JPS6059508B2 - Structure of continuous furnace workpiece removal part - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a non-oxidizing take-out part of a workpiece in a tunnel furnace that uses a flame curtain of flammable gas, such as a sintering furnace for powder metallurgy and a brazing furnace for metal parts. This makes it possible to significantly shorten the length of the tube.

This content will be explained using a sintering furnace for metal powder metallurgy as an example.

A molded product obtained by pressure-molding raw material powder (e.g., iron powder) into a predetermined shape is sent into a sintering furnace by a conveyor, and after being subjected to a predetermined heat treatment (e.g., 1100°C, 3-powder holding),
It is cooled to room temperature and becomes a sintered product. What is important in this heat sintering process is that the heat treatment must be carried out in a non-oxidized state, since the presence of oxides in the molded product will inhibit sintering. Therefore, a cyclic gas such as decomposed ammonia is used in the furnace atmosphere to remove the cyclic elements of the molded product, which are slightly oxidized during processing, and to prevent oxidation during sintering. Since the cyclic gas is flammable, it is usually sintered at the entrance and exit of the furnace core tube to form a flame curtain to prevent explosions caused by infiltration of outside air. The conventional structure of the furnace core tube outlet section is shown in FIG.

The sintered product 1 on the heat-resistant steel mesh belt conveyor 5 passes from the furnace core tube 3 to the water-cooled cooling tube 4 and reaches a fall start position 8. From this position, the sintered product slides down on the conveyor,
The chute 9 sends it to the next process. In the figure, 2 indicates a furnace body, and 6 indicates a conveyor driving drum. In this case, the sintered product is cooled in the cooling tube to near room temperature and then heated again by the frame curtain 7. At this time, if the surface temperature of the sintered product rises above the oxidation start temperature of this material,
The surface becomes dark gray due to oxidation, which significantly impairs the beauty of the product. In order to prevent this oxidation coloring, the temperature of the sintered product passing through the frame curtain may be lowered to below the oxidation start temperature.

This temperature is the sum of the temperature immediately before passing through the frame curtain and the temperature rise during passing. Therefore, methods for preventing oxidation can be divided into two methods: (1) lowering the temperature of the sintered product just before it passes through the frame curtain, and (2) minimizing the temperature rise when it passes through the frame curtain. The conventional method is (1
), the method used was to increase the supply of atmospheric gas, move the frame curtain closer to the outlet end, increase the effective length of the cooling section, or extend the length of the cooling pipe. . The method of the present invention is different from the conventional method and corresponds to the above (2).

The structure of the outlet of the cooling pipe according to the present invention is shown in FIG. As can be seen from this figure, a cover shown at 10 is attached to the tip of the cooling pipe in the conventional method. In this way, the position of the frame curtain can be lower than the starting point of the fall, so that the sintered product can pass through the frame curtain while sliding down from the conveyor. Therefore, the temperature increase in this portion becomes negligible, and it becomes possible to shorten the length of the cooling pipe by an amount corresponding to the amount of temperature increase in the conventional method. In addition, it is also possible to reduce the amount of atmospheric gas used. The content of the present invention will be explained from the content of experiments conducted in advance. Experiment In the exit section of the conventional shape shown in Fig. 1, the internal dimensions of the cooling pipe 4 are width 250Tn1 height 10h1 length 30m, conveyor feed speed 100m/min, atmosphere is decomposed ammonia gas, and flow rate is 21d. /h.

A sintered iron product with a diameter of 5" and a thickness of about 1" was used as a workpiece, and a cooling curve of the sintered product in the cooling tube was determined. The results are shown in Figure 3. The temperature of the sintered product, which was about 600°C at the cooling pipe entrance, gradually decreased to about 1.7rrI. At position 22, the oxidation start temperature 21 (185°C) was reached.
Thereafter, by heating with a frame curtain, the temperature was raised again from the lowest point to 110° C., and the maximum point shown in 23 was produced.
The heating time using the frame curtain is approximately 2 minutes, and the amount of temperature increase is 1
00°C, and the maximum temperature was 210°C. It was taken out. Discoloration due to surface oxidation was observed in all items. In order to take out the sintered product in a non-oxidized state using the conventional method, the maximum temperature of the sintered product in the oxidizing atmosphere, that is, the maximum temperature 23 in the frame curtain, must be lower than the oxidation start temperature. need to be lowered.

Therefore, the temperature increase from the oxidation start temperature -185°C -10
It is necessary to cool it in advance to a temperature below -85°C minus 0°C. This limit is at the position indicated by 24 in the figure, and the required length of the cooling pipe, to be more precise, the distance from the cooling pipe entrance to the frame curtain, is 3.5 m or more. Add to this the distance from the cooling pipe outlet to the end of the drum -0.
It was found that by adding 3m-, the sum of both requires 3.8m or more. By adopting the shape of the present invention, the time for the sintered product to pass through the frame curtain is less than 1 second, so from the heating time and amount of temperature increase in the above experiment, the amount of temperature increase in this method is 1°C or less. It is estimated that the amount is sufficiently negligible.

Therefore, the minimum length to extract the sintered product in a non-oxidized state,
In other words, the limit value of the distance from the cooling pipe entrance to the starting point of the fall is:
This becomes the point -1.7jL- indicated by 22 in FIG. Adding the dimensions of the cover portion to this, the total amount becomes approximately 20TrL. This makes it possible to significantly shorten the length compared to the conventional shape of 3.8wL, thereby saving equipment costs and floor space. Furthermore, the present invention also makes it possible to save on the amount of atmospheric gas used. FIG. 4 schematically shows the flow of gas near the outlet of a conventionally shaped cooling pipe. The relatively high temperature atmospheric gas 11 flowing out of the furnace core tube flows in the cooling tube toward the end. On the other hand, since the outside air 12 has a lower temperature than the atmospheric gas, it flows along the bottom surface of the cooling pipe toward the inner part of the pipe. That is, inside the pipe, atmospheric gas flows at the top and outside air flows at the bottom in opposite directions, and both are mixed and burn in the zone 14, which has a flammable composition, forming a flame curtain.The burned gas 15 flows through the outlet. The double layer is mainly caused by the temperature difference between the two gases, and the inflow of outside air is unavoidable.The corner 1 between the combustion surface and the horizontal surface
3 changes depending on the flow rate of the atmospheric gas, and when the flow rate is small, this angle also becomes small, and the position where the sintered product contacts the frame curtain moves to the inner part of the pipe, reducing the effective length of the cooling pipe. reduce Therefore, the required amount of atmospheric gas is the sum of the amount of combustion by the flame curtain and the amount required to bring the position where the sintered product comes into contact with the frame curtain closer to the end. On the other hand, in the method of the present invention, as shown in Fig. 5, the atmospheric gas flowing out from the cooling pipe accumulates in the case from the upper part and comes into contact with the low-temperature outside air at the lower end of the case, forming a frame curtain. do. In this way, the atmospheric gas flowing out from the cooling pipe serves to seal the inside of the case, and essentially no outside air flows into the cooling pipe. Therefore, in principle, the required amount of atmospheric gas only needs to be supplemented with the combustion amount, and the amount used can be reduced. These contents will be specifically explained using examples. Example As shown in FIG. 2, a cover was attached to the tip of the cooling pipe having the same cross-sectional shape as that used in the experiment, and the lower end was set as a horizontal surface, and the cover was placed from the axis 61 of the drum (diameter 300 mm). Also 100? It was placed in a low position.

In addition, the molded product inlet side of the furnace core tube was sloped and lowered, so that the upper surface of the inlet was on the same level as the lower end surface of the cover. The shape of the present invention manufactured in this way and the conventional shape described in the above experiment,
Table 1 shows the critical dimensions of the main parts that can be removed without oxidation estimated from experimental values, the required flow rate of atmospheric gas determined from experiments, and the presence or absence of oxidation coloring of the sintered product. As shown in this table, it was possible to downsize the device and reduce the amount of atmospheric gas used.

In this way, the present invention makes it possible to significantly shorten the take-out section and save the amount of atmospheric gas when taking out the workpiece in a non-oxidized state from the furnace, and is applicable only to the production of the above-mentioned sintered products. First, this method can also be applied to furnaces used for brazing and heat treating metal parts. In carrying out the present invention, as shown in Fig. 2, the shape of the cover provided at the tip of the cooling pipe is such that it covers a part of the drive drum and the open lower end prevents the workpiece from falling. It suffices if it is located below the starting point.

The preferred position of the lower end is 100 to 2 from the starting point of the fall.
00w1m below. Further, the angle 81 between the fall starting point and a line connecting this point to the center of the drum and the vertical plane is approximately 300 degrees.

[Brief explanation of drawings]

Figure 1 shows the conventional structure of the outlet of a tunnel furnace having a frame curtain, Figure 2 shows the structure of the present invention, and Figure 3 shows the cooling curve of the workpiece in the cooling pipe shown in Figure 1. , 4 and 5 are diagrams showing the internal gas flow in the structures of the conventional shape and the shape of the present invention, respectively.

Claims (1)

[Claims] 1. A device for taking out workpieces on a conveyor from a continuous furnace having a frame curtain, characterized in that the frame curtain is provided below the position where the workpieces start to slide off the conveyor. Oxidation extraction device. 2 A cover is provided at the tip of the outlet cooling pipe, and the shape of the cover covers a part of the conveyor drive drum, and the open lower end is connected to a straight line that makes 30 degrees with the vertical plane passing through the axis of the drum. The non-oxidation take-out device for a workpiece according to claim 1, which is located below the point of intersection with the circumferential surface.