SUR­VIV­ING MAG­NETISM

World of Watches (Singapore) - - Fea­tures -

Mag­netism is the bane of any me­chan­i­cal watch. A mag­netic field wreaks havoc on a move­ment’s ac­cu­racy by af­fect­ing the swing of the bal­ance wheel, and con­tin­ues to do so even af­ter it’s gone should the move­ment be­come mag­ne­tised. From ob­vi­ous sources like MRIS, to in­sid­i­ous ones like a hand­bag’s mag­netic clasp, this in­vis­i­ble force per­me­ates our daily life. Nat­u­rally, the per­fect sports chrono­graph must guard against it.

There are two ways to ren­der mag­netism moot. The first is to shield the move­ment us­ing a soft iron in­ner case, like what IWC does with some of its pi­lot’s watches. Such an in­ner case pro­tects the move­ment by redi­rect­ing the mag­netic field through it­self, while re­main­ing non-mag­ne­tised due to its soft iron con­struc­tion. The ad­van­tage of this method is its sim­plic­ity and low cost – craft­ing an in­ner case with this com­mon ma­te­rial is easy. In a suf­fi­ciently strong mag­netic field, how­ever, the soft iron in­ner case will be mag­net­i­cally sat­u­rated, and any “resid­ual” mag­netic field will still pass through it to af­fect the move­ment. In ad­di­tion, this prin­ci­ple re­quires a spe­cific de­sign – a sealed in­ner case that en­cases the move­ment – to work well. The dial and case back must thus have no cut outs lest the mag­netic field af­fects the move­ment through these holes.

The al­ter­na­tive to shield­ing a move­ment is mak­ing its reg­u­lat­ing or­gans am­ag­netic. The hair­spring, pal­let fork, and es­cape wheel can all be made in sil­i­con, which is non­mag­netic, thanks to im­proved pro­duc­tion tech­niques like DRIE (Deep Re­ac­tive Ion Etch­ing). As a sil­i­con hair­spring is al­ready cut specif­i­cally to pro­mote con­cen­tric breath­ing, the bal­ance as­sem­bly is free sprung and not reg­u­lated. This ne­ces­si­tates a vari­able in­er­tia bal­ance wheel with weighted screws on its rim for reg­u­la­tion, so the bal­ance wheel is not ren­dered in sil­i­con.

|| THE VER­DICT ||

In most en­vi­ron­ments, a soft iron in­ner cage is more than suf­fi­cient pro­tec­tion for a watch move­ment; the de­sign’s longevity at­tests to its ef­fec­tive­ness. Why stop there, though? Sil­i­con parts aren’t just im­per­vi­ous to mag­netism, but also re­quire lit­tle to no lu­bri­ca­tion while weigh­ing less than their tra­di­tional coun­ter­parts. The no holds barred op­tion will have to be sil­i­con.

The IWC Pi­lot’s Watch Chrono­graph has a soft iron in­ner cage

Left: Rolex’s Sy­loxi hair­spring Right: Sil­i­con pal­let and es­cape wheel vis­i­ble through the dial cut-out

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