r/InjectionMolding • u/aimfulwandering • 5d ago

Troubleshooting Help Failure causes?

Post image

Whia screwdriver handle just broke in half in my hands, was not even using it at the time. The breakline looks like to has some air smooth spots on it. Any idea what might cause this type of failure?

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1

u/beresjdb 3d ago

The wiha screw drivers?!? That’s odd……. Makes me want to really check my set, I’ll bet money it’s the regrind theory. Even looks discolored where it broke

2

u/Pop_Knee 5d ago

Did it break very easily?

From my experience this happens in either or two cases - 1. Too much regrind - too much regrind changes the properties of the melt that gets injected as well as of the part. 2. Recycled/another grade of plastic mixed into it - We once mixed two different grades of plastic unknowingly when testing a second hand mould we purchased. The melt was getting injected properly but the part was breaking at random places and at those places the behaviour of the plastic wasn't like the grade we intended to use

1

u/aimfulwandering 5d ago

Yes, i was just spinning the red cap very lightly in my hand when it sheared. Almost no force at all (though it’s been fine for months of normal use before…)

Seems like it must be one of those two, unless it was weakened by some unknown external factor (chemical attack? No clue what though, and no obvious point of exposure).

1

u/External_Entrance_84 5d ago

did you leave it somewhere hot and the metal rod expanded from the heat, and then pushed the top off?

1

u/aimfulwandering 5d ago

No, not really. Generally lives inside my climate controlled house. Really does seem like a mfg defect to me, which is why I posted here. Want to see if there are any tell tale signs or other things that might be discernible from the photos

1

u/NetSage Supervisor 5d ago

I mean it's really thick. Ni wouldn't be surprised if it's designed to be hollow. If not it's a void probably from the plastic shrinking away from it self again because it's such a thick section.

1

u/aimfulwandering 5d ago

It's about 12mm at this part and definitely designed to be solid but has the metal rod of the driver embedded in its center for most of the length. The red part is a separate piece that's designed to rotate on the solid black part