JPS642479B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for extinguishing a gas flame at the end of a welding operation in automatic gas welding. The gas pressure welding method does not require a power source and can produce joints with high joint strength, so it is widely used for on-site work on reinforcing bars and rails, and is also being used for joining steel pipes. The pressure welding process consists of steps such as injection, ignition, and extinguishing of flammable gas, and starting and stopping pressurization of the joint.
A widely used method is to perform the work automatically by sequentially executing these steps using sequence control. In the automatic gas pressure welding described above, gas flames have conventionally been extinguished in the following manner. When the joint portion is heated to the required pressure welding temperature, upsetting of the materials to be joined begins. When the upset reaches the set value, the burner is evacuated from the joining position and the supply of oxygen to the burner is stopped, and later the supply of combustible gas is stopped. Or, conversely, the supply is stopped in the order of the combustible gas oxygen. Gas supply is stopped by closing a solenoid valve provided in the gas pipe. The conventional fire extinguishing method described above had the following problems. (1) The risk of backfire cannot be completely eliminated. When extinguishing a fire, the flow rate decreases due to the stoppage of oxygen or combustible gas, which may lead to the flashback region shown in Figure 1. FIG. 1 is a diagram showing the conditions for flashback, with the horizontal axis representing the gas mixture ratio and the vertical axis representing the gas flow velocity. The range under curve a indicates a flashback region, and the range between curves a and b indicates a stability region. Further, the range above the curve b indicates the blowout region. In normal fire extinguishing, for example, when the supply of acetylene gas is stopped at point A, where combustion is stable, the gas mixture ratio changes toward point C along straight line c, which is the flow velocity. If it encounters curve b on the way, the gas flame will be blown out at point B. At point C, the acetylene gas has completely stopped. When the amount of oxygen and acetylene gas supplied is small, combustion occurs in the state shown at point A', and in this case, the gas mixture ratio and flow rate change along the straight line d. Then, backfire occurs at point D where it meets curve a. The same applies when stopping the supply of oxygen, and in the case of normal fire extinguishing, it changes along straight lines e and f, for example. The straight lines c, d, e, and f showing the mixture ratio and flow velocity during extinguishing shown here are trajectories based on theoretical values when the mixture ratio and flow velocity change in a very short time; in reality, the flow velocity decreases quickly and the mixture ratio changes. Since the change in speed is slow, the curve becomes convex downward as shown by the dotted line f', approaching the flashback range and causing flashbacks to occur more easily. Typical multi-hole craters, such as those used in gas pressure welding, can cause violent explosions if they backfire. Therefore, there is a high possibility that a major accident such as damage to the device may occur. (2) Pits or blowholes are likely to occur in the pressure welding part. When the acetylene is stopped, the gas flame intersects with curve b at point B, as shown in Figure 1, even though no backfire occurs, and the gas flame is blown out. Therefore, the molten part is exposed to oxygen and reacts with the oxygen to form bits or blowholes in the joint. Furthermore, when the oxygen is stopped, a soot-rich gas flame forms at points E and F, which reacts with the molten part to generate pits or blowholes. In order to avoid the occurrence of such defects, a method has been proposed to evacuate the burner before extinguishing the fire. However, this requires a separate burner retraction mechanism, which complicates the structure of the pressure welding device and makes it expensive. This invention was made to solve the above-mentioned problems that occur when extinguishing a fire in automatic gas pressure welding, and it is possible to extinguish a fire without causing any flashback or defects in the joints. This paper attempts to provide a fire extinguishing method for automatic gas pressure welding. In this invention, when extinguishing a gas flame in automatic gas pressure welding, nonflammable gas is supplied to a burner to which combustible gas and oxygen are supplied. Then, the supply of combustible gas and oxygen to the burner is simultaneously stopped at the same time as the supply of nonflammable gas, or after a slight delay. The supply of nonflammable gas will be stopped only after the fire has been completely extinguished.
Here, combustible gas refers to acetylene, propane, hydrogen, etc. Further, as the nonflammable gas, argon, nitrogen, carbon dioxide, etc. are used. In the present invention, by supplying the nonflammable gas as described above, a decrease in the flow velocity of the mixed gas of combustible gas and oxygen during extinguishing is prevented. Further, when extinguishing a fire, non-flammable gas is supplied and the supply of combustible gas and oxygen is stopped at the same time, so the fire is extinguished instantly. Therefore, during extinguishing, the state of the gas flame does not enter the backfire region shown in FIG. 1, and the fire can be extinguished without causing any backfire. Further, since the non-flammable gas is injected into the joint and the supply of combustible gas and oxygen is stopped at the same time, the joint does not come into direct contact with the combustible gas or oxygen. Therefore, molten metal and combustible gas or oxygen do not react to cause defects such as bits and blowholes. Further, according to the method of the present invention, since there is no need to provide a burner retraction mechanism, the structure of the pressure welding device becomes simple. In addition, there is no backfire, so there is no soot on the burner.
Burner maintenance is reduced and work safety is improved. This invention will be explained in more detail below. FIG. 2 is a schematic diagram of the heating system of an automatic gas pressure welding apparatus implementing the method of the present invention. As shown in the drawings, the oxygen cylinder 1, the acetylene cylinder 2, and the nitrogen cylinder 3 are provided with electromagnetic valves 4, 5, and 6 on their outlet sides, respectively, and are grounded to a ring burner 8 via an injector 7. In the injector 7, acetylene is drawn from the high velocity stream of oxygen and mixed with the oxygen. Further, a dry flashback preventer 9 is provided between the acetylene solenoid valve 5 and the injector 7. The opening and closing of the solenoid valves 4, 5 and 6 is controlled by a control device 10. The ring burner 8 heats the joint portion of the materials 11 to be joined from the surrounding area. Pressure welding is performed in the following steps. First, a small amount of acetylene gas is ejected from the ring burner 8 and ignited. When the ring burner 8 is ignited, oxygen and acetylene gas are supplied to the ring burner 8 at regular flow rates, and the joint portion of the materials 11 to be joined is heated. When the welding portion reaches the pressure welding temperature, the materials 11 to be welded are pressurized in the axial direction by a pressurizing device (not shown) to be welded. and,
Once the bonding is complete, the gas flame is extinguished. These steps are automatically executed by sequence control. As shown in FIG. 3, when extinguishing a fire, the supply of oxygen and acetylene is stopped and the supply of nitrogen is simultaneously started. The supply of these gases is stopped and started by closing the solenoid valves 4 and 5 and opening the solenoid valve 6 in response to a signal from the control device 10. The supply of nitrogen gas to the ring burner 8 is continued until the burner is completely extinguished, and the period of time is approximately 1 to 4 seconds. Note that the supply of nitrogen to the ring burner 8 may be started before the supply of oxygen and acetylene is stopped, as shown by the dotted line in FIG. The appropriate time to start supplying nitrogen early is within 3 seconds to avoid wasteful consumption of nitrogen. Also, if nitrogen is supplied too quickly, it will form a mixture of acetylene, oxygen and nitrogen and react with the molten part.
Defects may occur in the joint. The amount of nitrogen supplied is desirably 15% or more of the combustion gas amount (oxygen amount + acetylene gas amount) in order to purge oxygen and acetylene around the joint and prevent the occurrence of defects. If it is less than 15%, backfire may occur. Example A steel pipe (outer diameter 114.3 mm,
4.5mm thick) was automatically gas pressure welded.

[Table] Table 2 shows the results of welding 10 pairs of steel pipes under the above conditions in comparison with the conventional method.

[Table] Number of items in which failure occurred In the example shown in Figure 2, nitrogen was combined with acetylene and supplied to the injector 7, but oxygen may also be combined or supplied directly to the burner 8. You can do it like this.

[Brief explanation of drawings]

Figure 1 is a diagram showing the conditions under which flashback occurs, Figure 2
The figure is a schematic diagram showing the configuration of an apparatus for implementing the method of the present invention, and FIG. 3 is a diagram showing the timing of stopping and starting the supply of oxygen, acetylene, and nitrogen in the method of the present invention. 1...Oxygen cylinder, 2...Acetylene cylinder,
3... Nitrogen cylinder, 4, 5, 6... Solenoid valve, 8...
...Ring burner, 10...Control device, 11...
Material to be joined.

Claims (1)

[Claims] 1. When extinguishing a gas flame in automatic gas pressure welding, without evacuating the burner from the joining position, supply non-flammable gas at a flow rate of 15% or more of the combustion gas flow rate to the burner to which combustible gas and oxygen are supplied, and extinguish the non-flammable gas. A fire extinguishing method in automatic gas pressure welding characterized by simultaneously stopping the supply of flammable gas and oxygen at the same time as the supply of combustible gas and after a slight delay.