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Energy-saving skills and methods for casting

Author:Wanhe    Time:2019-11-04     Clicks:941


       Casting operation is a large energy-consuming enterprise in the machinery industry. The high energy consumption, low power utilization rate, severe pollution and poor economic efficiency restrict the development of casting operations. Rational use of power and vigorous efforts to save power are an important task in casting operations.

Energy-saving skills and energy-saving methods include the following aspects.

   First, the recovery and reuse of old sand

   The booming industry in Europe and the United States has always used old sand as a serious research topic, and has achieved a good research role, and has now been put into industrial production. When casting non-ferrous metal parts, cast iron parts and steel castings. The old sand is regenerated mechanically according to the sintering temperature of the old sand. Its regeneration rate is roughly 90%, 80% and 70%. The combination of old sand recycling and wet regeneration is the most economical and optimal choice. The two-stage wet regeneration removal rate (Na2O) is 85%-95%, and the single stage can reach 70%. 90% of the old sand is recycled and reused, and the quality is close to the new sand. British Richard (Research) uses thermal regeneration, which can improve the regeneration rate by about 10% to 20%. Moreover, the recovery period of the hot-process old sand recycling equipment is relatively short, and the general operation can recover the cost in two years. The recovered zircon sand that cannot be reprocessed by mechanical method is treated with thermal treatment, and the quality of reclaimed sand is better than that of new sand. In the United States, the annual consumption of sand for foundry operations is about 5 million tons. BastianKC and AllemanJE have found that old sand after casting is used for highway subgrade data. Thoroughly satisfied with the functional requirements of the materials used in the construction of highways. Its function is also superior to the new sand of the same variety.

    Second, the recycling of the binder

    Environmentally friendly sand core inorganic binder and sand treatment and regeneration skills have received more and more attention. Laempe's Beach-BoX inorganic binder is a fluid containing a variety of minerals. The core sand is 95% sand and 5% binder. For example, the casting is dry-removed, and the binder remains in the sand for activation. Binder, only need to add 2.5% water can be reused repeatedly without having to add new binder, which means that each batch of larger binder in the batch is only 1.6% by water removal. The chemical reaction of the binder component is hardened, and the application time is unlimited, but the relative humidity should not exceed 70%, and the mixed sand seal can be stored for a long time. FoundryAutomation and MEG's binders are powdery and are not used in the core, storage and casting process of aluminum alloys, and there are no environmental problems caused by resinous binders. The wet sand can be reused 85%, and the recovered data can be reused 100%.

   Third, the regeneration of mold and mold

   Since the 1990s, the countries of the United States and Europe will cast molds or molds that have been abandoned by the manufacturers. After special purification treatment, the components will be adjusted according to different needs of users to form a “recovery-recycled mold”. The key to the skill is to use advanced multi-stage filtration or centrifugation to speed up the process and obtain a more pure mold. MittererC found in the study of aluminum casting molds. Applying a hard film on the outside of the steel mold can be used to effectively resist the damage of hot cracking and corrosion by using the maintenance effect of nitrogen and carbide, and replace the thick oxy coating material with the film. Then it is useful to extend the mold application cycle. Its core skill is the PACVD skill, which is plasma chemical vapor accumulation.

   4. Energy-saving skills centered on smelting

   The energy consumption of the casting smelting part accounts for about 50% of the total energy consumption of the casting, and the casting waste caused by the melting causes accounts for about 50% of the total waste. Therefore, the selection of advanced and applicable smelting equipment and smelting process is the primary method of energy saving. Take the energy-saving skills of cast iron smelting as an example.

  (1) The implementation of hot air, water cooling and continuous operation, the long furnace age cupola to the large-scale, long-term continuous operation direction is an inevitable trend. Foreign foundry companies use it as an important energy-saving method. In recent years, China has also done a lot of work in these areas, and some enterprises have chosen it and achieved remarkable energy-saving effects. For example, the use of large-row double-layer air supply cupola technology can save coke 20%~30%, reduce waste rate by 5%, Si, Mn burn loss by 5%, 10%; water-cooled no furnace lining and thin furnace lining cupola The long-term operation time can save more than 30%; the hot air cupola is energy-saving and environmentally friendly.


  (2) Promote the double-melting process of cupola-electric furnace. Cupola-electric furnace double smelting is the advantage of using cupola preheating, high melting power and high superheat power of induction furnace to improve the quality of molten iron and reach the intention of reducing energy consumption. In recent years, the prices of raw materials such as coke and pig iron have risen sharply and the quality requirements of castings have become higher and higher. The use of electric furnace smelting has been increasing, and the use of nighttime low-valley electricity production has also achieved good economic and energy-saving effects.


   (3) Promote the use of foundry coke oven melting. The use of cast coke fuel is a useful step to improve the temperature and quality of molten iron. Most of the cupola furnaces abroad use casting coke. Because of the high price of foundry coke or because of the habits and other reasons, most domestic enterprises still use metallurgical coke. Even some companies use soil coke, which not only affects the quality of castings, but also consumes a lot of coke. If cast coke is used, the scrap rate can be reduced by 2%. Therefore, the development of casting coke production, the implementation of the use of casting coke is one of the ways to improve the quality of castings and reduce power consumption.


  (4) When the dehumidification air supply cupola uses metallurgical coke, the temperature of the molten iron is difficult to reach 1500 °C. If 3% oxygen-enriched air supply is used, it can be ensured, and the net energy per ton of iron can be reduced by about 10 kg of standard coal. The cupola dehumidification air supply is generally used in the wet area in the south, which can improve the temperature of the molten iron and reduce the burning of elements such as silicon and manganese. Improve the quality and melting rate of molten iron, and reduce the coke consumption by 13%~17%.


  (5) The cupola uses the computer to control the skills. The cupola uses a computer to control the active control including the batching of the machine, the active weighing of the charge and the melting process. The cupola is operated under optimized conditions to obtain high quality molten iron and suitable molten iron temperature. Compared with the craft control, it can save coke l0%~l5%.


  (6) Promote the use of high-pressure centrifugal energy-saving fans for cupola furnaces. At present, there are still many cupolas in China that use Roots or Yishi's volumetric fans, which consumes a lot of energy and noise. The high-pressure centrifugal energy-saving fan for cupola is used to save electricity by 50%~60%, and the melting rate is improved by about 33%.


   5. Energy-saving skills centered on the heating system


   The energy consumption of casting industrial kiln is second only to the melting equipment, accounting for about 20% of the total energy consumption. For various heating furnaces, drying furnaces, and annealing furnaces, skill transformation should be carried out from furnace type structure to incineration skills. The use of refractory insulation materials to transform existing kiln, energy saving effect is significant. For coal-fired industrial furnaces, the use of mechanical coal is more than 20% energy-saving. The coal-fired sand-type sand core drying furnace is changed to the open flame anti-burning method, which can save 15% to 30% of coal. For the core drying oven, the use of far-infrared boring skills can save 30%-40%. The use of oscillating aging to eliminate stress treatment for large castings can save more than 80% energy by using thermal aging treatment. The rapid annealing process of the malleable cast iron zinc atmosphere can save electricity or reduce coal consumption by more than 50%.


   Sixth, energy-saving skills centered on the selection of advanced and applicable modeling core skills and equipment


   At present, the energy consumption of several domestic molding processes is different from wet type l, self-hardening sand 1.2-1.4, and clay dry sand 3.5. Clay dry sand type has higher energy consumption and should be screened. Wet type energy consumption is lower, and adaptability is strong, which is one of the reasons why the wet type is still used. Advanced high pressure, static pressure, injection pressure, air blasting techniques and equipment should be selected according to casting quality requirements and casting characteristics, as well as self-hardening sand skills, lost foam casting skills and special casting skills. Replacing the clay dry type with resin self-hardening sand, water glass organic ester self-hardening sand and VRH molding core making process. It can improve the dimensional accuracy of castings and reduce the roughness of appearance, improve the quality of castings and reduce energy consumption. The special casting process is compared with the general clay sand. The dimensional accuracy of the casting is 2~4, the surface roughness is fine l~3, the quality is reduced by l0%~30%, the machining allowance is reduced by more than 5%, and the casting scrap rate is also greatly reduced. Inductive energy saving is significant. For every 1% improvement in the pass rate of castings, 8 to 10 castings per ton of molten iron can be produced, which is suitable for 5 to 7 kg of coal. The energy consumption of castings decreased by 1.25% for every 1% decrease in energy consumption. For every 1% drop in casting quality, energy consumption drops by 1.01%. It can be seen that advanced technology skills and equipment are selected. Improve the quality of castings. Declining the casting scrap rate is an important way to improve the power utilization rate and reduce energy consumption.


   Seven, the implementation of low-stress cast iron, as-cast ductile iron and other skills


   China's energy consumption for gray iron castings is 40-100kg standard coal per ton of castings, and the energy consumption for annealing and normalizing of ductile iron parts is 100-180kg standard coal per ton of castings. Except for a small number of enterprises producing car engines and internal combustion engine castings, it is not necessary to heat aging process. Most enterprises that produce such castings still use thermal aging to eliminate stress, which is one of the reasons for the high energy consumption of casting operations in China. Promote the production skills of thin-walled high-strength gray iron castings and the production skills of high-silicon cast iron parts, and produce castings for cylinders, cylinder heads and machine bed of passenger cars and internal combustion engines, and obtain low-stress cast iron parts that do not require thermal aging. Reach energy saving intentions. China's ductile iron castings have a large proportion of high-resistance ferrite ductile iron and high-strength pearlite ductile iron. Generally, annealing and normalizing treatment are used. The use of cast spheroidal graphite cast iron production technology eliminates the annealing and normalizing treatment process, saves power, and prevents the deformation and oxidation of castings caused by high temperature treatment. The use of ductile iron without the El casting process can improve the process yield rate by 10% to 30%, and the energy consumption is also significant. For example, in 2003, the total output of China's castings was 19.87 million tons, during which gray iron castings were 10.49 million tons, and ductile iron castings were 4.7 million tons. Therefore, the implementation of low-stress cast iron parts, as-cast ductile iron parts and ductile irons did not take place. Casting skills, energy saving and consumption reduction for all operations have important implications. The steel castings are made of thermal insulation and thermal insulation, which can improve the process yield from 60% to 80%.


   Eight, the implementation of cupola exhaust gas utilization and waste heat recovery skills


    At present, 90% of China's cast iron is produced by cupola smelting, and this situation will remain at a suitable long time. The use of waste heat in the casting operation will first gather on the cupola. When the cupola is smelted, a lot of flue gas is emitted. The flue gas contains flammable carbon particles and flammable gas, which constitutes environmental pollution and ruins a lot of heat energy. In the cupola furnace smelting, in addition to 38% to 43% of the useful heat used for smelting, the heat taken away by the flue gas is 7% to 16%, and the heat is not completely incinerated (combustible gas) is 20% to 25%, and the solid is not completely The heat of incineration is 3% to 5%. These heats account for 30% to 45%. It can be seen that the residual heat of the cupola melting has great potential. At present, the vast majority of the waste heat of the cupola in China is preheated by the dense ribs, the hot air temperature is about 200 °C, and the residual heat utilization rate is low. In recent years, some enterprises have used the long-burning hot air cupola for long-term operation, which fully utilizes the waste heat of the exhaust gas and the heat that can be incinerated by burning carbon particles and incineration gas, so that the hot air temperature reaches 600-800 ° C, cupola hot metal. The temperature reaches 1500--1550 ° C, and the melting power is improved by 45%. It not only achieves the purpose of energy saving and the improvement of the quality of molten iron, but also fulfills the requirements of environmental protection.


   Nine, develop advanced skills


   Through the improvement of casting equipment, casting materials and casting technology, the Japanese foundry industry has enabled foundry companies to save energy and reduce pollution and to reduce environmental pollution. For example, the modified cupola uses variable frequency control, adding dust removal equipment, reducing the power consumption by half, 60% of the exhaust heat is recycled, and the exhaust emission can reach any emission standard. The energy-saving molding machine after the transformation from the beginning, because the high-frequency oscillation is selected, the energy required is only 10% of the hydraulic molding machine. 3. Lost foam casting has advantages in producing net-scale castings. The composition of the pollution is very small, which is conducive to environmental maintenance, and is called the green casting process.


   The use of solar energy to treat scum and foundry sand in the essence of aluminum can save a lot of power. The primary equipment used in this treatment is a rotating, directly heated, drying oven. At DLR, Cologne, Germany, the production of solid waste using solar heat has now been carried out on a commercial scale and has been remelted with aluminum scrap. The traditional treatment method is prevented, and the energy required for the demand is high, which causes many enterprises to pile up the waste.


    It is always the use of a series of new research roles mentioned above. It will make the production of China's foundry industry enter the track of circular economy.

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