tilting pad radial bearing

WA AUKESH B E A R I N G S TilTing Pad Radial BeaRings dHB10 Metric Range 2 ConTenTs Benefits 2 General Description 3 Lubrication Systems and Sealing 5 Alternative Pad Materials & Design 6 Bearing Selection 7 Optional Features 11 Installation 17 Rotordynamic Studies 19 Size Tables 19 Size Codes 20 Enquiry Data Sheet 25 © Waukesha Bearings 2002-2009 1 3 Benefits of Tilting Pad Radial Bearings: • Hydrodynamically stable at high speed • Less sensitive to load direction • Less sensitive to shaft misalignment • Oil flow can be minimised • Able to use standard components • Spares consist of pads only Benefits of Waukesha Bearings: • The strength of a worldwide bearing group • Unique material options provide the widest range of hydrodynamic bearing solutions • Engineered designs that can be customised for specific needs • Complete design responsibility • Full technical support service – including rotordynamics • Quality assurance – approved to ISO 9001 • Magnetic Bearings offer a totally dry solution • The widest range of test rig validation and support Benefits of Waukesha Tilting Pad Radial Bearings: • Simple design – no seals required • Optimised lubrication for minimum power loss and bearing temperature • Alignment capability to suit all requirements • Compact designs of combined axial/radial bearings • Provision of static and dynamic performance data as standard • Contract drawings provided for every application • Optional North American range based on inch sizes BenefiTs Standard TJ Series bearings 2 4 Fig 1 (a) TF Series Bearing Arrangement Fig 1(b) TJ Series Bearing Arrangement TF & TJ Series Bearings Waukesha Tilting Pad Radial Bearings in these series consist of 4 or 5 pads located both circumferentially and radially by stop pins, and axially by end plates. See Fig 1a and b. The stop pins as well as locating the pads also function as oil supply nozzles. Standard pads are centre pivoted and are therefore suitable for either direction of rotation. Bearings are available with one piece or split housings to comply with machine assembly requirements. Waukesha Tilting Pad Radial Bearings are designed to transfer radial loads from rotating shafts with minimum power loss and optimum dynamic characteristics. They are available in three main ranges: • TF series – these are 4 pad bearings for shaft sizes 20-300mm. • TJ series – these are 5 pad bearings for shaft sizes 20-300mm. • Large range (TFB & TJB series) - these are 4 or 5 pad bearings for shaft sizes from 300mm upwards. The TF (4 pad) and TJ (5 pad) series are designed on similar principles and have identical outside dimensions. The large range has some different design features which are described separately below. The dimensions of these ranges are given in the Size Tables on Pg. 19. geneRal desCRiPTion 3 5 Fig 2 Definition of Clearance Terms (Preset Ratio) TJB400-280/2DF bearing with jacking combined with high performance copper chrome backed thrust pads Large Range Bearings TFB & TJB series For larger shaft sizes it is usually necessary to consider improved forms of pad pivot design to ensure high stiffness combined with ability to tilt and align; sealing requirements also can often be more onerous. The range shown in Table 4 of the Size Tables has been formulated to deal with these requirements and in particular a spherical pad pivot is provided which combines high stiffness with good alignment capability. Dimensions given in Table 4 are for b/d = 0.7 bearings: other b/d ratios can be supplied if required. Note that the various optional features available with the Style TF and Style TJ series are also available in the Large Range. Materials Standard pads are steel backed, lined with tin based whitemetal (babbitt) to specification ISO Sn Sb8 Cu4. Equivalent specifications are BS 3332/A and SAE12. The housings and endplates are steel for the standard bearing arrangement. Floating seals when used are normally manufactured in lead bronze and knife edge end plates in aluminium alloy. Preset Standard pads are supplied with positive preset (or preload) ratio in the range 0.35-0.55 when used with shaft diameters as recommended on Pg. 18. The definition of preset ratio is shown in Fig 2. 4 6 Fig 3 End Plate and Seal Options luBRiCaTion sysTeMs & sealing The standard Waukesha Tilting Pad Radial Bearing as shown in Fig 1(a) and (b) has the oil flow controlled by Directed Lubrication nozzles between each pad with the oil exits from each end of the bearing being largely free, only large clearance baffles being provided. This arrangement minimises power loss and oil flow while keeping pad temperatures low. While the standard system described above is ideal for the bearing itself, the machine location in which it is installed sometimes requires restriction of the end flow from the bearing, either at one or both sides: • Floating seals reduce the flow along the shaft to a minimum; if two floating seals are used, the main flow is directed through an orifice outlet usually at the bottom of the bearing. Details of the Waukesha range of floating seals are available on request. • Knife edge endplates, while less effective than floating seals, offer some control of end leakage. The four most common combinations of seal/end plate are shown in Fig 3 with the identifying Style codes. Oil supply pressure should be between 1 and 1.5 bar though in some circumstances pressures down to 0.5 bar can be used. These pressures should be available at the oil inlet annulus of the bearing; the bearing nozzles, orifices etc will be sized to give the correct flow at the specified supply pressure. 5 7 TJ 160-112/0 bearing with RPB25P faced pads for application with low viscosity hydrocarbon lubricant Whitemetal faced pads with copper chrome backing alTeRnaTive Pad MaTeRials and design Higher speeds, loads and operating temperatures of modern machines are increasingly taking bearing design beyond the limits of whitemetal. Heat soak at standstill can also be a problem. Waukesha can offer the widest choice of bearing materials where applications exceed the selection parameters indicated on Pg. 7 or lubricants other than oil are envisaged. Options available include: • RPB25P, an engineering polymer, especially offers outstanding potential for high ambient temperature applications and water lubrication, as well as being an electrical insulator and resistant to chemical attack. It can operate at temperatures up to 120°C higher than whitemetal. • Copper chrome backed pads faced with whitemetal typically will reduce the pad surface temperature by 20°C at higher speeds. • Steel backed pads faced withcopper lead can operate at temperatures up to 40°C higher than whitemetal but require a hardened shaft surface. Pivot Position Centre pivoted pads are standard as they are preferred for bi-directional running, foolproof assembly and minimum spare stocks. At higher speeds (above 60m/s) offset pivots can offer some bearing surface temperature reductions and the dynamic characteristics (stiffness and damping) may also be preferable for some applications; all bearings can be supplied if required with offset pivot pads (Style OP). Bearing with copper lead faced pads for 50 mm shaft at 60 000 min-1 6 8 Small TJ050-035/2D bearing with Directed Lubrication for high speed gearbox application BeaRing seleCTion A preliminary selection of bearing size should be made using the Size Tables on Pg. 19 as follows: 1. Firstly for the shaft diameter required refer to the b/d = 0.4 Size Table and check that the maximum load given is adequate. 2. If the load capacity is not adequate refer to the b/d = 0.7 maximum loads and then, if necessary, the b/d = 1.0 loads for the required shaft size. 3. If the required load capacity is still inadequate it will be necessary to consider using a larger diameter bearing. 4. Waukesha would normally propose 5 pad, TJ series, bearings; the characteristics of 4 pad, TF series, bearings may be preferred for specific applications. Load Capacity The load capacity of Tilting Pad Radial Bearings depends upon a number of different factors, principally shaft speed, lubricant viscosity and inlet temperature. Within the speed ranges and for the oil conditions shown in Fig 4(a), 4(b) and 4(c), the load capacities given in the Size Tables can be used. At speeds above and below these ranges, the load capacity of the standard bearing will be reduced and advice should be obtained from Waukesha. Other factors which need to be considered when assessing load capacity are: a) Direction of load – the load capacity of a tilting pad radial bearing is affected by the direction of the load relative to the pad positions. In the Size Tables the nominal load capacity is given for the two common orientations – ‘load on pad’ and ‘load between pads’. Note that for maximum load capacity with a vertically downward load, bearings can be supplied with two pads at the bottom (Style BP) as shown in Fig 6. b) Load at instant of start – at this condition the specific load* for a TJ series bearing should not exceed 1.4 MPa for on pad loading or 2.2 MPa for between pad loading. For a TF series bearing the loading should not exceed 2.0MPa for between pad loading. If these loads are exceeded the application may need either a larger bearing (to reduce the specific load) or the use of a hydrostatic (‘jacking’) system for use at starting and low speed: see Pg. 13 – Style J and Fig 10. Power Loss & Oil Flow Power loss data for Series TJ bearings is given in Fig 4(a), 4(b) and 4(c) for b/d = 0.4, 0.7 and 1.0 respectively. This is based on the oil conditions stated. Recommended oil flows are given for a 20°C temperature rise through the bearing. These figures can also be used for Series TF bearings with standard 75° arc pads. Pad width (mm) X shaft dia (mm) *Specific load (MPa) = Load (N) 7 9 Fig 4(a) Power loss and Oil Flow. TJ series.B/D = 0.4 8 10 Fig 4(b) Power loss and Oil Flow. TJ series.B/D = 0.7 9 11 Fig 4(c) Power loss and Oil Flow. TJ series.B/D = 1.0 10 12 Fig 5 Adjustable Pad Pivot – Style AP Fig 6 Two Pad Orientation – Style BP Fig 7 Curved Line Pivot – Style CL oPTional feaTuRes Standard bearings are available with a number of optional features identified by Style Codes as follows. Adjustable Pivots. Style AP In some cases especially on prototype units it is desirable to have the ability to alter the bearing clearance: this can be achieved within standard dimensions by having pads with adjustable pivots — see Fig 5. Pad Arc Length. Style AR Four pad bearings (Series TF) and five pad bearings (Series TJ) are normally supplied with 75° and 60° arc pads respectively. Series TF bearings can also be supplied with 60° arc pads by specifying Style AR60. Two Pad Orientation. Style BP This style – see Fig 6 – may be required either for maximum load capacity with a vertically downward load (see Pg. 7) and/or for its particular stiffness and damping characteristics. Curved Line Pivot. Style CL Standard Waukesha pads have a line pivot over half the pad length. While this offers significant ability to deal with misalignment, in some cases increased ability to deal with axial misalignment is required and the Style CL can be used – this offers a line pivot on a curved surface. See Fig 7. External dimensions of the standard bearing are not affected. 11 13 Fig 8 Temperature Sensor Installation — Style IT2 Fig 9 Proximity Probe Installation — Style IR Floating Seals. Style FL Where oil leakage along the shaft from one or both ends of the bearing must be kept to a minimum, floating seals are recommended – see Pg. 5. Temperature Sensors. Style IT1 & IT2 Bearings can be supplied either with provision for fitting temperature sensors (Style IT1) or, if desired, already fitted with sensors of Waukesha supply (Style IT2). A typical installation is shown in Fig 8. Information required when specifying Style IT1 is: • Sensor hole size required. • Number of sensor holes and in which pads (or Waukesha choice). • Position in pad and at which end (or Waukesha choice). When specifying Style IT2, information required is similar. In addition we need to know: • Type of sensor (RTD or thermocouple, single or duplex). • Electrical characteristics – for example 2 or 3 wire circuit for RTD’s, material pair for thermocouples. • Cable length and termination – for example is a terminal head required and if so what specifi- cation has it to meet. Proximity Probes. Style IR Bearings can be supplied with provision for mounting proximity probes on the end plates – see Fig 9. Information required when specifying this option is: • Sensor size – details of fastening required. • Number and position of probes. 12 14 oPTional feaTuRes (ConTinued) Fig 10 Hydrostatic jacking – Style J TJB series bearing with Flooded Lubrication for large turbo generator TJB series bearing with hydrostatic jacking in two lower pads Hydrostatic Jacking. Style J Bearings can be supplied with hydrostatic jacking in cases where there is a high load at the instant of start (see Pg. 7 – Load Capacity). Waukesha will specify the required oil supply quantity and pressure for the hydrostatic system when given the starting load conditions. See Fig 10 for a typical installation arrangement. Knife-edge End Plates. Style KN Where some control of the oil leakage from one end of the bearing is required, knife-edge end plates may be used — see Pg. 5. Offset Pivot Pads. Style OP Offset pivot pads, instead of the standard centre pivot pads, can be supplied as outlined on Pg. 6. 13 15 TJ250-140/0D bearing combined with high performance thrust bearing using copper chrome backed thrust pads Axial Loads. Styles TL & TP Bearings can be supplied with either single or double axial faces to accommodate axial loads – see Figs 11 and 12. The most compact arrangement is the Style TL with either uni- or bi-directional taper land faces or plain grooved faces – load capacities of these alternatives are given in Fig 11. To specify these the following Style codes should be used: Style TLG Plain grooved face Style TLU Taper land face (uni-directional) Style TLB Taper land face (bi-directional) For higher axial loads Style TP should be used which incorporates tilting pad faces from the Waukesha MS range as described in Designers Handbook No 5A. The unique system of Directed Lubrication with centre pivot pads will normally be used for Style TP axial faces. The codes TLG, TLU, TLB and TP specify a single axial face: if a double axial face is required a 2 suffix should be added i.e. TLG2 etc. If these features are required, the value of the axial load at the instant of start up as well as during running should be stated in the enquiry. 14 16 Sizes and Axial Load Capacity for Style TL (for single letter dimensions see main dimension tables – Pgs. 21-23) NOTE Load capacities for taperland faces are for preliminary guidance only: they are based on the high speed dotted line in FIG 4(a) with the same oil conditions Fig 11 Plain/taper land Axial Faces – Style TL (Assemblies with low/medium axial load capacity) 15 17 Sizes and Axial Load Capacity for Style TP (for single letter dimensions see main dimension tables – Pgs. 21-23) NOTE Tilting pad axial bearings are from the MS range as described in Designer’s Handbook 5A: see bearing selection comments for restrictions in use of maximum load capacity. Fig 12 Tilting Pad Axial Faces – Style TP (Assemblies with high axial load capacity) 16 18 Fig 13 Alternative Bearing Location Methods Methods of Location Bearings are available with alternative methods of location – see Fig 13. Diametral Clearance & Shaft Diameter This range of Tilting Pad Radial Bearings is based on a standard bearing ‘bore’ for all operating conditions; the necessary change in diametral clearance for various shaft speeds is obtained by varying the shaft diameter. This enables standard pads for each size to be used which simplifies customer records and minimises inventory. Waukesha’s recommended minimum diametral clearance at the pivots for normal usage is shown in Fig 14. In some circumstances clearances obtained from this figure can be reduced, but it is recommended that Waukesha be consulted before reductions are made. Note: Bearing clearance ratio = Diametral clearance over pivots Nominal bearing bore Fig 14 Minimum Diametral Clearance BEARING CLEARANCE RATIO insTallaTion 17 19 Fig 15 Bearing and Shaft Tolerances The example below will show how maximum/minimum figures can be established for both diametral clearance and shaft diameter when Waukesha standard Tilting Pad Radial Bearings are used. Example: It is desired to establish the clearances and shaft diameter for a TJ050-020/2DF which has to run at 17 385 min-1 maximum speed. (1) from Fig 14 bearing clearance ratio for 17 385 min-1 = 0.00173 therefore minimum diametral clearance = 0.00173 X 50= 0.087mm. (2) from Fig 15 tolerance on diametral clearance for 50 = 0.051mm therefore maximum diametral clearance = 0.087 +0.051 = 0.138mm. (3) maximum shaft dia = nominal size – minimum dia clearance = 50.000 – 0.087 = 49.913mm (4) tolerance on shaft dia from Fig 15 for 50mm = 0.016mm therefore minimum shaft dia = 49.913-0.016 = 49.897mm Shaft surface finish varies with size. A typical figure is 0.4 micron Ra (approx. 16 microinch CLA) for a diameter of 100mm. A hardened shaft is not usually required. Load Direction Relative to Pads The load capacity of a Tilting Pad Radial Bearing is affected by the direction of the load as mentioned on Pg. 7. When the load vector falls on the centre of a pad, the maximum specific load recommended is approxi- mately 2.1 MPa, and when it falls between the pads it is approximately 2.8 MPa. These values are used for the maximum loads given in the Size Tables on Pg. 19. 18 20 RoToRdynaMiC sTudies Waukesha can undertake full rotating machine studies, including response to unbalance and stability, and undamped natural frequency. These studies utilize bearing coefficients obtained from in-house computer design programmes. This calls for an exchange of data in some detail, and the effect of design features on machine stability can often be examined live on our computer screens. size TaBles Table 1: b/d = 0.4 bearings TF & TJ series 20-300mm shaft dia Table 2: b/d = 0.7 bearings TF & TJ series 20-300mm shaft dia Table 3: b/d = 1.0 bearings TF & TJ series 20-300mm shaft dia Table 4: b/d = 0.7 bearings TFB & TJB series 300-700mm shaft dia These tables show the sizes of the bearings which have been selected as described on Pg. 7. When the sizes have been confirmed from these tables, refer to Pg. 20 which shows how the full size code is produced by adding suffixes. All dimensions in these tables are in millimetres unless otherwise stated. Undamped Natural Frequency Analysis 19 Pedestal bearing assembly for gas turbine generator incorporating TJB series bearing with jacking 21 size Codes Code Nomenclature Waukesha Tilting Pad Radial Bearings are identified by a two part code which consists of the bearing size followed by a suffix indicating the type of construction. The size designation is shown in the left-hand column