An odd ball

Now in possession of a well-known brand of (wet/dry) battery-driven shaver, I was surprised to discover that embedded (pressed) into a recess of each cartridge of cleaner fluid is a single 2mm diameter steel ball.

The cartridges are injection moulded PP. Two mouldings, (a base and a top) are welded to form a closed tank. Moulded parts of the cleaner’s mechanism are POM.

I’m guessing that in production, the presence of the steel ball could signal that the cartridge is complete and ready for shipping; OR – that the razor cleaner mechanism has a means (electromagnetic?) of sensing that a cartridge has been inserted.

If the latter is the case, what puzzles me is that there are at least three ‘layers’ of moulded plastics between any sensor and the ball, a distance amounting to more than 8mm.

The ball has no detectable magnetism, but sticks to a magnet. In use, the cartridge, and therefore the ball remain perfectly still.

While this is just curiosity on my part, perhaps the upshot would interest model makers.

Any offers?

Sam

Edited to get rid of unexpected smiley face.

Edited By Sam Stones on 15/04/2021 04:59:41

It won’t be a reed switch if it is not magnetic - so we can discount that as the transducer.

Metal detector? Hall effect is basically a ‘magnetic disturbance?

Maybe a magnet in the shaver?

Ooh, perhaps there is a tiny radioactive gamma source, which is attenuated when a steel ball is interposed - that would be an electromagnetic wave.🙂 Could even be a radio wave?

Maybe a simple valve operated by a solenoid, to act as a metering system?

Possibly a little metal detector in there, somewhere?

Search the internet for a source of information on how they make it? Probably some little well-hidden patent listed?

Or just forget it and carry on with life?

Edited By not done it yet on 15/04/2021 06:37:10

maybe it's pressed into the hole to plug it once the cartridge is filled

+1 for Jason's suggestion - you see the same thing on disposable lighters.

Rob

Also used to block the outer ends of oil drillings in crankshafts etc.

Cheers, Tim

Also found similar use in older ink-jet cartridges to plug new hole when re-filling completed.
DaveD

I think Jason has the most plausible explanation.

Cleaner??? another marketing ploy invented in the 40 years since I wasted time on that activity.

Having convinced myself the ball had something to do with proximity detection, it didn’t enter my head that it could be a simple seal. Thanks for the idea Jason and others.

As for that hole being part of the filling process, I need to point out that …

1. The 2mm ball blocks a through-hole of about 1.5mm diameter,
2. The pump is lowered into the fluid cartridge down a hole about 29mm diameter,
3. The drain (or return) hole in the cartridge is about 13mm diameter,
4. The two holes are initially closed by a separate lid moulding heat staked in three places,
5. The stakes are deliberately friable allowing removal and disposal of the lid,
6. U/S or vibration welding was likely used for joining/sealing the base and top,
7. The shaver is not involved when installing the cleaner cartridge.

Assuming the steel ball is not for detection, the hole it blocks is rather small for filling. With larger holes 2, and 3, available for filling, the 1.5mm hole (into which the ball has been pressed), may be an air vent rather than a filling point.

Given that heat staking and welding were a part of assembly, I would assume the 1.5mm (vent?) hole could be closed by heat swaging.

The cleaning device has the ability to determine the presence or otherwise of (sufficient) fluid. Having now destroyed the cartridge and a new one lasting for at least three months, further investigation will have to wait.

Thank for your interest and comments,

Sam

PS - A cursory scan of the Internet failed to disclose the method of manufacture.

Edited By Sam Stones on 16/04/2021 03:27:43

A twist in the tail.

During a subsequent part of the postmortem, it suddenly dawned on me that the base and top of the fluid cartridge had been hot-plate welded and not as I suggested, ultrasonically or vibration welded.

It is a method used for joining and sealing the lid and container of automotive batteries ... (and many other things)

If that method of welding is not familiar and you'd like clarification, try **LINK**

Sam