NO165045B - INDUSTRIAL OVEN FOR HEAT TREATMENT OF THROUGH SUBSTANCES. - Google Patents

Abstract

The furnace (1) includes a furnace chamber (2) which at one end has a charging opening (5) and at the other end a chute (11). Between charging opening (5) and chute (11), there extends an endless conveyor belt (12) which, above the chute (11), is deflected in the direction of the charging opening (5). In order to avoid a constant heat loss through the empty section (17) of the conveyor belt (12) emerging from the furnace chamber, a heat transfer device (15) is provided in the region of the charging opening (5) between the cold working section (14) running in and the hot empty section (17) running out. <IMAGE>

Description

The invention relates to an industrial furnace for the heat treatment of continuous workpieces, as stated in the introduction of claim 1.

In such known industrial furnaces, the working section of the conveyor belt mainly runs horizontally from the inlet opening to the drop chute, where the conveyor belt is diverted 90° downwards,

to exit the oven chamber. Just above the lower end of the fall chute, this opens into a return channel for the return section of the conveyor belt. The conveyor belt is thus redirected through a new 90° in the fall channel, and then enters the return channel. The return channel extends below the actual oven, roughly up to the height of the inlet opening, where the return channel opens into a water siphon. The return section of the conveyor belt is then essentially gas-tight

out of the return channel and into the conveyor belt's drive device.

There, the belt is redirected again, now upwards and in the direction of the inlet opening. Between the drive device and the inlet opening, the conveyor belt passes a kind of table, where the workpieces are placed on the conveyor belt and on its working section then brought into the furnace chamber.

As the process temperature in the furnace is high, the conveyor belt usually consists of interconnected steel spirals and will therefore have a significant heat capacity. In the area near the fall channel, the conveyor belt will therefore take a significant amount of heat out of the furnace chamber. This amount of heat will only contribute to heating the surroundings in the return duct, and is otherwise lost to the treatment process. At the exit from the return channel, the conveyor belt has a temperature of less than 100°C. In the drive device, the conveyor belt is possibly further cooled, before it is loaded with blanks and enters the furnace chamber again through the inlet opening. Within the inlet opening, not only the cold workpieces, but also the cooled working section in the conveyor belt must be reheated to the process temperature. This either entails corresponding cooling of the process gases or necessitates the use of additional heating devices. In all cases, the conveyor belt must be supplied with heat energy again, to

compensation for the one lost in the return channel.

The amount of heat required for heating the conveyor belt may even be greater than the amount of heat required for heating the workpieces.

The purpose of the invention is therefore to provide an industrial furnace where the conveyor belt takes away less process heat.

This is achieved according to the invention by an industrial oven with the

characteristics specified in claim l's characteristics.

Because the return section is led back to the inlet opening inside

in the furnace chamber, the return section temperature will remain the same as the process temperature. The heat transfer device placed in the area of the inlet opening between the return section and the working section will provide a direct heat transfer from the return section to the working section. The heat transfer takes place in a counter current. This achieves two things: the return section is cooled to temperatures that exclude damage to the drive device, so that the parts of the drive device that come into contact with the conveyor belt do not need to be made of heat-resistant material. The heat released during cooling is taken up directly by the work section and transferred to the workpieces placed on it. Without additional external energy supply, the temperature of the working section is thus clearly raised in the direction of the process temperature. The heat energy taken out of the furnace chamber with the return section is transferred to the working section with relatively small losses and is thus returned to the furnace chamber-

A particularly favorable degree of efficiency is achieved when the heat transfer device is mainly arranged outside the furnace chamber.

A very effective and mechanically simple heat transfer device consists of a number of cylindrical rolls of heat-conducting material running across the width of the conveyor belt. These rollers are rotatably stored and extend at right angles to the direction of movement of the working section. The working section will run over the heat-transferring rollers and receive heat from them. Underneath the heat-transferring rollers is the return section, which is kept in contact with the circumferential fins on the rollers by means of pressure devices, so that the working section can transfer its heat to the rollers.

Such a pressure device for the return section can either consist of an essentially flat sliding track or of several pressure rollers stored parallel to the axis of the heat transfer rollers. The first-mentioned embodiment entails the advantage that it is simpler to manufacture, while the second embodiment will entail less drive forces for the conveyor belt. Depending on the design, the pressure rollers or the heat-transferring rollers are stored in an associated sliding guide, so that a respective roller can be moved in the direction of the sliding track or the heat transfer roller.

The heat loss in the conveyor belt can be further reduced if a pre-chamber is placed in front of the furnace chamber's inlet opening through which the conveyor belt passes and which in any case accommodates the heat transfer device and possibly also the drive device, as the pre-chamber has a filling opening for the introduction of workpieces.

Apart from the better thermal insulation, such an antechamber will

greatly prevent air from penetrating into the furnace atmosphere and thus possibly causing an unwanted change in the composition of the furnace atmosphere. The return section of the conveyor belt will, when it exits the furnace chamber, constantly bring furnace atmosphere into the antechamber, which in this way is flushed with furnace atmosphere. In this way, extraneous air that may enter together with the workpieces can be flushed out by the entrained furnace gases, through the filling opening. The above is related to the state of the art

water siphon is therefore no longer necessary.

Because, moreover, both the working section and the return section pass through the inlet opening, the furnace atmosphere loss will be less overall than with previously known designs.

It is particularly advantageous if the filling opening is arranged above the conveyor belt and, seen in the transport direction, in front of the heat transfer device. In this way, the entire length of heat transfer devices is utilized for the transfer of heat from the return section to the working section and to the blanks.

The inlet opening, which is particularly critical with regard to the loss of furnace gas, can be given a reduced light opening if a reversing device for the return section is arranged inside the furnace chamber and near the inlet opening, which reversing device lifts the return section in the direction towards the underside of the working section.

The drawing shows an embodiment of the invention. The drawings show: Fig.l a longitudinal section through an industrial furnace according to

the invention,

fig.2 shows the front chamber of the industrial furnace in longitudinal section,

but on a larger scale and without a conveyor belt, fig.3 shows the antechamber in section along the line III-III

in fig.l,

fig. 4 shows the industrial oven's oven chamber in section after

the line IV-IV, and

fig.5 shows a perspective section of the conveyor belt

as; used in the industrial furnace.

Fig.1 shows an industrial furnace 1 for continuous heat treatment of workpieces, for example for carburizing, nitriding, carbon nitriding or the like. The industrial furnace has an elongated heat-insulating lined furnace chamber 2. In the furnace chamber, heating pipes 3 run from side wall to side wall where burners are placed for heating the furnace atmosphere. The oven chamber 2 has on its end side 4 an inlet opening 5. In front of this there is a straight antechamber 6. The antechamber has a tubular shape and is also thermally insulated. The cross-section of the antechamber's approximately right-angled inner space 7 is flush with the inlet opening 5 and ends outwardly with a filling opening 8. 1 at the other end of the furnace chamber, a drop chute 11 is formed in the bottom 9 through which the workpieces traveling through the furnace chamber leave the industrial furnace 1. For the transport of capacity from the filling opening 8, through the antechamber 6 and through the furnace chamber 2, up to the drop chute 11, the industrial furnace contains an endless, heat-resistant conveyor belt 12 which can be set in motion by means of a drive device 13 placed in front of the antechamber 6. The section of the conveyor belt exiting the drive device 13 forms a working section 14. working section passes through the filling opening 8 and into the space 7 in the antechamber 6, passes there over a heat transfer device 15 described in more detail below, and then enters the inlet opening 5 and into the furnace chamber 2. Inside the furnace chamber 2, the working section is supported by a hearth 10. The hearth is shown in more detail in cross-section in fig.4. At the end of the hearth 10 facing the fall chute 11, a reversing device 16 for the conveyor belt 12 is arranged inside the furnace chamber. The reversing device is here formed by a freely rotatable cylindrical roller inside the furnace chamber 2. The width of the roller corresponds to the width of the used conveyor belt 12. In this way, the conveyor belt 12 is diverted over the chute's opening approx. 180° and goes back in the direction of the drive device 13. Objects lying on the working section 14 will thereby fall into the chute 11 and leave the furnace chamber 2. The section of the 'conveyor belt 12 that goes back, the return section 17, goes through the furnace chamber train back to the inlet opening 5.

In the vicinity of the inlet opening 5, there is a roller 18 which lifts the free-hanging return section 17 up towards the underside of the working section. This means that the inlet opening 5, through which the return section exits the furnace chamber, only needs to have a small light opening height. From the inlet opening 5, the return section goes to the heat transfer device 15 present in the antechamber 6, and then out through the filling opening 8 and into the drive device 13. The drive device 13 mainly includes two axis-parallel and rotatably stored rollers 19,20. The roller 19 acts as a tension roller for the conveyor belt 12, while the roller 20 can be driven slowly by a gear motor 21, for operation of the conveyor belt 12.

It should also be mentioned that under the roof of the oven chamber 2 there is a motor-driven ventilator 22 for influencing the oven atmosphere. The furnace atmosphere is monitored with regard to composition and temperature with a partial pressure probe 23 and a thermometer 24 .

The mentioned hearth 10 arranged inside the oven chamber 2 mainly consists, see fig. 4, of two parallel rails 25 and 26 running at a distance from each other. In the design example, these are attached to 4 cross beams 27 in the oven chamber. The beams 27 are loosely inserted into corresponding recesses 28 and 29 in the liner 31 in the oven chamber 2, see fig. 4.

As the angular rails 25 and 26 are to support the working section of the conveyor belt, they have a mutual distance which corresponds to the width of the conveyor belt. The conveyor belt has guide strips 32 and 33 placed along the edges. The purpose of these is to prevent items from falling off the belt.

With reference to Fig. 2 and 3, the heat transfer device 15 will now be described in more detail. The heat transfer device is located in the antechamber and is located between the conveyor belt's working section 14 and the return section 17.

the direction 15 serves to transfer it with the return section 17

out of the furnace chamber 2, heat is constantly carried over to it into the antechamber 6 and from there into the furnace chamber 2's inflow working section. Thereby it is achieved that the working section 17 is cooled to a manageable temperature after it has left the furnace chamber 2, so that no special heat-resistant measures or components are required in the drive device 13.

one, the heat produced by the return section is transferred to the working section 14, so that the heat loss from the furnace chamber 2 is thereby kept as low as possible.

In a realized industrial furnace, the following temperatures were measured on the conveyor belt: The return section 17 going out of the opening 5 had the same temperature as in the furnace atmosphere, that is approx. 800°C. At the end of the heat transfer device 15, that is near the filling opening 8, the return section had cooled from the aforementioned 800°C down to about 60°C.

The heat released below was transferred to the working section 14 covered with blanks, which at the filling opening 8 had a temperature of 40°C and at the inlet opening 5, after the heat transfer 15, was already heated to 600°C.

It should thus be clear that the heat transfer device

15 enables a clear improvement of the heat balance, because

in the heat given off by the return section 17 is not lost to the surroundings, but can be used for heating the working section 14 and the blanks.

In the design example, the inner space 7 of the antechamber is limited

) of a right-angled steel tube 41 in cross-section which extends

from the opening 8 and to the outside of the oven chamber's end wall 4. The steel pipe therefore forms the bottom 42, two parallel side walls 43,44 and the roof 45 in the antechamber's inner space 7. The antechamber's thermal insulation is placed on the outside of the steel pipe 42, if

>light opening width corresponds to the 12 width of the conveyor belt.

The heat transfer device 15 inside the steel pipe 41 is formed

of a total of 5 parallel and spaced apart rollers 46a to 46e. Each such roller consists of a steel tube with a width corresponding to that of the conveyor belt and placed at right angles to the direction of movement of the conveyor belt. The rear sides of the respective belt sections 14 and 17 are kept in contact with these steel pipes 46a to 46e, so that a thermal contact or a thermal bridge occurs between the two belt sections 14,17 running in opposite directions. The return section 17 runs on a flat and horizontally running sliding track 47 attached to the bottom 42, the width of which is slightly smaller than the distance between the conveyor belt's two guide strips 32 and 33, see fig.3. This provides a flat support for the return section 17 where the workpieces lie on the conveyor belt, and it is prevented that the conveyor belt 12 with associated guide strips 32,33 curves up from the sliding path 47. The sliding path 47 extends from the filling opening 8 to the inlet opening 5. There goes the sliding path into an inclined ramp 48 that extends into the furnace chamber 2. On the back of the return section 17 supported by the sliding path 47, the five heat transfer rollers 46a to 46e will be fitted, where the rollers can move relatively freely in height. The working section 14 runs in the antechamber 6 with its rear side towards the circumferential fins of the heat-transferring rollers 46a to 46e and is held in contact with the rollers under the influence of its own weight. The heat transfer rollers made of heat-conducting and heat-resistant material have an outer diameter between 10 and 80 mm, preferably

a diameter between 10 and 50 mm, and a mutual center distance of approx. 100 mm, whereby a significant suspension of the conveyor belt 12 between two adjacent heat transfer rollers is prevented.

In the two side walls 43 and 44, respective right-angled openings or slots 49a to 49e have been taken out. Here, the ends of the heat-transferring rollers 46a to 46e protrude with a relatively large radial clearance, as the length of the rollers is greater than

while the free distance between the two side walls 43 and 44. To prevent the heat-transferring rollers from gradually moving out

in the axial direction, outside the inner space 7 at each side wall 43 and 44 is attached a deflected flange 51,52 which only serves as a bearing surface for the respective adjacent end side of the heat-transferring rollers 46a to 46e.

When the guide strips 32 and 33 on the conveyor belt 12 protrude also on the back, more about this below, it will be necessary to step off the roller ends, as shown in fig.3,

thereby preventing the conveyor belt from going with its strips 32, 33 against the rollers 46a to 46e. In that case, the rear of the conveyor belt 12 will not be properly installed. If the cylindrical tube is used for the heat-transferring rollers 46, as is the case here, then it will be sufficient to insert cylindrical end tubes 53, in order thereby to achieve the desired taper in the end portions.

In order to prevent outside air from flowing into the oven chamber 2 to the greatest extent possible, a flap 54 is freely suspended above the filling opening 8. This flap slides on the working section 14 and is swung up by the passing workpieces lying on the conveyor belt. Furthermore, a flame curtain can be provided between the working section 14 and the return section 17 by means of burner nozzles 55. Such a flame curtain will further seal against the ingress of outside air. Should outside air still get into the antechamber, then such outside air will be flushed out by the oven atmosphere that leaves the antechamber 6 through the filling opening 8, which is particularly facilitated if the conveyor belt,

as shown in fig.5, is made particularly gas permeable.

A small flushing of the antechamber will then constantly take place

6 with oven zaimosphere over the entire cross-section of the inner space 7, which will effectively prevent air ingress into the oven chamber 2.

The conveyor belt 12 shown in a perspective section in Fig. 5 is made up of several flattened wire spirals 56a to 56c extending across the longitudinal direction of the conveyor belt. Adjacent wire spirals 56a, 56b respectively. 56b, 56c, are connected to each other by means of a respective round bar 57a to 57d. At each spiral end, two plates 58a to 58d are threaded onto each round rod. These plates form the previously mentioned guide strips 32 and 33. As shown, the plates are placed two by two adjacent round bars so that you get the overlap of the plates in the longitudinal direction of the conveyor belt shown in Fig.5.

Outside the plate 58a to 58d, the round bars 57a to 57d are bent off against an adjacent round bar and bent back into a hook shape with a grip around the adjacent round bar.

If the frictional forces acting on the sliding path 47 are too great, then it will also be possible instead of the continuous sliding path 47 to arrange further rotatably supported rollers under each of the heat-transferring rollers 46a to 46d, so that only unwinding movements will take place between the conveyor belt and the parts in the antechamber 6 that come into contact with the conveyor belt.

Claims (13)

1. Industrial furnace for the heat treatment of continuous workpieces, with a furnace chamber (2) which at one end has an inlet opening (5) and at the other end has a drop channel (11), with an endless conveyor belt (12) which at least with its workpiece carrying working section (14) passes through the furnace chamber from the inlet opening and to the drop chute, and with a drive device (13) for the conveyor belt, which conveyor belt in the area of the drop chute (11) is diverted against the direction of transport of the workpieces, as the working section (14) enters the furnace chamber (2) through the inlet opening (5) and the workpieces advanced on the conveyor belt exit the furnace chamber (2) through the drop chute (11), as well as with a second reversing device (20) for the conveyor belt arranged outside the furnace chamber and adjacent to the inlet opening, characterized in that the return section of the conveyor belt (12) (17) goes back inside the furnace chamber (2) and out through the inlet opening (5), and in that at the end of the conveyor belt adjacent to the inlet opening (5) there is a nordnet a heat transfer device (15) between the conveyor belt's return section (17) and the working section (14). 2. Industrial furnace according to claim 1, characterized in that the heat transfer device (15) is mainly located outside the furnace chamber (2). 3. Industrial oven according to claim 1, characterized in that the heat transfer device (15) is formed by several cylinder-shaped or cylindrical rollers (46a-46e) of heat-conducting and heat-resistant material running across the width of the conveyor belt (12), which rollers are rotatably stored and have contact with the working section ( 14), the return section (17) being kept in contact with the peripheral surface of the heat-transferring rollers (46a-46e) by means of pressure devices (47). 4. Industrial furnace according to claim 3, characterized in that the pressure device is formed by an essentially flat sliding track (47) along which the return section (17) slides and is supported by, and that each of the heat-transmitting rollers (46a-46e) is freely movable in right angle to the surface formed by the sliding track (47). 5. Industrial furnace according to claim 3, characterized in that the pressure device is formed by pressure rollers stored parallel to the axis of the heat-transferring rollers (46a-46e), and that for storage either of each pressure roller or of each of the heat-transferring rollers a sliding guide is arranged, in which each roller has a vertically displaceable guide 'in the direction of the other roller. 6. Industrial oven according to claim 1, characterized in that a pre-chamber (6) connected to the oven chamber through the inlet opening (5) is connected to the oven chamber, through which the conveyor belt (12) runs, and in which at least part of the heat transfer device (15) is located, which antechamber (6) has a filling opening (8) for introducing the blanks. 7. Industrial furnace according to claim 6, characterized in that the filling opening (8) is located above the conveyor belt and, seen in the direction of transport, in front of the heat transfer device (15:). 8. Industrial oven according to claim 7, characterized in that inside the oven chamber (2) and in the vicinity of the inlet opening (5) there is arranged a further reversing device (18) for the return section (17), with which the return section is guided up towards the underside of the working section (14). 9. Industrial furnace according to claim 3, characterized in that the heat-transferring rollers (46a-46e) are cylindrical tubes, the diameter of which lies between 10 mm and 80 mm, preferably between 10 mm and 50 mm. 10. Industrial furnace according to claim 1, characterized in that, viewed parallel to the direction of movement of the conveyor belt (12), the heat transfer device (15) has a length of between 0.5 m and 2 m. 11. Industrial oven according to claim 3, characterized in that at least five equally spaced rollers (46a-46e) are arranged as heat transfer device (15). 12. Industrial furnace according to claim 1, characterized in that the conveyor belt (12) is gas permeable. 13. Industrial oven according to claim 12, characterized in that the conveyor belt (12) consists of a number of spirals (56a-56c) arranged parallel to each other, adjacent spirals being connected to each other by means of a respective rod running through two neighboring spirals (57a-57c ).