Nylon 66, reason for break at stress? other than humidity chemical additives and overdry, abuse of regrind material ? any other recommendation I may consider

Normalized humidity content will give you optimum properties. Over drying will yield inconsistencies in molding viscosity and therefore irregularities in strength properties due to variations in molded in stress levels. Regrind % is always a negative factor when testing for strength values. Chemical additives---- I can't speak on this issue

Are you using the prime virigin PA66 or recycled ones? regrinds can cause problem also.

hi
If your processing is normal then the only reason for brake that left is too much stress on the part. reduce stress or make changes to your part.

drying : keep the material about 0.3 - 0.5 % humidity

mold temp : no less then 60 .deg. (if your wall thickness less then
about 2 mm)
melt temp : rear 260, tip 280-300

injection : as fast as possible

regrind : stay below 25%

holding prs.: 500-600 bar (absolute)

back prs. : 10-20 bar (plasticizing speed as slow as possible)

Put the parts in a plastic bag for 24-48 hours with a moist towel that has been wetted in normal tapwater. This will allow the parts to absorb moisture which will make the material tough. Very dry as molded nylon parts can be brittle depending on the grade

Check for the hating location and the process parameters for stressed injection.
gate location can have influence to stressed filling of the part

overpacking the mold? - (it will break the strands)
sharp corners in mold causing sheer?

Is the break ussually at the same spot? If so, is it where the flows come together? Lube and volitiles may be collecting at that spot, preventing a good weld.

Very much useful. Pls share more technical information on this PA 66 breakage issue. Thanks.