On sword breakedge,Maybe when you fight someone with a great rei power or when someone does a really powerfull attack against you like cero,resolve,and some other attacks.When it gets damaged it will be required for it to be taken to the squad 4 house to get it repaired by an npc or you can travel to the house you go to to get shinigami and talk to that npc who makes you one.Once they repair it and such,they will have to unequip there swords for a while and cant re-equip it to themselves until later(got this from when renji got defeated and had to let his sword heal).A zanpaktou is alive and is just real as anyoen else,so that means if there injured then they will have to heal some way just like any other person is hurt.If a zanpaktou is broken in its regular form then it will take a while.If it is broken in shikai form and its mastered then it will take less time.Same thing will happen with bankai if you have it mastered,doesnt bother me.

Zanpaktous can actually appear at any time i mean in Bounto arc Ichigo was stabbed by his own sword and he took it back also when he was fighting with Zaraki his soul slayer broke but again he got it back by talking ot his sword spirit, so there is no NPC that repair soul slayers.

Uh....whats that got to do with it gettin broke?

It means that if ur sword gets broken u can create a new one at any time.