The task force have established the failure modes and tested ASTM pump- ability reference oils in full scale engines. They have concluded that their data on failure and border-line pumping temperatures could be the basis for evaluating the ability of labo- ratory bench tests to predict oil pum- pability at low temperatures. They are now in the final phase of the pro- gramme, evaluating bench tests.

High temperature

Progress in the high temperature, high shear regime has not been so dramatic. Problems such as the development of viscometric tests for use at, say, 150°C have still to be resolved. The task force, however, believes that it can meet its targets: it seems that we can expect SAE to produce "a truly mean- ingful engine oil viscosity classifica- tion" by 1980.

High speed miler bearings Roiling element bearings operating at high speeds in the elastohydrodynamic lubrication regime are prone to oil starvation. A recent development may overcome these problems by repleni- shing the oil fllrn via the bearing cage.

The life of rolling element bearings is critically dependent on the thickness of the elastohydrodynamic oil film separating the elements and the raceways. Interferometric studies have shown that, unless there is suffici- ent oil ahead of the contact region to provide a medium for pressure build up, oil starvation occurs, leading to a drastic reduction in oil f'drn thickness. Beatings operating at high speeds or carrying thrust loads are particularly prone to starvation. Increasing the oil supply does not solve the problem.

Three way protection Designed for in-line mounting ahead of sensitive hydraulic components, a recent addition to the range of filters available is claimed to provide protec- tion in three ways. It removes conta- minants, indicates when the element needs cleaning, and incorporates an automatic partial by-pass. The Model 25.P filter will handle flow rates up to 163 litres/min at pressures up to 400 bars. Wire cloth, cellulose paper, and 'Glas-Pak' composite ele- ments are available with filtration ratings down to 3/.tin. The large element area gives a low pressure drop, about 0.7 bar at rated flows across a clean element, allowing long operating periods between services.

An external indicator for dirt build-up on the element is mechanically linked to the by-pass valve. It responds to any increase in pressure differential across the element. The mechanical indicator can be supplemented by a microswitch, to give an electrical signal for remote warning. If the signal is ignored, the partial bypass operates automatically. This prevents the development of a

high pressure differential across a dirty External indication o f the state o f the element - a common cause of element

filter can be supplemented by a collapse, microswitch to provide an electrical

Tell-Tale Filters, Peel Street, signa:for remote warning Morley, Leeds, UK

One possible solution is to replenish the oil supply from reservoirs between the rollers and the bearing cage. The ends of the spacers can be hollowed out to leave a radius of curvature smaller than the radius of the rollers. The reservoir formed in this way can be fed with oil from a jet in the bearing housing, via axial passageways in the spacers and a supply port. As the cage rotates, the port is periodic- ally aligned with the supply nozzle, thus replenishing the oil reservoirs.

A provisional patent for this invention has been fried. The National Research and Development Corporation are seeking licensees to develop the inven- tion for commercial applications.

R.D. Clark, NRDC, Kingsgate House, 66-74 Victoria Street, London SWl, UK

Cam followers Cam mechanisms with multiple, rigidly connected, roller followers are used in textile, packaging, and many other types of machinery. Flexibility of the elements and machining tolerances result in the followers periodically loosing contact with the cam, leading to noise and scuffing.

The National Research and Develop- ment Corporation have filed a patent for a cam-follower assembly with a pivoted or sliding roller. The roller is biassed to keep it in contact with the cam throughout the operating cycle and mounted to act substantially as a rigid element in the loaded part of the cycle. The biassing may be pro- vided by conventional or torsional springs, weights, or hydraulic loading. If desired, the range of movement of the roller in operation may be limited. This type of assembly may be part of a multiple cam follower assembly - for example, a conjugate cam-follower. It is claimed that larger tolerances and amounts of wear can be accepted than with conventional arrangements and that impulsive loading, noise, and scuffing, are reduced or eliminated.

R.D. Clark, NRDC, Kingsgate House 66-74Victoria Street, London SW1, UK

80 TRIBOLOGY international April 1977