Re: Disk drive "seals"

I've often wondered that, too. Anyone know?

Disk reading/writing heads fly very close to the rotating surface being written. Atmospheric dust is bigger than the gap,and could wreck the process.

Hard disks are assembled in clean rooms, so the internal space starts off dust-free. Atmospheric pressure inside the unit has to match outside air-pressure, but the two spaces are connected by a slightly porous air-filter that lets gas in and out, but no dust.

You could build a hermitically sealed disk drive, but you'd have to make the structure stronger if you did that, and it would cost more. And gas molecules would diffuse in and out anyway.

I would guess it depends on what the container is made from. Glass seems to be highly effective in preventing any diffusion if thermionic valves ('tubes') are anything to go by.

The filament does act a "getter", and most tubes included an explicitly introduced getter.

The filiament does not act as the getter in vacuum tubes. It is the plate that acts as the getter. In most tubes that use the plate it must be heated to red hot.

The heater in the Wike artical is a heater in the vacuum pump system, totally different than the vavuum tube.

The filament runs hot enough to evaporate a few atoms. When they condense on cooler surfaces inside the tube they do provide some getting action.

Heat is heat wherever it is generated. Classic getters generate a lot of condensation close to the getter itself, and trap an appreciable amount of residual gas when they are activated. Getter action to deal with the slow diffusion through the envelope can be slower, but it is the same mechanism.

The basic rules of drive repair are only open in a clean room, and thus the seals are to indicate actions that would actually void the warranty. Unlike the warranty stickers seen on appliances that are just there to scare off the curious. if you're in a clean room disassembling a hard drive the cost of the voided warranty is lost in the noise of all the other costs.

Certainly the first, I can't think of anything inside a drive that would be a danger to someone competent enough to open it, unless they going to eat the magnets or something dumb like that.

The value is avoiding unneccesary warranty returns.