Sliders slipping on top opening PVC window

The side sliders drop, about 1/16" so the window doesn't readily close.
I've pushed the window back up and tightened as much as I can but a couple of openings later it drops.
I don't know what the screws actually screw into.
I've though about just making a "'prop" from the bottom of the frame to the bottom of the slider so the weight is taken by the "prop", or use a self tapper below the slider as a stop?
Any suggestions before I wreck the window?
These
https://www.handlesandhinges.co.uk/upvc-window-hinges/
Top hung window sliders are the sort of thing I've got. Should I get some "super screws" 19mm?
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AnthonyL

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On Friday, 30 June 2017 19:22:51 UTC+1, AnthonyL wrote:

The (self tapping?)fixing screws should go into metal inside the frame. If the threads have stripped, all you can do is go to the next screw size up.
Sometimes they only go into the plastic, in which case I would put some "gorilla" glue in the holes, tighten and let go off.
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Sounds like crap. My old windows are the narrow gap kind but at least the frame iss made of anodised ally and I've never had any issues with slippage. Brian
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Top posting response:
The screws for the linkage seem to go into solid PVC.
I think that the previous owner never cleaned or oiled the hinge mechanism which was pretty well seized when we arrived and needed a good dose of WD40. My guess is that repeated forceful opening and closing has loosened the fixing.
Still leaves me with the question of how best to fix it as the screws just about have nothing left to grip on. Glue as Harry as suggested?
On Sat, 1 Jul 2017 11:27:57 +0100, "Brian Gaff"

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On Sat, 01 Jul 2017 11:22:32 GMT, snipped-for-privacy@please.invalid (AnthonyL) wrote:

Bigger screws, as you implied in your OP? Star washers between frame and hinge assembly and under the screw head to give more grip?
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Chris

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On Sat, 01 Jul 2017 11:22:32 GMT, AnthonyL wrote:

I had this problem in a few places - replacing broken hinges (the plastic sliding bit with the 'brake' tended to split) and the uPVC thread would come out with the screw. I looked around and all the 'proper' screws seeme to be the same diameter so I just went to TS and got some self-tapping, stainless steel, ones of a bit bigger dia. with the head and length to suit. Several years on and they're stii OK.
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Peter.
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On Fri, 30 Jun 2017 18:22:48 GMT, snipped-for-privacy@please.invalid (AnthonyL) wrote:

Not sure what screws you're referring to. Are they the screws that hold the whole hinge assembly onto the window frame, or the little friction-adjusting screws in the plastic slider?
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Chris

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The screws that hold the whole hinge assembly.
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AnthonyL

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