In 2019, the total global production of aluminum extrusion materials was approximately 37 million tons, with China reaching approximately 20.5 million tons, North America reaching approximately 2.5 million tons, Japan reaching nearly 810000 tons, and Germany reaching approximately 620000 tons. They are all products produced by hot extrusion method, and the ingot is heated to 320 ℃~520 ℃ before hot extrusion. The allowable maximum heating temperature for different ingots of alloys also varies, for example, for Series 1 alloys, it ranges from 400 ℃ to 470 ℃; The temperature range for 2-series alloys is 320 ℃ to 460 ℃; The 6-series alloy ranges from 480 ℃ to 520 ℃, making it the alloy with the highest allowable extrusion temperature. The highest allowable temperature for 6061 and 6063 alloys can reach 520 ℃, but such high temperatures are not commonly used, usually around 500 ℃. These two alloys are also the most commonly used alloys, accounting for 75% of the world's total production; The production of 2-series and 7-series alloy extruded materials accounts for less than 8% of the total production, mostly for aerospace, military, and other load-bearing structural materials.

　　In the production process of extruded materials, the processes that require heating and energy consumption include melting, heating of ingots before extrusion, heating of extrusion cylinders and molds, and heating and insulation of offline solution treatment and aging treatment. The heat source used can be electric heating (resistance or induction heating) or gas heating. In the past 10 years, extrutec GmbH in Radolfzell, Germany, has made great achievements in rapid gas heating systems. For example, the most prominent innovation in recent times is the Eco Shower Unit, which is an energy-saving water heating device connected to a long ingot gas heating furnace, In 2019, it has been promoted in Germany and the Middle East, with significant energy-saving effects and received high praise.

　　Economic spray heating technology

　　The Esu heating system of the extrusion technology company has significant energy-saving effects, with a long ingot conveyor preheated by water and connected to the gas furnace as a whole. Aluminum and aluminum alloys have high thermal conductivity (238 W/m · K at 0 ℃ to 100 ℃), which can absorb a large amount of heat in a short period of time and raise the temperature. However, the energy density of the furnace gas is low, and it cannot cause a significant increase in the temperature of the aluminum ingot in a short period of time. If a heat exchanger is used, this idea may be realized. Stefan Beer, an engineer at the extrusion technology company, invented the Essu heating system based on this idea, hence the system can also be translated as an economic spray heater. The heating method for this type of aluminum ingot is to first use a 360 ℃ gas furnace to heat the water in the heat exchanger. The water temperature can rise to 90 ℃, and when the ingot passes through the spray chamber, 90 ℃ water is sprayed onto the slowly advancing ingot. The time for the long ingot to pass through the spray heating chamber is 4-5 minutes. The length of the ingot heated to 90 ℃ is three times the length of the short ingot that needs to be extruded, and the water is circulating. The temperature of the flue gas coming out of the heat exchanger is 120 ℃~130 ℃, rather than the usual 250 ℃~300 ℃ of flue gas emitted by the gas furnace. The use of the ESU heating system can save about 15% energy, which is not a small fraction. For an enterprise with an annual output of several hundred thousand tons of extruded materials, it cannot be ignored.

　　After the long ingot is heated to 90 ℃ by spraying water, it immediately enters a conventional gas heating chamber or induction heating furnace. After heating to the extrusion temperature, it is cut into a specified length and then sent into the extrusion cylinder. The dirty water sprayed onto the long ingot flows into the filter, is filtered and reused, while washing the surface of the ingot clean.

　　Heating aluminum extrusion ingots with hot water not only saves energy, but also reduces the emission of greenhouse gas CO2, as the amount of fuel used - liquefied gas - has decreased. Another advantage is that the length of the heating furnace can be shortened, as the number of zones in the furnace can be reduced. Generally, the length of the furnace can be shortened by 1.5 meters.

　　practical application

　　By the end of 2019, there were four aluminum extrusion plants worldwide using or about to put into operation the ESU long ingot heating system. Three plants were located in Germany: Aluminium-Werke Wutoschingen (AWW), and new extrusion production lines were being built: Erbosloh Aluminum GmbH in Velbert; Extrutec GmbH. Another factory is an aluminum alloy extrusion company in the United Arab Emirates, which has also ordered one. The practices of these companies have shown that the investment in building hot water heating ingot equipment can be recovered in less than a year, and such a short payback period is rare.

　　The application shows that the new technology has four advantages: firstly, the gas furnace can be made shorter, which is currently the shortest furnace on the market; The second is that the ingot cleaning system can remove all dirt and adhered particles from its surface, which is beneficial for extending the life of the mold; Thirdly, all existing equipment and means can be utilized and are not abandoned; Fourthly, various temperatures can be accurately controlled. In addition, the German government also attaches great importance to the promotion of this technology, and the Federal Ministry of Environment provides certain rewards to enterprises applying this technology.

　　epilogue

　　The long ingot economic spray hot water heating technology for extrusion is a new cutting-edge technology with low investment and can be recovered in about one year. It is an energy-saving and emission reduction project that can be applied not only to new extrusion production lines, but also to the upgrading and renovation of existing production lines. China is currently constructing large-scale aluminum extrusion projects in the Heilongjiang and Guangdong regions. It is best to have an understanding of this technology and whether it is possible to introduce a new one. We also hope that existing aluminum extrusion enterprises have some understanding of this technology.