The lifeblood of a drill-mak­ing fac­tory

The Shed - - Twist drills -

The grind­ing of HSS to make drill bits pro­duces metal swarf, grind­ing-wheel par­ti­cles, and heat. The drill blank is flooded with Houghton flute-grind­ing oil to re­duce fric­tion; re­duce wear on the grind­ing wheels; carry away both heat and, sus­pended in the oil, the metal and alu­mina par­ti­cles formed by the grind­ing process.

“You can’t grind with­out oil,” is one of Rick Smith’s say­ings. This means that the Ka­iapoi fac­tory is plumbed through­out for oil, just like the cir­cu­la­tory sys­tem of some gi­gan­tic beast. One set of pipes, like an an­i­mal’s ar­ter­ies, car­ries cool, fil­tered oil to the ma­chines. These dan­gle from the fac­tory’s ceil­ing like out­sized plas­tic um­bil­i­cal cords. An­other set of pipes, vein like, car­ries hot, de­bris-laden oil away to the pumps — the heart of the sys­tem. There are two sep­a­rate net­works, with each hav­ing a set of fil­ters, heat ex­chang­ers, and pumps. One sys­tem cir­cu­lates 30,000 litres, the other 20,000 litres. The heat ex­chang­ers trans­fer the heat in the hot oil to the air, re­duc­ing the oil’s tem­per­a­ture from about 100°C to 40°C. Cooler oil is more vis­cous so it evap­o­rates less, col­lects heat from the work­piece bet­ter, and smokes less.

The par­ti­cles fil­tered out of the oil are valu­able be­cause they are rich sources of scarce met­als such as tung­sten, chromium, and cobalt. The fil­tered metal and grind­ing-wheel par­ti­cles are packed into drums and ex­ported to Asia to be re­pro­cessed. The grind­ing oil is suf­fi­ciently ex­pen­sive to make it worth­while to re­move as much as pos­si­ble from the fil­tered grind­ings by press­ing. The high-tech and pow­er­ful presses used to do this are made in the Ka­iapoi fac­tory. So far they have made six.

Mag­netite-coated HSS (top) and re­duced-shank HSS (bot­tom) twist drills

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