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Six -wheeled truckmixers still the most popular model

25th May 1973, Page 97
25th May 1973
Page 97
Page 98
Page 99
Page 97, 25th May 1973 — Six -wheeled truckmixers still the most popular model
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Which of the following most accurately describes the problem?

by Gibb Grace

BETWEEN 1961 and 1971 the proportion of ready-mixed concrete of the total cement market increased from 13.3 to 39.6 per cent and this year the industry will produce more than 30,000,000 cubic metres of ready-mixed concrete.

To cope with this expansion the truckmixer has become a very specialized vehicle and output of chassis is of the order of 1000 per year.

From the very beginning the name Foden has been synonymous with truckmixers, and today a large number of such machines are built on Foden chassis. The role of the truckmixer, like the tipper, is an arduous one with frequent off-road work, and a high chassis specification is not only desirable but imperative to achieve economic life.

As in all forms of transport. vehicle average sizes have gradually increased to improve operating efficiency in an effort to offset rising costs. Until recently the most popular size of truckmixer was the 5 cu metre (6.5 cu.yd) capacity mixer mounted on a 22-ton-gvw six-wheeler chassis, but now there is an increasing tendency towards larger units mounted on 24-ton-gvw chassis. It is now possible to get 5.5 cu metre (7 cu yd) and even 6.0 cu metre (8 cu yd) units on this type of chassis.

Fodens developed these heavyweight six-wheelers well ahead of the first legally operational date and already have a lot of experience at 24 tons, but 22-ton models are still available for those who require them.

Fodens offer three basic six-wheel chassis, two at 22 tons gvw and one at 24 tons gvw. The main advantage of the 22-ton model is its very compact overall size the outer axle spread of the model using a 17-ton rear bogie is only 14ft and the turning circle between kerbs only 45ft, which is better than some 16-ton four-wheelers. With an 18.5-ton rear bogie the outer axle spread increases to 15f1 1-fin and turning circle to 50ft. The same 18.5-ton bogie is used on the 24-ton-gvw chassis and the outer axle spread becomes 16ft lin, the minimum allowable under the C and U regulations at this weight.

High-tensile steel The chassis side-members of all three models are the same, ie high-tensile steel channel sections of 12in x 4in x lin section. The members are of constant section along their length and internal close-fitting 1 liin x 3in x +in channel-section flitches are used to reinforce the basic members in the higher stressed areas. This method produces a lighter and more flexible chassis design than the alternative possibility of having heavier-section -channel section without flitches.

The 15ft 1-fin centre-axle-spread chassis at 22 tons gvw uses a 5.25-ton front axle and the other two models use a 6.5-ton design. Each model uses a four-spring suspension bogie which is favoured in this application by Foden engineers as this type spreads the axle loads over a good length of chassis rather than concentrating them as is the case with the two-spring type. Singleor double-drive bogies are available and inter-axle and cross-axle differentials are available as options.

Standard tyre equipment on the bogies is 9.00 x 20-14 ply duals whether rated at 17 or 18.5 tons but 16.50 x 19.50 wide single tyres are an option at 17.00 tons and 18.0 x 19.5 wide singles an option at 18.5 tons. These tyres and one-piece rims save 4 cwt over the standard wheels and tyres. In the same way 11.00 x 22.5 tyres can replace the standard 10.0 x 20 front tyres and save a further -f cwt.

The drive-line specification for the three basic six-wheeler models is the same. The standard engine is the Gardner 6LX which is rated at 150 bhp but the 6LXB engine which is rated at 180 bhp is available as an option. Under the new 6 bhp/ton power requirement law a 22-tonner needs a minimum of 122 bhp and a 24-tonner a minimum of 144 bhp so in the case of a mixer using its own auxiliary motor the 150 bhp Gardner 6LX engine is sufficient.

However, if the mixer is driven via a power take-off from the truck engine the power it consumes must be subtracted from the nominal horsepower. At 24 tons gvw the spare capacity is only 6 bhp, which would be insufficient to drive a 6 cu metre drum and so the optional 180 bhp Gardner 6LXB engine would be needed. In either case the clutch used is a Foden-built 17in single ceramic plate type and the gearbox is a Foden eight-speed overdrive design. This is a constant-mesh box and as a result Only very short gear lever travel is necessary; it is of the range-change type and thus very easrto use.

The well-known 12-speed Foden box has a very wide ratio spread but needed considerable driver experience to give the best results, and Foden responded by introducing a much simpler-to-use model 758. The gear ratios are 12.25, 7.25, 4.90, 3.29. 2.20, 1.49, 1.00 and 0.77 to one: reverse is 9.8 to 1.

This gearbox copes easily with the torque of the Gardner 6LX or 6LXB engines and the low first gear is extremely useful when laying concrete in a ribbon, as in the case of kerbstone foundations. The low gear allows the driver to creep at just the right speed that the concrete needs to be delivered without the need to slip the clutch.

Cab replaced The long-standing S39 cab is now replaced on all Foden models, including truckmixers, by the new S80 full-width grp cab. Criticism has been voiced in some quarters that the design is fine for road work but not so good for site work because of the low, square front panel but in fact the cab corners are well protected by a heavy bumper and in the event of damage the corner panels are easily replaceable.

The new cab, on the other hand, offers a high standard of driver comfort. The driving position is good, instrumentation is comprehensive and easy to read, and visibility throughthe split screen is undistorted.

Maintenance has been given much thought and daily checks can be made simply by raising the hinged radiator grille. The radiator hinges forward, simplifying the changing and checking of fanbelts. For more major engine servicing the cab can be tilted by means of a small hand-operated hydraulic pump, in just a few minutes. To a large extent the 24-ton six-wheeler is now able to do the work for which a 26-ton eight-wheeler was needed before the higher vehicle gross weights were introduced last summer, and as a result the 26-ton eight-wheeler has lost favour to the 30-tonner.

However, Fodcns offer a threemodel range of eight-wheelers, viz 26, 28. and 30 tons gvw. The 26-tonner has an 18ft 44in outer axle spread and will take a 6.5 cu metre mixer unit; the 28-ton design has a 19ft 41-in outer axle spread and will take a 7.0 cu metre unit: and the 30-ton design has a 20ft 8, in outer axle spread and is suitable for mixers up to 7.5 cu metres capacity. In all cases, front and rear bogie spread is 4ft 6in.

Chassis frame members on the eight-wheelers are increased to 12in x 4in x in to take account of the longer wheelbases, and channel flitching is used as on the six-wheeler s.

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