Multi atmosphere vacuum sintering furnace for cemented carbide
The multi-atmosphere vacuum sintering furnace of cemented carbide consists of furnace body, insulation layer, heating body, transformer in front of furnace, distribution cabinet (including control system), vacuum pump, various connecting pipes and valves, etc. The system composition is shown in the following figure.
Vacuum sintering furnace body is double wall water cooling design, the inner layer is made of high quality stainless steel plate. The cooling water system consists of a feedwater branch pipe and a backwater tank. The optimum water flow of each system is manually adjusted. Hydraulic pressure detection is used to determine whether the cooling water pressure is within the normal working range.
The vacuum system is mainly composed of a rotary vane vacuum pump and a Roots vacuum pump. The vacuum measurement is accomplished by a coarse vacuum transmitter and a high vacuum transmitter. According to the requirement of vacuum degree in different sintering stages, the vacuum degree is controlled by position control vacuum valve in the control system. The solenoid valve is mainly used for power cut protection, and the pressure gauge is used for manual observation of vacuum. When the protective gases (hydrogen, nitrogen and argon) need to be filled into the vacuum furnace, the flow rate and the pressure in the furnace are controlled manually. If hydrogen is introduced into the furnace for degumming, the PEG valve and the exhaust valve should be opened and the released hydrogen should be ignited. Condenser is used to cool and solidify PEG glue or paraffin to avoid damage to vacuum system.
The insulation layer is a rectangular box made of five layers of carbon felt seams on a stainless steel mesh frame. The heater is a box-shaped whole made up of graphite heating elements. Its structure design can adapt to the heat expansion and contraction of heating elements during the heating and cooling process. The sintering chamber and the heater are separated by graphite shield, thus avoiding direct radiation of temperature and uniform working space temperature. Considering the safety of equipment, the strength and surface power of graphite heater, a transformer in front of the furnace is designed to supply power to the heater to obtain low voltage and high current. In the sintering chamber, there are three water-cooled copper poles sealed by vacuum, connected with the heater by graphite rod at high temperature, and insulated by special high-temperature ceramic bushing.
The temperature of vacuum furnace is measured by thermocouple. The temperature control device adjusts and calculates according to the given and actual temperature values. The phase-shifting control signal is sent to the trigger board. The original voltage of the transformer in front of the furnace is adjusted by three-phase voltage regulating circuit, and then the electric power of graphite resistance in the auxiliary side of the transformer is changed to control the furnace temperature.