Bevel gears Designed to assist both manufacturers and users of bevel gears in general engineering, BS 545 Bevel gears (machine cut) has recently been revised by BSI (British Standards Institution). This standard provides guidance on the design of bevel gears for the transmission of normal loads and is intended primarily for the general purpose user who does not possess specialist gear design resources and concerns only machine-cut conical gears connecting intersecting shafts which are mutually perpendicular.

The standard specifies tooth form, accuracy requirements and methods of determining load capacity under differ- ing operating conditions for metric module bevel gears of 20 ° pressure angle. It includes material stress data, worked examples of loacling calcula- tions and a list of instructions to be given to a supplier or manufacturer when gears are ordered. The revised edition incorporates the requirements of recent international standards for bevel gears and the list of ordering instructions has been added in view of the need for clear and precise informa- tion to be given.

Copies of BS 545 may be obtained from the BSI Sales Department, 101 Pentonville Road, London, UK, N1 9ND, price £18.00

Hydraulic oils Texaco have introduced a range of hydraulic oils which, it is claimed, can be used in all hydraulic systems, offers extended oil and equipment life and can be used under severe pressure and temperature ranges.

One of the greatly improved features of these Rando oils is their anti-wear property, achieved by the use of a zinc additive which minimizes wear in all types of hydraulic pump.

Rando oils have a universal application making them most suitable when there are varying types of pump operating within a system. They have excellent compatibility with steel, phosphor bronze and silver components over a wide range of temperatures.

Other improved features include: good resistance to oxidation and minimum tendency to hydrolise; improved filter-

ability, which increases the types of system in which oil can be used; and longer oil life due to improved thermal stability and hence greater resistance to sludging. The Rando range comprises eight oils, six in the HD series of varying viscosi- ties and two in the HDZ series which have been specially formulated to increase the oil viscosity index. The HDZ series has been designed so that equipment can be safely started at low temperatures, and can be used through- out a wide variation of ambient and system operating temperatures.

Texaco, 1 Knightsbridge Green, London, UK, SWlX 7QJ or Texaco Inc, 135 East 42nd Street, New York, NY 10017, USA

Gears in space Space satellites are becoming larger and more complex which means that the reliability and precision of the mechanisms within the satellite for controlling and moving the aerials, telescopes, solar panels etc must be continuously improved. In the past, for reasons of reliability and simpli- city, direct drives have been used between the drive motor and the moving component. With larger satellites, however, the drive motors necessary to produce the required torque are too heavy and the favoured solution is to use smaller motors and gearboxes with a resulting weight-saving.

A literature review has revealed surprisingly little information of direct relevance to designers about lubricants and materials which would ensure a 7 to 10 year lifetime in the high vacuum conditions of space. Experience gained from the use of conventional instrument gears running in air is of some value, because the requirements for low backlash, low torque and precision also apply to space applications. However, satellite gears must work reliably in vacuum and ultimately there is no substitute for testing the apparently most suitable gear materials and lubricants under actual space conditions. There is a particular need for information about the effects of load, speed and thermal cycling (due to the eclipsing of the satellite) on the wear and friction of the gears.

The European Space Tribology Laboratory (ESTL) within NCT is now acquiring this information. Two special rigs have been constructed for testing gears in high vacuum under a variety of loads, speeds and tem- peratures. The design is based on the universally accepted method of testing gears: a 'four-square' assembly. In this arrangement, the four gears are pre- loaded together using a spring to ~vind' them up. The assembly is then simply rotated by a motor without the need to transmit any torque to a final output shaft. The 'wind-up' load is adjusted to simulate the conditions in the satellite mechanism which is being investigated.

ESTL has been using these rigs to test gears for the past year. Weight- saving suggests the use of aluminium alloy gears and the ESTL tests have demonstrated that specially anodised aluminium alloy gears could meet the demands required on board the primary deployment mechanism of the Space Telescope solar array drive. The Space Telescope will shortly be launched on the American Space Shuttle. More recently, the test rigs have been used to look at material and lubricant combinations for gears on the latest generation of solar array drives. The conclusion is that conven- tional hardened steel gears will operate in vacuum if they are lubri- cated with a surface film of lead. The lead is applied by an ion-plating process developed and proven at ESTL and has been used successfully in the lubrication of ball bearings in space-craft. It is now interesting to find that the lead works well also for gears where some sliding motion is present. It is intended to look at the perfor- mance of other gear materials and lubricant systems (including lubrica- tion by low vapour pressure fluorinated grease). Tests on the performance of plastic gears and gears made in precipitation-hardening steels are in progress. The latter offer considerable advantages in gear manufacture in that hardening can be achieved with- out distortion and, therefore, loss of precision.

National Centre of Tribology, UKAEA, Risley, Warrington, UK, WA3 6AT

218 TRIBOLOGY international August 1982