I received this interesting question through linked-in...
Currently we have provided edge gating for appx. 25 dia @ 1.3 thk mm PC part.
We are planning for tunnel or submarine gate... When using polycarbonate material, what kind of gating should be provide?
When utilizing a submarine gate with PC, there are a few things to consider:
The biggest mistake people make when sub-gating with PC is to use too low an angle. The gate should angle into the parting line at least 60º. This will minimize the amount of deflection necessary to remove the gate from the mold.
Another mistake commonly made is to make the gate too long. The gate should get to the mold cavity as quickly as possible. This will reduce the amount of deflection necessary to remove the gate from the mold, thus reducing the chances of the gate remaining in the mold.
Lastly, if you are having success with a current gate size, we recommend using a smaller cross sectional area for the sub gate since it is very easy to remove steel and enlarge the gate later.
Pay close attention to your runner design, many molders will actually step the parting line behind the gate to allow more room for the runner system to bend as the gate is removed.