With the advent of modern frequency converting techniques, an additional negative influence on bearing life time has been discovered and continues to cause failures: bearing currents. However, there is only partial advantage for this increase, as the estimate for the bearing fatigue life under these conditions is L10 ≈ 2,100 hours (calculated with the SKF rating-life method). These represented a huge improvement in drive technology, increasing the switching frequency to 20 kHz, reducing harmonics and audible noise. Modern electric motors with frequency converters for regulating rotating speed suffer increased problems due to bearing currents at the rolling contact points. The advantages of polyurea-thickened, synthetic oils increase at higher temperatures. /�0��T�QNP9�mA%o�cE�3څb|9YP"F��Qֆ�!� ���� endstream endobj 102 0 obj 444 endobj 54 0 obj << /Type /Page /Parent 48 0 R /Resources 55 0 R /Contents [ 62 0 R 67 0 R 70 0 R 72 0 R 74 0 R 85 0 R 87 0 R 100 0 R ] /MediaBox [ 0 0 595 841 ] /CropBox [ 0 0 595 841 ] /Rotate 0 >> endobj 55 0 obj << /ProcSet [ /PDF /Text ] /Font << /F1 59 0 R /F2 60 0 R /F5 58 0 R /F8 64 0 R /F9 82 0 R /F10 76 0 R /F12 83 0 R /G1 69 0 R /G4 65 0 R >> /ExtGState << /GS1 89 0 R /GS2 91 0 R >> /ColorSpace << /Cs6 57 0 R >> /Shading << /Sh1 92 0 R >> >> endobj 56 0 obj << /Type /FontDescriptor /Ascent 714 /CapHeight 714 /Descent -191 /Flags 262176 /FontBBox [ -165 -221 1066 952 ] /FontName /HelveticaNeue-Medium /ItalicAngle 0 /StemV 114 /XHeight 517 /StemH 90 >> endobj 57 0 obj [ /ICCBased 90 0 R ] endobj 58 0 obj << /Type /Font /Subtype /Type1 /FirstChar 32 /LastChar 116 /Widths [ 278 278 444 556 556 1000 648 278 278 278 370 600 278 389 278 352 556 556 556 556 556 556 556 556 556 556 278 278 600 600 600 556 800 667 704 722 722 630 593 759 722 278 537 685 574 889 722 760 667 760 704 648 593 722 611 944 648 648 630 296 352 296 600 500 241 556 611 556 611 556 315 593 574 241 241 537 241 870 574 593 611 611 352 519 333 ] /Encoding /WinAnsiEncoding /BaseFont /HelveticaNeue-Medium /FontDescriptor 56 0 R >> endobj 59 0 obj << /Type /Font /Subtype /Type1 /Encoding /MacRomanEncoding /BaseFont /Helvetica >> endobj 60 0 obj << /Type /Font /Subtype /Type1 /Encoding /MacRomanEncoding /BaseFont /Helvetica-Bold >> endobj 61 0 obj 824 endobj 62 0 obj << /Filter /FlateDecode /Length 61 0 R >> stream New diagram In large chillers, centrifugal. The solid parts of the curves are in the green zone, delimited by the LTPL and the HTPL. \�� +G��� ��+�q��h�ws�c�e��AS��T��h���}����E�A�ˊ���l�wj��H��:mI�K��[�84ӕ�y�&j/Idd����&f.���'3�MU2ϛej��8ᠣy��� Im�q'�����P��_����o���߯��}z�z��OO�ޤ�i���~�����}�>�?N�8�'N�8�۴o � Ԍ3f���� ��/���X����l�(��/��7��N`0`�9P�}y"C��� � I just try to match up what was originally in there. In the following calculation, influencing factors of the actual application must be observed and their importance evaluated. Lubricating grease for rolling element bearings consists of thickener, oil and selected additives to improve desired properties. The value estimated from the diagram is the minimum grease life (L10) that can be attained in SKF lubricated-for-life deep groove ball bearings running under optimal operating conditions with inner-ring rotation at low loads. hbspt.cta.load(3951034, '0185d019-b885-48b3-81bb-598c6269bb64', {}); The speed factor, n*dm (RPM * mean diameter of the bearing), is a classification number for the rotational speed of the rolling bearing and is dependent on operating conditions. The following examples show that a higher GPF is not always an improvement. In table 1 GPF values are specified for factory-fill greases applied by SKF, together with speed limitations for the life calculation for each of the greases. In recent years, increased failures due to electrical arcing (highfrequency alternating current passing between the rotor and the frame through the bearing) in high-frequency drives have added to these issues. Today, the typical diameter of the nearly circular craters present in most common failures ranges from 1 to 4 µm. quality grease prefilled, this system can be used over a wide The allowable maximum speed of a grease-lubricated bearing varies with the type and size of bearing: with a high-speed angular contact ball bearing, the d mn value should be 140×104 as a guideline. f1 = Environmental media, degree of pollution (0.1 to 0.9) These centrifugal forces remove the oil from the contact surfaces at the time that it is most vital to the bearings function and survival. Anti-wear 5. For kinematically complex bearings (like axial cylindrical roller bearings with high sliding friction) the kf factor can reach values up to 90. A greased roller bearing in an electric motor is offered to demonstrate the possible grease service life. Figure 3. Application of a grease with higher GPF is often more expensive, so the extra costs must be justified. The above analysis has resulted in the new relubrication interval diagram in the SKF General Catalogue 5000, which is valid for an operating temperature of 70°C, using good quality lithium thickener/mineral oil greases. For lubricated-for-life bearings, the grease life is preferably defined as L10, which is in line with definitions for bearing fatigue life. Insulated gate bipolar transitors (IGBT) came onto the scene in the 1990s. As the grease reaches its dropping point, irreversible and spontaneous oil bleeding occurs and the grease loses its properties. f6 = Type of mounting, centrifugal energy (0.5 to 0.7). At the end of the running-in period, the operating temperature drops, indicating that the grease has been distributed. In these ranges it is not possible to predict grease life accurately on the basis of the general model. For relubrication, intervals in excess of 30,000 hours (~3½ years) are not advised, but there is no reason to maintain this limit for grease-life estimates for lubricated-for-life bearings. An important step was made by recognising different grease failures as a function of operating temperature. This base line is representative for bearings with steel cages and metal shields (2Z bearings). The equations behind this relubrication interval diagram are also used for the development of the dedicated diagram for lubricated-for-life bearings. ^��xNj0��[`�H#+σog�7 The larger numbers suggest greater surface areas and the greater total stress applied to the oil and thickener matrix. Often used in electric motors, alternators and in food machinery. A new sophisticated diagram ( diagram 1) was developed for lubricated-for-life deep groove ball bearings using the same model as for the relubrication diagram. Recommendations on how to account for the accelerated ageing of the grease with increasing temperatures and related limitations are given separately. Restrictions on speeds should not lead to distortion of curves in a general model, but must be defined per individual grease. Typical Fluting Pattern In some older models, larger bearings were apparently treated more conservatively, as these were often involved in applications with relatively high loads. As mentioned, there is a noticeable increase of electrical current damage due to highfrequency alternate current (AC). In practice, only a few grams of grease are used for lubricating rolling element bearings and this quantity typically lasts a long time.