I have created some paintings which I wanted to preserve without framing them. Is there any way to do so? How to keep them as it is? And for how long we can keep them as it is?
As has been mentioned in comments, oil paint takes forever to cure and the process can't be hastened. If you need to store it without risk of damage, your only options are hanging, a shelf rack or fixed in a crate/box. As for how long they can be kept unframed, the answer is forever (or as long as the painting exists). Framing does not alter canvas tension or add to frame stability. The frame is an aesthetic addition that can serve as a buffer between the painting surface and large flat surface while stored. Most risks of damage still apply to a framed piece.