, and limit switches 65, 61, 58, 'i0 and li. The switch 65 is in a position to be closed by the engagement of the outer end of one of the pusher bars 31 therewith when these bars are retracted. The switch 6l is in a position to be opened by the engagement of one spacer bar S therewith when the spacer bars are level with the hearth II. The switch 68 is so connected to one of the dogs I5 that the switch will open whenever the dogs swing outwardly to allow the upward passage of a pair of spacer bars. The switch 'lil is in a position to be opened by the engagement of one of the beams 28 therewith whenever these beams are raised to a predeter-v mined level. The switch li is in a position to be opened by the engagement of one of the beams 28 therewith whenever these beams are lowered to a predetermined level. The coil 54 is connected in series with the contact 59, the push buttonv 64, the limit switch 63, and the limit switch III, the contact 55 being in parallel with the push button 64. The coil 58 is connected in series with the contact 55, the push button 63, the limit switch 66, the limit switch 6l and the limit switch l5, the contact 60 being in parallel with the push button 63. It will be understood thatthe limit switch 6l is located slightly to the side of one pusher bar 3l so that it will not interfere with the operation of this pusher bar or the withdrawal of the spacer bar S.`

The operation of the invention will now be apparent from the above disclosure. Assuming that no billets are on the hearth II or in the passage I4, two spacer bars and a row of billets will be placed on the car 29, which will then be pushed inwardly through the opening` 24 on to the rollers 25. Push button 63 ywill then be closed, energizing coil 58, closing contacts 52 and 55, and opening contact 59. The motor 33 will then raise the screws 29 and beams 28, which will lift the car 28 with the billets thereon until the spacer bars on the car have passed somewhat above the upper ends of the dogs I5, whereupon the limit switch 19 will be opened, deenergizing the coil 58', opening contacts 52 and stopping the motor. It will be noted that the push button 53 need be closed only momentarily, for the contact 60 will shunt the same as soon as the coil 58 is energized; The yoperator will now close push button 64, energizing coil 54, closing contacts 5I and 56, and opening contact 55. 'Ihe motor 33 will then lower the screws 29 and beams 28 until the car 28 again rests on the rollers 25. The spacer bars S and the layer of billets carried thereon'will however be supported by the dogs I5. Continued downward movement of the beams 28 will open limit switch 'II, deenergizing the coil 54, opening `contacts 5l and 55, and closing contact 55, thus stopping the motor. Momentary closing of the push button 54 is all that is required, for the contact 56 will shunt the same as soon as the coil 54 is energized. The limit switch 68 will prevent lowering of the car until the spacer bar has been raised suinciently to allow the dogs I5 to swing inwardly beneath the same. The contacts 55 and 59 serve as electrical interlocks to prevent simultaneous energization of coils 54 and 58.

The car 20 will now be moved outwardly on to the rollers 26, and two more spacer bars and a layer of billets will be placed upon the car, which will then be pushed inwardly on to the rollers 25,.and the raising operation will be repeated. As the billets carried by the car move upwardly, they will engage the spacer bars which rest on the dogs l5 and lift these -bars with the billets thereon, relieving the dogs I5 of all load, whereupon the upwardly traveling spacer bars on the car will engage the cam surfaces 35 and push the dogs outwardly, the dogs then dropping inwardly beneath the spacer bars. This method oi charging will be continued until the passage I4 is filled with a stack of billets and spacer bars of such a height that one of the topmost spacer bars will engage the limit switch El (upon the raising of the beams 28) and open this switch before the limit switch 'I0 is opened.y This will stop the motor 33 with the upperv surfaces oi the topmost spacer bars at a predetermined elevation substantially flush with the hearth II, and this will be true irrespective of the size oi the billets. The pusher bars 31 will now be moved inwardly through the opening 39, by means of the motor 44, thereby shoving the upper layer of billets laterally on to the hearth I I. The pusher bars will then be withdrawn, and during their outward movement the latches 45 will engage the inner ends of the topmost spacer bars and move these bars outwardly through the opening 39 on to the conveyors 48, along which they will travel to a position near the loading point forthe car 20. The car 28 will continue to add layers of billets to the bottom of the billet stack, and the pusher bars 3l will continue to shove billets from the top oi the stack on to the hearth II until the hearth is filled. It will be noted that unless the pusher bars 3l are fully withdrawn, the limit switch 66 will be open, preventing operation of the motor 33 to raise the beams v28. This avoids the possibility of lifting the billet stack while the pusher ment of the stack will cause the gases to flow in intimate contact with the billets. As a result, the gases will leave the passage I4 at a comparatively low temperature, and the billets will be heated gradually and uniformly from the time they are added to the bottom of the billet stack to the time they are ready to be discharged from the furnace.

The parts are preferably so constructed and arranged that the row of billets on the hearth can be advanved intermittently a distance equal to the Width of one billet by the action of the pusher bars 3l, and for this purpose these pusher bars are adapted to be moved through a comparatively long stroke. This stroke isl preferably sufficient to allow inward movement of the pushers beyond the outer margin of the hearth I I for such a distance as is required to accommodate a complete layer of billets, in lateral contact with one another. Thus the pusher bars can be used to shove the top layer of billets from the stack on to the hearth and cause the entire row of billets to advance along the hearth sufficiently to drop one billet over the discharge knuckle of the furnace, whereupon the pusher bars can be withdrawn to remove the top spacer bars and then returned to advance the entire row of billets intermittently as required by the demands of the rolling mill. During this phase of the operation the car 20 will be withdrawn for a new layer of billets, the billet stack being supported in the meantime by the dogs I5. When the pusher bars have reached the limit of their inward movement, they will be withdrawn, and the motor 33 will be placed in operation to raise a new layer of billets into their path.

It will be apparent that the invention makes possible a very gradual and uniform heating of the billets, and a very eflicient utilization of the heat in the fuel. This is accomplished without requiring an excessively long furnace. The billets travel in counterflow relation to the heating gases, not only in the horizontal passage I2 but also in the vertical passage I4. As a result, the gases leave the furnace at a comparatively low temperature, and no recuperator or other heat-recovery apparatus is necessary. It is accordingly feasible to utilize unheated air for combustion purposes, and excessively high flame temperatures are avoided.

In Fig. '7 I have shown a slightly modified arrangement of the stack of billets. In this arrangement the spacer bars S are inclined slightly at an angle corresponding with the slope of the hearth II. This makes possible a somewhat more direct application of force by the pusher bars 3l.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. The method of heating metal billets comprising the steps ofburning fuel to form a stream of hot gases, moving the billets in a direction opposite to the ow of the gas stream and in heat exchange relation to the gases, thus causing the temperature of the gases to decrease in the direction of the flow of the gas stream, arranging the billets adjacent the higher tem pelature portion of the gas stream in a row with adjacent billets in lateral contact, and arranging the billets adjacent the lower temperature portion of the gas stream to form a stack of comparatively open formation.

2. The method of heating metal billets comprising the steps of arranging some of the billets in lateral contact with each other to form a substantially horizontal row, arranging other billets in superimposed layers to form a stack of comparatively open formation, burning fuel to form a stream of hot gases, passing the gas stream first over the row of billets to heat the same and then downwardly through the stack of billets to heat the same principally by convection, adding billets to the bottom of the stack, elevating the stack, and transferring billets from the top of the stack to said row.

3. The method of heating metal billets comprising the steps of arranging some of the billets in lateral contact with each other to form a substantially horizontal row, arranging other billets in superimposed layers separated by spacer bars to form a stack of billets located adjacent said row, all of the billets being parallel and the billets in each layer of the stack being spaced apart to provide openings for the flow of gases, adding billets and spacer bars to the bottom of the stack, elevating the stack, transferring the top layer of billets in a broadside direction from the stack to the row of billets, removing the spacer bars on which the said top layer had been supported, burning fuel to form a stream of hot gases, and passing the gas stream rst over the row of billets and then downwardly through the stack of billets.

4. A heating furnace for metal billets comprising a hearth, means providing a horizontal passage for the flow of hot gases above the hearth, a vertical flue through which the gases flow from the passage in a downward direction, means to support a stack of billets in the flue in an open formation to receive heat from the gases principally by convection, means to move the stack upwardly, means to add billets to the bottom of the stack, and means to transfer billets from the top of the stack to the hearth.

5. A heating furnace for metal billets comprising a vertical flue through which a stream of hot gases flows downwardly, a hearth adjacent the upper end of the flue, means to support a stack of billets in the flue in an open formation to receive heat from the gases principally by( convection, the stack including horizontal layers of billets with the layers separated by spacer bars, means to move the stack upwardly, means to add billets and spacer bars to the bottom of the stack, means to transfer the top layer of billets from the stack to the hearth, and means to remove from the furnace the spacer bars on which the said top layer had been supported.

6. A heating furnace for metal billets comprising a vertical flue through which a stream of hot gases flows downwardly, the flue being adapted to receive a stack of billets having an open formation to receive heat from the gases principally by convection, the stack including horizontal layers of billets with the layers separated by spacer bars extending transversely of the billets, reciprocable pusher bars arranged to move inwardly through the fiue and shove the topmost layer-of billets broadside from the stack, and latches mounted on the pusher bars and arranged to engage the inner ends of the topmost spacer bars during the outward movement of the pusher bars and thereby removesaid topmost spacer bars from the stack.

STRICKLAND KNE'ASS, JR.

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