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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.

This paper aims to investigate the scuffing load‐carrying capacity of three gear oils: a standard mineral lubricant containing extreme pressure and anti‐wear additives (M0) and two biodegradable saturated esters containing low toxicity additives (E1 and E2).

Four‐ball wear tests were performed, according to standard ASTM D4172. Results from the wear scar diameter and from ferrographic analysis of the test oil samples are presented and related to the lubricant properties. The physical, chemical and biodegradability properties of the lubricants are presented and compared.FZG gear scuffing tests were performed, according to standard DIN 51535, in order to evaluate the scuffing load‐carrying capacity of the two oils. Two reference tests were performed, A20/16.6/90 and A10/16.6/90.

Test results include scuffing load stage, maximum oil bath temperature, pinion weight loss and surface roughness measurement of the teeth flanks.

The paper provides information on the scuffing load‐carrying capacity of three gear oils.

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.

IN 1927 PACKARD introduced for the first time a hypoid rear axle in their private cars in order to keep the universal shaft tunnel in the passenger space as small as possible. Since then hypoid rear axles have been fitted to a very large extent in private cars of conventional construction (engine in front and rear wheel drive).

In order to ensure effective lubrication of industrial gears, it is first desirable to have a basic knowledge of the tribological implications in their design, ie, to study conditions which can arise when the interacting surfaces are in relative motion.

This paper's aim is to present the gear micropitting performance of two industrial gear oils: a standard mineral lubricant (CM) containing a special micropitting additive package and a biodegradable ester with low toxicity additivation.

Gear micropitting tests were performed on the FZG machine, using type C gears made of case carburized steel. Lubricant samples were collected during the tests for analyzing the wear particles generated during operation. Post‐test analysis included the visual inspection of the teeth flanks and the assessment of the micropitting area, the mass loss of the gear, the ferrometric analysis of the lubricant samples and the surface roughness measurement of the teeth flanks, below and above the pitch line.

The micropitting performance of the two lubricants was very similar, confirming the advantage of using the ester lubricant (CE) as an industrial gear oil, now that it is an environmentally friendly product.

The tests were only performed on carburizing steel and refer to the tested lubricants.

The study confirms the appropriateness of biodegradable ester oil to industrial gear applications, allowing the replacement of environmentally harmful gear lubricants. It shows that the micropitting protection conferred is similar to that exhibited by highly additivated CMs.

The paper shows the applicability of biodegradable CEs to gear lubrication, mainly where it concerns micropitting protection, and shows its potential advantages, together with the biodegradability.

AT THE INTERNATIONAL CONFERENCE ON GEARING arranged by the Institution of Mechanical Engineers in London from the 23rd to 25th September, a special session was set aside for the Discussion of Lubrication and the following papers were presented :—

GEAR oil testing is an enterprise involving large numbers of people and equipment and costing millions of dollars per year. It is used as a guide in the development of new gear lubricants (or even new machines) and also serves broad quality control purposes. Since the gear oil business is a multimillion dollar area and since it is serving a multibillion dollar automotive and industrial investment around the world, spending for gear oil testing can be well worth the costs. However, as in every other aspect of business, cost reduction in gear oil testing is becoming more and more a demand of the times. It is therefore important to take a critical look at the expenses incurred in this area, and decide if some of the tests can be eliminated without detrimental effects.

SINCE THE INTRODUCTION of the hypoid gear as the right‐angled drive in automotive rear axles there has been a constant demand for specialised lubricants, particularly for running‐in purposes. Requirements are gradually and constantly becoming more severe and standards of performance adequate 5 or 10 years ago may be marginal today and unacceptable in the future.

This paper reviews the performance features of a new generation of industrial gear oils, developed for both mineral and synthetic base oils. These new products were designed to provide the highest levels of protection against the relatively new wear mechanism called micropitting. However, great stress was placed on providing these new products with balanced performance capabilities, so that they will perform with high reliability in the wide variety of conditions to which modern industrial gear oils are exposed. Performance areas such as filterability, foam control, corrosion protection, water separation, oxidation control and bearing protection were of particular concern. This paper compares the overall performance of these new technologies with conventional commercial products and it describes the extensive rig and field‐testing used to confirm their performance. It also reviews the phenomenon of gear micropitting and optimum methods for its assessment.