You will find you visit Helheim multiple times during the adventure in God of War Ragnarok. One of the times you visit, you will find that you are held back by mechanical doors where you clearly have to freeze a gear but the gear is blocked by some metal bars, preventing you from being able to hit it with the frost of the leviathan axe.
You will have to make use of the hex arrows in order to be able to solve these puzzles. You are able to chain elemental explosions using these arrows. If you daisy chain them together, you will be able to get around the obstacles blocking you from being able to freeze the gears to stop the doors from falling back down.
How To Daisy Chain Sigil Explosions
The video guide above will show you how to get past each of the mechanical doors in Helheim. The process is the same for them all. Pull the wheel down to raise the door. Once it is in the raised position, you can daisy chain sigil explosions to freeze the gear. Here is how to do it.
When you shoot a hex arrow, it will create a pink dome around the impact area. This is the explosion zone. If you hit a sigil with the axe (or the blades) the explosion it creates will cover this area.
If you make it so two of these overlap, hitting one sigil will trigger the other to detonate. You can place three at one time so it is possible to chain three of these together at once to trigger an explosion.
If you shoot the same arrow twice, it will increase the radius so that you can chain the explosions when the sigils are even far away. This is key in getting past all of doors in Helheim that require you to freeze the gear.
Hitting Gear Behind Metal Bars In Helheim
All of the moving gears that you need to freeze are going to be hidden behind a metal mesh or some iron poles that will stop you from being able to hit the gear with the leviathan axe in order to freeze it. To get around this, you are going to need to use the hex runes like you can see in the video above or in the pictures and it will allow you to freeze the gears to stop the doors from falling back down and allow you to pass into the next area in Helheim.