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Frameless bulker of 1700 cu ft
Page 60
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• A special welded-aluminium frameless semi-trailer tanker has been produced by Metalair Ltd, Fishponds Road, Wokingham, Berks, which is the first of 10 identical bulk vehicles produced for Pickfords to carry carbon black. It is designed to carry 1700 cu ft of the material, discharge being by gravity from three low-level hoppers.
Carbon black has a density of 17/21 lb /cu ft, which may be contrasted with foundry sand having a density of 90/100 lb /cu ft. The shell of the Metalair tanker is pear-shaped and has an overall height of 13ft 5-i-in., the diameter of the main section of the shell being '8ft 2in. The size of the container is in its favour with regard to
resistance to bending and torsion, a high resistance being provided by 3 gauge aluminium sheet without the use of internal bracing members. Construction of the shell is similar to that of the company's grainbulker which can carry 1000 cu ft and Metalair says that this size of container is the smallest that could be produced without additional stiffening or the use of heavy gauge sheet. The shell of the first Pickfords vehicle is welded horizontally as well as vertically but the tanks of later vehicles will have shells formed with a single sheet of aluminium.
The main problem in the construction of the 1700 cu ft shell was to provide bending and torsional rigidity at the front end and this has been overcome by employing cruciform bracing in conjunction with a box-section cross bearer to transmit the stresses produced by the fifth wheel to the tanker shell.
The frameless structure is based on Taskers Illubery Owen tandem-axle running gear and the semi-trailer is hauled by a Guy Big J tractive unit equipped with a Gardner 6LXB diesel. Tare weight of the semi-trailer is 5 tons lcwt (the weight of the shell is 2+ tons) and the unladen weight of the outfit is 10 tons 12cwt. While the rated gvw is 32 tons, which legally permits a payload of 21 tons 8cwt to be carried, the service payload is 15/17 tons, depending on the grade of carbon black. Three-line air braking and Goodyear Hi-Miler Super Single tyres are used.
Controlled discharge is essential because the powder is fed (by nylon socks) to an underground conveyor and it is necessary to match output to the capacity of the conveyor.