The use of acetylene as the gas oxyacetylene for cutting and welding metal materials is a traditional process. It has high flame temperature, cutting, welding speed, the process is mature, the operating mode is familiar to the actual operators, etc. It also has the disadvantages of high cost, large pollution, and easy tempering during operation. Moreover, the acetylene gas has a wide range of explosion limits, a large operational risk, and high requirements for safety work, so people are constantly looking for other gas. Alternative acetylene gas.
Commonly used fuel gas mainly includes propane, propylene, butane, methane, liquefied petroleum gas, etc. For these hydrocarbon gases, the explosion limit is narrower than that of acetylene, and thus the operation safety is high. On the other hand, these gas flames The propagation speed is slower and the flame temperature is lower than that of acetylene. In actual use, there will be some differences in the performance and operation mode compared with acetylene gas.
With propylene as the gas for cutting metal, the workpiece is not easy to burn, the cut is smooth and flat, and the dregs are easy to remove. When cutting, compared with acetylene, the preheating time is slightly longer, but the cutting speed is equal to that of acetylene. In addition, the cost of propylene gas. Low pollution-free, easy to use, safe and reliable. Therefore, in the metal cutting, propylene gas has been more and more widely used.
However, compared with acetylene, the flame temperature of propylene gas is low, the flame propagation speed is not high, and the flame propagation speed is improved, which is the key to the replacement of acetylene gas by propylene gas.
1 experiment
1.1 Experimental Design <br> Industrial fuel gas has a common feature, that is, all gas needs oxygen to promote combustion, a gas suitable for welding in the oxygen combustion must have the following properties:
(1) The flame temperature is high.
(2) Flame propagation speed is high.
(3) has enough calorific value.
(4) The chemical reaction between flame and base metal and filler metal is the least.
In industrially practical gas, acetylene gas satisfies all the above requirements very well. Other gases such as propylene, propane, natural gas, and some specialized gases based on these gases have a sufficiently high flame temperature, but The flame propagation speed is low. When the ratio of oxygen to gas is high enough to form an effective propagation velocity, the oxidizing properties of these gases are too strong [1].
Therefore, in order to make the oxygen-propylene flame available for welding, we mainly need to increase the flame temperature and improve the flame propagation speed. At the same time, excessive oxidation of the workpiece and the filling material due to excess oxygen should be avoided to affect the welding quality. In [2,3], it can be known that some oxygen-containing organic compounds can be used as combustion activators for oxygen-propylene flames and can increase the flame propagation speed. This study mainly uses alcohol, in addition to oxygen-containing organic compounds to promote the combustion of flames. Ethers, ketones and other organic oxygen compounds. In the formulation process still needs to consider its compatibility with the main gas, volatile and other factors, it is necessary to add some oxidants, vaporizers, stabilizers and other auxiliary components.
The formula research will mainly be conducted in the following sections:
(1) Main gas: propylene.
(2) combustion activator.
(3) Vaporization agent.
(4) Flame propagation speed promoter.
(5) Cosolvent or dissolution stabilizer.
According to the actual situation, add or delete the above one or two components, the flame temperature as a probe to evaluate the merits of the formula.
1.2 Temperature Measurement <br> The instrument used for temperature measurement is WGJ-01 type precision optical pyrometer produced by Shanghai Automation Instrument Factory No. 3. The measuring range is 900～3200°C.
The brightness temperature S measured by an optical pyrometer is converted to true temperature T according to the following formula:
1/(T+273)=1/(S+273)+1.0404×10-4lgελ
Here ελ is the blackness coefficient of graphite 0.95.
1.3 Formulation experiment and measurement of flame temperature <br> Formulation 1: This formula is added with combustion activator, oxidation catalyst and dissolution stabilizer, and vaporization agent that can make these liquid additives evenly atomized. The whole additive amount is 10%.
Formula 2: The formulation mainly includes alcohol and ether additives that can increase the flame propagation speed, and the addition amount is 6%;
Formula 3: Add alcohol and ketone additives to this formula and add a certain amount of vaporizing agent. The total amount is 7%;
Formula 4: This formula adds alcohol, ether, used to increase the speed of flame propagation, and add oxidant and vaporizer, adding a total of 10%.
The flame temperature of the propylene fuel gas after adding the additives is shown in Table 1.
Table 1 Flame Temperature Measurement Results
Table 1 Measurement results of flame temperature
2 Experiments and results testing
2.1 Cutting Experiment <br> Using G01-30 oxygen-acetylene cutting torch, special plum-type oxygen-propylene cutting nozzle, cutting experiments were performed on steel plates with a thickness of 6-50mm, compared with oxygen-acetylene flames, pre-cutting The heating time is a bit longer, and requires a larger amount of oxygen, but after normal cutting, you can adjust the amount of oxygen again.
The cutting quality is better than that of oxygen-acetylene flames, mainly because the cuts are smooth and smooth, with less slag and easy to remove.
2.2 Welding experiment <br> Using H01-6A oxygen-acetylene welding torch, special plum blossom type welding nozzle, welding wire adopts 08Mn2Si welding wire containing deoxidizer, welding test on low carbon steel plates with thickness of 2, 3, and 6mm respectively. The results are shown in Table 2.
Table 2 Welding test results
Table 2 Testing results of welding
2.3 Mechanical properties of welding (1) Cold bending test A3 steel plate with a thickness of 3 mm was used, and the acetylene gas and the additive-propelled tetrapropylene gas were used for welding. The welding rod was type 08Mn2Si, and 5 were cut according to the cold bending test standard. The same sample. The test specimen was bent 180 °, the test results are shown in Table 3.
Table 3 Cold bending test results
Table 3 Testing results of cold bending
The results of the cold bending test showed that the specimens welded with acetylene were bent through 180° without cracking under the test conditions. All the five tests were qualified, while only three tests were performed with the propylene gas welded specimens with additives. Qualified, indicating that the bending strength of the welding site is slightly worse than that of acetylene welding.
(2) Tensile strength test using A3 steel plate with a thickness of 2mm, respectively, with acetylene gas and formula four propene gas welding, using flat mouth butt welding, welding rod model 08Mn2Si, according to the tensile strength test standard cut 4 same test Samples, test results are shown in Table 4.
Table 4 tensile strength test results
Table 4 Testing results of
3 results analysis
In theory, complete combustion of acetylene can be represented by the following chemical reaction equation:
C2H2+2.5O2─→2CO2+H2O+1344kJ/mol
However, in fact, the combustion is carried out in two stages. The first reaction takes place inside the flame (flame center) and is represented by the following chemical reaction equation:
C2H2+O2─→2CO+H2+464kJ/mol
The heat released by this reaction and the high temperature of formation are due to the decomposition of acetylene and the partial oxidation of the decomposed carbon.
When the ratio of the gas ejected from the torch nozzle is 1:1 as shown in the above reaction equation, the reaction results in a typical extremely bright blue flame, which is required when the relatively small flame is generated in the welded steel sheet. The combustion intensity, this flame is called a neutral flame. Because there is no excess carbon or oxygen to carburize or oxidize the metal, the product after the reaction is actually reductive, which is beneficial when welding steel.
Oxygen-acetylene flames, where the flame temperature is around 3100 °C.
In the outer layer of the flame, the carbon monoxide and hydrogen produced in one reaction and the oxygen in the surrounding atmosphere are combusted to form carbon dioxide and water vapor, which means that a secondary reaction takes place. The equation is as follows:
2CO+H2+1.5O2 
2CO2+H2O+880kJ/mol
Although the heat generated by the combustion in the outer zone is greater than the heat generated by the flame core, due to its large cross-sectional area, the outer flame has a lower combustion intensity and temperature.
The complete combustion of propylene can be represented by the following chemical reaction equation:
C3H6+4.5O2 3CO2+3H2O+2175kJ/mol
The theoretical oxygen consumption is 4.5:1.
The first reaction is:
C3H6+1.5O2 3CO+3H2+391kJ/mol
The oxygen-propylene neutral flame temperature at this time is 2870°C, and the secondary reaction of the oxygen-propylene flame is as follows:
3CO+3H2+3O2 3CO2+3H2O+1784kJ/mol
Therefore, for the oxygen-propylene flame, although the total calorific value of 2175 kJ/mol is greater than the total calorific value of the oxy-acetylene flame of 1344 kJ/mol, the calorific value of the first reaction and the temperature of the neutral flame are both low. For welding, especially when welding thick workpieces, the oxygen-propylene flame has certain defects.
Our test is to increase the total calorific value of combustion by increasing the total calorific value of combustion by adding additives to the propylene fuel gas. The purpose of improving the flame temperature is to increase the flame temperature. From the results of the experiment, the flame temperature is greatly increased after adding additives. The improvement, especially the torch flame temperature (oxidation flame) is higher, when applied to metal cutting, get a good cutting effect. The welding uses a neutral flame, while the neutral flame temperature to a large extent Constrained by the primary reaction of propylene, although in the test of Formula 4, the temperature of the neutral flame of propylene gas after adding the additive is 110°C higher than that of pure propylene gas, reaching 2980°C, but compared with the temperature of 3100°C of the neutral flame of acetylene. There is still a big gap.
4 Conclusion
1. Compared with pure propylene fuel, the flame temperature of propylene fuel after adding different additives has obviously increased, the temperature can be increased by 30～220°C.
2. Because the propylene gas after adding the additive, the flame temperature is improved, especially the oxidation flame temperature, so when applied to metal cutting, there is a big improvement, mainly to shorten the preheating time, improve the cutting speed, improve The quality of the incision, and reduce the gas consumption.
3. Propylene gas after adding additives, in which the flame temperature has also been greatly improved. Therefore, it can be used for the welding of low-carbon steels and aluminum, copper and other metals below 6mm. The welding quality is good.