Paper 7: Load Capacity, Stiffness and Flow Characteristics of a Hydrostatically Lubricated Six-Pocket Journal Bearing Supporting a Rotating Spindle

Abstract

This paper contains the results, plotted non-dimensionally, of extensive tests carried out on a 1–625-in diameter grinding machine spindle lubricated hydrostatically. The horizontal spindle is directly coupled to a variable-speed motor at one end and loaded vertically at the other. The spindle is not constrained to rotate at arbitrary eccentricity values, but is able to seek an equilibrium position depending upon oil flow and rotational speed. The attitude, oil film thickness, and eccentricity are measured by mutually, perpendicular capacitance probes arranged in the bearing housing. The results indicate considerably decreasing load-carrying capacity as the rotational speed increases, because the hydrodynamic effect tends to centralize the shaft in the bearing housing, thus nullifying the hydrostatic effect. Paradoxically the same effect causes an increase in oil film stiffness as it is generally defined. A summary of earlier work is included, notably that of Raimondi and Boyd who considered bearings of fixed eccentricity, and the paper also presents a theoretical analysis based on the pressure- and velocity-induced circumferential flow theories.

Characteristics of Externally Pressurized Journal Bearings with Membrane-Type Variable-Flow Restrictors as Compensating Elements

“…The loads exerted on the top and bottom of the membrane can be obtained by noting that they are equal to the load p ,~r r ,~ minus the load supported by two parallel cylindrical discs with a pressure of p, and pn on their inner and outer radii, respectively. This latter load is given by For the membrane to be in equilibrium, the load given by equation (25) must equal the product of the stiffness and displacement of the membrane, i.e., It is more convenient to express equation (33) in terms of a pressure ratio defined as the ratio of the recess pressure at zero eccentricity to the supply pressure, Le., (26) 2 loge! (r2/r1) Equation (26) can be written as…”

“…This latter load is given by For the membrane to be in equilibrium, the load given by equation (25) must equal the product of the stiffness and displacement of the membrane, i.e., It is more convenient to express equation (33) in terms of a pressure ratio defined as the ratio of the recess pressure at zero eccentricity to the supply pressure, Le., (26) 2 loge! (r2/r1) Equation (26) can be written as…”

Effects of Hydrostatic Pocket Shape on the FlowPattern and Pressure Distribution

“…In this context one can mention Shinkle and Hornung [1965], Leonard and Davies [1971], Ho and Chen [1979, 1980, 1984, Aoyama et al [1982], Chaomleffel and Nicholas [1986], Scharrer et al [199 a, b], Spica et al [1986]. A third group of investigators presented comparisons between their analytical/ numerical models and their own experiments for the thermofluid and dynamic behavior of the HJB [Heller, 1974, Betts and Roberts, 1969, Bou-Said and Chaomleffel 1988, Hunt and Ahmed, 1968. Finally, a fourth group of researchers have concentrated on the mechanics particular to the flow in cavities related to step bearings, spiral seal grooves and HJB.…”