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When the clearance oil film of hydrostatic bearing friction pair is in critical lubrication state, the phenomenon of zero flow of local lubricating oil will aggravate the oil film temperature rise, which needs to be solved.

In this paper, the critical lubrication parameter equation and the oil film temperature rise mathematical model are derived for the new type q1-205 double rectangular cavity hydrostatic bearing. Based on a combination of theoretical analysis, simulation and experimental verification, this paper analyzes the flow characteristics and temperature rise characteristics of the lubricating oil when the hydrostatic bearing is in a critical lubrication state under different operating conditions and finally obtains the critical lubrication state of the oil film.

This study found that the numerical simulations and the derived formulas agree with the results. When the oil film is in critical lubrication, the cross-section side flow of the oil side is almost zero. The heat cannot be taken away in time, resulting in the local temperature rise of the oil film, which causes serious heat accumulation.

It is concluded that the operating condition parameters corresponding to the critical lubrication state provide a theoretical basis for the selection of actual hydrostatic bearing operating conditions, which is of great scientific significance.

Presents theoretical results regarding the computational estimation of the critical rotational speed in smooth or of negligible roughness and waviness hydrodynamically lubricated journal bearings. Results were provided using a developed calculational simulation code adapted to modelling of hydrodynamic lubrication regime encountered in the operation of various conventional or unconventional configuration finite journal bearings (j‐b). It is concluded that empirical formulae of general character used to determine j‐b rotational speed critical domain may either considerably underestimate or overestimate operational magnitudes. This fact leads to the necessity of use of high values for rotational speed safety factors in order to assure liquid lubrication and to avoid j‐b contacts during operation. Relevant diagrams resulting from the present investigation show a direct estimation of critical j‐b operational magnitudes.

To develop a more realistic model for molecularly thin film hydrodynamic lubrication by incorporating the fluid inhomogeneity and discontinuity effects across the fluid film thickness in this lubrication.

The total mass flow of the fluid through the contact in a basic one‐dimensional molecularly thin film hydrodynamic lubrication is studied by incorporating the fluid inhomogeneity and discontinuity effects across the fluid film thickness, based on a simplified momentum transfer model between neighboring fluid molecules across the fluid film thickness. This flow is calculated according to the present approach and the theory of viscous flow between two contact surfaces. The total mass flow of the fluid through the contact in this lubrication is also calculated from conventional hydrodynamic lubrication theory, which was based on continuum fluid assumption in the whole lubricated contact. The ratio of this flow calculated from the present approach to that calculated from conventional hydrodynamic lubrication theory is here defined as the flow factor for a one‐dimensional molecularly thin film hydrodynamic lubrication due to the fluid inhomogeneity and discontinuity effects. Results of this flow factor are presented for wide operational parameters.

In the molecularly thin film hydrodynamic lubrication, when the fluid inhomogeneity and discontinuity across the fluid film thickness both are incorporated, the total fluid mass flow through the contact and thus the global fluid film thickness are increased. The combined effect of the fluid inhomogeneity and discontinuity across the fluid film thickness on the total fluid mass flow through the contact in this lubrication is determined by the operational parameter K=((∂p/∂xh²)/[6η_bulk(1−ξ)(u_a+u_b)]); when the operational parameter K is high, this effect is significant; when the operational parameter K is low, this effect is negligible. On the other hand, in this lubrication, when the combined effect of the fluid inhomogeneity and discontinuity across the fluid film thickness is incorporated, the shear stresses at the contact‐fluid interfaces are reduced and this reduction can be significant. This reduction may strongly depend on the value of the dimensionless discontinuity parameter Δ/D of the fluid across the fluid film thickness but weakly depend on the number n of the fluid molecules across the fluid film thickness.

An important and very useful research for the academic researcher and the engineer who are, respectively, engaged in the study and design of hydrodynamic lubrication on mechanical components especially of very low hydrodynamic lubrication film thickness. It is also important to the subsequent research of molecularly thin film hydrodynamic lubrication.

A new model of molecularly thin film hydrodynamic lubrication in one‐dimensional contacts is originally proposed and described by incorporating the fluid inhomogeneity and discontinuity effects across the fluid film thickness in this lubrication. This new model of molecularly thin film hydrodynamic lubrication is of importance to the theoretical study of molecularly thin film hydrodynamic lubrication.

Rolling bearing operation under mixed and boundary lubrication conditions may lead to heavy adhesive or abrasive wear, which may lead to wear-induced rolling bearing failure. The purpose of this paper is to investigate the wear protection capabilities of different grease compositions at varying temperatures. It is considered that the temperature influences the lubrication conditions, the behaviour of grease components, namely, bleed oil and thickener, as well as the tribofilm formation due to tribo-chemical interactions between additives and surfaces.

In this study, four different greases were produced on the basis of a mineral base oil by varying the thickener and the addition of ZDDP. Various grease-lubricated rolling bearing experiments were conducted in a wide temperature range from 0°C to 120°C. Subsequently, the wear pattern, tribofilm formation and grease structures were analysed. Thereby, the influence of the different grease thickeners and the performance of ZDDP as a common antiwear and extreme pressure additive was evaluated.

The results show a strong temperature-dependency and allow a classification of temperature ranges concerning wear protection. At low temperatures, all greases provide a very good wear protection without the evidence of additive-based tribofilm formation. In the experiments at elevated temperatures, ZDDP tribofilms were formed. The formation depends on the thickener type: in comparison to lithium thickener, polyurea thickener favours more protective tribofilms at the same temperature. The experimental results show that medium temperatures in the range of 40°C–60°C are critical concerning wear due to the insufficient tribolayer formation and limited load carrying capacity of the grease.

Temperature is a key operating parameter for grease lubrication in roller bearings. The experimental work enables consideration of different impact pathways of temperature by combining roller bearing tests and microanalysis.

WHEN METALS ARE SHEARED or “cut” a compressive force of high intensity is applied to the metal by the cutting tool. The metal crystals are subjected to this force and the resulting stresses cause certain crystals to slip or flow in various directions along planes of slippage, the direction of slip normally being along planes of greatest atom density.

The paper aims to focus on the individual contribution of water to the lubrication regimes in articular joints because understanding of these regimes is crucial not only for the treatment of diseases like osteoarthritis but also for the development of new implants to have a longer service cycle.

Cartilage specimen and the synovial fluid were both isolated from bovine knee joints that are enclosed by a synovial membrane under sterile conditions of a biosafety Level 2 (BSL2) cabinet. Subchondral bone was removed from the cartilage because it not only creates a stable base to place the specimen on the holder, but it also acts as a primary shock absorber protecting the overlaying cartilage under high-impact loads. A specimen holder specially designed for tests and was attached to the linear oscillation (SRV) test machine. The SRV test machine provides a reciprocating sliding motion between the cartilage samples that are submerged into the selected biological media. The entire system can be mounted on the BSL2 cabinet, sealed with the convoluted gaiter and transported to the SRV machine with a specifically designed handle for the entire system. The process ensures sterile conditions for tests on biological samples that are highly sensitive to the environmental conditions.

A remarkably low coefficient of friction value for distilled water constitutes more evidence to support the assumption of the impact of water in the friction behaviour of the cartilage-against-cartilage contact. As the fluid in articular cartilage (AC) effectively serves as a synovial fluid reserve and 70-80 per cent of its composition is distilled water, it can be stated that the tribotest system mimics the natural working conditions of an actual knee joint adequately.

Time and limited availability of the animal-driven samples led to a focus on certain parameters mentioned in the approach. A planned scan of parameter matrix, such as variation of load and speed, would allow deeper knowledge on the lubrication regimes.

Study of relevant tribological contact in human joints might give ideas on new designs for artificial joints.

Understanding of lubrication regimes is crucial not only for the treatment of diseases like osteoarthritis but also for the development of new implants to adapt motion of related joint.

Exclusion of water and application as the primary lubricant in the test system brings a new perspective to joint lubrication.

The purpose of this paper is to evaluate the cooling ability of minimum quantity lubrication (MQL) cutting fluid.

An experimental system is devised to find the heat transfer coefficient of MQL under simulated reaming conditions. Cooling rate of the specimen is measured with an infrared camera. The effect of air pressure and oil volume on cooling rate is tested. Metal cutting tests are performed to evaluate the effect of heat transfer coefficient on workpiece temperature.

Convective heat transfer coefficient for MQL increases with increasing air pressure. Oil volume has an indeterminate effect on the heat transfer coefficient; however, it is a dominant factor for controlling temperature during reaming.

The results of the study can provide guidance to optimize the temperature controlling ability of MQL for production.

There is limited information available in literature regarding the heat transfer coefficient of metal working fluids, particularly for MQL. In particular, experiments designed to investigate the effect of air pressure and oil volume on the heat transfer coefficient of the mist have not been previously documented. This information may be used to improve the overall cooling ability of MQL mist, thus increasing its effectiveness at controlling tool wear and maintaining part quality. The other major contribution of this work is to separate the role of the cooling and lubrication for controlling temperature while reaming aluminum. Prior to this study, there has been relatively little research performed for the reaming metal cutting operation, and still less for reaming with MQL. The nature of how metal working fluids control temperature is not fully understood, and this work provides insight as to whether cooling or lubrication plays the dominant role for reaming.

To solve the problem of oil film thinning when hydrostatic thrust bearings are overloaded or rotating at high speed, the dynamic pressure formed by tiny oil wedges is used to compensate, and the optimum height of oil wedges is determined by the compensation rate to improve the bearing capacity of hydrostatic thrust bearings.

This research method is aimed at the new type of double rectangular cavity static bearing with microbevel surface of q1-205. The wedge parameters of oil film were defined. The oil film lubrication performance of the bearing with the wedge parameters of 0, 0.02, 0.04, 0.06, 0.08 and 0.10 mm was simulated by the finite volume method, the comprehensive influence law of the wedge-shaped parameters on the vorticity and flow rate of the oil cavity pressure fluid was revealed. Finally, the oil cavity pressure changes of oil films with different wedge parameters under certain load and speed were tested by design experiments, and the theoretical analysis and simulation were verified.

This study found that the oil film wedge shape can well compensate the static pressure loss caused by the high-speed or heavy-duty operation of the bearing, but the dynamic pressure effect of the wedge shape does not always increase with the increase of the wedge height. The oil film exhibits superior lubrication performance in the range of 0.06–0.08 mm.

The original hydrostatic oil pad was designed as a microinclined plane, and the dynamic pressure caused by the microwedge of the oil pad was used to compensate the static pressure loss of the bearing. The lubrication performance of the oil film under the condition of varying viscosity was obtained by using the simulation method.

This paper proposes the lubrication characteristics of the worn slipper in the slipper–swashplate pair. The mathematical analysis of lubrication characteristics of slipper with the measured surface roughness distribution is introduced. Based on the results from the test rig, it carries out the result compassion in different operating conditions.

This paper introduces the measured surface roughness distribution of new and used slippers and generates the oil film thickness distribution with it. An average flow Reynolds equation of the pressure distribution is introduced too. The experimental results are carried out on a novel adjustable oil film thickness test rig.

The surface roughness of the worn slipper enlarges the reacting force and torque only if the oil film thickness is small. When the ratio of oil film thickness to the root mean square of surface roughness is much smaller than 3, the influence of it on torque is obvious.

Different surface roughness of worn slipper proposed in this paper has an influence on the lubrication characteristics. As the slipper is worn after a period of use, the changed lubrication characteristics should be considered in the slipper design.

IN this paper wear and tear is taken to mean not only wear of the liner but also of the piston ring assembly, and in the first part, published in the previous issue, the author wrote of a number of wear processes occurring separately or together. In Part II basic materials, stresses suffered by the engine in use and fuel combustion are considered.