Air cooling device and gradient descent furnace

Abstract

The invention discloses an air cooling device and a gradient descent furnace, and the air cooling device comprises an air cooling cylinder which is sleeved on a gradient furnace tube section of a gradient descent furnace tube in a gradient region; the cooling fins are arranged on the air cooling cylinder in an annular array mode, upward air grooves are formed between the adjacent cooling fins, and an annular array assembly is formed; the surrounding cover is arranged on the annular array assembly in a sleeving mode and matched with the upward air groove to construct an upward air channel, the height of the surrounding cover is smaller than that of the cooling fins, the surrounding cover is arranged in the middle of the annular array assembly, an air outlet is formed in the upward air groove part exposed out of the upper portion, and an air inlet is formed in the upward air groove part exposed out of the lower portion; the air supply cavity is an annular cavity, is arranged at the radiating fins on the lower side of the enclosure in a surrounding manner and is communicated with the air inlet; and the air supply device supplies cooling air to the air supply cavity. According to the air cooling device, the target temperature gradient can be obtained more easily.

Description

Technical Field

[0001] The invention relates to an air cooling device suitable for a gradient descent furnace, and also relates to a gradient descent furnace equipped with the air cooling device. Background Art

[0002] A temperature gradient furnace is a furnace that is divided into different temperature zones according to the different temperatures of the various zones in the furnace. Each zone corresponds to a corresponding temperature, and there are effective insulation devices between the temperature zones. The "insulation" involved is actually insulation under the condition that the temperature zones are connected, and is actually formed by external forced cooling. The gradient descent furnace in the embodiment of the present invention is a temperature gradient furnace.

[0003] A descending furnace is a process equipment used in the field of materials science, and can also be called a vertical lifting heat treatment furnace. It mainly includes an upper furnace body and a lower furnace body, and a gradient zone between the upper furnace body and the lower furnace body. It is also equipped with a lifting mechanism, a heating system and a control system. Since the latter three are not related to the improved parts of the present invention, they will not be repeated here.

[0004] The descending furnace is mainly used for the workpiece to stay in different temperature zones for a specified time to achieve a predetermined heat treatment effect. There may be a large temperature gradient between the two temperature zones, which is called a gradient descending furnace. Obviously, for a descending furnace, in order to meet the transfer of workpieces between the two furnace bodies, the upper furnace body and the lower furnace body should be connected. The realization of the temperature gradient is on the one hand due to the process temperature in the upper furnace body being higher than the process temperature in the lower furnace body, so that no heat convection will be generated. At the same time, in order to reduce the thermal impact of the upper furnace body on the lower furnace body, it is often necessary to use forced cooling in the gradient zone to cool down the section, thereby forming a transition zone and forming temperature isolation.

[0005] At present, the down-going furnace mainly adopts forced cooling, but the commonly used cooling method is mainly to configure a water jacket in the gradient zone, and then cool the gradient zone with the help of a cooling circulation pump and a water tank. The process temperature of the down-going furnace is often very high. Although the cooling water tank has better cooling capacity due to the relatively large specific heat capacity of water, the cooling cycle is often implemented in a relatively closed circulation system, and the water in the water tank will quickly reach the boiling point. Although the water in the water tank can also be cooled in some implementations, such as setting an evaporator or configuring an air cooling device for the water tank separately, it is bound to increase the cooling link of this equipment, and the overall structural size is relatively large. In particular, as the water temperature increases, the demand for adjustable temperature gradient will be realized under the condition of dynamically variable cooling medium, and the overall implementation difficulty is relatively large. Summary of the invention

[0006] The object of the present invention is to provide an air cooling device which is relatively easy to adjust the temperature gradient and more easily obtain the target temperature gradient by means of air cooling instead of liquid cooling. The present invention also provides a descending furnace equipped with the air cooling device.

[0007] According to a first aspect of an embodiment of the present invention, there is provided an air cooling device for cooling a gradient zone of a gradient descent furnace, the air cooling device comprising: An air cooling cylinder is mounted on a gradient furnace tube section of a gradient descending furnace tube located in a gradient zone; The heat sink is arranged in an annular array on the air cooling cylinder, and upward wind slots are formed between adjacent heat sinks to form an annular array assembly; A shroud is mounted on the annular array assembly and cooperates with the upward wind slot to construct an upward wind duct, and the height of the shroud is shorter than the height of the heat sink, and is centrally arranged on the annular array assembly, and the upper exposed part of the upward wind slot constitutes an air outlet, and the lower exposed part of the upward wind slot constitutes an air inlet; The air supply cavity is an annular cavity, which is arranged around the heat sink on the lower side of the enclosure and is connected to the air inlet; and An air supply device supplies cooling air to the air supply cavity.

[0008] Optionally, the heat sink has a notch in the middle or is composed of an upper heat sink and a lower heat sink with a given distance between them.

[0009] Optionally, the height of the notch or the given distance is one tenth to one eighth of the height of the enclosure.

[0010] Optionally, the height of the air supply cavity is 1.1 to 1.5 times the height of the air inlet; The air supply cavity is structured as an air knife with a communicating opening or a communicating slit at the bottom.

[0011] Optionally, the air supply cavity is equipped with at least two air inlet pipes, and the number of the air inlet pipes is no more than six; The air inlet pipes are evenly arranged in the circumferential direction of the air supply cavity.

[0012] Optionally, an upper cover plate is provided at the upper end of the air cooling cylinder, and the upper cover plate radially extends to be at least flush with the enclosure, so as to determine the upper wall of the air outlet and reduce the impact on the upper furnace body.

[0013] Optionally, a seat plate is provided at the lower end of the air cooling cylinder to reduce the impact on the lower furnace body.

[0014] Optionally, a sleeve is provided between the air cooling cylinder and the gradient furnace tube section, and there are separation gaps between the sleeve and the gradient furnace tube section, as well as between the sleeve and the air cooling cylinder.

[0015] Optionally, the air supply device is equipped with a flow meter and a regulating valve.

[0016] According to a second aspect of an embodiment of the present invention, a gradient descent furnace is provided, and the air cooling device described in the first aspect of the embodiment of the present invention is arranged in a gradient zone of the gradient descent furnace.

[0017] In an embodiment of the present invention, the air cooling device provided has an air cooling cylinder which is sleeved on the gradient furnace tube section of the gradient descending furnace tube located in the gradient zone, and then a heat sink is arranged in an annular array on the air cooling cylinder, thereby forming an annular array assembly, and a hood with a slightly smaller height is provided, which is centered on the annular array assembly, so that a section of the annular array assembly is exposed above and below, and while determining the upward air duct, an air inlet and an air outlet are also constructed. An air supply cavity is also provided, which is an annular cavity, and each air inlet is covered on the lower side of the hood, and is connected to each upward air duct through the corresponding air inlet. The air-cooled cooling air is supplied to each upward air duct through the air supply cavity, and the heated cooling air can be directly discharged through the air outlet, and there is no requirement for sealing performance. In view of the fact that there is no need to assist other cooling devices, ambient air can be directly used as the cooling medium, and the overall structure is relatively compact. At the same time, since, for example, the heated hot air can be discharged, the temperature of the cooled air is relatively stable, making it easier to obtain the target temperature gradient. The overall adjustment depends on the changes in the surrounding environment, and the changes in the surrounding environment are often relatively stable, making the adjustment relatively easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the main structure of a gradient descent furnace in one embodiment.

[0019] Figure 2 for Figure 1 AA section view.

[0020] Figure 3 It is a schematic diagram of the coordination structure of the air cooling device and the furnace tube in one embodiment.

[0021] Figure 4 Schematic diagram of the assembly structure of an air cooling device on a gradient descent furnace in one embodiment.

[0022] Figure 5 Schematic diagram of the main cross-sectional structure of an air cooling device in one embodiment.

[0023] Figure 6 It is a schematic diagram of the main structure of the air cooling device in one embodiment when the air knife is not provided.

[0024] Figure 7 It is a schematic diagram of the top view of the structure of the air cooling device in one embodiment without the wind knife and the upper cover plate.

[0025] Figure 8 It is a schematic diagram of the main structure of the air cooling device in one embodiment when the wind knife and the hood are missing.

[0026] In the figure: 1. lower furnace body, 2. gradient zone, 3. upper furnace body, 4. flow meter, 5. furnace tube, 6. pressure regulating valve.

[0027] 21. Seat plate, 22. Wind knife, 23. Air inlet pipe, 24. Fixing buckle, 25. Air outlet, 26. Shroud, 27. Air cooling cylinder, 28. Sleeve, 29. Upper cover.

[0028] 271. upper heat sink, 272. notch, 273. lower heat sink, 274. upward air duct. DETAILED DESCRIPTION

[0029] Figure 1 and Figure 2 The main body of the product shown is a general configuration of a gradient descent furnace and has nothing to do with the embodiments of the present invention. The parts of the gradient descent furnace except the cooling device will not be described in detail below.

[0030] The following is a brief description of the basic structure of the gradient descent furnace and the air cooling device. Figure 1 and Figure 2 As can be seen in FIG. 1 , the gradient descending furnace has an upper furnace body 3 and a lower furnace body 1 . The upper furnace body 3 and the lower furnace body 1 are different at least in process temperature, and the process temperature of the upper furnace body 3 is higher than the process temperature of the lower furnace body 1 . However, the furnace cavities of the two furnace bodies are connected, as shown in FIG. Figure 2 The same furnace tube 5 is used in the structure shown. When the workpiece is transferred between the two furnace chambers, it is necessary to perform appropriate interruption in the gradient zone 2. This interruption is a temperature interruption rather than a physical interruption. Therefore, an adaptive cooling device is required to generate a temperature gradient in the furnace tube section of the furnace tube 5 in the gradient zone 2, thereby generating a transition zone in the furnace tube section of the furnace tube 5.

[0031] For the convenience of description, the furnace tube section of the furnace tube 5 located in the gradient zone 2 is called the gradient furnace tube section.

[0032] From the perspective of the basic reference system, the gradient descent furnace is a vertical furnace, and the furnace body is generally a rotating body. Therefore, the gradient descent furnace has definite axial, circumferential and radial directions, and its axial direction is its height direction. Unless otherwise specified in the following text, this basic reference system shall prevail.

[0033] The basic structure of the air cooling device includes an air cooling cylinder 27, a heat sink, a cover 26, an air supply cavity and an air supply device, wherein the air cooling cylinder 27 serves as a mounting base for the heat sink or is fixed to the air cooling cylinder 27 as a whole, the air supply cavity is an annular cavity, and the air supply cavity, the air cooling cylinder 27 and the furnace tube 5 should have relatively good coaxiality.

[0034] The air cooling tube 27 is a cylindrical structure, and is made of a material with relatively good thermal conductivity, such as aluminum, aluminum alloy, copper, copper alloy and other metal materials, or non-metallic materials with relatively good thermal conductivity, such as ceramics.

[0035] The air cooling cylinder 27 is sleeved on the gradient furnace tube segment, and can be directly connected, indirectly connected, or not connected to the gradient furnace tube segment. The connection here specifically refers to a mechanical functional connection to achieve the desired function of the connection, rather than an indirect continuum physically existing.

[0036] Air cooling cylinder 27 Figure 4 In the illustrated structure, there is a certain span between the furnace tube 5. In addition, the air cooling tube 27 is Figure 4 In the illustrated structure, it can be directly fixed on the seat plate 21 shown in the figure, or it can be fixed on Figure 8 The upper cover plate 29 shown in the figure may also be fixed to both of them, and is generally fixed to one of them and connected to the other.

[0037] In other implementations, there may only be a positioning relationship and a supporting relationship between the air cooling cylinder 27 and the upper cover plate 29 and the seat plate 21, without the need for reliable fixation. For example, an annular groove is opened on the seat plate 21 for positioning the air cooling cylinder 27, and the stability of the position is achieved based on gravity support.

[0038] The materials of the heat sink and the air cooling tube 27 can be the same or different. When the same material is used, they can be manufactured as a whole, for example, by integral casting using cast aluminum material, that is, the heat sink and the air cooling tube 27 can be integrally cast using, for example, casting.

[0039] The heat sink and the air cooling cylinder 27 can also be made separately and then combined into one later. For example, the air cooling cylinder 27 is a steel cylinder or an aluminum cylinder, and the heat sink is located on a sleeve. The whole is in the shape of a straight blade impeller and can be mounted on the air cooling cylinder 27 with the help of the sleeve.

[0040] In some implementations, the heat sink may be welded to the air cooling cylinder 27 by, for example, welding.

[0041] Relatively speaking, it is preferred to manufacture the air cooling tube 27 and the heat sink in one piece, as this structure can reduce thermal resistance.

[0042] Combination Figure 7 and Figure 8 It can be seen that the heat sinks are arranged on the air cooling cylinder 27 in a circular array. For the convenience of description, the assembly formed by the heat sinks of the array is referred to as a circular array assembly.

[0043] The heat sinks of the annular array have the same shape. Under this condition, the ends of the heat sinks must be located on a cylindrical surface. This is common knowledge in the mechanical field and will not be described here. For the convenience of description, the cylindrical surface is called the circumscribed cylindrical surface.

[0044] from Figure 7 As can be seen in the figure, there are gaps between the heat sinks on the annular array assembly on the air cooling tube 27, which appear as through grooves in the up and down directions, and are recorded as upward air grooves.

[0045] The cooling wind runs from bottom to top, which is adapted to the characteristics of the high process temperature of the upper furnace body 3 and the low process temperature of the lower furnace body 1 as mentioned above, and produces a hedge, which is conducive to obtaining a relatively good cooling effect.

[0046] The enclosure 26 is mounted on the annular array assembly to construct the upward air duct 274. The enclosure 26 can be tightly fitted with the annular array assembly, such as an interference fit or a transition fit. The tight fit is close to connection, especially the interference fit, which can also be generally referred to as an interference connection. It should be noted that the enclosure 26 and the annular array assembly can be loosely fitted (i.e., clearance fit) or have a gap to facilitate assembly and reduce interference under thermal expansion and contraction.

[0047] When the enclosure 26 and the supporting annular array assembly are tightly matched, the enclosure 26 is fixed to the annular array assembly by means of the tight fit. If the enclosure 26 and the annular array assembly are loosely matched or there is an assembly gap, the enclosure 6 and the annular array assembly can be fixed by radial screws or locked with set screws (commonly known as jackscrews).

[0048] exist Figure 6 As can be seen in the figure, the height of the enclosure 26 is relatively small, that is, shorter than the height of the heat sink. Under this condition, the enclosure 26 is centrally arranged on the annular array assembly, and the enclosure 26 cannot completely cover the upward wind slot on the centrifugal side of the upward wind slot, so that a section is exposed at the upper and lower ends of the upward wind slot, and the height of the upward wind duct 274 is shorter than the height of the upward wind slot. Therefore, the upper section of the upper and lower exposed sections constitutes the air outlet 25, and the lower section constitutes the air inlet.

[0049] It should also be noted that there is no special requirement for the tightness of the connection between the enclosure 26 and the annular array assembly, and the impact on the cooling capacity is relatively small.

[0050] It can also be seen that the height of the upward air slot is greater than the height of the upward air duct 274, or in other words, the upward air duct 274 constitutes a part of the upward air slot.

[0051] A plurality of upward air ducts 274 are formed by the cooperation of the enclosure 26 and the annular array assembly. Based on the uniform arrangement of the heat sink fins in the axial direction of the air cooling cylinder 27, the upward air ducts 274 are uniformly arranged around the air cooling cylinder 27 to form an upward air duct annular array.

[0052] The number of the upward air ducts 274 should be no less than twelve, but should not be greater than thirty-six. The more the number of the upward air ducts 274, the smaller the cross-sectional area of ​​each upward air duct 274, the greater the flow resistance, and the more obvious the elbow effect of the part where the upward air duct 274 enters and discharges the gas, so that the cooling gas is more evenly dispersed in the circumferential direction of the air cooling cylinder 27. However, for this reason, if there are too many upward air ducts 274, the flow resistance will be greatly increased.

[0053] Preferably, the number of the upward air ducts 274 is twenty-four.

[0054] Furthermore, the air supply cavity is constructed as an annular cavity, which surrounds the heat sink arranged on the lower side of the enclosure 26 and is communicated with the air inlet.

[0055] Regarding the communication mode between the air supply cavity and the air inlet, it can be realized in the following manner. First, it is determined that the upper side of the cavity wall of the annular cavity can be welded to the lower edge of the enclosure 26, and the side of the cavity wall facing the heat sink, that is, its centripetal side, is open, and the lower side is connected to, for example, Figure 6 The seat plates 21 shown in the figure are welded or connected in other ways. For example, the lower end of the cavity wall of the air supply cavity is determined to be a flange, and the flange cooperates with the sealing ring and is connected to the seat plate 21 by a flange connection.

[0056] The connection between the enclosure 26 and the cavity wall can also be made by flange connection, which will not be described in detail here.

[0057] Correspondingly, an air supply device is configured for the air supply cavity to provide cooling air to the air supply cavity.

[0058] It should be known that centralized air supply is commonly used on the factory side, especially for various gas-using equipment, which generally use a compression system to supply air (cooling air) to save overall costs. In other words, the air supply cavity can be connected to the factory air supply system through a pipeline system, and the air supply system constitutes the air supply device.

[0059] When air is supplied to the annular air supply cavity through a pipeline, a proximity effect is generated, that is, the upward air duct 274 close to the pipeline can obtain more cooling air, and conversely, the upward air duct 274 far from the pipeline can only obtain a small amount of cooling air. In a preferred embodiment, the heat sink has a gap 272 in the middle or is composed of an upper heat sink 271 and a lower heat sink 273 with a given distance between them. When there is a gap 272 or the upper heat sink 271 and the lower heat sink 273 have a given distance, it is equivalent to the upward air duct 274 being connected at the gap 272, for example, and turbulence is generated, so that the cooling gas is secondary distributed here, which is conducive to more uniform cooling of the gradient furnace tube section in the circumferential direction.

[0060] Furthermore, the height of the notch 272 or the given distance is one tenth to one eighth of the height of the enclosure 26. The height of the notch 272 should not be too large, otherwise the effect of constructing the upward air duct 274 will not be prominent enough. Specifically, when the height of the notch 272 is relatively large, its secondary distribution effect may be more obvious, but it will affect the effect of the primary distribution.

[0061] For example, the height of the notch 272 should not be too small, otherwise the effect of the secondary distribution will be relatively weak. When the airflow has a certain speed, it will have a certain inertia, and the lateral diffusion of the gas in the direction of the airflow will be relatively weak, especially under the condition that the restraining effect of the upward air duct 274 is relatively obvious. In other words, if the height of the notch 272 is relatively small, there will be almost no secondary distribution effect.

[0062] The height of the notch 272 or the given distance is preferably 10.9% of the height of the enclosure 26, which is approximately one tenth.

[0063] Furthermore, the height of the air supply cavity is 1.1 to 1.5 times the height of the air inlet, in order to obtain relatively good dispersion, which is conducive to relatively uniform distribution of the cooling gas in each upstream air duct 274.

[0064] Correspondingly, the air supply cavity is constructed as an air knife 22 with a connecting opening or a connecting slit at the bottom. In the mechanical field, the air knife 22 refers to a mechanical device that can generate a relatively high wind pressure, that is, it can cause the gas to be ejected, so that, for example, cooling air can pass quickly in the upward air duct 274, and the gradient-down furnace can obtain a relatively large gradient in the gradient zone.

[0065] In addition, the use of the wind knife 22 means that the air pressure in the air supply cavity is relatively high, which is conducive to the air supply cavity supplying air evenly to each upward air duct 274.

[0066] exist Figure 3 and Figure 4In the illustrated structure, the air supply cavity is equipped with two air inlet pipes 23 , which is beneficial for making the wind pressure in various parts of the air supply cavity relatively balanced, thereby helping to make the wind pressure between the upward air ducts 274 relatively balanced.

[0067] Obviously, the more the intake pipes 23 are, the more balanced the wind pressure between the upward air ducts 274 will be. However, the number of intake pipes 23 should not be too many, otherwise it will lead to difficulties in piping. Therefore, the number of intake pipes 23 should not be too many, and should not be more than six.

[0068] Correspondingly, the air inlet pipes 23 are evenly arranged in the circumferential direction of the air supply cavity.

[0069] See also Figure 3 and Figure 4 An upper cover plate 29 is provided at the upper end of the air cooling cylinder 27 to shield the upper end of the upward air trough from the upper end to reduce the impact on the upper furnace body.

[0070] Correspondingly, the upper cover plate 29 is obviously an annular plate, which should be able to allow the furnace tube 5 to pass through.

[0071] Furthermore, the upper cover plate 29 radially extends to be at least flush with the enclosure 26 , and further extends outwards to an extent that does not exceed the outer edge of the lower end surface of the upper furnace body 3 .

[0072] The existence of the upper cover plate 29 makes the air outlet 25 form a curved pipe, and the outgoing airflow is generally discharged in the form of an outward spray.

[0073] In addition, an annular connecting cavity pipe can be arranged at the air outlet 25 to connect the upward air troughs, so as to facilitate the heated gas to be led out of the factory building or put into other heat utilization equipment.

[0074] Furthermore, a seat plate 21 is provided at the lower end of the air cooling cylinder 27 to reduce the impact on the lower furnace body 1. The rest of the structure of the seat plate 21 refers to the upper cover plate 29. In addition, the seat plate 21 can also be used as a base plate of the air cooling device, which has more options.

[0075] In addition, from Figure 2 and Figure 4 As can be seen, a lower furnace plug is provided at the lower end of the upper furnace body 3, and an upper furnace plug is provided at the upper end of the lower furnace body 1, which is beneficial to heat preservation and reduces the influence of the air cooling device on the process temperature in the two furnace bodies.

[0076] In addition, Figure 5 In the illustrated structure, a sleeve 28 is provided between the air cooling cylinder 27 and the gradient furnace tube section, and the sleeve 28 is made of a corundum tube. Moreover, there is a separation gap between the sleeve 28 and the gradient furnace tube section, and between the sleeve 28 and the air cooling cylinder 27, so as to uniformly cool the gradient furnace tube section in the circumferential direction.

[0077] Also in Figure 3In the illustrated structure, the air supply device is equipped with a flow meter 4 and a regulating valve 6 to adjust the cooling capacity of the air cooling device according to different process objects, so as to obtain different temperature gradients.

Claims

1. An air cooling device for cooling the gradient zone of a gradient descent furnace, characterized in that: The air cooling device comprises: An air cooling cylinder is mounted on a gradient furnace tube section of a gradient descending furnace tube located in a gradient zone; The heat sink is arranged in an annular array on the air cooling cylinder, and upward wind slots are formed between adjacent heat sinks to form an annular array assembly; A shroud is mounted on the annular array assembly and cooperates with the upward wind slot to construct an upward wind duct, and the height of the shroud is shorter than the height of the heat sink, and is centrally arranged on the annular array assembly, and the upper exposed part of the upward wind slot constitutes an air outlet, and the lower exposed part of the upward wind slot constitutes an air inlet; The air supply cavity is an annular cavity, which is arranged around the heat sink on the lower side of the enclosure and is connected to the air inlet; and An air supply device supplies cooling air to the air supply cavity.

2. The air cooling device according to claim 1, characterized in that: The heat sink has a notch in the middle or is composed of an upper heat sink and a lower heat sink with a given distance between them.

3. The air cooling device according to claim 2, characterized in that: The height of the notch or the given distance is one tenth to one eighth of the height of the enclosure.

4. The air cooling device according to any one of claims 1 to 3, characterized in that: The height of the air supply cavity is 1.1 to 1.5 times the height of the air inlet; The air supply cavity is structured as an air knife with a communicating opening or a communicating slit at the bottom.

5. The air cooling device according to claim 4, characterized in that: The air supply cavity is equipped with at least two air inlet pipes, and the number of the air inlet pipes is not more than six; The air inlet pipes are evenly arranged in the circumferential direction of the air supply cavity.

6. The air cooling device according to claim 1, characterized in that: An upper cover plate is provided at the upper end of the air cooling cylinder, and the upper cover plate radially extends to be at least flush with the enclosure, so as to determine the upper wall of the air outlet and reduce the impact on the upper furnace body.

7. The air cooling device according to claim 1 or 6, characterized in that: A seat plate is provided at the lower end of the air cooling cylinder to reduce the impact on the lower furnace body.

8. The air cooling device according to claim 1, characterized in that: A sleeve is also arranged between the air cooling cylinder and the gradient furnace tube section, and there are separation gaps between the sleeve and the gradient furnace tube section, as well as between the sleeve and the air cooling cylinder.

9. The air cooling device according to claim 1, characterized in that: The air supply device is adapted to be equipped with a flow meter and a regulating valve.

10. A gradient descent furnace, characterized in that: An air cooling device as claimed in any one of claims 1 to 9 is provided in the gradient zone of the gradient descending furnace.

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