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Causes of vacuum degassing furnace failure

Views: 2     Author: Site Editor     Publish Time: 2022-09-19      Origin: Site

The failure of vacuum furnace equipment can be roughly divided into system leakage, steam supply failure, valve failure, condenser failure, vacuum pump failure, instrument failure, mode setting error, etc.

Vacuum furnace failure types

System leak

Generally speaking, slight leakage has little effect on the system, but since the vacuum furnace equipment is mainly composed of multiple components: exhaust pipes, jet pumps, condensers, etc., which are connected in series, the superposition of leakages in various places will cause failures and cause damage to the system. As a result, pumping takes a long time or cannot enter a high vacuum. The reasons for the leakage are as follows:

1. The sealing leakage of the tank cover and its accessories is mainly caused by the dislocation of the tank cover, the burning of the sealing strip or the entry of foreign objects such as steel slag, and the loose flange connection. Such faults are easy to find and can be eliminated in time.

2. The exhaust pipe and its accessories are leaking. The exhaust pipe includes flexible elbows, pipe bodies, maintenance manholes, sewage outlets, etc. The sewage outlets under E. and E. are blocked or blocked by foreign objects and cannot be sucked together. The probability of occurrence is high, and frequent inspection and cleaning are required. This kind of failure phenomenon is basically the same as the first item, and it is not difficult to deal with.

3. Valve leakage. The vacuum furnace is equipped with a large number of valves, such as steam shut-off valve, check valve, air-breaking valve, slag pressure valve, etc. Among them, the number of steam shut-off valves is the largest and the working conditions are the worst. Pressure difference, temperature, vibration, etc. ., the possibility of leakage is high. The leakage of the valve allows steam or air to enter the suction system, which affects the suction effect of the nozzle and increases the load of the vacuum pump. Such failures need to stop production, take a lot of time, and cause the loss of steam. Therefore, key valves are generally selected from brands with reliable quality and high cost performance, such as FISHER, KOSO, etc.

4. Structural leakage. The pump body or exhaust pipe is eroded and corroded by steam, exhaust gas, particulate matter, etc., and the equipment body or welding seam is prone to damage, cracking, desoldering, etc. It is generally concentrated on the diffuser section of the pumps at all levels and the connection between the pump body and the condenser. Therefore, daily inspection and maintenance of these parts are required.

Steam supply failure

The working steam used by the jet pump of the vacuum furnace is provided by a fast boiler with a design capacity of 14t/h. The pressure and temperature of steam are the two main indicators for judging the quality of steam. According to the design, the steam pressure of the system needs to be stable between 1.4~1.7Mpa. However, in actual use, when the gauge pressure of the on-site sub-drum is lower than 1.45Mp., the pumping capacity of the vacuum pump will be significantly reduced, and the phenomenon of vacuum degree rebound will occur. 

Theoretically, whether the steam is overheated or saturated has little effect on the pumping performance of the pump. However, due to the influence of the heat loss of the pipeline and the expansion and cooling of the steam in the nozzle, a certain amount of condensed water will be formed, and the condensed water will be pumped in the lower air pressure. The gas pipeline is very easy to vaporize and absorb a lot of heat, which will cause the nozzle to freeze and block in severe cases. Therefore, the working steam generally needs to ensure a superheat of 10~20℃. Such faults are most sensitive to the E1 nozzle with the smallest diameter, which is manifested as the high vacuum cannot enter or even rebound after the E1 is turned on. Installing steam traps at the lowest position of the steam sub-drum and each steam pipeline can improve this kind of situation to a certain extent.vacuum refining furnace company -Chnzbtech

Valve failure

Most of the on-site valves are electronically controlled pneumatic valves. In addition to the leakage of the valve body, there will also be problems such as low control air source pressure, low control voltage, line failure, solenoid valve failure, valve pneumatic head leakage or blocking, valve core blocking or falling off, etc. The reason is that the valve does not move or the action is not in place, and the failure is realized that the pumping capacity of the system does not increase or the vacuum degree rebounds when the valve moves. If the condensate valve fails, it will also be accompanied by an abnormal increase in the temperature of the condenser and an alarm.

Condenser failure

C1, C2, C3 condensers are connected in series between the vacuum pumps at all levels of the system according to the functional requirements. Their main function is to remove the condensable steam in the mixed gas and reduce the load of the lower vacuum pump. The end condenser C3 has the function of silencing. Excessive condensate temperature, insufficient pressure or flow, unreasonable distribution, rotten or blocked nozzles, and broken inline water pipes will all lead to a decrease in the condenser effect, and the accumulation of steam that is not condensed in time will increase the load on the vacuum pump. The fault phenomenon is the abnormal rise of the condenser temperature and the rebound of the vacuum degree. In addition, the vacuum pump is provided with baffles at the suction port in the condenser. Once these baffles are rotten and missing, the condensed water will enter the Laval nozzle and affect its suction capacity. The failure probability of the main condenser C3 is relatively high.

Vacuum pump failure

1. The most common cause of vacuum pump failure is the turbulent flow caused by the accumulation of smelting dust on the inner wall of the pump, which affects the pumping capacity of the pump.

2. The Laval nozzle is the core component of the vacuum pump. When foreign matter is blocked, worn, or the connecting flange gasket is dislocated, the function of the nozzle will drop or be lost.

3. The steam pipe of the nozzle in the mixing chamber is made of ordinary steel, which is easy to rot and break. After damage, it will seriously affect the pumping performance of the nozzle of this stage. When the leakage is large, it will even lead to a sharp drop in the system steam pressure. Consider using stainless steel pipe instead.

4. The nozzle and the pump body are connected by flange, and the coaxiality of the two is required to be high, and the error value is generally required to be no more than 1.5mm. After dismantling, replacing the nozzle or the connecting pipeline before the nozzle, it is found that the pumping capacity of the pump of this stage has decreased, and it is necessary to check whether the coaxiality error caused by the installation and manufacture of the vacuum pump nozzle meets the requirements.

Vacuum gauge failure

In view of the range and accuracy of the instrument, there are high, medium and low vacuum gauges installed on site. The fault can be preliminarily judged by comparing the degrees of vacuum gauges at all levels. For example, when the high vacuum gauge shows 1.0mba., the reading of the upper vacuum gauge is generally about 2.2mba. . The vacuum gauge needs to be sent to the authoritative department for inspection and calibration on time.

Mode setting error

During the pumping process, the control program compares and judges the detected vacuum degree in the tank and the mode setting, and automatically opens and closes the steam valve, check valve and condensate valve of the vacuum pump at all levels. Improper or wrong mode settings can result in wasted steam, poor extraction or even failure.

Other reasons

If the argon gas pipeline is damaged or the valve leaks, so that a large flow of argon gas enters the vacuum tank, it will lead to increased vacuuming time or high vacuum can not enter. In addition, due to insufficient ladle clearance, high viscosity of steel slag, and violent carbon-oxygen reaction, slag pressing operations need to be performed more frequently, which will affect the speed and effect of vacuuming.

The appearance of vacuum furnace equipment is mostly covered with sound-absorbing and heat-insulating materials, so its faults are more concealed, and it is more difficult to judge and deal with. Therefore, in the usual commissioning or production process, it is necessary to accumulate some data and experience as much as possible, such as various media parameters under normal conditions: temperature, pressure, flow rate, etc., the actual consumption of steam of each nozzle, the compression capacity of the vacuum pump, and the consumption to a specific vacuum degree. time, the thickness of the pipe wall of the vulnerable parts of the pipeline and the pump body, the pressure maintaining and anti-discharge ability of the system, etc. These parameters help to quickly judge and deal with equipment failures.

The daily cleaning, inspection and maintenance of equipment such as exhaust pipes, vacuum pumps, and condensers is the most economical and effective way to control the failure rate of vacuum furnaces. Matters needing special attention: When maintenance and maintenance personnel need to enter the vacuum tank, vacuum pump, hot water well and other parts for operation, they must confirm that there is no toxic and harmful gas such as CO in the area, and at the same time ensure that there is sufficient oxygen content inside, otherwise Accidents such as suffocation or CO poisoning may be caused.

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