Infrared Annealing Techniques

[M&M]

Stress cracking of PC points towards a low steel temps. if you have an oil heater you should look at running that tool up around 220-240 degrees F. Also a slow rate of fill will help lower stress.

You will loose some cycle time but you just might loose the need to anneal all together.

Good luck

[Will Call]

There is a weld line over the surface and this line is causing cracking after sterilization. I increased the mold up to 95C degree but the line is still in there.

http://www.valueplastics.com/technical/ ... mation.pdf

and increase the vents in the mold.

[rickbatey]

I would suggest you change the hoses and connections, then take the water temp to 100°C and above, depending on what the unit can supply. You can also increase the melt temp to provide a better knit line. Sounds like the weld strength is causing the failures, so hotter mold and melt will make the weld strength better and could reduce your failures.
Is there any way to move the knit line?
Rick.

[kuyakut]

Shouldnt you wait for at least 4 hours to cool down the parts before annealing?. I come across with that kind of problem before. Although knitlines can not be eliminated but u can reduce the size by using high injection speed and high mold temperature.

Kuyakut

[rickbatey]

Increasing the vents gets the trapped air, and gasses/volatiles from the melt out of your molded part. These being trapped in the knitline of the part, can cause the breaking and failures you have.
Based on the failure numebrs you have listed, this failure is from the part/mold design and process changes may not be enough to solve long term. Since the problem is in the same location, then the melt flow fronts are consistent but the part is marginal. Hotter mold and melt temps can help improve the knitline strength. But it may NOT be enough. I doubt that annealing will improve the parts as there is poor weld strength in the part, and it will break when stressed.
At times you cann add localized thicker areas to a mold by grinding away some of the core material. This is done to move the knit line to a position that may not break. Changing or improving the gating can also solve the issue. It could also be you have too much pressure loss and until changes are made; the parts will continue to break!
Rick.

[tangstrong]

In my understanding, your problem is weld line crack after annealing.

1.Increase MT should help,but this have deformation temperature limitation,I think you can try 110 degree C MT
2.Cracking issue have cavity No dependency as your description, so I think may be flow balance should be optimized.
3.I don't know the shape of this product,if the strength around current weld line place isn't strong enough, I am not sure if any possibility change gate position to move weld line.
4.At last, if appearance of this product is very strict required, there is way to make it better, "IHTC",Induction Heating Temperature Control.