Its the cooling Stupid! #1  (Waterlines for Dummies)

Everybody understands waterlines, right? Wrong.  First is the placement: in P-20 steel you should be 1.5 to 2.0 diameters away from the mold surface.  Too close and you get a cold spot, too far and it won't pick up the heat.  Waterlines should be 2.5 to 3.0 diameters away from each other for the same reasons.  With more conductive metals they can be farther away. Stainless steel conducts heat 30% less than normal tool steel waterlines in stainless steel should be closer.  Since most injection molded parts are boxes, we're prone to putting the ejector pins in the corners.  When we do that, we can't put a waterline in the corners where there is a maximum heat buildup.  Putting waterlines in the corners and using stripper plates or other ejector mechanisms will cool your parts faster.

Don't put a waterline within one diameter of the surface.  Remember a waterline is rarely a totally smooth hole.  The micro-scratches in the hole are stress risers.  Too close to the surface and the steel flexing under normal processing conditions will cause a crack.

Call with questions
Bill Tobin – President WJT Associates
wjtassociates.com
303 604 9592