Tham khảo tài liệu 'mechanical engineers data handbook episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 90 MECHANICAL engineer s data handbook Let m mass of shoe k spring stiffness x deflection of spring p coefficient of friction F radial force on drum N rotational speed a angular velocity Torque capacity 2 shoes T 2fir mra 2 kx where a 2nN. Dynamometers The power output of a rotary machine may be measured by means of a friction brake. The forces are measured by spring balances or load cells. Other types of dynamometer include fluid brakes and electric generators. Torque absorbed T r Ft F2 Power P 2nNT Bearings The full analysis of heavily loaded plain bearings is extremely complex. For so called lightly-loaded bearings the calculation of power loss is simple for both journal and thrust bearings. Important factors are load capacity length to diameter ratio and allowable pressure on bearing material. Information is also given on rolling bearings. Lightly loaded plain bearings Let p power L length D diameter n absolute viscosity t radial clearance inner radius r2 outer radius N rotational speed APPLIED MECHANICS 91 Journal bearing 2nìN1DìLp t Thrust bearing Thrust bearing Load capacity for plain bearings Machine and bearing Load capacity p MPa Length diameter L D Automobile and aircraft engine main bearings 4-12 Automobile and aircraft engine crankpin bearings 4-23 Marine steam turbine main bearings Marine steam turbine crankpin bearings 2-4 Land steam turbine main bearings Generators and motors Machine tools Hoisting machinery Centrifugal pumps .7 Railway axle bearings Bearing load w Load capacity p - 4------ Projected area LD This assumes a uniform pressure actually the maximum pressure is considerably higher. 92 MECHANICAL ENGINEER s DATA HANDBOOK Bearing materials Metals Brinell Thin shaft Load capacity p Maximum Material hardness hardness MPa temperature C Tin base babbitt 20-30 150 150 Lead base .
