Polyesters Outlast Steel Five Times
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IN a review of new materials available Ito transport undertakings, Mr. K. Blenkle, a director .of the Berlin undertaking and Mr. P. Reynaert, a director of the Transport Company of 'Brussels (Soc. des Transports Intercom.) quoted information from public transport operators to show that about 30 per cent. performed major vehicle overhauls after about 300,000 kilometres, (187,500 miles) representing a service period of four to five years. In approximately 45 per cent. of the cases, oil engines ran without a major overhaul for the same period.
Although oil engines had an. operating life of up to 400,000 km. (250,000 miles) pistons often had to be renewed between 150,000 and 200,009 km. (43,750-125,000 miles) which showed that the development of a durable piston had not reached an advanced stage.
To obviate corrosive deposits, in engine cooling systems, 10 per cent of the undertakings preferred to use brass Or copper materials. The formation .of lime, in the system could be avoided by treating the water with a poly-phosphate solution, but this could be corrosive if evaporation increased its concentration above the acceptable limit. Addition of an oil emulsion was unsatisfactory because the emulsion could become unstable. In the case of brass pipes an aluminium solution having arsenic and phosphor ingredients could be commended.
Increased Wearing Properties
Referring to brakes, the authors claimed that ring inserts of cast iron increased the wearing properties and reduced the operating noise of cast-steel drums, which were not otherwise very satisfactory for vehicles on urban services. Further improvements were necessary.
Integral body construction was employed by 20 per cent. of the undertakings. Light alloy construction would be preferred to other forms if arc-welding did not reduce joint strength. Riveting light-alloy structure was not satisfactory because overlapping limited the weightsaving advantage, and both maintenance and repairs were costly.
Monocoque. integral construction offered optimum weight saving, but the plates were liable to buckle. The sandwich method was preferred in which the outer skin of each component part formed the main support member. Spun glass could be employed in conjunction with Moltopren foam resin to provide adequate strength, heat insulation and the prevention of condensation, for doors. roofs, floors and the upper decks of vehieles. A great advantage of polyesterbased materials was that the life of the outer surface was at least rive times that of a painted steel panel, to which could be added the merits of light weight, freedom from corrosion and so on.
Dealing with seat upholstery, the authors claimed that press-assembled Durofol or moulded polyester sections offered the greatest weight saving and had advantages with regard to hygiene. Approximately 23 per cent. of the undertakings employed foam-rubber cushions, whilst 6 per cent.. preferred a. feather base.
In the case of light-alloy body construction a first coat of wash primer should be used, because it was not affected by spot welding. White lead could not be employed with aluminium because of corrosion. Paints with an artificial resin basis had been adopted by the majority of undertakings for the outer coat on account of its resilient properties.
As indicated by 31 per cent, of the replies the necessity to equip air springs with shock absorbers had created a preference for the hydro-pneumatic type. About 36 per cent. were in favour of retaining conventional springing because of its easy maintenance. It was probable that auxiliary rubber suspensions would be developed to meet the general need for constant-periodicity systems.
Protection of insulating materials Was shown by the authors to be a major problem in operating trolleybuses. They stated, however, that new vehicles with insulation other than the wood type could be safely garaged in the open.