What material is best used for the lid?
For a project of which I can not go into specifics, we have issues piercing a lid made out of PP. The only thing I can say is that it is for medical purpose. There is a lid with dimensions height 3,7mm, diameter 5,35mm and the wall thickness of the lid that has to be pierced is 0,15mm.
In the lid an adapter is mounted. This happens in two steps. First step is clicking the adapter in the lid without piercing the lid. After all the parts have been assembled together and a test has to be made, the adapter will be pushed further into the lid and in the process piercing the lid. Adapter is made out of a standard PA6 and the lid we wanted to make out of a PP, but suggestions here are welcome. We are within limits free to choose a material that will break easily without breaking of some of the material of the lid. Distance between the fist and the second click of the adapter in the lid is approx. 2mm. So in that 2mm the lid has to be broken in such a way that a fluid like water will fall through the broken lid into a container due to gravity. There is no pressure in the system. Shot weight of the lid is 0,08 grams and of the adapter is 1 gram. Does anyone have any suggestions about what material is best used for the lid? Any other suggestions are also welcome. Thank you in advance.
It's difficult to give more than some generalities without design details, but here are a few thoughts.
a) Are your actually piercing through a clean cut or more like bursting (i.e. ragged
edged)? Either way your shape of this section of the adaptor will be critical to "pierce"
the lid clean and without lose particle.
b) I would be a little weary about using PA6 to "pierce" through a PP.
Is it possible to use PP with some talc additive (5, 10 or even 20%)?
This would make the breaking/piercing, bursting or perforating much easier (as you
are using 2 relatively pliable materials) and with tests you can easily determine which
would be the best % of filler for optimum performance.
If not possible consider a slightly "harder" adaptor material.
Hope this thoughts are of some use to you.
In regards to the liquid being retained try around with different surface structures until you achieve a lotus type effect. I feel that the worst structure you can have in your case would be polished.
suggestion for your products adapter and lid.
We always can see the metal punch shears the metal sheet with a clean edge. there are 2 important factors:
Punch is harder then the sheet.
Clearance is precise
in you case i think it is not the problem of the material. it should be the problem if you can use the adapt " shears " the lid. So the problem is the clearance. I did not see your product, but currently i think you could try to make the a step underneath the lid which its inner diameter is 5.35. And your adapter its outer diameter can be 5.30 ( just a suggestion, it should be fine turned during the test ), when they are assemblied, the adaper can punch the lid...
Ken, also thank you for your comment. we did exactly what you described above. in our case the PA6 is rigid enough to make the punch. It does not bend nor slide. In our opinion at the moment the real issue is the material fromm which the lid is made from. We will try next week a talcum filled PP with a high melt. The lid should break easy but not splinter. As for the lotus effect, we do not have the lotus effect. Exactly the opposite.
I will post the results of our tests next week.