Hydraulic oils

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 differing operating conditions for metric module bevel gears of 20 ° pressure angle. It includes material stress data, worked examples of loacling calculations 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 information to be given.

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 viscosities 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 throughout 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 simplicity, direct drives have been used between the drive motor and the moving component. With larger Copies of BS 545 may be obtained satellites, however, the drive motors from the BSI Sales Department, 101 necessary to produce the required Pentonville Road, London, UK, N1 9ND, torque are too heavy and the price £18.00 favoured solution is to use smaller motors and gearboxes with a resulting Hydraulic oils weight-saving. Texaco have introduced a range of A literature review has revealed hydraulic oils which, it is claimed, can surprisingly little information of be used in all hydraulic systems, offers direct relevance to designers about extended oil and equipment life and lubricants and materials which can be used under severe pressure and would ensure a 7 to 10 year lifetime temperature ranges. in the high vacuum conditions of space. Experience gained from the use One of the greatly improved features of of conventional instrument gears these Rando oils is their anti-wear running in air is of some value, property, achieved by the use of a zinc because the requirements for low additive which minimizes wear in all backlash, low torque and precision types of hydraulic pump. also apply to space applications. Rando oils have a universal application However, satellite gears must work making them most suitable when there reliably in vacuum and ultimately are varying types of pump operating there is no substitute for testing the within a system. They have excellent apparently most suitable gear compatibility with steel, phosphor materials and lubricants under actual bronze and silver components over a space conditions. There is a particular wide range of temperatures. need for information about the effects Other improved features include: good of load, speed and thermal cycling resistance to oxidation and minimum (due to the eclipsing of the satellite) tendency to hydrolise; improved filteron the wear and friction of the gears.

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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 temperatures. The design is based on the universally accepted method of testing gears: a 'four-square' assembly. In this arrangement, the four gears are preloaded 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. Weightsaving 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 conventional hardened steel gears will operate in vacuum if they are lubricated 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 performance of other gear materials and lubricant systems (including lubrication 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 without distortion and, therefore, loss of precision. National Centre of Tribology, UKAEA, Risley, Warrington, UK, WA3 6AT