Applications of cutting in Continuous casting billet >>
Hydrogen, as a green energy medium, can also meet resources, environment and sustainable development's requests that no other gases can match. In 1999，using Oxy-hydrogen flame for the continuous cast products cutting technology successfully applied to the continuous cast products cutting field, it has undertook continuous developments and improvements. More than 100 sets of caster and 450 sets of billet, rectangular billet and plate slab use Oxy-hydrogen gas as cutting flame (energy medium). So it make a significant contribution to the work of saving energy and reducing consumption of our country's steel enterprise.
Metal cutting is a metal and oxygen burning exothermic chemical process. In the process of cutting, the main effect of flame is to heat the metal to its ignition point. Burning the hyperbaric oxygen with metal will release a lot of heat, the formed metal oxides will blow away by hyperbaric oxygen flow. Then the metal will be cut off. The technology of the Electrolyzing Water Oxy—hydrogen Generator in the Continuous Cast Products Cutting, using the made oxy-hydrogen as a medium energy, is to bum the billet to its ignition point in order to cut off it.
Burning level is the comprehensive index of the heat performance degree. The size of the combustion intensity depends on the burning speed and total calorific value of the gas flame. The size of the combustion intensity of acetylene is the highest among all kinds of gas. Hydrogen's combustion intensity rank only second to acetylene's for its high burning speed, though it has a low total calorific value. The temperature of the billet has a great impact on the speed of cutting, the cutting speed will be doubled if the casting billet's temperature reaches 800°C than normal.
There is carbon element in fossil fuel materials. In cutting process, there will form viscous iron carbide ( Fe+C—FeC )，so, after cutting Continuous casting billet, there are many slag which are not easy to clean up, it need precise rectifier before the steel rolling process. However, using Oxy-hydrogen produces fewer slag, which are easy to clean up, than using other fuels. Meanwhile, the Oxy-hydrogen gas has a straight flame with good collectivity so that we will get a small kerf and a flat cutting surface.
The Oxy-hydrogen gas, which is non-toxic, would not harm the staffs health. There is no pollution after burning. It accord with environmental protection requirement make hydrogen by Electrolyzing water is low-cost, safe, reliable and not limited by region. Therefore, the usage of Oxy-hydrogen meets the request of green plants construction.
Use Oxy-hydrogen as the burning gas in cutting can create considerable economic benefit and social benefit. The economy-technology analysis of the Continuous Cast Products (150mm*150mm) Cutting by using Oxy-hydrogen, as follows:
1. Basic Data
1.1 Based on 4 sets of billet continuous casters of 4 strands, with a total output of 600000 tons for 6m/each.
1.2 Withdrawal speed: 2.7m/min; cutting cycle:45s
1.3 Oxy-hydrogen flame cutting:
150mm*150mm,s Continuous Cast Products; the generator’s power consumption (each):22KW/h; electricity cost: accord with RMB 0.5yuan/KW
1.4 Pipeline oxygen: RMB 0.5yuan/m3; coke oven gas: RMB 1.2yuan/ m3 The cost of production of steel per ton: accord with RMB 2,500yuan/ton
1.5 Cutting gun gas flow: 16mVh
1.6 Basic data calculation:
Single billet weight: 0.15m*0.15m*7.8t/m3=l .053t
billet steel equivalent number: 600,000+1.053t/per=569801 pieces
Billet unit weight(t): 0.15m*0.15m* 1 m*7.8t/m,=0.1755t
2. Cost-to-use of propane gas. Coke oven gas, Oxy-hydrogen gas and other gases
2.1 propane gas cutting
Propone gas is the by-product of the petroleum chemical industry, with high ignition point, slow burning speed and poor reactive characteristic. It is generally used as fuel. Since 1960s, the experiments of its，application in the industrialization process has been embarked worldwide. The developed gas, like Terry, Sharp, Flamex and Chemtane gas, are actually just add some additives or a certain proportion of propylene. Bccausc Propane and Propylene arc the by-products of the petroleum chemistry industry, it is hard to guarantee the stability of their effects due to their geographical origin, batch and additives’ prosperities and quantity. And besides, the vaporization effect is quite unsatisfactory under low temperature in winter.
The burning chemical equation of propane: C3H8+502=3C02+4H20, from which we can know a volume unit of propane need 5 times volume unit of mixed oxygen.
Propane consumption of each cutting: 16m7h+3600s/h*45s=0.20m3 Mixed oxy-fuel combustion of each cutting: 0.20m3*5=1.0m3 The follow sheet is the Cost-to-use of propane gas (RMB 4,500yuan/ton=RMB 8.33yuan/m')
2.2 Coke oven gas & Acetylene gas cutting
The burning chemical equation of Acetylene (C2H2): 2C2H2+502=4C02+2H20 The burning chemical equation of Carbonic oxide (CO): 2CO+ 02=2C0,
After purification, the coke oven gas is a colorless, smelly poisonous gas. Its' main components are: H2(60%), CH4(22〜26%)，CO(6〜9%)， CnHm(4.5%) and impurities like C02, N2, 02. The burning volume ratio of Coke oven gas and mixed oxygen volume is 1:1 basically. Thus, we can figure out the cost of ton steel (150mm* 150mm, 6m/each) oxygen consumption is RMBO. 14yuari/ton. The price of Coke oven gas is around RMB1.2yuan/m3，the direct ton steel cost is RMB1.3yuan/ton, a little higher than oxy-hydrogen. When the investment is made only for continuous cast products cutting, it is not economical and practical.
Acetylene, as a traditional cutting gas, is widely used in metal cutting process with high flame temperature and calorific value. However, due to its, high production cost, can reach above RMB 4yuan/ton, and the existence of some safe and pollution problems, there are fewer manufactures adopt this kind of fuel.
2.3 Continuous Cast Products Cutting by Oxy-hydrogen Gas
The chemical equation of electrolyzing water (H20): 2H20=2H:+02 The burning chemical equation of hydrogen (H2): 2H2+02=2H20
The made Oxygen itself, by electrolyzing water, meet the burning need of Hydrogen without any low oxygen gas (mixed oxygen gas). The direct usage cost only exist in the electricity which can save massive fund in buying Mixed Oxygen gas. The economic analysis of Oxy-hydrogcn is listed as follows:
Under the condition of constant flame, the ton steel cutting cost is in inverse proportion to withdrawal speed, has nothing to do with the scale.
3.Economic Efficiency Comparison
From the above calculation we can see that using oxy-hydrogen gas cutting has a better economic efficiency. Below sheet is an efficiency comparison of 600,000 tons annual production (150mm* 150mm, size 6m) between oxy-hydrogen gas and propane gas:
We can see from the sheet and know that the usage of Oxy-hydrogcn gas has a prominent economic efficiency.
4.Billet Cost Impact
There is carbon element in fossil fuel materials. In cutting process, there will form viscous iron carbide(Fe+C—> FeC), so, after cutting Continuous casting billet, there are many slag which are not easy to clean up, it need precise rectifier before the steel rolling proccss. However, using Oxy-hydrogcn produces fewer slag, which arc easy to clean up, than using other fuels. Meanwhile, the Oxy-hydrogen has a straight flame with good collectivity so that we will get a small kerf and a flat cutting surface.
1. Acetylene gas
Acetylene, belongs to unsaturated hydrocarbons, is a kind of asphyxiating gas with active chemical property. It is flammable and explosive. Its，ignition temperature is 460〜440°C and the explosion limit mixed with air is 2.5%〜80.0%. Its, relative density is 0.906 in 15.6°C, smaller than air's. It is easy to catch fire and cause explosion accidents for its’ slow leak diffusion so as to obey the operation rules strictly.
Propane belongs to saturated Hydrocarbons. Its’ ignition temperature is 515~543°C and have a smaller explosion limit mixed with air which is 2.5%〜80.0%. Its’ relative density is 1.52 in 15.6°C, bigger than air’s. It will harm worker's health for its’ high toxicity. Propane gas would not bum-back for its' quick burning speed. It will accumulate in low-lying place when leakage happens so that worker must strictly in accordance with the operation rules. In 2001，there was a propane gas converge-wires explosion accident happened in a steel plant which is a serious threat to the operating personnel and production equipment safety.
3.Cokc oven gas
After purification, the coke oven gas is a colorless, smelly poisonous gas. Its’ ignition temperature is 550〜650 °C and the explosion limit mixed with air is 4.27%~37.59%. It is easy to happen safety accidents like poisoning, catching fire and explosion.
Oxy-hydrogen gas, with a low price, has no pollution and toxicity so that it will not harm the operator's health. Its, ignition temperature is 580〜590°C and the explosion limit mixed with air which is 4.0%〜74.2%. Its' relative density is 0.069 in 15.6°C, smaller than air's. Oxy-hydrogen gas is produced through the electrolysis of water which is used immediately what is produced. It is operated under normal atmospheric pressure, without large scales of storage and transportation over long distances. Thus, it is very safe and there is no danger. Due to the smaller density than air, even if happened the leak accident, the gas will not gathered together, but rising and spreading rapidly, they won't harm the operating personnel's physical health. The oxy-hydrogen generator is not a kind of pressure vessel so that its, operation is not under the administration of The Labor and social security department.
Using Oxy-hydrogen gas in cutting do not increase the consumption of oxygen gas so as to omit the preheat gas consumption. It is used immediately what is produced, so we do not need large scales of storage and transportation. This alleviate the workers' labour intensity on condition of the high utilization ratio of working hours.
The Oxy-hydrogcn gas has a straight flame with good collectivity so that we will get a smaller (about 10% ) kerf than other gas did and a relative flat cutting surface with fewer slag. All of these save a lot of time such as clean-up and subsequent processing.
The inner gas pressure of generator is low, not belongs to a kind of pressure vessel. The low management demand and the equipped multilevel security device protect the safety of operation. The produced Oxy-Hydrogen gas is produced through the electrolysis of water which is used immediately what is produced. It is operated under normal atmospheric pressure, without large scales of storage and transportation over long distances. Thus, it is very safe and there is no danger.
The generator’s production process is non-pollution. The process of Oxy-hydrogen's burning produce only water, is non-toxic, smokeless and odorless, which will not harm the operator's health. So，the Oxy-hydrogen gas is real green.
Application in Machinery Processing Industry >>
The Oxy-hydrogen gas has been applied into billet cutting since 1963. Under decade's year's development and application, the technology has become well-developed which has applied into industries like Heavy Machinery, chemical equipment, boiler manufacture, locomotives manufacture, petrochemical, aerospace, Automobile, machinery manufacturing, panel processing, pattcrnmaking, hydropower industry and so on.
Cutting characteristics of Oxy-hydrogen gas:
1 .Meets different needs of flame such as neutral flame, carbonizing flame and oxidizing flame
2.Cutting surface smooth & flat, no residue and dregs
3 .Narrow cutting edge, saving material, less heat affected zone and no deformation
4.No hidden trouble of burnning-back ensure cutting safety
5.Low pollution, environment friendly
6.High economic efficiency, save 70〜75% and > 40% investment compares to Acetylene gas and Propane gas
Range of application
1 .Suitable for low,middle carbon steel and low-alloy steel under 300mm.
2.CompatibIe to manual,semi-automstic and automatic cutting machine.
Cutting of the marine deck steel
Usually the structural steel used for construction of common strength ship contains carbon at a rate nearly from 0.18% to 0.23%, so this is a kind of low carbon steel. Due to marine deck steel's high thickness and a good adaption to different shapes, most of users prefer to acetylene gas for cutting, but the cutting requirements of marine deck steel (see below) may lead you to make a better choice at using oxy-hydrogen gas.
1. Oxy-hydrogen pressure must be properly supplied. When pressure is too high, the cutting edge will become wider and coarse. When pressure is low, the ferric oxide slag can not be blown away.
2. Preheating flame's energy rate shall be properly supplied. If it's too high,the cutting edge will be melted. If it's too low, the cutting process will be interrupted so the cutting edge is not smooth and flat.
3. The cutting speed should be appropriate. If too fast, it will generate a big lag and will be difficult to cut the plate through. And the iron slag bursts up and easy to cause backfire, or if too slow, the two ends of the steel plate is easy to melt, and the spark fly backward or even cause a big deformation and waste the cutting gas at the same time.
4. The cutting torch should keep clean and without iron slags on the cutting head. The holes inside cutting head should be specially kept smooth. Since the traditional acetylene gas exists lots of defects like the large energy cost, environment pollution, easy flame disperse, difficult speed control, and unable to give a full guarantee of the cutting quality, the oxy-hydrogen has gradually become an alternative heat resource to replace the acctylcne.
Advantages of Applying Oxy-hydrogen Generator to Cut the Marine Deck Steel:
1. No need for low pressure oxygen, an easy control at cutting speed.
2. Smooth cutting edge reflecting metallic luster, especially no nitridation layer which can have the metal put into welding process after cutting
3. No slag on cutting lower edge: The exothermic reaction of the oxygen and iron at cutting can produce extra heat. Meanwhile, it produces FeO slag with a lower surface tension which can improve the fluidity of the metal on cutting edge and produce a smoother surface with no slag and form a smaller cutting edge bevel.
4. The Oxy-hydrogen has a smaller heat effective zone which reduce cutting deformation and improve cutting precision.