Table of Contents

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 within it.- D. Definition of the examples.- G. Comparison with measurements.- H. Power balance at the cathode.- I. Summary of the results concerning cathode phenomena in arcs between non-refractory electrodes.- J. The power balance at the anode.- K. Cathode of refractory materials as carbon and wolfram.- L. Why is the voltage of a short arc of the order of 10 V?.- M. Movement of the arc spot.- N. Current-voltage characteristics of arcs. Arc life.- § X.- § XI.- Author and literature index.