Plastic Thread Failure

[ThreadDesign]

Hello Everyone,
The plastic thread on my HDPE bottle attaches to an ABS plastic pump (for a soap dispenser).
The plastic thread cracked. Maybe because the pump was screwed on too tight and it caused a leak.

Is this a design failure or a material failure?
Is HDPE the wrong material? (It tore apart after prolonged stress creating a crack)
What is the function of the "flat-ring" on the bottom thread of most plastic water bottles?

Pics



Sincere thanks for any advice
Victor

 

[MacGyverS2000]

If I'm putting on a vehicle's rim and I break off the lugnut after torquing too hard, is that a design failure? No, it's an installation failure. A design failure would be making the lugnut too thin. In your case, a design failure would be making the neck too thin, leading to a user's ability to break off the threaded portion... not saying that's what happened here, but you need to understand the difference between the two.

HDPE is used for containers all of the time, so I see no issue with the material.

I do not know the purpose of the ring with any certainty, but I can guess (and structural isn't one of them). My first guess would be it provides a stop for connectors being threaded on... soda and water bottles used to have these, but I haven't seen one on a bottle in quite a while). My second guess would be a form of intentional flashing (gated part?), a place for extra plastic to flow during the creation of the thicker threads compared to the rest of the container. But now you're getting into an area I'm not as familiar with.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[hendersdc]

Where does the ABS part bottom out on your bottle? It should bottom out on the outermost face of the threaded portion of the bottle. If not, you could be tightening the pump so much that it is pulling the threads away from the body of the bottle, causing the cracking.

Is force applied to the assembled pump/bottle? If the pump is manually actuated someone could easily press on it hard enough to cause damage to the bottle.

The bottom ring on beverage bottles also seems to act as a retainer for the portion of the cap that breaks off after the bottle is first opened.

 

[ThreadDesign]

Hi Hendersdc,
[ul]
[li]I think your right about the female-threads ripping the male-threads away from the bottle.[/li]
[li]And I think you're also right that a water bottle's flat-ring functions to prevent the cap from being over tightened by the machine.[/li]
[li]BTW: The mated pump and bottle are housed into fixed positions to prevent damage when force is applied to the pump.[/li]
What is "bottoming-out"?
[li]Is it the point during tightening when an external physical resistance prevents further tightening? [/li]
[li]If yes, then it appears that at my bottle's bottom-out point... the flexing of the material allows further tightening beyond the bottom-out point which then leads to ripping the material[/li]


[/ul]

thanks for your insight, it's shown me more to consider.


Victor