JPS6023175B2 - Metal strip heating method and heating furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for directing a stream of hot gas (this term includes gas mixtures) over an object that needs to be vertically processed or that needs to be held at a predetermined temperature. The invention relates to a heating furnace of this kind, in particular (but not exclusively) for heating strip or sheet material (hereinafter simply referred to as strip).

When objects need to be heated to high temperatures, large gas flows are required, which can result in large heat losses.
Although in a few cases such heat losses can be reduced to some extent by gas circulation, practical problems have limited the effectiveness of such techniques.

That is, for a few applications, the gas must pass through narrow passages that present considerable resistance to gas flow, in which case it is necessary to exert pressure on the gas to obtain the required circulation. , compressor, or similar equipment is required. However, there is an upper temperature limit at which pressurizing devices of this type, such as those currently in use, can operate satisfactorily for only a certain period of time. According to one aspect of the invention, a furnace chamber having a longitudinal strip bearing surface therein and a gas cushion for providing a gas cushion between the strip bearing surface and a metal strip traveling within the furnace chamber; In a heating furnace equipped with a gas and a supply gas supply device, a recirculation flow path for the furnace chamber gas is formed in the furnace chamber, and the gas supply device recirculates the furnace chamber gas using the supplied supplementary gas. It has an incentive system that promotes

Such a construction allows the pressure energy required to produce rapid circulation of the gas to be delivered to the gas without the need for placing a blower, compressor or other device (hereinafter simply referred to as blower means) into the circulation flow circuit. Since the blower means can be operated at a temperature lower than the temperature of the circulating gas inside the furnace chamber, the energy level of the gas introduced into the chamber is between 2 and 6 times the self-weight of the gas. It has been discovered that double the amount of gas circulation could easily be made to occur along the gas circulation circuit. At the same time, gas circulation in the furnace has the effect of lowering heat losses, which would be large if the gas were allowed to escape freely into the atmosphere after passing over the object. Of course, it is impossible to prevent a certain amount of gas from escaping the furnace;
It is desirable to introduce a fresh passage of gas into the blower means to compensate for losses incurred, and preferably the furnace has an injector for circulating gas through the chamber. One or more internal passageways are provided for returning to the vicinity of the means.

the gas is heated outside the furnace, and/or
Alternatively, it can be heated by heater means placed inside the furnace. The main heat source for the object may consist of circulating gas. The heating capacity of the gas can be supplemented, for example, by electric resistance heating elements mounted on the furnace head or by direct radiant heat from gas-fired heat sinks. Alternatively, the primary source of thermal energy for the object may be provided by a heater, such as an electrical resistance heating element, located within the furnace chamber. In two or three cases, a portion of the gas which has passed over the object is circulated through blower means and leaves the chamber if the temperature of the hot gas exceeds the temperature at which said blower means can operate satisfactorily. Means such as a heat exchanger may be provided to cool the gas.

In a few cases, means may also be provided for varying the proportion of recycled gas and fresh gas delivered into the chamber.

For two or three purposes, by using the heat exhausted from the gas to heat the fresh gas introduced to the blower hand before it is introduced to compensate for gas losses from the device. Heat loss from the device can be further reduced.

However, in a few cases, the recycle gas and the fresh gas may be mixed directly in suitable proportions before being introduced into the blower means, thus eliminating the need for additional cooling means. , the gas temperature can be reduced to a temperature at which the blower means can operate satisfactorily.

For example, the invention applies to a furnace containing an object in a chamber such that the gas is directed onto the surface of the object in the form of a number of jets that present considerable resistance to gas flow.

Such furnaces are used for jet heating objects in the form of sheets or strips of material, by forcing gas under pressure through a suitably apertured plate, commonly known as a jet plate. A jet is obtained, in which case a reduction is applied to the gas flow in order to compensate for pressure losses in the circuit, which are particularly high when passing through the jet plate and when passing through the heater or heat exchange means used to generate the thermal energy. It is necessary to apply pressure energy. However, the invention also applies to furnaces in which the objects are housed in baskets or pans so as to offer considerable resistance to gas flow.

In this case, with the aim of producing a high, uniform heat transfer level,
High pressure energy is required to force the gas flow through and between the objects. Particularly in the case of heat treatment of metal strips, the furnace has a considerable length in order to carry out the appropriate heating of the strip as it passes through the furnace chamber; A plurality of blowers are preferably introduced into the chamber through a plurality of injector means spaced at regular intervals along the length of the chamber, each supplying gas to one or more injector means. However, it is also possible to use a single blower means in common for all injector means.

When a furnace is used to heat a strip of metal or other material, said strip being fed into a chamber of the furnace substantially horizontally or at a slight angle, the injector means direct the gas under pressure. Injected into the lower part of the chamber, gas may be passed through the chamber and upwardly to provide a gas cushion that acts as a support for the strip passing through the chamber. Accordingly, in another aspect of the invention, a continuous heat treatment furnace for metal strip, wherein the strip is supported on a gas cushion as the strip progresses through the furnace, comprises a furnace chamber including a longitudinal metal bearing surface; injector means for directing gas under pressure into the furnace chamber so as to cause rapid circulation of at least a major portion of the gas within the furnace, and so as to create a gas cushion intermediate the bearing surface and the metal strip traveling through the furnace. and means for directing circulating gas onto the strip bearing surface.

Preferably, the gas introduced into the furnace is dense to limit the volume required for supporting the strip.

If a light gas such as hydrogen is used, a large amount of gas will have to be used. Furthermore, the gas can be selected to create a protective or reducing atmosphere within the furnace chamber. As an example,
The gas is a mixture of nitrogen and hydrogen; in other examples, nitrogen is a mixture of hydrogen. The furnace chamber may be provided with a plurality of lateral baffles that divide the lower part of the furnace into a plurality of compartments into which gas under pressure can be directed.

The gas flow rate into each compartment can be controlled independently of the gas flow rate into other compartments, thus making it possible to adjust the floating height of the strip in each zone of the furnace as desired. It is possible. Such possibilities arise, for example, when passing the strip through the furnace or if the thickness of the strip passing through the furnace varies, and also because of any fluctuations in the strip, furnace or gas flow locally with respect to flotation. This is useful when a problem arises.

In a few cases, different gases at different temperatures are fed in through the same injector means, but with such a construction the proportions of the gas components are controlled in different parts of the furnace or on a time basis. Each gas flow rate can also be adjusted to vary the .

The present invention will be described below with reference to embodiments shown in the drawings.

Referring first to FIGS. 1 and 2, the illustrated furnace is constructed for heating continuously moving metal strip and has an elongated chamber 2 through which the strip is fed substantially horizontally, and The furnace is closed at both ends except for a narrow horizontal slot 3 for the insertion and removal of the strip therein.

An inner wall 6 is arranged between the two side walls 4 and 5 of the heating furnace,
This inner wall runs along the entire length of the furnace adjacent to the side wall 4;
The inner wall 6 and the other side walls 5 delimit the furnace chamber and these inner walls 6
A horizontal plate 7 is provided between the side wall 5 and the side wall 5. This plate 7 has a plurality of gateways 8, and is located slightly below the slot 3, as shown in FIG. The strip is heated by a gas or gas mixture passed into the chamber by a suitable blower 9 and means of a suitable type for heating this gas to a suitable temperature are provided as indicated at 10. It is placed between the blower and the chamber, or alternatively, the gas is heated after it enters the chamber. Under pressure gas is introduced into the lower part of the furnace through a plurality of injectors 11 arranged at regular intervals along the side wall of the furnace so as to direct the gas into the chamber midway between walls 5 and 6; The pressure is such that the gas is forced upwards through the openings 8 in the horizontal plate 7 and directed in the form of a jet to the underside of the strip.

Moreover, at such a gas velocity injected into the furnace, the gas heats the strip 1 and then passes at high speed from the top to the bottom of the chamber through the passage 12 intermediate the inner wall 6 and the side wall 4. A sufficient pressure drop for circulation is created near the injector 11.

By circulating the gas through the furnace in this manner, heat losses are significantly reduced and the need for a blower in the gas circulation path is eliminated. A portion of the gas escapes from both ends of the furnace, but this loss is compensated by fresh gas sent to the proar through the inlet tube.

In the second furnace shown in FIG.
instead of an internal heater, e.g. an electrical resistance heating element 14
These heaters are suitably mounted against the furnace walls 5 and 6 below the plate 7.

Additionally, a portion of the gas from the top of the chamber 2 is recycled to the blower 9 to reduce the amount of fresh unheated gas required. Since the temperature of the gas leaving the chamber 2 is usually higher than can be reliably withstood by a conventional blower, a heat exchanger 15 is provided between the chamber and the blower 9 to cool the gas. .

means (not shown) for varying the proportions of recycle gas and fresh gas sent into the furnace through the injector 11;
is provided.

Also, as shown at 14, an electric heating element may be additionally arranged in the passageway 12 or in place of the heat transfer element 14.

Other forms of heating means can also be used, for example a gas burner located at the bottom of the chamber. In the second variant furnace shown in FIG. 4, a heat exchanger 10 is used to increase the temperature of the fresh make-up gas before it enters the proa 9, thereby further reducing the heat losses of the system. .

In a few cases, no heat exchanger is used at all, and the fresh gas at a suitably low temperature is mixed with the recycle gas in appropriate proportions to cool the recycle gas before it returns to the blower. Make it. In each of the furnaces shown, the strip 1 is fed horizontally through the furnace, but it is also possible to feed the strip vertically or along an inclined plane into the furnace, in which case the injector 11 is fed horizontally through the furnace. The structure of the furnace, such as its layout, will be changed accordingly.

However, if the strip is fed horizontally or slightly downwardly at an angle, the pressure of the gas injected into the furnace will not only heat the strip, but also create a A gas cushion may be present.

In such cases, the lower portion of the chamber of a furnace such as that shown in FIGS. The upper ends of the lateral vertical walls end just below the level of the slots 3, allowing each compartment to be associated with a respective injector 11.

Such a structure prevents local flotation from occurring due to other conditions existing in other areas of the furnace;
Also, for example, by controlling the gas flow through each injector 11 or by closing the return passage 12 against a lateral wall (
(not shown) makes it possible to adjust the gas flow in a particular area by dividing it into a plurality of separate compartments and throttling the appropriate area. In the second and third cases, it is necessary to direct the hot gas in the form of a jet against both sides of the strip 1, and a furnace for carrying out this purpose is shown schematically in FIG. In this furnace, the heating furnace chamber 2 has a pair of horizontal jet plates 7A and 7B arranged above and below the pit hole 3, and these plates allow the gas coming from the injector 11 to pass through the holes 8 of the plates 7A and 78, respectively. The velocity of the gas directed into the furnace through the inductor 11, which is arranged to be directed towards the upper and lower surfaces, is such that the gas is returned from the middle part of the plate through the passage 12 to the main part of the furnace, in which the gas is It is directed through the holes in the jet plate to the strip, again as shown in FIGS. 1-4.

The furnace shown in FIGS. 6 and 7 also has a structure for heating a continuously moving metal strip 1 and has an elongated chamber 2 through which the strip is fed horizontally or in a slightly downwardly inclined direction.

More specifically, the furnace has a water-cooled inlet section 14, a heating section 15, and an outlet cooling section 16. The inlet to the furnace as well as the outlet 2 from the inlet are provided with pressure seals 17 to minimize gas loss to the atmosphere. The strip is fed into the furnace along a floating table 17, and is conveyed from the furnace to the roller table 1 by a pair of pinch rolls 20'.
It is pulled out on top of 9. As mentioned in the previous embodiment, the gas under pressure passes through the engine 11 to the heating zone 15.
The gas is compressed in a blower 9 and passed through a heater 10 into a manifold 21 that communicates with each injector.

The lower part of the heating zone 15 is divided into several sections by a plurality of spaced transverse vertical walls 22 .

The upper edge of the wall 22 terminates just below the furnace inlet and outlet levels, and each compartment is supplied with compressed gas through a respective injector 11 or batch. Such a structure prevents large local flotation from occurring due to different conditions existing in other parts of the furnace, and also controls the flow of gas through each injector 11, etc. within each zone. It is also possible to adjust the flow. As shown in FIG. 7, each injector 11 extends through the heat-resistant lined side wall 4 of one of the furnaces and directs the compressed gas into the enrichment chamber 2 through an inlet 23 made in the hearth.
Discharge into 4.

The hearth comprises two vertical walls 25, 26, each having at its upper end a lip 27 angled outwardly at a small angle and running horizontally along the entire length of the hearth. Heat transfer elements 28 are mounted on the side walls of the chamber.

Also provided in the upper part of the side wall 4 is a conduit 29 for conveying gas from the chamber to an external gas circulation circuit. This external gas circulation circuit includes a cooler 30, a blower 9, a dryer 32, and a heater 1.
0 and 2 injector manifolds 21. The compressed gas is sent from the mamanifold 21 to the injector 11'. In operation of the furnace illustrated in FIGS. 6 and 7, the metal strip is introduced into the furnace through the inlet seal 17 and, as it passes through the chamber, fills the enrichment chamber 2.
It is held above the lip 27 by being supported on a cushion of gas sent from the 4. The enrichment chamber 24 receives pressurized gas from the injector 11. Gas jets coming from injector 11 cause gas already present in the furnace to flow through passage 23 into enrichment chamber 24. 7th
As shown by the arrow in the figure, the gas coming out of the enrichment chamber 24 passes between the opposing surface of the lip 27 and the strip.
It returns to the vicinity of the injector 11 through the side channel 32 and is fed into the enrichment chamber 24 again. A portion of the cycle gas is withdrawn from the furnace through conduit 29, cooled, then compressed, dried, heated, and then returned to the furnace through injector manifold 21. Processing in which the amount of gas required to generate the heat to raise the strip to the required temperature and at the same time the amount of gas required to support it during passage through the strip furnace corresponds to each other. In this case, no additional heat source other than the thermal energy contained in the gas is required.

That is, in the illustrated furnace, thermal energy input to the gas is obtained from heater 10 and heater element 28 is removed or turned off. However, for processes where the amount of strip passing through the furnace is large and/or the desired strip temperature exceeds the gas temperature, additional heat sources are required. In these cases, the electrical resistance heating element 2
8, or a gas radiator tube placed in the chamber produces direct radiant heat to heat the strip. Such conditions are found during the freezing process of strips produced by roll compaction of metal powder, in which case the desired temperature for Fusen steel is in the range 1000-1400 qo. By using the injector 11, it is economically and easily possible to rapidly circulate the internal gases of the furnace to produce the large gas volumes required to support and heat the strip within the furnace. Ru. Such conditions are particularly important where the nature of the heated strip requires relatively expensive furnace gases. For example, in the case of fusen steel strip made by roll compacting ferrous steel powder, an injector is used to feed the bearing gas into the bottom of the furnace chamber in an atmosphere consisting of a gas mixture of argon gas and hydrogen. It is desirable to carry out sintering, in which case the gas mass that can be delivered into the enrichment chamber 24 is increased by a factor of 2:1 to 6:1 due to the induced internal circulation compared to the gas mass that is delivered outside the interior. Ru. Further, even greater savings can be made by withdrawing some of the gas that has passed over and past the strip to the outside of the furnace for circulation to the blower compressor 9 and back into the furnace.

[Brief explanation of the drawing]

1 and 2 are a perspective view and a cross-sectional view of a first embodiment of a heating furnace according to the present invention, FIG. 3 is a cross-sectional view of a second embodiment of a heating furnace according to the present invention, and FIG. is a modified view of the heating furnace of FIG. 3, FIG. 5 is a cross-sectional view of another embodiment of the heating furnace according to the present invention, and FIGS. 6 and 7 are diagrams of still other embodiments of the heating furnace according to the present invention. , respectively, are a plan view and a cross-sectional view. 1...Strip, 2...Chamber, 3...Slot hole
, 4, 5...Side wall, 6...Inner wall, 7...Plate, 8
...Sekiguchi, 9...Proa, 10...Heating means, 1 1
... Injector, 12... Circulation passage, 13... Fresh gas introduction pipe, 14... Heater, 15... Heat exchanger, 2
1... Manifold, 22... Partition wall, 23...
Opening, 24... Full chamber, 26, 27... Lip,
28... Heater, 29... Conduit, 30... Cooler, 3
1...Drya. Boat going. Z by G. 2. Persimmon G. 3. Persimmon G. 4. Thousand ships. 5. FIG. 6 FIG. 7

Claims (1)

[Scope of Claims] 1. A furnace chamber having a longitudinally extending strip bearing surface therein, and a supply of gas to provide a gas coupling between said strip bearing surface and a metal strip advancing within the furnace chamber. In the heating furnace, a recirculation flow path for the gas in the furnace chamber is formed in the furnace chamber 2, and the gas supply device recirculates the gas in the furnace chamber by the supplied supplementary gas. A heating furnace characterized by having an injector 11 that promotes. 2. Said strip bearing surface consists of a plate 7 with a number of openings 8, said plate 7 being located directly below the path followed by the metal strip during its progress through the furnace, and said recirculating gas passing through said openings 8 in said plate 7. 2. A heating furnace according to claim 1, wherein the metal strip passes upwardly into contact with the underside of a metal strip traveling through said furnace chamber. 3. said strip bearing surface comprises two substantially parallel members 2;
5, 26, and the two members 25, 26 are provided at a distance smaller than the width of the metal strip to be heat treated in the furnace, as set forth in claim 1. heating furnace. 4. The heating furnace according to claim 3, wherein the substantially parallel members 25, 26 have their upper ends inclined outwardly at a small angle with respect to the horizontal plane. 5. The strip bearing surface consists of vertical walls 25, 26 having an outwardly inclined strip 27 at its upper end;
Claim 1, characterized in that the recirculating gas is configured to flow through the groove (24) formed by the vertical walls (25, 26) and along the lip (27).
Heating furnace described in section. 6 the lower part of the furnace chamber is divided into several compartments by a plurality of regularly spaced transverse vertical walls 22;
6. A furnace according to claim 1, characterized in that the upper edge of the wall (22) terminates directly below the level of the inlet and outlet levels of the metal strip. 7. The small amount of gas being recirculated in the furnace chamber is
Claim 1, characterized in that it is drawn out of the furnace chamber via an external conduit 29, by which it is conveyed to the blower 9, compressed and reintroduced into the furnace through the injector 11. The heating furnace according to any one of items 1 to 6. 8. The heating furnace according to claim 7, wherein a heater 10 for heating gas is provided between the blower 9 and the injector 11. 9. The heating furnace according to claim 7 or 8, wherein new gas corresponding to the loss that escaped from the furnace chamber is sent to the blower. 10. A furnace as claimed in any one of claims 1 to 9, characterized in that a plurality of electrical heating elements (28) are mounted within the furnace chamber for heating the recirculated gas. 11 In a method of heating a metal strip while providing a gas cushion by supplying gas between the strip bearing surface extending in the longitudinal direction inside the furnace chamber and the metal strip, the gas inside the furnace chamber is heated by supplying supplementary gas from an injector. A method of heating a metal strip, characterized in that the metal strip is recirculated.