Precautions for daily use of vacuum furnace

Vacuum furnace drying is divided into three stages:
① The water discharge period is 0~200 ℃, which is the discharge period of water in the insulation layer of the vacuum furnace and moisture in the vacuum furnace body. It is necessary to check the vacuum degree of the vacuum furnace, and the insulation time is long.
② The temperature zone with a large amount of exhaust gas from the vacuum furnace is generally around 500 ℃. Due to the large amount of exhaust gas from the vacuum furnace, the temperature rise does not exceed 50 ℃/h. The heat preservation time is generally over 60 minutes.
③ The heat preservation period is around 1200 ℃, and every 100~200 ℃ increase in heating requires a period of heat preservation. Excessive heating can easily damage the insulation layer and cause incomplete venting of the vacuum furnace.
(1) Prepare operating procedures for the use and maintenance of vacuum furnaces, establish operating records and repair files for vacuum furnaces, count the accumulated operating hours, strengthen daily maintenance of vacuum furnaces, grasp the trend of changes in equipment technical status, identify early signs of failure and damage, avoid repairs that are of the nature of emergency repair, and prepare parts for repair of vacuum furnaces in advance in a targeted manner based on the working load and operating conditions of vacuum furnaces, Prepare a vacuum furnace operation and maintenance plan. For example, the service life of vacuum furnace heating elements is related to many factors such as operating temperature, product media in the vacuum furnace, product quantity, and operating conditions. Under the condition of processing and production 24 hours a day, the replacement of vacuum furnace heating elements and heat shields is performed approximately every two to three years. This depends on the type of brazing work and the number of times it is used. Vacuum furnaces generally have a lot of leakage faults in the spring and autumn seasons, and vacuum furnaces that have been idle for a long time are prone to leakage faults during secondary use. At this time, it is necessary to conduct vacuum leak detection. Generally, the pressure rise rate is measured once a month for vacuum leak detection (under normal temperature, close all vacuum valves, stop the operation of the vacuum system, read a number after 10 minutes, and then read a number after 1 hour. The difference between the two numbers is the value of the pressure rise rate), and master the trend of equipment leakage. If the vacuum equipment is continuously stopped for a week, it should be idle operated once (for oven drying). During leak detection of the vacuum system, in addition to temporary emergency maintenance using vacuum mud paste, a helium mass spectrometer leak detector can be used for vacuum leak detection if there is a helium mass spectrometer leak detector. If there is no helium mass spectrometer leak detector, a medical needle can be used to suck acetone or ether to the suspected leak point and observe whether the vacuum gauge reading has changed. Blind plates with holes for inserting vacuum silicon tubes can also be made to block vacuum pipelines in sections for leak detection. After finding the leakage point, carry out maintenance (generally, the sealing ring is aging frequently). Regularly check the oil of the slide valve pump, Roots pump, maintenance pump, and diffusion pump of the vacuum furnace. If it is found that the oil emulsifies with water and the vacuum drops, it is necessary to replace the above four pump oils. The oil level and oil quality should be checked weekly. The diffusion pump oil diffusion pump can be cleaned by chemical acid cleaning if there is carbon deposit.
(2) After the maintenance of the vacuum furnace, it is necessary to regularly inspect it at the initial stage of use, to check whether the temperature of the vacuum furnace gauge after use is consistent with the actual temperature of the furnace (regular verification and calibration of vacuum gauges, temperature controllers, thermocouples, voltmeter, and ammeters), and to check whether there is overheating damage, uneven temperature, or whitening of the three-phase heating body. For three-phase high-temperature vacuum furnaces and vacuum resistance furnaces with a capacity exceeding 100kW, an ammeter should be installed in each phase and each heating zone. If the vacuum furnace temperature and instrument indication are found to be abnormal, timely analyze and handle them.