Moving rocks between the quarry face and the crusher has always been an arduous job, with enormous trucks hauling the rocks about the place.
However, it was all too common for rocks to be moved in small pick-up trucks, or by cart which was obviously a very low-production way of doing things.
Early in the history of moving rocks, the market was cornered by US-based firm Mack. The company developed a new model – the AC – back in 1915, which could carry a payload of up to ten tonnes.
While this sort of payload is far removed from the 300 tonnes and more seen today, it was a vast improvement on the few hundredweight that other early trucks could manage.
As the First World War was raging, Mack secured a large order from the British army, where the coalscuttle-shaped bonnet prompted the nickname ‘bulldog’ as it gave the truck a sort of droopy-mouthed appearance. The name stuck and later the firm adopted the tough canine as its hood
mascot ornament.
Of course, construction projects got ever bigger, and while most companies were trying to survive the great depression, Mack tasked itself with building a truck suitable for the most enormous project in America at the time – the Hoover dam.
Known as the model AP, the newcomer retained the chain drive and rather vintage appearance of the original, the engine, chassis and rockbody had been enlarged and extended to give the truck a 25 tonne payload – more than two and a half times more than the original. As the truck was given solid wheels and special suspension for the loads, it became unsuitable for highway use, and so creating the first true off-highway truck.
Many people outside the PMV fraternity think that ‘off-highway’ means that these trucks have superior off-road capabilities. Of course, the opposite is true.
Quarry roads should be smoothly graded so as to keep the truck chassis from twisting when the truck is carrying a load. Also, tyres for these things are mind-bogglingly expensive, and anything to prevent excess wear should be considered.
The current largest off road haul trucks are the Liebherr T282B and the Caterpillar 797B which both have payloads of 400 short tons. Even though these trucks are similar in capacity the Caterpillar is referred to as a mechanical truck since it uses a big diesel engine(or sometimes two) and big transmissions to power the rear wheels.
The Liebherr is referred to as a diesel electric truck since it uses a diesel engine linked to an alternator that generates electricity which is converted to AC used to power two giant electric motors found on the rear wheel assemblies, similar to a locomotive. Besides Liebherr and Caterpillar, Hitachi, Terex, Komatsu and others also fabricate such off road haul trucks in different capacities. Rock on.