Thermal cutting machine and dust collecting method thereof

Details Thermal cutting machine and dust collecting method thereof Thermal cutting machine and dust collecting method thereof

2002-10-08

2003-12-16

Walberg, Teresa (Department: 3742)

Electric heating

Metal heating

By arc

C219S121480, C219S121580

Reexamination Certificate

active

06664495

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a thermal cutting machine including a dust collector and a dust collecting method thereof.
BACKGROUND ART
Conventionally, when a metal plate material (hereinafter, called a workpiece) is thermally cut with plasma arc or laser light, fumes and a high pressure gas (hereinafter, called a flue gas) occur from a back surface of the cut material, and deteriorate the working environment in a factory, and therefore various arts of effectively collecting the flue gas are developed.
For example, Japanese Utility Model Laid-open No. 51-42841 discloses the constitution in which i) a cutting table is divided into small chambers, and branch exhaust pipes, which have openable and closable valve mechanisms in the respective small chambers and communicate with a dust collector for filtering out powder dust via a main exhaust pipe, and ii) means for opening only the branch exhaust pipe in the small chamber in which a plasma torch performs cutting, correspondingly to the position of the plasma torch, which is under cutting operation, are provided. It is described that this constitution makes it possible to collect dust intensively and effectively only in the small chamber where a flue gas is caused by plasma cutting.
Japanese Patent Application Publication No. 52-32343 discloses the art of dividing a cutting table into small chambers, including a limit switch for detecting the position of a plasma torch under cutting operation, and opening only a damper in the small chamber where the plasma torch is performing cutting operation. It is described that the above-described constitution makes it possible to collect dust intensively and effectively only in the small chamber where a flue gas is caused by the plasma cutting.
Japanese Patent Application Publication No. 60-43231 discloses the art of a comparatively large-sized plasma cutting machine provided with a gas duct partitioned perpendicularly to the moving direction of a carriage loaded with a plasma torch, a set of suction hood and blast hood mounted on the carriage and each faced to the aforementioned gas duct of the cutting table, and a dust collector mounted on the carriage. According to this constitution, the suction hood provided at the carriage moves together with the torch, and therefore the conventional dampers required in the respective small chambers become unnecessary, which makes the structure simple and low in cost. In addition, it has the effects of improving dust collecting efficiency by compulsory circulation by an air current from the blast hood to the suction hood, and the like.
Japanese Utility Model Laid-open No. 2-87591 discloses the art of providing a set of an intake system and an exhaust system at positions sandwiching fumes, a combustion gas and the like, which occur during laser beam machining, sending the fumes, the combustion gas and the like with the intake system at one side to the exhaust system at the other side, which discharges them outside the laser machine. It is described that this constitution improves exhaust efficiency.
According to Japanese Utility Model Laid-open No. 5-9760, as shown in
FIG. 8
, in a plasma machine including a flue gas chute
32
under a torch
31
, air blow pipes
33
are placed at the upper edge of a chute
32
. The above Laid-opened Utility Model has the constitution in which the air blow pipes
33
has a plurality of discharge holes
35
which discharge air inside the air blow pipes
33
into the chute
32
and form air curtains in a space between the outer edge of a workpiece
34
and an inner edge of the opening of the chute
32
. According to the above constitution, a dust collector of the plasma machine, which is capable of absorbing and collecting a flue gas occurring during plasma machining such as cutting or welding at high efficiency, is disclosed.
However, the aforementioned conventional dust collecting apparatuses have the following problems.
(1) In the first and second prior arts disclosed in Japanese Utility Model Laid-open No. 51-42841 and Japanese Patent Application Publication No. 52-32343, the method of only sucking and discharging a flue gas into and from the exhaust chamber inside the table is adopted in each case, thus providing low exhaust efficiency. Above all, the fumes occurring during plasma cutting are very small powders of the order of &mgr;m floating in a high-temperature gas, and since its specific gravity is lighter than air at room temperature, it rises in the air. Accordingly, when cutting is performed at the position in the vicinity of the exhaust port, fumes are immediately sucked into the exhaust port, thus causing no problem. However, when it is performed at the position away from the exhaust port, the problem that the fumes spread along the back surface of a workpiece and leak out of a space between the workpiece and the table along the edge of the workpiece arises, as it also becomes the problem in Japanese Utility Model Laid-open No. 5-9760 that is previously described as the prior art. The size of the workpiece is not always the same as that of the table, but some workpieces are smaller with respect to the table, and in this case, the space becomes larger, thus causing the disadvantage that the dust collecting efficiency reduces and the amount of leaking fumes is increased.
(2) In the third prior art described in Japanese Patent Application Publication No. 60-43231, the dust collector, the blast hood and the suction hood are mounted on the carriage, which is originally provided for moving the plasma torch. As a result, a large carriage is required, and it is only proven in a large-sized plasma cutting machine called a gantry type (for example, the table with its machining area in size of 3 m×12 m). However, in comparatively small-sized plasma cutting machines which are generally produced in volume (for example, the table with its machining area in size of 1.5 m×3 m), it is difficult to provide the dust collector, the blast hood and the suction hood at the carriages in terms of space, and no example of its utilization is found at present.
In the third prior art, the exhaust gas including fume occurring in the gas duct is purified by the dust collector, and is directly used from the dust collector as push air (air is sent to the gas duct inside the table). This method is a simple method, since no device for push air is required. However, an exhaust gas in plasma cutting is at high temperature, and if it is used as push air, an upward current occurs because of the specific gravity being small. Even if the push air is blown toward the exhaust port, fumes escape upward, thus causing the problem that the recovery efficiency is low. Further, in the third prior art, the blast hood and the suction hood are provided at the carriage which moves. Consequently, when a cutting operation in which the carriage is sent at high speed is performed, the blast hood and the suction hood are moved to the next section in the state in which fumes remain in the section of the table, thus causing the disadvantage that the residual fumes leak out of the machine.
(3) The fourth prior art described in Japanese Utility Model Laid-open No. 2-87591 discloses the art of the method for pushing a flue gas into the exhaust chamber with the air blow device in a laser machine, and sucking and exhausting the flue gas with the exhaust system (hereinafter, called a push-pull method). However, the cutting table is not divided, and the exhaust chamber is not divided into a plurality of exhaust chambers, the entire cutting table has to be exhausted, thus requiring a large-sized dust collector with a strong suction force. Since the exhaust chamber is not divided into a plurality of exhaust chambers in the fourth prior art, the exhaust chamber necessarily becomes large, and the sectional area changes sharply among the air blow port and the exhaust port facing each other, and the exhaust chamber between them, thus causing disturbance in the current of the exhaust gas inside the exhaust chamber to cause an eddy and stagnation. Acco

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