Snap Closure Spec's 2

[Adrian2]

Dear Folks;

I have to specify a snap closure on a cylindrical device much like the snap on and off caps you see on bottles of shampoo and other pharmaceutical products. The snap closure would comprise of a raised ring which would snap into a corresponding circular depression on the mating part.

Where could I find spec's for the design of these closure's. Particularily with respect to required dimensions related to force required to pull them apart.

Is something freely available on the internet or at least inexpensive to purchase somewhere ?

Many thanks in advance for your consideration

Adrian Dunevein
aaadrafting.com

 

[CouplingKing]

I don't know of any specifications, but it may be worth buying a plastic tub/bottle and actually measuring it. At least it will give you an indication of what people do.

Alternatively you could try to contact the PPMA (process & packaging machinery association I think), they are a trade body that represent companies in the packaging industry and may be able to help. They must have a website, probably PPMA.com.

Hope this helps.

CK

 

[unclesyd]

Can't help with the dimensions but can give one word of advice. A lot of these closures are patented so be careful you don't inadvertently copy one. A local molding company got into a lot of grief over the use of patented design. In fact they closed up.

 

[plasgears]

Contact DuPont. They have a comprehensive plastic design manual that addresses snap closures. It's better to have analytical basis for design than making a guess.

 

[stel8]

Two books are probably the best in this field:

1. Tres Paul - Designing plastic parts for assembly, Hanser Publishing, ISBN 1569901996, 1995
2. Bonenberger Paul - The first snap-fit handdbook, Hanser Publishing, ISBN 1569902798, 2000

Both have examples and calculations for snap-fit closures. Try used books on amazon.com or ebay.com

I would be interested in DuPont manual; where can I get it?

 

[stel8]

google.com got this site:

http://www.engineersedge.com/snap_fit_straight.htm

It does not look like your application but it is a start.

 

[stel8]

this will make you very happy:

http://www.rpi.edu/dept/mane/deptweb/student/snapfit/index2.htm

 

[TheAnswerGuy]

Adrian2,

It is not so much the snap area that is going to cause trouble for you as the living hinge area will. My suggestion is that you go to the store and buy one of those small "M&M" candy containers (platic tube w/snap lid) and take some measurements. That type of closure will help to answer most all of your questions. You may be just as well off to buy an off-the-shelf closure from Sequist Closures. Seaquist is the company that does most of the closures for the shampoo bottles.

 

[Adrian2]

Dear Answer guy and all;

Thanks for all your help. I have been studying BIC pen caps and the like, despite getting strange looks at my local office supply store. After all how times do you see someone checking competing pens and pencils with a vernier caliper !

The annular ring snap closures mentioned in the links provided did allow me to calculate opening and closing force. By using the dimensions of pen cap lids I could verify those values were an answer and not a joke, as one of my old teachers used to say.

It seems it is cheaper to provide protruding nubs on the inside of the cap rather than a continuous annular ring. Since in my case simple locking is required rather than locking and sealing. This is the route I will investigate further. The formulas provided dont really address this but the insertion and retention load values have to be less for a "nub-style" closure.

Stars and attaboys to all!

Adrian Dunevein
aaadrafting.com