The disclosure of International Application No.PCT/JP2009/055744 filed Mar. 24, 2009 including specification, drawings and claims is incorporated herein by reference in its entirety.
The present invention relates to a scale removing method and scale removing apparatus wherein the internal surface of a steel pipe is subjected to blasting process where abrasive particles are ejected through a high-pressure jet nozzle and hit the internal surface of the steel pipe.
Steel pipes are often subjected to heat treatment depending on the usage purpose thereof. For improving the quality of steel pipe, it is important to remove scale (descaling) formed on the inner and outer surfaces of steel pipe at the time of heat treatment. A blasting has been known as the method for removing scale from the internal surface of steel pipe. In the blasting, scale formed on the inner surfaces of steel pipe is removed by impacts of an abrasive particle such as iron, stainless steel, alumina, or quartz sand. The blasting involves, for example, sand blasting, shot blasting, and grit blasting. A high-pressure jet system, a negative-pressure suction system, or a combination of these two systems is adopted as the abrasive particle ejecting method.
In the blasting apparatus of high-pressure jet system, for example, a steel pipe is placed on turnable rollers, and while the steel pipe is rotated, a high-pressure jet nozzle is inserted from an end part of the steel pipe and is moved in the longitudinal direction with an abrasive particle blown onto the internal surface of steel pipe through the high-pressure jet nozzle, whereby scale is removed by impacts of the abrasive particle to the internal surface of steel pipe. Dust particles after blasting are usually collected by a dust collector provided in an end part on the opposite side to the end part of steel pipe from which the high-pressure jet nozzle is inserted.
In the blasting apparatus of negative-pressure suction system, for example, a suction machine is installed at one end of a steel pipe, and while the interior of steel pipe is maintained at a negative pressure by the suction machine, abrasive particles are charged from the other end in the state, whereby scale is removed by the impacts of the abrasive particle, moving in the steel pipe, to the internal surface of the steel pipe.
The blasting apparatus of high-pressure jet type has a disadvantage that a large equipment space is required because a pipe for transporting the abrasive particles to the nozzle (transportation pipe) has a long length. The blasting apparatus of negative-pressure suction type has a disadvantage that the scale removing capability is low because the impact angle of abrasive particles is low.
In order to compensate for these disadvantages of the blasting apparatuses, in Patent Document 1, the present applicant disclosed an invention relating to scale removing equipment wherein: a first high-pressure jet blasting section for subjecting the internal surface of one pipe end part of a steel pipe to blasting; a second high-pressure jet blasting section for subjecting the internal surface of the other pipe end part of the steel pipe to blasting; and a negative-pressure suction blasting section for subjecting the internal surface of the overall length of steel pipe to blasting are arranged in juxtaposition, and steel pipe transfer devices are provided between these blasting sections. In this invention, scale formed near the end part of steel pipe, which is less liable to be removed by the negative-pressure suction blasting, is removed by the high-pressure jet blasting.
Patent Document 1: JP11-320413A
As a blower used for the dust collector for high-pressure jet blasting, a blower having a low capacity (usually, about 40 kW or lower) is used as compared with the blower used for the suction machine for negative-pressure suction blasting (90 kW or higher). The reason for this is as described below. The suction machine for negative-pressure suction blasting must create a negative pressure in the steel pipe to produce an air flow sufficient to transport the abrasive particles, whereas in the high-pressure jet blasting, the abrasive particles are transported by the high-pressure jet nozzle, so that the purpose of the dust collector therefor is merely to collect dust particles (abrasive particles and chips thereof, removed scales, etc.).
The reason for this is that during the blasting, the flow of abrasive particles and air are produced in the steel pipe 3 by the abrasive particles ejected through the high-pressure jet nozzle 2, and due to the ejector effect thereof, air of about several times the flow rate of the high-pressure jet nozzle 2 flows into the steel pipe 3 from a portion near an end part of steel pipe (the left end part in the figure).
It can be thought that the capacity of the dust collector is increased to solve the above-described problem. However, since the ejector effect is increased or decreased depending on the inside diameter of the steel pipe, it is not preferable from the viewpoint of energy saving that the suction capability of dust collector be designed so as to match the case where the ejector effect is great.
The present invention has been made to solve the above problems, and accordingly an object thereof is to provide a scale removing method and scale removing apparatus wherein the ejector effect is reduced, and dust particles do not scatter into the atmosphere even with a low-capacity dust collector in high-pressure jet blasting.
The present invention has been made to solve the above problems, and the gist thereof is a scale removing method shown in item (1) and a scale removing apparatus shown in item (2).
(1) A method for removing a scale formed on an internal surface of a steel pipe by subjecting the internal surface of the steel pipe to a blasting process wherein abrasive particles are ejected through a high-pressure jet nozzle and collide with the internal surface of the steel pipe, wherein the blasting process is performed while air is restrained from flowing into the steel pipe from an end part of the steel pipe along with the transfer of the abrasive particle.
(2) An apparatus for removing a scale formed on an internal surface of a steel pipe by subjecting the internal surface of the steel pipe to a blasting process wherein abrasive particles are ejected through a high-pressure jet nozzle and collide with the internal surface of the steel pipe, wherein the apparatus has: the high-pressure jet nozzle for ejecting the abrasive particles; a dust collector for collecting dust particles after blasting; and restraining means for restraining air from flowing into the steel pipe from an end part of the steel pipe along with the transfer of the abrasive particles.
As the scale removing apparatus shown in the above item (2), for example, any mode of items (a) to (c) described below is preferably adopted.
(a) The dust collector is installed so as to be capable of collecting dust particles from a pipe end on the opposite side to a nozzle insertion end of the steel pipe, and the restraining means is formed of a plate material having a size capable of covering the nozzle insertion end of the steel pipe and has a through hole where the high-pressure jet nozzle can be slid.
(b) The dust collector is installed so as to be capable of collecting dust particles from a pipe end on the opposite side to a nozzle insertion end of the steel pipe, and the restraining means is attached to the outer periphery of the high-pressure jet nozzle and is formed of a disc-shaped plate material having an outside diameter equivalent, to an inside diameter of the steel pipe so as to be capable of sliding in the steel pipe.
(c) The restraining means, which is formed of a plate material having a size capable of covering the end part of the steel pipe, is installed at a pipe end on the opposite side to a nozzle insertion end of the steel pipe, and the dust collector is installed so that dust particles can be collected from the same pipe end as the nozzle insertion end of the steel pipe.
According to the present invention, dust particles do not scatter into the atmosphere even with a low-capacity dust collector in high-pressure jet blasting, so that energy can be saved, and at the same time, the work environment can be improved.
An embodiment of the present invention will now be described with reference to
Thereby, during blasting, air can be restrained from flowing into the steel pipe 3 from the end part (the left end part in the figure) of the steel pipe 3. Therefore, dust particles produced by blasting can be collected even if the capacity of the dust collector is not increased.
An example of a scale removing apparatus 7 in accordance with the present invention is shown in
The other example of a scale removing apparatus 7 in accordance with the present invention is shown in
The other example of a scale removing apparatus 7 in accordance with the present invention is shown in
An expandable material such as rubber is desirably used as the restraining means. The restraining means is not subject to any special restriction if it is configured so as to be capable of restraining air from flowing into the steel pipe from the end part of the steel pipe. For example, in the example shown in
In the case where scale is removed throughout the overall length of steel pipe by using the high-pressure jet nozzle, the length of the transportation pipe must inevitably be increased, and also the amount of abrasive particles to be ejected must be increased. Therefore, the abrasive particles remain easily in the pipe. If the remaining amount of abrasive particles increases, the work for moving the transportation pipe is sometimes difficult to do. For this reason, the scale removing apparatus of the present invention is especially effective in removing scale at the pipe end of steel pipe by using the high-pressure jet nozzle.
In order to verify the effects of the present invention, an experiment was conducted where pipes having different inside diameter is prepared the high-pressure jet nozzle was first inserted from one end of each pipe, and then air was ejected while the nozzle jet pressure (nozzle pressure) was changed variously, whereby the flow rate of air at the pipe end on the opposite side to the nozzle insertion side was examined. In this experiment, the inside diameter of the abrasive particles transfer pipe was set at 5.27 mm, and the amount of air discharged from the pipe end part when air is blown into the steel pipes having different inside diameters by using the high-pressure jet nozzle (nozzle pressure: 4.9 to 39.2 N/cm2) was measured. The measurement results are shown in
If the in-pipe air flow rate is 2 Nm3/min or lower, all dust particles produced at the time of blasting can be removed even with a low-capacity blower of 14.0 kW (diameter: 100 mm, 1750 rpm, −5000 mmAg). However, if the in-pipe air flow rate exceeds 5 Nm3/min, the above-described low-capacity blower is insufficient to collect dust, and dust particles are liable to scatter into the atmosphere. Therefore, the in-pipe air flow rate must be controlled so as to be 5 Nm3/min or lower, preferably 2 Nm3/min or lower.
As shown in
Next, an experiment was conducted where pipes having different inside diameter is prepared, the restraining means of the present invention shown in
As shown in
Successively, the same experiment as the above-described one was conducted by using the restraining means shown in
Next, to study the conditions where dust particles are not produced, steel pipes each having an outside diameter of 88.9 mm, 114.3 mm, and 177.8 mm were prepared, the high-pressure jet nozzle (nozzle diameter: 10.0 mm) was inserted into the steel pipe from one end of steel pipe, and the abrasive particles were blown (jet flow rate: 5.9 Nm3/min) and was sucked by the dust collector connected to the other end of steel pipe (suction flow rate: 11.9 Nm3/min), whereby the production state of dust particles and the in-pipe flow rate at this time were examined. The ratio of suction flow rate to jet flow rate (hereinafter, referred to as “Yc”) was 2. As shown in
Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
According to the present invention, dust particles do not scatter into the atmosphere even with a low-capacity dust collector in high-pressure jet blasting, so that energy can be saved and the work environment can be improved.
1. abrasive particles transfer pipe
2. high-pressure jet nozzle
3. steel pipe
4. dust collector
5. dust particles
6. restraining means
7. scale removing apparatus
Number | Date | Country | Kind |
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JP2008-079439 | Mar 2008 | JP | national |
Number | Date | Country | |
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Parent | PCT/JP2009/055744 | Mar 2009 | US |
Child | 12887092 | US |