In the process of metal pressure processing, heating technology has a great impact on product performance. At present, this problem has aroused great attention of industrial countries all over the world.
As we all know, the purpose of forging parts is: first, forming; second, forging internal defects such as looseness and shrinkage cavity. For large forgings, due to the larger size and weight, the higher quality requirements, and the limited forging ratio, it is obvious that the main purpose is to forge the internal defects such as porosity and shrinkage cavity. Forging heating is an essential process in forging production, and the heating furnace is an important thermal equipment in forging production. Therefore, continuous development of the heating furnace technology is also one of the important measures to improve forging quality.
Although there are many types of forging heating furnaces used for forging hydraulic press, most of them are trolley type furnaces. Most of the tool operators are equipped on large and medium-sized forging hydraulic presses abroad, and some countries are equipped with medium and small rail operators on forging hydraulic presses.
Development of forging heating furnace abroad
The former Soviet Union has developed various fast heating furnaces and devices, and has conducted a lot of research on the furnace type with little (no) oxidation heating, thermal system, combustion device and furnace mechanization, automation and computer technology, in order to obtain the best effect. In the late 1980s, they used the rapid heating system to increase the productivity by 15~30%, and the fuel consumption also decreased significantly. In recent years, Russia’s rapid heating system has made new progress. The direct cost of the fast heating furnace is lower than that of any furnace heated by gas, oil or electricity. It has become an important heating device for energy saving and productivity improvement.
The forging heating furnace in Japan is mainly flame furnace. Its furnace types include: trolley furnace, box furnace, rotary furnace and pusher furnace. The box type furnace accounts for about 80% of the forging industry. Although this type of furnace has low thermal efficiency, poor working conditions and heating quality, it can still be widely used due to its adaptability to variety changes, good versatility and low equipment costs. Pusher furnace is an energy-saving furnace, in which the thermal efficiency of multi row pusher furnace can be increased by more than 30. Japan’s main measures to reduce the fuel consumption of the heating furnace are: 1. Determine a reasonable forging temperature and heating time, and cancel the soaking phase. Some factories believe that as long as the furnace temperature meets the process requirements, it can enter the insulation stage, and should strive to compress the soaking stage or cancel it.
Control the proportion of air and fuel, and control the furnace pressure. Strengthen the utilization of waste heat, install a preheater on the industrial furnace, preheat the air to 200~500e, and achieve an average energy saving effect of 30. Adopt high-efficiency furnace type, strengthen management and improve furnace operation rate. The large-scale forging heating furnace in Japan has already realized mechanization and automation of operation, and complicated thermal calculation is completed by computer.
When the forging exceeds the furnace capacity, the method of external extension tube and external protection shall be adopted. If the extended tube outside the furnace is used for local heating of forgings (the temperature inside the tube is about 400~500e), the tube can be free of smoke exhaust holes; If it is necessary to use it for heating or heat treatment of long parts (the temperature in the cylinder is higher than 500e), a smoke outlet shall be set on the cylinder, and a smoke exhaust pipe shall be set to make the gas in the cylinder convection well. The lining of long cylinder is usually made of unshaped refractory materials. This kind of powdery unshaped refractory is similar to refractory concrete, and it is easy to solidify after adding water. V-shaped reinforcement is also required in the lining, which is similar to the role of reinforcement in concrete structures. In use, the inner lining of the cylinder can be used for at least 3 years, except that the joint between the cylinder and the furnace door is easy to be damaged due to high temperature and needs to be repaired frequently.
In the 1980s, measuring and control instruments were installed in the industrial furnace of the hydraulic locomotive room of Muroran Factory in Japan. Some of the specifications of the hydraulic press and the supporting heating furnace are smaller than those of our country. There are 4 sets of 10, 20, 80100MN hydraulic presses in the hydraulic locomotive room of the plant, 15 sets of heating furnaces and 4 sets of holding furnaces, which are divided into two groups, respectively serving 10, 20MN hydraulic presses and 80100MN hydraulic presses. In addition, there are 3 annealing furnaces in the workshop, and 22 furnaces in the whole workshop.
The 100MN hydraulic press of Denghe Plant of Sheffield Forging Co., Ltd. is equipped with three fixed furnaces and three trolley type furnaces, which are respectively arranged on both sides of the hydraulic press. The furnace was technically reformed in the late 1980s.)) The furnace was lined with ceramic fiber, saving more than 25% of fuel.
The earliest successful research on rapid heating technology in Britain was in 1969.
British Gas Corporation Research and Derel # PtetnDirisionMidlands Research Station is the birthplace of high-speed burner and rapid heating technology. Then Fairbank Brcarey purchased the production license of the research station, manufactured the first rapid heating device, and installed it in the coil spring factory of Woodhead. At the third annual meeting of the International Die Forging Research Association and the International Trade Conference in the late 1970s, British Gas introduced rapid heating technology as an important new energy-saving technology.
Another index to measure the technical level of the heating furnace is the heating unit consumption of forgings. The unit consumption of forging heating furnace forgings in industrial developed countries is generally low.
As early as the 1970s, the industrial developed countries had tool operators to cooperate with forging hydraulic presses for forging production. For example, the 100MN and 80MN hydraulic presses of Muroran Factory in Japan are equipped with tool operators with a clamping weight of 2.5t.
The 80/135MN hydraulic press of Japan Takasa Factory is equipped with a tool operator with a load torque of 250kN # m. The 60MN hydraulic press of the Seida plant in Japan is equipped with a 2t tool operator. Small hydraulic presses are also equipped with tool operators. For example, 7.5MN hydraulic presses in Seita Factory and 10MN hydraulic presses in Shikawa Factory in Japan are also equipped with tool operators and also serve as loading and discharging machines.
In addition to providing tool operators, they also took the following measures to improve production efficiency:
(1) Give full play to the production efficiency of the hydraulic press, and try not to occupy the power station of the hydraulic press. In all hydraulic locomotive workshops in Japan, large section gas cutting devices capable of cutting 1000~3000mm in diameter are selected according to their own needs, so as to cut off the steel ingot riser and the forging head and save the time of the hydraulic machine.
(2) In the hydraulic locomotive room, there are lifting tongs of various specifications to facilitate the lifting and transportation of forgings, ingots and blanks. The specification of tong is generally 3~430t
(3) There are many special tools. For example, there are three-point anvils for forging large cylinder forgings, arc anvils for forging work rolls, reversing anvils for forging retaining rings, external forging devices for forging large rings, and compaction anvils of various specifications. Another tool has many uses, such as<1500mm horse pole, which can not only expand the hole, but also be used for elongation, and can also be used as a sleeve.
(4) A manipulator for removing surface defects of forgings is arranged beside medium and small hydraulic presses. The technical specifications of the manipulator shall be determined according to the needs of forgings.
(5) Strengthen the production management, strictly implement the forging process procedures, and constantly improve the technical level of workers, so that most workers can master a variety of skills to facilitate adjustment. For example, most of the workers in the hydraulic locomotive workshop of Muroran Factory in Japan have more than three types of work licenses, so that the labor force can be used reasonably.
(6) The shutdown maintenance time of the hydraulic compressor ([2 weeks/year), and the daily maintenance is mostly carried out by sections without shutdown.
In addition, foreign hydraulic presses are also equipped with some rail operators.
Development of forging heating furnace in China
The forging capacity of China’s machinery industry has reached a certain scale. Its annual output is only lower than that of Japan, the United States and Russia, ranking fourth in the world, and it can forge large steel ingots weighing up to 260t. However, there is still a certain gap between developed countries and forging heating furnace in terms of thermal efficiency, furnace maintenance technology and forging energy consumption.
The hydraulic locomotive workshop of the Second Heavy Machinery Group has forged 260t large steel ingots, which is representative. The hydraulic locomotive room is equipped with a 120MN hydraulic press and 6 forging heating furnaces. Including: 5m@13m Two trolley type heating furnaces, each with a maximum loading capacity of 600t and a maximum furnace temperature of 1350e; 4m@36m One trolley type heat treatment furnace, with the maximum loading capacity of 300~500t and the maximum furnace temperature of 1000e. In addition, the workshop also has a 31.5MN hydraulic press, which can forge the maximum ingot of 50t. There are 4 forging heating furnaces and 6 forging machinery of 3/2000, including: [email protected] Two trolley type heating furnaces, each with a maximum loading capacity of 230t and a maximum furnace temperature of 1260e In the past 40 years, the Second Heavy Machinery Group Co., Ltd. has carried out a major transformation on the heating furnace. For example, the local structure adopts the whole fiber pasted large plate structure; High speed burner and flat flame burner are used; The furnace door structure has been improved, so as to improve the production level.
The 10000 ton hydraulic press and its supporting forging heating furnace of the First Heavy Machinery Group are basically similar to those of the Second Heavy Machinery Group. The forging heating furnace of Shanghai Heavy Machinery Factory matched with 10000 ton hydraulic press is slightly smaller.
At present, the development of forging heating furnaces in various enterprises focuses on improving productivity, improving product quality and reducing energy consumption. The main measures are: the furnace wall structure with large plates pasted with full fiber, the automatic burner with high-speed temperature regulation, the automatic control of furnace pressure, the automatic compaction of furnace door, the sectional movable furnace body, the electric self control of furnace car and the computer temperature control, etc.
Automatic pressing of furnace door can prevent flame from emitting and heat from escaping, shorten heating time and enhance heat preservation effect. The cost of installing ceramic fiber on the inner wall of the furnace is equivalent to that of installing refractory materials, but the heat insulation effect is much better. There is still a certain gap between the energy consumption of domestic forgings and that of foreign industrial developed countries. The average unit consumption is 1000~1200kg standard coal/t, preferably 600~700kg standard coal/t; And that of Muroran Plant in Japan is 270kg standard coal/t
Development Direction of Forging Heating Furnace in China
In order to improve the production capacity and product quality of forging heating furnaces in China, the following measures should be taken in the future:
(1) The energy management shall be strengthened, the energy management system of the heating furnace shall be carefully implemented, the production scheduling of the forging heating furnace shall be strengthened, and the forgings to be burned shall be reasonably arranged to make the heating furnace operate normally with load.
(2) In order to meet the matching requirements of hydraulic press, the technical equipment of forging heating furnace should be properly strengthened to avoid heating large workpieces with medium and small furnaces.
For the heating elements that exceed the furnace capacity, it can be solved by using the mature external extension cylinder and height modification methods abroad (Muroran Factory in Japan).
(3) Carefully improve the technical transformation of the furnace, reasonably select the furnace type and burner, make full use of waste heat, and achieve instrument control.
(4) Using new lining materials is an important measure to improve productivity and save energy. The clay castables, refractories, ramming materials and coating materials that have been used in China have achieved great results. For example, clay bonded castables are used in metallurgical steel rolling reheating furnaces and soaking pits, and are generally recognized as long-life energy-saving lining materials; The water-cooled pipe of the heating furnace wrapped with fire-resistant plastic has also been promoted nationwide, and has received good energy-saving results.
(5) According to the experience at home and abroad, a plan for improving the forging heating furnace is formulated, and the implementation of the plan is checked regularly to catch up with the production and quality of furnaces in various enterprises as soon as possible.