RU2052780C1 - Method and device for checking air-proofness of volume, preferably volumes of melting furnaces - Google Patents

Abstract

FIELD: test equipment. SUBSTANCE: large volumes are pumped out till achieving low vacuum (15-10 mm of mercury column). Then fixed portion of residual gas is cooled to temperature of 15-20 deg C by separating gas from liquid. After inleakage time passed, identical gas portion plus inleaked gas are cooled till achieving the same temperature. Air-proofness standard is determined from dependences known, by referring this standard to normal temperature. Device has two vessels with inlet and outlet valves, temperature detectors and coolers. Each vessel is mounted in parallel to vacuumizing line. EFFECT: improved reliability. 2 cl, 1 dwg

Description

 The invention relates to the field of testing equipment and can be used to control the tightness of products, for example pneumohydraulic systems of various devices, various volumes, mainly volumes for vacuum melting.

 A known method of tightness control using mass spectrometric helium leak detectors, which consists in the fact that the controlled product is placed in a closed storage volume, the product is filled with control gas to an excessive test pressure, and the change in the concentration of the control gas in the storage volume is measured for a given period of time.

 This method is difficult to implement for monitoring the tightness of large-sized systems, for example, volumes of smelting furnaces, because of the need to have complex and expensive equipment for large-volume vacuum chambers inside which the furnace is located.

Currently, the only method [1] for monitoring the tightness of melting furnaces is used, taken as a prototype, which consists in measuring the leakage of ambient gas into a disconnected volume. The method consists in the fact that the controlled volume is vacuumized to an average vacuum (1 · 10 ^-1 1 · 10 ^-3 mm Hg) (Vacuum technology. Handbook. M. Engineering, 1985, S. 6-7), hermetically shut off and withstand a certain time, measuring the final pressure P _to .

 A known unit [2] selected as a prototype of the claimed device, containing a vacuum pump connected by a vacuum line, including a valve and a pressure sensor with a test volume.

 The disadvantage of this method and device, taken as a prototype, is that in the case of the presence of liquid (water) in sealed volumes, considerable time is required for operations to control the tightness. This is due to the fact that the constant evaporation of a liquid during evacuation does not make it possible to determine the tightness of an object. Tightness can only be determined when all the liquid has evaporated. This takes a long time and requires significant energy consumption.

 The purpose of the invention is to reduce the time of tightness control by determining the tightness rate due to leakage from the environment into the evacuated volume.

The volume is vacuumized to a vacuum of 15-10 mm Hg. after hermetically overlap gas is cooled first fixed portion to a temperature T _to minus 15-20 ^{° C,} measuring P _k1 finite residual gas pressure. After the leakage time, the second fixed portion of the gas of exactly the same volume is cooled to the same temperature and P _{k2 is} measured for the final pressure of the residual gas plus the leakage gas during the leakage time. The tightness rate is determined by the well-known formula, leading it to normal temperature:
Q (Δ P · V) / τ • (T _okr / T _k ), where Δ P P _k2 P _{k1 is the} pressure of the gas flowing during the leak, Pa;
V measured volume, m ³ ;
τ leakage time, s;
T _okr ambient temperature, K;
T _{to the} final temperature for cooling portions of gas, K.

 This goal is achieved in the device for checking the tightness, containing a vacuum pump, a vacuum line, characterized in that it is equipped with two calibration tanks installed parallel to the vacuum line, gas inlet and outlet valves, pressure monitoring units, temperature sensors and refrigeration units installed on each calibration capacity.

It is the ability to check for tightness at low vacuum is the novelty of the invention. This feature is achieved in that the first portion of the residual gas is cooled gas remaining in the vacuum system, after pumping, to minus 15-20 ^{° C} and the pressure is measured after cooling, and then the same portion of the cooled gas caught in the same volume after exposure, and also measure pressure. But the pressure in the second volume will consist of the pressure of the residual gas and the pressure of the gas penetrating the measured volume as a result of leakage. This allows you to measure true leakage at low vacuum. What is impossible to measure in the way taken as a prototype. This is due to the fact that at low vacuum intense evaporation of liquids (water) occurs. That is why the prototype is pumped to an average vacuum (P 1 · 10 ^-1 1 · 10 ^-3 mm Hg), i.e. in the prototype, evaporation of all the liquid trapped in the measured volume is carried out. This takes an extremely long time, reduces productivity and increases energy costs for obtaining products.

Based on experimental data, this method should only be used when evacuating to a vacuum of 15-10 mm Hg. This is due to the fact that it is known that the pressure of saturated water vapor at t20 ^о С is equal to 17 mm Hg. This means that in a vacuum of 17 mmHg and less, effective evaporation of the liquid occurs, and at a higher vacuum, the efficiency of evaporation of the liquid decreases sharply and the claimed method is not very effective. When evacuating to a vacuum of less than 5 mm Hg the time for evacuation of the entire system will be quite large and therefore the end of the process of checking the tightness practically coincides with the known method. Upon cooling, a portion of gas to a temperature above minus 15 ^{° C} the saturated vapor pressure is relatively high, and therefore with the precision instrumentation, reduced accuracy of determination of leaks. When cooled below -20 ^{° C} is increased and therefore the time of cooling time checking tightness becomes comparable with the known method.

 The drawing shows a device for implementing the proposed device. The device contains a test volume (furnace volume) 1, connected by a vacuum line 2 with a pressure sensor 3 through a valve 4 with a vacuum unit 5. Tanks 6, 7 with inlet valves 8, 9 and outlet valves 10, 11 are docked to the vacuum line devices 12, 13 pressure control. Each of the containers is equipped with temperature sensors 14, 15 and refrigeration units 16, 17.

The device operates as follows. At the initial moment, all valves are open. The volume under test 1 is evacuated through a vacuum line 2 with a valve 4 using a vacuum unit 5, constantly monitoring the rate of vacuum drop through the pressure sensor 3. Simultaneously connected tanks 6, 7 are evacuated in parallel. In the case when the test volume is tight and there is no moisture in this volume, a powerful vacuum unit 5 quickly pumps out the test volume to the required vacuum (1 · 10 ^-5 mm Hg) and tightness can be check in a known manner.

 In the case when the furnace is leaky or there is moisture in it, the vacuum does not reach such a value in such a short time (≈20 min). In this case, the pressure is set within 15-5 mm Hg. (for 10-15 minutes) and is at some specific level, for example 10 mm Hg. quite a long time.

To determine sealed whether the volume and it is the moisture or the amount of leaking, and it has a gap, overlap valves 4, 9, 11, comprise a refrigeration unit 17, is cooled container 7 to a temperature, e.g., minus 15 ^{° C} and measured After cooling in vacuum P _k1 on the device 13. After a time delay, for example 3-4 minutes, cover flaps 8, 10, the receptacle 6 is cooled to the same temperature (-15 ° ^C) refrigeration unit 16 and measure the vacuum P _k2 on the device 12 .

It is by the difference of the final pressures that the tightness rate of a particular melting furnace is determined, because both the first and the second tanks will have gas that remains without evacuation after steam (the steam condenses during cooling), but if the gas pressure increases in the second tank, it will increase only due to leaks. Since the pressure is measured at sub-zero temperatures, and the tightness rate is given for normal temperatures, the resulting tightness rate will be underestimated. In order to determine the true norm of tightness, it is necessary to multiply the obtained tightness norm by T _okr / T _to . Therefore, the tightness rate will be determined by the formula:
Q (Δ P · V) / τ · (T _okr / T _k ), where Δ P P _k2 P _{k1 is the} pressure of the gas flowing during the leak, Pa;
V measured volume, m ³ ;
τ leakage time, s;
T _okr ambient temperature, K;
T _{to the} final temperature for cooling portions of gas, K.

 When applying the proposed method and device for a specific melting furnace, if 6MDX type gauges are used to measure vacuum, it allows, firstly, to measure vacuum very accurately, and secondly, to automate the process of determining tightness by introducing an information processing unit. This can significantly improve the quality of smelting, reduce rejects, increase production, reduce energy consumption by reducing the time of preparation of the furnace for smelting.

Claims (2)

1. The method of monitoring the tightness of the volume, mainly the volume of smelting furnaces, which consists in the fact that the volume is vacuumized to a predetermined vacuum, hermetically shut off and withstand a certain leakage time, and the tightness rate is determined by leakage from the environment into the evacuated volume, characterized in that the volume vacuum to a vacuum of 15 - 10 mm RT. Art. after a tight shut-off, cool the first fixed portion of gas to a temperature of T _to minus 15 - 20 ^o C and measure P _{to 1} - the final pressure of the residual gas, then after the leak-in time, cool the second fixed portion of gas of exactly the same volume to the same temperature and measure P _{to 2} - the final pressure of the residual gas plus leakage gas during the leakage, and the tightness rate is determined by the well-known formula, bringing it to normal temperature

where ΔP = P _k2 -P _k1 pressure of the gas leaking during the leakage time, Pa;
V is the measured volume, m ³ ;
τ is the leakage time, s;
T _{about to p} - ambient temperature, K;
T _to - the final temperature of the cooling portions of gas, K.  2. A device for monitoring the tightness of the volume, mainly the volume of melting furnaces, containing a vacuum pump, a vacuum line, a valve and a pressure sensor installed in the vacuum line, characterized in that it is equipped with two calibration containers installed parallel to the vacuum line, gas inlet and outlet valves, pressure monitoring nodes, temperature sensors and refrigeration units installed on each calibration tank.

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