I would like to know the problem why my safety door, which as soon as released from the grip, swings open freely on its own, up to 180 degree.

Not sure what safety door is, but a door that doesn't stay in the position you leave it in, is usually not plumb. I have seen suggestions of removing a pin and putting a slight bend in it, to correct the problem but I have never tried that myself.

I have this problem to.