How is this molded PVC part made?

Hello All-
I wonder if anyone knows from experience how an object like this PVC hot water bottle is made?

It seems that the ‘neck’ is too narrow to pull a core out of a dip mold. Considering the opening on top it doesn’t seem extrusion blow-molded… Are these injection molded in two separate halves and welded toegether?..or…

Usually these kinds of things are formed in sheets and then RF welded around the edges like a blister pack.

That makes sense- thank you for the input Cyber.

Slush molded. Like rotomolding with liquid PVC that gels on the inside of a heated mold. Same as rubber duck or boots.

  • 1 – Slush Molded

The “stopper” detail might be kind of hard to get with a welding operation.
hot water bottle 1.jpg
another product (German)
hot water bottle 7.jpg
hot water bottle 2.jpg
But carefully check out this remarkable old image … it’s huge. But it’s still an enigma… If there is a mandrel on the inside how do they get it out, and what forms the end detail that the stopper fits into…? In the top photo, it looks like there is a black insert for the stopper that is inserted into the vulcanizing mold, but that still leaves us with how is the interior formed.

Photo identified as B.F. Goodrich, 1939.

The process might have changed over time. I don’t think Sean Penn does the nightshift there, anymore.


Knew that guy looked familiar… interesting old-school process shot though, don’t you think?

Oh wow that old-school process image is amazing! The resolution and quality of the photo when you click on it is great (got any more of those?!?)

You can clearly see the entire mandrel at the bottom of the image- with a few strips of rubber laid on it ready to go into the compression mold. I guess he pulls it off by hand.

Okey, in the light of this thread being featured on the main page just in time for the easter holidays I took a more serious approach and delayed my return to the family for one more hour of research. After some deep digging I’v learned, that the German manufacturer of hot water bottles “fashy” takes pride in having “revolutionised” the manufacturing process to the use of “thermoplastic” materials instead of rubber in 1968.

In fact the process today will be a form of blowmoulding, the best hints can be found in this french patent filing from 1978:

Today one can find some pictures of “hot water bottle mould” on Alibaba as expected:

This as far as I could get without actualy visiting a plant. Sorry mates, still no clue on the Sean Penn time travel,
which is a much more involving matter, altogether.

Happy Easter (Holidays), everyone !