Patent Grant
8246901
1. Field of the Invention
The invention relates to a retort furnace for the heat treatment, for example, the blank annealing, annealing under nitrogen or nitrogen/hydrogen, nitriding, or nitrocarburizing of metal workpieces.
2. Description of the Related Art
Retort furnaces for the heat treatment of metal workpieces are known in manifold configurations according to the prior art, for example, according to DE-AS 2 010 433, DE-OS 27 54 034, DE 30 28 952 C2, DE 31 43 532 A1, DE 36 31 389 C2, and DE 103 38 431 A1.
The invention does prefer horizontal retort furnaces, which essentially have a recumbent tubular retort, a furnace housing which encloses the retort with thermal insulation, and a unit for heating the retort, but it is also transferable to other constructions of retort furnaces.
The retort typically has
During the heat treatment, the heating to temperatures up to 650° C. is substantially supported by convection. An effort is made for an intensive circulation of the furnace atmosphere which encompasses the workpieces on all sides within the retort. For this purpose, circulation assemblies and gas guiding aids situated in the area of the retort are used.
In particular during the heat treatment, the retorts are subjected to high strain. They are implemented having wall thicknesses greater than 8 mm because of the dimensional stability.
At least in the retort furnaces of the above-described type, in contrast, spot-shaped stresses result in the lower part of the retorts, which are horizontal in this case, due to the batch weights and the support elements of the receptacle frameworks. It is disadvantageous that the stresses rise with increasing batch weight, while in contrast the carrying capacity of the retort material decreases with increasing furnace temperature. Therefore, the loading capacity and the efficiency of the heat treatment of the workpiece batches of such retort furnaces are limited.
The technical world has already concerned itself with preventing harmful strains of retorts during the heat treatment of metal workpieces. However, such solutions only relate to the relief of the retort floor in the case of vertically situated retorts by supports and/or by load-carrying means for support in relation to a housing as described, for example, in DE 2 054 666 A.
The strain of the retorts due to the batch weights themselves and their receptacle frameworks was taken into consideration, but the efficiency of the heat treatment was not increased.
Furthermore, a compensator technology (IHU) was known from the exclusively vertical furnace construction, in which the entire batch load rests on a heat resistant pedestal made of concrete and is supported thereon. The retort, whose impact is compensated for via a compensator, can thus be implemented having a thinner wall thickness, and its service life lengthens because of the reduced load.
However, in addition to undeniable advantages, disadvantages also result from this solution, such as:
In addition, a heat treatment furnace, in particular a pressure sintering furnace having a furnace housing and an insulation cage, which is held by the furnace housing and forms a boiler room and encloses it at a distance, and a muffle, which is situated in the interior of the insulation cage, envelops the workpiece batch, and delimits an insulation space with the insulation cage, was already described in DE 103 12 650 B3. It also comprises so-called supports as a type of receptacle framework for the batch. Transferring this solution to retort furnaces according to the species of the type described at the beginning would not result in increasing the efficiency of the heat treatment of the workpiece batches and the loading capacity of the retorts.
The object of the invention is, in the case of retort furnaces which essentially have a tubular metal retort, a furnace housing enclosing the retort, and a unit for heating the retort,
The invention fundamentally achieves this stated object in that the weight of the batch and the receptacle framework is decoupled from the retort and the receptacle framework is connected to means for support on the furnace housing and these means are guided gastight in passages of the walls of the retort and the surrounding furnace housing.
In contrast to the prior art, the retort is therefore not only relieved of the weight of the batch and the receptacle framework, but rather the stated object is also achieved of increasing the efficiency of the heat treatment of the workpiece batches, reducing the mass and the wall thickness of the retort, orienting the retort to the function of the gastight closable treatment or batch space, and achieving an increased loading capacity of the retort overall.
In the implementation according to the invention, the receptacle framework is connected by suspension to means for support on the furnace housing.
For this purpose, the furnace housing has crossbeams for attaching the means, and the means are connected via joints to both the receptacle framework and also via the crossbeams to the furnace housing.
The passages in the walls encompass incorporated pipes having gastight compensators, which compensate for a length expansion and ensure a movement freedom of the means in the pipes during heat-related expansions of the retort in particular.
Furthermore, appropriate seals and, in addition, cooling bags, which are filled with a coolant such as water, and insulators for protecting the compensators from high heat are assigned to the pipes having the gastight compensators.
A completed embodiment according to the invention provides that the pipes incorporated in the walls are each partitioned using removable flange connections into a first or bottom part and second or top part, the bottom part being incorporated in at least one of the walls and the top part being incorporated in the crossbeam. The top part has a folded bellows sleeve which assumes the function of the compensator, and the bottom part is enclosed by the cooling bag.
At least one module, which forms the pipes having compensators, such as the top part having the folded bellows sleeve assuming the function of the compensator, or the bottom part enclosed by the cooling bag, is situated so it is replaceable.
Finally, the invention is also implemented in that the retort having the means for support on the furnace housing can be taken out without removing the means in that the wall of the furnace housing has a removably situated segment, which encloses an area of the passages.
Various design solutions may be listed by a person skilled in the art for this purpose, which ensure that at least one of the features relating to the subject matter of the invention is fulfilled, such as
The function of the retort is reduced to the gastight closure of the treatment space solely by these design measures according to the invention, and the thickness of the wall of the retort can thus be reduced from 10 mm to 5 mm, for example.
In addition, the reduction of the wall of the retort causes a more rapid heat conduction through the wall, whereby the heat transfer speed increases.
Through the direct transfer of the heat between the reduced wall of the retort to the batch, the possibility also results of dispensing with gas guiding conduction units such as gas guiding cylinders, which would act as disadvantageous radiation shields in this case. This in turn causes cooler furnace gas to heat more rapidly in contact with the retort.
In the associated drawings
The invention is described in greater detail on the basis of a constructively implemented example.
According to
Heating elements (not shown here), are received by the furnace housing 2, which heat the retort 3 having the treatment or batch space 10 for the heat treatment of the workpieces as a batch in a protective gas atmosphere. In addition, a ventilator unit (not designated) and a conduction unit (not designated) for guiding the protective gas atmosphere in the retort 3 are assigned to the retort furnace 1.
The retort 3 is closed at one end—also not designated here—and is provided at the other end with a charging opening, which is closable gastight by a cover, for the batch.
The implementation of these parts, which are only shown for the sake of completeness but are not designated, are not significant for the function according to the invention here.
In relation to the prior art discussed at the beginning, the invention is distinguished by the combination of the following features with respect to the receptacle framework 8 having the following novel design principle:
This revised principle provides the condition in order to
It can be seen from
Furthermore,
The pipes 6.1 are connected to the crossbeams 9 to form gastight units by means of the compensators 7 and insulators 7.3 as well as seals (not shown). The compensators 7 allow the compensation of movements which the pipes 6.1 experience during the heat-related expansion of the retort 3. The cooling bags 7.2, which are filled with water, for example, and the insulators 7.3 prevent undesirable heating of the compensators 7.
The fulfillment of the stated object of the invention is completed in that the function of the retort 3 is reduced to the gastight closure of the batch space 10 and a more rapid atmosphere change may be implemented and contaminants of the protective gas atmosphere and harmful effects on the heat treatment process are avoided.
The reduction achieved according to the invention of the thickness of wall 3.1 of the retort 3 causes more rapid heat conduction, whereby the efficiency of the heat treatment is increased.
Furthermore, the reduction of the wall thickness causes a decrease of the retort weight. Energy is thus saved during the heating of the furnace to the heat treatment temperature.
Overall, it has been shown that batch weights of up to 5 tons may be heat treated as intended using this design principle according to the invention.
At least one module formed of the pipes 6.1 and the compensators 7 is adapted as a disposable/replacement part, for example, which is shown in particular in
Another advantage of the invention is also effectively realized in that the retort 3 having the supporting means can be taken out of the furnace housing 2 without disassembly of the furnace housing.
For this purpose, the wall 2.1 of the furnace housing 2 has a removably situated segment (not shown in greater detail)—which encloses an area of the passages 6—and which is not described in detail here because of the multiple design possibilities according to the conditions cited at the beginning.
However, in
Overall, the exemplary embodiment shows that to decouple the weight of the batch and the receptacle framework 8 from the retort 3, the receptacle framework 8 is connected by a suspension to means 5 for support on the exterior of the furnace housing 2. The support means 5 are supported on top of the furnace housing by the crossbeams 9 and connected to the receptacle framework 8 and also to the crossbeams 9 by connecting joints 4 on the furnace housing 2.
The invention is not restricted to the design configuration shown in the drawings and described above. Accordingly, to decouple the weight of the batch and the receptacle framework 8 from the retort 3, the receptacle framework 8 can alternatively be connected vertically to support means 5 for support on the furnace housing 2 and the support means 5 can be supported on the bottom by crossbeams 9 on the bottom of the furnace housing 2, for example.
Further design embodiments are possible in the scope of the idea of the invention, of how
The effects achieved by the design arrangement according to the invention of the suspension of the receptacle framework 8 provide a substantial usage value increase and an increased availability of retort furnaces in the applicable industry.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20 2008 009 980 U | Jul 2008 | DE | national |
This application is a Division of International Application No. PCT/DE2009/000963 filed Jul. 13, 2009 which designates the United States. The entire disclosure of said international application is incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20110115138 A1 | May 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/DE2009/000963 | Jul 2009 | US |
| Child | 13012185 | US |
