Method for estimating contamination factor, η c, based on lubricant cleanliness

Transcription

1 Method for estimating contamination factor,, based on lubricant cleanliness A more detailed estimation of for oil or grease lubrication is based on: oil cleanliness level or oil ilter rating grease cleanliness levels related to operating conditions ISO oil contamination classiication and oil ilter rating The standarethod for classifying the contamination level in a lubrication system is described in ISO 6. In this classiication system, the result of the solid particle count is converted into a code using a scale number (table 1 and diagram 1). One method for checking the contamination level of bearing oil is the microscope counting method. This method uses two particle size ranges: µm and 1 µm. Another more modern method is to use an optical automatic particle counter in accordance with ISO The calibration scale of the automatic counting method differs from that of the microscopic counting method. It uses three particle size ranges, indicated by the symbol (c), e.g. µm(c), 6 µm(c) and 1 µm(c). Typically, only the two larger particle size ranges are used, as the larger particles have a more signiicant impact on bearing fatigue. Typical examples of contamination level classiications for lubricating oils are /1/1 (A) or /1/13 (B), as shown in diagram 1. Example A indicates that the oil contains between 16 and 3 particles µm and between and particles 1 µm per millilitre of oil. A ilter rating is an indication of ilter eficiency and is expressed as a reduction factor (β). The higher the β value, the more eficient the ilter is for the speciied particle size. The ilter rating β is expressed as a ratio between the number of speciied particles before and after iltering. This can be calculated using n 1 β x(c) = KK n where β x(c) = ilter rating related to a speciied particle size x x = particle size (c) [μm] based on the automatic particle counting method, calibrated in accordance with ISO n 1 = number of particles per volume unit larger than x, upstream of the ilter n = number of particles per volume unit larger than x, downstream of the ilter The ilter rating β only relates to one particle size in μm, which is shown in the index, such as β 3(c), β 6(c), β 1(c), etc. For example, a complete rating β 6(c) = 7 means that only 1 in 7 particles, 6 μm or larger, passes through the ilter. ISO classiication allocation of scale number Number of particles per millilitre oil over incl. Table 1 Scale number > , 9 1,3,,6 1,3 7,3,6 6,16,3,,16,, 3,,,1, 1,,1 1

2 < j z ISO classiication of contamination level and examples for particle counting Diagram 1 Determining when the contamination level is known Number of particles per millilitre of oil larger than indicated size , 1,3 6, 3, 1,6, 1,3 6, 3, 1,6, 1,3 6, 3, 1,6 A = microscope particle count ( /1/1) B = automatic particle count (/1/13) 6 B Factors to determine contamination levels for an oil lubricated application in accordance with ISO 1 Table Filtration ratio ISO 6 Circulating oil lubrication with in-line ilters Oil lubrication without iltration or with off-line ilters β x(c) Basic code c 1 c c 1 c β 6(c) = /13/1,6,663,6,6796 β 1(c) = /1/1,3,997, 1,11 β (c) = 7 /17/1, 1,639,133 1,67 β (c) = 7 /19/16,16,336,6,16 /1/1,11 3,97 A 1 1 Scale number > A Particle size [µm] B Particle size (c) [µm] Once the oil contamination level is known, either from the microscope counting method or the automatic particle counting method (both in accordance with ISO 6) or indirectly as a result of the iltration ratio that is applied in an oil circulation system, this information can be used to determine the factor. The factor cannot be derived solely from a particle count. It depends largely on the lubrication conditions, such as, and the size of the bearing. A simpliieethod in accordance with ISO 1 is presented here to obtain the factor for a given application. From the oil contamination code (or iltration ratio of the application), the contamination factor is obtained, using the bearing mean diameter =, (d + D) [mm] and the viscosity ratio for that bearing. Oil lubrication Diagrams to, page 3 and, provide typical values for the factor for circulating oil lubrication systems with in-line ilters. Diagrams 6 to 1, page and, provide typical values for the factor for oil lubrication without iltration or with off-line ilters. Similar contamination factors can be applied in applications where an oil bath shows virtually no increase in the contamination particles present in the system. Alternatively, if the number of particles in an oil bath continues to increase over time, due to excessive wear or the ingress of contaminants, this must be relected in the choice of the factor used for the oil bath system as indicated in ISO 1. As an alternative to the diagrams, the following simpliied equation can be used q c w n c = a 1 3P where a = c 1,6, and a 1 The values of c 1 and c are listed in table.

3 Diagram factor for circulating oil lubrication with online ilters β 6(c) =, ISO 6 code /13/1 1,,9,,7,6,,,3,,1 [mm] 1 1 Diagram 3 factor for circulating oil lubrication with online ilters β 1(c) =, ISO 6 code /1/1 1,,9,,7,6,,,3,,1 [mm] 1 1 Diagram factor for circulating oil lubrication with online ilters β (c) 7, ISO 6 code /17/1 1, dm,9, 1,7,6 1,,,3,,1 3

4 Diagram factor for circulating oil lubrication with online ilters β (c) 7, ISO 6 code /19/16 1,,9,,7,6,,,3,,1 1 1 Diagram 6 factor for oil lubrication without iltration or with off line ilters ISO 6 code /13/1 1,,9,,7,6,,,3,,1 [mm] 1 1 Diagram 7 factor for oil lubrication without iltration or with off line ilters ISO 6 code /1/1 1,,9,,7,6,,,3,,1 [mm] 1 1

5 Diagram factor for oil lubrication without iltration or with off line ilters ISO 6 code /17/1 1,,9,,7,6,,,3,,1 1 1 Diagram 9 factor for oil lubrication without iltration or with off line ilters ISO 6 code /19/16 1,,9,,7,6,,,3,,1 1 1 Diagram 1 factor for oil lubrication without iltration or with off line ilters ISO 6 code /1/1 1,,9,,7,6,,,3,,1 1 1

6 Table 3 Factors to determine contamination levels for a grease lubricated application in accordance with ISO 1 Contamination level Operating conditions c 1 c High cleanliness Normal cleanliness Slight to typical contamination Severe contamination Very severe contamination very clean assembly; very good sealing system relative to the operating conditions; relubrication is continuous or at short intervals sealed bearings that are greased for life, with appropriate sealing capacity for the operating conditions clean assembly; good sealing system relative to the operating conditions; relubrication according to manufacturer s speciications shielded bearings that are greased for life with appropriate sealing capacity for the operating conditions clean assembly; moderate sealing capacity relative to the operating conditions; relubrication according to manufacturer s speciications assembly in workshop; bearing and application not adequately washed prior to mounting; ineffective seal relative to the operating conditions; relubrication intervals longer than recommended by manufacturer assembly in contaminated environment; inadequate sealing system; too long relubrication intervals,6,6796,3 1,11,177 1,7 1),11,66,617,6 1) When mm, use 1,677 Grease lubrication Diagrams 11 to 1, page 6 to, provide typical values for the factor for grease lubrication, considering ive levels of contamination as shown in table 3. Here, the simpliied equation can be used. SKF recommends using the online SKF Bearing Calculator when estimating for use in the SKF rating life calculation. factor for grease lubrication high cleanliness 1,,9,,7,6,,,3,,1 Diagram

7 Diagram 1 factor for grease lubrication normal cleanliness 1,,9,,7,6,,,3,,1 1 1 Diagram 13 factor for grease lubrication slight to typical contamination 1,,9,,7,6,,,3,,1 1 1 factor for grease lubrication severe contamination Diagram 1 1,,9,,7,6,,,3,,

8 Diagram 1 factor for grease lubrication very severe contamination 1,,9,,7,6,,,3,,1 1 1