Something has come up. It means that we must re-visit the post on the old and new diggers.
The trigger for this was the comparison drawn by The Lad between the old, 1935 Quarry Shovel and one modern machine that JCB, its maker, calls a Tracked Shovel. The Lad is not a student specifically of heavy earth movers so he made a couple of assumptions as he wrote the post. One assumption was that if a particular design was in a museum; it no longer, shall we say, appeared in the wild. The second assumption was that a large manufacturer of current modern earth movers will produce all the different types.
A little further browsing soon showed both to be in error. Caterpillar Inc is a very large, US based company specialising in Mining equipment. Its catalogue soon revealed to the surprised gaze of The Lad the error of assuming that the Museum machine had become extinct. There were some machines they now called Electric Rope Shovels. Here are some pictures that you can find along with much more data at https://mining.cat.com/cda/layout?m=435120 .
Look familiar? Apart from the trebling or even quadrupling in size [note the size of the control cabins in all three and the access stairway in the third machine], these modern machines are still of the same design or general architecture as The Abbey Pumping Station Museum Steam Navvy. The increase in size of these modern machines brings with it a major increase in strength. The machine in the first image above is the smallest of the range and the load capacity of the dipper is 20 tonnes whilst that in the third image is the largest and its payload is a mere 120 tons. The latter machine itself weighs in at well over 1000 tons.
The market for such machines across the globe is probably not large and so accounts for the second assumption of the previous post being in error as such an enthusiastically commercial company as JCB declines to make such machines. Engineers still have to operate and try to turn an honest profit in the global marketplace.
The engineering aspects of the replacement of steam with hydraulic rams for machines of the size of the Ruston Bucyrus Quarry Shovel of 1935 is, however, still absolutely true. But there is more to it than that. First of all we have to be clear that those two machines – old and new – were not designed for the same objectives.
It is surpassingly vital that, in whatever project the engineer is pursuing, she is very clear as to her objectives. It frequently needs a lot of effort to get them right. If they are not right then the project can fail altogether or at least be mired in confusion. If there is neither of those two outcomes, it may become too expensive for what it does. In this latter case a good piece of jargon is to be ‘not cost-effective’. This piece of jargon was introduced by Robert McNamara, once of CEO of the Ford Motor Co in the US, and later Secretary of Defence for President Kennedy. He attempted to bring a scientific approach to Defence procurement and thus had a considerable effect on President Eisenhower’s military-industrial complex, the US Defence industry] http://en.wikipedia.org/wiki/Robert_McNamara ,
However, The Lad is getting side-tracked again: let us return to the diggings.
The old machine reigned in quarries and opencast mines. It had as its objective the removal of large quantities of the ore which is the stuff that you want – pay dirt. Or, first, the overburden, which is the dirt or rock covering the ore.
The new Tracked Excavator has as its main design objectives a somewhat different type of task. It is to carry out landscaping [shall we say – engineering of the shape of an area of land] or carving out trenches. Its workplace is the brown or green-field of a building site; the route of a new road. That is not to say that it cannot turn its hand to removing ore or overburden it is just that it is not designed exclusively for this task.
The modern Electric Rope Shovel also has as its home the quarry and open-cast mine although many of these are now much larger than they used to be in the first half of the Twentieth Century. This, of course is the driver of the design of the modern Cat machines. Why do they not use hydraulic rams? There will be a limit to the operationally effective length of a hydraulic ram due to its method of manufacture. The Lad does not know for certain, but he suspects that it is limited by the size of grinding machines for the bores and rods of the ram. [Perhaps someone will comment and correct him if necessary.] If the machine design needs to exceed that limit, then other methods have to be used or, perhaps in this case, sticking with the old ones. The Lad believes that the geometry of the jibs and big machines required rams too long for effective manufacture and the pull of cables became a good principle to retain. With the use of cables, the original architecture was not easily bettered.
Then there is the ‘electric’ of the title Electric Rope Shovel. It is electric powered too. The prime mover is not mounted on board and lugged around. It is firmly ground based somewhere in the mine. It will be large, heavy – and efficient – power generator. Power is supplied to the Shovel by cable.
Beware as an engineer of assumptions. The Lad does not say that in the day-to-day engineering assumptions will never be made. Sometimes to allow the job to proceed, they have to be made. Just make sure that they are robust. Then, never let the assumptions drift on as correct; check their correctness properly as soon as possible.
Caterpillar Inc has just this year completed a takeover of another earthmoving machine firm. It was that firm, not Caterpillar Inc, which designed this giant Shovel. The name of that other firm was? Bucyrus. Does the name ring a bell? It is the US company that licensed the UK firm Ruston in the 1930’s to build the 52B Steam Quarry Shovel.
Engineering is one of the three drivers in the advancement of the human race. This blog aims to give to career seekers and also to the general public a taste of how this might be so. They are not well served by the current media. It is an engineer posting: not a ‘scientist’. It describes real professional engineering as it is in the real world usually in the present and occasionally as it was in the recent past.