Circuit breakers, relays, terminals, microphones, current collectors and commutators, all operate with electric contacts. Industry is making extensive use of contacts with ever-increasing demands on efficiency. The need of up to date reliable theories as well as of formulas and tables for applications is becoming pressing. This book is an attempt to meet this need. As is the case in many other branches of technology today, problems which arise in the field" of electric contacts involve insight in various other disciplines of physics, including parts which have not yet developed to such an extent that they. are treated in elementary text books. Con sidering the lack of introductions to some topics of this kind it is felt that orienting chapters, for instance, on the tunnel effect, the theory of the arc, the structure of carbon, and the band theory of electric conduction in solids might be valuable for many readers. In order not to burden the main text with such chapters they have been presented as appendices. Several chapters have been devoted to the theory offriction and wear.

Inhalt
I Stationary Contacts.- § 1. Introduction. A simplified summary of the theory of stationary electric contacts.- § 2. The contact surface.- § 3. The contact resistance. General theory.- § 4. Calculation of constriction resistances with constant resistivity.- § 5. Constriction resistances when conditions deviate from those in § 4, but with ? still being a constant.- § 6. Thermal constriction resistance.- § 7. Films on contacts.- § 8. The contact surface as a function of load and elastic as well as plastic properties of the members.- § 9. The relation between contact load and resistance, particularly at moderate and high load.- § 10. Contact resistance on freshly cleaned contacts at very small contact loads.- § 11. The inductance of a current constriction. Skin effect.- § 12. Electrodynamic repulsion in a symmetric contact of a non-magnetic material.- § 13. The capacitance of a contact. Electrostatic attraction in a contact.- § 14. Measurement of the load bearing contact area.- § 15. The relationship between electric potential and temperature in a current constriction which is symmetric with respect to the contact surface; that is, the ?? relation.- § 16. The ?? relation in cases of dissymmetry.- § 17. Köhler effect.- § 18. The influence of the Joule heat on constriction resistance.- § 19. Distribution of the temperature in a symmetric constriction with circular contact surface at given current.- § 20. Temperature distribution in the constriction of a contact with circular contact surface and members with very different conductivities.- § 21. Resistance voltage characteristics of clean symmetric contacts. Softening and melting voltages.- § 22. Development of the temperature in a current constriction.- § 23. The growth of tarnish films on metals.- § 24. Water films, local cells and rusting.- § 25. Thermoelectric effects.- § 26. Observations on the tunnel effect.- § 27. Fritting of tarnish films.- § 28. RU-characteristics of contacts with thin alien films.- § 29. Adherence in dry contacts which are not heated to any influential extent by the current.- § 30. Adherence in contacts that are heated by the current passing through them. Resistance welding.- § 31. About stationary contacts in practice.- § 32. Dimensioning a contact with respect to its heating.- § 33. Contact effects in carbon microphones.- § 34. Contact noise in a stationary contact.- § 35. Contact with semiconductors. Rectification. Transistors. Static electrification.- § 36. Carbon-pile rheostats. Electric resistance of pressed powders.- II Sliding Contacts.- § 37. Survey concerning friction and wear.- § 38. Early observations on the high friction in clean metallic contacts in vacuum, and the influence of admitted gases.- § 39. Boundary lubrication.- § 40. Theory of friction and wear on carbon contacts. Lubrication by means of solid lubricants as graphite and molybdenum disulphide.- § 41. Measurements on specific friction force.- § 42. Stick-slip motion. The temperature in currentless sliding contacts.- § 43. Statistical study of the electric conduction and the friction of sliding contacts. Radio-noise in sliding contacts.- § 44. Friction wear in metallic contacts without current.- § 45. Electrical performance of carbon brushes on rings and commutators when arcing is excluded.- § 46. The temperature in a contact between a carbon brush and a copper ring or commutator.- § 47. Wear and friction in the brush-ring contact.- § 48. Commutation problems.- § 49. Current collectors for trolley cars.- III Electric Phenomena in Switching Contacts.- § 50. Definitions and high power breakers.- § 51. Ignition of arcs in switches.- § 52. Discharge transients.- § 53. VI-characteristics of the stationary arc in air, and their use for calculating the duration of short arcs.- § 54. Electric Oscillations generated by d-c arcs.- § 55. Bouncing.- § 56. Mechanical erosion and tarnishing phenomena that are typical for sliding and switching contacts.- § 57. Methods to suppress or minimize arcing during switching.- § 58. Arc duration in contact making with voltage below 200 to 300 volts.- § 59. Arc duration on breaking contact. Single circuit.- § 60. Arc duration and other phenomena in an arc quenching circuit according to wiring Diagram (60.01).- § 61. Quenching of arcs by resistance parallel to the operating contact or parallel to the inductive coil.- § 62. Distinct types of arcs in relay contacts.- § 63. Material transfer in switching contacts.- § 64. Measurement of the material transfer in switching contacts, particularly with normal electrodes.- § 65. Bridge material transfer in the shape of pips and spires.- § 66. Theory of the electric material transfer in switching contacts. History of this theory.- § 67. Numerical example on the calculation of material transfer for a silver contact with capacitive arc quench.- § 68. Mercury switches.- § 69. Application of statistics to surety of contact make.- § 70. The choice of contact material and contact shape for practical applications.- IV History.- § 71. History of early investigations on contacts.- Appendices.- § I. Hardness, strain hardening, atomic diffusion phenomena as recovery and creep.- A. Survey of the theory of plastic deformation of solid bodies and of diffusion phenomena.- B. Hardness as defined by the ball indentation test.- C. Brittle materials.- D. The work consumed by a plastic deformation.- § II. Electronic conduction in solids.- A. Energy band scheme.- B. Distribution of the electrons on the energy levels of a band, with special reference to the conduction band of a metal.- C. Potential barrier. Thermionic emission of electrons.- E. Semiconduction.- F. Potential barriers and equilibrium conditions in contacts.- § III. Tunnel effect. Thermionic emission and field emission.- A. Theoretical basis for the calculations. Classes I and II of calculation procedure.- C. Tunnel resistivity.- D. Comparison between tunnel current and thermionic current according to formula (III,13).- E. Tunnel effect when both electrodes are of the same semi-conducting material.- F. Remark concerning the field strength.- § IV. Structure, electric and thermal conductivity of carbons.- A. Introduction. Graphite latice.- B. Carbon grades.- C. Graphitization.- D. Electric conductivity of carbons.- E. Heat conductivity of carbons.- § V. Hydrodynamic or thick film lubrication.- § VI. Remarks about threadlike metallic formations.- § VII. Some fundamental formulas concerning the electric discharge.- A. Introduction. Kinetic fundamentals.- B. Drift velocity.- C. Thermal ionization. Saha's equation.- D. Plasma.- E. Current in vacuum restricted by the space charge of the current carriers.- § VIII. General theory of the arc that appears in relays.- A. Introduction.- B. Reminder of elements of the theory of electric discharges in gases.- C. Thickness of the cathode layer and metal vapor pressure …