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Every large factory contains a number of gear boxes and there may be several large reduction units with specially designed and somewhat complicated lubricating systems. Their correct maintenance is as important as any other piece of mechanism but frequently, because they are presumed to run trouble‐free for many years, they receive little attention. If correctly maintained, the life of gear units can exceed that of most other items of plant, but sometimes wear does take place before it should, and it is often very difficult to pin the cause down to hard facts. It is the purpose of these articles to help the Lubrication and Plant Engineer to diagnose gear failures that are caused, or helped, by imperfect lubrication. It is essential, first, to know something of the work that the lubricant must do, its properties and methods of application. The first article, therefore, deals here with duties and properties whilst the second will illustrate some typical methods of application. The third will deal with the recommendations for lubricants issued by various gear makers and the reader should then be in a position to assess the reasons for gear failures, several of which will be discussed and illustrated in the final section of this series.

A failure mode called “flank breakage” is increasingly observed in cylindrical and bevel gears. Up to now, there was no calculation method available to determine the load‐carrying capacity related to flank breakage in bevel gears. Therefore, a research project was initiated to investigate the described failure mode in bevel gears and to develop a calculation method to predict the risk of flank breakage of such gears. The purpose of this paper is to describe this project.

The presented research project contained: determination of the decisive influence parameters in experimental investigations with bevel gears; development of a model to explain flank breakage in bevel gears; and development of a calculation method and design rules to avoid flank breakage.

In systematic tests, the influenced parameters of flank breakage were investigated. Besides the load torque, especially the case depth and the core hardness turned out as decisive parameters. A higher sulfur concentration in the material does not seem to be critical. The analysis of damage patterns of test and practical gears showed that the initiating crack always started below the surface in the region of the transition from case to core. For unidirectional loading, the crack propagates to the active flank on the one side and to the tooth root on the other side. On the basis of these findings, a local and a simplified calculation method were developed to estimate the risk of flank breakage.

With the described calculation method, it is now possible to evaluate running gears according to their risk of flank breakage and design new gears with a sufficient safety factor to avoid this failure.

Previous articles in this series were as follows :— January, Duties and Properties of a Gear Lubricant ; February, Typical Methods of Applying Worm Gear Lubricants; March, Typical methods of applying Gear Lubricants to Spur, Helical, etc. Gears, including Force Feed Systems and Employing the Gear Lubricant as a Hydraulic Medium. We now give principal gear manufacturers' recommendations for lubricants and shall then discuss gear failures in later articles.

Besides other approaches, fuel savings in automotive applications and energy savings, in general, also require high‐efficiency gearboxes. Different approaches are shown regarding how to further improve gearbox efficiency. This paper aims to address these issues.

The paper takes the following approach: theoretical and experimental investigations of bearing arrangements and gear design as well as lubricant type and lubricant supply to the components lead to efficiency optimisation.

No‐load losses can be reduced, especially at low temperatures and part‐load conditions when using low‐viscosity oils with a high viscosity index and low oil immersion depth or low spray oil supply of the components. Bearing systems can be optimised when using more efficient systems than cross‐loading arrangements with high preload. Low‐loss gears can contribute substantially to load‐dependent power loss reduction in the gear mesh. Low‐friction oils are available for further reduction of gear and bearing mesh losses. All in all, a reduction of the gearbox losses in an average of 50 per cent is technically feasible.

Results from different projects of the authors and from the literature are combined to quantitatively evaluate the potential of power loss reduction in gearboxes.

This paper aims to provide an analytic technique for determining the convection heat transfer and temperature of oil jet lubricated spur gears.

A multiphase flow model is developed to calculate the convection heat transfer coefficients on different gear faces during different contact conditions. The frictional heat is calculated and a method to distribute between the two gears is developed. A finite element model is established to calculate the temperatures in both meshing and cooling processes.

The convection heat transfer coefficients on different surfaces are obtained successfully. Area-related formulae are developed to calculate the heat distribution coefficients. The gear temperature reaches a maximum at the beginning of meshing, then reduces and gets minimum at pitch point, after that it increases again. The gear temperature descends rapidly to steady temperature during the short time of jet cooling process. The tendency of computational results coincides well with the experimental results.

The research presented here could be used in the design phase of the jet lubricated spur gears. The precise temperature is obtained to assess the thermal capacity of gears, from which the gear parameters and oil supply conditions could be adjusted and designed.

The purpose of this article is to present a method for the analysis of the quality of the bevel gear at the development level.

A non-commercial aircraft bevel gear design support system was developed. The system utilises matrix and vector calculi to model the technological machining systems and to analyse the contact of the designed pair. Both the technological model and the design model offer the possibility of manipulating the calculated parameters. This enables independent selection of the pinion/gear engagement, making it possible to achieved the desired contact pattern (its shape, position and size) and/or minimise motion transmission deviation. This article presents an analysis of the meshing of the aircraft transmission designed in two variants.

The newly developed non-commercial transmission design support system offers the capability to freely adjust mesh quality indicators. The first step is to perform automated technological calculations for a specific geometry of gear members, on the basis of which gear and pinion flanks are developed. Then, numerical models of tooth flanks are configured in the designed pair, and tooth mesh quality is verified. Quality indicators are provided in the form of summary contact pattern and the motion graph. In the subsequent step, changes are made to basic geometry of pinion tooth flank. After satisfactory mesh indicators have been reached, the transmission is tested for assembly errors and additional corrections are made to the geometry of the pinion tooth surface, as required. The above methodology guarantees that the assumed quality indicators are achieved on the physically cut transmission.

Fast preparation of the technology with guaranteed high mesh quality is a significant factor in the competitiveness of an industrial plant which implements a new bevel gear in its manufacturing activities.

The visualisation of the results of the use of the application allows the user to easily interpret the analysed contact pattern and take appropriate decisions as to the necessity of making corrections.

OVER THE PAST FEW YEARS interest has grown in Britain and elsewhere in the use of extreme‐pressure (e.p.) lubricants (or more correctly perhaps, though less conveniently, load‐carrying additive lubricants) for marine main propulsion gearing, and many ships now go to sea with such lubricants in their main systems. Several technical papers on the development of such lubricants have been contributed recently, for example by Elliott and Edwards and Socolofsky and others, the main purpose of this paper is to indicate present and likely future marine main reduction‐gear requirements and to discuss how far these are met by the developments in extreme‐pressure lubricants.

The main role of the gears is to ensure smoothness and noiseless service, required power transmission, precision of processing, necessary degree of efficiency and so on. Lubrication is of significant importance to the protection of gears from tribological processes which cause failure of gears. The aim of this study is to investigate the influence of lubricating oils on the reliability of gears. The experimental investigation of the influence of some industrial oils on the tribological behaviour of gears of machine tools has been carried out at a metalworking factory. The paper presents the following: the classification of industrial oils for gears; the flow‐chart of the choice of the industrial oil for gears; the analysis of the symptoms and the causes of failure to gears; the reliability curves of gears in the function of tribological properties of lubricating oils under the operating conditions of investigation here presented. The reliability of gears was found to be affected by both the type of lubricating oil and the viscosity grade.

A BAC One‐Eleven aircraft departed Stansted for Gatwick on its first flight subsequent to a B2 Maintenance Check. On selection of landing gear up after take‐off, the red gear‐unsafe light remained on, indicating that the landing gear was not fully retracted. In addition, an abnormal vibration from the nose landing gear area was noted. The landing gear lever was lowered and the annunciator lights then indicated that both main gears had locked down, but that the nose gear had not, which latter was confirmed by the nose gear mechanical indicator. Standsted Air Traffic Control informed the crew, after a fly‐past with landing lights on, that the nose landing gear appeared to be down. The landing gear free‐fall lever was then operated and as there was no change in indications the lever was returned to its normal position in order to retract the main landing gear doors and prevent possible damage by runway contact should the nose landing gear collapse on landing. Checklists cautioned against returning the lever to normal in flight, but did not cater for the situation where free‐fall lever operation did not achieve full gear extension. It was noted that the Checklist caution was at odds with a placard adjacent to the free‐fall lever warning only that the ‘lever must not be reset until normal gear lever is selected down’ and thus implying that an in‐flight reset was acceptable.

Early magnetic-geared motors have a high transmission torque density. However, the torque due to the coil is low because the permanent magnets in the stator become a large magnetic resistance when the current is applied to the coil. The purpose of this paper is to propose magnetic-geared motors which have a high transmission torque density and torque due to the coil. In addition, the proposed magnetic-geared motors are compared with past magnetic-geared motors and the effectiveness is verified by using finite element analysis.

A new magnetic-geared motor which has permanent magnets in the stator slot are proposed. The torque due to the coil increases by removing permanent magnets at the tip of the stator of past magnetic-geared motors. The permanent magnets placed in the stator slots are all magnetized to the outward direction and then the stator teeth are all magnetized to the inward direction. The maximum transmission torque and torque constant are compared.

The proposed magnetic-geared motor has a slightly smaller maximum transmission torque than the early magnetic-geared motors. However, the maximum transmission torque of the proposed magnetic-geared motor is high enough for practical uses. The torque due to the coils is higher than the early magnetic-geared motors.

The proposed magnetic-geared motor has originalities in its structure, especially in the permanent magnets in the stator slots.