Plastic Case

Ah, a plebe!

Adamson, you're going to have to be more detailed with your question/s. There might be someone here who knows what you're talking about but I'm certainly not one of them.

You've fallen into a common trap (one I've been seeing a lot of lately). You're assuming that everyone knows what your 19 word question means. I expect you're going to receive a a few negative comments so be warned.

Part of the solution is to ask the right questions...(overheard on the radio this afternoon from a DJ named Jackie).

Ok. I will be elaborating my question. I am a design engineer and currently I am doing a modification for an existing plastic case of a handset device. The plastic case is constructed in a way that it has a top and bottom cover. The two parts are joined by mating protruded part from each. See illustration below. Now, the requirement is to make this case IP64 compliant. Two ideas are currently being looked into; 1. To have an o-ring in the groove to seal the case. But the groove is only about 0.873mm in width. 2nd idea is to increase by 2mm the wall going to the inside direction of the plastic to accomodate a sort of rubber sealant to be compressed by the surface. This will make the total thickness of the wall to 4.5mm.

Now, what I would like to ask is that if I go for that thickness, would I be having trouble with sink marks? was there any other way for me to make the seal IP64 compliant? thanks.

Okay, not exactly my area of expertise but I'll tell you what I know.

I've seen o-rings that are 0.5mm in diameter so 0.873mm is not a problem. It's just a matter of finding someone who can supply your needs. The problem I see with this is that the o-ring will tend to increase the gap between the top and bottom:

If that's not a problem, then well and good.

As for your second idea, whether sink marks occur depend on the outside temperature as far as I know. If the surface of your rubber sealant cools faster than the inside, the surface will solidify first and then the inside will cool and shrink, pulling in the surface and creating the sink mark. One possible solution would be to apply your sealant in a hot environment and then slowly cool the environment so that the surface and the inside of your sealant cools at the same rate.

I can't tell you anything about what temperature and rate of cooling you'll be needing, unfortunately. You may have to do that by trial and error anyway.

Here's another idea:

Personally, I'd like to stick to the simplest and easiest so I'd go with the o-ring option. Just find a supplier and present your problem. They can even tell you what material you'll need to use. Good luck.

thanks for the info.

I have checked with the supplier and so far the smallest cross section of the o-ring is 1.02mm. I am redesigning now to make use of gasket.

If you are molding out of ABS, styrene, Polycarbonate, etc .080in is a good starting point for wall thickness. You can go to 1/8 or 3/16inch but your material usage goes up astronimicaly as well as your molding cycle time because of the extra pressure and cooling required to keep from molding sink marks. You must also consider draft angles and fillet radii because they have an effect of the cross section thickness of your part and therefore on the sink marks that may be molded. If you are using a filled material that also has an effect on the sink marks. If you are making your case of polyethylene or polyporpylene which have a high shrink factor you will have more problems with sink also.