10
$\begingroup$

Sparks from electrical welding or from electrical grinding damage surfaces of glass or tiles while they do not damage the leather apron and even plastics. For example protecting glass in the old welding helmets has to be replaced frequently while the rest of the helmet, even plastic parts of it are not damaged at all. The recent helmets even do not have glass protection but use a plastic cover which does not show any damage after use.

There is probably something fundamentally different between materials which bounce back hot iron pieces (droplet) and which melt and hold hot droplets, which results in permanent damage. Crystal lattice, temperature of melting, chemical reaction, surface tension?

$\endgroup$
  • $\begingroup$ I suspect that a large part of this is due to the fact that for a piece of leather "damaged" means "has a hole in it" whereas for a glass visor it means "is too chipped to see through anymore", which will happen much sooner. $\endgroup$ – By Symmetry Nov 13 '17 at 16:24
  • 1
    $\begingroup$ Building on By Symmetry's comment, glass is much easier to damage by a short, rapid transfer of heat than either plastic or leather. If a droplet lands on glass, it dumps heat into a small spot on the glass, which expands; since the glass around this spot is relatively unheated, the hot spot flakes off due to shear stresses. Plastic doesn't shear off due to its flexibility and in leather only a few fibers burn away, so both materials remain intact under these conditions. $\endgroup$ – Asher Nov 13 '17 at 16:54
  • $\begingroup$ @Asher, that's an answer. $\endgroup$ – stafusa Nov 13 '17 at 18:21
  • $\begingroup$ Often the small glowing droplets don't just damage the glass, they even get stuck halfway in it, so apparently the glass melts very quickly. I'm amazed that this doesn't happen with plastics! $\endgroup$ – Zaaikort Nov 14 '17 at 10:43
  • $\begingroup$ Maybe it's worth mentioning that the damage occurs (mostly) when welding or grinding iron or steel, not other metals like copper or brass. $\endgroup$ – Zaaikort Nov 14 '17 at 11:03
2
$\begingroup$

Building on By Symmetry's comment:

I suspect that a large part of this is due to the fact that for a piece of leather "damaged" means "has a hole in it" whereas for a glass visor it means "is too chipped to see through anymore", which will happen much sooner.

Glass is much easier to damage by a short, rapid transfer of heat than either plastic or leather. If a droplet lands on glass, it dumps heat into a small spot on the glass, which expands; since the glass around this spot is relatively unheated, the hot spot flakes off due to shear stresses. Plastic doesn't shear off due to its flexibility and in leather only a few fibers burn away, so both materials remain intact under these conditions.

$\endgroup$
  • $\begingroup$ Might be worth copying the comment by By Symmetry (or at least paraphrasing it) in case it gets deleted in the future. $\endgroup$ – Kyle Kanos Nov 14 '17 at 0:26
  • $\begingroup$ @KyleKanos good point, I'll do that. $\endgroup$ – Asher Nov 14 '17 at 0:27
  • $\begingroup$ By Symmentry - the leather gloves does not seem to be damaged at all, ask welder. The glass is not broken, the metal particles melt into it directly. $\endgroup$ – Vladimir Smutny Nov 15 '17 at 8:17
  • $\begingroup$ @VladimirSmutny having some welding experience myself I can attest that leather welding gloves catch droplets in their coarse surface fibers and show burn marks. I've never worn a leather apron while welding but I imagine the smoother finish makes a difference in whether the droplets stick long enough to leave marks. $\endgroup$ – Asher Nov 15 '17 at 15:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.