Recently we were talking with the manager of one of the larger copper concentrators in Arizona when he took off on the subject of overengineering and standardization and engineers who practiced the former but had no acquaintance with the latter. The particular reason for his wrath at that moment was $70,000 worth of conveyor head. tail, and other pulleys of every size, shape, and description that were cluttering up his warehouse and drawing much dust but earning no interest on the money he had spent lor them. He said he was forced to carry this enormous inventory because the engineer-constructor had designed everything to the last gnat’s eyebrow and he didn’t think there were more than two pulleys of the same size in the place.
If we assume an average cost of $30,000 per pulley in that warehouse, he would have seventy pulleys on hand and waiting to be used. Now. that seems to be a lot of pulleys, since equipment such as that isn’t supposed to fail with any degree of frequency, so we questioned his need to have them all on hand. Here he had us. He said that even the pulleys were overengineered to the point that there weren’t two dollars’ worth of spring in each of them and they seemed to collapse with regularity. When considering that an hour’s downtime on a large
grinding mill can cost many thousands of dollars, we can see why he had to keep his own spares instead of relying on the manufacturer s supply in some other, perhaps distant, city.
We wonder what it would really cost the owner to have only one common diameter for head. tail, and bend pulleys for each conveyor width in his plant. Would it pay to standardize only 24-inch-wide. 36- inch-wide. etc.. belts instead of buying these sizes plus in-between sizes also? Wouldn’t it pay to buy the next larger size bearing for a few bucks more instead of paying time and a half plus call-out pay (to say nothing of lost production) to get a mechanic out of bed at two o’clock in the morning to replace a bearing that wouldn’t take an overload?
We had the additional thought of standardizing about half the existing motor sizes we usually use but our double-E chief down the hall rather pointedly asked if we wanted our conveyors to be yanked out by the roots when they overloaded and the oversize motors wouldn’t overload and kick out. He went off mumbling something about high-voltage ore dressers.
Looking back on this now. we wonder if the problem wasn’t the owner’s fault by demanding that the capital cost be kept to a minimum. It could also
have been the owner’s fault by not having the mill and maintenance superintendents oversee the engineer during the design phase of the plant. Thise thought reminds me of a statement made many years ago by an old miller:
“There is hardly anything in the world that some man cannot make a little worse and sell a little cheaper, and the people who consider price only are this man’s lawful prey.”
The Circulating Load: Practical Mineral Processing Plant Design by an Old-Tie Ore Dresser