Positive pressure specification leak
With the stagnation of China's light industry, alcohol, natural gas, chemical, medical, aerospace and other industries have been stagnating to ultra-low pressure and ultra-low temperature. The tightness of the seal has always proposed new technical requirements. The most acute leak detection method in the society is "mass spectrometry" and positive pressure leak detection normally adopts the sniffer method or the mass spectrometer sniffer accumulation method. And the correctness of leak detection in this step should be evaluated with positive pressure leaks. Therefore, creating a decent leak-free appearance, which is unnecessarily changed by heat, is extremely important.
First, the production of positive pressure leaks The leaks are holes, pores or other structures on the wall of an opener that allow gas or liquid to flow from one side of the wall to the other under the effect of the pressure difference or depth difference on both sides of the wall. When there is a pressure difference or a difference in depth between gases, gas fixation is formed. Gas fixation through a leak is usually called disclosure. In the theoretical use, it is revealed that in two states, leakage occurs from low pressure (above atmospheric pressure) to the atmosphere and from the atmosphere to vacuum.
The leak can be a negative pressure leak or a positive pressure leak. The important decision depends on the operating conditions. At an outlet pressure of 100 (1 & plusmn; 5%) KPa, an inlet pressure of less than 1KPa, and a heat of 25 & plusmn; 5 ° C, the dew point is lower than 25 ° C, and the flow rate through the leak is used to calibrate the atmospheric leak rate.
At the outlet pressure (greater than 100KPa & mdash; 20000KPa), the inlet pressure is 100KPa, the heat is 23 & plusmn; 7 ℃, the leak rate value is the same. The leak is a positive pressure leak. It is subject to pressure, heat and gas species.
Positive pressure leaks are rarely used in non-metallic conduction type, which features fast response, no accumulation, stable leakage rate, and difficult to block. The normal positive pressure leakable flattenable type and oxygen-free copper flattened type in front of the eyes. The biggest deficiency is that as the pressure increases, the leakage rate value decreases with the pressure, so that it cannot be restored to its original value, and the leaky core deforms. Due to the nature of the data, leaks used for low pressure become prohibitive.
1, the choice of data
1) Kovar & mdash; nickel-cobalt-iron alloy. Among them, 17-18% cobalt, 28-29% nickel, and the rest is iron. Kovar cold processing promotes the r-phase transition & alpha; therefore, it must be annealed, and the non-metallic fracture caused by excessive pressure makes it very small to make conductive leaks, from 10-4 to 10-6 Pam3 / s.
2) Oxygen-free copper. Copper content & ge; 99.99%, low oxygen content, easy for machining, good tensile strength and spread, easy oxidation at low temperature. "Aeruginite" is easily generated in the atmosphere, and it can make leak holes from 10-4 to 10-6 Pam3 / s. The conductive oxygen-free copper leak is subjected to low pressure, and the leak will deform and make it impossible to recover.
3) Monel alloy. It is a nickel-copper alloy, 2/3 nickel and 1/3 copper. It is a typical agent of refined nickel-copper alloys. It has both high strength, ductility, weldability and high-quality corrosion resistance. It has better strength than stainless steel at low temperatures.
Performance: Tensile strength: 6: 450 & mdash; 500 (soft rod), 600 & mdash; 850 (hard rod); processing rate 60%; spread rate 25 & mdash; 40%; hardness HB: 135 (soft material), 210 (hard material ); The elastic modulus is 170KN / mm2.
2. Production of leaks:
The production of through-conduction flat leaks has been popular for 40 years, and they are all similar. Because the user ’s leak volume, outlet pressure, and inlet pressure are opposite, the manufacturing process is very different, especially the annealing heat, freshness, and leakage. She is under pressure and so on.
The leakage rate scale can reach (10-4 & mdash; 10-10Pam3 / s), the production of positive pressure leak hole with outlet pressure (0.11MPa & mdash; 20MPa) and inlet pressure of 0.1MPa.
Second, the calibration of positive pressure leaks Positive pressure leaks are calibrated and installed normally using two methods of constant volume and constant pressure. On this basis, various steps such as the cumulative comparison method, the standardized gas method, the flow comparison method, the pressure comparison method, and the mass spectrometer method have been studied, but the constant volume method and constant pressure method are the foundation. 1997 American Institute of Materials and Testing & quot; Specification Standard for Calibration Gas Reference Leaks & quot; & quot; E908-82 & gt; & quot ;. The standard capillary & mdash; water column displacement method is a constant pressure method, and the gas accumulation method is a constant volume method. The European Committee for Standardization in 1995 (CENTC138WFG / 6n3rev3) also adopted a similar capillary & mdash; water column displacement method. Swiss Balzers company in 1995 built a constant pressure method based on the calibration of the positive pressure leak. In China, the constant pressure method is adopted, and the measurement scale is 10-7 & mdash; 10-5Pam3 / s. We adopted mass spectrometry calibration, and the correct data were provided by 510 National Defense Science and Technology Commission metrology stations.
Third, the comprehensive test data and consequences of the number of ten leak test and user motivation is good. The following is a record of the test data.