Vacuum differential pressure casting control system

The system uses a single-chip microcomputer control technology, has a variety of uses vacuum mixing, remelting refining and vacuum differential pressure casting, effectively solve the technical problems in the precision casting process. After the process parameters of the system's casting process are input to the computer through the human-machine interface, its working process is completely controlled by the microcomputer program. The smelting process adopts a temperature-changing stirring composite process in which the particles and the melt are mixed at a relatively high temperature and the particles and the melt are fully wetted at a relatively low temperature, thereby ensuring the high quality of the composite material melt. The microcomputer-controlled vacuum differential pressure pouring process eliminates the harmful influence of the outside air, overcomes the disadvantage of poor fluidity of the particle-reinforced composite melt, and fills the mold according to a certain pressure difference curve under the control of the single-chip microcomputer, ensuring that the casting is suitable Solidified under pressure and cooled, high-density, complex-shaped thin-walled composite precision castings are obtained.

2 System Composition and Function of Each Part The casting furnace is divided into upper and lower sealing chambers. The molten metal of the composite material is held in the crucible of the lower sealing chamber, and the casting mold is installed in the upper sealing chamber. The upper and lower seal chambers are connected by the infusion tube in the molten metal of the lower seal chamber. The structure of the control system consists of a single-chip microcomputer main control unit, hydraulic system control, vacuum pump control, pressure and pressure difference control, furnace temperature control, stirring motor control and leakage alarm system.

The system uses the 8031 ​​as the main controller, extending the program memory, data memory, 8279 programmable keyboard/display chip, MCi4499 serial single-chip microcomputer main control unit leak alarm hydraulic system pressure collection vacuum pump system pressure collection furnace temperature control with "stirring i The upper seal chamber is composed of a sealed chamber control chamber melting furnace control system structure display chip, 8155 parallel port expansion chip, 0809A/D conversion chip, etc. This unit is used to complete the process parameter setting, pressure collection, smelting and casting process, The real-time control and display of the pressure and pressure difference of the lower seal chamber, the operation control of the hydraulic pump and the stirrer motor, and the safe operation control after the leak alarm.

2.2 Control of hydraulic system The furnace body of the casting furnace is heavy. Because the mold is installed in the upper sealing chamber, in order to facilitate the loading and unloading of the upper body and remove the casting, the design adopts a hydraulic service mechanism. The hydraulic control system controls the operation of the hydraulic pump. The operation of lifting and lowering the upper furnace body can be achieved by operating the computer keyboard or the manual button. The vacuum pump control system is used to control the vacuum pump and the vacuum to maintain the operation and stop of the pump, so as to ensure the upper casting process. , Vacuum requirements for the lower seal chamber. The system has two operating modes, automatic and manual.

2.4 Pressure and differential pressure control The Motorola-type integrated silicon pressure sensor is used to detect the vacuum degree of the upper and lower seal chambers of the casting furnace. The output signal of the sensor is amplified by the instrumentation amplifier and sent to the A/D converter. The signal after A/D conversion is sent to the main control unit of the single-chip microcomputer. The single-chip microcomputer adjusts the vacuum pump system according to the preset process parameters according to the collected pressure information. During the entire filling and cooling process, the pressure and pressure difference between the upper and lower sealing chambers and the time adjustment are completely controlled by the single-chip microcomputer.

2.S Furnace Temperature Control System This system completes furnace temperature regulation and control during the melting of composite materials. This design uses a K-type thermocouple and two measurement points are set in the heating chamber of the lower seal chamber. Shimadan's SR24 intelligent temperature controller was used to implement adaptive control of the furnace temperature. Thermostat can self-tuning PID parameters, temperature control accuracy of 0.3%, temperature control range of 0 ~ 1200C. Set the temperature of the furnace through the keyboard, set by the two sets of display set the furnace temperature and the actual furnace temperature.

2.6 Mixing motor control In order to obtain a high-quality composite melt, the system adopts a variable-temperature stirring composite process in which the particles and the melt are mixed at a relatively high temperature and the particles and the melt are fully wetted at a relatively low temperature. The central main stirrer speed adjustment range is 0 ~ 1500rpm, the peripheral auxiliary stirrer speed adjustment range is 0 ~ 200rpm. The stirring motor control has the speed control and the steering control function, and can display the stirrer rotational speed in real time.

2.7 Leakage alarm system For casting equipment that fills molds by pressure or crystallizes under pressure, incidents of leakage due to filling of high-temperature molten metal during the casting process often occur, often resulting in serious consequences, which greatly threaten the staff and The safety of the equipment. The system and the computer control system work together, if there is a leak alarm, and automatically open the pressure control valve, so that the molten metal back into the lower seal chamber, to ensure the safe operation of the entire system, effectively overcome the manual observation Blindness.

3 Vacuum Differential Pressure Filling and Pressure Regulating Process The entire shimming pressure regulating process of casting molding is completely completed under the control of a single chip microcomputer. The filling pressure regulation curve is as shown.

In the figure, the solid line is the change curve of the vacuum degree of the upper seal chamber, and the dotted line is the change curve of the vacuum degree of the lower seal chamber. Before starting pouring, first press the key of the computer keyboard to adjust the pressure of the process parameters A, P2, AP, A~, At2, Ak, where 6 is the degree of vacuum that the upper and lower seal chambers should reach in the depressurization process. At atmospheric pressure, AP is the pressure difference between the upper and lower seal chambers during the filling process. It is the time required to set the pressure difference for the molten metal filling. At2 is the charge regulation time, and At3 is the regulator during the solidification period. time.

3.1 Buck process Buck process corresponds to the curve segment. The vacuum pump is started at the same time to apply vacuum to both the upper and lower seal chambers, and the upper and lower seal chambers are maintained to have the same degree of vacuum during vacuum pumping. According to the capacity of the equipment, the vacuum is drawn to the set point at the fastest rate.

3.2 The suction casting process The suction casting process corresponds to the curve segment. When the upper and lower seal chambers are evacuated at the same time, they need to be regulated for a certain period of time (SC section of the curve). When the time arrives, the filling mold is started. At this time, the lower seal chamber starts to draw in air to reduce its vacuum while maintaining the upper seal chamber vacuum. constant. When the pressure difference between the cavity of the lower seal chamber and the upper seal chamber reaches the set value of AP, the seal chamber stops air intake. Because there is a vacuum difference between the upper and lower seal chambers, the vacuum degree of the upper seal chamber is high, and the vacuum degree of the lower seal chamber is low, and the liquid metal in the crucible will be injected into the cavity from the lower side in the anti-gravity direction through the infusion tube.

3.3 Step 5 of the corresponding curve of the boost process. After the pressure difference between the upper and lower sealing chambers is formed, the charging pressure regulation time is maintained in the condition that the AP pressure difference remains unchanged. When the filling time reaches the time set by At2, pressure is maintained under the condition that the filling pressure difference AP remains unchanged, and the solidification environment of the casting gradually changes to atmospheric pressure. During the pressure adjustment process during the period of 5 to t6, Keep the change rate of the pressure in the upper and lower seal chambers equal, that is, meet the coffee/dt=dP/mountain.

At this stage, the upper and lower seal chambers simultaneously ingest air at the fastest possible rate, but the pressure difference AP should be strictly maintained until the lower seal chamber pressure reaches an atmospheric pressure.

3.4 Solidification process The solidification process corresponds to the segment of the curve. At 6 o'clock, the pressure in the lower seal chamber reached an atmospheric pressure. The upper seal chamber still maintains the pressure difference from the lower seal chamber, and the casting enters the solidification period under a constant pressure difference. When the casting reaches f7, the casting is completely solidified. After that, the inlet of the seal chamber is controlled to reach an atmospheric pressure. At this point, the mold filling process is complete.

4 Application of Vacuum Differential Pressure The important application areas of precision melting and casting technology are the production of complex, thin-walled, high-precision aluminum-based composite castings in the defense industry such as aerospace, aviation, electronics, and weapons. The use of this design developed and produced a number of remote sensing calibration device castings, after a rigorous ground assessment, to achieve the first application of metal matrix composite castings in China's own space optical remote sensor.

Cryogenic Globe Valve

Cryogenic Globe Valve, Low Temperature Globe Valve Supplier, Cryogenic Globe Valve Manufacturer, Stainless Steel Globe Valve, Cryogenic Valve Manufacturer

Wenzhou Kolink Valve Co., Ltd. , https://www.kolinkvalves.com