Strange behavior of PP

[abuhafss]

Hi

Pls see the attached photos. These strips are injected in PP.

When the strip is bent gently it breaks at the center. When checked randomly, all the strips broke almost at the same point. (1st photo)

Surprisingly, when any broken piece half is bent it does not breaks even at very acute angle. (2nd photo)

Can somebody explain me what could be the reason and how to solve the issue.

Thanks in advance.

[oldtool]

Were are you gating?

[Louis]

I'm thinking center gate - pushing it from one end to the other might be troublesome.

[abuhafss]

Thanks for your response.

And sorry I could not understand the term GATING.
However, I attach another photo of strip injected with SAMICA. The result is perfect.
The strip is basically an adjustable hanging strip which, of course, needs to be bent at the center.

SAMICA is quite expensive than PP, that's why I am working on PP.

[Yoda]

It sounds like you have a weld line in there some how. Where does the plastic enter the caviy (gate)?

[abuhafss]

I have found a solution for my problem.

The attached picture shows the actual injected piece.
The main gate was distributed into 2 gates for each piece, I blocked the cavity in the mold for the portion indicated by yellow circle. Now the main gate has only 1 sub gate for each side.

[tangstrong]

According to your picture and your description,since you already blocked one gate of each product, the breakage wouldn't be caused by weld line.But I notice the break happens around the gate, if so, that might be caused by stress concentration, because once you cut the gate, the surface must have some defects.

(sorry,I just noticed you mean that problem have been solved......by block one gate.)

[Will Call]

Gate it on one end and put a good vent on the other. Problem solved.

[oldtool]

You could even gate in the center and vent both ends. Just one gate in the center of the part. The gate is where the plastic enters the cavity. (Cavity is the area cut away to make the part)

[PVCSKI]

I solved an identical problem by blocking one gate on each cav. I ran it in ABS- glued off gate-retested then sent to toolmaker to weld gates.