Looking for Ferrous Inclusions in Copper Wire
One of the first real research projects I ever did, was to look for small ferrous inclusions in copper wire. This was during a vacation job from Liverpool University at Enfield Rolling Mills. It was I think the third summer I spent there and it was all good training for the future.
My problem was to look for small pieces of iron in thin copper wire, that was being drawn smaller to make electrical cable. Even the smallest piece of iron of the order of ten micrograms can do bad damage to the dies that shape the copper. To complicate matters the wire was travelling at something like 3,000 feet per minute, although I can’t remember exactly what the speed was.
I remember building a frame from Dexion, with pulleys at three corners, so that a cotton sash cord could be passed round these and an electric motor at the fourth. The cord was used as I could slip straightened lengths of wire into it to simulate the wire. I can also remember drilling the wire down its length to insert very small pieces of iron in the middle. The whole was sealed with copper wire, as I wanted to make sure that the only magnetic material was the speck of iron.
The person who’d tried the problem before had used a detector based on permanent magnets with a coil in the middle. It didn’t work too well, as you got a pulse when the wire entered and left, with only a small blip from the iron.
I used a longer detector based on an electromagnetic coil, with the detecting coil in the middle. The idea was that any eddy currents created by the start of the wire would die down before the detecting coil. I’m not sure if I got the maths right, but it did work and I got a nice one cycle wave on the Cossorscope, with two smaller ones when the wire entered and left. Note that in those days of 1966, you had to develop miles and miles of paper film to get your results from the oscilloscope. Although I should say that there were plenty of good Textronix ones at the University, but then it was so much better funded than industry.
It wasn’t perfect but it would have been good enough to say that a coil of wire didn’t contain anything bigger than so many micrograms. I think in the end they solved the problem, by better hygiene in the wire drawing, so that there was no need to apply a qualitative test.
But I was rather proud of what I had done as a nineteen year old and have always felt that the technique has other applications.
The Anonymous Widower 
My father was a metallurgist at BICC and ICI in the early part of his career – I had a few lessons in welding. I still have some old BICC cable somewhere.
Comment by Marc | June 13, 2011 |
Be careful it doesn’t get nicked. I was coming down from Edinburgh on the train to Kings Cross on Saturday and that line has suffered badly from thefts. They even take the overhead 25,000 volt cable. As soon as thery put new stuff up, it gets nicked again. Cable theft has always been a problem on that line. I did so,e work for BR about twenty years ago and after they put in fibre-optic signal cables, that used to get repeatedly cut by the thieves in the vain hope they’d replace it with nickable copper.
Comment by AnonW | June 13, 2011 |
[…] that he might have been the Howard after whom the local telephone exchange in Enfield was named. Enfield Rolling Mills, who were my father’s biggest customer and where I worked for a couple of summers, had a […]
Pingback by Memories of Wood Green « The Anonymous Widower | August 21, 2011 |