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Design of Aerostatic Bearings

Design of Aerostatic Bearings
J. W. POWELL B.Sc.(Eng.), Ph.D.
274 Pages

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The technology of gas lubrication has advanced considerably during the past decade. Ten years ago there were virtually no externally pressurized (aerostatic) gas bearings in industrial use in this country, and apart from the pioneering research of G. L. Shires at N.G.T.E. and of Robinson and Sterry at A.E.R.E. very little had been learned about their performance and application. About this time, however, two research programmes began which were to lead to a number of manufacturers marketing products with aerostatic bearings. The first was at the National Engineering Laboratory, where a team led by H. L. Wunsch pioneered the application of air bearings to grinding spindles, machine slideways and form measuring instruments. This work was taken up and developed commercially by the Churchill Machine Tool Co. Ltd., who now supply an air bearing wheelhead as standard equipment on most of their range of precision grinding machines. The second research programme was carried out at the University of Southampton under the leadership of the late Dr. N. S. Grassam. The work was primarily concerned with the problems of operating bearings at very high speeds and in 1962 there evolved the air turbine dental drill, operating at 500,000 r.p.m., which was probably the first mass produced air bearing product. The Dental Manufacturing Co. Ltd. have continued production to the present time and have achieved a peak output of 1,500 units per month. The year 1963 saw the birth of Westwind Turbines Ltd., another offshoot of the Southamp- ton programme, which has ever since devoted itself entirely to the application of air bearings to machine tools and scientific instruments. Several thousand of Westwind's 100,000 r.p.m. drilling spindles are employed in the precision drilling of electronic printed circuit boards throughout the world's computer industries.

Aerostatic bearings have now become firmly established in such applications as precision grinding, micro hole drilling and a variety of instruments such as roundness measuring machines and turbine flowmeters for gases. They are being tried in an ever-increasing range of applications in machine tools, textile spindles and turbo-machinery. The purpose of this book is to place at the disposal of the design engineer who is facing these challenges a survey of the experience gained from the many and diverse applications of aerostatic bearings which have already been successfully accomplished. Most aspects relating to design have been covered, including basic theory, design methods, materials and manufacture and inspection and installation. In addition to emphasizing the advantages that aerostatic bearings have been shown to possess, stress has also been laid upon their limitations and areas of difficulty. Theory has been kept to a minimum consistent with a proper understanding of design procedures, and emphasis has been placed upon many practical features which have determined the success or failure of past applications. Although this book is primarily intended to assist designers, those engaged in teaching gas lubrication will also find something of value in its pages.

relating to design have been covered, including basic theory, design methods, materials and manufacture and inspection and installation. In addition to emphasizing the advantages that aerostatic bearings have been shown to possess, stress has also been laid upon their limitations and areas of difficulty. Theory has been kept to a minimum consistent with a proper understanding of design procedures, and emphasis has been placed upon many practical features which have determined the success or failure of past applications. Although this book is primarily intended to assist designers, those engaged in teaching gas lubrication will also find something of value in its pages.

TOC

  • Selection of bearing type
  • Types of gas bearing
  • The aerostatic journal bearing
  • Comparison of bearing types
  • Aerostatic and hydrostatic bearings
  • Advantages and limitations of aerostatic bearings
  • Theory of aerostatic lubrication
  • Flow between parallel plates. .
  • Flow through feed holes
  • Jet and slot combinations
  • Flow through slots in series
  • Friction in bearings
  • Uses of the theory of aerostatic bearings
  • Design of journal bearings
  • Feasibility study Jet-fed bearings
  • Slot-fed bearings
  • Example of design procedure
  • Design of thrust bearings
  • Feasibility study Combination of two thrust bearings
  • Thrust faces fed by journal exhaust gas
  • Example of design procedure
  • Hybrid journal bearings
  • Aerodynamic journal bearings
  • Hybrid journal bearings
  • Design of hybrid bearings
  • Design examples Application of design method
  • Spindles driven by a belt
  • Spindles driven through a flexible coupling
  • Spindles with air turbine drive
  • Spindles with electric motor drive
  • Static shaft bearings Bearings for high-speed machines
  • Dynamic stiffness and damping
  • Whirl induced by unbalance
  • Inversion
  • Self-excited whirl Small clearance journal bearings
  • Design procedure for high-speed machines
  • Rubber stabilized bearings
  • Characteristics of rubber stabilized air bearings
  • Other methods of delaying whirl onset
  • Properties required of gas bearing materials
  • The problem of aerostatic instability
  • Theory of aerostatic instability
  • Avoidance of aerostatic instability
  • Methods of damping aerostatic instability
  • Applications of aerostatic bearings
  • Applications to grinding machines
  • Applications to drilling machines
  • Applications to lathes and boring machines
  • Applications to medical environment
  • Applications to turbine flowmeters for gases
  • Applications to scientific instruments
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