On Fri, 21 Dec 2012 08:52:44 +0000, Danny D. wrote:

I don't understand.
http://www2.picturepush.com/photo/a/...g/11697515.jpg

I guess you're saying that the old spring was exposed to the elements
while it was in the wound state - and yet - the backside of the spring
isn't exposed to the elements so the backside is noticeably less rusted.

I wrote to Richard Kinch and to Dan Musick at DDM Garage doors, to
ask them about this weathered line in my broken torsion spring:
http://www2.picturepush.com/photo/a/...g/11697515.jpg

Both engineers kindly responded with great information that explains
this anomaly and, interestingly, which provides a useful homeowner
'trick' to know when your springs might be slipping over time!

First, Dan at DDM Garage Doors explained that many springs have this
reverse wound spiral because dust collects at the TOP of the spring.

As G. Morgan astutely surmised, this linear collection of dust on a
wound spring, over time, causes differential weathering, which shows
up as a straight line on a wound spring.

When that wound spring breaks, the weathering shows up as a reverse spiral
on the unwound spring.

Interestingly, Richard Kinch provided ways to make use of this featu
1. We can PAINT a line on a wound spring to judge slippage over time
2. We can LOOK at an unwound spring and count the number of turns
3. We can LOOK at an unwound spring and determine the chirality

Of course, there are OTHER ways to note slippage, turns, and chirality,
but this feature can be used as a doublecheck!

Indeed, there are still lessons to be learned even AFTER installing
a typical garage door torsion spring!