JED-593清洁度要求

JED-593 : 2006-11 Page 2WABCO Specification3 Cleanliness classes3.1 DefinitionThe permissible level of residual contamination and the permissible types of particles are defined according to the function of the part.Several classification methods are used to define the permissible limits of residual contamination. Due to the high quality requirements for WABCO devices, WABCO uses the particle size distribution method.In general, the devices or parts shall not contain any solid particles (e.g. metal particles, plastic par-ticles, elastomer particles) having a longest dimension > 1 mm.3.1.1 Particle size classesISO 16232 and VDA 19 classify the particles according to their largest dimension.Particle sizeclass Size [µm] B 5 ≤ x < 15 C 15 ≤ x < 25 D 25 ≤ x < 50 E 50 ≤ x < 100 F 100 ≤ x < 150 G 150 ≤ x < 200 H 200 ≤ x < 400 I 400 ≤ x < 600 J 600 ≤ x < 1000 K1000 ≤ xWABCO uses this classification. The smallest particle size classes B and C, indicating values below 25 µm, are currently not being used at WABCO because no functional impairment has so far been reported in these cases.3.1.2 Cleanliness levelsISO 16232 and VDA19 define cleanliness levels which allow the logarithmic indication of the number of particles per particle size class. The number is related to a standardized area of 1000 cm² or, for liquids, to a standardized volume of 100 cm³.In devices, the only area considered is the functional surface area, for instance, the passage area of compressed air. The functional surface area is that part of the device’s surface which is decisive for the function of the device. It is precisely specified in the Inspection Specification, Doc. Code 636. If the area is smaller or greater than 1000 cm², an appropriate conversion has to be made.JED-593 : 2006-11 Page 3WABCO SpecificationNumber of particles per 1000cm² or 100cm³ Cleanliness levelMore than up to and including00 0 0 0 0 1 1 1 2 2 2 4 3 4 8 4 8 16 5 16 32 6 32 64 7 64 130 8130 250 9 250 500 10 500 1x10³ 11 1x10³ 2 x10³ 12 2 x10³ 4 x10³ 13 4 x10³ 8 x10³ 14 8 x10³ 16 x10³ 15 16 x10³ 32 x10³ 16 32 x10³ 64 x10³ 17 64 x10³ 130 x10³ 18 130 x10³ 250 x10³ 19 250 x10³ 500 x10³ 20 500 x10³ 1x106 21 1 x106 2 x106 22 2 x106 4 x106 23 4 x106 8 x106 248 x106 16 x1063.1.3 WABCO cleanliness classesWABCO defines cleanliness classes for devices and parts in order to have a clear allocation of par-ticle size classes to the relevant permissible cleanliness levels.The WABCO cleanliness class IV corresponds to the revision status B of JED-593.JED-593 : 2006-11 Page 4WABCO Specification3.2 Allocation of the WABCO cleanliness classes3.2.1Functional assessment of the device or partThe best method of allocating cleanliness classes is the functional assessment, taking into account• the function of the device or part and the evaluation of the effect of foreign particles on thefunction• the determination of the device/part areas to be included in the test, thus the actual surface • the media involved (e.g. oil, water, air).Only the careful analysis and assessment of the function can be the basis for the definition of meaningful cleanliness classes for devices or parts. In doing so, the individual residual contamina-tion limits have to be coordinated for parts working together.3.2.2 Determination of the actual conditionIf the device or part does not provide any indicators for the allocation of the cleanliness class, the allocation can be based on experience. For this purpose, the cleanliness class of the predecessor or a similar device or part is documented. The cleanliness class for the new device or part is derived from these data.Moreover, all the failures in the field and in the process which were due to contamination have to be taken into account.Please note: This approach requires the tolerances, the operational requirements and the func-tions of the device or part in question to be comparable!3.3 Documentation of the determined WABCO cleanliness classesThe documentation of the requirement is made in the Outline Drawing or Component Drawing by in-dication of JED-593, the cleanliness class and the functional surface area A F , see example. The functional surface area is the area for which the cleanliness requirement is specified. For the execu-tion of the analyses, this area must be described in an Inspection Specification, Doc. Code 636, or visualized by a sectional drawing included in the Inspection Specification document. In most cases, those areas which are subjected to normal ambient conditions in later operation will be excluded from the consideration.Example: JED-593 Class IV, A F = 450 cm²In certain cases, for instance components for electronic assemblies, the permissible degree of con-tamination has to be related to special material properties of the particles, such as c onductivity or hardness. In this case, this shall be made visible by special indication. Example: JED-593 Class X (conductive material), A F = 50 cm²JED-593 : 2006-11 Page 5WABCO Specification4 Determination of the technical cleanliness4.1 Extraction procedureBasically, the extraction is a cleaning process. The extraction method is selected in accordance with the properties of the device or part, such as geometry and material, and adhesion mechanisms of the particles on the device or part. Four parameter fields apply to the method.1. Cleaning medium2. Temperature3. Mechanical aspects4. Exposure timeDuring the extraction procedure care must be taken to prevent additional particles from detaching. It also has to be ensured that no particles are ingested by the equipment or cleaning medium, thus affecting the result of the analysis.The aim consists in washing off the unbound particles present on the functional surface area of the device or part, in order to collect these particles for analysis. The capability of this extraction proce-dure is proven once at the start in the form of a documented test.The qualification of the extraction conditions is assessed by repeated rinsing performed on the same inspection lot, on the basis of the decreasing behaviour. At the end of this process, the determinedcleanliness value shall be max. 10 % of the sum of all extraction steps.JED-593 : 2006-11 Page 6 Moreover, it shall be determined whether the function of the overall system is exposed to a risk dueto grease-bound particles. If this is the case, a grease-dissolving medium shall be used. Ethyl alco-hol is not suited for this purpose. A special cleaning medium shall be indicated in the Inspection Specification, Doc. Code 636.4.1.2 TemperatureThe extraction procedure is performed under normal laboratory conditions, i.e., with a normal room temperature prevailing and the cleaning medium having the same temperature. Any deviation from these conditions has to be specified in the Inspection Specification. It must be observed that such a deviation requires considerable work on the test equipment.4.1.3 Mechanical aspectsThe extraction procedure aims at detaching the dirt particles from the part. In the simplest form, this can be do by using a wash bottle. All functional areas have to be accessible to visual inspection.A more reproducible procedure is the pressure rinsing method using a defined pressure. The pres-sure of the jet of test liquid shall not detach any particles which in normal operation would firmly ad-here. Definitions going beyond the use of wash bottles shall be given in the Inspection Specification.The use of ultrasonic baths is permitted, but it requires the entire part to be immersed in the solvent.4.1.4 Exposure timeThe exposure time shall ensure that all the particles adhering to the surface are definitely detached.4.2 Analysis methodWABCO applies the particle size distribution analysis with microscopy, because the gravimetric analysis is not useful for large devices having particle quantities of less than 10 mg. Below this limit, the capability of weighing methods is normally insufficient, and external influences, such as humidity, affect the result of the analysis.4.2.1 FilteringIn case of considerable particle quantities or large quantities of grease, a filter cascade should be used. Normally, the use of a simple filter should be aimed at, because this facilitates the determina-tion of the distribution curve. In case of application of a filter cascade, the distribution shall be de-termined for each individual filter, and the results shall be summed up.The selection of the mesh size has to be based on the fact that the mesh has only two dimensions.It must be ensured that all relevant particles, i.e., also the oblong ones, are caught by the filter or the cascade. For WABCO, this means that the filters applied have a maximum mesh size of 5 µm.The filters used for the analysis with light-microscopic means shall provide the highest possible con-trast.4.2.2 Determination of the particle size distributionThe lower limit of the particles considered is defined to be 25 µm. On a microscope equipped with camera, the entire filter is read into an image processing program, and the number of particles per size class is counted. The size is the largest dimension in top view. In the evaluation, the repeatabil-ity of illumination, grey values and contrast has to be observed.The setting mode can be taken from the manufacturer’s description of the analysis system; it shallbe documented for the relevant evaluation.WABCO Specification。