Fri, 15 Jun 2018 03:29:31 +0000

Automatic control of double chamber vacuum brazing furnace

In order to improve the work efficiency, we designed for user 1 double chamber vacuum brazing furnace, including heating and cooling chamber, thus shortening the vacuum brazing process, when the first heating furnace after completion of welding, through the drive mechanism, from the heating chamber after welding the parts into the cooling chamber for cooling, then still remain a vacuum heating chamber, and has a high temperature. Parts in the cooling chamber to cool down soon, after again from cold chamber into the furnace to be welding parts, 2 for pumping air into vacuum state, when the vacuum degree reaches a certain value, the components into 2 furnace heating room, is this furnace need not begin from room temperature to heat, but at a high temperature heating, shorten the heating time, heating chamber also don’t like a single chamber furnace need cooled to below 100 ℃ (according to the technological requirements set out temperature), so both saving energy and saving time. Vacuum brazing furnace is a mechatronics equipment for brazing in vacuum atmosphere. It consists of vacuum system and heating system. E., when the vacuum degree reaches to vacuum brazing process of heating, heating system parts heating and melting solder, soldering part is finished, the process control by temperature control meter, after the completion of the heating process, for cooling, when the temperature of the furnace to melt temperature, when this is complete the vacuum brazing process.
1. Vacuum brazing mechanism of vacuum brazing is not applied in vacuum atmosphere solder and connection parts of a method of advanced process can use general method to soldering the connection of material and structure, and compact, with excellent mechanical properties and corrosion resistance of braze welding head. This process not only in aviation, aerospace, atomic energy and electrical instrument such as cutting-edge industries become indispensable means of production, and in petroleum, chemical industry, automobile and tools and related machinery in the field of obtained the promotion and popularization. In the process of soldering, solder heated liquid state, through the role of the wetting liquid to solid, and brazing gap capillary effect, make the liquid solder to fully into the compact and fill all the brazing gap, and with the parent metal of each physical chemistry, forming new alloy, after condensing crystallization, get qualified braze welding head. Vacuum plays the role of protection, degassing, purification and evaporation in brazing. Vacuum brazing compared with other brazing method, has the following advantages: a. in all brazing process, by soldering parts under vacuum conditions, there will be no oxidation, carburization, metamorphic phenomenon such as decarburization and pollution; B. During brazing, the whole part is evenly heated with little thermal stress, and the deformation can be controlled to a minimum, which is especially suitable for precision product brazing. C. It is easy to release volatile gases and impurities under vacuum conditions, so as to improve the performance of matrix metals; D. No porosity and inclusion defects in the weld; E. Multiple adjacent welding seams or multiple components can be soldered at one time; F. The heat treatment process can be completed simultaneously in the brazing process; G. Solderable basic metal.
2. The vacuum furnace control system is the necessary equipment to realize the vacuum brazing process, its work performance is good or not, directly affect the brazing quality, especially the reliability of the electric control system of vacuum furnace. The vacuum furnace is a two-chamber furnace, which consists of a heating chamber and a cooling chamber. Think in terms of vacuum brazing process, control the vacuum furnace should possess the following conditions: a. vacuum unit, pneumatic system, pressure regulating system, cooling system and gas system of manual and automatic control. B. Automatic control of heating system. C. Manual and automatic control of workpiece transmission mechanism.
2.1 the vacuum system includes mechanical pump, diffusion pump, main valve, bypass valve, high vacuum valve, hot chamber vacuum valve and cold chamber vacuum valve, etc. Mechanical pump for coarse vacuum unit, it is a kind of variable capacity pump, with the aid of blade continuous operation in the pump cavity suction and the gas compression, and finally by the vent discharge, to achieve the purpose of the extraction, the power source of the mechanical pump is 1 three-phase ac motor, the control system of reach it off and disconnect the ac contactor pump work and stop. High vacuum oil diffusion pump for high vacuum device, it was based on the diffusion pump oil as working medium of high vacuum pump, its former level is equipped with mechanical pump, at the bottom of the diffusion pump is equipped with a certain amount of oil diffusion pump, after diffusion pump electric furnace heating liquid oil into oil, steam, oil vapor by high-speed jet nozzle, the vacuum system of the gas molecules to the oil vapor jet diffusion, and collisions among the oil vapor molecules gain kinetic energy, and the gas molecules is, according to the direction of oil vapor jet from the upper nozzle compressed to the former level by level, and finally reached the outlet, again by the previous level of mechanical pump into the atmosphere, complete extraction. The diffusion pump furnace consists of three sets of resistance wires, which are connected with 220V ac respectively. The power supply is controlled by ac contactor. Heating system is composed of heating power and heating elements, including heating power magnetic voltage regulator, magnetic voltage regulator is a kind of no mechanical transmission, non-contact voltage regulator, can take the load (heating element) smoothly stepless voltage regulation, its voltage regulation by dc excitation control, according to the different control signals to realize closed loop control. Dc excitation power supply is controlled by power regulator (bidirectional thyristor). Temperature controller through the furnace temperature thermocouple detected current value and the difference between the set point, after the PID operation, output 1 4 ~ 20 ma dc signal, to control the bidirectional thyristor conduction Angle, to further control the magnetic saturation voltage magnetic voltage regulator, to achieve automatic control of heating current, the furnace temperature and setting the heating curve is consistent. When the furnace condition changes, there may be the actual temperature and the set value deviation, then by temperature control meter of self-tuning function to correct the deviation vector, make its temperature in strict accordance with the set curve. The heating element is the load of the heating power supply, and its material is made of high-temperature molybdenum belt, which can work at high temperature for a long time. The resistance of the heating element should match the magnetic voltage regulator, otherwise there will be no temperature rise or high magnetic temperature rise. The main circuit of heating power supply is three-phase 380V ac power supply, controlled by ac contactor and controlled by temperature controller.
2.2 control circuit design of two-chamber vacuum furnace circuit design (only PLC control is shown), as shown in figure 2, the PLC adopts omron CQM1 model, in which PA206(CPU unit) and ID213 are input units and OC222 in two groups are output units. To meet the control cabinet panel operation, automatic control, signal detection and alarm, input unit including the front-rear starting, workpiece car movement, hot insulation switch, vacuum unit start-stop, charging valve, fan operation, purge valve, heating, vacuum valves and selection of operating knob switch, and the limit switch and alarm signal; Output unit including heating ac contactor, vacuum unit, artifacts, vacuum valve, hot insulation, air valve, charging valve, pressure valve, relief valve, indicator light and executive components such as sound and light alarm. Manual operation is mainly used to debug and maintain the vacuum furnace. After the input operation, the control is to execute the component action accordingly. The automatic operation is applied to the normal operation of the vacuum furnace. It is controlled automatically by the detected automatic control signal, judged by the CPU, according to the application program. The heating curve is controlled by oulu 818 intelligent temperature controller.
2.3 the block diagram of automatic control program according to the requirements of vacuum brazing technology, the vacuum furnace shall automatically complete the work piece transmission, vacuum extraction, heating, inflation, cooling, etc. Automatic control procedure 1 – vacuum unit; 2 — cooling chamber; 3 – gate; 4 — heating chamber; 5 – magnetic voltage regulator; 6 — electric control cabinet.
3. Maintenance and repair
3.1 daily maintenance a. Check whether the sealing ring of the furnace door is damaged. If there is any dirt on the sealing ring, clean it in time. B. Check whether the heating elements (molybdenum belt), furnace bed and molybdenum screen in the furnace are in good condition, and repair and replace the damaged parts in time. C. When there is pollution in the furnace, vacuum the dust with a vacuum cleaner and wipe the reflector screen and heating elements of the heating chamber with a silk cloth dipped in alcohol; If the inside wall of furnace body has smeary, dip in gasoline with cotton cloth first remove smeary, dip in alcohol with cotton cloth again wipe. D. when the furnace is finished, it should be vacuumed to a certain degree. E. Check the oil level of the mechanical pump, and add new oil to 1/2 of the oil mark when the oil level is lower than the mark line; When found mechanical pump oil emulsion (oil-water mixture, thick and white) phenomenon, to replace the old oil in time, the method is unscrewed the mechanical pump oil drain pressure cap, let out the old oil, put some new oil from the oil hole, flush the pump cavity 2 ~ 3 times, then tighten the mechanical pump oil drain pressure cap, inject new oil from oil hole to the 1/2 (shoulds not be too much), tighten the mechanical pump gas pore pressure cap. During this process, the gassing/discharge hole seal ring should be prevented from being damaged and replaced immediately if there is any damage. F. After each shift, clean the outside of the furnace with cotton cloth to remove dust and grease from the mechanical and diffusion pumps.
3.2 during regular maintenance of equipment, a thorough inspection shall be conducted at least once a year. A. Inspect and clean the furnace body. Check whether the sealing ring of the furnace door is in good condition and replace the seriously damaged heating element and damaged element in the furnace. In furnace with a vacuum cleaner to remove dust, with silk cloth dips in alcohol wipe the oven door sealing ring, sealing ring and applied on vacuum grease, dip in with cotton gasoline wipe the oven door wall in figure 2 the principle diagram of the PLC control and furnace lining. Vacuum the furnace after cleaning. B. Check the mechanical pump. Check the running state of the mechanical pump, check whether the belt of the mechanical pump is in good condition, if there is any damage, it should be replaced. C. Check and maintain the diffusion pump. Remove the main valve and the vacuum between the diffusion pump connecting pipe, and the diffusion pump and the screw connection of the cold trap, falling below the diffusion pump three support bar (before the unload diffusion pump heating furnace), remove the diffusion pump, from top to bottom in turn device in the discharge pump, if there is oil pollution on the oxidation and diffusion pump oil should be poured into clean containers, clean with gasoline pump cavity, then dip in with 450 # water sand paper gasoline wipe the pump inside the device, and then use silk cloth dips in alcohol swab nozzle components, pump casing, and various sealing ring, is clean dry and shade, the injection of 3 # diffusion pump oil diffusion pump, to besmear good vacuum grease on sealing ring, will be after the completion of the assembly of different parts Connect to the system. D. Maintain bypass, main and high vacuum valves. Remove bypass valve, main valve and high vacuum valve, and check the operating condition of each valve
3.3 general failure cause analysis and treatment vacuum furnace after fault occurs, the first thing to the main reason for the failure analysis judgment, and the point of failure may exist, and then make a deal, the last is the concrete maintenance. The most common general fault such as vacuum pump, analysis and processing according to the following ideas: a. analysis judgment vacuum pump will not come up, is due to the loss of vacuum suction unit itself, or the vacuum system leakage points, using segmentation method for judgment. B. In a vacuum unit, is it a mechanical pump or a diffusion pump? C. In a vacuum system, it is difficult to analyze and determine the air leakage point, because there are many sealing parts, but the air leakage point is often prone to occur in places where people have moved. Vacuum furnace in the process of the work, the position of regular exercise and frequently open parts, such as the oven door to open and close, often in the process, may have sundry paste on the oven door seal, sealed oven door is bad, produce oven door air leakage. D. Gradually reduce the scope, and when the scope is reduced, it is easy to make accurate judgment and shorten the maintenance time. E. In the specific maintenance process, especially for devices unfamiliar to you, remember the sequence and process of disassembly, and prevent the damage caused by human factors.
3.4 emergency treatment method for abnormal situations a. heating elements are fired or short-circuited. Appeared in the process of heating, flint, heating current meter pointer will significantly oscillation amplitude, and frequency is higher, in the right circumstances, must immediately shut off the heating power, such as furnace temperature down later, check again. When a short circuit occurs in the heating element, the over-current protector is connected and the power is automatically cut off. If the temperature in the furnace is high, the emergency treatment method b of abnormal conditions shall be adopted. B. abnormal power outages. Abnormal power, under the condition of the normal supply of compressed air, all levels of the valve quickly closed, if it is under high temperature condition, immediately opened the tap water, with cooling furnace, diffusion pump and other components, in order to open the cooling water diffusion pump heating furnace at the same time, so that rapid cooling diffusion pump oil. If there is neither circulating water nor running water, the diffusion pump heating furnace can be moved out of the bottom of the diffusion pump as soon as possible, which is beneficial to reduce the oil temperature of the diffusion pump. Conclusion the control system of vacuum furnace is reasonable and running well after field debugging and operation