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The performance of spherical and conical spiral groove bearings lubricated with a Newtonian, incompressible liquid is investigated. This work covers both complete and incomplete filling of the bearing gap with a liquid. In an incompletely filled bearing gap a gas-to-liquid interface occurs. Under radially eccentric operating conditions the location of the interface is related to the pressure distribution in the lubricating film. Part I treats a theory based on the smooth pressure concept. A perturbation method serves to determine the pressure distribution and, in the case of an incompletely filled bearing gap, also the location of the gas-to-liquid interface. From the pressure distributions, different for the two cases, formulas have been derived for the radial and axial load capacity. Comparison of the results obtained with this perturbation method with the results obtained with a numerical method lead to the conclusion that the former results can be used in practice as long as practically no cavitation occurs in the bearing. Previously reported experiments with spiral groove journal bearings confirm this. In spiral groove bearings the groove dimensions which lead to a satisfactory operation of the bearing are generally such that even with fairly marked eccentricities there is practically no occurrence of cavitation. Part II will treat the results obtained with the theory of Part I.

The theory developed in Part I is applied to the solving of problems encountered in practice. The manner in which the axial and radial load capacity and stiffness depend on bearing dimensions, particularly on groove dimensions, is shown. The important aspect that spherical and conical spiral groove bearings, just as spiral groove journal bearings, can be stable even if not subjected to a radial load is investigated. A necessary condition for the stability of these bearings in the radially unloaded state is shown to be the complete filling of the bearing gap with a lubricant. In the case of an incompletely filled bearing gap the interaction between the gas-to-liquid interface and the pressure distribution in the lubricating film is such that these bearings have a negative stiffness.

A spiral groove journal bearing has two significant advantages, compared with a plain journal bearing. These are the self-sealing capabilities and the favorable stability properties of the bearing under no-load or light-load conditions. Under eccentric operating conditions the axial width of the liquid film in such a bearing varies in the circumferential direction. The shape of the gas-to-liquid interface and its effect on load capacity and stability are investigated both theoretically and experimentally. It appears that there is a considerable difference in the shape of the gas-to-liquid interface, depending on whether it is the housing or the shaft that has spiral grooves, or more generally, on whether the load vector is rotating with respect to the grooves or not. It has further been found that the free boundary has an unfavorable effect on the stability of unloaded spiral groove journal bearing. A deep groove in the circumferential direction, close to the gas-to-liquid interface, can practically cancel this unfavorable effect.

Herringbone grooved journal bearings can have full liquid film lubrication without a continuous external lubricant supply. An attempt has been made to determine the operating conditions at which no leakage occurs. In the many experiments performed with transparent housings the speed was raised until breakdown of the air-to-liquid interface in the bearing gap occurred, and hence leakage commenced. It appears that breakdown of the interface in a completely grooved bearing can be such that it leads to leakage either via the plain surface or via the grooved surface of the bearing. Some speculative theories concerning the breakdown of the interface are considered.

The load capacity and power loss of spiral groove bearings, lubricated with a Newtonian, incompressible liquid with a viscosity depending on temperature only, are determined by solving the continuity and momentum equations analytically and the energy equation for the grooves and ridges numerically. It is assumed that the total flow perpendicular to the relative velocity of the bearing parts is zero. This implies that the generated heat is discharged by conduction to the bearing parts only. The effect of the "thermal entrance region" is investigated.

Self-acting helical-grooved journal bearings, lubricated by an incompressible Newtonian liquid and operating under laminar conditions, have under favorable conditions a negligible leakage due to the inward pumping action of the grooves. During concentric running, the axial position of the gas liquid interface created in the grooved section of the bearing does not vary in circumferential direction (local effects due to a finite number of grooves are not taken into account). During eccentric running, however, the width of the liquid region, i.e., the interface varies in circumferential direction due to pressure differences in the lubricant film. For a complete herringbone journal bearing the interaction between the shape of the interface and the pressure distribution has been studied both theoretically and experimentally.