High temperature vacuum hot pressing furnace
The hot pressing furnace is used for EC ceramics (silicon carbide and zirconia) under high pressure protection atmosphere. Alumina, silicon nitride, and metal materials (cemented carbide) were sintered by hot isostatic pressing.
Furnace body part
1. The whole furnace body is a vertical shell structure, the inner layer is made of SUS304 stainless steel, the outer layer is made of carbon steel, and the inner and outer barrels are welded into a whole. A jacket is formed between the two layers to cool through water, which can take away the heat transferred to the inner wall of the furnace shell; the flange plane is provided with a sealing groove and the "O" ring vacuum is adopted. Seal, and design water-cooled device (to prevent the aging of the "O" ring too high temperature) in the middle of the furnace with air hole, thermocouple temperature hole and observation hole.
2. The upper part of the furnace body is the furnace cover, which is welded by the inner (304 stainless steel) outer head and the flange (304 stainless steel), using a double-layer water sandwich head structure, the middle can be cooled through water; the opening of the furnace cover is by mechanical manual way, built-in hydraulic press, opening labor-saving, the top of the furnace shell is equipped with pressure head (top pressure head), pressure transmission. The sensing device and the compressing device are provided with a deflation valve, and the furnace body is equipped with an infrared temperature measuring hole and an observation hole.
3. The bottom part of the furnace is equipped with electrode introduction device, air inlet valve, down pressure head and sensor which can display displacement distance, etc. The pressure head is made of stainless steel (SUS304) and circulating cooling water is provided.
4. The heating body is made of resistive graphite, which is processed into a three-phase heating body connected with the electrode, and the three-phase power supply of the furnace control system is connected to three lead-out electrodes by copper bars after the transformer is depressurized to form a control loop; the electrode devices all have water-cooling cycles.
5. The heat-insulating screen around and on the top of the furnace is made of graphite felt, which is processed into an integral heat-insulating system, which can be easily installed and maintained. The bottom of the furnace is equipped with graphite presses made of high-strength graphite, which can be used to adjust the height of the mould during hot pressing.
1. Hydraulic system is composed of electric hydraulic press, relief valve, electromagnetic directional valve, hydraulic cylinder and fixed frame. The hydraulic cylinder is mounted in the middle of the furnace base. Hydraulic oil enters the oil cylinder through the electric hydraulic system, through the relief valve and the electromagnetic reversing valve, which makes the oil cylinder rise and fall, realizes the function of regulating and maintaining the pressure, and realizes the function of automatically adjusting the pressure by setting the intelligent digital display program instrument according to the user's technological requirements. It also has over voltage alarm and security locking function.
2. There are beams, bases, long columns and grates on the fixed frame.
The vacuum system consists of a 2X-70 mechanical pump (Sichuan Nanguang) equipped with a vacuum pressure differential valve (to prevent sudden power failure, mechanical pump oil backfilling), a K-300 diffusion pump (Sichuan Nanguang) equipped with a cold trap (to prevent oil vapor from entering the furnace), a 200mm pneumatic high vacuum flapper valve, a 50 pneumatic butterfly valve, a protective atmosphere valve (Ar, N) relief valve. Vacuum pressure gauge and other components, vacuum pipe and pump connection using metal corrugated hose quick connection (to slow down vibration), vacuum measurement by the digital display composite vacuum meter.
1. Power supply is a low-voltage transformer and SCR voltage regulator, 380V three-phase power through a step-down transformer, voltage down to 30V, and then through the cable to the electrode. This system has the functions of soft start, soft turn off, constant current and over current protection.
2. Temperature control is realized by digital temperature program controller according to the process curve set by the user. It has PID self-tuning function and can also be manually controlled according to the user's needs.
3. The whole vacuum hot-pressing furnace has the functions of water pressure under-voltage, over-temperature, over-current automatic interlock, alarm and protection to cut off the main power supply. The alarm state is indicated by sound and light.
Water cooling system
Cooling water from the main pipe into the shell, cover, furnace bottom, electrode, up and down pressure head, mechanical pumps, diffusion pumps, etc. need to be cooled, and then aggregated to the chiller water tank (additional). Each cooling water has manual valves, and can adjust the flow volume as required. The water inlet pipe is equipped with an electric contact pressure gauge. When the water pressure is lower than the set value, the control system will alarm with sound and light, and automatically cut off the heater power supply.
The pressure of the outlet pipe is more than 1.5 kg, the diameter of the inlet pipe is 2.5 inches, and the diameter of the outlet pipe is 2.5 inches.
Maintenance and maintenance
The cooling water outlet temperature should not exceed 50 C. If the water pressure is insufficient or the local temperature rises too high, the power supply should be stopped, and find out the reason, after returning to normal. Cooling water quality should be noted that the hardness should not be too high, do not contain sediment. The cooling water is 0.2MPa and the cooling water consumption is about 3000kg/h.
If the furnace is ready to shut down for a period of time, compressed air will be used to clean the remaining water in the cooling water, which can prevent corrosion and extend the life of the equipment.
Regularly replace the diffusion pump oil and mechanical pump oil, and regularly add the diffusion pump oil to the seals to make lubricating oil.
Often pay attention to the heater of the diffusion pump, can be used to measure the current method to detect whether the resistance wire is burnt.
The air ballast valve on the mechanical pump should be opened when the gas containing steam is pumped, otherwise the oil in the mechanical pump will be polluted and the limit vacuum degree will be reduced.
When the electric furnace is stopped, clean it in the furnace, and then store it in vacuum.
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