Cavities blockage

[holar09]

My cap mould has been having problems , the cavities get blocked easily, some of them have 'short mould', I have been flushing it, and after 2 days 5 or 6 cavities get blocked again. The material is clean, if I increase the Injection pressure, I will start having flash. What can I do?

[iautry1973]

When you are saying they get "blocked" what are they getting blocked with? That would help with troubleshooting.

[holar09]

When you are saying they get "blocked" what are they getting blocked with? That would help with troubleshooting.

Nothing, material will just stop coming out, and the cavity will be hot, sometimes it will be forming warps

[chrisprocess]

What material?
Cold/hot runner? Hot tip cavities? Valve gate?
Fill time? back pressure? Melt temp? Injection pressure?
How is venting?

Material may be freezing off or gassing out

[rickbatey]

I’d bet it’s something in the colorant. Try running parts without color and see if it happens. Last thing you probably need a melt filter with the ability to filter particles smaller than the tips.
Rick

[holar09]

What material?
Cold/hot runner? Hot tip cavities? Valve gate?
Fill time? back pressure? Melt temp? Injection pressure?
How is venting?

Material may be freezing off or gassing out

HDPE, hot runner, hot tip, fill time about 12secs, melt temp - 220, pressure -75

[holar09]

I’d bet it’s something in the colorant. Try running parts without color and see if it happens. Last thing you probably need a melt filter with the ability to filter particles smaller than the tips.
Rick

Can the colourant cause blockage?

[Pilot]

how big are the caps? the 12 sec inj. time for HDPE is a loooong time….

[chrisprocess]

shot weight?
12s does seem like a long time - I'm not so sure how much process control you have with this fill time

[michaelhurley87]

Could be that you are timing out during injection. Check all heaters. Maybe take an actual "Melt Temp" reading of the material if you have the ability. Do you see fluctuations in fill time when all parts come out and when cavities are blocked? Are there differences in peak pressure at transfer?