Development direction of mesh belt furnace:
 The mesh belt furnace production line adopts pollution-free DX gas tempering blackening technology, and pollution-free blackening technology utilizing tempering waste heat has replaced the traditional polluting blackening process. The thermal pollution of the mesh belt furnace is zero.
Detailed introduction to the mesh belt furnace:
After more than half a century of development, the first-generation mesh belt furnace gradually developed from heating under an oxidizing atmosphere to the second generation with protective atmosphere and less oxidation heating, and further to the third generation with controlled atmosphere heating and the fourth generation with computer management. In today's 21st century, what are the characteristics of the development of the mesh belt furnace?
Today, the driving force for the development of heat treatment mesh belt furnaces, like other products, comes from market demand, and the achievements of development come from technological progress. China's reform and opening-up policy has greatly promoted and accelerated the development process of the heat treatment industry.
Mesh belt furnace technology in the 21st century will have distinctive characteristics of the times, featuring four major characteristics: intelligent heat treatment, high-quality heat treatment, low-cost heat treatment, and clean heat treatment.
1．1 Intelligent heat treatment
Researchers and developers use the latest CAD programs and heat treatment databases, computer simulation technology and control technology, and adopt highly flexible and intelligent integrated control and management systems for mesh belt furnaces and their production lines.
In the future, operators of mesh belt furnaces will only need to input the quantity of workpieces to be processed and drawings into the computer, and the complete set of equipment will automatically process high-quality products.
At present, real-time multi-project operation control of the entire system has been realized, such as controlling loading thickness, mesh belt speed, temperature, carbon potential, etc. Full-screen monitoring and control of the movement of batch feeding can be achieved. Complete process program control is possible, and 9999 processes can be stored. It can fully record the process parameters detected during equipment operation (part number, material, temperature, carbon potential, etc.) and send them to the computer for processing and storage. They can be accessed and printed at any time. Records can be stored for ten years. Password-based hierarchical control is implemented, with complete level separation. It includes a heating-up program for a new furnace, and the shutdown heating-up program can effectively carry out the heating-up process, etc.
1．2 High-quality heat treatment
The quality dispersion rate is zero, and heat treatment distortion is zero. Quality control measures:
Loading control system: weight, quantity, and uniformity are controllable. Tip-bucket type, suction cup type, magnetic belt type, stepped type, and vibrating type material systems have been widely promoted and adopted. The loading rhythm is automatically controlled with variable frequency speed regulation. The direction of parts is automatically arranged. Loading thickness is monitored in real time. This provides assurance from the source for the accurate execution of the heat treatment process.
Equipment temperature control: furnace temperature stability is ±1℃, furnace temperature uniformity is ±10℃, and cooling treatment temperature uniformity is ±5℃. On-off temperature control will be eliminated.
Atmosphere control in the furnace: furnace atmosphere uniformity, 0.05% oxygen probe, decarburization air pump, carbon potential controller, and furnace gas regulator can be reliably matched and widely used on mesh belt furnaces. Suitable for nitrogen-methanol atmosphere, methanol-propane (benzene) atmosphere, endothermic atmosphere, exothermic atmosphere, etc. The development of combined multivariable carbon potential control technology using oxygen probes and infrared instruments, as well as the emergence of other new carbon potential control technologies, can not only improve the precision and stability of carbon potential control, but also better adapt to atmospheres prepared from various gas sources. Dual oxygen probe two-zone carbon potential control technology further optimizes the control of carburizing and carbonitriding case quality. The emergence of steam-eliminating devices for aqueous quenching in continuous mesh belt furnaces stabilizes the furnace atmosphere and ensures the precision of carbon potential control. New developments in methanol gasification and cracking technology, together with the widespread use of furnace stirring fans, have further improved the uniformity of the furnace atmosphere. Furnace shell sealing and welding methods not only save energy but are also conducive to the long-term stability of the furnace atmosphere.
Quenching tank control: in order to ensure the uniformity of workpiece hardness and reduce part deformation, development has progressed from simply reducing cooling speed in the past to focusing on improving cooling uniformity. The quenching tank is equipped with an adjustable-speed powerful agitator, with attention given to the flow field of the quenching tank and emphasis on the temperature uniformity of the quenching tank. The temperature of the quenching tank can be controlled. Computerized testing instruments for cooling medium performance have also been accepted by many users.
Heat treatment distortion control; adopts an extended heating zone in the quenching furnace for stress relief. Uses a fully enclosed, insulated, controllable graded quenching oil tank. The temperature uniformity of the quenching medium is 5℃. The quenching tank and lifting machine discharge system are designed to prevent bumping and damage. In order to reduce the retained austenite content of bearing parts and control the slight deformation after bearing machining, it will become common to add a cooling treatment device after quenching in mesh belt furnace production lines.
1．3 Low-cost heat treatment
In the 21st century, with China's accession to WT0, Chinese enterprises will be placed in the environment of competition in the international market, and the market will more urgently need heat treatment equipment with high quality and reasonable price. And heat treatment equipment with high quality and reasonable price will be low-cost heat treatment equipment rather than low-price heat treatment equipment. The cost of heat treatment equipment consists of five parts: equipment procurement cost, equipment operating cost, equipment maintenance cost, equipment labor cost, and heat treatment failure handling cost.
Usually, equipment procurement cost accounts for only 5—10％ of the total equipment cost. Therefore, equipment manufacturers will not strive to provide low-price heat treatment equipment, but rather strive to provide low-cost heat treatment equipment.
For this reason, mesh belt furnaces designed and manufactured according to RMs (reliability, maintainability, supportability) engineering theory are widely welcomed．
Furnace type selection: design should first start with model selection and correctly choose a muffle or non-muffle furnace type.
Heat-resistant steel selection: for high-quality Fe—Cr—Ni, Fe—Ni—Cr, and Ni-based alloy materials, reasonable material selection should be made according to the furnace working temperature range and heat treatment process, so as to extend the actual service life and make the performance-price ratio more reasonable. Muffle life can reach 2—5 years, mesh belt 2—4 years, tray roller 5一1O years, radiant tube 2—4 years, and fan 5—10 years.
Instrument and electrical component selection: highly reliable PLC programmable controllers, SRC heating modules, adaptive digital display temperature controllers, and carbon controllers are commonly used, enabling fault-free operation throughout the entire service life cycle of the equipment.
Sensor component selection: the service life of the oxygen probe for atmosphere control is 1 year, the carbon potential control accuracy is ±0．05％, the thermocouple service life is more than 5 years, and the control accuracy is ±0．05％
Refractory material selection: 0.48 ultra-light anti-carburizing bricks, ultra-light insulation boards, and refractory cotton are used, with a service life of 5 years.
Common defect prevention devices: buffer pads to prevent burr knocking damage to parts; baffles to prevent parts from bouncing out and scattering; torque limiters to prevent parts from bouncing out and jamming the transmission
mechanism; spray washing devices to prevent part adhesion: groove-type lifting devices to prevent part adhesion; mountain-shaped and drum-type drying devices for liquids difficult to dry off. Enlarging and extending the tempering furnace ensures high hardness uniformity, etc.
(2) Maintainability: automatic display of fault points; after a fault occurs, the front section of the fault point automatically stops; automatic audible and visual alarm 3 equipped with special maintenance tools, etc.
(3) Supportability: sincerely serving users and thinking of users everywhere is no longer an empty phrase. More and more manufacturers openly promise that upon receiving a help call from the buyer, they will promptly assist the buyer in solving the problem; if the problem cannot be solved over the phone, personnel will be dispatched immediately. The seller sets up a spare parts warehouse for the buyer. The seller establishes a forecasting system for the spare parts required by the buyer. With the development of emerging network technologies, remote control has become a reality, and the cooperation between suppliers and users will become more tacit. The application of new processes and new technologies will further reduce costs.
(4) Energy saving: the heat treatment “Tenth Five-Year Plan” requires that the average power consumption of heat treatment specialized plants in major industrial cities nationwide be reduced to below 500KWh／t. The energy utilization rate of mesh belt furnaces will increase to 360—420 KWh／t (including quenching, cleaning, and tempering).
Technologies such as heat exchanger technology, waste heat utilization technology, furnace shell gas-tight welding technology, and energy-saving technology that reduces furnace surface area (such as cylindrical type) are widely adopted. The use of 0．48 ultra-light anti-carburizing bricks, ultra-light insulation bricks, ultra-light insulation boards, and refractory cotton furnace-building technology keeps the furnace wall temperature rise at 6℃. Rapid cooling technology is adopted for tempering furnaces. High-pressure fan oil-blowing oil-saving technology is adopted. Using generated atmosphere with air plus propane and the like can save 80％ of atmosphere cost. With the realization of the domestic west-to-east gas transmission project, mesh belt furnaces directly using primary energy natural gas will be used more widely, bringing significant overall energy-saving effects. The promotion and application of equipment process energy-saving technology will shorten the heat treatment process cycle, such as zero holding-time heat treatment for carbon steel parts; direct quenching after thin-layer carburizing (carbonitriding) omitting tempering; and dual oxygen probe two-zone carbon potential control shortening the time for carburizing and carbonitriding processes, etc., will be more widely applied.
1．4 Clean heat treatment
In 1992, the World Summit on Environment and Development adopted “Agenda 21”, advocating the development of cleaner production. In 1995, China officially listed cleaner production as a key common technology for development and promotion in the “Decision on Accelerating Scientific and Technological Progress”. Further promotion and development of various clean heat treatment technologies and cleaning technologies. During the “Tenth Five-Year Plan” period, emissions of various wastewater, waste gas, and waste residue must meet relevant national standards and regulations, and by 2015 efforts should be made to achieve nearly zero environmental pollution from heat treatment production. Mesh belt furnaces of the 21st century will reduce environmental impact to zero during the production process. Water-based quenching media will increasingly replace quenching oil. Quenching oil realizes online closed-loop control, using advanced oil-water separation technology and oil purification technology (the separation effect of the oil-water separator can be less than lOPPM. Centrifugal oil cleaners can remove 1Lt of impurities in oil). The recovery rate of electrostatic recovery technology for oil fume pollution can reach 0．999. Clean combustion degreasing methods are implemented by extending the heating zone length of quenching mesh belt furnaces.
The mesh belt furnace production line adopts pollution-free DX gas tempering blackening technology, and pollution-free blackening technology utilizing tempering waste heat has replaced the traditional polluting blackening process. The thermal pollution of the mesh belt furnace is zero.