Blow molded container with latching bellows.

[meganine]

I am working on the part design for a collapsible container that has a center section made up of bellows (similar to the picture below). The intention is that as the container is emptied out, the bellows could be latched one-by-one and the container would become shorter to permit easier access to the remaining product inside.

The current part design is based on about half a dozen different samples we've purchased and the small amount of reference material we've found (unfortunately, there isn't much out there). We built a prototype mold based on the part design to test, and unfortunately the bellows on the test parts are not staying latched (i.e. when released, the bellows bounce back to their full length).

The mold was built to accomodate both stretch blow molding and extrusion blow molding. We've used PET, LDPE, and PP, as well as different preform/parison weights of each material. In all of our produced samples, the bellows rebound like a spring.

We can either focus on the molding process or revise the design and modify the tool; and there is not a consensus in the group. Unfortunately, I would be guessing as to what the next step would be because I have very little reference material to fall back on.

Is there reference material available that could help me determine the next step? Does anyone know of a company out there that specializes in latching bellows?

 

[meganine]

Sorry, here's the correct link for the image.

 

[MikeHalloran]

I think the trick is that the bellows are molded with extra large flank angles and extra radial depth beyond normal design guidelines. ... which are themselves rather scarce.

Best advice I can give is to find a local blow molder and work with him. I haven't found any who are big on math, but they love to screw around with stuff.

I'll save you one experiment: One of my friends got the bright idea of molding a bellows as a helix, so it could be cut off at any length, screwed into an end fitting and bonded.
If you play with a compression spring long enough, or go to the trouble of bonding a film to its OD, you'll see why our continuous bellows didn't work as intended. Shear between the coils makes the spring, or the helical bellows, remarkably stiff in compression. Unbelievably stiff, actually, given the typical wall thickness and the material.


Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

A fair number of patents come up when googling various terms (I used "bistable bellows" to find a few more). There is usually some knowledge to be gained by researching these snippets of prior art.

 

[MatthewL]

Don't know if this is too late for you, but I have seen food and drink containers sold that are supposed to work like you described. I think it was on late night infomercials, so take it with a BIG grain of salt. Check out "as seen on TV" shops or websites for possible leads.

Matt

Quality, quantity, cost. Pick two.

 

[MikeHalloran]

I have some of those telescoping bowls.
They work pretty much as advertised.

... well, except for tending to collapse when you pour in warm stew unless you make a specific effort to support the rim. You'll probably only do it once.



Mike Halloran
Pembroke Pines, FL, USA