JPH0614890U - Roller hearth atmosphere furnace with atmospheric intrusion prevention device - Google Patents

Abstract

(57) [Summary] [Objective] In a roller hearth furnace that continuously heat-treats the processed product, it is necessary to perform firing in a neutral or reducing gas atmosphere depending on the processed product. At that time, in order to prevent the invasion of the atmosphere as much as possible and obtain a stable heat treatment effect, it is necessary to seal the gas at the entrance and exit of the furnace. [Structure] In a roller hearth furnace that calcines a processed material in a neutral gas or a reducing gas atmosphere, gas injection parts are provided at the inlet and outlet of the furnace, and the height of the furnace ceiling is adjusted according to the size of the processed material. A feature is that a plurality of variable partition plates and a plurality of partition walls fixed to the lower part of the furnace are installed to prevent atmospheric air from entering the furnace.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a roller hearth furnace that conveys electronic circuit boards and electronic components by rollers and continuously heat-treats them, and particularly relates to a roller hearth atmosphere in which the furnace has a neutral or reducing gas atmosphere.

[0002]

[Prior art]

 Conventionally, Ag, Au, etc. have been used as wiring conductor materials for electronic circuit boards made of alumina, zirconia, etc., and electronic parts made of barium titanate, etc. Cu has come to be used. However, when Cu conductors printed and attached to electronic circuit boards and electronic components are dried and baked in the atmosphere, they will combine with oxygen in the atmosphere and they will no longer function as they should be. It had drawbacks. Therefore, it is necessary to reduce the oxygen concentration as much as possible by making the inside of the furnace a neutral atmosphere of nitrogen gas or argon gas or a reducing atmosphere in which hydrogen gas of about 5 to 10 vol% is added to nitrogen gas. 3 and 4 show an example of a roller hearth atmosphere furnace manufactured by a conventional technique. At the upper part of the hood, a gas ejection tube 3 having a large number of gas nozzles and a curtain 10 made of ceramic wool or stainless thin plate are provided. The car ten 10 has a slit-like curtain that can move freely back and forth, and serves to block air from entering the furnace. A gas ejection pipe 4 having a large number of gas nozzles is provided under the hood. The roller 8 for conveying the processed material is gas-sealed, and is connected to the drive motor by a chain and rotates. Finely processed products such as electronic parts are put in the sheath 6. The sheath 6 is further placed on the base plate 7. The base plate 7 advances by the rotation of the rollers 8. In order to maintain the inside of the furnace in a neutral atmosphere or a reducing atmosphere, a neutral gas or a reducing gas is ejected from the gas ejection pipes 3 and 4. At the upper part of the hood, there is a gap of about 5 to 10 mm between the curtain 10 and the sheath 6, and the gas blown out from the gas ejection pipe 3 can prevent the invasion of the atmosphere to some extent. At the bottom of the hood, gas is blown out from the gas ejection pipe 4, but it has become clear that the atmosphere enters the bottom of the hood. The structure of the outlet hood is similar to this. FIG. 4 is an example of baking an electronic circuit board. Since the roller hearth furnace is capable of continuous firing, it is suitable for high-mix low-volume production. In some cases, electronic circuit boards are baked immediately after electronic components are baked. The electronic circuit board 14 may be relatively large in shape as compared with an electronic component, and may be directly placed on a base plate and baked. In this case, since the height of the curtain 10 cannot be adjusted in the vertical direction, the gap between the curtain 10 and the electronic circuit board 14 becomes large, and the atmosphere easily enters. Atmosphere also easily enters from the bottom of the hood. As shown in Fig. 4, when there is a large gap between the curtain 10 and the processed material, the gas flow rate from the gas ejection pipe 3 should be about three times as large as that in Fig. 3 in order to prevent air from entering from the upper part of the hood. It is necessary to flush more. Further, the curtain 10 has slits for maintaining flexibility, and even in the case of FIG. 3, air may enter through the slits.

[0003]

[Problems to be solved by the device]

 However, in the conventional structure as shown in FIGS. 3 and 4, since the height of the curtain 10 at the upper part of the hood at the entrance and the exit of the roller hearth atmosphere furnace cannot be adjusted, an electronic circuit having a low height as shown in FIG. When the substrate 14 is baked, a large gap is created between the curtain 10 and the electronic circuit substrate 14, and unless a large amount of gas is ejected from the gas ejection pipe 3, the atmosphere will enter the furnace, and The oxygen concentration of 100 ppm or more. In the situation of FIG. 4, in order to keep the oxygen concentration in the furnace at 100 ppm or less, the gas amount of about 3 times or more of that in the case of FIG. 3 is required. Radiant heat in the furnace leaks from the gap, which is a structure that is contrary to energy conservation. Next, in the lower part of the hood, spouting a small amount of gas from the gas spouting pipe 4 is not effective, and since atmospheric air may enter from the bottom of the hood due to convection, it was necessary to spout a large amount of gas. From the above, the conventional structure requires a large amount of gas and is very uneconomical in terms of energy saving.

[0004]

[Means for Solving the Problems]

 The roller hearth atmosphere furnace with an air intrusion prevention device of the present invention is provided with a hood at the inlet and outlet of the furnace, and a plurality of partitions whose height can be adjusted depending on the material to be processed in the hood and the ceiling of the hood together with the gas ejection pipe. It is characterized by a plate and a plurality of fixed partition plates installed in the lower part of the hood to prevent air from entering.

[0005]

[Action]

 With these configurations, the atmospheric gas in the furnace can always maintain a stable oxygen concentration, and the height-adjustable partition plates at the top and bottom of the hood are adjusted according to the height of the processed material, and the gas is blown out. It is possible to prevent the atmospheric air from entering the furnace and to block the radiant heat from the furnace to prevent heat loss simply by ejecting the gas from the pipe. Furthermore, the fixed partition plate at the bottom of the hood has a gap of about 5 mm from the bottom surface of the base plate, and by injecting gas from the gas ejection pipe, it is possible to prevent the invasion of the atmosphere from the bottom of the hood, and the gas ejection The amount can be reduced compared to the conventional one.

[0006]

【Example】

 An embodiment of the present invention is shown in FIGS. FIG. 1 is a front cross-sectional view and a side cross-sectional view of a hood provided with gas ejecting pipes 3 and 4 and a partition plate 1 at an inlet portion of a roller hearth atmosphere furnace. A base plate 7 is placed on the roller 8, and a sheath 6 on which electronic components and the like are loaded is placed. The roller 8 is fixed to the hood 9 with a bearing having a gas seal, and is connected to a drive motor by a chain to rotate. The base plate 7 advances by the rotation of the roller 8. The partition plate 1 is fixed to the hood 9 by a screw-shaped stopper 2 with a gap of 5 to 10 mm from the sheath 6. The partition plate 1 is a screw-shaped stopper 2, and the height can be adjusted vertically. The gas ejection pipes 3 and 4 have a large number of nozzles arranged in a row, and have a structure for ejecting gas outward. In the case of the upper part of the hood, the ejected gas is discharged to the outside through the gap between the partition plate 1 and the sheath 6. In the case of the lower part of the hood, it is discharged to the outside through the gap between the partition plate 12 and the base plate 7. Therefore, the atmosphere does not enter the furnace, and the interior of the furnace is constantly filled with neutral gas such as a residual oxygen concentration of about 100 ppm to prevent the oxidation of electronic parts. FIG. 2 shows an example of printing an electronic circuit board. The electronic circuit board 14 is placed on the base plate 7 and baked. In this case, the partition plate 1 is lowered and the height of the partition plate 1 is adjusted so that the clearance with the electronic circuit board 14 is about 5 to 10 mm. As shown in FIG. 1, when the partition plate 1 is raised, the atmosphere is prevented from entering the furnace and radiant heat from the furnace becoming large. The combination of the partition plate 1 and the gas ejection pipe 3 (upper part of the hood) and the combination of the partition plate 12 and the gas ejection pipe 4 (lower part of the hood) are less effective with one, and the greater the number, the more effective the effect is. large.

[0007] Table 1 shows the oxygen concentration (ppm) measurement results in the furnace. The first and second steps from the top of Table 1 are for the conventional method (combination of curtain and gas ejection tube), and the first step is the measurement result of oxygen concentration when electronic parts are loaded on the sheath. Is. Even in the holding zone in the furnace, it was 100 ppm or more, which was caused by the intake of air from the bottom of the hood. The second stage is a case where the electronic circuit board is placed on the base plate, and for comparison, the gas flow rates are all set to the same values as in the first stage. The flow rates are the same for the third and fourth stages because they are compared under the same conditions. In the case of the second stage, there is a large gap between the curtain and the electronic circuit board, and the atmosphere has entered the furnace. Therefore, the oxygen concentrations in the temperature rising zone, the holding zone, and the cooling zone show considerably higher values than the results of the first stage. Even in the holding band, 100 ppm cannot be held at all. The third and fourth stages are the results of carrying out the present invention (combination of a partition plate and a gas ejection pipe). The third stage is the case where electronic components are loaded on the sheath, and the oxygen concentration is maintained below 100 ppm throughout the furnace (heating zone, holding zone, cooling zone). Compared to the first stage, it is shown that the air intake from the bottom of the hood is completely eliminated by the partition plate. The fourth stage is the case where the electronic circuit board is placed on the base plate. By adjusting the height of the partition plate at the top of the hood closer to the electronic circuit board, the gap between the partition plate and the electronic circuit board becomes smaller than in the second stage, and 100 ppm is maintained throughout the furnace at the same gas flow rate. However, the effect of a partition plate whose height can be adjusted up and down appears. In addition, experimental results show that the partition plate blocks the radiant heat from the inside of the furnace to save about 5% of energy.

[0008]

[Effect of device]

 As described above, according to the present invention, a partition plate and a gas ejection pipe whose height can be adjusted up and down are provided at the upper part of the hood at the entrance and exit of the roller hearth furnace having the temperature rising zone, the holding zone, and the cooling zone. By providing a large number of units, it is possible to prevent the invasion of the atmosphere from the upper part of the base plate, block the radiant heat from the inside of the furnace, and prevent the heat loss. Furthermore, by adjusting the partition plate up and down according to the height of the processed material and maintaining the gap between the partition plate and the processed material for about 5 to 10 mm, the oxygen concentration in the furnace can be reduced to 100 ppm or less at the same flow rate. It can be maintained. In addition, since a large number of fixed partition plates and gas injection pipes are provided at the lower part of the inlet and outlet hoods, it is possible to prevent the invasion of the atmosphere from the lower part of the roller, and moreover, a fixed partition plate and the bottom surface of the base plate are provided. By opening a gap of about 5 mm, the gas flow rate from the gas ejection pipe can be reduced to 1/3 to 1/2 of the conventional flow rate. The practical effect is great in terms of saving gas consumption and saving energy.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a hood portion at a furnace inlet when electronic parts are loaded on a sheath and baked in a roller hearth atmosphere furnace of the present invention.

FIG. 2 is an explanatory view showing a furnace inlet hood portion when an electronic circuit board is placed on a base plate and baked in the roller hearth atmosphere furnace of the present invention.

FIG. 3 is an explanatory diagram showing a state of a furnace inlet hood portion when electronic components are loaded on a sheath and baked in a conventional roller hearth atmosphere furnace.

FIG. 4 is an explanatory view showing a furnace inlet hood portion when an electronic circuit board is placed on a base plate and baked in a conventional roller hearth atmosphere furnace.

[Explanation of symbols]

 1 Upper Partition Plate 2 Screw-shaped Stopper 3 Upper Gas Ejection Pipe 4 Lower Gas Ejection Pipe 5 Gas Nozzle Hole 6 Saya 7 Base Plate 8 Roller 9 Hood 10 Curtain 11 Electronic Circuit Board 12 Lower Partition Plate 13 Furnace Body

Claims (1)

[Scope of utility model registration request] 1. In a roller hearth furnace for firing a processed product in a neutral gas or reducing gas atmosphere, a hood is provided at an inlet and an outlet of the furnace, and a gas ejection pipe is provided in the hood and a ceiling part in the hood. Roller hearth atmosphere furnace with an atmospheric intrusion prevention device, which is equipped with multiple partition plates whose height can be adjusted depending on the processed material and multiple fixed partition plates at the bottom of the hood to prevent atmospheric intrusion. .