AL6 Load Measuring Wheelset
|Following the introduction of
the Liner trains in the late 1960's, which consisted of bogie flat wagons carrying various
lengths of containers, several track-buckling
derailments occurred involving these vehicles1.
In the two cases referred to below at reference 1, the cause of the track buckling was the incorrect installation of the then new Continuous Welded Rail (CWR) combined with the excessive hunting of the Gloucester Ridemaster three-piece bogies of the vehicles, which imparted excessive lateral forces into the track. You could comb your hair in the reflection of the wheel treads of Freightliners, they were so highly polished through constant hunting.
This lead during the early 1970's to the DM&EE successfully experimenting with a Load Measuring Wheelset (LMW) under a Freightliner wagon (see here). The LMW was borrowed from the R&DD who further expanded this area of investigation with LMW's fitted to HSFV1 and later to Decapod.A complete knowledge of the forces that occur between wheels and rails is essential to an understanding of the dynamics of a railway vehicle. They are also of fundamental importance to the life of the track beneath. A load measuring wheel was developed which measured these forces very near to the point of generation. It was probably unique at the time in giving accurate and continuous signals of all three components of the contact force. An adequate calibration rig to measure outputs and all cross sensitivities was recognised as an essential item of equipment as was the processing equipment to rid the signals of impurities. These were both successfully commissioned by the R&DD. Wheels of this type hade previously been used successfully by BR for some 6 years on experiments including curve and turn-out negotiation, derailments at speeds up to 45 mile/h and stability investigations to 125mile/h.
Around the same period the AL6 locomotives, with their nose-suspended traction motors giving them a high unsprung mass, were knocking seven bells out of the WCML infrastructure and the locos were suffering from various problems themselves.
Often when cab riding on test trains one would witness the driver lifting his backside off the seat and bracing himself against the seat back when approaching white ballast patches. This was to cope with the tremendous vertical displacement when the loco traversed the patches. These were caused by the locos' constant hammering of the track, pulverising the ballast in places.
One aspect of the wider investigation into the performance of these locomotives was the manufacture and fitting of a LMW to an AL6 locomotive for a trial period. The specially designed and manufactured wheel set was very expensive as each spoked wheel was machined from a solid blank .
The author was a junior on the Testing Section at the time and was roped in to attach the myriad strain gauges to the wheels. Gauges were attached to measure vertical, lateral and longitudinal forces - so there were a lot of gauges on each wheel. Once completed the wheelset was wired up into Wheatstone bridges and painted to protect it from the elements.
AL6 locomotive No:E3164 similar to the locomotive fitted with the LMW
The AL6 LMW - note the painted ID numbers on the 12 spokes. From the state of the wheel it looks like it has some way to go before completion.
The problem of passing the electrical signals from the rotating wheel was solved by the application of slip rings on each end of the axle.
I remember that it was taken to the DB Testing Station at Minden, West Germany for calibration - but I didn't get the chance of a trip there! This went to the senior engineers.
The wheelset was trialled on the locomotive for a period on the WCML but was very problematical and the Project was eventually abandoned.
1 Track buckling derailments involving Freightliner trains occurred on CWR at Berkhamsted on 12th June 1968 and Auchencastle on 14th June 1968
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