What causes pivot bar to fail?

A handy person from Pittsburgh, PA says:

I emailed you around the beginning of the year for replacement pivot bars for my vinyl windows. My old bars had become bent and would not hold the windows open. (See link to our previous discussion thread)

You were able to provide me with the right replacement part, 26-403 and I was able to install them. About a month ago, I discovered that the new parts had bent just like the old ones.

What could be causing this? I can't believe they would fail so quickly (less than six months). Although the parts are cheap I don't want to buy new ones every four to six months.

Could there be something else wrong with my windows?
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Paul from SWISCO responded:
Hmmm... when you tilt the sash in, is the window fully closed? You have to open it a few inches before you tilt it in, or else it will damage the pivot bar. Could that be the problem? Also, how heavy is the sash? The window manufacturer design for this tilt bar was not made for a heavy sash.
A handy person from Pittsburgh, PA says:
I never tilted the sashes in after replacing the bars. Just opened and closed the windows, so I don't think that was it.

Not sure how heavy the windows are. I can try and get a bathroom scale. I do know they're about 32 x 29", vinyl, double pane windows. Not sure what that would be, 20 lbs, maybe?

I'm including a pic of the windows in question. It's the bottom windows that are the issue.

If this tilt bar is not strong enough for my windows, how would I go about finding one that is?
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Tom from SWISCO responded:
20 pounds actually isn't that heavy. I'm not sure why your pivot bars are being damaged. How are the balances? Are they functioning properly? Do they operate smoothly?
A handy person from Pittsburgh, PA says:
The spring balances seem to be okay, I guess. They are red tipped, which I understand is an indication of how much weight they can support. With the windows removed, I can pull down on the pivot shoe when attached to the balances, but it takes a fair amount of force.I wouldn't say the move super easy, but I don't detect any sticking points when moving them.
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Tom from SWISCO responded:
Those are the only reasons I can think of for why your pivot bars are being damaged. If everything is as you says it is, then there's no reason for them to be breaking as they are. I am sorry we can't offer more advice.
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