Magnus,
[email protected] wrote on 01/20/2009 04:47:26 PM: > Joseph M Gwinn skrev: > > [email protected] wrote on 01/20/2009 04:32:15 PM: > > > >> Bruce Griffiths skrev: > >>> The relatively low thermal conductivity of the steel can will help > >>> considerably in avoiding thermal damage if the heat is > >> applied to the joint. > >>> If the can were copper it would be much more difficult to avoid > > thermal > >>> damage. > >> When I needed to have a McCoy oscillator can opened my > trusty good old > >> friend Sten did the usual trick of pre-heating the can and then when > >> applying heat to the solder the thermal difference is lower and hence > > the > >> heat-flow away from the joint. Didn't take much time and I think the > >> oscillator is 100% intact. > >> > >> Pre-heating and hot air are his main tools for tricky > soldering jobs. He > > > >> has low fatality rate on problems like that. This is why we > let him do > >> that kind of stuff at work. > > > > I imagine that Sten works *very* fast. I've found that when soldering > > thermally sensitive things like small coil bobbins made of > nylon that a > > high temperature and relatively large iron is best - the > terminals come up > > to temperature almost instantly, and it's all over before theheat can > > spread and melt the bobbin. > > > > Hot air has the advantage over a flame that overtemperature > is less likely > > with hot air. > > Actually, the pre-heating takes a bit of time... but then it doesn't > take much effort to push the solder over to melting and it took > relatively little time. The pre-heating doesn't go all the way up there, > so melting of plastics isn't really a problem. > > The pre-heating trick actually makes the big soldering iron rest most of > the time... > > We have boards with so much ground/power grids that it is really a > headache to do without pre-heating, which is similar to the iron case > soldering problem. > > So, doing it this way makes it go fast. I think we are talking about different things. For getting chips off a big multilayer board, preheat plus hot air is a standard way to go, but we are talking about how to unsolder a steel can with foam insulation within. Slow heating to near soldering temperature is likely to yield a heap of goo. The point of the torch method is to heat the can's solder seam up *fast*, so the solder melts before the foam. Joe _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
