Technical White Paper

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1 Technical White Paper XX.XXXX Component Cleanliness of Fluid Systems in Automotive and Hydraulics Complying with ISO Standards Abstract: As the presence of particulate contamination in the lubricant is the major cause of failures and short component life of fluid systems, companies in a variety of industries are focusing attention in achieving and maintaining system cleanliness. The presence of machining and assembly debris in the fluid system at start-up and during the initial running phase will cause a substantial increase in the wear rates of the system, further generating large particles, with the consequential loss in performance and component life. It will also increase the probability of sudden and catastrophic failure of the system. To achieve clean components requires appropriate manufacturing, cleaning and measurement processes. Accurate assessment of the effectiveness of components and parts cleanliness is related to given contaminant extraction methods, analysis and data reporting. ISO standards are continually being developed to control procedures and implement a consistent cleanliness evaluation process. This paper explains the processes in these standards and how similar procedures have been adapted to suit the requirements of the above industries. It also gives guidance and recommendations on the implementation of these standards so that the best use can be made of them. The fluid power industry was the major developer of ISO standards through ISOTC131/SC6 until 2002 when the automotive industry embarked on a project to develop their own standards through ISOTC22/SC5. Although the processes used would be very similar to those developed by TC131/SC6, the automotive industry considered that their requirements were sufficiently different to warrant new standards. For example, the automotive industry focus is on the incidence of small numbers of large particles (>1000 μm - so called killer particles ) residual after production as they could have serious safety consequences, whereas these particles should be filtered out of fluid power systems during production. This resulted in the publication of the 10 parts of ISO16232 [1] in This split development has led to small differences in both terminology and procedures. For instance, the process of removing particles from components is called extraction in ISO16232, but this process is included in the term collection used in ISO18413 [2]. Both groups are committed to rationalizing these differences. This document summarizes the standard practices related to contaminant extraction, collection, analysis and data reporting for cleanliness evaluation of manufactured parts and components, specifically being applied to the fluid systems (lube, fuel and hydraulics) in automotive and fluid power markets. 1. Introduction The need for component cleanliness was first identified in the 1960s when the aircraft industry started using hydraulic flight systems. The last 10 years has seen more and more industrial sectors implement component cleanliness programs as they realize the technical and commercial benefits. 2. Contaminant Extraction Methods 2.1 Extraction selection with geometry The selection of the most suitable extraction method(s) is guided by the followed principles: Extraction method must be selected for the geometry of the component so that the extraction liquid can reach the controlled surfaces. Filtration. Separation. Solution.SM

2 Extraction method must be directed to only remove particles from the controlled surfaces. Component geometry must allow the particle to be transported away by the extraction method. Extraction method must be validated. ISO18413 provides recommendations for selection of contaminant extraction methods: - Pump/Motor - End-use simulation method. - Valve Cylinder - End-use simulation method. - Manifolds/System - End-use simulation method. - Gear/Shaft/Plates - Pressure rinse or ultrasonic. - Spool/Pistons - Pressure rinse or ultrasonic. - Reservoir - Pressure rinse or agitation. - Hose/Pipe - Agitation or ultrasonic. To obtain repeatable results, the process attributes must be consistent. 2.2 Agitation extraction method (Slosh test) The contaminants are extracted by partially filling the component with a known volume of test liquid (between 30 to 50% of the component volume), sealing its openings, and agitating or sloshing it in order to detach the particles from the controlled surfaces and suspend them in the test liquid for subsequent analysis. The efficacy of the agitation method depends on type of agitation, duration of agitation and choice of test liquid. This method is only suitable for hollow components like hoses or pipes whose size is such that they can be readily and consistently agitated. Applicable standards: ISO16232 Part 2; ISO18413 Clause Pressure rinse extraction method The contaminants are extracted from the controlled surfaces of the component by pressure rinsing with a jet of filtered test liquid which removes the particles from the surfaces and carries them away for subsequent analysis. The pressure rinse liquid dispenser is a device for providing clean test liquid at a suitable pressure and a flow rate capable of extracting the particles in an effective manner. The efficacy of pressure rinsing depends on pressure, flow rate, distance, angle, shape and size of the nozzle, rinsing time and liquid volume per unit area. Applicable standards: ISO16232 Part 3; ISO18413 Clause Ultrasonic vibration extraction method The contaminant is removed by subjecting the item to ultrasonic vibration. The principal characteristics of the ultrasonic equipment are power, frequency and bath size. In general, by applying transducers to the floor or wall surfaces of the bath, it is possible to achieve a high degree of homogeneous sonic distribution. For partially closed hollow components a Sonotrode transducer can be used. Applicable standards: ISO16232 Part 4; ISO18413 Clause Functional test bench extraction method (End-use simulation) The component is installed in a validated test bench which is supposed to simulate the component s functional operation. The circulation of the liquid under known conditions detaches the contaminants from the controlled surfaces and transfers them to the test liquid, for subsequent analysis. The flow of the test liquid is achieved either by pressure or by vacuum. In the case of an active component, depending on the function principle, the component is actuated either by an external device or by the traversing liquid. In reality, this test is a flushing bench as component manufacturers will rarely subject the component to the service conditions seen in service. Applicable standards: ISO16232 Part 5; ISO18413 Clause Extractions for cylindrical pipe of hydraulic, lube and fuel components This section outlines the extraction methods to assess the cleanliness of the wetted inner side of cylindrical or pipe type of hydraulic, lube, fuel components and subassemblies. 3.1 Extractions of the contaminant from passages or holes of component The functional test method, according to ISO16232 and ISO18413, is able to properly and effectively detach the particles that are residual in narrow flush passages like drain or return lines in a manifold block or casings. 3.2 Extractions of the contaminant from inside of hydraulic tube and hose Flushing rig complying with ISO16232 Part 5 is best to validate cleanliness of hoses and pipes and this needs a flow rate to give turbulence in the pipe with a Reynolds Number (Re) of >4000 i.e. well into the turbulent regime. And a variable delivery pump is desirable to suit component size. The viscosity used in these test rigs is usually higher than usual extraction liquids because of the minimum viscosity required by the circulating pump. The rig should also include on-line particle counting so that the progress of flushing can be continuously monitored and terminated when a RCL is achieved. This approach can achieve considerable savings in costs over more conventional methods of collection. It is recommended that at least 10 ml extraction liquid/cm 2 of wetted surface area is used for pressure rinsing hoses and pipes. If the calculated amount of extraction fluid is less than 2 liter, then 2 liter shall be used or if it exceeds 20 liter, 20 liter shall be used, unless otherwise specified. 2

3 4. Protocol and Validation for Contaminant Extraction 4.1 Package during transportation If particles are detached during transportation of the test components and/or from packaging, these have to be included in the cleanliness test. They are collected using appropriate extraction method(s). During handling and storage of test components, it shall be safeguarded that no contaminants are deposited on or removed from controlled surfaces. To prevent loss of particles during transport it may be necessary to seal openings in the test components with either tape or a suitable plug. Applicable standards: ISO16232 Part 2, 3, 4 & 5; ISO18413 Clause Blank test A blank test is performed to verify that the environment, operating conditions, and equipment used in the extraction procedure do not contribute a significant amount of contamination to the component being analyzed. To ensure process consistency, a blank test should be performed at regular intervals using identical test parameters. For the determination of system blank values, identical conditions as experienced during testing of the component are applied but with the component omitted (see 3.3). If the blank level exceeds 10% of the cleanliness of the component (presumed or measured), then either the process or environment is too dirty and re-cleaning is necessary, or the contamination level of the component is to low and it is necessary to increase the number of test components analyzed in order to collect more contaminants and thus fulfill the 10% limit. 4.3 Validation of contamination extraction process It is essential that the contamination extraction procedure is validated, so that its effectiveness is confirmed. Contamination Level Ci Extraction Step Figure 1. Validating the extraction process. C N 10% ΣCi n n 1 End point reached BLANK LEVEL The process is: Determine the most suitable extraction method and the operating parameters. Perform two extractions and for each of two samples to establish either the total mass of contaminants or total number of particles. Note that ISO16232 requires the extraction of three samples. For particle numbers, this should include the total numbers of particles larger than the smallest particle sizes specified in the inspection document. Divide the result of last sample by the sum of all the results obtained. If the value obtained is less than 10% of this sum, the end point is reached and the extraction is complete. The cleanliness level of the component is the sum of the extractions. If the value obtained is >10%, further extraction is necessary. If six extractions have been performed without reaching the 10% value, then the extraction parameters are not suitable and will have to be modified. 5. Relating the Cleanliness of a Hydraulic System and the Components ISOTR10686 [3] was written to link the required cleanliness level (RCL) stated by the customer for the finished system to the components in that system, including the hydraulic fluid. It calculates and manages cleanliness requirements of components and sub-assemblies that make up a system (and the fluid filling it) so as to achieve the RCL for the final system. It has two approaches: the bottom up approach (5.1) in Figure 2 and the top-down approach (5.2) in Figure 3 and these are described below. The first step for both methods is to determine the particle load (Nt) from the RCL, thus: Nt = maximum particle counts size allowed at the stated in RCL at size multiplied by the system volume. Consideration should be given to the unit volume used in the RCL, whether N/mL in the case of ISO4406 [4] or N/100 ml for other coding systems. If the contamination brought in by the assembly process is known, it can either be subtracted from the load Nt or added to the contamination brought in by each component or subassembly to make the relevant item. The particulate contamination of a new hydraulic system is the sum of the particles brought in by each component and sub-assembly that makes up the system and by the filling fluid. Thus if the cleanliness level of each component (i.e. the bottom) and of the fluid is known, then the final cleanliness of the system (i.e. the top) can be theoretically determined or predicted. 5.1 Bottom-up approach The process is described in Figure 2. Here the components are tested and the contamination level for each is obtained and these are summed. If the contamination brought in by the assembly process is known, it is added to the contamination 3

4 brought in by each component or sub-assembly to make the relevant item. This total is then compared with the allowance Nt and if this value is above Nt then the RCL has to be achieved by either making other components cleaner by cleanliness trading or the end user has to accept a dirtier product. One way of achieving additional cleanliness is to make the system fluid virtually particle-free by using a high efficiency filling filter. ISO4406 RCL (volumetric particles/ml) Calculate the fluid cleanliness level Calculate the number of particles allowed (ISO4406 level X system volume) Add all contamination and compare with allowance Measure component cleanliness achieved (results of same surface cleanliness level) Figure 2. Bottom-up approach. 5.2 Top-down approach Trade off with other components to achieve RCL Calculate the number of particles allowed ISO4406 RCL (volumetric particles/ml) Results of same volume cleanliness level Apportion numbers to components (Vc/Vt) Set component cleanliness and measurement achievements Trade off with other components to achieve RCL Figure 3. Top-down approach. Here the contamination load Nt is used to define the cleanliness specification for each component by apportioning Nt to the components on the basis of the relative volume of system fluid that they contain, i.e. Nc=Nt*Vc/Vt. This is a more proactive approach than the bottom-up approach in Figure 2. The component is then cleanliness tested and the result is compared to the specification. If it above the specification then there are two options: The result is accepted and the additional cleanliness has to be obtained by making other components cleaner. The component is made cleaner. 6. Analysis Methods 6.1 General A variety of standard, contaminant analysis methods and data reporting formats are available to produce the required part or component cleanliness data. Both ISO16232 and ISO18413 describe three basic contaminant analysis methods: gravimetric particle size, distribution and chemical composition. Largest particle size is included in particle size evaluation. The major difference separating ISO16232 and other standards is the requirement to analyze all of the extraction liquid so that all particles in the extraction are analyzed and the larger ( killer ) particles, typically at much lower concentrations, are not missed. Because of this need, the microscopic procedures of ISO16232 are completely automated using image analysis. 6.2 Gravimetric analysis method This method determines the weight of contaminant extracted from the component and deposited on a membrane filter. The contaminant is separated from the test liquid by filtration through a membrane filter under controlled conditions and deposited on its surface. The mass of contaminant is determined by subtracting the initial weight of the membrane filter from the final weight. Note that ISO16232 specifies a 5 μm filter as small particles are not considered important to this industry as they are to the fluid power industry. ISO4405 uses a pore size of 0.8 μm. Applicable standards: ISO16232 Part 7; ISO18413 Clause 6.3; ISO4405 [5] 6.3 Particle counting by microscope Here the contaminant in the extraction liquid is filtered through a membrane filter and particles deposited on its surface. After drying the membrane filter, its surface is observed using a microscope and the particles are sized and counted on the basis of their longest dimension. In the case of ISO18413, ISO4407 is specified and there is no restriction on the pore size of the membrane filters provided that it retains particles of the minimum stated size. Also, there is no restriction on the volume filtered provided that the aliquot is representative. ISO4407 [6] uses manual or automatic 4

5 (image analysis) and allows statistical counting i.e. counting a proportion of the membrane and then factoring up. As statistical counting can mean that critical and larger particles may be missed, ISO16232 stipulates the requirement to count all the extraction liquid hence counting all of the membranes. Although this can be performed manually it takes a long time, causes operator fatigue and is subject to errors. For these reasons ISO16232 only specifies image analysis (Part 7). ISO16232 Part 8 also gives the option of counting using the scanning electron microscope (SEM) with an image analysis package. Another major difference is seen with ISO4407 and ISO16232 Parts 7 & 8 as ISO4407 presents the data as cumulative particle counts (particles greater than a given size), whereas ISO16232 presents data in size intervals as differential counts. Although the data is convertible, the resulting codes are not comparable. Applicable standards: ISO16232 Part 8; ISO18413 Clause 6.4; ISO4407 The contaminant collected from controlled surfaces and deposited on a membrane filter is examined to determine its chemical composition by means of appropriate instrumentation. For the ISO18413, the technique is not specified and any technique can be used, such as a manual assessment using an optical microscope, scanning electron microscope (SEM) equipped with energy dispersion x-ray emission spectroscopic analysis (EDX) or an x-ray fluorescence spectrometer (XRF). In ISO16232, the chemical elemental composition is determined by SEM/EDX analysis only. With ISO the particle size distribution (6.3) and particle nature can be performed at the same time. Applicable standards: ISO16232 Part 8; ISO18413 Clause 6.5 In the case of ISO18413, after a representative portion of the particles, the number and size of particles is determined by automatic particle counter (APC) using light extinction sensors using (ISO11500 [7] ). In the case of ISO16232, particulate contaminant extracted from automotive components is transferred to a test rig which features an in-line automatic light extinction particle counter instrument. The complete volume is passed through the APC and analyzed. The size range of particles that can be measured by using APCs is limited to >70 μm(c), because of the method of calibration used (ISO11171 [8] ). However, the calibration can be extended to other sizes provided that it is agreed and included in the inspection document. This technique is only applicable to measuring particles contained in clear and single phase liquids. The presence of optical interfaces will cause errors. Applicable standards: ISO16232 Part 9; ISO18413 Clause 6.6 (ISO11500) 6.6 Largest particle size Some organizations require largest particle size data. This is determined by microscopic evaluation of the longest particle or particles based upon their largest dimension. 7. Data Presentation and Reporting There are major differences in the way that data is reported in the various standards, thus: ISO16232 reports interval counts (differential counts). ISO18413 reports cumulative counts. All three ISO standards abbreviate the particle count data into component cleanliness coding systems as described below. These systems are based on a geometric power series with a constant to describe the range in number from very clean to very dirty in a convenient way. Note that the numbers of particles quoted are rounded up or down to two significant figures. Also the codes can only be compared if the particle count data is presented in exactly the same way. The Component Cleanliness Code (CCC) for ISO16232 is written as a sequence, enclosed in parentheses and separated by slashes, of alphanumerical pairs specifying all or several of size classes. The capital letters A or V printed before the parentheses indicates if the code refers to 1000 cm 2 of wetted surface or to 100 cm 3 of wetted volume of the component, for example, ISO16232 CCC = V(B20/C16/D18/E12/F12/G12/H8/I0/J0/K00). A code similar to that in ISO16232 is being developed for the fluid power industry under ISO21017 [9]. 8. Conclusions and Recommendations These standards are used for auditing the cleanliness of components before their assembly into a system. The cleanliness level of components shall be managed by the specification established by two parties who are the supplier and end-user. The following are recommended to ensure efficacy of the cleanliness evaluation process: When implementing a cleanliness audit of components, the contaminant extraction method should be reviewed to ensure their efficacy and compliance to ISO16232 and ISO Blank tests should be performed on all equipment used for extracting and analyzing particles from components to verify or to validate the cleanliness of the equipment and environment. If the blank level exceeds 10% of the measured or presumed component value, it is necessary to either investigate the cleanliness of the various procedures or if it is acceptable, to increase the number of test components analyzed in order to collect more particles and thus fulfill the 10% limit. 5

6 The extraction method should be selected for the geometry component and be validated. The pressure of test liquid should be adjusted to obtain a jet of sufficient power to remove and transport the particles from the controlled surface without degrading or dissolving the surface material of the component. The selection of the nozzle is equally important and may have to be changed to suit the location e.g. a needleshaped jet is used for drillings and narrow passages and a fan-shaped nozzle is used for flat surfaces. Since wet lubricant components transmission and engine usually generate more particles compared to hydraulic components, it is recommended these are measured with primarily gravimetric method and particle counting method concomitantly in ISO16232 and ISO In case of industrial hydraulic component cleanliness, the cleanliness requirement should be consistent with the known and/or anticipated function or application of the part or component. For fluid power system, ISO12669 [10] is currently being drafted to give more consistent and logical approach to determining the cleanliness level required for modern systems. 9. Reference [1] ISO16232, Road Vehicles - Cleanliness of components of fluid circuits. [2] ISO18413, Hydraulic Fluid Power - Cleanliness of parts and components - Inspection document and principles related to contaminant collection analysis and data reporting. [3] ISO/TR10686: Hydraulic Fluid Power - Method to relate the cleanliness of a hydraulic system to the cleanliness of the components and hydraulic fluid that make up the system - Fluid Contamination - Determination of particulate contamination by the counting method using an optical microscope. [4] ISO4406, Hydraulic Fluid Power - Fluids - Method for coding the level of contamination by solid particles. [5] ISO4405, ISO4405:1991 HFP Fluid Contamination - Determination of particulate contamination level by the gravimetric method. [6] ISO4405, Hydraulic Fluid Power - Fluid Contamination - Determination of particulate contamination by the counting method using an optical microscope. [7] ISO11500: 2008, Hydraulic Fluid Power - Determination of the particulate contamination level of a liquid sample by automatic particle counting using the light-extinction principle. [8] SO11171:2010: Hydraulic fluid power - Calibration of automatic particle counters for liquids. [9] ISO DIS 21017: Hydraulic Fluid Power - Cleanliness of parts and components - Expression of level of particulate contamination. [10] ISO12669 under development: Hydraulic Fluid Power - Method for determining the required cleanliness level (RCL) of a system. 6

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