The heating equipment often used in the laboratory includes muffle furnace, high-temperature furnace, tubular furnace and other common heating equipment. Most of the research on raw materials such as metals, ceramics, polymers and so on must be vacuumized for experiments. The vacuumizing performance index of the tubular furnace is stronger. However, the operation process of most laboratory staff is not necessarily reasonable, which may lead to the low vacuum value in the tubular furnace and excessive residual air, It may lead to the reduction of the precision of the test and the failure to meet the standard conditions of the test.
In view of this phenomenon, Zhengzhou Nuotai technical personnel summarized the vacuum phenomenon of tubular furnace, listed the key problems and reasonable practical operation methods
In order to improve the precision of vacuum pumping, we first summarize the significance and function of vacuum pumping in the tubular furnace. First, the significance of vacuum pumping is to reduce the air inside the tubular furnace, so that the test raw materials come out of an oxygen-free environment, and then eliminate the oxidation-reduction reaction of the test raw materials.
Why is the vacuum low? Why can’t the experiment reach the ideal situation?
Low vacuum value has the following phenomena;
First, the vacuum pump is aging, and the original vacuum value is low;
Second, the vacuum pipeline is aging, the pipeline leaks, and the interface leaks;
The sealing ring of the third tubular furnace is aging and the assembly method is incorrect.
The solution is as follows: firstly, replace the aging pipeline and sealing ring, and check whether the interface part leaks. Especially, many manufacturers use the quick-connect gas pipe interface to meet the requirements of vacuum pumping, which causes hidden gas leakage and is difficult to check. Secondly, apply vacuum silicone grease on the sealing ring to improve the sealing performance of the sealing ring, and focus on the sealing effect of the sealing ring assembled at the flange.
The vacuum pump performance index of tubular furnace is not good, and the vacuum pump with higher accuracy can be replaced to carry out the experiment. The price of vacuum pump commonly used in tubular furnace ranges from 1000 to 3000, and the price of molecular pump is tens of thousands of yuan.
However, in order to save costs, we can fill the tube furnace with nitrogen, argon and other inert gases according to the meaning of vacuumizing, so as to reduce the concentration of oxygen so that the experimental raw materials are not prone to oxidation-reduction. The operation process is as follows:;
First, we connect the vacuum pump and nitrogen cylinder to the tubular furnace, then close all valves, open the vacuum pump and vacuum valve, check the pressure gauge and wait until the vacuum value of the vacuum pump is stable, then close the vacuum valve and vacuum pump; Then open the gas cylinder and open the air inlet valve. After the pressure gauge returns to normal pressure, close the air inlet valve. At this time, the air concentration in the tubular furnace decreases, but there is still residual air. We can repeat the steps to obtain higher purity nitrogen and then remove the air. If higher purity test is required, we can repeat the steps several times. Pay attention to the sequence of opening and closing the pump valve cylinder.
Some laboratory tubular furnaces must be tested in vacuum. The precision of vacuum pump is very high, but it can’t meet the experimental requirements. It may be that the vacuum pump is closed directly after vacuum pumping without closing the vacuum valve, because the vacuum pump will return air when it is not working, which may cause air to enter the tubular furnace tubes. We only need to close the vacuum valve after vacuum pumping to completely solve this problem.