I purchased two of these Irwin folding utility knives, they seemed like a clever design that addressed the failures of every other folding ‘Stanley blade’ knife I have owned.
Above is the Irwin knife, the blade is secured by a dog on the button shown at top, and the button is blocked from being depressed except when the knife is folded at 45° as shown.
How well does it work?
Well, in my short experience with two different knives, when cutting thick corrugate cartons with the knife fully unfolded (using original supplied IRWIN brand blade), the blade can be pulled out a few mm, jamming between the case halves, the button and the cam operated blocking push rod.
Above is a pic of the parts in the jammed position when the folding part is removed and one side of the blade case is removed.
The safest way to un-jam the blade is to simply loosen the four Philips head screws a couple of turns. That will allow removal of the blade. The screws can then be retightened, and a blade inserted.
This is quite an intricate mechanism, I suggest you not try to dismantle it if the above works for you.
Analysis
Dismantling the knife did you reveal any hint of wear or damage, so it is a design failure.
There was not a hint of lubricant in the knife I disassembled, and I am confident it would benefit from lubrication.
How do you prevent this?
Don’t use the knife, or use it only on light work.