🚀 go-pugleaf

On 10/06/2012 11:14 AM, krw@att.bizzzzzzzzzzzz wrote:
> On Sat, 06 Oct 2012 07:06:22 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net>  wrote:
>
>> On 10/05/2012 07:47 PM, krw@att.bizzzzzzzzzzzz wrote:
>>> On Fri, 05 Oct 2012 19:00:56 -0400, Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net>   wrote:
>>>
>>>> George Herold wrote:
>>>>>
>>>>> On Oct 5, 2:51 pm, Jeff Liebermann<je...@cruzio.com>   wrote:
>>>>>> On Thu, 04 Oct 2012 10:03:21 -0400, Phil Hobbs
>>>>>>
>>>>>> <pcdhSpamMeSensel...@electrooptical.net>   wrote:
>>>>>>>> Yep.  As I understand it (possible wrong), AC filaments break in the
>>>>>>>> middle, mostly from vibration flexing.
>>>>>>
>>>>>>> I don't think so, because there's no mechanism for that, as I said.  The
>>>>>>> wire is fully annealed at all times, so there's no possibility of
>>>>>>> progressive fatigue failure.
>>>>>>
>>>>>> Oscillating filament light bulb:
>>>>>> <http://www.youtube.com/watch?v=t_DwwNVA-7Q>
>>>>>> Whether the earths magnetic field is strong enough to induce such
>>>>>> oscillations is questionable.
>>>>>>
>>>>>> While digging for the apparently mythical lifetime test data on
>>>>>> incandescent light bulbs, I've found numerous theories on why
>>>>>> filaments fail.
>>>>>
>>>>> Grin,  the internet as a 'fire hose' of information.  I went searching
>>>>> for something that contained "Philips tech. rev." and found a
>>>>> reference to the following article,
>>>>>
>>>>> H. Horster, E. Kauer and W. Lechner � The Burn-out Mechanism of
>>>>> Incandescent Lamps Philips Technical Review 32,155-164, 1971.
>>>>>
>>>>> It was referenced in "Illuminating Engineering - Page 32 - Google
>>>>> Books"
>>>>>
>>>>> But nothing about turn on failure... sigh.
>>>>>
>>>>> Here is a patent by some of the same guys at Philips... lots of stuff
>>>>> about the filament getting hottest in the middle.
>>>>>
>>>>> http://www.freepatentsonline.com/3868159.html
>>>>> (Actually a decently written patent.)
>>>>>
>>>>> George H.
>>>>>
>>>>> Tungsten evaporation, causing hot spots, is the most
>>>>>> common.  One suggested that thermal cycling hardens the tungsten and
>>>>>> makes it brittle.  Another suggested that the inrush current causes a
>>>>>> mechanical shock if it hits at the 60Hz peak, instead of at the zero
>>>>>> crossing.  Yet another speculates that the temperature differential
>>>>>> between the hot filament, and the relatively cold mounting structure
>>>>>> may cause cracking.
>>>>>>
>>>>
>>>> I can believe that the filament is hottest in the middle.  It's
>>>> furtherst from the support, so whatever conductive heat sinking there is
>>>> will be less, but more than that, it sees the radiative input from the
>>>> rest of the filament on both sides instead of just one.
>>>
>>> Aren't the filaments welded to the elements at the ends?  It would seem that
>>> this would cause a narrowing.  ISTR most filaments broken near the supports,
>>> which would be counter to the hotter-in-the-middle theory.
>>
>> The feedthroughs are made of Dumet, which is basically 42Ni stainless
>> with a borated copper coating to bind to the glass.  It's much
>> lower-melting than the tungsten, so spot-welding them together shouldn't
>> affect the tungsten much.
>
> Welding5 is welding.  Metal has to flow, no?

Sure, but not the tungsten, just the steel.  The melting point 
difference is more than that between copper and solder, so it's more 
like brazing than normal welding.

>>
>> A necked-down hot spot is a stress concentration point, and ones nearer
>> the support would have more mass hanging off them.  When the filament
>> jumps at turn-on, hot spots at the ends will probably more torque applied.
>>
>>> My theory is that bulbs tend to fail when turned on because of the thermal
>>> shock but only because they were about to fail anyway.  Cycling, itself,
>>> doesn't have a huge effect on longevity, certainly not a factor of two.
>>>
>>>> Sort of similar to the case of a long solenoid, whose B field at the
>>>> ends is half what it is in the middle.
>>>
>>> Do they only burn out when energized?  ;-)
>>
>> I've never seen one burn out that wasn't energized.
>
> OK, perhaps I sh6ould have said *as* they-re energized (to keep th6e corollary
> with light bulbs burning out when turned on).
>
>> But you're the big-iron transmitter guy.
>                           ^^^^^^^^^^^
>
> Huh? I think you have me confused with someone else.
>
>> Gotta run, I have a bunch of guys coming to
>> the lab in a few minutes, and I have to start the coffee pot!
>
> Most important.  Get the good stuff.

Stew Leonard's Espresso Roast, roasted fresh daily in sunny Yonkers. 
Best beans I've ever come across, and worth the trip.  Always a crowd 
pleaser.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net