PAES 310-2001 Engineering Materials Journal Bearings PDF

PHILIPPINE AGRICULTURAL ENGINEERING STANDARD PAES 310: 2001 Engineering Materials – Journal Bearings for Agricultural Machines – Specifications and Applications Foreword The formulation of this National Standard was initiated by the Agricultural Machin...

PHILIPPINE AGRICULTURAL ENGINEERING STANDARD PAES 310: 2001 Engineering Materials – Journal Bearings for Agricultural Machines – Specifications and Applications Foreword The formulation of this National Standard was initiated by the Agricultural Machinery Testing and Evaluation Center (AMTEC) under the project entitled "Enhancing the Implementation of the AFMA Through Improved Agricultural Engineering Standards" which was funded by the Bureau of Agricultural Research (BAR) of the Department of Agriculture (DA). This standard has been technically prepared in accordance with PNS 01-4:1998 (ISO/IEC Directives Part 3:1997) – Rules for the Structure and Drafting of International Standards. It provides specifications and proper application of journal bearings. The word “shall” is used to indicate requirements strictly to be followed in order to conform to the standard and from which no deviation is permitted. The word “should” is used to indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that certain course of action is preferred but not necessarily required. In the preparation of this standard, the following references were considered: Baumeister, Theodore (ed.) 1997. Mark’s handbook for mechanical engineers. 10th Edition. Mc Graw Hill Book Company, USA. Faires, V. M. 1969. Design of Machine Elements. Macmillan Company, New York USA. Miller, W. S. (Ed.) 1974. Machine design, Bearings, Vol. 39 No. 34. Penton Publishing Co., Cleveland, Ohio. Shigley, Joseph, E. 1977. Mechanical engineering design. 3rd Edition. Mc Graw Hill Book Company, USA. Quayle J. P. (Ed.) 1971. Kempe’s engineer’s yearbook. Volume 1. Morgan-Grampian Book Publishing Co. Ltd, London. C-60 PHILIPPINE AGRICULTURAL ENGINEERING STANDARD PAES 310:2001 Engineering Materials – Journal Bearings for Agricultural Machines – Specifications and Applications 1 Scope This standard establishes specifications and provides sufficient technical information for the proper application of journal bearings for agricultural machinery. 2 Reference The following normative reference contains provisions which, through reference in this text, constitute provisions of this standard: PAES 305:2000, Engineering Materials – Shafts for Agricultural Machines – Specifications and Applications 3 Application Journal bearings are designed to support and mount rotating shafts. They are used in drives where quietness in operation and rigidity is a requirement. Other advantages of journal bearings are low cost, less space requirement, good capacity to absorb shock loading, and its life is generally not limited by fatigue. 4 Definitions 4.1 journal bearing sleeve bearing a cylinder which surrounds the shaft and is filled with some form of fluid lubricant 4.2 journal the part of the rotating shaft , axle, roll or spindle that turns in a bearing 4.3 lubricant a medium that supports the shaft preventing metal to metal contact 5 Nomenclature Nomenclature of journal bearings is presented in Figure 1. C-61 PAES 310:2001 Journal / shaft Le ngt h D ess hi ckn ll t Wa Bearing Clearance Figure 1 – Nomenclature of journal bearings 6 Types 6.1 Hydrodynamic bearings In a hydrodynamic bearing, fluid is drawn into the region between the moving parts of the bearing by virtue of its adhesion to the surfaces of the bearing and of its viscosity and due to the shape of the bearing surfaces, pressure is generated within the fluid, which keeps the bearing surfaces separated. In a fully hydrodynamic bearing therefore there is no contact between the moving parts of the bearing, and theoretically no wear. 6.2 Hydrostatic bearings In a hydrostatic bearing, the load is carried by fluid pressure generated outside the bearing, unlike the hydrodynamic bearing where the load is sustained by fluid pressure self-generated by the bearing. The essential requirement for hydrostatic lubrication is therefore that a sufficient fluid pressure can be supplied and retained. It is not necessary that the working fluid shall have viscosity or shall adhere to the bearing materials, or in fact that there shall be relative motion in a bearing. A hydrostatic bearing will operate whether the bearing is rotating or not, so that this type of lubrication is peculiarly suitable for cases where loads must be carried statically or with very slow motion, and where low friction is required. 6.3 Boundary lubrication bearings The essential requirements of a boundary lubrication system are such that the lubricant shall “wet” the surfaces involved, and that the shapes and surfaces roughness of these shall be such as to keep the load to acceptable peak values. 6.4 Dry bearings Dry bearings operate without significant fluid film to separate the moving surfaces therefore low friction materials, or materials impregnated with a lubricant, must be used. 7 Designation Journal bearings are designated by its bore diameter, length, and wall thickness (see Figure 1 for dimensions of journal bearings). C-62  PAES 310:2001 8 Materials Materials and properties of journal bearings are presented in Table 1. Table 1 – Properties of journal bearing materials Hardness, Tensile strength, Hardness, Tensile strength, Material Material BHN MPa BHN MPa Metals Plastics Lead babbitt 21 68.95 TFE D60 20.68 Tin babbitt 25 75.84 Nylon M79 75.84 Copper lead 25 55.16 Phenolic M100 68.95 Silver 25 158.58 Acetal M94 68.95 Cadmium 35 - Polycarbonate M70 58.61 Aluminum alloy 45 151.68 Polymide E52 68.95 Lead bronze 60 234.42 Other nonmetallics Tin bronze 70 310.27 Rubber - - Steel 150 517.11 Wood - 7.58 Cast iron 180 241.32 Carbon-graphite 75 13.79 Porous metals Cemented tungsten carbide A91 896.32 Bronze 40 124.11 Fused aluminum oxide A85 206.84 Iron 50 172.37 Aluminum H55 103.42 9 Specifications Specifications of journal bearings are presented in Table 2. Table 2 – Size ranges of journal bearings Bore Wall thickness, Length-bore ratio mm mm Cast bronze 1 to 3 (can be as large as 6 for 4.8 - 127 1.6-12.7 (for small bores to 25.4mm) small bores) 6.4-12.7 (for bores to 127 mm) Porous metal (Plain) 3.2 - 101.6 0.8-6.4 (for small bores to 25.4) 1 to 2 3.2-6.4 (for bores to 101.6) Porous metal (Flanged) 4.8 - 50.8 1 to 2 1.6 - 3.2 Plastic 4.8 - 177.8 Varies with type of backing for plastic 0.8 - 6.4 NOTE Sizes shown in the table are only representative. Bearing catalogs should be consulted for accurate dimensions 10 Recommended design practices 10.1 Bearing clearance Bearing clearances for steady and dynamically loaded cases are given in Figures 2 and 3, respectively. C-63 PAES 310:2001 0.20 254 229 Guidance for Minimum Clearance - mm 203 0.15 178 152 127 0.10 102 76 51 25 0.05 Journal Ø in mm. 0 100 500 1,000 3,000 Speed , rpm Figure 2 – Minimum clearance guidance curve: Steadily loaded bearings 0.15 Minimum diametral clearance - mm 0.13 m m m/m 0 80 rp m 0 127 50 00 0 0.0 1, 1,0 60 0.10 0 40 00 2,0 0.08 00 0 4,0 5,00 00 6,0 000 3,0 00 7, 0.05 pm 0r 00 8, 0.03 /mm 2 7mm 0.01 0 76 51 102 127 152 178 229 254 203 25 Journal Diameter - mm Figure 3 – Minimum clearance guidance curve: Dynamically loaded bearings C-64  PAES 310:2001 10.2 Heat generation Frictional heating, a most common cause of bearing failure, is a function of sliding velocity, bearing pressure, and coefficient of friction. Therefore if the coefficient of friction remains constant for a range of loads and speeds, a rough indication of heat load is provided by the PV factor. PV limits for different bearing materials are presented in Tables 3 and 4. Exceeding any of these four factors (see Table 3) affects normal bearing life. Under certain conditions they can be exceeded. The maximum load that can be carried for various PV can be determined through Figure 6. Table 3 – PV limits for porous-metal bearing materials PV Bearing Pressure, (MPa) Sliding velocity Material (MPa x m/s) Static Dynamic (m/s) Bronze 1.751 55.158 13.789 6.10 Lead-bronze 2.802 24.131 5.515 7.62 Copper-iron 1.225 137.896 27.579 1.14 Hardenable 2.626 344.740 55.158 0.18 copper-iron Iron 1.050 68.948 20.684 2.03 Bronze-iron 1.225 72.395 17.237 4.06 Lead-iron 1.751 27.579 6.894 4.06 Aluminum 1.751 27.579 13.789 6.10 Table 4 – PV limits for non-metallic bearings Load Capacity Material Temperature (°C) Sliding velocity (m/s) PV (MPa x m/s) (MPa) Phenolics 41.368 93 12.70 0.525 Nylon 6.894 93 5.08 0.105 TFE 3.447 260 0.52 0.350 Filled TFE 17.237 260 5.08 0.350 TFE Fabric 413.688 260 0.76 0.875 Polycarbonate 6.894 104 5.08 0.105 Acetal 6.894 93 5.08 0.105 Carbon-graphite 4.136 399 12.7 0.525 Rubber 0.344 67 20.32 - Wood 13.789 71 10.16 0.420 11 Markings 11.1 The following information shall be marked on the casing: a) Manufacturer’s name, trademark and address b) Manufacturer’s designation 11.2 The following information shall be marked on the bearings: a) Manufacturer’s name and/or its trademark b) Manufacturer’s designation C-65 PAES 310:2001 for for for for for 3,802,047 2,626,919 1,751,279 1,225,895 1,050,768 1.27 12.70 220,633 206,844 137,896 96,527 82,737 1.52 10.16 275,792 275,792 206,844 137,896 2.03 344,740 7.62 344,740 413,688 275,792 137,896 2.54 413,688 206,844 6.10 482,636 482,636 5.08 551,584 344,740 206,844 551,584 275,792 620,532 3.81 20,000 4.06 689,480 620,532 413,688 689,480 275,792 3.56 482,636 344,740 5.08 3.05 551,584 10,000 413,688 1,034,220 620,532 344,740 2.54 1,034,220 689,480 482,636 7,000 413,688 Shaft Diameter ( mm ) 551,584 5,000 2.03 1,378,960 620,532 482,636 4,000 1,378,960 689,480 551,584 Surface Velocity ( m / s ) 1,723,700 1,034,220 10.16 3,000 1.52 620,532 1,723,700 Unit Load ( Pa ) Unit Load ( Pa ) Unit Load ( Pa ) Unit Load ( Pa ) Unit Load ( Pa ) 2,068,440 689,480 2,000 2,068,440 1,378,960 1,500 1,034,220 15.24 1.02 2,757,920 1,723,700 le 1,000 2,757,920 1,034,220 mp 1,378,960 Shaft Speed ( rpm ) 2,068,440 20.32 Exa 700 0.76 3,447,400 3,447,400 4,136,880 1,378,960 25.40 500 4,136,880 2,757,920 1,723,700 400 4,826,360 1,723,700 4,826,360 2,068,440 300 0.51 5,515,840 3,447,400 6,205,320 5,515,840 2,068,440 38.10 200 6,205,320 4,136,880 2,757,920 6,894,800 6,894,800 150 0.36 4,826,360 2,757,920 50.80 5,515,840 3,447,400 100 6,205,320 3,447,400 10,342,200 4,136,880 0.25 10,342,200 6,894,800 4,826,360 4,136,880 76.20 70 0.20 13,789,600 5,515,840 4,826,360 50 13,789,600 6,205,320 5,515,840 40 10,342,200 6,894,800 101.60 0.15 6,205,320 30 8,273,760 6,894,800 20,684,400 127.00 20 0.13 20,684,400 13,789,600 9,652,720 8,273,760 Figure 6 – Load speed chart for determining bearing dimensions or load according to PV limit C-66  PAES 310:2001 12 Safety 12.1 Make drive inspection on a periodic basis. Inspect bearings for wear and tear, for quality of lubricant, and for its alignment. Tightness setscrews should also be inspected periodically. Screws used for mounting should also be inspected regularly. 12.2 Use bearings with proper markings. 12.3 Use shafts as specified in PAES 305:2000: Shafts for Agricultural Machines. C-67 PAES 310:2001 Annex A (informative) Procedure for determining bearing dimensions A.1 Given parameters Determine the size, material of a steadily loaded bearing for a drive with a shaft speed of 1,500 rpm, a shaft diameter of 25 mm and a load of 6.5 MPa. A.2 Surface velocity The surface velocity can be determined through Figure 6. At 1,500 rpm and shaft diameter of 25 mm, the surface velocity is 2.16 m/s. A.3 PV limits and bearing material` Using Figure 6, the acceptable PV limit at a load of 6.5 MPa is 1,751,279 PV. With this PV limit, the bearing material can be selected using Tables 3 and 4, select the material with a higher PV value. Thus the material that can be used is lead bronze. A.4 Wall thickness From Table 2, wall thickness for bronze may range from 1.6 mm to 12.7 mm. For specific dimensions of thickness, consider requirements for the drive then refer to bearing catalogs. A.5 Minimum clearance Using Figure 2, the minimum clearance for 1,500 rpm and 25 mm shaft diameter is approximately 0.055 mm. A.6 Bearing specification For the given drive, use a lead bronze bearing with a 25 mm bore diameter, and wall thickness range of 1.6 mm to 12.7 mm. Bearing length depends on space limits, availability of bearing, and cost. Bearing catalogs shall be consulted for detailed specifications. C-68