Sealing reachs the automatic test technology of leak

3 ／ of 001cm Min. Hypothesis test specimen is tire of a car (in-house cubage makes an appointment with 40 litres of) , so old leak rate was equivalent to dropping in the pressure in 10 years 10 4 Pa, so it is considered as sealed, be still of leakage? If every 3 seconds appear a so big bleb, be equivalent to 0.

Leak of 3 ／ Min leads 01cm, in a year pressure can drop 10 4 Pa, should be regarded what still do not leak to be leakage again right now? The permission of freezer compressor leak rate is pressure of 10 5 Pa issues 16 × to leak every year 1g fluorine Lyons, this is equivalent to leak leading is 8.

4 × 10 - 7cc ／ Min. Should put forward " leakage and do not leak " when the problem, it is rate of affirmatory allowable leak actually, when such leak when workpiece lead ＜ Vperml, sentence for sealed, leakage should be when leak leads ＞ Vperml. Underwater range estimation is a kind of quite accurate test method, can come true through the observation with careful handlers. Definition of underwater range estimation is high, low-cost, another significant advantage depends on detecting can determine leak position at the same time. The defect of this kind of method is, the level of handlers of its be decided by (repeatability low) , pitch time is long, can wet workpiece. These also are the accounts that use automatic detector. In batch production, the leak that is medium with air detects already was applied extensively. Its reason is: ● reliability is high objective, mensurable quality states 　 ● it is easy that ● of short 　 of time of 　 ● test invests ● of tall 　 of precision of ● of low 　 of little, use charge not to injure workpiece 　 ● ● of the 　 in bringing into product line easily demarcate in view of following domains, air is automatic leak detects will receive more wide application: The environmental protection of requirement 　 ● of record of ● of 　 of requirement of quality of product of ● of 　 of requirement of ● 　 ISO9000, statistic and analysis asks 　 ● factory designs 2 tests index to check index to include two data: Test pressure and permit leak rate. Central problem is: How old leak rate can assure workpiece to do not have liquid leak below working requirement. Allow to leak rate follows specific applying and differ, it depends on a lot of elements. For instance: The succeeding activity key below the material of workpiece, structure and status of afore-mentioned real work. Lead in leak lesser (liquid leak rate is almost 0) below the circumstance, air is compared with what liquid leak leads imponderable piece, to older leak rate, both viscosity is compared than can be what leak leads approximately. Same, workpiece wall condition of thick, surface and loose structure (cast trachoma, cranny) also have crucial effect. Normally, allow leak rate to want reference given test pressure, and the working status option that tests pressure imitate follow-up, this raises a question that checks pressure grade above all, it is the direction of the test next. The concern problem that leak rate and test pressure can encounter when checking pressure certainly. Loose degree tall, leak rate and test pressure become direct ratio; Loose degree low, leak rate compares decrescent with what check pressure (1) seeing a picture. Graph because 1 leak rate and proof pressure relation are small leak is not stable when underwater range estimation, let time and change. Accordingly, when if want to use underwater range estimation after take offense tries,deciding further, must consider this one issue to go in. When leak allows to lead certainly in industrial production, considering from economic angle is crucial, the test should be to be below requirement as far as possible accurate, is not more accurate better. If allow leak rate to be decided those who compare need is lowly, percent defective can increase, manufacturing cost can rise. Final permission leak rate must decide through the experiment, below certain circumstance, also can be decided by experience numerical value or commendatory numerical value. In checking for the leak of medium with air (measure pressure or discharge) , leak rate gives out with Min of standard cm3 ／ , if use special gas (for instance helium enrages) , express with S of ／ of 10 2 Pa 1 normally. 3 ／ of 1 Std Cm what need of 　 of S of ／ of L of 　 of 10 2 Pa points out 60 × of Min ＝ is 1 Std Cm 3 ／ Min is standard reference conditions below (0 ℃ , 1. 10 5 Pa) is full of 013 × 1cm the tolerance of 3. 1Std Cm 3 not be to point to three-dimensional measure, however with three-dimensional dimension denotive tolerance. Because of this Std Cm 3 ／ Min is denotive it is mass flow is not bulk discharge. Detect to leak, will strictly tell, if leak is led,with Std Cm 3 ／ Min expresses, it is to use mass flow law to still be measured with pressure law no matter, measure signal to must try to amend in order to remove the effect of atmosphere and environmental temperature. If be not done so, leak rate should represent with cm3 ／ Min or Ml/min. Standard reference conditions and the average difference that check status are in 10% the left and right sides. Express spare parts of 1 car engine to allow leak to lead name of value citing <DIV Align=center> to check pressure (10 5 Pa) allows × leak is led (Std Cm 3 / Min) cylinder body - water covers crankcase casting pig 1.

0 ～ 1.

12 hydraulic pressure of 510 ～ oil duct 2.

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6 aluminium of 05 ～ pledge water is covered 1.

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5 hydraulic pressure of 54 ～ oil duct 2.

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The 4 Qi that take energy of life are in charge of 03 ～ inlet plenum 1.

0 ～ 1.

50 water of 530 ～ are covered 1.

0 ～ 1.

5 water pump of 54 ～ 1.

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Alloter of qualitative fuel of 5 about 8 aluminium 4.

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1 ～ the air sealing with different 1</DIV>3 namely the automatic air impermeability test that leak experiment method is medium with air, work eligibility depended on prediction of a person's luck in a given year of the airy below the pressure difference that checks around. But airy prediction of a person's luck in a given year cannot be measured directly piece, and can change through pressure only, workpiece and gas source are apart (pressure measures law) , the tolerance that perhaps flows into workpiece, workpiece and gas source are linked together (discharge measures a way) expression comes out, no matter pressure law or discharge method have,be out of shape differently. 3.

1 pressure is measured in industrial leak test, pressure is measured is the commonnest method, in test antrum lesser circumstance falls, can detect 0.

1cc/min or smaller leak are led. Opposite pressure or absolutely pressure measure a law to have a test unit and compositive change, measure the characteristic with systematic oneself the minorrest volume, and reliability is high, measure range wide, test signal resolution depends on use test pressure. In test pressure higher case falls, the precision that difference pressing law measures wants prep above absolutely pressure law, because of its resolution and use test pressure have nothing to do. Pressure falls measuring is to be measured fill with be being pressed, the working status with normal imitate. The way is measured in different pressure in, step up law accepts temperature change, the influence with seal unit and workpiece not steady volume is less than step-down law, it is OK to press what force of law middling pressure lifts to measure too did not balance level, and because do not get a test,pressure is restricted, use test pressure does not suffer those who measure component to measure limits limitation. 3.

2 discharge measure what discharge measures to measure signal and test cubage to have nothing to do, signal is measured to be reduced as the accretion that checks cubage in be being measured unlike pressure. This is an advantage when demarcate, measure signal direct correspondence at passing the aeriform discharge of leak demarcate appearance, need to know exact test dimension no longer in demarcate process, also need not consider to decide leak is led. Bulk discharge method, need not detect at leak commonly in be being used at flow control however, if using same measurement component (difference presses sensor) before undertaking step-down law leak checks, to aeriform system medium free passageway undertakes discharge monitoring. In mass flow law, test signal has nothing to do with test cubage not only and also have nothing to do with test pressure, however direct correspondence leads Std Cm at standard leak 3 / Min, computation wants to permit leak rate in be being measured unlike pressure law. 4 measure a law to undertake leak checks a complete automatic leak test to include 4 level with pressure: ● aerates ● of 　 of 　 ● balance measures 　 ● exhaust 4.

1 aerate level is measured workpiece undertakes aerating by constant pressure, aerate when to end, can control by time or pressure. Through aerating ascendant curve can be opposite the pressure of level roughly to be measured cubage tries estimation, whether the self check a powerful person that in perhaps checking an instrument, is linked together with workpiece is in " " the position. 4.

2 balances level must be stabilized in testing system of this one phase come down, aerate the wave motion of level must stop, change of test airy temperature also must disappear, the gas that enters work expands in charge valve place and cool, and former the air in workpiece is compressed and warm up, if pursue 2 cylinder body - the water of crankcase is covered detect in 4 leak the temperature curve place of level is shown, latter is aerating level takes dominant place. Graph 2 temperature and pressure change curve detect the pressure in antrum and temperature are identical also changing. If want to make a weather strip tries leakage appearance,the directive is 0, need when constant temperature condition, should achieve however " complete balance " the metre that needs time compares normal batch production to allow far is long. 3 kinds of methods shorten balance time: ● compensation aerates compensation aerates point to aerate level with tallish at detecting the atmospheric pressure of pressure aerates, to the balance level falls to detect pressure, expand in this in the process, the gas inside the antrum that be measured is cooling, can be opposite so " not complete balance " try to compensate. To a weather strip, charge baric force through the change, although obtain 0 directives possibly also after brief balance, and still can shorten aerate time. ＝ of ● referenced container is measured container is in testing system of the poor leak that control a standard, join in referenced side a weather strip, so that aerating,two side have balance level pressure sensor same position, such but offset their influence. Because obtain 0 directives to be not the end that leak tests,● measures time ahead of schedule, so the simplest is balance time through measuring level to shorten ahead of schedule. Till balance time can reduce the systematic condition to the front of measuring level to show no longer. Such, to a weather strip, its measure a result to may not be " 0 " and for " X " . So scrap value also must try to amend accordingly. In real work, 3 kinds of afore-mentioned methods often are used together. 4.

3 measure level to be measured leakage of the airy in antrum will produce a pressure to fall, this can press sensor to measure through difference go out to be differred at the pressure of referenced container relatively, also can measure a pressure change through pressure sensor, measurement technique sees the graph is shown 3 times. Graph 3 difference press measurement technique (A) and opposite pressure measurement technique (B) 　 aerates, balance time but according to experience set, but measure time to be able to use wave justice side - Ma slightly special aeriform equation computation goes out: P. Here, we measure the temperature in the process suppose changeless, criterion equation turns into: P. V ＝ constant is changed into the form that step-down law leak detects, equation turns into: P １ . P2 of V ｔ ＝ . Pat of V ｔ ＋ . １ of the P in V L type -- measure level to be measured in the begining the P2 of pressure 　 　 inside antrum -- measure level end to be measured the ｔ of V of pressure 　 　 inside antrum -- Pat of 　 of 　 of cubage of the antrum that be measured -- atmosphere 　 　 VL -- the aeriform bulk of leak (, １ of P2 ＝ P - Δ P, the equation that measures a process turns into: Δ P. Pat of V ｔ ＝ . V L 　 or Pat of Δ P ＝ . 　 of ｔ of V of V L ／ is notable is pressure did not check in formula, test pressure is right the pressure change in the antrum that be measured does not have an influence, lead a condition to fall in identical leak namely, no matter check pressure,be 0.

It is identical that the pressure in 1MPa or 1MPa workpiece falls. But leak rate lifts as test pressure and increase, test pressure and the impact that leak leads see a picture 1. Specific to some test, measure time to be able to go out by computation leaving type: RP of T ｍ ＝ . V ｔ . 60 ／ Pat. ｍ of the T in V L type -- measure time, RP of 　 of S 　 　 -- waste site, pat of 　 of 　 of mmH2 O 　 -- atmosphere force, ｔ of V of 　 of 　 of mmH2 O 　 -- the cubage that be measured, l of V of 　 of cm3 　 　 -- leak rate, had told before the influence of cm3 ／ Min5 to measuring an outcome, undertake with air leak detects the gas that cannot measure a leak directly, and the influence that can carry power of internal pressure of the antrum that be measured only detects come out. According to gaseous equation, also can affect besides the change of leak, temperature and bulk be measured the pressure inside antrum, want to undertake the leak of high accuracy checks so, should make sure because leak is caused,measures pressure change is merely above all. 5.

1 measure precision to be able to be reduced because of following influence 5.

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1 temperature influence must assure to measure level air temperature to keep changeless, or measure accurate ground to repeat identical temperature change every time. To satisfy this one requirement, all parts that concern with the test are like gas of the workpiece that be measured, test, seal unit to wait must have identical temperature, or the difference in temperature that measures every time is identical. In normal production condition falls, this can come true approximately only. The temperature compensation method of JW FROEHLICH (patent date: DE-C-3106981) oneself proof be iterationed is effective method. Whether to need those who allow leak to lead correspondence to depend on with law of this one party measure what signal change and temperature influence cause to measure signal to change than. 5.

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2 cubage change is measuring level to want to assure to change without cubage, if because check pressure to make,cubage increases, be equivalent to imitate leak. If because the osculatory pressure of sealed pressure head makes,cubage is reduced, can compensate the leak of original existence, to avoid weather strip " bilge shrink " , must decide weather strip dimension and sealed pressure, assure to be below encapsulated situation, there is the contact that block iron between weather strip and workpiece. Because be in,pressure law is measured in, cubage size and leak rate size are direct and relevant, cubage error is sure to cause measure an error. 5.

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The repeatability of 3 appearance trying leakage produces stand or fall of used quality of appearance trying leakage, its are absolutely precision is not the first, however repeatability. The repeatability of the instrument is comprised by all sorts of errors that form a part, if measure sensor, electron to measure unit, a powerful person, pipeline, booster to wait, the typical repeatability of the appearance trying leakage of correct set is worth is: Absolutely pressure or opposite pressure try leakage appearance 1 ～ 10Pa(depends on test pressure) 　 difference presses 1Pa5 of appearance trying leakage.

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The precision that 4 demarcate leak detects still depends on the precision of demarcate device, it is to use below most circumstance those who install the flowmeter of a bobber in the instrument is adjustable a powerful person undertakes leak imitate, this kind of method application is convenient, but 3% what the precision of flowmeter is span only. Same bobber detects hard sometimes, and reading precision is low. Accurate demarcate method is will same (weather strip) in putting clamping apparatus, successive imitate allows leak, this can enrage the implementation of a powerful person on road branch through workpiece, this a powerful person must be moved permit leak rate. We have the leak with good demarcate to lead certain simulation unit, still have nicety adjustable shut-off valve, leak is led but from 0.

3 ／ Min removes 1cm set, good with a demarcate from the air of leakage of a powerful person demarcate appearance is measured, resolution is 0.

01Std Cm 3 / Min. 5.

2 appearance trying leakage cannot decide the leak place of workpiece 5.

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1 sealed and lax appearance trying leakage cannot decide it is sealed and bad that loose place returns the quality of a material that leak comes from workpiece, if appear continuously unqualified, may be sealed problem is like balata ageing, or test system interior has leak. 5.

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2 accumulate leak in automatic leak test, those who measure is to accumulate leak (concentration measures) , every alone leak is less than such likelihoods permit leak rate, and accumulate leak to be more than allow a value, right now workpiece is sentenced to be reject erroneously. However, must appear suppose when allowing leak to lead certainly the most severe leak case. 5.

Because the surface is damp,the exterior circumstance leak of the 3 container that be measured is met and be concealed, cannot detect, can leave show in status of the following job however. Make clear to the test of casting pig cylinder body, below dry state leak rate amounts to 80cm 3 / the workpiece of Min, in damp condition (cutting fluid) fall to cannot detect however leak. Although high-pressure undertakes,detect also be no good. Because this makes sure workpiece is dry,detect in leak in it is very necessary. CNC Milling